One Liners
- Impression compound flows 6% in mouth temperature
- Maximum impression compound type 1 flow = 16%
- Butyl rubber + choloform tray adhesive = Polysulfide
- Impression compound filler = French chalk
- Most cytotoxic = Polyether
- Fusion temp impression compound = 45C
💡Alginate
Alginate composition
| Component | Approx. % | Function |
|---|
| Diatomaceous earth | 60% | Filler; increases strength/stiffness |
| Calcium sulfate | 16% | Reactor → supplies Ca²⁺ |
| Potassium alginate | 15% | Soluble alginate |
| Zinc oxide | 4% | Filler; influences physical properties & setting time |
| Potassium titanium fluoride | 3% | Gypsum hardener |
| Sodium phosphate | 2% | Retarder |
💡Agar
Composition
| Fact | Agar |
|---|
| Type | Reversible hydrocolloid |
| Liquefaction temperature | 70–100°C |
| Gelation temperature | ~37–50°C |
| Main active ingredient | Agar polysaccharide |
| Major constituent | Water |
| Special equipment | Conditioning unit |
| Hydrophilic | Yes |
| Accuracy | Very high |
| Tear strength | Low |
| Pour | Immediately |
| Main advantage | Accurate + works well in moist field |
| Main disadvantage | Special equipment + thermal discomfort |
Agar:
70–100°C → liquefies
37–50°C → gels
💡ZINC OXIDE–EUGENOL
| Component | Function |
|---|
| ZnO | Main reactive component |
| Vegetable/mineral oil | Plasticizer |
| Eugenol | Reactive component |
| Rosin | Speeds reaction + smoother product |
| Filler | Body |
| Resinous balsam | Improves flow and mixing |
💡ELASTOMERIC IMPRESSION MATERIALS
There are 4 major elastomers:
| Elastomer | Other name |
|---|
| Polysulfide | Mercaptan / Thiokol |
| Condensation silicone | Condensation polysiloxane |
| Addition silicone | PVS / VPS – polyvinyl siloxane |
| Polyether | Polyether elastomer |
💡BIG COMPARISON TABLE
MOST → LEAST
| Property | Order |
|---|
| Accuracy | Polyether > Silicone rubber > Polysulfide > Alginate > Agar (as given in lecture) |
| Stiffness | Polyether > Addition silicone > Condensation silicone > Polysulfide > Hydrocolloids |
| Tear strength | Polysulfide > Addition silicone > Polyether > Condensation silicone >> Hydrocolloids |
| Dimensional stability | Addition silicone > Polyether > Polysulfide > Condensation silicone > Hydrocolloid |
| Permanent distortion (low → high) | Addition silicone → Condensation silicone → Polyether → Polysulfide |
| Flexibility | Polysulfide highest |
| Elastic recovery | Addition silicone highest |
| Hydrophilicity | Polyether highest; agar/alginate also hydrophilic |
| Setting speed | Polyether relatively fast; polysulfide relatively slow |
💡ELASTOMER COMPARISON
| Property | Polysulfide | Condensation silicone | Addition silicone | Polyether |
|---|
| Working time | Longest | Good | Shorter | Short |
| Setting | Slowest | Moderate | Fast | Fast |
| Tear strength | 🥇 Highest | Low | High | Moderate |
| Flexibility | 🥇 Highest | High | High | Low |
| Stiffness | Lowest | Moderate | High | 🥇 Highest |
| Elastic recovery | Lowest | Good | 🥇 Best | Very good |
| Dimensional stability | Moderate/poor | Poor | 🥇 Best | Excellent |
| Shrinkage | Moderate | High | 🥇 Lowest | Low |
| By-product | Water | Alcohol | None* | None |
| Hydrophilic | Good | No | Usually hydrophobic | 🥇 Best |
| Moisture tolerance | Good | Poor | Poor unless hydrophilized | 🥇 Best |
| Custom tray | Yes | Yes | No | No |
| Cost | Lower | Lower | Higher | Higher |
| Odor | Unpleasant | Pleasant | Pleasant | Pleasant |
| Special issue | Lead/odor | Alcohol evaporation | Hydrogen + latex inhibition | Water absorption |
| Pouring | Within ~1 h | Immediately | Delayed pour acceptable | Delayed pour acceptable |
💡COMPOSITION TABLE
| Material | Base | Catalyst/accelerator | Important MCQ component |
|---|
