Dental materials

In short

Dental materials science is the study of the metals, ceramics, polymers and composites used to restore, replace and reproduce oral tissues, and of the physical, mechanical and biological properties that decide whether they survive in the mouth. The oral cavity is a hostile service environment — 37 °C, pH swinging from 7 to below 4, loads of 100–800 N, thermal cycling from 0 to 60 °C — so material selection is as clinical a decision as the cavity preparation. The subject is examined in BDS second year (university theory and viva, with a practical on gypsum, wax, alginate and acrylic manipulation) and recurs heavily in NEET MDS, INI-CET and AIIMS PG papers, where it is high-yield and formula-light but detail-dense. It is also the core knowledge for jobs with dental material manufacturers and importers in India — Prevest DenPro, DPI, Confident Dental, GC India, 3M India, Dentsply Sirona, Ivoclar, Shofu — in product management, regulatory affairs (CDSCO), QA and dental laboratory CAD/CAM work.

Explained

Properties that define a dental material

• Stress = force per unit area (MPa); strain = deformation per unit original length (dimensionless). Proportional limit is the highest stress with a linear stress–strain relation; elastic limit the highest stress with no permanent deformation; yield strength is taken at 0.1% or 0.2% offset strain because the elastic limit cannot be read precisely.
• Elastic modulus (E) = stiffness, the slope of the elastic region. Enamel ≈ 84 GPa, dentin ≈ 18 GPa, composite 10–16 GPa, amalgam ≈ 50 GPa, zirconia ≈ 210 GPa, PMMA ≈ 2.4 GPa. A luting cement under a crown should be stiff; a denture base liner should not be.
• Strength values that matter: compressive strength (brittle materials are tested in compression — amalgam ≈ 400–500 MPa at 24 h, conventional GIC ≈ 90–180 MPa), diametral tensile strength (indirect tensile test for brittle materials), flexural strength (3-point bend — the relevant test for composites and ceramics, ISO 4049), shear bond strength (adhesives, 15–30 MPa to enamel).
• Resilience = energy absorbed up to the proportional limit (area under elastic part); toughness = total energy to fracture; fracture toughness (K_IC, MPa·m^0.5) measures resistance to crack propagation from a flaw — the key number for ceramics (feldspathic ≈ 1, lithium disilicate ≈ 2.5, zirconia ≈ 5).
• Hardness: Knoop (KHN) and Vickers (VHN) for brittle materials (micro-indentation), Brinell/Rockwell for metals, Shore A for elastomers and soft liners. Enamel ≈ 343 KHN, dentin ≈ 68 KHN; a restorative much harder than enamel abrades the opposing tooth.
• Creep = slow permanent deformation under static load — a classic amalgam failure mode, linked to marginal breakdown; high-copper amalgams keep creep below 1% (specification limit 3%).
• Thermal properties: conductivity (enamel and dentin are insulators; metals conduct, hence liners under deep metallic restorations), diffusivity, and coefficient of thermal expansion α — tooth ≈ 11 ppm/°C, composite 25–40, amalgam ≈ 25, inlay wax 300–400 (the highest of all dental materials). CTE mismatch drives percolation at margins.
• Other physical properties: flow, setting and dimensional change, water sorption and solubility, colour (Munsell hue–value–chroma, measured as ΔE), translucency, fluorescence, radiopacity (expressed in mm equivalent of aluminium; required so a restoration or sealer is visible on IOPA).
• Biological properties: biocompatibility, pulpal response, allergenicity (nickel, methacrylate monomers, eugenol), cytotoxicity and mutagenicity testing per ISO 10993 series with ISO 7405 for dentistry-specific tests.
• Rheology and surface: thixotropy and pseudoplasticity (why a monophase impression material flows under syringe pressure but not off the tray), wetting and contact angle, surface energy, adhesion (mechanical interlocking dominates in dentistry; true chemical adhesion only in polycarboxylate and glass ionomer).

