Final corrected 16-17 Operative (2)

compositesWhen restoring a darker shade of composite, keep in mind the following:• UV light is better than visible light• You must keep the light 2 mm away or more• You should cure for longer than normal• Darker shades have less chemical bonding 50 copyright © 2016-2017 Dental DecksOPERATIVE

• You should cure for longer than normalImportant points to remember when using a visible light-curing unit: • Hold the light as close to the resin as possible — within 2 mm to be effective. • Place a shield between the light tip and the operator’s eyes. Patients who have had recent cataract removal should have protection also. Note: Studies have shown that the visible light used in polymerization of photo-activated materials can cause retinal damage — always use a shield and eyeglasses for protection. • For deep restorations, you have to cure the composite in increments — if you don’t, the deeper areas will not be cured. Important: No more than 1.5 mm to 2 mm increments should be light cured at one time. • Make sure the bulb in the light is still powerful enough — they have commercially available products to test the bulb. • With darker resin shades, cure a little longer. Tooth Preparation: Amalgam versus Composite Characteristic Amalgam CompositeOutline form Include carious areas Same May extend to break proximal contact Same Include adjacent suspicious areas Do not; seal these areasPulpal depth Uniform 1.5 mm Remove caries; not usually uniformAxial depth Uniform 0.2-0.5mm inside DEJ Remove caries; not usually uniformCavosurface margin Create 90-degree margin 90 or greater degreesBevels None (except gingival) For esthetics, do not bevel margins that are on functional pathsTexture of prepared walls Smooth RoughCutting instrument Burs DiamondsPrimary retention form Convergence occlusally None (established by roughness & bonding)Secondary retention form Grooves, slots, locks, pins, bonding Bonding; grooves for Class III & V prepsResistance form Flat floors, rounded internal line angles Not neededBase indications Provide approximately 2 mm between Not needed pulp and amalgamLiner indications Ca (OH)2 over direct or indirect pulp Same capsSealer Gluma desensitizer when not bonding Sealed by bonding system used

compositesWhich of the following is commonly added to bis-GMA organic resins to reduceviscosity, increase cross-linking, and hardness?• EGDMA• UEDMA• PMMA• TEGDMA 51 copyright © 2016-2017 Dental DecksOPERATIVE

• TEGDMADental resin composites typically contain a mixture of soft, organic resin matrix (monomer)and hard, inorganic filler particles (ceramic). Other components are included to improve theefficacy of the combination and initiate polymerization. The resin matrix consists of mono-mers, an initiator system, stabilizers, and pigments. The inorganic filler consists of particlessuch as glass, quartz, and colloidal silica. The matrix and filler are bonded together with acoupling agent. The performance of resin composites depends on these basic components.The recent improvement in these materials has primarily focused on filler technology, but theresin monomers have remained largely unmodified.The organic resin matrix is a high-molecular-weight monomer, such as bisphenol A glycidylmethacrylate (bis-GMA) or urethane dimethacrylate (UEDMA). bis-GMA, which stands for2,2-bis [4(2-hydroxy-3-methacryloxypropoxy) phenyl]-propane, is an aromatic methacrylate.Terminal methacrylate groups provide sites for free radical polymerization; it sets to arelatively rigid polymer because it has two benzene rings near its center.Two disadvantages of bis-GMA are its questionable color stability and high viscosity; highviscosity is the result of its -OH groups which hydrogen bond; to lower the viscosity,manufacturers add low-molecular-weight (low-viscosity) monomers like triethyleneglycoldimethacrylate (TEGDMA) and ethylene glycol dimethacrylate (EGDMA); these reduce thebis-GMA's viscosity, increase cross-linking, and increase hardness. Another monomerfrequently used as the matrix for resin composites is UDEMA. This monomer was introducedin 1974 and is a brittle material with low viscosity.Important: The high filler content and the bis-GMA resin matrix drastically reduce thecoefficient of thermal expansion (as compared to the unfilled acrylic resins). The filler alsoreduces polymerization shrinkage and increases hardness.

compositesThe main ingredient in traditional acrylic resin temporary materials forintraoral fabrication is:• Ethyl methacrylate• Isobutyl methacrylate• Bis-GMA• Ethylene imine• Methyl methacrylate 52 copyright © 2016-2017 Dental DecksOPERATIVE