| Polysulfide | Polysulfide polymer + TiO₂ filler + plasticizer | PbO₂ + sulfur + oils/fillers | PbO₂ initiator |
| Condensation silicone | α-ω hydroxyl-terminated polydimethylsiloxane + silica filler | Alkyl silicate, commonly tetraethyl orthosilicate, + tin catalyst | Tin catalyst + alkyl silicate |
| Addition silicone / PVS | Hydrosilane-containing siloxane polymer + fillers | Divinyl polysiloxane + platinum catalyst + fillers | Platinum catalyst |
| Polyether | Polyether polymer with terminal ethyleneimine/aziridine groups + silica + plasticizer | Aromatic alkyl sulfonate ester + fillers/plasticizer | Aziridine + sulfonate ester |
💡Factors affecting elastomer working/setting time
| Factor | Effect |
|---|
| ↑ Temperature | ↓ Working time + ↓ setting time |
| ↓ Temperature | ↑ Working time + ↑ setting time |
| High humidity | Particularly accelerates polysulfide setting |
| Mixing ratio | Changes curing rate; do NOT deliberately alter base/catalyst ratio |
| Mixing quality | Improper mixing → incomplete/uneven polymerization |
| Accelerator/catalyst concentration | More accelerator generally speeds setting |
| Contaminants | Can inhibit setting, particularly PVS |
| Latex/sulfur contamination | Can inhibit platinum-catalyzed addition silicone |
💡POLYSULFIDE
| Feature | Polysulfide |
|---|
| Other name | Mercaptan / Thiokol |
| Main polymer | Polysulfide |
| Catalyst | Lead dioxide (PbO₂) |
| Setting time | 3–8 min |
| Humidity effect | ↑ humidity → faster set |
| Temperature effect | ↑ temperature → faster set |
| Tear strength | HIGHEST of elastomers |
| Flexibility | HIGHEST |
| Permanent deformation | HIGHEST |
| Elastic recovery | ~95% |
| Dimensional stability | Poor |
| By-product | Water |
| Hydrophilicity/wettability | Good |
| Odor | Unpleasant |
| Taste | Unpleasant |
| Tray | Custom tray required |
| Pouring | Within ~1 hour |
| Cost | Relatively low |
| Major disadvantage | Poor dimensional stability + messy/odor |
💡CONDENSATION SILICONE
| Feature | Condensation silicone |
|---|
| Polymer | Hydroxyl-terminated polydimethylsiloxane |
| Cross-linker | Alkyl silicate |
| Common cross-linker | Tetraethyl orthosilicate |
| Catalyst | Tin compound |
| By-product | Ethyl alcohol |
| Dimensional stability | Poor |
| Shrinkage | ~0.3–0.5%/24 h |
| Hydrophilicity | Hydrophobic |
| Tear strength | Low |
| Working time | Relatively good |
| Tray | Custom tray required |
| Pouring | Immediately / within ~1 h |
| Common technique | Putty-wash |
| Cost | Relatively economical |
💡ADDITION SILICONE / PVS
| Feature | Addition silicone / PVS |
|---|
| Other names | Vinyl polysiloxane / VPS |
| Polymerization | Addition |
| By-product | No reaction by-product |
| Catalyst | Platinum |
| Elastic recovery | BEST |
| Dimensional stability | BEST |
| Shrinkage | LOWEST — ≤0.05%/24 h |
| Hydrophobicity | Traditionally hydrophobic; hydrophilized versions available |
| Tear strength | Lower than polysulfide |
| Tray | Stock tray can be used |
| Automix | Yes |
| Storage | Can be delayed |
| Multiple pours | Possible |
| Important problem | Hydrogen gas |
| Latex problem | Sulfur inhibits platinum catalyst |
💡POLYETHER
| Feature | Polyether |
|---|
| Polymer | Polyether with terminal ethyleneimine/aziridine groups |
| Initiator | Aromatic sulfonate ester |
| By-product | None |
| Hydrophilicity | Highest / very hydrophilic |
| Accuracy | Very high |
| Stiffness | HIGHEST |
| Dimensional stability | Very good |
| Water absorption | Yes |
| Working/setting | Relatively fast |
| Tray | Stock tray can be used |
| Pseudoplastic | Yes |
| Tear strength | Low |
| Removal | Difficult in undercuts |
| Taste | Bitter |
| Catalyst irritation | Possible |
| Storage | Good under dry conditions |
