EtiologyBased Dental and Craniofacial Diagnostics

88 Chapter 8 Figure 8.21 Examples of macrodontic permanent maxillary central incisors. (Upper left) Bilateral, macrodontic teeth with notches in the incisive edge. (Upper right) Unilateral, left-side macrodontic incisor without notches. (Lower left) Right-side, unilateral macrodontic incisors with a notch. Also shown as a radiograph (lower right). (Lower right) A radiograph of the patient shown in the lower left photograph. The incisive notch has been repaired. Note the broad root and wide pulp cavity. Permanent dentition: crown, root, and increased length of the anterior cranial fossa and the length of pulp the sella turcica. Asymmetry in the nasal cavity has also been observed (Figure 8.22). These observations are examples of how Malformation of incisors, canines, premolars, the morphology of the dentition and the underlying bone can be and molars interrelated. Incisors Different crown and root malformations are common. Single median incisor Another malformation of the maxillary central incisors is the single median maxillary central incisor Maxilla (SMMCI) (Figure 8.23). This malformation also demonstrates Macrodontia Two types of incisor malformations are related to the interrelationship between the incisors and the frontonasal abnormal development of the frontonasal field. One is the field. The central incisor is a broad tooth located midaxially and macrodontic central incisors which can appear with or without appears to be composed of the two lateral components of two a notch on the incisive edge (Figure 8.21). This malformation is central incisors. The root can be a single, broad root or a root also named double teeth or connate teeth and is more common in divided apically into two parts (Figure 8.24). This means that the males than in females. The macrodontic incisor is often seen as midaxial structures of the normally occurring central incisors are an isolated feature but can also occur in syndromes combined missing. A midline deficiency is also seen in the jaw and with mental retardation (KBG syndrome). Cephalometric anal­ sometimes also in the brain (see Chapter 13). In this condition, ysis has revealed several deviations in size measurements of the the frontonasal field is not enlarged, as in the case of macrodontic frontonasal field related to macrodontic incisors, including incisors, but rather appears diminished as the midaxial tissue

Deviation in tooth morphology and color 89 Figure 8.23 Two intraoral photographs of SMMCI in the permanent dentition. Note the symmetrical morphology of the incisor and the absence of the frenulum labii superioris. (Upper) Normal transverse jaw relation. (Lower) Bilateral crossbite in the transverse plane and reverse overjet. These occlusal relationships mean that the treatment for these two individuals must be different. Figure 8.22 Sections from orthopantomograms from two children aged block is missing. The anterior cranial fossa is significantly eight years (upper) and 14 years (lower) with macrodontic incisors and reduced in length and fusion of the frontal lobes of the brain asymmetry in the nasal cavity indicating involvement of the skeleton in has been described (see Chapter 13). Why these conditions concerning incisor malformations in the frontonasal field are sometimes interrelated with mental disabilities and sometimes not is a question for neurologists. The two conditions are examples of interrelationships between the dentition, the underlying jaw bone, and the cranial base. The etiology seems to be an ectomesenchymal deficiency midaxially. Other incisor malformations The maxillary central incisors can also appear malformed, seemingly due to ectodermal mal­ function. Examples of such malformations are crowns which ◀ the frontonasal field. (Upper) The primary maxillary incisors in the right side appear fused and with a filling. The succeeding permanent tooth appears to be macrodontic. The left permanent incisor is rotated. Note the asymmetrical morphology of the left and right nasal cavities (stars). (Lower) A case with a macrodontic, right maxillary central incisor. Note the bent nasal septum (red arrow) and the asymmetry of the left and right nasal cavities (yellow stars).

90 Chapter 8 Figure 8.24 Root morphology of a central incisor in SMMCI. Note the split apical root. Figure 8.25 Intraoral photographs demonstrating talon cusp malformations in the permanent maxillary incisors. (Inset) A radiograph illustrating this cusp. appear shovel-shaped, screwdriver-shaped or with a talon cusp different morphologies and locations (Figure 8.27). The depth of (Figure 8.25). Severe invagination and other abnormal morphol- the invagination reflects the severity of the malformation. Why ogies also occur in the central incisors (Figure 8.26). these malformations occur can only be hypothesized. Some invaginations occur in the medial aspects of the incisor crown Lateral maxillary incisor The lateral maxillary incisors can be and appear as an extra, medially located half incisor attached peg-shaped and they can be categorized by invaginations of to the later incisor (Figure 8.28). From an embryological

Deviation in tooth morphology and color 91 Figure 8.26 Four radiographs demonstrating four different types of malformations among the permanent maxillary central incisors. (Upper left) There appears to be a severe invagination in the right central incisor. (Upper right) Less severe invaginations in the four maxillary incisors. (Lower left) Extremely broad, macrodontic incisor with a plump and broad root. Two invaginations can be observed. (Lower right) Severe malformation where the etiology cannot be explained. perspective, the invagination is due to a dysfunction in the inner narrow crowns can occur in the lateral incisors as well as other enamel epithelium. For comparison, imagine this invagination as types of morphological deviations (Figure 8.32). a well covered by enamel on the walls and on the floor at the bottom. This error means that there is a localized lack of enamel Root length Root lengths can differ significantly from very production in the bottom of the well. The enamel along the sides short roots to extremely long roots (see Figure 4.18). Short builds up normally and a deep hole (invagination) is formed in root anomaly is a malformation condition which can be seen this area due to lack of enamel production. in all four incisors and which might be explained by genetic deviations in these fields. The condition is inheritable (see Also broad and/or severely malformed lateral incisors can be Chapter 11). observed (Figure 8.29). Fusion can occur between lateral and central incisors or between a lateral tooth and a supernumerary Mandible tooth in this region (Figure 8.30). It can also appear as a Fusion of the incisors can appear among the permanent, man­ macrodontic incisor (Figure 8.31). This might be due to a dibular, central, and lateral incisors (Figure 8.33). Macrodontic deficiency in the mucosa of the early tooth bud. Minor and

92 Chapter 8 Figure 8.27 Intraoral radiographs from a child 10 years of age. The right maxillary lateral incisor is malformed and the left appears with a medially located invagination. Figure 8.28 Dental films from four different children demonstrating severe malformation medially in the permanent maxillary lateral incisors. The malformations can appear as evaginations (black arrows) or as deep invaginations leading to inflammation in the medial aspect of the tooth (blue arrows). Figure 8.29 Severe malformations of the permanent maxillary lateral incisors. These are all inexplicable cases. It might be that these malformations are related to malformations at the borderline between the frontonasal and maxillary fields.

Deviation in tooth morphology and color 93 Figure 8.30 Example of fusion between a lateral incisor and a central incisor (or a supernumerary incisor). (Far left) Dental film taken before the operation. (Center left) The fused teeth appear anteriorly. Behind these, another incisor can be seen. (Center right) The fused teeth after removal viewed in the anterior (left) and posterior (right) aspects. (Far right) Radiographs of the fused teeth in the frontal view (upper) and in the axial view (lower). Notice the separation of the pulp chambers. Figure 8.31 Two intraoral photographs from a child eight years of age demonstrating permanent, macrodontic, maxillary lateral incisors (stars). Note the notches on the incisive edge. Figure 8.32 Demonstration of narrow crowns and late development of the permanent maxillary lateral incisor. (Left) Section from an orthopantomogram demonstrating part of the right maxilla in a child 12 years of age. Notice the diminutive crown of the permanent lateral incisor. The root has not begun to develop at this late stage. Note also the agenesis of the permanent maxillary canine and the screwdriver-shaped, permanent maxillary central incisor. (Right) Section from an orthopantomogram from a child 13 years of age demonstrating tapered maxillary lateral incisor crowns and normal root length.

94 Chapter 8 Figure 8.33 Photographs and a radiograph demonstrating fusions between permanent mandibular incisors. (Upper left) Clinical photograph of a fusion between the permanent mandibular lateral incisor and a supernumerary mandibular incisor. (Upper right) Fusion between central and lateral mandibular permanent incisors. (Lower left) A macrodontic mandibular incisor in the mandibular incisor region. This could be a fusion between a lateral incisor and a supernumerary incisor. (Lower right) Radiograph demonstrating fusion between a central and a lateral permanent incisor in the mandible. Note the broad pulp cavity in the root and crown. incisors can also occur (see Figure 8.33). Short roots might also be observed (Figure 8.34). Canines Malformations of the canines, including plump and short roots, can occur but are rare (Figure 8.35). Extremely long roots have also been observed but are also very rare (Figure 8.36). Premolars Evagination Evagination, which is an out-bulging of enamel, may also have an embryological explanation connected to the inner enamel epi­ thelium (Figure 8.37). Evagination occurs most often in the mandibular second premolar and is often seen in the Asian population. When the evagination becomes worn down through occlusion, the pulp can become infected and a periapical inflam­ mation occurs. Cusp morphology Figure 8.34 Dental film demonstrating short roots in the permanent In the premolar and molar teeth, deviations can occur in cusp mandibular central incisors. morphology and cusp number. This appears most often in relation to syndromes. Molarization of premolar crowns may also be observed (Figure 8.38).

Deviation in tooth morphology and color 95 Figure 8.35 Radiographs illustrating abnormal morphology of the canines in the mandible and the maxilla. (Two far left) Short roots of the permanent mandibular canines. The etiology is unknown. (Center) A mandibular canine with two root channels (arrows). (Two far right) Permanent maxillary canines with an abnormal root complex. The etiology is not known. Figure 8.36 Radiographs demonstrating extremely long roots of the canines in the permanent dentition. (Upper) An orthopantomogram displaying extremely long maxillary canine roots. The etiology is not known. Source: Reproduced with kind permission of Dr Inga B. Árnadóttir, University of Reykjavik, Iceland. (Lower) An orthopantomogram from a child 11 years of age with cystic fibrosis. Note the very long roots, especially in the permanent mandibular canines. Root morphology are short, and eruption deviations occur. In nonsyndromic Short or seemingly abrupt root formation occurs often in the individuals, one or two macrodontic molars may be present second premolars (Figure 8.39). The cause is not known. There is (Figure 8.43). Diminutive molars can also occur (Figure 8.43). In also no clear explanation for a long root anomaly (Figure 8.40). the molars, the most severe ectodermally derived morphological deviation is the taurodontic root morphology (Figure 8.44). Root deviations in the premolars include narrow roots, plump Taurodontism can be subdivided into grades of severity. roots, extra roots, and short roots (Figure 8.41). Pulp cavity Molars In the pulp cavity, so-called pulp stones or calcifications can be The cusp morphology can differ in molars. Figure 8.42 demon­ observed (Figure 8.45). The etiology behind these stones is strates crown and root morphologies in three children with still not known. It could be hypothesized that these calcifications Down’s syndrome where the crowns are small, the roots or obliterations appear in teeth with alterations in the

96 Chapter 8 Figure 8.37 Demonstration of periapical inflammation processes due to crown malformation in the mandibular second premolars. (Left) Invagination (black arrow) in a second mandibular premolar. The inflammation has caused the periapical inflammation which is marked by yellow stars. (Right) An intraoral photograph of the mandibular permanent molars and second premolar as well as a dental film of the same teeth. The arrow marks a “crater” which remains after an evagination in the enamel has been worn down during occlusion. Bacteria have entered this “crater” and caused inflammation in the pulp which has resulted in a periapical inflammation (yellow star). Figure 8.38 Demonstration of molarization which can occur in the first and second mandibular premolars. (Left) A section from a dental cast illustrating molarization of the first mandibular premolar. (Upper right) A section of the mandibular dentition from a child demonstrating molarization of the second premolars (arrows). These premolars appear with a broad crown. The roots of the premolars appear normal. (Lower right) A section of the mandibular dentition from a child demonstrating molarization of the second premolars (arrows). These premolars appear with a broad crown. The roots of the premolars appear short and apparently arrested in formation. The roots of the neighboring molars (first and second permanent molars) have abnormal root morphology. This case seems to have a general root deviation.

Deviation in tooth morphology and color 97 Figure 8.39 Radiographs demonstrating abnormal development of the premolars and canines. (Upper left) Short root of a second mandibular premolar. Note the taurodontic root shape of the second permanent molar. The etiology is not known. (Upper center) Short root of a second maxillary premolar. The etiology is not known. (Upper right) An unusual flexion in the root of the second mandibular premolar. The etiology is unknown. (Lower left) Orthopantomogram demonstrating short roots in the premolars. It appears as though the roots have been “cut off” (formation suddenly arrested) (arrows). This child has a severe asthma problem and is medicated. The etiology should be investigated. (Lower right) A short canine and first premolar in the mandible where no other short roots are present. The etiology could be an innervation deviation in the canine/premolar field but has not been verified in this case. Figure 8.40 Examples of abnormal root lengths in different dental and health conditions. (Far left) Long roots in molars and premolars observed in a case with agenesis of all permanent canines. It should be investigated whether this long root anomaly is a general characteristic for dentitions with canine agenesis. (Left center) Extremely long molar roots in a patient with Nance–Horan syndrome. (Right center) Long roots and broad crown morphology in a patient with oculodentodigital syndrome. (Far right) Short molar roots and broad molars observed in a child treated for retardation in body growth.

