Dental Materials — 30-Min Notes

1. Dental Amalgam

• Composition: Ag 65%, Sn 25%, Cu 6%, Hg 50% (mixed as powder & mercury ratio).

• Setting reaction: γ + Hg → γ1 + γ2 phases.

• High-copper alloys reduce γ2 phase → less corrosion.

• Properties: good compressive strength, poor tensile strength, durable.

• Disadvantages: mercury toxicity, corrosion, aesthetics.

• High-yield NEET MDS: γ2 phase → weak & prone to corrosion.

2. Dental Cements

• Types: Zinc phosphate, Zinc polycarboxylate, Glass ionomer, Resin-modified GIC.

• Zinc phosphate: exothermic, low pH initially, mechanical retention.

• Polycarboxylate: chelation with calcium → mild pulp irritation.

• GIC: fluoride release → anticariogenic.

• Resin cements: adhesive, high strength, used for veneers/crowns.

• Tip: GIC = glass powder + polyacrylic acid

3. Impression Materials

• Elastic: Alginate (irreversible hydrocolloid), Agar (reversible hydrocolloid), Elastomers (PVS, Polyether, Polysulfide).

• Non-elastic: Impression plaster, ZOE, Wax.

• Alginate: irreversible, cheap, hydrophilic, low tear strength.

• PVS: dimensionally stable, elastic recovery excellent, commonly used for crowns/bridges.

• Tip: PVS = gold standard for final impressions.

4. Direct Restorative Materials

• Composite resins: resin matrix + filler + initiator.

• Light-cure vs self-cure.

• Properties: aesthetics, bond to enamel/dentin (with etching), wear-resistant.

• Glass ionomer: chemical bond, fluoride release, lower strength than composite.

• High-yield NEET MDS: Hybrid composites: better strength + aesthetics.

5. Indirect Restorative Materials

• Dental ceramics: porcelain, feldspathic, zirconia.

• Alloys: Noble (Au, Pt, Pd), Base (Ni, Cr, Co).

• Properties: high compressive strength, brittle (ceramics), ductile (alloys).

• Tip: PFM = porcelain fused to metal.

6. Endodontic Materials

• Root canal sealers: Zinc oxide-eugenol, Resin-based, Bioceramic (MTA).

• Gutta-percha: thermoplastic, inert, obturation material.

• High-yield: MTA → apexification, perforation repair.

7. Impression Tray Materials

• Metal trays: rigid, stable.

• Plastic trays: disposable, less rigid.

• Custom trays: reduce distortion, uniform thickness of impression material.

8. Dental Wax

• Types: pattern wax (casting), bite registration wax, baseplate wax.

• Properties: malleable, low melting point, burns out cleanly for casting.

9. Key High-Yield Points (Repeated in MDS Exams)

• Amalgam γ2 phase → weak & prone to corrosion.

• High-copper amalgam → eliminates γ2 phase.

• GIC = fluoride release, chemical bond to tooth.

• PVS = gold standard for final impressions.

• Hybrid composites → strength + aesthetics.

• MTA → apexification, perforation repair.

• PFM → porcelain fused to metal.