Elastomeric Impression Materials PDF

Elastomeric Impression Materials (Rubber Impression)  These are Elastic Impression materials called “non aqueous” elastic impressions (Hydrocolloids are aqueous elastomeric materials) Used for taking 2ry Imp.(Dentulous or edentulous) They can be electroplated because of their hydro...

Elastomeric Impression Materials (Rubber Impression)  These are Elastic Impression materials called “non aqueous” elastic impressions (Hydrocolloids are aqueous elastomeric materials) Used for taking 2ry Imp.(Dentulous or edentulous) They can be electroplated because of their hydrophobicity.(except !!!!) They can be stretched easily and highly recovered on load removal (NO Complete recovery) They set by Polymerization Reactions. They offered solutions to main problems associated with hydrocolloids: (Adv. Over Hydrocolloids) Poor tear strength Poor dimensional stability. why????? Can’t be electroplated  Viscosity classes according to different % of filler content Low (light body) Medium (regular) High (heavy body) Putty (Extra heavy) (available in Silicones only) 1- Light-bodied Also referred to as syringe type, or wash type. Used because of its high flow (record fine details) applied on and immediately around the prepared teeth. 2- Regular and heavy-bodied Often referred to as tray-type materials and they are much thicker. Used to fill the tray because its stiffness force the light-bodied mat. around the prepared teeth and tissues. 3- Putty consistency Used as tray material, containing the highest amount of fillers.  Packaged as a paste in a tube or as putty in a jar. Also known as the accelerator, it is packaged as a paste in a tube, as a cartridge, or as a liquid in a bottle with a dropper top or as a jar  All rubber base impressions set via Polymerization Reaction: It is the Formation of large polymer molecules from smaller monomer molecules. It includes Chain lengthening &crosslinking It is an exothermic reaction (increase in temperature) Associated with polymerization shrinkage  Types: 1. Condensation polymerization: Formation of large polymer molecule with release of by-product Main cause of dimensional instability Examples (condensation silicone and polysulfide) 2. Addition polymerization: Formation of large polymer molecule without release of by-product Examples (polyether and addition silicone)  Elastomeric Impression Materials Polysulphide Silicones Polyether Condensation silicon Addition Silicon Hydrophobic type Hydrophilic type Form of supply: Supplied as two pastes (base & catalyst) in collapsible tubes It comes in Light/regular/heavy consistency.  Composition 1- Base paste (white in color) Polysulfide polymers with two terminal and one pendant SH- group (mercaptan) Tio2 as filler to increase the strength Dibutyl phthalate as a plasticizer to control the viscosity. 2-Catalyst paste (dark brown or grey brown in color) lead dioxide (brown in color) Fillers  Setting Reaction: Condensation polymerization reaction It is an exothermic reaction (increase in temperature), associated with polymerization shrinkage and release of water as a reaction by- product.  Advantages Disadvantages 1. Poor dimensional stability (water by- 1. High flexibility product) compared to other elastomers 2. High tear strength 2. Long setting time 3. Long working time 3. Messy because of Lead Dioxide: bad 4. Lower cost compared to silicones and odor, staining clothing polyethers 4. Needs custom/special trays (to allow thickness of 2-3 mm ????)  Forms of supply: 1. Two paste system (base –catalyst) 2. Base paste and low viscosity liquid catalyst 3. Two putty system Composition: Base (Paste in a tube or jar (putty)) Poly-dimethylsiloxane with reactive terminal OH group Fillers Catalyst (Paste in a tube or liquid in a dropper) Alkyl silicate (cross-linking tetraethylorthosilicate). Stannous octate act as activator / catalyst Setting reaction Condensation polymerization reaction. Cross-linking occurs between the siloxane polymer and the alkyl silicate in the presence of the activator with the release of ethyl alcohol as reaction by-product.  Advantages Disadvantages Poor dimensional stability, due Better elastic properties to evaporation of ethanol by Clean, pleasant product Stock tray (no need for special Hydrophobic, this results in its tray) in putty-wash technique poor wettability Good working and setting  Forms of supply: as Condensation silicon Composition: Base: Low Molecular Weight Polymer (Polymethyl-Hydrosiloxane) Fillers. Catalyst Divinyl polysiloxane. Platinum salt as activator Fillers Setting reaction Addition polymerization reaction Hydrogen atom s along the polymethyl-hydrosiloxane react with vinyl groups of divinyl-polysiloxane after their activation by platinum salt with no release of reaction by-product.  Problem related to setting reaction of Addition Silicone Impression 1. Side reaction releasing hydrogen gas may occur Effect Pinpoint voids in the immediately poured stone casts. How to Avoid? 1. Addition of noble metals such as platinum or palladium to act as scavenger for the released hydrogen gas. 2. Wait for 1 hour before pouring the impression to allow the evolution of hydrogen gas.  Problem related to setting reaction of Addition Silicone Impression 2- Sulfur contamination from vulcanized rubber (latex) gloves It can Poison The Platinum containing catalyst → Retardation or no polymerization in the contaminated area of the impression leading to imp distortion during removal from patient’s mouth. This problem can be solved by either: 1.Washing gloves thoroughly with soap and water 2-Wearing plastic gloves over latex ones  Advantages Disadvantages Highly accurate Expensive High dimensional stability Short working time Stock or custom trays Lower tear strength Multiple casts Possible hydrogen gas release Easy to mix & Pleasant odor producing bubbles on die. Hydrophobic  Hydrophilized Addition Silicon Introduced to overcome inherent hydrophobicity of addition silicone. Effect of their inherent hydrophobicity ↓ Ability of the material to properly wet the soft tissues. ↓ The wetting of the soft die materials to its surface Mechanism of hydrophilization By adding Surfactants (surface tension reducing agent) to the paste. This allows the impression material to wet soft tissue better and be poured in stone more effectively. Forms of supply: As Polysulphide Composition Base: Low molecular weight polyether with terminal imine (aziridine ring). Fillers (Colloidal silica). Plasticizers (Dibutyl phthalate). Catalyst: Aromatic sulfonic acid ester (attack and open the reactive terminal ring). Fillers. Plasticizers. Setting reaction: The material sets via Ring Opening Addition Polymerization reaction. No reaction by product. Mechanism 1) The catalyst dissociate → form cations (R+ ) 2) Form cations (R+ )→ attack and open the aziridine ring of the prepolymer 3) The prepolymer become charged at its terminals (-NR-CH2-CH2*) → it react with nitrogen atoms of adjacent unreacted prepolymers Thus Lengthening Of The Chain Occurs.  Advantages Disadvantages Highly accurate. Expensive Good dimensional stability. Short working time Stock trays. High stiffness leading to difficulty in Good surface detail. removal from undercuts Pour within one week (delay pour) Bitter taste due to good elastic behavior. Low tear strength Multiple casts. Absorbs water (can’t be electroplated) Good wettability.