Impression materials

• Classification: rigid/non-elastic — impression plaster, impression compound, zinc oxide–eugenol (edentulous secondary impressions); elastic — hydrocolloids (agar, reversible; alginate, irreversible) and elastomers (polysulfide, condensation silicone, addition silicone, polyether).
• Alginate (irreversible hydrocolloid): sodium or potassium alginate + calcium sulfate dihydrate (reactor) + trisodium phosphate (retarder, reacts first) + diatomaceous earth (filler) + zinc oxide + potassium titanium fluoride (gypsum hardener). Sets by cross-linking into calcium alginate. Water/powder ratio and water temperature control setting time (hotter water = faster).
• Alginate limitations: imbibition (water uptake, expansion) and syneresis (exudate, shrinkage), so pour within about 10–15 minutes and store at 100% humidity meanwhile; tears easily; poorest accuracy — unsuitable for crown and bridge, fine for study models, orthodontic models and removable prosthesis primary impressions. Classified as Type I fast-set and Type II normal-set, and as dust-free formulations for safety.
• Addition (vinyl poly)siloxane: platinum-catalysed, by-product free, best dimensional stability and elastic recovery; can be poured days later and poured twice. Latex gloves inhibit the platinum catalyst — use vinyl/nitrile gloves. Hydrophobic unless surfactant-modified.
• Condensation silicone: ethyl alcohol by-product evaporates → significant shrinkage; polysulfide: long setting time, best tear strength, foul odour, stains clothing; polyether: hydrophilic (good in moist fields and for implant impressions), stiff and high modulus — difficult removal around divergent abutments, absorbs water on storage in disinfectant.
• Viscosity classes (ISO 4823): putty (type 0), heavy (1), medium/monophase (2), light (3). Techniques: putty–wash one-stage and two-stage, monophase, and dual-arch.
• Disinfection is mandatory practice: immersion or spray with 2% glutaraldehyde, 1% sodium hypochlorite or iodophor — alginate only briefly (spray-and-bag) to avoid distortion.

Gypsum products, waxes, investments and casting

• Gypsum chemistry: calcium sulfate dihydrate is calcined to hemihydrate; on mixing, the reaction reverses and is exothermic: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O + heat. Plaster (β-hemihydrate) is irregular and porous → needs more water; stone (α-hemihydrate, autoclave-calcined) is dense → less water, more strength.
• ISO 6873 types: Type 1 impression plaster; Type 2 model plaster (W/P ≈ 0.45–0.50); Type 3 dental stone (0.28–0.30) for casts; Type 4 die stone, high strength–low expansion (0.22–0.24); Type 5 high-expansion die stone, to offset base-metal casting shrinkage.
• Lower W/P ratio = higher strength, shorter setting time, greater setting expansion. More spatulation shortens setting time; accelerator = potassium sulfate; retarder = borax. Wet strength is roughly half the dry strength.
• Waxes: inlay wax (Type I hard for direct, Type II for indirect patterns), casting wax, baseplate wax, sticky wax, boxing wax, utility wax. Key problems are flow and residual stress release — a pattern must be invested immediately, never stored, or it warps.
• Investments: gypsum-bonded (α-hemihydrate binder + quartz/cristobalite) for gold alloys below ~1,000 °C; phosphate-bonded for base-metal and metal-ceramic alloys; ethyl-silicate-bonded for very high fusing. Expansion sources — setting, hygroscopic and thermal — together compensate the alloy's solidification shrinkage (gold ≈ 1.25%, Ni-Cr/Co-Cr ≈ 2.0–2.3% linear).
• Casting sequence: wax pattern → sprue → invest → burn out (wax eliminated, mould expands) → melt and cast (centrifugal or pressure) → quench/bench cool → divest → pickle → finish. Defects: incomplete casting (insufficient venting/low mould temperature), nodules (air bubbles), fins (mould cracks), porosity (back-pressure, shrink-spot, gas), oxidation.

