22 Dental Materials Practice Questions & Answers

1. 1. A preparation for an amalgam restoration has been excavated close to the pulp, leaving only a thin layer of remaining dentin. The dentist asks for a material placed in the deep floor of the preparation in a layer of roughly 0.5 to 1 mm that will insulate the pulp against the thermal conductivity of the metal and support the restoration against condensation forces. Which category of material is being described?

   • A.A cavity varnish, because its thin sealing film blocks the transfer of heat and cold
   • B.A luting-consistency cement flowed thinly across the entire preparation
   • C.A calcium hydroxide liner applied only as a thin film over the deepest point
   • D.A cement base built up to about 0.5 to 1 mm on the pulpal floor✓ Answer

   Thickness determines function: a varnish is only a sealing film and a liner is a thin, usually medicated layer that protects and stimulates reparative dentin, but neither has the bulk needed to insulate. Only a base, placed in a layer of roughly 0.5 to 1 mm or more, provides thermal insulation against the high thermal conductivity of metal and enough mechanical support to resist condensation pressure.

   Source: ADA Council on Scientific Affairs / ADA Oral Health Topics: liners, bases and cavity varnishes (pulpal protection); DANB General Chairside Exam Outline IV.11Report a problem with this question

2. 2. An assistant activates and triturates a pre-capsulated high-copper amalgam for the time set on the amalgamator, and the mass that is expressed into the amalgam well is dull, dry, grainy, and crumbles as it is loaded into the carrier. What is the correct action?

   • A.Discard the mix and triturate a fresh capsule using the time and speed specified by the manufacturer✓ Answer
   • B.Add a small amount of additional mercury to the mass and remix it by hand
   • C.Return the same capsule to the amalgamator and mix longer until the mass looks shiny
   • D.Condense it promptly, since a dry appearance affects only the surface finish

   A dull, dry, crumbly mass is under-triturated: the mercury has not fully wetted and reacted with the alloy particles, so the set restoration would be weak, rough and prone to corrosion and fracture. Trituration time and speed cannot be corrected after the fact, and mercury is never added chairside, so the only acceptable answer is to discard the mix and start over exactly as the manufacturer directs.

   Source: ANSI/ADA Specification No. 1, Alloy for Dental Amalgam (manufacturer trituration parameters); DANB General Chairside Exam Outline IV.1Report a problem with this question

3. 3. Which statement correctly describes the federal effluent requirement and the accompanying American Dental Association best management practices that govern amalgam waste in a general dental office?

   • A.Chairside trap and vacuum line trap contents may be placed in the sharps or biohazard container
   • B.Scrap amalgam should be heat sterilized in the autoclave before it is sent to a recycler
   • C.A bleach-containing line cleaner should be run weekly to dissolve amalgam particles in the suction lines
   • D.An amalgam separator meeting the recognized standard with at least 95% removal efficiency must be used, scrap amalgam is never discharged to the sewer, and line cleaners with a pH below 6 or above 8 are not used✓ Answer

   The federal dental effluent rule requires dental practices that place or remove amalgam to install a separator meeting the recognized amalgam separator standard, which specifies at least 95% removal of amalgam solids, and to follow two best management practices: no discharge of scrap amalgam to the sewer and no oxidizing or acidic line cleaners outside a pH of 6 to 8, because those cleaners dissolve bound mercury and release it into the wastewater. Amalgam scrap and trap contents go to a licensed recycler, never to the autoclave, the trash, or the sharps container.

   Source: EPA Dental Office Category effluent guidelines, 40 CFR Part 441 (separator per ANSI/ADA Specification No. 108 or ISO 11143, ≥95% removal) plus ADA Best Management Practices for Amalgam WasteReport a problem with this question

4. 4. A deep posterior preparation about 5 mm in depth is being restored with a light-cured hybrid resin composite, and the operator places and cures the material in increments no thicker than 2 mm rather than filling the preparation with one bulk mass. What is the principal reason for that technique?