98 Chapter 8 Figure 8.41 Root morphology in permanent premolars which can be considered within a normal range. (Upper left) Forked premolar roots with an apical separation of the root pulp into two branches. (Upper right) Extremely long roots of premolars. This was a general finding among premolars in this dentition. (Lower left) Abnormal pulp morphology in the premolar roots. The etiology behind this is not known. This case could indicate a mild degree of dentinogenesis imperfecta. (Lower right) Radiograph of a maxillary first premolar with two roots. Arrows mark the two root channels. ectomesenchymal fiber layer in the peri-root sheet (Figure 8.46). Arrested tooth formation (possible disruption) without In Klinefelter’s syndrome, deviant pulp morphology is a char­ known etiology acteristic trait (Figure 8.47). In some cases, a tooth, often a premolar or a molar, might become arrested in root formation without known cause. This can occur Tooth color bilaterally, as illustrated in Figure 8.48, or unilaterally (see For all permanent teeth, color changes can occur and can both be Chapter 4). Arrest in root formation can also be caused by virus congenital or acquired. attack (Figure 8.49). Syndromes Trauma In syndromes such as Turner’s syndrome, the teeth are generally The most common disruption factor is believed to be trauma smaller than normal. In tuberous sclerosis which also affects the which can disturb tooth morphology in several different ways ectoderm, the enamel surface contains pits. In SMMCI, there is a (Figure 8.50). Dirsuption of the incisors can be seen anteriorly syndrome-specific morphological change in the crown (see due to trauma in the primary dentition. Disruption of normal Figure 8.23). A syndrome-specific morphological change in premolar development can be seen in cases with early retention the root can also be observed in Klinefelter’s syndrome where (ankylosis) of primary molars (Figure 8.51). the molar roots appear taurodontic. Virus attack and diseases Disruption in the permanent dentition Factors that can disrupt normal tooth development include A disruptive change in tooth morphology can occur during congenital diseases such as kidney diseases and virus attacks different periods of tooth formation. The permanent incisors as well as bacterial infections (Figures 8.52 and 8.53). Leprosy is a and first molars start formation during the prenatal period while bacterial attack (Mycobacterium leprae) which causes nerve the remaining permanent teeth mostly form postnatally. inflammation and affects the innervation in the body as well

Deviation in tooth morphology and color 99 Figure 8.42 Radiographic and intraoral photos from three different children with Down’s syndrome. (Upper) An orthopantomogram demonstrating a Down’s syndrome dentition with normal morphology and a normally occurring canine premolar transposition in the maxillary left region. (Lower left) A dental radiograph of the mixed dentition showing short molar roots. (Lower center) Slight color changes in the enamel and a worn primary molar. (Lower right) Teeth that are well spaced and with partially obliterated pulp chambers. Figure 8.43 Permanent molars with congenital, abnormal crown morphology. (Upper left) Section from an orthopantomogram demonstrating enlarged crowns on the permanent mandibular second molars. (Lower left) A single mandibular permanent molar in the right side with location and a morphology which makes it difficult to determine whether the tooth is a first or second molar. (Lower center) Section from an orthopantomogram demonstrating a third molar tooth germ with a crown that is unusually broad. The etiology behind such large molars is not known. (Right) An example of a diminutive third maxillary molar crown.

100 Chapter 8 Figure 8.44 Sections from orthopantomograms demonstrating taurodontia of the permanent molars. (Far left) Taurdontia of the second permanent molars in the maxilla and in the mandible. (Center left) Taurodontia in the maxillary first permanent molar and in the second permanent molars (not completely taurodontic morphology). (Center right) Taurodontia of the first mandibular permanent molar. It is rare for the first molar to be taurodontic while the second molar is not. (Far right) Taurodontia of all observable molars in the radiograph. Figure 8.45 Obliterations or “pulp stones” in the crown pulp cavity and in the root pulps in permanent molars. (Upper left) A section from an orthopantomogram demonstrating a pulp stone in the permanent maxillary first molar (arrow). (Lower left) Total obliteration of the pulp in the permanent mandibular first molar in the right side. It is difficult to see whether a pulp stone is present in the second molar. (Center) Pulp stones that appear as calcified islands are visible in the permanent maxillary molars and in the permanent mandibular first molar in the jaw. (Right) These three figures are sections from dental films and an orthopantomogram. They demonstrate completely calcified crown pulps in each molar. This case is from a patient with Ehlers–Danlos syndrome which is a connective tissue disorder. The etiology is a defect in the structure, production or processing of collagen. as in the peri-root sheet in the maxillary incisors. The teeth Ghost teeth become arrested in development as illustrated in Figure 8.54. Ghost teeth are an example of tooth disruption within a devel- This condition illustrates how a change in morphology can be opmental field which also affects the primary and permanent provoked by a bacterial infection. dentition (see Figure 8.16). The etiology is not known but disruption occurs within one or two developmental fields. Operation Operations of the ear and face can disturb the innervation Medication and treatment regionally. This can also affect normal tooth development in Chemotherapy can disrupt tooth development at different stages. the primary and permanent dentition (see Figure 8.13). Early chemotherapy disrupts the formation of several teeth while

Deviation in tooth morphology and color 101 Figure 8.46 Histological sections from a primary molar and a permanent molar both with obliterations (pulp stones). (Upper) A section through the pulp chamber of a primary mandibular second molar removed due to arrested eruption (see Chapter 10). Note the hard tissue formation along the upper wall and centrally in the pulp chamber. (Lower) These figures together illustrate a secondarily retained first molar (see Chapter 10) with pulp stones. The radiograph to the left visualizes the retained first molar with an occlusal level that is different from the neighboring teeth. In this dentition, pulp stones were present in all the molars. The retained first molar was surgically removed and investigated histologically. Inserted inside a black box is an overview of the crown with the pulp chamber marked by a smaller, blue box. A magnification of the tissue within this box appears in the histological section to the right. A mass of hard tissue appears centrally in the pulp chamber (unbroken arrow). Note that hard tissue is also present along the upper wall (broken arrow). Source: Reproduced with kind permission of L. Kieffer-Kristensen. Figure 8.47 Sections from two orthopantomograms demonstrating root morphology in Klinefelter’s syndrome (genotype 47,XXY). (Left) Taurodontism in the primary first molars in the maxilla and mandible of a child. (Right) Taurodontism demonstrated in the first permanent molars in the maxilla and mandible of a child. Obliteration in the pulp chamber is apparent in the maxillary first molar.

102 Chapter 8 Figure 8.48 Radiographs from three different children demonstrating arrest in tooth formation of the permanent maxillary first molars. (Upper) In this child, the maturation process of the first permanent molars in the maxilla has apparently ceased. The etiology behind this arrest in formation is not known. (Lower) An orthopantomogram demonstrating that the maturation process of the first permanent molars in the right side of the maxilla has ceased. Notice the contralateral maxillary first molar which has already erupted. (Inset) A close-up of a maxillary first molar from another patient demonstrating the absence of root membranes. Figure 8.49 Section from an orthopantomogram demonstrating the mandibular dentition in a patient 18 years of age. Note the bilateral, asymmetrical root lengths. There appears to be a regional left-sided arrest in root formation which has affected the canine/premolar region and the molar region at approximately six years of age. At that time, a severe virus infection might have attacked the nerves innervating the canine/premolars and molars. This has been proven in former, similar cases. late childhood chemotherapy has a lesser effect (Figure 8.55). The molar incisor hypoplasia (MIH) condition (Figure 8.59) is Two treatments well known for disrupting tooth formation are plagued by enamel changes on the incisors and first molars. The chemotherapy and radiation therapy due to leukemia and cause of this is not known. MIH can be quite painful and may in tumors (Figure 8.56). In Figure 8.57 tooth development before extreme cases lead to extraction. The etiology is possibly a and after radiation therapy is demonstrated. It appears that disruption by external factors during or shortly after birth. radiation has arrested root formation and that the root mem­ brane has disappeared radiographically. Tetracycline, a former Linear scleroderma en coup de sabre medication option, is an example of a disruptive factor, changing This is also a disruptive condition for teeth undergoing develop- both the color and the shape of developing teeth. ment. The etiology of en coup de sabre, which is a local scleroderma, is not known. The condition can be recognized Fetal alcohol syndrome is an example which demonstates early on postnatally but generally intensifies with age. Sclero­ how maternal intake of alcohol can change tooth morphology derma en coup de sabre is a rare, ectomesenchyme and skin (Figure 8.58). Eruption can also be disturbed in fetal alcohol condition where dense collagen is deposited in a localized groove syndrome.

Deviation in tooth morphology and color 103 Figure 8.50 A dental film from a child 13 years of age in whom a trauma in the maxillary incisors at the approximate age of six years has arrested the root formation of the right maxillary permanent central incisor. Figure 8.51 Sections from orthopantomograms demonstrating how ankylosis of a primary molar can disturb the formation of the succeeding premolar. (Left) In this case from a five-year-old child, arrested eruption has occurred in the primary mandibular first molar in the right side. This arrest has changed the position of the first premolar succeeding the impacted primary tooth. (Right) In this case from an 11-year-old child, arrested eruption of the second primary mandibular molar in the left side has changed the morphology of the succeeding second premolar.

104 Chapter 8 Figure 8.52 An intraoral photograph of a lateral and a central incisor in the maxilla. The enamel structure and the brownish enamel color indicate periods of intrauterine illness. The upper, white contour of the central incisor is from the postnatal period when the disease was treated. Figure 8.53 Morphological changes in teeth due to congenital diseases. (Left) Section from an orthopantomogram from a child born with a lymphatic system disease (lymphangioma). Both the permanent first molars and primary second molars are affected in the crown and the roots through the entire dentition. The permanent teeth which start formation postnatally are seemingly unaffected. (Center) Section from an orthopantomogram of a child born with sickle cell anemia. All the permanent teeth appear with a large crown, a diminished pulp chamber, and narrow roots. (Right) Section from an orthopantomogram from a child born with an infection showing abnormal root development of the first permanent molars in the entire dentition. The distal root on the permanent mandibular first molar is especially severely malformed. Figure 8.54 Maxillary incisors from two different anthropological crania affected by leprosy which is a chronic infection caused by the bacteria Mycobacterium leprae. (Left) These four maxillary incisors were arrested in root formation at the age of approximately 7–8 years. The central incisors are more severely affected than the lateral incisors. (Right) These three maxillary incisors were arrested in root formation at the age of approximately four years. The central incisors (stars) are clearly more severely affected than the lateral incisor. The roots of the central incisors are arrested in formation and have a conical morphology (arrows). Source: Reproduced with kind permission of T. Söderqvist.

Deviation in tooth morphology and color 105 Figure 8.55 Orthopantomograms from two different children between the Figure 8.56 Orthopantomograms demonstrating arrest in tooth formation ages of eight and 10 years who have received radiation treatment due to due to cancer treatment. The type of treatment is not specified. (Upper) leukemia in early childhood. Note the severe malformations of the The treatment in this case resulted in short roots in the premolars, permanent first molars. (Upper) The molars in the mandible are canines, and molars. Furthermore, the permanent second molars in the characterized by absence of the distal roots. In the dentition, narrow maxilla are severely underdeveloped and appear much smaller than usual. second premolars are a sign related to the treatment. (Lower) In this case, (Lower) The treatment in this case resulted in arrest of root formation in there is delayed eruption of the incisors. Notice the severe malformation of the mandibular first molars. It is difficult to determine whether the all the permanent first molars. The first premolars appear narrow. permanent first molars in the maxilla also have arrested root formation. The dentition has an otherwise normal appearance with late eruption of the incisors. Figure 8.57 Section from two orthopantomograms taken 1½ years apart in the same individual. (Upper) This radiograph was taken for preparation of an orthodontic treatment plan before knowing that the patient would shortly after be receiving chemotherapy. The inserted square marks the area that has been magnified to the right. Note the circular contour of the apical alveolus in the magnification. (Lower) This radiograph was taken 1½ years later than the upper radiograph. In the period between these two radiographs, the patient received chemotherapy. Notice how the chemotherapy has affected the contour of the root alveolus and apparently the root membrane as well. The square marks the magnification area seen to the right. In the magnification, the alveolus contour that was present 1½ years ago has disappeared. Information on the further development of the roots was not available.

