22 Dental Materials Practice Questions & Answers

1. 1. A preparation is cut so close to the pulp that the dentist estimates less than 0.5 mm of dentin remains over the pulp horn. What does the assistant prepare, and where is it placed?

   • A.A thin varnish film, painted over the enamel margins and the pulpal floor
   • B.A thick zinc phosphate base, placed over the whole prepared dentin surface
   • C.A thin calcium hydroxide liner, placed on the deepest dentin near the pulp✓ Answer
   • D.A thick glass ionomer base, placed over the axial walls and the cavosurface

   Very deep dentin calls for a liner, not a bulk base: calcium hydroxide stimulates the odontoblasts to lay down reparative secondary dentin, and it is confined to the deepest spot because a thick layer of it compresses under condensation and undermines the restoration.

   Source: ADA Oral Health Topics, pulp capping and cavity liners for deep preparationsReport a problem with this question

2. 2. A large amalgam is planned and the dentist wants the pulp insulated from temperature changes conducted through the metal. Which application accomplishes that?

   • A.A varnish film brushed as a sealing layer over the floor
   • B.A cement base built up in bulk on the pulpal floor✓ Answer
   • C.A liner flowed as a thin wash over the deepest dentin
   • D.An adhesive resin cured as a thin film across the floor

   Thermal insulation is a function of bulk. Metal conducts heat and cold readily, so only a base with real thickness on the pulpal floor slows that transfer; varnish and liners are films measured in fractions of a millimetre and insulate essentially nothing.

   Source: ADA Oral Health Topics, dental cements used as bases beneath metallic restorationsReport a problem with this question

3. 3. Why is cavity varnish not placed under a resin composite restoration?

   • A.Its resin film interferes with bonding of the adhesive to dentin✓ Answer
   • B.Its alkaline pH neutralizes the etchant and prevents demineralization
   • C.Its fluoride content reacts with the filler and discolors the margins
   • D.Its thermal conductivity draws curing light heat toward the pulp

   Varnish works by laying down a sealing film of resin in solvent, and that film sits exactly where the adhesive needs to contact and infiltrate dentin. The same objection rules it out under glass ionomer, which needs bare tooth structure for its chemical bond and fluoride exchange.

   Source: ADA Oral Health Topics, cavity varnishes and their compatibility with adhesive restorative materialsReport a problem with this question

4. 4. A triturated amalgam capsule is opened and the mass is dull, dry, and crumbles when it is picked up. What does the assistant do?

   • A.Condense the mass at once before any more working time is lost
   • B.Add a drop of mercury and triturate the mass a few seconds longer
   • C.Knead the mass in a gauze square until it looks shiny and cohesive
   • D.Discard the mix and triturate a fresh capsule at the correct setting✓ Answer

   Dull and crumbly is the classic sign of under-trituration, and the alloy-mercury reaction cannot be restarted once it has gone wrong. Adding mercury changes the proportion the capsule was manufactured to hold, and kneading only warms and contaminates the mass, so the ruined mix is thrown away and a new capsule is triturated at the manufacturer's time and speed.

   Source: ADA Oral Health Topics, dental amalgam handling and triturationReport a problem with this question

5. 5. A triturated amalgam mix is soupy and sticks to the walls of the capsule. Which statement describes what happened and its effect?

   • A.It was triturated too long, and its working time is shortened✓ Answer
   • B.It was triturated too briefly, and its working time is shortened
   • C.It was triturated too long, and its setting expansion is increased
   • D.It was triturated too briefly, and its setting expansion is increased

   Over-trituration drives the reaction further before the mix ever reaches the tooth, so the mass is wet and sticky and begins hardening sooner; the assistant loses the time needed to carry, condense and carve. Under-trituration produces the opposite appearance, a dry crumbly mass.

   Source: ADA Oral Health Topics, dental amalgam trituration and working characteristicsReport a problem with this question

6. 6. How is scrap amalgam collected at chairside handled once the restoration is finished?

   • A.It is sealed in a red biohazard bag and handled as regulated medical waste
   • B.It is kept in a labeled closed container and sent to a licensed recycler✓ Answer
   • C.It is rinsed down the operatory drain because the separator will capture it
   • D.It is placed in the sharps container and processed with contaminated sharps

   Amalgam waste is a mercury problem, not an infection problem, so the biohazard and sharps streams are the wrong route and both end in incineration, which volatilizes mercury. Scrap is stored dry in a closed labeled container and shipped to a licensed recycler, and the chairside trap and separator exist to keep particles out of the drain rather than to justify rinsing them there.

