Impression Materials and Digital Impressions - 2.1 PDF

**[Impression materials and digital impressions - 2.1]** **Mode of setting** **Mode of setting** **Non-elastic** **Elastic** ---------------------------------- ---------------------------------------- -------------------------------------------- Chemic...

**[Impression materials and digital impressions - 2.1]** **Mode of setting** **Mode of setting** **Non-elastic** **Elastic** ---------------------------------- ---------------------------------------- -------------------------------------------- Chemical reaction - irreversible Impression plaster, zinc oxide eugenol Alginate, polysulfide, polyether, silicone Physical reaction - reversible Impression compounds, impression waxes Agar **Hydrocolloids** - Sol = liquid where colloid particles are dispersed Gel = semi-solid state where particles form a network trapping the liquid **Alginate** Cost effective - - - - - Reaction Sol stage = sodium alginate dissolves in water → sol Gelation stage = Ca2+ ions + sodium alginate → calcium alginate gel **Material** **Composition** **Purpose** ---------------------------------- ----------------- ------------------------------------------- **Sodium or potassium alginate** 15-20 Colloidal particles as basis of gel **Calcium sulphate dihydrate** 14-20 Creates irreversible gel with alginate **Potassium sulphate** 10 Ensure set of gypsum materials **Trisodium phosphate** 2 Retarder to control setting time **Diatomaceous earth** 55-60 Filler to increase thickness and strength Properties Dimensional stability - - Tear strength - - - Handling Mixing - - Set time - - Accuracy - - Clinical scenarios - **Agar** Reaction Physical change (thermal reversible relation) Sol at \>70 degrees - - Back to gel\ Gel = cooling 37-45 degrees Sol \< --- Gel = heating 70-100 degrees **Material** **Composition** **Purpose** ------------------------ ----------------- -------------------------------------------- **Agar** 12-15 Colloidal particles as basis of gel **Potassium sulphate** 1 Ensures set of gypsum **Borax** 0.2 Strengthens gel **Alkyl Benzoate** 0.1 Antifungal agent **Water** 85 Dispensing medium for colloidal suspension Properties Dimensional stability - - - - Tear strength - - Handling Equipment: - - Working time - sufficient due to poor cooling Setting time - rapid once cooled (few mins) Accuracy - Clinical scenarios - Comparison  **Synthetic elastomers** - - Types: - - - - 0 = very high consistency (putty) 1 = high consistency (heavy bodies) 2 = medium consistency (medium bodies) 3 = low consistency (light bodies) ⬆️ Filler content = ⬆️ Viscosity, dimensional stability ⬇️ Setting contraction **Silicone - Addition curing** Composition: - - Reaction - - **Material** **Component** **Purpose** -------------------- ------------------------------------------------------ --------------------------------------------- **Baste paste** Polymethylhydrosiloxane (liquid silicone prepolymer) Polymerised and cross linked to form rubber Inert filler eg silica Controls viscosity Pt containing catalyst eg Chloroplatinic acid Catalyst **Catalyst paste** Divinylpolysiloxane (liquid silicone prepolymer) Polymerised and cross linked to form rubber Inert filler eg silica Control viscosity **Silicone - Condensation curing** Composition: - - Reaction - - - **Polyethers** Composition: - - Reaction - **Material** **Component** **Purpose** -------------------- --------------------------------------------- ----------------------------- **Base paste** Imine-terminated prepolymer Cross linked to form rubber Inert filler eg silica Controls viscosity Phthalate (plasticiser) Aids mixing **Catalyst paste** Ester derivative of aromatic sulphonic acid Initiates cross linking Inert filler eg silica Control viscosity **Polysulphides** Composition: - - Reaction - **Material** **Component** **Purpose** -------------------- ------------------------------------------- --------------------------------------------- **Base paste** Polysulphide prepolymer - thiol group Polymerised and cross linked to form rubber Dibutyl phthalate Controls viscosity Inert filler eg chalk or titanium dioxide Controls viscosity **Catalyst paste** Lead dioxide Reacts with thiol group Sulphur Involved in setting reaction Inert oil Forms paste with lead oxide and sulphur Comparison of synthetic elastomers **Non - elastomers** - - - Types: - - - - **Impression plaster** Composition: - - Reaction - - **ZOE impression plate** Composition: - - Reaction - **Impression compound** Composition: - Reaction - Rigid at mouth temp **Impression waxes** Composition: - - Setting reaction - - Comparison of non - elastomers  **Digital impressions** 1. 2. 3. 4. Types: - - Advantages: - - - - - - Disadvantages: - - - - - Key words: **Addition Silicone:** Synthetic elastomer with good dimensional stability and high\ accuracy **Condensation Silicone:** Sets by condensation polymerisation, releasing by-products\ (ethyl alcohol) leading to shrinkage **Polyether:** Hydrophilic synthetic elastomer with good dimensional stability and detail\ reproduction **Polysulfide:** Synthetic elastomer known for high tear strength and long working time **Impression Plaster:** Non-elastomeric, rigid material used for edentulous impressions **ZOE Paste:** Rigid, non-elastomeric material with excellent dimensional stability **Impression Compound:** Thermoplastic material that softens upon heating and hardens\ upon cooling (reversible physical change) **Impression Waxes:** Malleable materials used for corrective impressions and bite\ registrations