106 Chapter 8 Figure 8.58 Section from an orthopantomogram from a child 10 years of Figure 8.60 Intraoral photograph illustrating permanent incisors in the age with fetal alcohol syndrome demonstrating the abnormal morphology same patient with ectodermal dysplasia shown in Figures 6.12 and 8.18. of the pulp cavity in the right mandibular permanent first molar. Fetal Note the multiple agenesis and the severe change in crown morphology in alcohol syndrome can affect the dentition in various ways, depending on the permanent maxillary central incisors. the severity of the condition. of the head and neck area, resembling the stroke of a saber. It may Ectodermal dysplasia involve the oral cavity, but the severity and relation to this facial Ectodermal dysplasia is a condition with various diagnoses and abnormality are unknown. Though it appears that the skin is various gene involvement possibilities. Pointed incisors without affected, the etiology could also primarily be related to the an incisive edge and narrow teeth in dentitions with multiple underlying ectomesenchyme. This proposal is based on the agenesis are common features. However, characteristics of ecto­ fact that the enamel, which has an ectodermal origin, is seemingly dermal dysplasia may not all appear together (Figure 8.60). normal while the dentin and cementum of the tooth root, with Characteristics such as thin, light hair and soft nails are common ectomesenchymal origins, are malformed. findings which make diagnosis easier but these features are not always present. The roots in ectodermal dysplasia are usually Self-mutilation narrow and pointed while the pulp cavities can appear large. This can also be a disruption factor. Dysplasia in the permanent dentition Dentinogenesis imperfecta Dysplasia can be localized and limited to a developmental field. This is a condition in the permanent dentition where especially However, it can also occur generally in the dentition. the tooth color can vary. The color is most often brownish (Figure 8.61) but can also be observed as yellow and gray Segmental maxillary/mandibular dysplasia (Figure 8.62). The pulp cavities calcify early after eruption. These Segmental maxillary dysplasia and segmental mandibular dys­ teeth, now without pulp cavities, have a characteristic appearance plasia are dysplastic developments that occur within fields. In the which is illustrated in Figures 8.61 and 8.62. The ectomesen­ affected fields, malformed teeth, agenesis, and ectopic eruption chyme is affected in this condition. Abnormal appearance of pulp may be seen. The local bony tissue has a dysplastic character. For cavities can also occur in dentindysplasia in which the shape of more information see Chapters 7 and 10. the root is also abnormal (Figure 8.63). Figure 8.59 Intraoral photographs and a schematic drawing illustrating the location and extent of the molar incisor hypoplasia (MIH). The first molars are affected by brown mineralization disturbances. The incisors also have minor defects which cannot be seen on the photographs. The drawing to the right marks the four areas where MIH affects this dentition. The etiology behind this condition seems to be related to perinatal disturbances in calcium deposits. What creates this disturbance is still not clear. The affected molars are often painful and treatment options include the extraction of the affected molars as well as orthodontic treatment for correction of severe crowding.

Deviation in tooth morphology and color 107 Figure 8.61 Intraoral photograph and an orthopantomogram from a patient with dentinogenesis imperfecta. Note the brownish color of the teeth, the normal morphology, and the absence of pulp contours (seen on the radiograph). Figure 8.62 Images from a patient with a dysplasia condition which might be dentinogenesis imperfecta. (Far left) An intraoral view of the dentition. Notice the grayish color of the enamel and the normal tooth morphology. (Center left) An orthopantomogram demonstrating a clear borderline in the permanent molars between the white enamel and the gray dentin. The roots appear shorter than expected for dentinogenesis imperfecta. (Right) Two dental films displaying the permanent mandibular incisors and permanent maxillary incisors. The roots are short and there is a total absence of pulp chambers. Figure 8.63 Demonstration of the abnormal appearance of pulp cavities in a patient with dentin dysplasia which is a disturbance in dentin formation. Amelogenesis imperfecta Osteogenesis imperfecta In amelogenesis imperfecta, the enamel is abnormal and the This type of dysplasia is characterized by bone tissue that appears condition is therefore categorized as an ectodermal disorder. The gritty. The teeth can appear normal or similar to the dentition severity of this condition varies enormously, with teeth appear­ from a patient with dentinogenesis imperfecta (Figure 8.67). This ing in several shades of brown. A severe case is demonstrated in is an ectomesenchymal disorder. Figure 8.64 and a less severe case in Figure 8.65. The pulp of the teeth is not affected as in dentinogenesis imperfecta but these Dental deviations seen in the condition called dysostosis teeth do have eruption problems. See Chapter 10 for more cleidocranialis appear in Figure 8.68 (see Chapter 13 for more information. information). Enamel hypoplasia Abnormal dental development: fields and Enamel hypoplasia is a condition in which small pits occur in the bilateralism enamel surface. Such pits might be associated with diseases in childhood but the condition can also occur in healthy individuals Dental abnormalities occur sporadically in single teeth. This without a sickness record. In these cases, the cause of the pits is could be due to pathological, late formation of the crown or root. not known. Meanwhile, there are diseases in which enamel pits Dental abnormalities can also occur in several teeth in the same are a phenotypic trait, such as tuberous sclerosis. Uneven enamel dentition belonging to the same developmental field. This has desposition can also occur (Figure 8.66). been demonstrated in cases where virus attack has disturbed

108 Chapter 8 Figure 8.64 Demonstration of a severe type of inherited amelogenesis imperfecta in two brothers. (Upper) The characteristic observations are the brown color of the teeth, the severe tooth malformations, eruption deviations, and normal pulp cavities. (Lower) The same characteristics are observed in the brother’s dentition. A white arrow points towards the right mandibular permanent canine which has a pointed top due to lack of enamel. On the corresponding orthopantomogram to the right, a white arrow indicates the same tooth and the abnormal shape of the mandibular canine. Figure 8.65 An orthopantomogram demonstrating a less severe case of amelogenesis imperfecta. Note the very thin enamel and the abnormal morophology of the permanent second and third molars. Figure 8.66 Intraoral photographs demonstrating localized and general enamel dysplasia in the dentition. (Left) The enamel contour in the maxillary front and especially on the maxillary permanent canines is very irregular. In this case, eruption problems occurred in the left side of the maxilla (see also Figure 10.20 from the same patient). (Right) In this case, an uneven enamel surface appears on the permanent maxillary central incisor. There are no other known deviations in the dentition.

Deviation in tooth morphology and color 109 Figure 8.67 Orthopantomograms from three family members with Figure 8.68 Two orthopantomograms from two different patients osteogenesis imperfecta which is a congenital condition involving defective diagnosed with cleidocranial dysostosis. (Upper) Orthopantomogram from connective tissue due to deviant collagen production. (Upper) The an 11-year-old child with extremely delayed eruption of the incisors and dentition appears normal. However, it is difficult to see root pulps in the maxillary first molars. 3D imaging revealed supernumerary tooth buds in permanent first molars. (Center) In this dentition, there are many teeth the mandibular premolar region. (Lower) Orthopantomogram from a without normal pulp structures. The dentition can appear similar to a patient with several supernumerary teeth as well as ectopia and eruption dentition from a patient with dentinogenesis imperfecta. It is well known problems. that one of the osteogenesis imperfecta types also involves dentinogenesis imperfecta. (Lower) This patient has broad pulp chambers as opposed to • Does the condition have an ectodermal, mesodermal or neuro­ the above family members. Still, there is a deviation in the dentin which is ectodermal origin? based on a collagen defect. • Was it provoked by virus, bacteria, medical treatment or dental formation locally (Figure 8.69). The occurrence of dental trauma? deviations in these cases appears unilaterally. Bilateral occur­ rences often have a congenital etiology or are caused by a general • Does it involve the jaw bone? The brain? disease. Based on the answers to these questions, you might be able to answer the question: “is it a malformation, a disruption or a dysplasia?” With the answer, it becomes possible to predict further dental developmental patterns and to create an etiol­ ogy-based treatment plan. How to analyze the etiology behind Highlights and clinical relevance deviation in tooth morphology: is it malformation, disruption or dysplasia? • The morphological deviations of crowns and root can occur within a region (field) in the dentition. If this is the case, it will There are several steps in the evaluation of a dental deviation. It is not spread outside this region. This is important knowledge for important to consider the following. etiology-based diagnosis as well as for prediction and treat­ • Is it a normal variation or is it pathological? ment planning. • Is it a pre- or postnatal disturbance? If prenatal, what could it be • A morphological deviation in the dentition can be a symptom (disease, virus, medically induced)? of deviations in the underlying bone and possibly in the brain. • Does it occur regionally or generally? • Does it occur within a field, within several fields or without field • Observe carefully for extraoral signs of ectodermal deviations. Ectodermal deviation does not only cause agenesis but also borders? deviation in tooth morphology which can make orthodontic • Does it occur unilaterally or bilaterally? treatment contraindicated (see Chapter 11).

110 Chapter 8 Further reading Figure 8.69 Orthopantomograms from two children six and seven years of Hørberg M, Lauesen SR, Daugaard-Jensen J, Kjær I. Linear scleroderma age demonstrating regional dysplasia of the teeth. The etiology behind this en coup de sabre including abnormal dental development. Eur Arch rare defect is not known but might be associated with a periodic Paediatr Dent 2015;16 (2):227–231. disruption of the ectomesenchyme or the innervation. (Upper) In this case, the right maxillary canine/premolar and molar fields are involved. The Jensen BL, Kreiborg S. Development in the dentition in cleidocranial teeth appear as shadows and the condition is therefore also called “ghost dysplasia. J Oral Pathol Med 1990;19:89–93. teeth.” Whether the second molar in the affected region appeared later is not known. (Lower) The radiograph displays agenesis and dysplasia Kenrad A, Christensen IJ, Kjær I. Craniofacial morphology of the localized to the right mandibular canine/premolar and molar regions. This frontonasal segment in patients with one or two macrodontic maxil­ is a case of mandibular “ghost teeth.” It seems at this stage that the lary cental incisors. Eur J Orthod 2013;35:329–334. permanent second molar will develop normally. A section of a follow-up radiograph from five years later is inset in the upper left corner. This Kjær I, Bagheri A. Prenatal development of the aveolar bone of human demonstrates that the second molar developed later but that the root deciduous incisors and canines. J Dent Res 1999;78:667–672. morphology is deviant and the tooth is apparently unable to erupt. The eruption problem might be caused partly by the mandibular ramus. Kjær I, Daugaard-Jensen J. Interrelation between fusions in the primary dentition and agenisis in the succedaneous permanment dentition seen from an embryological point of view. J Craniofac Genet Dev Biol 2000;20:193–197. Kjær I, Strøm C, Worsaae N. Regional aggressive root resorption caused by neuronal virus infection. Case Reports in Dentistry, 2012; Article ID 693240. Koch G, Poulsen S. (eds). Pediatric dentistry. A clinical approach, 2nd edn. Blackell, Chichester, 2009. Lexner MO, Bardow A, Hertz JM, Nielsen LA, Kreiborg S. Anomalies of tooth formation in hypohidrotic ectodermal dysplasia. Int J Pediatr Dent 2007;17:10–18. McCulloch KJ, Mills CM, Greenfeld RS, Coil JM. Dens evaginatus from an orthodontic perspective: report of several clinical cases and review of the literature. Am J Orthod Dentofacial Orthop 1997;112:670–675. Møller-Christensen V. Lebrosy changes of the skull. Odense University Press, Odense, 1978. Neville BW, Damm DD, Allen CM, Bounot JE. Oral and maxillofacial pathology, WB Saunders, Philadelphia, 1995. • There are conditions of the maxillary incisor teeth that are congruent with malformations in the brain. It might therefore be the dentist who is the first to diagnose a given condition. • Use the diagrams in Chapter 3 when making an etiology-based diagnosis of the dentition.