   Source: EPA effluent guidelines for the dental category and ADA best management practices for amalgam wasteReport a problem with this question

7. 7. A manufacturer directs that a composite be placed in increments of about 2 mm, each cured before the next. What does that increment limit address?

   • A.Light is attenuated within resin, so deeper material cures incompletely✓ Answer
   • B.Filler particles settle down, so deeper material becomes resin-rich
   • C.Oxygen diffuses into resin, so deeper material stays tacky for good
   • D.Heat builds during the reaction, so deeper material scorches the pulp

   A curing light has a limited depth of cure because the resin scatters and absorbs the beam as it travels, so monomer near the floor of a bulk increment never reaches adequate conversion; the same reason explains why dark and opaque shades need longer exposure. Thin increments also reduce the shrinkage stress pulling on the margins.

   Source: ADA Oral Health Topics, resin composite placement and depth of cureReport a problem with this question

8. 8. What does checking a curing light with a radiometer tell the assistant?

   • A.Whether the light battery lasts through a full day of scheduled visits
   • B.Whether the light emits wavelengths that are hazardous to the operator
   • C.Whether the light tip was sterilized between one patient and the next
   • D.Whether the light still delivers enough intensity to polymerize resin✓ Answer

   Output falls off as bulbs age, batteries weaken, and resin builds up on the guide, and none of that is visible to the eye because the light still looks bright. A radiometer reports irradiance, which is what actually determines whether the photoinitiator absorbs enough energy in the blue range to convert the monomer.

   Source: ADA Oral Health Topics, dental curing lights and monitoring of light outputReport a problem with this question

9. 9. Why is the tacky surface film on a cured composite increment left undisturbed before the next increment?

   • A.It holds adhesive solvent that must evaporate before shade is judged
   • B.It holds residual etchant that keeps demineralizing the dentin below
   • C.It holds unreacted filler that hardens when the surface is polished
   • D.It holds free monomer that copolymerizes with the increment above✓ Answer

   Oxygen in the air inhibits polymerization at the very surface, leaving a thin layer of monomer that never converted. That layer is what chemically joins one increment to the next, so wiping it away with alcohol or cotton between layers creates a weak internal seam.

   Source: ADA Oral Health Topics, incremental placement of resin composite and the oxygen-inhibited layerReport a problem with this question

10. 10. In total-etch bonding, what does 35 to 37 percent phosphoric acid do to the smear layer on cut dentin?

    • A.It hardens the layer into a barrier that seals the tubules shut
    • B.It removes the layer and opens the tubules for resin infiltration✓ Answer
    • C.It dissolves the layer and precipitates salts that plug the tubules
    • D.It leaves the layer intact and roughens it for the adhesive to grip

    The smear layer is a film of cut dentin debris and denatured collagen that plugs the tubule openings and would keep resin from reaching sound dentin. Phosphoric acid strips it away and demineralizes the surface, exposing a collagen mesh and open tubules that the adhesive infiltrates to form the hybrid layer; self-etch primers instead dissolve and incorporate the smear layer rather than removing it.

    Source: ADA Oral Health Topics, dentin adhesion, the smear layer and hybrid layer formationReport a problem with this question

11. 11. After etched dentin is rinsed, why is it blotted rather than dried with a strong air blast?

    • A.Drying cools the dentin surface and slows the set of the adhesive resin
    • B.Drying evaporates the primer solvent before it reaches the tubules
    • C.Drying collapses the demineralized collagen and blocks resin infiltration✓ Answer
    • D.Drying strips the oxygen-inhibited layer that the adhesive needs to bond

    Etching leaves a scaffold of demineralized collagen standing in water. Blast that water away and the fibrils mat down on themselves, and the adhesive can no longer weave through them, so bond strength falls; leaving the dentin visibly moist keeps the scaffold open for wet bonding. Enamel is the opposite and is dried to a frosty white.

    Source: ADA Oral Health Topics, wet bonding technique for total-etch dentin adhesivesReport a problem with this question

12. 12. A root-surface lesion in an older adult at high caries risk must be restored where isolation is imperfect. Which property makes glass ionomer the choice?