   • A.Each increment must be etched separately with phosphoric acid before the next one will bond to it
   • B.The oxygen-inhibited surface layer prevents one increment from joining the next, so thin layers are needed to avoid it
   • C.Composite sets by an acid-base reaction whose speed depends on the total mass placed
   • D.Light energy is attenuated as it passes through resin, so a thicker layer would remain incompletely polymerized at its base, and one large mass concentrates polymerization shrinkage stress at the margins✓ Answer

   Depth of cure is limited because the resin scatters and absorbs the curing light, so beyond roughly 2 mm the bottom of an increment receives too little energy and stays soft, weak and irritating to the pulp. Incremental placement also reduces the shrinkage stress generated as the resin polymerizes, which is what pulls the material away from the cavity walls and produces marginal gaps, microleakage and postoperative sensitivity.

   Source: ADA Council on Scientific Affairs guidance on resin-based composites (depth of cure and polymerization shrinkage); ANSI/ADA Standard No. 27, Polymer-Based Restorative MaterialsReport a problem with this question

5. 5. A visible light curing unit is being used to polymerize composite increments throughout a restorative appointment. Which practice is appropriate for the dental team?

   • A.Resin that has cured onto the light tip should be left undisturbed so the tip is not scratched
   • B.The patient and team shield their eyes with the amber filter shield or protective eyewear, and the unit's output is checked periodically with a radiometer✓ Answer
   • C.The tip should be held several centimeters away so the beam spreads over the whole restoration at once
   • D.Because the unit emits no ultraviolet radiation, looking directly at the tip while curing is harmless

   The high-intensity blue light used to activate camphorquinone is a recognized retinal hazard even though it is not ultraviolet, so an amber filter or protective eyewear is required rather than optional. Output also degrades over time, and resin or debris on the tip further reduces irradiance, so the tip must be kept clean and the irradiance verified with a radiometer; otherwise increments that appear cured are actually under-polymerized.

   Source: ADA Council on Scientific Affairs statement on dental visible light curing units (blue-light ocular hazard; radiometer verification of irradiance)Report a problem with this question

6. 6. Cutting a preparation leaves a layer of ground dentin debris, the smear layer, covering the dentin surface and plugging the dentinal tubules. In an etch-and-rinse (total-etch) adhesive procedure using 35% to 37% phosphoric acid, what happens to that layer, and what does it mean for handling the dentin afterward?

   • A.The smear layer is unaffected by the etchant and serves as the surface to which the adhesive bonds
   • B.The etchant hardens the smear layer into a protective barrier, so no bonding agent is needed on dentin
   • C.The smear layer is removed by air drying alone, and the dentin should be dried until it appears chalky white before the adhesive is applied
   • D.The acid dissolves the smear layer, opens the tubules and demineralizes intertubular dentin so the adhesive resin can infiltrate the exposed collagen, which is why the dentin is left slightly moist rather than desiccated✓ Answer

   Phosphoric acid removes the smear layer and its tubule plugs and demineralizes the surface dentin, leaving a scaffold of collagen fibrils that the adhesive resin must infiltrate to form the hybrid layer that produces the bond. If that dentin is then desiccated with air, the collagen network collapses and the resin cannot penetrate it, which lowers bond strength and is a common source of postoperative sensitivity; enamel, by contrast, is dried until it looks chalky white.

   Source: ADA Oral Health Topics: adhesive dentistry/dental bonding — smear layer removal by 35–37% phosphoric acid and hybrid layer formationReport a problem with this question

7. 7. A Class II amalgam is being placed on the mesial of a mandibular first molar using a universal (Tofflemire) retainer positioned on the buccal with a matrix band around the tooth, and a wedge is inserted into the gingival embrasure from the lingual. What does the wedge accomplish?