• Methyl methacrylateFor both inlays and onlays, plastic (acrylic) provisional restorations are fabricated prior to thefinal restoration being cemented. Their physical properties enable them to withstand occlusalforces and the adverse oral environment for short periods. These temporaries must: restoreand maintain proximal contacts, restore and maintain the occlusion, restore and maintain toothcontours, and the margins should be closed and flush with the tooth.Methyl methacrylate, ethyl methacrylate, and ethylene imine resins have been employed toproduce provisional restorations. However, methyl methacrylate (MMA) is by far the mostcommon. It is the liquid monomer that is mixed with the polymer polymethyl methacrylate(the powder). The monomer partially dissolves the polymer to form a plastic dough.Note: The monomer is polymerized by the action of an initiator (benzoyl peroxide).Important: MMA maintains the occlusal and interproximal contact relationships.Remember: Polymerization should not go to completion in the mouth for fear of overheat-ing the pulp and that the provisional will not be able to be removed from the tooth.Note: These provisionals are usually cemented in with a ZOE cement.Classification for provisional restorations: - Intracoronal Restorations: • ZOE-based and/or ZOE-based temporaries - Preformed Provisional Shell Crowns: • Polycarbonate Crowns • Metal Alloy Crowns - Custom-Fabricated Provisional Crowns: • MMA-like products (MMA/PMMA, IBMA/PBMA, EMA/PEMA) – self-cure • Epimine-imine products – self-cure • Bis-acryl, bis-methacryl, bis-GMA-like – self-cure, dual cure, VLC - Resins and Composites

compositesWhen considering an unfilled resin material versus a filled resin product,please compare the properties of thermal conductivity and marginal leakage,respectively:• Lower, Lower• Lower, Higher• Higher, Lower• Higher, Higher 53 copyright © 2016-2017 Dental DecksOPERATIVE

• Lower, Higher*** Lower thermal conductivity, higher marginal leakageUnfilled resin restorations change temperature quite slowly when compared to metallicrestorations because of their low thermal conductivity and diffusivity. However, unfilledresins do have some undesirable characteristics such as a high coefficient of thermalexpansion, which is 7 to 8 times that of the tooth.The first materials that were used as esthetic materials were based on silicate cements. Dueto solubility problems, the silicate cements were replaced by unfilled acrylic resins.Unfilled acrylic resins contracted excessively during polymerization, permittingsubsequent marginal leakage, and were not strong enough to support occlusal loads. Theseunfilled acrylic resins have been replaced by filled resins (also called composite resins).A filled resin is one in which an inorganic inert filler (usually silica or quartz) has beenadded to the resin matrix. 1. The compressive strength of the unfilled resin is low; the yield strength Notes and tensile strength are even lower. 2. Unfilled resins are the softest of all restorative materials (low wear resist- ance — no filler) 3. Compared with amalgam, filled resin, direct gold, and silicates, unfilled resins show the greatest extent of marginal leakage related to temperature change (percolation).Remember: A low coefficient of thermal conductivity is most characteristic of currentlyavailable cement bases.

compositesAcid etching enamel prior to placement of a composite restoration is required forall of the following reasons EXCEPT one. Which one is the EXCEPTION?• Conserves tooth structure• Reduces microleakage• Provides micromechanical retention• Increases esthetics 54 copyright © 2016-2017 Dental DecksOPERATIVE

• Increases esthetics*** This is false; acid etching does not increase the esthetics of the enamel margin. Donot be confused by the fact that you acid etch the bevel, which itself functions forretention and esthetics.One of the most effective ways of improving the marginal seal and mechanical bondingof composite resins to tooth structure is to condition or pretreat the enamel with acid priorto insertion of the resin. This procedure is referred to as \"acid-etch\" technique.Purposes of acid etching: 1. Increases surface energy, which promotes wetting and adhesion. 2. Chemically cleans the tooth structure, which also promotes wetting and adhesion. 3. Creates micropores for micromechanical retention by removing the smear layer. Important: Acid etching paves the way for resin “microtags,” which produces a much improved bond of the resin to the tooth. The effective tag length, as a result of etching on adult anterior teeth, has been demonstrated to be approximately 7 to 25 mm .This \"acid-etch technique\" conserves tooth structure, reduces microleakage, improvesesthetics, and provides micromechanical retention.Notes 1. The aim is to cause maximum enamel dissolution with minimum precipita- tion of calcium phosphate salts. 2. Studies indicate that acid-etched composite resin restorations have the best initial seal (microleakage), however, over time, this weakens (amalgam has the best seal over time).

compositesEnamel etching is typically completed with:• 37% phosphoric acid• 13% phosphoric acid• 37% hydrochloric acid• 13% hydrochloric acid 55 copyright © 2016-2017 Dental DecksOPERATIVE

• 37% phosphoric acidStandard acid etching of enamel involves the application of 37% phosphoric acid for 15seconds with a 15-second rinse and a 15-second drying to roughen the surface of theenamel. This forms little tags approximately 7 to 25 mm in length, providing mechani-cal retention. When using the acid etch technique, all enamel cavosurface margins shouldbe chamfered or beveled (this process forms obtuse angles).Beveling the enamel margins of anterior resin composite preparations is recommendedprior to etching to: • Reduce microleakage • Improve esthetics: by gradually blending the resin composite into the enamel • Increase bond strength: transversely cut enamel, when etched, provides a stronger bond to resin composite than etched, longitudinally cut enamel.This occurs because the end of enamel rods are more completely exposed to the etchant and, therefore, more effective etching is accomplished and more retentive tags are produced.Remember: Once you etch the tooth, it cannot be contaminated with saliva. If it iscontaminated, you must complete the entire etching procedure again.Notes 1. The depth of enamel dissolution caused by acid etching is approximately 10 to 15 microns. 2. Little correlation exists between resin tag length and enamel/resin bond strength. 3. Although liquid etchants produce a more uniform etch and a greater number of tags than do gel etchants, no difference in bond strength has been demonstrated between the two.