CHAPTER 9 Deviations in tooth number: normal and pathological variations including syndromes Deviation in tooth number can occur both as hypodontia, where • Maxilla – 54 individuals with agenesis of both lateral incisors, there are too few teeth present (called agenesis), and as hyper­ 48 individuals with agenesis of one lateral incisor, three dontia where there are too many teeth present (called supernu­ individuals with agenesis of one central incisor. merary teeth). • Mandible – 47 individuals with agenesis of one incisor, 15 Agenesis: possible etiologies individuals with agenesis of two incisors, 11 individuals with fusion of incisors. There are three tissue types that can cause agenesis: the dental lamina (ectoderm), the ectomesenchyme (mesoderm), and the • Maxilla and mandible – nine individuals with agenesis of neuroectoderm (innervation). A schematic representation canines and/or molars. appears in Figure 4.2. New genes are constantly being identified Agenesis in the incisor region appears in the location in as the etiological explanation for agenesis. In this book, the focus is on tissue types and genes will not be discussed in detail. As an which the nerve paths end (diagram in Figure 9.2). This might example, deviations in the p63 gene (gene product) cause indicate an innervation etiology but other explanations may be agenesis. Figure 4.3 illustrates how the gene product is expressed applicable. in the ectodermal tissue. In seven of the 215 cases it was demonstrated that the It can be debated whether a disruption factor can cause permanent lateral incisor in the mandible or maxilla was present agenesis. This aspect will be discussed later. in cases where the primary lateral incisor was absent. Also absence of the primary canine and presence of the permanent Agenesis of the primary and permanent canine have been observed (Figure 9.3). dentition: hypodontia Solitary median maxillary central incisor (SMMCI) is a Primary dentition agenesis syndrome characterized by one single incisor in the primary Agenesis in the primary dentition is rare (0.1–0.6 %). The teeth dentition as well as in the permanent dentition (see most often missing are the mandibular central incisors followed Figure 8.5). The single central incisor is considered to be by the mandibular lateral incisors (Figure 9.1). malformed as it essentially appears as a fusion of the lateral sides of a left and a right central incisor. The medial sides are The question that often follows is: “if the primary tooth is completely absent. This means that the single central incisor of absent, is the permanent tooth also absent?” The answer is that the the SMMCI condition is symmetrical along the midline axis. permanent tooth will be missing if the ectoderm is dysfunctional. This midline tissue absence is not restricted to the incisor However, if the innervation has not (by neuronal path-finding) region but is also observed along the frontal midline of the rest reached the primary tooth bud in time, this could be the cause of of the cranium up to the vertex. Thus the central incisor in agenesis. If this is the case, then there is still a chance that the SMMCI expresses a tooth malformation intergrated with a jaw innervation has reached the permanent successor which accord­ malformation of ectomesenchymal origin. Characteristics are ingly develops even if the primary tooth is absent. the short interocular distance, diminutive or absent spina nasalis anterior, a short nasal bone, and reduced crista galli In a Danish national study of referred radiographic material including deviations in the nasal septum and the anterior wall from 215 patients with agenesis in the primary dentition (99 were of the sella turcica. In some cases, brain malformations are boys, 80 were girls and 36 patients without gender information), observed (see Chapter 13). the distribution of agenesis was as follows. Agenesis of the canines and molars in the primary dentition is extremely rare. Cases are demonstrated in Figure 8.7 as well as in Figure 9.4. These cases also demonstrate deviation in tooth morphology similar to the deviations seen in ectodermal dysplasia (see Chapter 8) indicating an ectodermal etiology. Etiology-Based Dental and Craniofacial Diagnostics, First Edition. Inger Kjær. © 2017 John Wiley & Sons, Ltd. Published 2017 by John Wiley & Sons, Ltd. 111

112 Chapter 9 Figure 9.1 Agenesis of primary incisors. (Upper left) Radiograph of agenesis of a mandibular central incisor. Three permanent incisors are observed. (Upper center) Radiograph portraying agenesis of two primary mandibular central incisors. There are no apparent permanent central incisors in the radiograph. (Upper right) Radiograph portraying agenesis of the left primary maxillary lateral incisor. No permanent lateral incisor is present. (Lower left) Intraoral photograph of the incisor/canine region in a 3½-year-old child demonstrating absence of the left maxillary central incisor. (Lower right) Radiograph of the same child. There appears to be agenesis of the primary central incisor. The permanent lateral incisors are absent. Permanent dentition agenesis Prevalence and etiology The teeth most often congenitally missing are the mandibular second premolar (43% of patients with agenesis) followed by the maxillary second premolar (24%), the maxillary lateral incisor (19%), and the mandibular central incisor (7%). Figure 9.2 Demonstration of the innervation pathways to the maxillary Figure 9.3 Orthopantomogram from a child with abnormal tooth and mandibular incisors as well as the areas frequently affected by morphology. It is difficult to determine which teeth are permanent and hypodontia. (Left) Orthopantomogram (OP) from a child with agenesis of which are primary. It appears that there is no primary canine in the right the maxillary lateral incisors as well as the primary and permanent side of the mandible though a permanent anlage is present. The same mandibular central incisors. Drawn on the OP are orange lines (marked I) situation is apparent in the maxilla. indicating the bilateral innervation in the maxilla and in the mandible to the incisors. In the maxilla, these are the nasopalatine nerves and in the mandible, the lowest lying nerves in the bilateral inferior alveolar nerve bundles (see Chapter 2). (Right) Schematic drawing illustrating the occlusal view of the maxilla (upper) and mandible (lower). The teeth are marked by black signatures. The teeth colored red are those commonly affected by agenesis. In the maxilla, these are the lateral incisors, the second premolars, and the third molars. In the mandible, they are the central incisors, the second premolars, and the third molars. The arrows indicate the direction of the innervation to the different tooth groups.

Deviations in tooth number 113 Figure 9.4 Orthopantomogram from a child four years of age demonstrating the following congenital missing teeth in the maxilla: right, first primary molar, primary canine, primary incisors; left, primary canine or primary lateral incisor. There is agenesis of a large number of permanent teeth in this patient. There are many published works on agenesis of permanent Figure 9.6 A demonstration of the association between occurrence of teeth and nearly all of these studies are based on radiographic agenesis of the second premolar and of the interrelationship between material. Questions about why agenesis occurs are predominantly agenesis and late maturation of the first premolar. (Upper) An answered from a genetic perspective. Essential reports on agenesis orthopantomogram demonstrating agenesis of a second premolar in the in relation to genetics exist but how genes affect their target tissues maxilla as well as in the mandible. The right mandibular second premolar is often unknown. It is interesting that it is most often the last and the left maxillary first premolar are late in maturation. (Center) An tooth in the jaw field which is missing and that the teeth that are orthopantomogram demonstrating bilateral agenesis of the mandibular present within the same field can be delayed in maturation. This is second premolars and bilateral delayed maturation of the second depicted in Figures 9.2 and 9.5. Etiologically this might indicate premolars in the maxilla. (Lower) Diagrams illustrating the significant that the innervation or perhaps the ectomesenchyme extending to interrelationship between agenesis of the second premolars (marked by this region has an influence on the pattern of agenesis. arrows) in the mandible and in the maxilla. M, Male; F, female. Gray indicates the united male and female grouping, red the female group, and Bilateralism in the occurrence of second premolar blue the male group. Source: Kenrad et al. (2013). Reproduced with agenesis permission of Springer. A new study on patterns of second premolar agenesis involving 4756 individuals demonstrated that 193 individuals had agenesis Figure 9.5 Right side of an orthopantomogram demonstrating of one or both mandibular second premolars while 99 individuals malformations and agenesis in the premolar and molar regions of the had agenesis of one or both maxillary second premolars. An mandible. Two lines are drawn on the OP indicating the right-side interesting finding was that in the combined male and female innervation pathways to the canines and premolars (green, C/P) and to the group, there was a bilateral association between agenesis in the molars (blue, M). These nerves comprise the uppermost nerve paths in the right and left sides of the jaws as well as between the upper and inferior alveolar nerve bundle. lower jaw in the left side. There appear to be gender differences in these associations. Females demonstrated a significant associa­ tion between bilateral agenesis of the second premolar in the maxilla and in the mandible but not between the jaws. In contrast, males demonstrated bilateral association of occurrence of agenesis of the second premolar in the maxilla but not in the mandible. The male group also showed a significant association between agenesis of the second premolar in the maxilla and in the left-side mandible, but not in the right-side mandible. Tooth maturation can be delayed in a field with agenesis as well as in the contralateral field (Figure 9.6). When it comes to etiology, the question is “how can we explain this interrelationship between developmental fields?” One

114 Chapter 9 Agenesis of single teeth Single tooth agenesis can occur in the molar, canine, premolar, and incisor regions (Figure 9.8). Agenesis of several teeth In these cases, it should be considered whether the case is agenesis within a field or not. Agenesis in the molar fields is demonstrated in Figure 9.9, and agenesis in premolar fields is shown in Figure 9.10. Agenesis of canines can occur in just one region, in two regions or in all four regions (Figure 9.11). From a genetic point of view, different patterns of agenesis are associated with genotypic deviations. Concerning agene­ sis in the molar field, the Pax9 gene has been studied. As this gene is also decisive for early tooth formation in the primary dentition, it could be suggested that the occurrence of permanent molar agenesis is caused by a defect in signaling between the Pax9 gene and the ectomesenchyme in the molar field. Figure 9.7 Frontal radiograph of a human cranium illustrating the Multiple agenesis trigeminal ganglia (black) and the schematic innervation from the ganglia The etiology behind multiple agenesis is predominantly ecto­ toward the dentition. Red indicates the peripheral nerves for the incisors, dermal dysplasia (Figure 9.12). See the following section on green indicates the nerves to the canines and premolars, while blue syndromes, dysplasia, and hypodontia. indicates the innervation to the molars. Source: Kjær (2012). Reproduced with permission of Elsevier. Syndromes, disruption, dysplasia, and hypodontia answer could be the coordination between the nerves to the Syndromes maxilla and mandible within the trigeminal ganglia (Figure 9.7). Single median maxillary central incisor (SMMCI) is an example The nerves in the trigeminal ganglia arise from the neural crest of a syndromal occurrence of both one single primary and cells, but how the left and right sides of the neural crest are permanent maxillary incisor (see Figure 8.5). developmentally associated in the head region is unknown. It could be suggested that signals from the axial notochord influ­ In Rieger syndrome, agenesis occurs of maxillary incisors in the ence the bilateral neural crest edges. A right–left pattern is frontonasal field (Figure 9.13). common in normal body development. In Ellis–van Creveld syndrome, where the cartilage is affected, agenesis of the mandibular incisors and sometimes also of the canines occurs (Figure 9.14). The anterior region of the mandible has been formed in cartilage (see Chapter 1) and agenesis in this Figure 9.8 Three radiographs of the permanent incisors. (Left) Agenesis of the mandibular permanent central incisors. (Center) Agenesis of a mandibular permanent central incisor. The lateral incisor has migrated medially so no space is left where the central incisor should have been. (Right) Agenesis of primary and permanent maxillary lateral incisors.

Deviations in tooth number 115 Figure 9.9 Radiographs portraying agenesis of various permanent molars. (Left) Agenesis of the permanent first and possibly also the second molar in the right maxilla. In the left side, all three permanent molars are present. The etiology behind the agenesis in the case is not known. (Upper center) Agenesis of a mandibular permanent second molar in the left side. In this case, agenesis of the permament lateral incisors also occurs. (Lower center) Orthopantomogram demonstrating agenesis of all four permanent second molars. (Upper right) An orthopantomogram demonstrating agenesis of all permanent molars. (Lower right) An orthopantomogram demonstrating agenesis of the maxillary permanent molars and the second mandibular molar in the left side. syndrome likely occurs due to deviation in the ectomesenchyme. Figure 9.11 Agenesis of permanent canines. (Upper) A section of the In this syndrome affecting the incisors, the etiology seems to be maxilla from an orthopantomogram demonstrating agenesis of the linked to the ectomesenchyme. permanent maxillary canines. Agenesis of the canines can occur in one, two, three or all four fields. In the present case, there was also agenesis of In mandibular cleft syndrome, agenesis of the mandibular the second premolar in the mandible. It is characteristic for patients with incisors also occurs in the mental region of the mandible agenesis of permanent canines not to have other specific deviations. (Figure 9.15). (Lower) Orthopantomogram demonstrating agenesis in the left side of the mandible of the central lateral incisors and the left mandibular canine. In Down’s syndrome, agenesis occurs frequently in the com­ monly observed agenesis pattern (Figure 9.16), but is relatively more frequent in the mandibular incisor region. The total frequency of agenesis (third molar excluded) in Down’s syn­ drome is 81% while the occurrence in nonsyndromal indidivuals is about 8%. In combined cleft lip and palate, agenesis occurs mostly in the lateral incisor region (see Chapter 13). In ADULT (acrodermatoungual lacrimal tooth) Syndrome, agenesis occurs in association with finger and toe malforma­ tions. In such a case, it can be assumed that the agenesis (which is not restricted to fields) is due to an ectodermal deviation because the formation of the hand and foot also depends on the ectodermal tissue layer. In the early develop- ment of the limbs, the ectodermal layer (ectodermal ridge) Figure 9.10 An orthopantomogram demonstrating agenesis of all Figure 9.12 An orthopantomogram demonstrating a case with multiple premolars. Agenesis of premolars can also occur in one, two or three agenesis of permanent teeth. fields. The present case demonstrates agenesis in all four.

116 Chapter 9 Figure 9.15 Section from an orthopantomogram from a patient with mandibular cleft syndrome demonstrating agenesis of the mandibular incisors in the mental region. Figure 9.13 Dentitions with congenitally missing permanent maxillary central incisors. (Upper) Orthopantomogram demonstrating Reiger’s syndrome with absence of all permanent incisors in the maxilla. (Lower) Clinical photograph of a case with congenital absence of central incisors. A syndrome was not diagnosed. plays a significant role in the outgrowth of the extremities and later also finger and toe formation. Disruption In some cases, where virus attack has disturbed the Schwann cells covering the peripheral nerves, tooth disturbances can occur within one or several fields. Absence of teeth can also be observed in such cases, in which it is believed that disruption by virus attack could be the main etiology behind the agenesis condition (Figure 9.17). Disruption by chemotherapy might disturb early tooth development and might explain the absence of teeth in Figure 9.14 The mandibular section of an orthopantomogram Figure 9.16 An intraoral photograph of an adult with Down’s syndrome demonstrating absence of the incisors in a case with Ellis–van Creveld demonstrating agenesis of the permanent maxillary lateral incisors as well syndrome. The permanent canines appear malformed. as the mandibular incisors. There is only one primary incisor left but three permanent incisors are missing.