   • A.It holds the retainer against the buccal surface so the band does not loosen during condensation
   • B.It adapts the band tightly to the gingival margin so amalgam cannot extrude as an overhang, and it separates the teeth slightly so a proper proximal contact remains after the band is removed✓ Answer
   • C.It substitutes for the matrix band when only two surfaces are involved in the preparation
   • D.It supplies the retention for the restoration, because amalgam bonds chemically to the dentin walls

   The band alone stands away from the tooth at the gingival floor, so condensed amalgam can escape and set as an overhanging ledge that traps plaque and inflames the gingiva; the wedge presses the band against that margin and seals it. Because the band also has thickness, the slight tooth separation the wedge creates is what allows a proper contact to be present once the band is removed. Amalgam is retained mechanically by the preparation design, not by any chemical bond.

   Source: ADA guidance on Class II amalgam contour and prevention of gingival overhangs; DANB General Chairside Exam Outline, Domain III (matrix systems)Report a problem with this question

8. 8. A patient with a high caries rate and gingival recession needs a Class V restoration on an exposed root surface, and conventional glass ionomer is selected instead of composite. Which property of glass ionomer most supports that choice?

   • A.It has greater compressive strength and wear resistance than resin composite
   • B.It is unaffected by moisture while it sets, so no isolation of the operating field is required
   • C.It is the most esthetic restorative available and polishes to a higher luster than composite
   • D.It bonds chemically to enamel and dentin without a separate etch-and-bond step and releases fluoride that can be recharged, which is anticariogenic at the margin✓ Answer

   Glass ionomer sets by an acid-base reaction between polyacrylic acid and fluoroaluminosilicate glass, and the carboxyl groups form a true chemical bond with calcium in enamel and dentin, which suits a root surface where enamel for etching is absent. The fluoride released from the glass, and taken up again from toothpaste and topical fluoride, protects the margin in a high-risk patient; the trade-offs are lower strength and wear resistance, poorer esthetics, and marked moisture sensitivity during setting, so the fresh surface still must be isolated and protected.

   Source: ADA Oral Health Topics: glass ionomer restorative materials (chemical adhesion, fluoride release); ANSI/ADA Standard No. 96 / ISO 9917-1, Dental Water-Based CementsReport a problem with this question

9. 9. Zinc phosphate cement is mixed for a crown cementation by incorporating the powder into the phosphoric acid liquid in small increments, spread over a large area of a cool, dry glass slab, over roughly a minute and a half to two minutes. Why is the mix handled this way?

   • A.The powder-liquid reaction is strongly exothermic, so a cool slab and small increments spread over a large area dissipate the heat, neutralize the acid gradually and lengthen working time, while moisture on the slab would change the liquid's water content and ruin the mix✓ Answer
   • B.The cold slab allows extra powder to be added later to thicken a mix that has become too runny
   • C.Chilling the slab speeds the set so the crown can be seated sooner after mixing
   • D.The slab must be cold enough to collect condensation so that the cement will not stick to the glass

   The reaction between zinc oxide powder and phosphoric acid liquid gives off substantial heat, and heat accelerates the set, so a cool slab acting as a heat sink plus incremental addition over a wide area keeps the mass workable long enough to seat a casting. The slab must nevertheless be dry, because condensation adds water to a liquid whose water content is precisely balanced; extra water and late additions of powder both change the powder-to-liquid ratio and produce a weaker, more soluble cement.

   Source: ANSI/ADA Standard No. 96 / ISO 9917-1, Dental Water-Based Cements (zinc phosphate), with manufacturer proportioning and mixing instructionsReport a problem with this question

10. 10. A tooth prepared for an all-ceramic crown that will be luted with resin cement is to wear a provisional restoration for two weeks. Why does the dentist specify a non-eugenol temporary cement for that provisional?

    • A.Zinc oxide–eugenol cements set permanently and the provisional could not be removed later
    • B.Eugenol permanently discolors ceramic restorations to a gray shade
    • C.Eugenol irritates vital pulp tissue and is contraindicated on any tooth that has not had root canal treatment
    • D.Residual eugenol left on the preparation inhibits the free-radical polymerization of resin, weakening the set and the bond of the resin cement at the final appointment✓ Answer

    Eugenol is a phenolic compound that acts as a free-radical scavenger, so traces remaining in the dentin surface interfere with the polymerization of bis-GMA and similar resins and leave the adhesive interface under-cured. Eugenol itself is sedative rather than irritating to the pulp, which is why zinc oxide–eugenol is otherwise a common temporary cement; it is simply incompatible with any restoration that will be bonded, so a non-eugenol product is used and the preparation is cleaned thoroughly before bonding.