Direct restoratives and cements

• Dental amalgam: Ag-Sn alloy powder (γ phase, Ag₃Sn) + mercury. Reaction gives γ₁ (Ag₂Hg₃) and, in low-copper alloys, γ₂ (Sn₇₋₈Hg) — the weakest, most corrosion-prone phase. High-copper amalgams (admixed or single-composition, Cu 13–30%) eliminate γ₂ by forming η′ (Cu₆Sn₅), raising strength and lowering creep and marginal breakdown.
• Amalgam manipulation: correct Hg/alloy ratio, mechanical trituration (over-trituration = hot, crumbly, short working time; under-trituration = grainy, weak), condensation in increments, carving, burnishing. Delayed expansion occurs only with zinc-containing amalgam contaminated by moisture (hydrogen gas evolution). Advantages: cheap, durable, technique-tolerant, self-sealing by corrosion products. Limitations: non-aesthetic, no adhesion, needs retentive preparation, mercury handling.
• Resin composite: matrix (Bis-GMA, UDMA, Bis-EMA with TEGDMA diluent), filler (silica, quartz, barium/strontium glass for radiopacity), silane coupling agent, initiator system (camphorquinone + tertiary amine, activated at ~468 nm blue light) plus inhibitors (BHT) and UV stabilisers. Classified by filler size — macrofill, microfill, hybrid, microhybrid, nanohybrid, nanofill — and by handling — flowable, packable, bulk-fill.
• Polymerization shrinkage 2–3% by volume generates stress proportional to the C-factor (bonded to unbonded surface ratio), causing cuspal deflection, debonding and post-operative sensitivity. Controlled by incremental layering (≤2 mm), soft-start curing, flowable stress-breaking liners and low-shrinkage monomers. ISO 4049 requires depth of cure ≥1.5 mm and flexural strength ≥80 MPa for materials indicated for occlusal surfaces (≥50 MPa otherwise).
• Adhesion: 37% phosphoric acid etch for 15 s on enamel creates micro-retention for resin tags; on dentin, the primer/adhesive forms the hybrid layer (Nakabayashi) within demineralised collagen. Generations in practice: total-etch (3-step and 2-step), self-etch (2-step and all-in-one) and universal adhesives containing 10-MDP, which also bonds chemically to hydroxyapatite and zirconia.
• Glass ionomer cement (GIC): fluoroaluminosilicate glass powder + polyacrylic/itaconic–maleic acid copolymer; acid–base setting with early calcium polyacrylate and later aluminium polyacrylate cross-links. Chemical bond to tooth via ionic interaction with calcium of hydroxyapatite, fluoride release and recharge, CTE close to tooth, biocompatible. Weak in tension, poor wear resistance and initially moisture-sensitive. Types: I luting, II restorative, III liner/base; plus metal-reinforced, resin-modified GIC (HEMA, dual set) and compomer.
• GIC and ART: atraumatic restorative treatment with hand instruments and high-viscosity GIC is central to Indian school and rural public-health dental programmes where electricity and suction are unavailable.
• Other cements and pulp materials: zinc phosphate (the long-standing benchmark luting cement, initial pH ~2, needs pulpal protection), zinc oxide–eugenol (sedative, temporary), zinc polycarboxylate (first cement to bond chemically to tooth), resin and self-adhesive resin cements (ceramic and fibre-post luting), calcium hydroxide (liner, pH ~12, stimulates reparative dentin), MTA and calcium silicate cements (Biodentine) for pulpotomy, apexification, perforation repair, root-end filling; gutta-percha with ZOE, calcium hydroxide, resin (AH Plus) or bioceramic sealers (ISO 6876) for obturation.

Ceramics, polymers and prosthetic materials

• Dental ceramics are brittle, strong in compression, weak in tension, and fail from surface flaws (Griffith); glazing and the absence of grinding damage therefore matter as much as composition. Progression: feldspathic porcelain (~60–90 MPa flexural) → leucite-reinforced → lithium disilicate (~360–400 MPa, pressable and CAD/CAM) → alumina → zirconia 3Y-TZP (~900–1,200 MPa, toughened by stress-induced tetragonal-to-monoclinic transformation; susceptible to low-temperature degradation) and the more translucent 4Y/5Y zirconias. Classified by ISO 6872 into classes by strength and indication.
• Metal-ceramic (PFM): the alloy's CTE is kept slightly above the porcelain's (about 13.5–14.5 vs 13–14 ppm/°C) so that on cooling the porcelain is left in mild compression; a mismatch cracks the veneer. Bonding needs an oxide layer and, in Ni-Cr/Co-Cr alloys, careful oxidation control.
• Casting alloys (ISO 22674): high-noble and noble gold alloys (Types I–IV by strength/hardness), silver-palladium, Ni-Cr and Co-Cr base metals (cheap, stiff, high E — the workhorse of Indian labs), commercially pure titanium and Ti-6Al-4V, and Co-Cr/Ti for RPD frameworks. Nickel and beryllium are the allergy and occupational-hazard concerns.
• Denture base PMMA: powder (PMMA beads + benzoyl peroxide initiator + pigments) and liquid (MMA monomer + hydroquinone inhibitor + glycol dimethacrylate cross-linker). Mixing stages: sandy → stringy → dough (packing stage) → rubbery → stiff. Heat cure by a long low-temperature cycle (e.g. 74 °C for 8 h then boil briefly) to avoid gaseous porosity from monomer boiling; other porosities are contraction (insufficient dough) and granular (monomer loss).
• PMMA issues: ~7% volumetric (≈0.5% linear) polymerization shrinkage, thermal shrinkage on cooling, residual monomer (irritation and allergy), water sorption and the processing errors that cause an increased vertical dimension. Self-cure (chemically activated, amine accelerator) is weaker with more residual monomer; light-cure and injection-moulded/CAD-milled bases are the newer options. ISO 20795-1 sets minimum flexural strength and modulus, with heat-cured material held to a higher bar than autopolymerised — quote the current edition's figures rather than memorised ones.
• Other prosthetic materials: high-impact and flexible nylon (polyamide) bases, resilient soft liners and tissue conditioners, denture cleansers, orthodontic brackets, wires (stainless steel, Ni-Ti with shape memory and superelasticity, beta-titanium) and elastomeric modules, titanium implants with SLA/anodised surfaces and zirconia abutments.