Deviations in tooth number 117 Figure 9.17 Orthopantomogram demonstrating absence of the mandibular Figure 9.19 Orthopantomogram demonstrating abnormal development in permanent second molar in the left side. The first molar has arrested in the right mandibular premolar field. This is a regional, segmental, eruption (see Chapter 10). A blue line (M) marks the innervation to the mandibular dysplasia involving congenital absence of the second premolar molar field. It is presumed that a virus infection infecting the myelin and ectopia of the canine and first premolar in the field. Two years of sheath of the nerve has disturbed the region, which might be the etiology orthodontic treatment were performed in order for the first premolar and behind the absence of the second molar. This could be an acquired canine to erupt, but the treatment was not successful (see inset top left). agenesis due to early disruption of the odontogenesis of the second molar. Only the first premolar could be moved slightly, but it never penetrated the mucosa. A regional dysplasia in the bone tissue might have been the reason for the difficulties in treating this patient. specific regions (Figure 9.18). This may occur if chemo­ therapy is given during the period in which the mucosa begins tooth formation. Dysplasia Dysplasia in ectomesenchymal tissue (bone) and in ectodermal tissue (oral mucosa) can cause agenesis. Dysplasia in ectomesenchymal tissue In cases with segmental dysplasia in the maxilla or mandible, agenesis occurs in relation to localized tissue dysplasia. This is exemplified in segmental maxillary and segmental mandibular dysplasia (Figure 9.19). Figure 9.18 Left side section from an orthopantomogram of a child who Dysplasia in ectodermal tissue received chemotherapy at the age of two years. The right side has the same There are many different types of ectodermal dysplasia and the molar appearance. There seems to be agenesis of the mandibular second agenesis pattern can differ accordingly. molar while the maxillary second molar is just a tiny, narrow tooth which does not resemble a maxillary molar. In this case, it is assumed that the Multiple agenesis of primary and permanent teeth occurs chemotherapy treatment has disrupted the molar formation, resulting in frequently in patients with anhidrotic ectodermal dysplasia an agenesis-like condition in the mandible and a malformed second molar (Figure 9.20). The agenesis pattern in the permanent dentition in the maxilla. may be observed in only one jaw (see Figure 9.20) but it can also be characterized by agenesis within fields, such as the molar or premolar fields, or it may be sporadic. The teeth present are often small in size and with deviant morphology. Also, the condition incontinentia pigmenti is associated with tooth agenesis. In this condition, the pattern of agenesis is often asymmetrical and affects teeth which are normally stable in their occurrence (Figure 9.21). It is uncertain whether the teeth ever were formed in the initial stages or whether they are formed and then disintegrated during later development. This disintegration has been seen in prenatal ectodermal dysplasia (see Figure 4.6).

118 Chapter 9 Figure 9.22 Orthopantomogram from a child demonstrating supernumerary teeth in the maxillary incisive region as well as agenesis of the mandibular second premolar. Supernumerary teeth and agenesis rarely occur in the same dentition. This case is not a characteristic supernumerary case, which usually includes the presence of the third molars and broad incisors. When supernumerary teeth occur in a case like this, the supernumeraries are often located in the maxillary front. Figure 9.20 Multiple agenesis in ectodermal dysplasia. (Upper) (Figure 9.22). When this does arise, it is seen especially in cases of Orthopantomogram of the dentition in a child with anhidrotic ectodermal supernumerary teeth in the maxilla. dysplasia demonstrating multiple agenesis. (Lower) Orthopantomogram of the dentition in a child with ectodermal dysplasia. Notice the malformed Supernumerary teeth in the primary and teeth and multiple agenesis. permanent dentition: hyperdontia Supernumerary teeth: possible etiologies Primary dentition supernumeraries Hyperdontia is rare in the primary dentition. The occurrence is Characteristic of dentitions with supernumerary teeth is that, estimated to be 0.3–0.6% and is mostly seen in the incisor regions contrary to agenesis, the teeth are wide and the third molars are (Figure 9.23). Supernumerary primary canines are a rare finding nearly always present. The genes involved in extra tooth devel­ (see Figure 9.23). opment have been studied experimentally but how a genetic deviation affects an extra outgrowth of the dental lamina is not Permanent dentition supernumeraries known. It is rare to observe supernumerary teeth in a dentition In the permanent dentition, hyperdontia occurs with a frequency where agenesis also occurs, but this does happen occasionally of 0.1–3.6% and is most often observed in the maxillary incisor region. Figure 9.21 Orthopantomogram from a child with incontinentia pigmenti Mesiodens and maxillary incisors demonstrating multiple agenesis, malformed teeth (especially maxillary A mesiodens occurs in approximately 1% of the human popu­ central incisor), and ectopic eruption. This case revealed severe resorption lation and nearly always in the maxillary incisor front. The during orthodontic treatment of ectopia. mesiodens is an extra tooth that can have various shapes (Figures 9.24 and 9.25). A classic mesiodens is located right on the midline, covering the interincisal suture on a radiograph. However, bilateral extra tooth buds in the central incisor region have also been called mesiodentes (Figure 9.26). It is question­ able whether the classification of mesiodentes is sufficiently clear. Supernumerary incisors, most often laterals, occur unilaterally and bilaterally with a normal anatomical appearance or with narrow crowns and malformed roots (Figure 9.27). In cleft lip cases, supernumerary laterals are a common finding (Figure 9.28) while this is not the case in combined cleft lip and palate (see Chapter 13). In cleft lip and palate syndromes, the shape and number of teeth in the dentitions of the three cleft groups are

Deviations in tooth number 119 Figure 9.23 Supernumerarity of primary and permanent incisors. (Left) Intraoral radiograph from the left maxillary incisor region of a child. The primary central and lateral incisors are fused and a supernumerary primary lateral incisor appears posteriorly fused. In the permanent dentition, no supernumeraries occur. (Center) Section of an orthopantomogram from a child demonstrating the incisor region. A supernumerary primary as well as permanent lateral incisor appear. The right, permanent central incisor is delayed in emergence. (Right) Intraoral radiograph demonstrating supernumerary, primary canine (or incisor?) in the left side of the maxilla. The most posteriorly located extra tooth is malformed. There appears to be supernumerarity in the permament dentition as well. different. This observation may support the general belief that Mandibular incisors the etiology and genotypes behind the cleft syndromes are Supernumerary central and lateral incisors can occur in the different. Another observation is that in the cleft lip condition, mandible (Figure 9.29). in which the dental arch has not been united, supernumerary teeth may occur in this region. This suggests that the etiology Supernumerary premolars behind the supernumerary teeth is rooted in the dental lamina. Most often, these extra tooth buds occur quite late in the In the combined cleft lip and palate condition, in which there is dentition (Figures 9.29 and 9.30). In cleidocranial dysplasia, it also a gap in the lateral maxillary region, supernumerary teeth are is characteristic that several extra tooth buds occur in several normally not present. The etiology behind this is that the deviant different regions, but specifically in the premolar region (see gap arose by a different mechanism than the gap that appears in Chapter 15). isolated cleft lip. In the combined cleft lip and palate, the entire gap in the maxilla arises due to the malformation of the soft tissue Supernumerary canines and molars palatine shelves (see Chapter 13). This can occur in cleidocranial dysplasia as well as in cases without a known diagnosis. From an etiological point of view, Figure 9.24 A schematic overview of mesiodentes with different it is characteristic that supernumerary teeth occur in dentitions appearances and locations in the maxilla. (Upper left) Drawing of the with broad teeth in which the third molars are nearly always normal permanent incisors in relation to the intermaxillary suture. (Upper present. The etiology might be interrelated with an extra out­ right) A supernumerary tooth appears close to the left permanent growth in the terminal regions of the dental lamina from where maxillary central incisor. (Lower left) Two supernumerary teeth appear the primary and permanent dentitions are formed. close to permanent maxillary central incisors. (Lower right) A mesiodens located axially, covering the intermaxillary suture. An extra second molar can occur (Figure 9.31) and also a fourth molar can occur either in one region or in several regions. Figure 9.33 demonstrates radiographic images from identical twins, one of whom has two fourth molars in the maxilla while the other has two fourth molars in the mandible. This finding supports a genetic background for the occurrence of supernu­ merary teeth. Figure 9.31 demonstrates six molars in the right maxillary molar field. The explanation for this rare pattern of super­ numerarity could be a unilateral duplication of the palatal developmental field and accordingly, the etiology should be found in the right neural crest. This viewpoint also supports the notion of a genetic background for the occurrence of supernumerary teeth. Figure 9.32 also illustrates a seldom case of a supernumerary canine. Figure 9.34 demonstrates an anthropological case with supernumerary molars in the

120 Chapter 9 Figure 9.25 Different examples of mesiodentes (stars) displayed in radiographs of various children. (Upper left) Section from an orthopantomogram of an axially located and erupted, broad mesiodens with a talon cusp. (Upper right) Bilateral mesiodentes covering the permanent central incisors. (Lower left) Bilateral mesiodentes covering the permanent central incisors. (Lower center) Unilateral mesiodens blocking emergence pathway of the permanent maxillary central incisor. (Lower right) Bilateral mesiodentes between the central incisors. maxilla upper jaw and in the lower jaw as well as a mesiodens has a short stature and a reduced clavicle formation (see in the maxilla. Chapter 15). Syndromes, dysplasia, and supernumerary How to analyze the etiology behind teeth deviation in tooth number Hyperdontia can be a local finding without known etiology. However, it can also be part of a syndrome (cleft lip and It is important to consider whether the deviation in tooth number palate) or it can be caused by a dysplastic change in the cells occurs as a normal variation in the dentition or whether it is and tissue (cleidocranial dysplasia). In cleidocranial dyspla­ related to a syndrome or a dysplasia condition. sia, the mesodermal bone tissue is dysplastic and the patient Figure 9.26 Orthopantomogram from a child demonstrating supernumerarity of the maxillary permanent central incisors. Frontal sections from a CT scan are inserted in the lower part of the figure. The sections are organized in order from most anteriorly cut (left) to most posteriorly cut (right). The two center figures illustrate the supernumerary incisors.

Deviations in tooth number 121 Figure 9.27 Different examples of supernumerary permanent incisors with close to normal morphologies. The stars indicate the teeth which are presumed to be the supernumeraries. (Upper left and center) Intraoral photographs demonstrating supernumerary, permanent central incisors in the right side of the maxilla. (Upper right) Supernumerary central incisors have erupted between the normal, permanent central incisors. These supernumeraries are narrow compared to normal incisors. The sister of this patient has macrodontic central incisors. (Lower left) Section from an orthopantomogram from a child with six permanent incisors in the maxilla. (Lower right) Section from an orthopantomogram from a child with five permament incisors in the mandible. Figure 9.28 Supernumerary permanent lateral incisors in a cleft lip Figure 9.29 Orthopantomograms demonstrating supernumerary patient. There is also a cleft in the alveolar bone. The two lateral incisors premolars observed late in the mature dentition where premolars have close to the bony cleft are marked by stars. already erupted. (Upper) Supernumerary premolars in the mandible. The patient is 17 years old. Inset is a 3D scan from another patient demonstrating the location of a supernumerary premolar compared to already erupted teeth. (Lower) Supernumerary premolars in the maxilla. The patient is 15 years old. These orthopantomograms demonstrate characteristic dentitions with supernumerary teeth. All the teeth are present, including the third molars, and the teeth are broad.

122 Chapter 9 Figure 9.30 Occurrence of supernumerarity observed in the different In hypodontia cases where the condition is not related to developmental fields. (Upper) Orthopantomogram demonstrating syndromes, the etiology can be explained by the innervation supernumerary teeth in all four canine/premolar fields. (Lower) pattern, by the ectomesenchyme or possibly by the ectoderm. Orthopantomogram demonstrating permanent, supernumerary molars The condition might also be caused by disruption, as (ninth tooth) in all four molar fields. observed in chemotherapy or virus attack (see Figures 9.17 and 9.18). In hyperdontia, innervation does not play a significant role, but the ectomesenchyme and the ectoderm in the dental lamina appear to be primarily involved. The regional occur­ rence of supernumerary teeth is most often seen in the lateral maxillary region and the second mandibular premolar region as well as posteriorly in the molar region. This pattern of occurrence indicates that the etiology could be an extra outgrowth of the dental lamina in field border regions (this is still hypothetical). Disruption can apparently not explain hyperdontia (cleft lip is not a disruptive phenomenon; see Chapter 13). The frequency of hyperdontia in isolated cleft lip cases might be related to a disruption of the dental lamina occurring on the borderline between the frontonasal and maxillary fields. Figure 9.31 Supernumerary, maxillary permanent molars are rare. The figure demonstrates this condition in three different patients. (Upper) A supernumerary first or second permanent molar in the left side of the maxilla appears on the dental cast (left) and radiographically in a section from an orthopantomogram (right). It is difficult to see the supernumerary molar on the radiograph. (Lower left) A patient with supernumerary molars in the maxilla. In the right maxilla, there appears to be an eighth, ninth, and tenth tooth. The etiology could be an extra palatine field which may have arisen due to an extra palatine area on the neural crest. (Lower right) A section from an orthopantomogram from a child demonstrating an extra tooth resembling a premolar in the left maxillary molar field. Whether this is a supernumerary molar or whether it is a transposition between the first molar and a supernumerary premolar cannot be confirmed.