compositesWhen preparing a Class V composite preparation, you can have _______rounded internal line angles because it is ________ to compress composite intothem than amalgam.• more, easier• less, harder• more, harder• less, easier 56 copyright © 2016-2017 Dental DecksOPERATIVE

• more, easier*** When restoring teeth with composite resin, it is much easier to compress thematerial into rounded line angles.The outline form of a Class V restoration is not always uniform, as it will vary depend-ing on the location and amount of caries or decalcification ¾ the size and location of thecarious lesion determines the outline form of the cavity preparation. When the carious tis-sue has been removed and the margins are on reliable enamel or dentin, the outline willusually be rectangular with the corners round, ovoid, or kidney-shaped, very much re-sembling the amalgam Class V preparation except that the internal line angles are muchmore rounded.Recent research indicates that preparations with bevels are more resistant to microleak-age as compared with those without bevels when an acid-etch technique is used. Thebevel permits the acid to attack the enamel rods at the appropriate angle for maximum ef-fect. The cavosurface margin is beveled wherever it is placed on enamel -- this is a majordifference between composite and amalgam preps. When possible, an enamel bevel 0.2to 0.5 mm wide is advocated as the final stage of preparation. This bevel is etched and pro-vides retention for the restorative material as well as improving the marginal seal andmaintaining the strength of the resin with sufficient bulk. Retentive grooves supplementthe etched enamel retention (these grooves are placed in both incisal and gingival axial lineangles).Note: Whenever possible, use a composite syringe to place the composite resin in therestoration ¾ this will minimize the possibility of trapping air in the final restoration.

compositesWhich one of the following is the most important event for dentin bonding?• Smear layer removal• Smear plug removal• Peritubular dentin decalcification• Intertubular dentin decalcification 57 copyright © 2016-2017 Dental DecksOPERATIVE

• Intertubular dentin decalcificationDentin bonding systems (DBS) consist of 3 components: • Etchant: Typical acid conditioners include phosphoric acid, EDTA, maleic acid, and citric acid. • Primer: is designed to penetrate through the remnant smear layer and into the intertubular dentin to fill the spaces left by dissolved hydroxyapatite crystals. This allows the primer to form an interpenetrating network around dentin collagen. Note: The bonding primer is based on hydrophilic monomers, such as hydroxyethyl methacry- late (HEMA). • Bonding agent: unfilled resin adhesive is applied. The resin is then cured (light-, self-, or dual-cured). This layer can now bond to composite or amalgam.Examples of current dentin bonding system designs: 1-component systems (EPB) • AQ Bond (Sun Medical) 2-component systems (EP + B) • or Touch & Bond (Parkell) • CLEARFIL SE BOND & LINER BOND 2V (Kuraray) • Adper Prompt L-Pop (3M-ESPE) • TYRIAN SPE (Bisco) 2-component systems (E + PB) • Optibond Solo SE Plus (Kerr) • Syntac Single -Component (Ivoclar/Vivadent) 3-component systems (E + P + B) • One Coat Bond Self-Etching Bond • Scotchbond Multi-Purpose Plus (3M) (Coltene/Whaledent) • Permaquick (Ultradent) • Bond-1 (Jeneric/Pentron) • Bond-It (Jeneric/Pentron) • ALL-BOND 2 (BISCO)Generations of Dentin Bonding Systems (DBS): 1. First-Generation DBSs (bonded to smear layer) 2. Second-Generation DBSs (modified/removed smear layer) 3. Third-Generation DBSs (modified/removed smear layer; produced hybrid layer) 4. Fourth-Generation DBSs (optimized for smear layer modification + dentin wetting): three-step etch & rinse 5. Fifth-Generation DBSs (Reduced-Component Bonding Systems): two-step etch & rinse 6. Sixth-Generation DBSs (True One-Component Bonding Systems): subdivided into Type 1 (i.e., two-step; acidified primer and adhesive applied separately) and Type 2 (i.e., one-step; self-etching adhesives are mixed and applied). 7. Seventh-Generation DBSs: adhesives require no mixing and are simply placed in one step.Notes 1. Dentin and enamel bonding strengths are similar for current total-etch products. 2. Most total-etch dentin bonding systems bond better to moist dentin, use Aqua-Prep or Gluma Desensitizer to keep dentin moist. 3. Enamel bonding is fast, strong, and long-lasting; dentin bonding is slower, may be strong, but may not be long lasting.