    • A.It expands as it sets and seals the margin under heavy load
    • B.It bonds micromechanically to enamel and resists occlusal wear
    • C.It sets by light activation and reaches full strength immediately
    • D.It bonds chemically to dentin and releases fluoride over time✓ Answer

    Glass ionomer sets by an acid-base reaction between polyacrylic acid and fluoroaluminosilicate glass, and the carboxyl groups bond ionically to calcium in tooth structure, so it does not depend on an etch-and-bond sequence that moisture would ruin. Its continuing fluoride release, which can be recharged from toothpaste and rinses, is what suits a patient whose caries risk is the real problem.

    Source: ADA Oral Health Topics, glass ionomer restorative materials and fluoride releaseReport a problem with this question

13. 13. How does resin-modified glass ionomer differ from a conventional glass ionomer?

    • A.It removes the polyacrylic acid, giving a faster set and more translucency
    • B.It adds a light-cured resin, giving greater strength and lower solubility✓ Answer
    • C.It adds silver particles, giving more radiopacity and higher fluoride release
    • D.It removes the fluoride glass, giving a better polish and less water uptake

    The resin component polymerizes on command under the curing light while the acid-base reaction continues underneath, so the material gains early strength and resists dissolving in oral fluids without giving up the chemical bond to tooth or the fluoride release. The trade-off is water sorption and expansion, which is why it is avoided under many all-ceramic units.

    Source: ADA Oral Health Topics, resin-modified glass ionomer materialsReport a problem with this question

14. 14. How is an assembled universal (Tofflemire) retainer and matrix band positioned for a Class II amalgam?

    • A.The diagonal slot faces occlusally and the retainer sits on the lingual
    • B.The diagonal slot faces gingivally and the retainer rests on the buccal✓ Answer
    • C.The diagonal slot faces distally and the retainer rests on the occlusal
    • D.The diagonal slot faces mesially and the retainer rests on the palatal

    The band is seated so that the diagonal slot opens toward the gingiva, which lets the whole retainer be lifted straight off occlusally once the amalgam is carved, and the retainer body rides on the buccal so it stays clear of the tongue and the operator's working field. Reversing either one traps the retainer and tears the set restoration on removal.

    Source: ADA Oral Health Topics, matrix systems for posterior restorationsReport a problem with this question

15. 15. Why is a wedge placed interproximally before an amalgam is condensed?

    • A.It holds the dam clamp off the gingival tissue during condensation
    • B.It seats the band against the gingival margin and prevents an overhang✓ Answer
    • C.It keeps the band clear of the adjacent tooth so a contact can form
    • D.It compresses the papilla so the matrix lifts away without bleeding

    A matrix band is a flat strip and does not hug the curved gingival floor on its own, so amalgam condensed against the gap escapes below the margin as an overhang that holds plaque and inflames the papilla. The wedge pushes the band tight at that margin and, in doing so, separates the teeth slightly to compensate for the band's thickness.

    Source: ADA Oral Health Topics, matrix bands and wedges in Class II restorationsReport a problem with this question

16. 16. The operatory is warm and the alginate is gelling before the tray can be seated. What does the assistant change on the next mix?

    • A.Mix with warmer water, leaving the powder and water measures unchanged
    • B.Mix with extra water, leaving the powder measure and spatulation unchanged
    • C.Mix with cooler water, leaving the powder and water measures unchanged✓ Answer
    • D.Mix with less powder, leaving the water measure and spatulation unchanged

    Water temperature is the control the assistant is meant to use, because it changes the rate of the chemical reaction without changing the proportions: cooler water slows gelation and buys working time, warmer water speeds it. Altering the powder-to-water ratio instead dilutes the material and yields a weak, tacky impression that tears and distorts.

    Source: ADA Oral Health Topics, irreversible hydrocolloid (alginate) impression materialsReport a problem with this question

17. 17. A cast cannot be poured for twenty minutes after an alginate impression is removed. How is the impression held meanwhile?

    • A.Disinfected, then wrapped in dry gauze and refrigerated until use
    • B.Disinfected, then submerged in a bowl of cool water until poured
    • C.Disinfected, then left open on the counter to air dry until poured
    • D.Disinfected, then kept in a sealed bag at full humidity until poured✓ Answer

    Alginate is a hydrocolloid and loses or gains water in either direction: left dry it exudes fluid and shrinks by syneresis, and soaked in water it swells by imbibition. Both distort the impression, so the only stable holding condition is saturated air, and even then the cast is poured as soon as possible.