    Source: ADA Oral Health Topics: dental cements (eugenol inhibition of resin polymerization); ANSI/ADA Standard No. 30, Dental Zinc Oxide–Eugenol and Zinc Oxide Non-Eugenol CementsReport a problem with this question

11. 11. The occlusal surface of a newly erupted permanent first molar has been cleaned, isolated with cotton rolls and a dry angle, etched, rinsed and dried to a chalky white appearance in preparation for a resin sealant. Before the sealant is applied, the cotton roll shifts and the etched enamel is wet with saliva. What is the most appropriate next step?

    • A.Apply a fluoride-containing prophy paste, rinse, and then place the sealant
    • B.Place the sealant and extend the curing time to compensate for the moisture
    • C.Rinse the surface, re-isolate the tooth, dry it, and etch it again before placing the sealant✓ Answer
    • D.Dry the surface thoroughly with the air syringe and place the sealant

    Saliva deposits glycoproteins that coat the etched enamel within seconds, and drying does not remove that film; the resin can then no longer flow into the microporosities to form the resin tags that retain the sealant. The surface must be rinsed, re-isolated, dried and re-etched, because moisture control failure after etching is the leading cause of sealant loss. Fluoride-containing prophy paste is also avoided before sealant placement since its residue interferes with etching and bonding.

    Source: ADA Council on Scientific Affairs / AAPD evidence-based clinical practice guideline on pit-and-fissure sealants (isolation and re-etching after salivary contamination)Report a problem with this question

12. 12. An assistant is mixing regular-set (Type II) alginate in a warm operatory, and on the previous attempt the material gelled before the tray could be seated. Keeping the manufacturer's ratio of one scoop of powder to one measure of water, what is the correct way to gain more working time without weakening the impression?

    • A.Add one extra measure of water to the same number of scoops of powder
    • B.Spatulate more slowly, stretching the mixing time to a full 90 seconds before loading the tray
    • C.Use one less scoop of powder with the same measure of water
    • D.Mix with cooler water, leaving the scoop-to-water-measure ratio unchanged✓ Answer

    Alginate gels through a chemical reaction between potassium alginate and the calcium sulfate reactor, and the rate of that reaction is temperature dependent, so cooler water slows gelation and lengthens working time while warmer water shortens it. Altering the water/powder ratio also changes setting behavior, but it does so by diluting or concentrating the reactants, which reduces tear strength and accuracy, so water temperature is the accepted chairside control. Spatulating more slowly consumes working time rather than creating it.

    Source: ANSI/ADA Standard No. 18, Alginate (Irreversible Hydrocolloid) Impression Material; Bird & Robinson, Modern Dental Assisting, alginate manipulationReport a problem with this question

13. 13. An alginate impression for a study model has just been removed and rinsed, but the cast cannot be poured for about 40 minutes because the laboratory area is in use. What should the assistant do with the impression in the meantime?

    • A.Leave it uncovered on the counter so the surface dries before pouring
    • B.Immerse it in intermediate-level disinfectant for the full 40 minutes
    • C.Submerge it in a bowl of cool water until the laboratory area is free
    • D.Wrap it in a damp (not dripping) paper towel to hold it at 100% relative humidity and pour it as soon as possible✓ Answer

    Alginate is a hydrocolloid gel whose accuracy depends on keeping its water content constant: left in open air it loses water and shrinks (syneresis), and left standing in water or an immersion disinfectant it absorbs water and swells (imbibition), and either change distorts the impression. Storage at 100% relative humidity in a damp towel or a humidor keeps water neither gained nor lost, but it only delays distortion, so the impression is still poured as soon as possible (ideally within about 10 minutes). Disinfection of alginate is done by the spray-wrap-spray method rather than prolonged immersion for exactly the same reason.