goldA gold onlay you placed last week fails. Which of the following reasons is mostlikely responsible for the failure?• You “capped” the functional cusp• You “shoed” the functional cusp• You “capped” the nonfunctional cusp• You “shoed” the nonfunctional cusp 58 copyright © 2016-2017 Dental DecksOPERATIVE

• You “shoed” the functional cusp*** Important: \"Shoeing\" is never indicated on functional cusps.Onlay preparations: • Resistance form: two types of cuspal protection: 1. \"Capping\": refers to the complete coverage of functional cusp with 1.5 mm of gold. 2. \"Shoeing\": refers to veneering of nonfunctional cusp by means of a slight finishing bevel. Note: Except in situations demanding a minimal display of gold (primarily the facial cusps of maxillary molars and premolars), capping is always preferred over shoeing.Shoeing CappingOnlay preps have: • Improved resistance to fracture due to cuspal coverage • Thickness of gold on occlusal (1.0 mm on nonfunctional cusp and 1.5 mm on functional cusp) resists deformation • Reliance on tapering lingual and buccal walls for retention • Reciprocation of mesial and distal axial walls (near parallel) • External extensions over the cusps add retention if nearly parallel to line of draw

goldRapid cooling (by immersion in water) of a dental casting from the hightemperature at which it has been shaped is referred to as:• Annealing• Tempering• Quenching• None of the above 59 copyright © 2016-2017 Dental DecksOPERATIVE

• QuenchingThis usually is undertaken to maintain mechanical properties associated with a crystallinestructure or phase distribution that would be lost on slow cooling.Two advantages gained in quenching: 1. The noble metal alloy is left in an annealed condition for burnishing, polishing, and similar procedures — it maintains its malleability and ductility. 2. When the water contacts the hot investment, a violent reaction ensues. The invest- ment becomes soft and granular, and the casting is more easily cleaned.Remember: The set of 3 processes (annealing, hardening and tempering) is collectivelyknown as “heat treating.” • Annealing is the softening of a metal by controlled heating and cooling to make its manipulation easier. It makes the metal tougher and less brittle. • Tempering is hardening something by heat treatment

goldWhich of the following situations defines an indication for a Class II gold inlay?• A young patient with high caries rate• A patient with little money to invest in dental work• A patient very concerned about esthetics• A patient with a large lesion, buccal-lingually• A patient with low caries rate but a history of periodontal problems 60 copyright © 2016-2017 Dental DecksOPERATIVE

• A patient with low caries rate but a history of periodontal problemsDisadvantages and contraindications for a Class II gold inlay: • Expense: gold is 6 to 7 times more expensive than amalgam • Time: at least two visits are necessary • Minimal lesions: best restored with gold foil • Large lesions: if cavity width exceeds one-third the intercuspal width, the tooth should receive cuspal coverage • In patients with a high caries rate • Young patients • Color: not estheticAdvantages and indications for a Class II gold inlay: • Tooth contours: where optimum contour and surface finish is desired to maintain periodontal health • Strength • In patients with a low caries rate • Use against another gold restoration • BiocompatibleNote: A gold inlay is defined as a cast gold restoration that derives its retention fromthe internal walls of the cavity preparation.Remember: • noble metal- metal that is resistant to oxidation; includes gold, platinum, palladium, and other platinum metals. • nonprecious metal- relatively inexpensive base metal, such as nickel, chromium, and cobalt. • precious metal- an expensive metal; includes gold, platinum group metals, and silver.

goldGold alloys _________ upon solidification in the investment. This needs to becompensated for by an equal amount of _________ of the mold.• shrink, expansion• expand, shrinkage• shrink, shrinkage• expand, expansion 61 copyright © 2016-2017 Dental DecksOPERATIVE

• shrink, expansionGypsum bonded investments are used with Type I, II, and III gold alloys. Gold alloysused for cast gold restorations shrink on solidification. Therefore, it is necessary tocompensate for the solidification shrinkage of the specific alloy used by expanding themold enough to equal the shrinkage.The dimensional compensation necessary is accomplished by two methods of expansion: 1. Setting expansion: occurs as a result of normal crystal growth but can be enhanced by allowing the investment to set in the presence of water, producing hygroscopic expansion. 2. Thermal expansion: is achieved through the normal expansion that occurs on heating the silica (quartz or cristobalite). Note: The amount of expansion depends on the particular refractory material used (cristobalite produces greater expansion than does quartz). Important: Thermal expansion is the principal cause for mold expansion.Variables that influence expansion: • The older the investment is, the less it will expand • If the water/powder ratio is increased, the expansion is reduced • The longer the spatulation time, the greater the expansion • The longer the time between mixing and immersion in a water bath, the less it will expandNote: During solidification of an alloy, the number of grains forming depends on the rateof cooling and the presence of nucleating agents.

goldWhich of the following finishing margins is essentially a hollow ground bevel,creating more bulk of restorative material near the margin and providing agreater cavosurface angle?• Knife edge• Beveled shoulder• Chamfer• Shoulder 62 copyright © 2016-2017 Dental DecksOPERATIVE