Deviations in tooth number 123 Figure 9.32 Radiographs demonstrating supernumerarity of permanent molars and canines which are rare findings. (Upper left) A patient with an extra tooth bud between the first and second permanent mandibular molars in the right side. (Upper right) Section from an orthopantomogram from a child with extra tooth buds between the first and second permanent mandibular molars. Severe eruption deviations were observed in the maxilla. The patient is under observation for a diagnosis. (Lower left) Sections from an orthopantomogram with supernumerary canines bilaterally. (Lower right) Section from a radiograph demonstrating the right side of the maxilla with a supernumerary canine. Source: Reproduced with kind permission of Eirik Torjuul Halvorsen. Highlights and clinical relevance • Tooth agenesis occurs both restricted to jaw fields and unrestricted. • There is a bilateral concurrence of agenesis occurrence, as well as concurrence in the agenesis pattern between the jaws. • The pattern of agenesis occurrence and the pattern of super­ numerary teeth occurrence indicate different tissue etiology behind the conditions. • It has been shown that agenesis within a field is followed by late maturation of other teeth in the field, as well as in the contralateral jaw field. This is important to bear in mind when creating a treatment plan. Figure 9.33 Orthopantomograms from identical twins at age 13½ years. Figure 9.34 Anthropological human jaws in the occlusal view One twin (upper) has maxillary fourth molars (marked by stars) while the demonstrating supernumerary molars in the maxilla and in the mandible other (lower) has mandibular fourth molars (also marked by stars). as well as a mesiodens midaxially in the maxilla.

124 Chapter 9 • Agenesis has different etiologies related to different tissues. aetiological factor behind dental anomalies. Orthodont Waves • Supernumerary teeth occur in dentitions with large teeth and 2012;71:1–16. Kjær I, Daugaard-Jensen J. Interrelation between fusions in the primary often also with the presence of third molars. dentition and agenesis in the succedaneous permanent dentition seen from an embryological point of view. J Craniofac Genet Dev Biol Further reading 2000;20:193–197. Kjær I, Becktor KB, Nolting D, Hansen BF. The association between Brook AH. A unifying aetiological explantion for anomalies of human prenatal sella turcica morphology and notochordal remnants in the tooth number and size. Arch Oral Biol 1984;29 (5):373–378. dorsum sellae. J Craniofac Genet Dev Biol 1997;17:105–111. Kjær I, Kocsis G, Nodal M, Christensen LR. Aetiological aspects of Brook AH, Griffin RC, Smith RN, et al. Tooth size patterns in patients mandibular tooth agenesis – focusing on the role of nerve, oral with hypodontia and supernumerary teeth. Arch Oral Biol 2009; mucosa, and supporting tissues. Eur J Orthod 1994;16:371–375. 54:63–70. Lomholt JF, Russell BG, Stoltze K, Kjær I. Third molar agenesis in Down Syndrome. Acta Odontol Scand 2002;60:151–154. Daugaard-Jensen J, Nodal M, Skovgaard L, Kjær I. Comparison of the Nordgarden H, Reintoft J, Nolting D, Hansen BF, Kjær I. Craniofacial pattern of agenesis in the primary and permanent dentitions in a tissues including tooth buds in fetal hypohidrotic ectodermal dyspla­ population characterized by agenesis in the primary dentition. Int J sia. Oral Dis 2001;7:163–170. Paediatr Dent 1997;7:143–148. Rølling S. Hypodontia of permanent teeth in Danish school children. Scand J Dent Res 1980;88:365–369. Hansen L, Kjær I. A premaxilla with a supernumerary tooth indicating a Rølling S, Poulsen S. Oligodontia in Danish school children. Acta developmental region with a variety of dental abnormalities: a report Odontol Scand 2001;59:111–112. of nine cases. Acta Odontol Scand 2004;62:30–36. Schalk-van der Weide Y. Oligodontia. A clinical, radiographic and genetic evaluation. Thesis, University of Utrecht, 1992. Kenrad JB, Christensen IB, Kjær I. Gender differences in patterns of Stockton DW, Das P, Goldenberg M, D’Souza RN, Patel PI. Mutation of second premolar agenesis observed in 4,756 individuals. Eur Arch PAX9 is associated with oligodontia. Nat Genet 2000;24:18–19. Paediatr Dent 2013;14 (6):397–403. Kjær I. New diagnostics of the dentition on panoramic radiographs – focusing on the peripheral nervous system as an important

CHAPTER 10 Tooth eruption and alveolar bone formation: abnormal patterns including syndromes Pathological eruption of primary teeth preemergence phase. The four types of primary molar impaction are demonstrated in the mandible in Figures 10.4, 10.5, 10.6, and Abnormal times for eruption 10.7. Severe arrest of a primary molar in the maxilla is also Late eruption can be a normal condition but it can also be illustrated in these figures. The etiology behind this impaction is abnormal. Late eruption can be due to lack of function of the not fully understood. tissue layers which are important for the eruption process (e.g. deviated ectoderm in ectodermal dysplasia). If the eruption In the most severe cases, the permanent premolar can be sequence deviates from the normal pattern described in previous seen occlusal to the primary molar or at a position lateral to chapters, it could be linked to a genetic deviation, for example the impacted molar (see Figures 10.4–10.6). This indicates Down’s syndrome, in which the primary molars may erupt at the ankylosis of the primary molar very early in life at a time when same time as the incisors (Figure 10.1). Eruption is delayed in the permanent tooth bud is still located side by side with the Down’s syndrome but whether this is related to the peripheral primary molar, or perhaps at a time when the permanent tooth nervous system (PNS) is not yet elucidated. There is very little has not yet started to develop (see Figure 10.2). The normal information on pathological eruption patterns in the primary eruption of a primary molar seems to be a necessity for the dentition. permanent molar to enter its location underneath and between the roots of the primary molar. As an ankylosed primary molar The early interaction between the primary and permanent cannot move, the premolar will never enter the location below tooth germs is essential for normal development of the dentition the primary molar, but will erupt independently. If space (Figure 10.2). At the time when the primary dentition begins to allows, the premolar will erupt to an ectopic position in the shed, this interaction has an influence on the permanent denti­ jaw or to a position occlusal to the primary molar. In the most tion (see Figure 10.2). severe cases of arrested eruption, the primary molar roots are needle-shaped and the succeeding premolars are displaced and Total failure to erupt malformed. This is an example of disruption in a permanent Absence of eruption in the primary dentition is extremely rare. It tooth caused by ankylosis of a primary tooth bud. In cases with can occur in Gapo’s syndrome or in a condition supposed to be retention of a primary molar, an overeruption of the antago­ Gapo’s syndrome (Figure 10.3). In this syndrome, not only the nistic primary molar can sometimes be observed. Impaction of primary but also the permanent teeth are unable to erupt. It is a first primary molar and of several first primary molars is believed that the epithelial lining in the follicle and along the peri­ illustrated in Figure 10.6. root sheet could be abnormal. Arrested eruption of single teeth Pathological eruption of permanent teeth Eruption problems in the primary dentition of normally devel­ oped children occur especially in the molar teeth. Impacted (or Abnormal times for eruption retained) primary first and second molars are a frequent obser­ Ectopic location of tooth buds and blockage of the eruption path vation, especially the second molar. There are four types of create deviations in eruption (Figure 10.8). primary molar impaction, from less severe to very severe. In severe cases, the impaction influences the permanent successor. Not much is known about the etiology behind eruption times/ In the most severe cases, the primary molar impaction occurs periods of the permanent dentition. It seems reasonable that the before the molar starts its eruptive movement. This means that active growth of a child, which reflects endocrine conditions the arrest in eruption is a primary retention occuring in the influencing the body height and the jaw growth, also influences these periods of eruption. Etiology-Based Dental and Craniofacial Diagnostics, First Edition. Inger Kjær. © 2017 John Wiley & Sons, Ltd. Published 2017 by John Wiley & Sons, Ltd. 125

126 Chapter 10 follow this eruption pattern, the eruption process is deemed pathological. Examples are illustrated in Chapter 6. The etiologies behind such deviations are uncertain. In extreme cases and in cases where tissue abnormalities such as dys­ genesis are involved (for example, osteogenesis imperfecta), the patient must be referred to a physician for proper diagnosis and treatment. It is important also to remember the influence of the innerva­ tion on tooth eruption. Teeth in a field with the same innervation therefore often have the same temporospatial eruption pattern. Eruption deviations can occur within one field or within several fields, and they can be unilateral (Figure 10.9) as well as bilateral (Figure 10.10). Unilateral asymmetry in the eruption pattern is seen in the Proteus syndrome, in which an overgrowth in one side of the jaw can be associated with early eruption in the same side. Figure 10.1 Intraoral photographs of a child with Down’s syndrome 4½ Ectopic eruption of maxillary canines years of age. Note that the second molars in the maxilla (arrows) and in There are two types of ectopic permanent canine eruption in the the mandible are undergoing eruption while the lateral incisors have still maxilla. Labially or buccally erupted canine is one type and not fully erupted. The first primary molars and canines have not erupted palatally erupted canine is another. Ectopic canine eruption can either. This photographs demonstrate a deviation in the normal eruption be unilateral or bilateral. Referring to Chapter 12, there is a sequence. Source: Reproduced with kind permission of Drs Jón Ólafur difference in the two dentitions where the canines erupt labially Sigurjónsson and Sigurður Rúnar Sæmundsson. and palatally respectively. Two main periods are recognized in which the permanent The etiology behind labial ectopia is lack of space, while the teeth erupt. The first occurs at about 6–8 years of age, when the etiology behind palatal ectopia is presumably a defective eruption incisors and first molars erupt. The second period comes mechanism or reduced space in the maxilla. Whether the defect is approximately four years later at puberty, where the canines, in the crown follicle, root membrane, periodontal membrane or premolars, and seconds molars erupt. If a child’s teeth do not maxillary bone is not always clear. A common characteristic of dentitions with palatally located canines is that the dentition in general has many malformations such as invaginations, tauro­ dontia, and peg-shaped incisors. Studies have shown that unilateral palatine canines often have dentitions with invaginations and peg-shaped laterals. In con­ trast, cases with bilateral canines often, but not always, have taurodontia of the molars and agenesis of the third molars. This might indicate different etiologies for unilateral and bilateral occurrence of palatal canine ectopia. If this is so, then the bilateral Figure 10.2 The interrelationship between the primary and permanent dentition during early formation and eruption of primary and permanent teeth. (Left) Two illustrations indicating a developing primary molar (green), the nearby early tooth bud (blue) of the permanent tooth (left drawing). Later, the permanent tooth takes a position below the primary molar. What guides the permanent tooth to this position is not yet understood. It is presumed that the eruption path of the primary molar is diagonally directed so that the primary tooth becomes positioned occlusal to the premolar. (Center) Intraoral photograph of a two-year-old child demonstrating delayed eruption of the left maxillary lateral incisor. This tooth erupted half a year after the photograph was taken. Later agenesis of the permanent left maxillary lateral incisor was noted. This figure demonstrates the interrelationship between agenesis in the permanent dentition and delayed eruption in the primary dentition. (Right) Intraoral photograph of a dentition where the premolars have erupted but the deciduous teeth have not been shed. This figure illustrates an abnormal interrelationship between shedding of the primary dentition and eruption of the permanent dentition.