    Source: ANSI/ADA Standard No. 18 (irreversible hydrocolloid); CDC Guidelines for Infection Control in Dental Health-Care Settings, dental laboratory asepsis (spray-wrap-spray for hydrocolloid impressions)Report a problem with this question

14. 14. A student asks what actually makes agar a reversible hydrocolloid and alginate an irreversible hydrocolloid. Which statement correctly states the difference?

    • A.Agar changes from sol to gel and back again with temperature alone, while alginate gels through a chemical reaction that reheating cannot undo✓ Answer
    • B.Agar requires a calcium sulfate reactor in the mix, while alginate requires none
    • C.Agar sets by a chemical reaction, while alginate sets purely by cooling
    • D.Agar is a rigid impression material, while alginate is an elastic impression material

    The reversible/irreversible distinction is about the type of change the material undergoes: agar undergoes a physical sol-to-gel change driven by temperature, so heating liquefies it again and the same material can be reused, while alginate undergoes a chemical reaction between potassium alginate and calcium sulfate that permanently forms a new compound. Both are hydrocolloids and both set into elastic gels that can be withdrawn over undercuts, so elasticity is not the distinguishing feature, and it is alginate, not agar, that contains the calcium sulfate reactor.

    Source: ANSI/ADA Standard No. 128 (reversible hydrocolloid/agar) and ANSI/ADA Standard No. 18 (irreversible hydrocolloid/alginate)Report a problem with this question

15. 15. A crown preparation was managed with retraction cord and a ferric sulfate hemostatic agent, and the assistant kneaded the polyvinyl siloxane putty while wearing natural latex gloves. When the impression is removed, the material against the preparation is gummy and unset even though the rest of the impression is fully polymerized. What is the most likely cause and correction?

    • A.The impression was removed before the manufacturer's setting time had elapsed; hold the tray longer next time
    • B.Unequal amounts of base and catalyst were extruded from the automix gun; discard the cartridge and open a new one
    • C.Sulfur from the latex gloves and the sulfate hemostatic poisoned the platinum catalyst; use vinyl or nitrile gloves and rinse the preparation thoroughly before impressing✓ Answer
    • D.The rinse water used on the preparation was too cold, which slowed polymerization; rinse with warm water instead

    Polyvinyl siloxane (addition silicone) polymerizes by way of a platinum catalyst, and sulfur compounds bind that catalyst and stop the reaction, a localized inhibition that shows up as an uncured, gummy layer exactly where the contaminated surface or contaminated fingers touched the material. Natural latex gloves, latex-contaminated retraction cord, and sulfur-containing hemostatics such as ferric sulfate and aluminum sulfate are the classic sources, so the assistant handles putty with vinyl or nitrile gloves and the preparation is rinsed thoroughly before the impression is taken. A dispensing error or premature removal would affect the whole mix, not only the material at the preparation.

    Source: ANSI/ADA Standard No. 19, Elastomeric Dental Impression Materials; Eakle & Bastin, Dental Materials, addition silicone catalyst inhibition by sulfur compoundsReport a problem with this question

16. 16. A final impression is planned with polyether for a patient who has tipped teeth, periodontal bone loss, and pronounced interproximal undercuts. Which statement about polyether should guide how the assistant prepares for and handles this impression?

    • A.It should be stored in water or a soaking wet towel so it does not shrink before the cast is poured
    • B.It is the most flexible of the elastomers, which makes it the material of choice around severe undercuts
    • C.It is accurate and tolerates a slightly moist field, but it is very stiff when set, so undercuts are blocked out and the tray is removed with a single firm pull along the long axis of the teeth✓ Answer
    • D.It sets by evaporation of an alcohol byproduct, so it must be poured within a few minutes of removal

    Polyether is hydrophilic, which lets it record detail in a slightly moist sulcus, but its set material has the highest stiffness of the common elastomers, so it can lock into undercuts around tipped or periodontally involved teeth and be painful or difficult to remove unless undercuts are blocked out and the impression is snapped out in one motion along the long axis. Polyether is also the elastomer most prone to imbibition, so it is stored dry rather than in water or high humidity. The alcohol byproduct that demands an immediate pour belongs to condensation silicone, not polyether.