Standards, regulation and Indian practice

• Global specifications are the ISO/TC 106 series, historically numbered as ADA/ANSI specifications: ISO 4049 (polymer-based restoratives), ISO 21563 (hydrocolloid impression materials, superseding the withdrawn ISO 1563 for alginate), ISO 4823 (elastomeric impression materials), ISO 6873 (gypsum), ISO 15854 (casting and baseplate waxes), ISO 24234 (dental amalgam, superseding ISO 1559), ISO 9917-1 and -2 (water-based cements, and resin-modified), ISO 3107 (zinc oxide–eugenol), ISO 6876 (root canal sealers), ISO 6872 (ceramics), ISO 22674 (metallic materials), ISO 20795-1 (denture base polymers), ISO 7405 and ISO 10993 (biological evaluation).
• BIS publishes Indian Standards for dentistry largely as identical adoptions of these ISO documents (cited as IS/ISO …) through its Medical Devices and Hospital Planning division. Many older standalone IS numbers for dental materials have been withdrawn or superseded, so verify the current number and year on the BIS portal before quoting one in an answer.
• Regulation: dental materials and devices are regulated by CDSCO under the Medical Devices Rules, 2017 (framed under the Drugs and Cosmetics Act, 1940), risk-classified A, B, C or D. Licensing became mandatory in phases — Class A and B from 1 October 2022, Class C and D from 1 October 2023 — so all devices now need registration/licensing — manufacturing licences MD-5 (Class A/B, State Licensing Authority) and MD-9 (Class C/D, CDSCO), import licence MD-15, with ISO 13485 quality systems expected. Most dental consumables fall in Class A or B.
• Mercury: India is a party to the Minamata Convention on Mercury (ratified 2018), which requires phase-down measures for dental amalgam — encapsulated amalgam, amalgam separators, and avoidance in children, pregnant and breastfeeding women. Amalgam is not banned in India; the clinical trend is strongly towards composite and GIC.
• Professional framework: dental education and practice now sit under the National Dental Commission Act, 2023 (the National Dental Commission replacing the Dental Council of India); biomedical waste from dental clinics, including amalgam and lead foil, is handled under the Bio-Medical Waste Management Rules, 2016 as amended. GST on most dental materials falls in the standard slabs (the 5%/18%/40% structure effective 22 September 2025) — confirm the current HSN-wise rate before quoting it.

Key points

• Stress–strain curve - proportional limit, elastic limit, yield strength (0.1–0.2% offset), ultimate strength and elongation all read off one plot.
• Elastic modulus - stiffness, independent of strength; enamel ≈ 84 GPa, dentin ≈ 18 GPa, PMMA ≈ 2.4 GPa.
• Creep - time-dependent permanent deformation; high in low-copper amalgam, correlates with marginal breakdown.
• CTE mismatch - composite expands 2–3× more than tooth, causing marginal percolation and staining.
• W/P ratio - lower water means stronger, faster-setting gypsum with greater setting expansion.
• Gypsum types - Type 2 plaster, Type 3 stone (casts), Type 4 die stone (strong, low expansion), Type 5 (high expansion).
• Alginate - irreversible hydrocolloid, cheap, poor stability; syneresis and imbibition demand pouring within ~10–15 min.
• Addition silicone - best accuracy and recovery; platinum catalyst poisoned by latex gloves.
• Polyether - hydrophilic and stiff; preferred for implant impressions, hard to remove from divergent abutments.
• γ₂ phase - Sn-Hg, weakest phase of low-copper amalgam; eliminated in high-copper alloys as Cu₆Sn₅.
• Delayed expansion - only in zinc-containing amalgam contaminated with moisture during condensation.
• Composite shrinkage - 2–3 vol%; stress scales with C-factor; managed by ≤2 mm increments.
• Hybrid layer - resin-infiltrated demineralised dentin collagen; the basis of dentin bonding.
• GIC - chemical bond to tooth, fluoride release, tooth-like CTE; weak in tension, key material for ART.
• Calcium hydroxide and MTA - pH ~12 liner and calcium silicate repair material respectively.
• PFM rule - alloy CTE slightly greater than porcelain's leaves the veneer in compression.
• PMMA dough stage - the only correct packing consistency; porosity types are gaseous, contraction and granular.
• Regulation - Medical Devices Rules, 2017 under CDSCO; ISO/BIS specifications; Minamata amalgam phase-down.