Tooth eruption and alveolar bone formation 127 Figure 10.3 Radiographs from a child, age unknown, with a syndrome presumed to be Gapo’s syndrome. In this syndrome, neither the permanent nor the primary teeth are able to erupt. (Upper left) An orthopantomogram after surgical removal of the primary dentition. The permanent dentition did not erupt following the procedure. (Upper right) Profile radiograph of the child. (Lower) Section of an orthopantomogram at the age of four years when the primary dentition was still present in the mandible. Source: Reproduced with kind permission of Drs Jón Ólafur Sigurjónsson and Sigurður Rúnar Sæmundsson. cases have a more skeletally influenced etiology while the uni- problems in the lower jaw (Figures 10.12, 10.13, and 10.14). lateral cases would be due to an eruption disruption localized to However, mandibular ectoptic canine eruption can also be the maxillary front (Figure 10.11). observed in cases without space problems. It is presumed that early diagnosis and treatment of slightly tilted mandibular Ectopic eruption of mandibular canines canines can prevent the development of horizontally positioned Mandibular ectopic canine eruption is often observed in cases canines, which make orthodontic treatment extremely difficult with delayed maturation of the canines and severe space and in most cases impossible. Figure 10.4 Different degrees of retention of primary molars. (Upper left) Four schematic drawings of the grades of severity of a second primary molar retention, which increase from left to right: (1) a minor difference in occlusal level compared to the first permanent molar, (2) a greater difference in occlusal level compared to the first permanent molar, (3) occlusal level of the primary molar at the gingival level and (4) completely retained second molar with an ectopic location of the crown of the premolar on the occlusal surface of the second primary molar. Ectopia of the premolar can also occur lateral to the primary molar. This last, most severe case illustrates the earliest possible type of retention of a primary mandibular molar, in the prenatal or perinatal period. (Upper right) An intraoral photograph of a retained maxillary first primary molar in a child five years of age. This molar appears at the gingival level. The radiograph to the right demonstrates a retained mandibular second primary molar. The molar appears at the gingival level. Both figures to the right demonstrate grade 3 severity of retention. (Lower) Three radiographs demonstrating three different situations of the most severe grade of retention of the mandibular second primary molar. (Left) The crown of the premolar is located occlusally to the second primary molar (see also schematic Drawing 4). (Center) Retention of the second primary molar and ectopia of the permanent second premolar crown. (Right) Demonstration of the first permanent molar tilting in over the retained second primary molar. In the lower right corner, the crown of an ectopic second premolar is observed. Source: Kjær et al. (2008). Reproduced with permission of John Wiley & Sons.

128 Chapter 10 Figure 10.5 Overview of orthopantomograms and sections of orthopantomograms demonstrating retention of primary molars in the mandible and maxilla. (Upper left) Retention of a right mandibular primary molar in a child four years of age. The retention has appeared early (pointed root morphology). The maxillary primary second molar has overerupted. It is likely that there is agenesis of the mandibular premolar. (Upper right) Demonstration of a right mandibular primary molar retention in a child five years of age. The second premolar in the region of retention appears to be disturbed. (Lower left) Demonstration of a retained left maxillary primary second molar in a child five years of age. (Lower right) Demonstration of a retained right maxillary primary molar. The second premolar in the region has an ectopic location. Figure 10.6 Overview of orthopantomograms and sections of orthopantomograms demonstrating retention of primary molars in the maxilla (upper) and in both the maxilla and mandible (lower). (Upper left) Radiograph demonstrating retention of a maxillary first primary molar before eruption of the permanent first molar. (Upper right) Radiograph demonstrating retention of a maxillary second primary molar after eruption of the permanent first and second molars at the age of 13 years. This is an undesirable situation where the second primary molar should have been extracted at the stage demonstrated in the upper left radiograph in another child. (Lower) Demonstration of an orthopantomogram in which all second primary molars are retained. The second molars in the mandible were retained earlier than the second primary molars in the maxilla. Notice the needle-shaped roots of the mandibular primary molars and the ectopic location of the crown of the mandibular second premolar crowns. In the maxilla, the retention is not as severe as in the mandible and the crowns of the second premolars have a normal location. Treatment is not needed in the maxilla. Meanwhile, in the mandible, the primary second molars should be extracted and space retainers inserted.

Tooth eruption and alveolar bone formation 129 as well as in the maxillary molar region. Less common is transposition in the mandible (see Figure 10.16). It is interesting that transposition can be observed between fields as well as within fields. In transposition cases, it could be hypothesized that the dermatomes (a dermatome is an ecto­ dermal/skin segment innervated by one specific spinal nerve) are overlapping in the transposition regions. The overlapping of dermatomes is a well-known phenomenon in other parts of the body but has apparently not been described in the dental arch. Ectopic eruption of molars, premolars, and other teeth First molar Ectopic eruption of the first molar can result in resorption of the second primary molar. This can occur in just one primary molar, but also in all four permanent molars (see Chapter 11). The etiology behind this eruption pattern is not known, but studies have demonstrated that approximately a quarter of cases with ectopic permanent canine eruption had ectopic first molar eruption at the time when the first molar erupted five years earlier. The explanation for the association between the canine ectopia and the first molar ectopic eruption patterns has not been elucidated. Figure 10.7 Section from an orthopantomogram (upper) and a dental Second molar film (lower) demonstrating that space problems due to abnormal The second molar can also erupt ectopically. Figure 10.17 shows eruption patterns in primary molars can occur early. (Upper) The left an extreme case in which the second molar erupts in the mandibular second molar is retained in a child 3½ years old. The mandibular ramus. An example of a cyst which has displaced roots are apparently arrested in development and ankylosed. The first a tooth bud is shown in Figure 7.3. permanent molar has already tilted mesially, indicating a later mesial eruption. The second mandibular premolar does not appear in the Third molar radiograph. Treatment is surgical removal of the second primary Ectopic eruption of the third molar is most often caused by molar when the child is ready to accept the treatment but as agenesis space problems in the mandible due to the anterior border of occurs, immediate treatment is not necessary. (Lower) Dental film the ramus, and in the maxilla due to a lack of growth in the from a 7½-year-old child. The radiograph was taken due to transverse palatal suture and lack of apposition in the tuber observation of the first permanent molar, which has not erupted. It region. The third molar can erupt in several different direc­ appears that the second premolar has an ectopic location which tions (Figure 10.18). apparently obstructs the eruption path of the first permanent molar. This radiograph also demonstrates that an ectopic premolar can occur without retention of the primary second molar. (See Figures 10.4 and 10.6 for examples of ectopia of the second premolar in connection with retention of the primary molar.) The etiological consideration in cases with lack of space is that Premolar and incisor the reduced space for the tilted canine becomes aggravated when If there are no obstructions in the eruption path, then ectopia of the neighboring teeth erupt continuously. premolars and incisors nearly always occurs due to malposition­ ing of the early tooth bud (Figures 10.19 and 10.20). Not only Transposition radiographic observations but also anthropological observations Another type of ectopic canine eruption is transposition which can clearly illustrate extreme ectopia (see Figures 10.17 and can occur in the maxilla and the mandible. Transposition is most 10.19). Large, ectopic devations of the incisors may also occur, often a positional interchange between the maxillary canine and obstructing normal eruption (see Figure 10.20). the maxillary first premolar (Figures 10.15 and 10.16). Transpo­ sition can also be seen between the canine and the lateral incisor, Arrested eruption after trauma Arrested eruption of permanent incisors can occur after trauma in either the primary or the permanent dentition – examples are shown in Figure 10.21.

130 Chapter 10 Figure 10.8 Overview of dental films and sections of orthopantomograms demonstrating ectopia of permanent teeth which inhibits normal eruption. (Upper left and center) The premolars are located “upside down.” There is no known explanation for this type of ectopia. (Upper right) A follicular cyst might be the cause of ectopia of the right mandibular permanent canine and first premolar. (Lower left) The section is from a 17-year-old patient. A maxillary third molar has apparently inhibited the left maxillary permanent second molar in eruption. At this stage, it is not possible to distinguish whether the second molar is ankylosed or merely blocked in eruption. It is likely that the second molar is ankylosed and that this might be the cause of the ectopic third molar. (Lower right) The section is from a 13-year-old child. The ectopic position of the right mandibular second molar seems to be due to a lack of space. The ectopia of the second premolar occurs in a region where severe caries have occurred in the second primary molar (which has recently been extracted). Figure 10.9 An orthopantomogram of a child nine years of age Figure 10.10 Two orthopantomograms from the same child at age 11 demonstrating arrested eruption of the left mandibular first permanent years (upper) and 15 years (lower). The radiographs demonstrate molar and absence of the second molar in the region. The crown follicle development of the dentition due to secondary retention of the first on the first molar appears enlarged around the crown. The molar is mandibular molars and presumably also arrested eruption of the right primarily retained and the treatment is surgical exposure of the crown. maxillary molar. (Upper) It appears that arrested eruption of the left This treatment normally ends with a natural eruption. It can be maxillary primary second molar has occurred. It seems that also the right hypothesized that there has been a virus infection in the left mandibular first maxillary molar has arrested in eruption. (Lower) Four years later, the branch of the left inferior alveolar nerve and that this infection has caused first mandibular molars appear secondarily retained with a vertical alveolar the arrest in eruption and has destroyed the tooth germ for the second process bordering the teeth, indicating that the teeth have ankylosed. It molar. If so, then this is an example of an acquired agenesis (which seems that also the right maxillary molar has arrested in eruption. It is correctly should be named aplasia). characteristic that the arrest in eruption occurs bilaterally. The etiology behind this abnormal eruption pattern is not known.

Tooth eruption and alveolar bone formation 131 Figure 10.11 Three orthopantomograms from children aged 12–14 years Figure 10.13 Two orthopantomograms from the same child demonstrating bilateral palatal canine ectopia combined with changes in demonstrating ectopic mandibular canines. (Upper) Radiograph at the age the incisor, premolar, and molar regions. (Upper) The dentition is of 11 years showing a tilted mandibular canine in the right side of the characterized by agenesis of the right maxillary lateral incisor and by the mandible. (Lower) Radiograph at the age of 13 years demonstrating the conical left maxillary lateral incisor. (Center) In this case of palatal canine same canine in a now nearly horizontally located, ectopic position. (Inset) ectopia, the maxillary laterals appear malformed. (Lower) The ectopic A profile radiograph from the child, where the canine appears in the canines point in a direction that makes guided eruption and orthodontic mental region. The question in this case is whether the ectopia observed treatment impossible. Agenesis of the left second premolar occurs in the could have been prevented by treatment at the age of 11 before the canine mandible. Taurodontic molars occur in the maxilla. tilted completely to a horizontal position. At the age of 13 years, treatment of this condition is highly problematic. The etiology behind ectopic canines seems to be a space problem, but this has not been proven. Arrested eruption due to lack of space Arrested eruption due to obstacles in the Crowding in the dental arch can result in arrested eruption. Also eruption pathway space in the jaws, for example in the mandibular ramus region, is Arrested eruption of the permanent teeth can occur due to a factor which can affect the normal eruption process. supernumerary teeth or other obstacles in the eruption path (Figure 10.22). Figure 10.12 Anthropological cranium demonstrating bilateral ectopia of the mandibular canines. (Left) Frontal radiograph showing the tilted position of the mandibular canines marked by yellow stars. (Right) A photograph of the frontal, lower cranium demonstrating that the mandibular canines have penetrated the outer mandibular cortical bone.

132 Chapter 10 Figure 10.14 Three-dimensional scanning of a child 13 years of age with an ectopic left mandibular canine. The images illustrate the location of the canine. Primary retention of molars, premolars, and distinguish and therefore to diagnose these two types of primary incisors retention correctly. Primary retention is defined as an arrest in eruption before emergence. In most cases, this arrest is due to malfunction of the Typical primary retention dental follicle or the character of the overlying ectomesenchyme The permanent tooth most often affected is the first molar (hard tissue). This is the typical understanding of primary (Figure 10.23). The tooth stops its eruption movements before retention. Meanwhile, ankylosis in teeth that have not penetrated emergence. In some cases with arrested eruption of the first the mucosa also exists. This is atypical, and it is difficult to molar, the second and third molars are late in development when Figure 10.15 The jaws from an anthropological cranium demonstrating bilateral ectopia (transposition) of the canines which have penetrated the outer cortical bone of the maxilla.

Tooth eruption and alveolar bone formation 133 Figure 10.18 Radiographs demonstrating ectopic permanent molars. (Upper) Two radiographs demonstrating a unilateral ectopic third mandibular molar (left) and bilateral ectopic second molars (right). The etiology behind this ectopia is not known. (Lower) Bilateral ectopic third maxillary molars. The etiology is not known, but may be due to reduced space. Figure 10.16 Orthopantomograms demonstrating transposition in the Figure 10.19 Photograph of an anthropological human mandible from the maxilla and the mandible. (Upper) Canine and first premolar transposition lingual aspect. Note the furrow marked by the arrows (presumably for is observed in the right maxillary region in a child 11 years of age. The innervation) to the ectopic premolar marked by a star. (Inset) A radiograph dentition is without other deviations. (Inset) A clinical intraoral photograph taken from the same perspective demonstrating the ectopic premolar (black taken in the occlusal view showing that the correct orthodontic treatment star). Note also the appearance of two mandibular channels marked by yellow for transposition is often a persistence of the transposition. (Upper middle) arrows. This might indicate the external furrow with innervation to the Bilateral maxillary transpositions of maxillary canines and first premolars premolar and the inner mandibular channel which innervates the other teeth in a child nine years of age. The first permanent molars appear in the mandible. This observation is important for understanding why “two taurodontic. (Lower middle) Unilateral transposition of a supernumerary mandibular channels” are sometimes observed. One is an outer furrow and lateral incisor in the mandible and a canine in the right side. (Lower) the other is the normally developed mandibular channel. This is a congenital Transposition of a mandibular canine and a lateral incisor in the left side. malformation in the peripheral nervous system. This might be the reason for Note the persistence of the left, mandibular primary canine. ectopia, but cannot be proven from an anthropological case. Figure 10.17 Photographs of an ectopic second molar in the coronoid process of the mandible. (Left) The molar appears on a human skeleton in the coronoid process of the mandible (arrow). (Center) Radiograph of the cranium illustrating the molar with a long root in the coronoid process. (Right) A dental film of the molar illustrated in the prior images. Notice that there are two root pulps which are apically united in a common hard tissue formation. On the inside of the coronoid process, there seems to be a furrow (presumably for innervation) which approaches the apical area of the root. The contour of this furrow appears in the radiograph marked with an arrow.