    Source: ANSI/ADA Standard No. 19, Elastomeric Dental Impression Materials (polyether stiffness and dimensional stability); Eakle & Bastin, Dental MaterialsReport a problem with this question

17. 17. A two-step putty/wash polyvinyl siloxane impression is being taken for a full crown. Which description of the viscosities and tray preparation is correct?

    • A.Light-body wash is syringed around the preparation to capture fine detail while heavy-body or putty in the adhesive-coated tray supplies bulk and forces the wash into the detail✓ Answer
    • B.Light body is used alone in a perforated tray, because elastomeric impression materials do not require tray adhesive
    • C.Heavy body is syringed around the preparation because a thicker material records the margins more sharply
    • D.Light body is loaded in the tray and heavy body is syringed, because the tray material must be the more flexible of the two

    Light-body (wash) material has the low viscosity needed to flow into the sulcus and reproduce fine margin detail, while heavy-body or putty has the body to fill the tray, support the wash, and hydraulically drive it into those details when the tray is seated. Elastomers do not lock mechanically into a tray the way alginate does, so the tray is painted with the matching tray adhesive and allowed to dry before loading; perforations alone are the retention method for alginate.

    Source: ANSI/ADA Standard No. 19, Elastomeric Dental Impression Materials (viscosity classes and use of tray adhesive)Report a problem with this question

18. 18. A cast is needed that will carry a die on which a crown is fabricated. Model plaster is mixed at roughly 50 mL of water per 100 g of powder and high-strength die stone at roughly 20 mL of water per 100 g. Which choice and rationale is correct?

    • A.Type IV high-strength die stone, because its lower water/powder ratio leaves fewer water-filled voids and yields a denser, harder, stronger set cast✓ Answer
    • B.Type IV high-strength die stone, because it contains no calcium sulfate hemihydrate and therefore cannot expand on setting
    • C.Type II model plaster, because a higher water/powder ratio increases the compressive strength of the set gypsum
    • D.Type II model plaster, because the extra water produces a smoother and therefore more accurate surface

    All gypsum products are calcium sulfate hemihydrate that rehydrates to the dihydrate, and only the amount of water needed to wet the particles takes part in the reaction; any excess water is left behind as porosity when it evaporates. Because of that, strength and surface hardness are inversely related to the water/powder ratio, and die stone, whose dense regular particles need only about 20 mL per 100 g, sets far harder than model plaster at about 50 mL per 100 g, which is why Type IV is specified for dies.

    Source: ANSI/ADA Standard No. 25, Dental Gypsum Products (Types I-V); water/powder ratio versus strength of set gypsumReport a problem with this question

19. 19. An assistant is preparing to pour an impression in dental stone and wants a cast free of bubbles at the cusp tips and incisal edges. Which technique is correct?

    • A.Add extra water to the mix so that it flows into the teeth without needing the vibrator
    • B.Drop large increments over the anterior teeth first so the incisal edges fill before the mix thickens
    • C.Place the powder in the bowl first and add water to it a little at a time until the mix looks right, then fill the whole arch at once
    • D.Measure the water into the bowl first, add the weighed powder to the water and let it slake, then vibrate small increments into one corner of the most posterior area and let the mix flow around the arch ahead of itself✓ Answer

    Adding weighed powder to pre-measured water lets each particle wet evenly and lets trapped air escape during slaking, whereas adding water to powder traps dry lumps and air. Filling from one corner of the most posterior area with small increments on a vibrator makes the mix roll forward around the arch and push air ahead of it, so voids are not sealed into the cusp tips and incisal edges. Adding extra water to improve flow would raise the water/powder ratio and produce a weaker, more porous cast.

    Source: ANSI/ADA Standard No. 25, Dental Gypsum Products; Bird & Robinson, Modern Dental Assisting, mixing and pouring gypsum castsReport a problem with this question

20. 20. Before a final impression is poured, the assistant must build a wall around the periphery of the impression so the base of the cast forms at a uniform height without a second pour. Which wax is used for this?