Formulas and examples

Example 1 — compressive strength of amalgam. A cylindrical amalgam specimen 4 mm diameter fractures at 5,400 N.

• A = (π/4) × 4² = 0.7854 × 16 = 12.57 mm²
• σ = 5,400 / 12.57 = 429.6 MPa → a normal 24-hour value for a high-copper amalgam (expected range ~400–500 MPa).

Example 2 — flexural strength of a composite (ISO 4049 bar). Bar 25 × 2 × 2 mm, span L = 20 mm, fails at F = 40 N.

• σ = (3 × 40 × 20) / (2 × 2 × 2²) = 2,400 / 16 = 150 MPa
• This exceeds the 80 MPa minimum for an occlusal-indication restorative, so the batch passes. If the same bar failed at 20 N, σ = 75 MPa — a fail.

Example 3 — die stone mixing and setting expansion. 100 g Type 4 die stone at W/P 0.22, setting expansion 0.08%, used for a 60 mm wide arch segment.

• Water = 0.22 × 100 = 22 mL
• Expansion = 60 × 0.08/100 = 0.048 mm = 48 µm — enough to matter for a full-arch framework, which is why Type 4 is specified low-expansion while Type 5 (0.10–0.30%) deliberately over-expands to offset base-metal casting shrinkage.

Example 4 — thermal mismatch at a composite margin. Composite α = 30 ppm/°C, tooth α = 11 ppm/°C, restoration width 4 mm, a hot-to-cold swing ΔT = 30 °C.

• Differential strain = (30 − 11) × 10⁻⁶ × 30 = 5.7 × 10⁻⁴
• Differential movement = 5.7 × 10⁻⁴ × 4 mm = 2.28 × 10⁻³ mm ≈ 2.3 µm per cycle — repeated thousands of times, this is the percolation that stains and leaks margins.

Example 5 — casting shrinkage compensation. A gold crown pattern measures 10 mm; alloy solidification shrinkage 1.25% linear. Investment gives 0.30% setting plus 0.90% thermal expansion.

• Shrinkage to compensate = 10 × 1.25/100 = 0.125 mm
• Mould expansion supplied = 10 × 1.20/100 = 0.120 mm
• Deficit = 0.005 mm (5 µm) — within the cement film thickness, so the casting fits. For a Co-Cr alloy shrinking 2.3%, the same investment would leave 110 µm of misfit, which is why phosphate-bonded, higher-expansion investments are mandatory for base metals.

Example 6 — light-curing energy. A LED unit at 600 mW/cm² for 40 s delivers 0.6 × 40 = 24 J/cm². A 1,200 mW/cm² unit for 20 s delivers the same 24 J/cm², but exposure reciprocity does not hold reliably — shortening time at higher irradiance can reduce degree of conversion and depth of cure, so follow the manufacturer's stated time, and verify output with a radiometer.

Where it is used

• Clinical dentistry: restorative and endodontic material selection, crown and bridge impressions, complete and partial dentures, orthodontics — every operative decision in a BDS internship and in private practice.
• Dental laboratories and CAD/CAM centres: die stone and investment work, Co-Cr and PFM casting, zirconia and lithium disilicate milling and sintering, 3D-printed models, surgical guides and try-in dentures; large labs in Mumbai, Delhi NCR, Bengaluru, Chennai and Kochi, plus export labs serving overseas clinics.
• Manufacturing and quality control: Prevest DenPro (Jammu), DPI, Confident Dental Equipments (Bengaluru), Anabond Stedman, Shiva Products, and the Indian arms of GC, 3M, Dentsply Sirona, Ivoclar and Shofu — roles in formulation, batch testing against ISO/BIS methods, and shelf-life studies.
• Regulatory affairs and medical-device consulting: CDSCO licensing (MD-5/MD-9/MD-15) under the Medical Devices Rules, 2017, ISO 13485 audits, technical files and biocompatibility dossiers — a growing graduate career path for BDS holders who do not practise.
• Sales, product management and clinical training: dental product specialists demonstrating adhesives, bulk-fill composites, impression systems and implant kits to clinicians; CDE programmes and hands-on courses.
• Public health and academia: GIC-based ART and pit-and-fissure sealant programmes under school and district oral-health initiatives; postgraduate research and thesis work in Dental Materials, with institutional ethics committee clearance for any clinical trial.