• ChamferA chamfer is essentially a hollow ground bevel. Instead of a flat diagonal cut across the cavosur-face margin, the chamfer is \"scooped out,\" creating more bulk of restorative material near themargin and providing a greater cavosurface angle.Cavosurface angle configurations that are used when preparing a tooth for a cast gold restora-tion: • A bevel is a diagonal cut across the cavosurface margin that is flat in one dimension only and curved in its other dimensions. It involves the external ends of enamel prisms and follows a continuous curved outline. It can be either a short bevel, which cuts only the external one-third of the enamel prisms, a full bevel involving the entire thickness of enamel, or a wide bevel in volving not only enamel but some dentin, as well. • A plane is a diagonal cut across the cavosurface margin that is flat in all dimesions. A plane may involve the entire thickness of enamel (which it usually does) or most of it, but cannot be curved in any direction. Completed preparation for a Class II gold inlay. Note the bevel on the cavosurface margins

goldWhich of the following allows for proper retention when preparing a tooth for adisto-occlusal Class II gold inlay?• Undercut on mesial• Undercut on buccal and lingual walls• Occlusal lock (dovetail)• None of the above 63 copyright © 2016-2017 Dental DecksOPERATIVE

• Occlusal lock (dovetail)When designing a Class II preparation for an inlay, an occlusal lock or dovetail shouldbe established to prevent proximal dislodgement. Also, the marginal ridges of posteriorteeth that are restored with cast gold should be rounded to help form the occlusalembrasures and be in contact with the cusps of the opposing teeth. Marginal ridgesshould be the same height as the adjacent tooth’s marginal ridge (or else you can createan interference in retrusive movement).Notes 1. The cement does provide some retention; however, the preparation design does as well. The cement’s main function is for marginal seal, not retention. 2. When removing a Class II inlay, the method of choice is to cut through the isthmus to remove the occlusal and proximal pieces one at a time. 3. The restoration will not seat if there are undercuts. Actually this holds true for all cast metal restorations. See picture above of a Class II inlay prepara- tion.

goldA patient arrives at your office with their full gold crown in hand. They explainto you that another dentist delivered it just last week. You then examine thecrown and the preparation. What is the most likely reason the the crown fell off?• There was very little cement in the crown• The preparation was only 4 mm high• The preparation walls were tapered at about 15°• The margins were jagged and undefined 64 copyright © 2016-2017 Dental DecksOPERATIVE

• The preparation walls were tapered at about 15°Taper provides the optimal friction between the walls and the casting, which is the mainretention. The ferrule (or height) of the preparation also provides the friction and, thus,retention, but 4 mm is enough (3 mm is minimal).Important: For maximum retention of cast gold restorations, the axial walls should be asparallel as possible and as long as possible. Retention is directly proportional to the area ofthe axial walls and their parallelism. No undercuts should be present.Retention form depends on: • Length of walls (minimum 3 mm): the longer the wall, the greater the amount of draft/draw. • Taper of walls. Important: provides for draw or draft (for the casting to be placed onto the tooth) but also provides for an appropriate small angle of divergence (2 to 5 degrees per wall) from the line of draw, which will enhance retention form. Key point: More parallel = more retentionAdvantages of cast gold restorations: • They are very strong and able to withstand the forces of mastication • They are ideal for occlusal rehabilitation • They are kind to the gingival tissueDisadvantages of cast gold restorations: • Esthetics • Cost • Time-consuming • Difficulty of technique • The need to use cement, which is the weakest point in the cast gold restoration • Gold has a high thermal conductivity

goldThe lab calls your office and asks if you want a particular casting done in a baseor a noble metal. Which of the following responses is appropriate?• Base, because the patient has a bad bruxing habit• Noble, because the patient has a bad bruxing habit• Base, because the patient wants a gold tooth• Noble, because the patient wants a gold tooth 65 copyright © 2016-2017 Dental DecksOPERATIVE

• Base, because the patient has a bad bruxing habitAn alloy is a mixture of two or more materials that are mutually soluble in the liquid state.A pure metal solidifies at a constant temperature, whereas alloys solidify through a rangeof temperatures.Base metal alloys (also called nonprecious metals) are based on active metallic elementsthat corrode but develop corrosion resistance via surface oxidation that produces a thin,tightly adherent film, which inhibits further corrosion. Example: Cobalt-chromium alloysform a Cr2O3 oxide film, which passivates the surface. Base metals are less resistant tocorrosion. Base metal alloy advantages are principally found only in their strength andlow density.Types of alloy systems: (classified on the basis of the type of structure that forms as theysolidify) • Solid solution alloys: the metals freeze without segregation of the individual constituents. Note: Are generally used in dentistry because they have a very homogenous structure and provide maximum strength. • Eutectic alloys: separate into individual grains of the respective constituents. Exhibit complete liquid solubility but limited solid solubility. Example is the silver- copper system.Remember: Noble metals are very resistant to corrosion and do not oxidize oncasting. Noble systems for dental use are based on the noble or precious metal elementsgold, silver, palladium, and platinum.