    • A.Boxing wax✓ Answer
    • B.Utility wax
    • C.Inlay wax
    • D.Sticky wax

    Boxing wax is a processing wax supplied as a long, soft, pliable strip precisely so it can be adapted around the periphery of an impression to form a container that holds the gypsum at a uniform base height. Sticky wax is brittle at room temperature and becomes tacky when heated, and is used to temporarily join broken appliance pieces for laboratory repair; inlay wax is a pattern wax that must burn out cleanly; utility wax is used to extend or cushion tray borders and to cover orthodontic brackets that irritate tissue.

    Source: Bird & Robinson, Modern Dental Assisting, classification of dental waxes (pattern, processing and impression waxes)Report a problem with this question

21. 21. A bis-acryl provisional crown has been fabricated for a tooth that will receive an all-ceramic crown seated with resin cement in two weeks. Which cement should the assistant prepare for the provisional, and why?

    • A.A definitive resin-modified glass ionomer luting cement, because its fluoride release protects the preparation
    • B.Zinc phosphate cement mixed to luting consistency, because it gives the provisional adequate retention for two weeks
    • C.A zinc oxide-eugenol temporary cement, because its sedative effect on the pulp prevents postoperative sensitivity
    • D.A non-eugenol temporary cement, because eugenol residue left on the dentin inhibits resin polymerization and lowers the bond strength of the resin cement✓ Answer

    Eugenol is a free-radical scavenger, so residue absorbed into dentin during provisional cementation interferes with the polymerization of adhesive and resin cement and measurably reduces bond strength, which is why a non-eugenol provisional cement is selected whenever the definitive restoration will be resin bonded or resin cemented. The provisional cement must also be deliberately weak so the temporary can be removed without damaging the preparation, which rules out definitive luting cements such as zinc phosphate or resin-modified glass ionomer.

    Source: Bird & Robinson, Modern Dental Assisting, provisional coverage and temporary cementation; ADA Oral Health Topics, eugenol inhibition of resin polymerizationReport a problem with this question

22. 22. A patient finishing a course of take-home whitening with 10% carbamide peroxide trays asks whether the existing tooth-colored composite restoration on an upper central incisor will lighten along with the enamel. What should the patient be told?

    • A.Whitening agents do not lighten restorative materials, so the composite will need to be replaced to match, and shade matching and bonding are delayed about two weeks after bleaching✓ Answer
    • B.The composite will lighten at the same rate as the enamel because peroxide diffuses through resin as readily as through tooth structure
    • C.The composite should be replaced on the same day the last tray is worn so that both shades can be recorded together
    • D.Carbamide peroxide lightens composite but not porcelain, so only crowns and veneers ever need to be replaced

    Peroxide whitening works by oxidizing pigmented organic molecules within tooth structure, and composite, porcelain, and cements contain no such chromogens to break down, so restorations keep their original shade and can end up looking dark against newly lightened enamel. Replacement is therefore planned after whitening, and it is deferred roughly two weeks because residual oxygen released from the peroxide inhibits resin polymerization and lowers bond strength, and because the shade continues to stabilize after the final tray.

    Source: ADA Council on Scientific Affairs / ADA Oral Health Topics: Whitening (tooth whitening does not lighten restorations; delay bonding after bleaching due to inhibited resin polymerization)Report a problem with this question

Practice questions based on the DANB Radiation Health and Safety (RHS), Infection Control (ICE), and General Chairside Assisting (GC) content outlines, CDC dental infection-prevention guidance, the OSHA Bloodborne Pathogens Standard, and ADA/FDA radiographic selection criteria. DANB, CDA, RHS, ICE, and GC are marks of the Dental Assisting National Board; this site is not affiliated with or endorsed by DANB. The duties a dental assistant may legally perform — and any radiography permit or certification required — are set by your own state dental board. Confirm current requirements with that board and with DANB before testing. About the DANB exams →