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Supporting Lab materials: Impression materials - Coggle Diagram
Supporting Lab materials:
Impression materials
1. Alginate (Irreversible Hydrocolloid)
Main Composition & Roles
Sodium Alginate: Water-soluble polysaccharide from seaweed; main reactive ingredient and gel-former.
Calcium Sulfate: The reactor/cross-linking agent; provides Ca2+ ions to convert sol into an elastic gel.
Fillers (Diatomaceous Earth): Improves handling, increases strength/rigidity, and reduces stickiness.
Trisodium Phosphate: Controls working time by delaying gelation.
Potassium Titanium Fluoride: Accelerates gypsum setting and ensures a hard, smooth dental cast.
Key Properties
Hydrophilicity: Natural affinity for water; allows adaptation to moist oral tissues but leads to water interaction issues.
Viscosity: Resistance to flow; controlled by powder-to-water ratio and filler amount.
Dimensional Stability: Relatively poor; highly affected by syneresis and imbibition.
Tear Strength: Low; requires adequate thickness and rapid removal to prevent tearing.
Water-Related Clinical Effects
Imbibition: Absorption of water causing expansion.
Syneresis: Loss of water causing shrinkage.
Management: Store in 100% relative humidity (damp gauze) and pour in gypsum within 10–15 minutes.
2. Dental Waxes
Composition
Components: Mineral (Paraffin), Plant (Carnauba), Animal (Beeswax), Synthetic waxes, and additives like resins or oils.
Thermoplastic Nature: Soften when heated and harden when cooled.
Reasons for Blending
Adjust melting range.
Improve hardness and strength.
Control flow and plasticity.
Reduce brittleness.
Main Uses
Clinical/Lab: Patterns for crowns/bridges, denture base trials, bite registrations, and tray modifications.
Lost-Wax Technique: Acting as a pattern that is eventually replaced by metal or ceramic.
Physical Properties
Thermal Expansion: Very high compared to other materials; small temperature changes can distort patterns.
Flow: Deformation under load; high flow is needed for manipulation, low flow for stability.
Residual Stress: Builds from uneven cooling; causes distortion after removal.
3. Dental Gypsum
Basic Chemistry
Main Ingredient: Calcium Sulfate Hemihydrate (CaSO4⋅½H2O).
Reaction: Hemihydrate + Water → Dihydrate + Heat (interlocking crystals).
Types & Classifications
Type II (Model Plaster): Irregular, porous particles; low strength; used for study models.
Type III (Dental Stone): Denser particles; moderate strength; used for diagnostic and denture casts.
Type IV (High-Strength Stone): Very dense crystals; low expansion; used for precise crown and bridge dies.
Type V (High-Expansion Stone): High strength and expansion; compensates for casting shrinkage of certain alloys.
Performance Factors
Strength/Hardness: Increases from Type II to Type V.
Setting Expansion: Crystal growth causes outward pressure; Type IV is specifically designed for minimal expansion (0.05–0.10%).
4. Abrasives & Polishing (Acrylic Resin)
Abrasive Agents
Pumice: Used for intermediate smoothing to remove fine scratches.
Calcium Carbonate (CaCO3): Very fine, mild abrasive used for final high-gloss buffing.
Sequential Polishing Steps
Gross Trimming: Acrylic trimmer for bulk reduction.
Coarse Finishing: Stone burs for refining margins.
Intermediate Smoothing: Rubber polishers or silicone wheels.
Pre-polishing: Brush or felt wheel with pumice slurry.
Final Buffing: Cotton wool or felt buff with CaCO3 paste for luster.
Clinical Impact
Reduces plaque accumulation.
Improves patient comfort and esthetics.
Prevents trauma to oral tissue