Interview questions

• Q: Why is compressive strength quoted for amalgam and GIC but flexural strength for composite and ceramic? A: Brittle materials are much weaker in tension than compression, and clinical failure of thin restorations and veneers occurs in bending — so flexural (and diametral tensile) tests represent the real loading better.
• Q: What is the γ₂ phase and why do high-copper amalgams matter? A: γ₂ is Sn₇₋₈Hg, the weakest and most corrodible phase of set low-copper amalgam. High-copper alloys convert tin into Cu₆Sn₅ instead, giving higher strength, lower creep and far less marginal breakdown.
• Q: A patient reports sensitivity after a deep posterior composite. What material factors explain it? A: Polymerization shrinkage stress with a high C-factor causing cuspal deflection and debonding, incomplete cure at depth, and inadequate dentin seal — addressed with ≤2 mm increments, adequate curing energy and a proper adhesive protocol.
• Q: Why must latex gloves be avoided with addition silicone putty? A: Sulfur compounds in latex poison the platinum catalyst and inhibit setting, leaving the surface uncured.
• Q: What is syneresis and imbibition in alginate? A: Syneresis is exudation of liquid from the gel causing shrinkage; imbibition is water absorption causing expansion. Both distort the impression, so it is poured promptly and stored at 100% humidity.
• Q: How does GIC bond to tooth structure? A: By ionic chemical bonding — polyacrylic acid carboxyl groups displace phosphate and complex with calcium in hydroxyapatite — unlike composite, which relies on micromechanical retention.
• Q: Why does lowering the water/powder ratio of stone increase setting expansion? A: Fewer water molecules mean a denser nucleus packing, so growing dihydrate crystals intermesh and push against each other more, producing greater outward expansion along with higher strength.
• Q: How is casting shrinkage compensated in the lost-wax technique? A: By the investment's setting, hygroscopic and thermal expansion, totalling roughly the alloy's linear solidification shrinkage; phosphate-bonded high-expansion investments are used for base-metal alloys that shrink about 2.3%.
• Q: Why must the porcelain's coefficient of thermal expansion be slightly lower than the alloy's in a PFM crown? A: On cooling, the alloy contracts more and places the porcelain in mild compression, which brittle ceramic tolerates well; a reverse mismatch leaves it in tension and it crazes.
• Q: What is the dough stage and why is packing at any other stage wrong? A: It is the non-sticky, mouldable consistency of PMMA; packing earlier causes monomer loss and granular porosity, packing later gives incomplete flow, contraction porosity and lack of adaptation.
• Q: Which Indian regulation governs the import and manufacture of dental composites? A: The Medical Devices Rules, 2017 under CDSCO, with risk classification and licences MD-5/MD-9 for manufacture and MD-15 for import; most dental consumables are Class A or B.
• Q: Does India's Minamata commitment ban dental amalgam? A: No — it requires phase-down measures such as encapsulated amalgam, amalgam separators and avoidance in children and pregnant women; amalgam remains legal but is being displaced clinically by composite and GIC.

Common mistakes

• Confusing strength with stiffness — calling a high-modulus material "strong" or quoting GPa for strength and MPa for modulus.
• Mixing up gypsum types and their water/powder ratios, or stating that more water gives a stronger cast.
• Writing that amalgam always expands on setting — delayed expansion needs both zinc and moisture contamination.
• Claiming composite bonds chemically to dentin; the bond is micromechanical through the hybrid layer (only GIC and polycarboxylate bond ionically).
• Placing a bulk increment of composite and then blaming shrinkage on the material rather than the technique and C-factor.
• Pouring alginate hours later, or storing a wax pattern overnight, and attributing the misfit to the laboratory.
• Quoting withdrawn ADA/IS specification numbers from old textbooks instead of the current ISO/IS edition, and forgetting the CDSCO Medical Devices Rules, 2017 framework entirely in viva answers.

Related topics

Dental anatomy and tooth morphology · Oral histology and embryology · Operative dentistry and cavity preparation · Prosthodontics and crown and bridge · Endodontic materials and obturation · Biomedical device regulation in India