134 Chapter 10 Figure 10.20 Radiographic image of an ectopic left permanent central Figure 10.22 Section of an orthopantomogram demonstrating arrest in incisor in a region with supernumerary teeth. The etiology might be a local molar eruption due to odontoma in the mandible and ectopic third molar disturbance in the dental lamina. in the maxilla. compared to the contralateral teeth (Figure 10.24). In such cases, obstacles in the eruption path. If obstacles occur, then they must the retention and delay in maturation has been caused by virus be removed before proceeding with treatment. In Chapter 17, attack in the molar field – for example, mumps in childhood (see examples are given of primarily retained molars which have Figure 9.17). received treatment too late. It is important to observe the position of the tooth, spacing, Atypical primary retention (ankylosis) follicle, and root morphology before treatment. Surgical expo­ In these cases, the molars have ankylosed to the bone before sure of the crown is an appropriate treatment when the molar is beginning their eruptive movement. This can be diagnosed not located deeply and when there is space in the eruption when the molar roots are short and underdeveloped and the pathway. In such a treatment, the ideal conditions are that the crown follicle is absent (Figure 10.25). Surgical exposure is not crown follicle is large like a balloon and the root apex is not yet helpful here. The condition may occur in molars, premolars, closed. Otherwise, surgical treatment is dubious. It is also dubi­ and incisors (Figures 10.25 and 10.26). It is often difficult to ous in cases with space problems and deviations in bone tissue. In know whether the retention is typical or atypical. The condi­ association with surgical exposure, it is important to be aware of tion is therefore often treated first as a typical primary reten­ tion with the risk of having to extract the tooth later (see Figure 10.25). The diagnostics and treatment planning are further complicated by the fact that there may be more than one tooth within a field that is ankylosed (see Figure 10.26). This is important to keep in mind while presenting possible treatment options to the patient and parents. Figure 10.21 Arrested eruption of the left maxillary permanent lateral Secondary retention of molars, premolars, and incisor after a trauma four years earlier. Note the vertical alveolar bone incisors contour which indicates an arrest which is likely due to ankylosis. Secondary retention is defined as an arrest in eruption after emergence. This means that the tooth is arrested due to ankylosis or hypercementosis. These conditions result in the inability of the periodontal tissue to reorganize and adapt to eruptive

Tooth eruption and alveolar bone formation 135 Figure 10.23 This is a case of primary retention of the first permanent mandibular molar. The drawing (upper left) illustrates the structures involved in tooth eruption. In primary retention, the problem is predominantly that the upper crown follicle is unable to break down (resorb) the overlying bone tissue. A deviation in the bone tissue could also be a reason for the inability of the crown follicle to resorb. (Lower left) Section from an orthopantomogram illustrating the right first mandibular molar with an extended crown follicle. The question at this time was whether the tooth had the ability to erupt on its own. Surgical removal of the crown follicle and the bone covering the molar was performed. (Lower center) A year after the first radiograph was taken, the root of the first molar has developed further and the tooth has erupted but not to the occlusal level. (Right) The orthopantomogram demonstrates the same dentition 2½ years after the surgery. The first molar has now reached the occlusal level. Compared to the contralateral molar, the root is curved and shorter but the tooth is fully functional. (Inset) An intraoral photograph taken at the same time as the orthopantomogram. Source: Reproduced with kind permission of Dr N. Smith. movements. The most severe retention is seen in the first molar. growth intensity on the alveolar bone is less than in the period As mentioned in Chapter 6, there is a significant growth of the when the first molar erupts. alveolar process after the first molar has emerged. If the first molar is not able to continue eruption after emergence, it stops The reason for the periodontal dysfunction which leads to and the surrounding teeth erupt normally and induce alveolar secondary retention might be a traumatic chewing causing bone growth. This process can result in a significant difference in bleeding in the interradicular area of the molar as shown in the occlusal level of the first molar and the surrounding teeth Figure 10.29. However, the etiology could also be abnormal (Figures 10.27 and 10.28). It appears clinically as if the retained functioning of the periodontal membrane. The etiology behind molar is sinking deeper and deeper into the gingiva, but the true secondary retention may be linked not only to the epithelial explanation is that the tooth does not follow the natural post- lining but also to other cell layers in the peri-root sheet. It can be emergence eruption of the surrounding teeth. Rather, it does not believed that in traumatic cases, an interradicular bleeding might initiate the upward growth of the alveolar bone. This difference in result in resorption processes which are later repaired by bone, occlusal level is not so significant in the second molar region resulting in ankylosis. In cases with retention of molars, the level because the second molar erupts at a time after puberty when the of the alveolar process is not horizontal but oblique (see Figures 10.28 and 10.29). This reveals that the alveolar process does not Figure 10.24 Two sections from the same orthopantomogram from a child seven years of age illustrating asymmetric development in the left and right sides of the mandible. The development of the first and second mandibular molars in the left side is normal for this age but differs from the right side where the first molar is primarily retained with shorter root length. The right second molar is delayed compared to the second molar in the left side. The teeth are marked with red arrows. This asymmetrical development is believed to be caused by a virus attack in the peripheral innervation on the right side. The attack has delayed the development and possibly also changed the structures influencing the eruption of the first molar. This could involve the crown follicle and/or a change in the root membrane.

136 Chapter 10 Figure 10.25 Two orthopantomograms demonstrating permanent first in the peri-root sheet demonstrate how these layers are disor­ molars which have never penetrated the oral mucosa. These are the first ganized close to the ankylotic process. mandibular molar in the left side (upper) and the first permanent maxillary molar in the right side (lower). They have a deviant root It has been shown that after removal of a secondarily retained morphology and no crown follicle. Furthermore, the right second first molar, the second and third molars can also be ankylosed. The maxillary molar has not formed. This is a type of primary retention in reason for this abnormality limited to the molar field is not clear, which there is no causal explanation. Surgical exposure of the occlusal but it indicates an ectomesenchymal or neuroectodermal regional surface does not provoke eruption in these two cases. deficit (possibly virus or bacteria provoked), and not only a traumatic injury to a single tooth. This condition is comparable form by apposition when the tooth eruption is arrested. Histo­ to the atypical primary retention described previously. It can be logical studies have shown that molars with secondary arrested difficult to assess whether the tooth in question is primarily eruption are ankylosed, but that they often also display hyper­ retained or has emerged initially and then been overgrown by cementosis on the root surface (Figures 10.29 and 10.30). Mean­ gingiva and alveolar bone. If this is the case, it is classified as a while, it can be difficult to pinpoint an ankylotic area secondary retention which at the point of diagnosis strongly histologically because it can be very small. Hypercementosis is resembles a primary retention. The etiology behind secondary a process which is presumed to occur secondarily to ankylosis. arrested eruption seems to be a local disruption of either a single Immunohistochemical markings of the three main tissue layers molar or a developmental field with several molars. In cases in which all molars within a field (specifically in the maxilla) are retained, it can be difficult to determine the etiology. In various cases, surgical exposure of the primarily retained maxillary first molar proves to have no effect on the eruption movements. The other molars in the same field do not erupt either. This could be a localized condition or a primary failure of eruption. Premolar and incisor Secondary retention in premolars and incisors can occur in single teeth or within fields of teeth. Both conditions are demonstrated in Figures 10.31 and 10.32. Primary failure of tooth eruption The eruption of premolars and/or molars can become arrested before occlusion. This leads to primary failure of tooth eruption. It is characteristic that all the teeth which are located posteriorly from the most anteriorly affected tooth (often the canine) fail to erupt. This means that the patient has a bilateral or unilateral open bite (Figures 10.33 and 10.34). Orthodontic treatment is ineffective. Primary failure of eruption is a condition which can occur in both the permanent and primary dentition (Figure 10.35). Studies have shown that the periodontal membrane is not recognizable. The border between the root dentin and the bone tissue has a straight course. This is demonstrated in Figure 10.35. The condition can be inherited and can, in such cases, be the result of a mutation in a parathyroid hormone receptor gene. More often, however, the cause is not known. Figure 10.26 Section from an orthopantomogram illustrating Retention of teeth due to virus attack asymmetrical molar eruption in the maxilla. It was difficult to decide Retention can be local or general. whether the right first molar was primarily or secondarily retained. The dentist decided to extract the first molar and learned in the following years Arrest in root formation and/or retention can be seen in all that none of the molars in the right side were able to erupt. Such regional teeth. Studies have documented that virus attack on the peripheral arrest in eruption occurs sometimes in the maxilla. As a result, nerves can provoke this reaction, as shown in Figure 10.36. The information about the consequences of this regional arrest must be viruses in question could cause meningitis, mumps or herpes provided to the patient and parents when the first molar is extracted. zoster (Figure 10.37). Various developmental fields can be affected (Inset) A figure from another patient where the innervation to the molar by arrested eruption due to virus attack. This might also be the region is marked by a blue line. Maturation of the first molar has stopped. etiology behind the conditions demonstrated in Figures 10.26, Bacterial or virus attack might be the cause of this condition. 10.31, and 10.32 which show innervation pathways.

Tooth eruption and alveolar bone formation 137 Figure 10.27 The figure illustrates secondary retention of the first maxillary molar in the right side in two different patients. Secondary retention is a retention which appears after the tooth has emerged through the mucosa. (Left) An intraoral photograph from a nine-year-old child with an impacted first maxillary molar in the right side (arrow). Note that there is a filling in the molar. This filling was laid at the time when the first permanent molar was at the same occlusal level as the second primary molar. This first molar is ankylosed and the tooth does not follow the continous eruptive movements of the primary molars. Surgical removal of the right maxillary molar is recommended. (Right) An orthopantomogram from a 17-year-old patient. The first maxillary molar in the right side is secondarily retained due to ankylosis. At the time of the radiograph, the tooth was hardly visible in the mouth. The treatment is surgical removal of this first molar. (Inset) A section of a radiograph from an adult patient where the first permanent molar has completely “disappeared” from the oral cavity and where the second molar has erupted ectopically and “covered” the crown of the first molar. Surgical removal of the secondary retained first maxillary molars is recommended. Retention due to nonshedding of primary teeth extraction of the primary teeth, preferably before root closure The association between resorption of a primary tooth and the of the permanent teeth (Figure 10.38). root formation of the succeeding permanent tooth is a condition which expresses normal developmental patterns of the primary The reason for the eruption difficulties could be that the crown teeth and normal emergences of the permanent teeth. If the follicles of the permanent teeth are unable to provoke resorption balance between resorption and eruption is disturbed, the pri­ of the primary teeth. Also a pronounced epithelial cell layer has mary teeth may be shed too early or too late. If they are shed too been identified in the interradicular region of the primary molars. late or not shed at all, the eruption process in the remaining teeth Such eruption disturbances can be inherited (Figure 10.39), and may stop. Such a condition can be seen in hyper-IgE syndrome are also often seen in cases without a hyper-IgE diagnosis. which is a congenital disorder characterized by high serum IgE Occasionally, it is related to skin problems and/or other ecto­ levels, recurrent skin infections, and frequent pneumonia. This dermal abnormalities. condition can be diagnosed late and can also produce problems with eruption of the permanent teeth. Treatment involves Abnormal eruption in syndromes and dysplasia Abnormal eruption occurs in syndromes such as cherubism (Figure 10.40), in which there is a change in the crown follicle. The genotype is well known (4p16.3) but the eruption deviation has not been explained. In other syndromes, eruption is delayed. The condition normalizes after puberty. Eruption deviations also occur in other syndromes and in dysplasias. The following conditions will be exemplified: • amelogenesis imperfecta • ectodermal dysplasia • linear scleroderma en coup de sabre. Figure 10.28 Illustration of a secondarily retained first molar in the right Amelogenesis imperfecta side of the mandible. The tooth is ankylosed and is not visible in the In amelogenesis imperfecta, the teeth are ectopically positioned mouth due to overgrowth of the gingival tissue. The tooth must be in the jaws (Figure 10.41), and the eruption occurs late. A close- removed. (Inset) A schematic drawing indicating that ankylosis often up of a severe condition which also has delayed eruption is begins interradicularly (blue arrow). The reason for this is not clear, but it demonstrated in Figure 10.41. Many inexplicable cases of erup­ could be that trauma during mastication has lead to bleeding in the space tion deviations appear in the clinic. These cases may also be due between the roots, which may have disorganized the periodontal to deviations in the osseous tissue but remain undiagnosed. membrane interradicularly. The resorption process in the region is unable Figure 10.42 illustrates a less severe case of amelogenesis to reorganize the periodontal membrane and ankylosis is the result.