goldOf the following, which is a correct match between the gold cast alloy componentand its effect?Select all that apply.• Gold ¾ decreases ductility and malleability• Gold ¾ increases resistance to tarnish and corrosion• Copper ¾ hardens the alloy• Silver ¾ color modifying 66 copyright © 2016-2017 Dental DecksOPERATIVE

• Gold — increases resistance to tarnish and corrosion • Copper — hardens the alloy • Silver — color modifying*** Gold actually increases ductility and malleability. Effects of the Various Constituents on Gold Casting AlloyCompound Major Effect on Gold Casting AlloyGold (Au) Increases resistance to tarnish and corrosion; increases ductility and malleabilityCopper (Cu) Increases hardnessSilver (Ag) Main purpose is to modify the orange color of copper; reduces melting temperature; increases ductility and malleabilityPlatinum (Pt) Raises melting temperature; increases tensile strength; decreases the coefficient of thermal expansion; reduces tarnish and corrosionPalladium (Pd) Raises melting temperature; increases hardness; acts to absorb hydrogen gas which can cause porosities in the casting; prevents tarnish and corrosion; has a very strong whitening effect on gold alloys even when used at a low concentration (i.e., 5 wt%)Zinc (Zn) Acts as an oxygen scavenger and prevents oxidation of the other metals during the manufac- turing process; increases fluidity and decreases surface tensions, which increases castability

goldHigh-gold alloys used for cast restorations are:• Greater than 20% gold or other noble metals• Greater than 30% gold or other noble metals• Greater than 50% gold or other noble metals• Greater than 75% gold or other noble metals 67 copyright © 2016-2017 Dental DecksOPERATIVE

• Greater than 75% gold or other noble metalsFour Types of High-Gold Alloys: 1. ADA type I: highest gold content, 83% noble metals. Intended for small inlays. Easily burnished due to high ductility. 2. ADA type II: greater than 78% noble metals. Intended for larger inlays and onlays. Can also be burnished. 3. ADA type III: greater than 75% noble metals. Intended for onlays and crowns. Capable of being heat-treated. 4. ADA type IV: greater than 75% noble metals. Intended for bridges and removable partial dentures. Also capable of being heat-treated. Hardest of high-gold alloys. Type Hardness Yield Strength (MPa) Percentage Elongation (%)I Soft <140 18II Medium 140-200 18III Hard 201-340 12IV Extra-Hard >340 10• Medium-gold alloys are 25% to 75% gold or other noble metals• Low-gold alloys are less than 25% gold or other noble metals• Gold substitute alloys are alloys not containing gold. These alloys are called passive becausethey form some type of protective layer (surface oxide film) that offers maximum resistance tocorrosion. Examples include: Palladium-silver alloys and cobalt-chromium alloys.Remember: The karat of a gold alloy is the number of parts that are pure gold, on the basis of24 parts as a unit (thus, 24 karat is 100 % gold, while 18 karat is 75% gold). Fineness is meas-ured on the basis of parts of pure gold per 1,000 (1,000 fineness is 100% gold, while 500 fine-ness is 50% gold). Pure gold is only used in the foil restoration.

goldThe following statements describe an MOD gold cast onlay preparation. Whichwould you have to change to ensure that the onlay will be successful?• The mesial box has an axiopulpal line angle that is longer from facial to lingual than the axiogingival line angle• From facial to lingual, the distal axiopulpal line angle is longer than the mesial axio- pulpal line angle• The mesial and distal axial walls converge• The distal box has an axiopulpal line angle that is shorter from facial to lingual than the axiogingival line angle 68 copyright © 2016-2017 Dental DecksOPERATIVE

• The distal box has an axiopulpal line angle that is shorter from facial to lingual than the axiogingival line angleRemember: • When preparing teeth with short clinical crowns, the facial and lingual walls should have a minimal gingival-to-occlusal divergence angle for maximum retention. • From facial to lingual, the axiopulpal line angle of an onlay preparation is longer than the axiogingival line angle (if it were not, the preparation would be undercut and the onlay would not seat). • For a cast onlay or inlay, ALL axial walls must be convergent or there will be an undercut and the restoration will not be able to be seated.Notes 1. The bevel (0.5 mm width) on the cavosurface margin permits closer adaptation of the gold margin because the thinner margin of gold overlying the bevel is more ductile and is able to be burnished. The desirable metal angle at the margins of onlays is 40 degrees, except gingivally, where the metal angle should be 30 degrees. Note: You can burnish a 30- to 40-degree gold margin, less than 30 degrees may be too thin and break, greater than 40 degrees may be too thick and will not burnish. 2. During cementation, the finishing (burnishing) of the margins of a cast gold restoration should be started as soon as the restoration is well seated into the preparation. 3. While preparing a tooth to receive an inlay or onlay, a gingival bevel is used to remove unsupported enamel and to compensate for casting inaccuracies. Gingival margin trimmers, carbide finishing burs, or fine, tapered diamonds are used to place this bevel. 4. This gingival margin is always placed gingival to the contact area.