    Source: ADA Oral Health Topics, storage and dimensional stability of alginate impressionsReport a problem with this question

18. 18. A polyvinyl siloxane wash stays tacky and unset around the preparation. What is the most likely cause?

    • A.Sulfur from latex gloves or latex retraction cord touched the prep✓ Answer
    • B.Water from the air-water syringe pooled in the prepared cavity
    • C.Heat from the operating light warmed the cartridge before mixing
    • D.Alcohol from the disinfectant wipe was left on the tray surface

    Addition silicone sets through a platinum catalyst, and sulfur compounds poison that catalyst on contact, so the material nearest the contaminated surface never polymerizes. Latex gloves, latex-handled cord and some hemostatic agents are the usual sources, which is why vinyl or nitrile gloves are worn and the cord is handled with clean instruments.

    Source: ADA Oral Health Topics, addition silicone (polyvinyl siloxane) impression materials and set inhibitionReport a problem with this question

19. 19. Why is a polyether impression never stored in water or in a wet paper towel?

    • A.It releases hydrogen gas, which water holds against the impression
    • B.It is hydrophobic and repels water, which traps bubbles on the surface
    • C.It is hydrophilic and absorbs water, which distorts the impression✓ Answer
    • D.It releases alcohol as it sets, which water dilutes and slows the set

    Polyether's affinity for water is the same property that lets it record a slightly moist sulcus so well, but it works in both directions: standing water is taken up into the set material, which swells and no longer matches the prepared tooth. Store it dry and pour it within the manufacturer's window.

    Source: ADA Oral Health Topics, elastomeric impression materials and their storage requirementsReport a problem with this question

20. 20. Two casts are poured from one impression: one product mixed at about 30 mL of water per 100 g of powder, the other at about 50 mL per 100 g. How do they compare?

    • A.The 30 mL cast is denser and stronger, and it sets in less time✓ Answer
    • B.The 50 mL cast is denser and stronger, and it sets in less time
    • C.The 30 mL cast is more porous and weaker, and it sets in less time
    • D.The 50 mL cast is denser and stronger, and it sets in more time

    Only enough water to convert the hemihydrate to dihydrate is needed chemically; everything beyond that stays as free water, evaporates and leaves voids. Dense regular stone particles wet out with far less water than porous irregular plaster, which is why a low water-to-powder ratio yields the harder, stronger, faster-setting cast used for dies.

    Source: ADA Oral Health Topics, gypsum products and the water-to-powder ratioReport a problem with this question

21. 21. A provisional crown will be worn for two weeks and the definitive crown will be seated with a resin cement. Which provisional cement is selected?

    • A.A cement without eugenol, because eugenol inhibits resin polymerization✓ Answer
    • B.A zinc oxide eugenol cement, because eugenol soothes newly cut dentin
    • C.A zinc phosphate cement, because its strength holds the provisional firmly
    • D.A glass ionomer cement, because its fluoride protects the cut margins

    Eugenol is a phenol that scavenges free radicals, and free radicals are exactly what a resin cement relies on to polymerize. Residue soaks into the cut dentin over two weeks and cannot be scrubbed out completely, so the definitive cement cures poorly and the bond strength drops; zinc phosphate and glass ionomer are also too retentive for a provisional.

    Source: ADA Oral Health Topics, provisional restorations and eugenol interference with resin cementsReport a problem with this question

22. 22. Why is zinc phosphate cement mixed in small increments over a wide area of a cool glass slab?

    • A.To raise the pH of the mix before it contacts the prepared dentin
    • B.To keep the powder dry so the liquid does not pick up room moisture
    • C.To carry off the heat of the reaction and lengthen the working time✓ Answer
    • D.To break up filler clumps so the cement film stays an even thickness

    The reaction between zinc oxide powder and phosphoric acid liquid is strongly exothermic, and heat accelerates it, so a mix made all at once on a warm or small surface stiffens before the crown can be seated. A cold slab and a large mixing field pull that heat away, and adding powder in stages lets each portion react before more is introduced.

    Source: ADA Oral Health Topics, zinc phosphate luting cement mixing techniqueReport 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 →