goldWhen preparing a Class V cavity preparation for direct filling gold, you shouldensure that you have all of the following EXCEPT one. Which one is theEXCEPTION?• Rounded internal line and point angles• Small retentive undercuts placed in the axio-occlusal and axio-gingival line angles• Mesial and distal walls that flare and meet the cavosurface at a 90° angle• An axial wall that is convex and follows the external contour of the tooth 0.5 mm into dentin 69 copyright © 2016-2017 Dental DecksOPERATIVE

• Rounded internal line and point anglesClass V cavity preparation for direct filling gold: • The outline form is usually either trapezoidal (most popular) or kidney-shaped. The axial wall is placed .5 mm into dentin (this will make the occlusal wall slightly deeper than the gingival wall because there is a thicker layer of enamel making up the occlusal wall). The mesial and distal walls are placed at the line angles of the tooth. *** Remember: For any Class V prep (whether for amalgam, composite, or direct fill ing gold), the outline form is determined by the extension of the carious lesion. • The retention form is attained by sharp internal line and point angles (axio-gingival and axio-occlusal). • The resistance form is provided by flat mesial and distal walls and a convex axial wall which parallels the external surface of the tooth.Note: The axial wall is convex in a mesiodistal direction to conserve tooth structure andminimize pulpal irritation.Important: The rubber dam is essential to prevent contamination of the gold withsaliva. A cervical clamp usually is necessary to retract the gingiva (#212 Ivory clamp). Thehole that is to be punched in the rubber dam for the tooth that is being restored shouldbe located facial to the normal alignment with the adjacent teeth.

goldThe purpose of a sprue former is to create a passage for material to flow into theinvestment.The diameter of the sprue pin should be equal to or greater than the thickestportion of the pattern.• Both statements are true• Both statements are false• The first statement is true, the second is false• The first statement is false, the second is true 70 copyright © 2016-2017 Dental DecksOPERATIVE

• Both statements are trueThe purpose of the sprue former or sprue pin, as it is usually called, is to provide aningate or sprue in the investment through which the molten alloy can reach the moldafter the wax has been eliminated.The size of the sprue former depends to a considerable extent on the type and size of thepattern, the type of the casting machine to be used, and the dimensions of the flask or ringin which the casting is to be made. Generally, however, for the average-size pattern, sprueformers smaller in diameter than approximately 1.5 mm are contraindicated. If a sprue istoo small, the molten metal freezes completely in this area first, and localized shrinkageporosity results. The general rule for sprue pin diameter when using a centrifugal type ofcasting machine is that the diameter of the sprue pin should be equal to or greater thanthe thickest portion of the pattern.As a general rule, it is desirable to attach the sprue at the point of greatest bulk in thepattern. There is less chance of distortion on attaching the sprue, and the molten metal ismore apt to remain liquid in this area until the entire mold is filled. The direction of thesprue former is also important. It should never be attached at a right angle to a broad flatsurface of the mold. The entering hot metal impinges the mold surface at this point tocause turbulence of the metal, which, in turn, creates a shrinkage void or suck-backporosity. When the same pattern is sprued at an angle of 45° to the proximal wall, asatisfactory casting is obtained.

goldDental wax patterns (i.e., inlays, onlays, crowns) should be invested as soon aspossible after fabricating to minimize change in the shape caused by:• Reduced flow• Drying out of the wax• Relaxation of internal stress• Continued expansion of the wax 71 copyright © 2016-2017 Dental DecksOPERATIVE

• Relaxation of internal stressThe three types of inlay waxes differ in terms of melting point and flow: 1. Type A: hard or low-flow wax that is rarely used except in some indirect techniques 2. Type B: medium-flow wax that is used in some direct techniques. 3. Type C: soft or high-flow wax that is used in indirect techniques for the construct- ion of inlays, onlays, and full crowns.The essential ingredients of a successful inlay wax are paraffin wax, gum dammar, andcarnauba wax with some coloring material. Paraffin wax is generally the main ingredi-ent, usually in a concentration of 40 to 60%. Gum dammar is added to the paraffin toimprove the smoothness in the molding. It also increases the toughness of the wax.Carnauba wax is quite hard and tends to decrease the flow of a wax.Note: However the pattern is prepared, it should be an accurate reproduction of themissing tooth structure. The casting can be no more accurate than the wax pattern. Thewax pattern should be invested as soon as possible after fabrication to minimize changesin shape caused by relaxation of the internal stresses in the wax.

goldAfter waxing a pattern for a full-gold crown on #30, you proceed to creating aninvestment using a gypsum-bonded material. You read that the investmentcontains 65% silicon dioxide filler in the material. What is the primary purposeof this material?• Provide strength for the set investment to withstand casting forces• Increase the setting time to give you more time to work• Create a detailed negative reproduction of your casting pattern• Provide thermal expansion properties to compensate for casting shrinkage 72 copyright © 2016-2017 Dental DecksOPERATIVE

• Provide thermal expansion properties to compensate for casting shrinkageMain components of gypsum-bonded investments: 1. A refractory filler which is a form of silicon dioxide (SiO2), such as quartz or cristo- balite, comprises 60% to 65% of the investment. These two compounds have different crystal structures and, therefore, have different thermal expansion coefficients. Key point: This refractory filler regulates and provides the thermal expansion for the investment. 2. The binder (which is a gypsum matrix of a calcium hemihydrate) comprises 30% to 35% of the investment. This is the material that hardens after being mixed with the liquid and, thus, holds the investment together (adds strength). The actual or effective setting expansion depends on the gypsum content plus the water/powder ratio. Key point: Using a thinner mix (which contains more water) of a gypsum-bonded investment will decrease the setting expansion, increase the setting time, increase the porosity of the set material, and ultimately weaken the set material. 3. Modifiers are added to modify various physical properties of the investment. These modifiers include magnesium oxide, sodium chloride, boric acid, graphite, or potass- ium sulfate.Dental investments serve three important functions: 1. A detailed reproduction of anatomical form. 2. Enough strength to withstand the heat of burnout and the actual casting of the molten metal. 3. Compensation expansion equal to the alloy solidification shrinkage.

goldAll of the following are indications for a cast gold onlay EXCEPT one. Which oneis the EXCEPTION?• Restoration of large lesions• Restoration of ideal occlusion in cases of drifting, hypo- and hyper eruption, etc.• Restoration of optimum contour and proximal contact• Restoration of brittle teeth (endodontically treated)• Restoration of a tooth as an abutment for removable prosthesis, creating ideal guiding planes, rest seats, and undercuts• Restoration of teeth to meet patient preference for gold• Restoration of a tooth with minimal ferrule, where a full-coverage crown would not have enough retention 73 copyright © 2016-2017 Dental Decks OPERATIVE

• Restoration of a tooth with minimal ferrule, where a full-coverage crown would not have enough retentionImportant: If a tooth is not a candidate for a full-coverage crown, it is not a candidate for an onlay. Atooth that does not have a minimum of 1.5 mm of ferrule effect will need a core buildup, crownlengthening, or both.A ferrule effect is defined as the envelopment of the tooth structure by a crown. According to recentstudies, 1.5 mm of tooth structure is sufficient to ensure the transmission of the forces of mastication toboth the post and the tooth. A tooth that is fractured at the gum-line offers no form of resistance totransversal forces. The post must take on the entire load, and it is inevitable that cementation fails.Requirements for a good ferrule effect: • 1.5 to 2 mm of buccal and lingual subgingival tooth structure • 1 mm of tooth thickness after adequate preparation • 4 mm of suprabony tooth structureThe main advantage of the onlay is that it can permanently restore and reinforce a tooth by aconservative technique. Although conservation of tooth structure is desirable, such action is offset bya lack of retention. It has been shown that conservative onlays have inferior retention compared to fullcrowns. This is due to the crown’s greater axial surface area.Notes 1. Retentive features: parallelism of vertical surface (axial walls) is the primary retentive feature of an onlay preparation. Sharp point and line angles add to retention. 2. Auxiliary retentive features include a box or a groove. These features may be indicated where inadequate surface area of vertical walls is present. A box offers a greater increase in surface area, thus greater retention than a groove, but it is also more costly in terms of lost tooth structure. 3. The location of the gingival margin in the preparation of proximal surfaces is influenced by the amount of retention required, the need to extend gingivally to clear the contact area and convenience form.

goldOn delivery of your first crown, you notice that the margins are open when youattempt to seat the crown in the mouth. Which of the following should you checkfirst?• The occlusal contacts• The proximal contacts• For a void on the crown’s interior• For a nodule on the crown’s interior 74 copyright © 2016-2017 Dental DecksOPERATIVE

• The proximal contactsIf a casting fails to completely seat on a prepared tooth, one should first check forresidual temporary cement or other debris on the prepared tooth. Once all the temporarycement and other debris are removed, the first step in fitting the casting in the mouth isto adjust the proximal contact areas. The second step to check if a gold crown isn'tseating properly after proximal contact areas have been evaluated is for internal distortionspresent from the casting.Very important points: 1. When seating a casting, the initial interferences are usually the proximal contacts. Complete seating of the restoration can be verified by an x-ray and a sharp explorer used at the gold tooth margin. 2. When seating cast gold restorations, the occlusion of the restoration should be to the same degree that teeth contact in that quadrant and on the opposite side (use shim stock to check occlusion). 3. Initially, if a cast restoration is in hyperocclusion, the patient will complain of cold sensitivity and pressure in the tooth. If the restoration is not adjusted, the tooth will become very cold-sensitive, show signs of mobility, and there might be recession of the facial gingival tissue.