Elastomeric Impression Material Part II PDF

ELASTOMERIC IMPRESSION MATERIAL Part II Dr. Nesma Amer  Elastomeric Impression Materials Polysulphide Silicones Polyether Condensation silicon Addition Silicon Hydrophobic type Hydrophilic type  Viscosity cl...

ELASTOMERIC IMPRESSION MATERIAL Part II Dr. Nesma Amer  Elastomeric Impression Materials Polysulphide Silicones Polyether Condensation silicon Addition Silicon Hydrophobic type Hydrophilic type  Viscosity classes according to different % of filler content Low (light body) Medium (regular) High (heavy body) Putty (Extra heavy) (available in Silicones only) Form of supply: Supplied as two pastes (base & catalyst) in collapsible tubes It comes in Light/regular/heavy consistency.  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 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 Better elastic properties Poor dimensional stability, due Clean, pleasant to evaporation of ethanol by Stock tray (no need for special product tray) in putty-wash technique Lower tear strength Good working and setting Hydrophobic, this results in its time poor wettability 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.  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 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.  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.  Properties Of Rubber Base Materials 1- Working and setting time W.T & S.T are longest for polysulfide, and shortest for polyether. 2- Rheological properties: All elastomers are viscoelastic with high elastic recovery if they are strained rapidly. Order of best elastic recovery: Addition silicones > Polyether > Condensation silicones > Polysulfide.  Increase shearing force during mixing results in decreasing the viscosity of Polyether And Addition Silicone impression materials. Clinical significance Pseudoplasticity of addition silicone and polyether allows the manufacturer to formulate one-step materials or Monophase Materials (when syringed, it flows rapidly and allows the material to adapt well to the preparation).  Properties Of Rubber Base Materials 3- Flexibility and stiffness: Polysulfide has the least stiffness (most flexibility) of the elastomeric impression materials, while polyether is the stiffest material (after polymerization). Clinical significance Stiffness is very important during the impression removal from the patient mouth as with presence of loose teeth it may be exfoliated with the effect of this rigidity.  Properties Of Rubber Base Materials 4- Dimensional stability Sources of dimensional change: Polymerization shrinkage. Loss of by-product during the condensation reaction. Thermal contraction from oral temperature to room temp. Imbibitions when exposed to water, disinfectant or a high humidity resulting in expansion.  Properties Of Rubber Base Materials For greatest accuracy, the models and dies should be poured immediately (within 30 minutes) for condensation silicones and polysulfide. Dimensional stability of addition silicone and polyether materials suggests that these impressions can be poured within the first 24 hours up to one week.(MULTIPLE CASTS)  Properties Of Rubber Base Materials 5- Tear strength: It is affected by the manner of removal of the materials (rapid removal increases tear strength) 6- Detail reproduction All elastomeric impression materials are capable of reproducing fine details accurately and compatible with gypsum products.  Properties Of Rubber Base Materials 7- Wettability The lack of wettability of some impression materials can be avoided by the use of surfactant that is added to addition silicone to increase wettability Polyether has the best wettability. (WHY?) 8- Shelf life The tubes or containers must be tightly closed in a cool, dry environment. Manipulation Of Elastomeric Impression Materials I-Mixing system: A. Hand mixing B. Static automixing C. Dynamic mechanical mixing ІІ-Impression techniques 1.Multiple mix technique (dual-viscosity tech.) 2.Monophase technique. 3.Putty-wash technique. a. Two-stage (reline) technique. b. Single-stage technique.  I- Mixing A.Hand mixing Major problem with using hand mixing is incorporation of air bubbles into the impression material cause void formation on the impression surface. Hand Mixing Putty Consistency  I- Mixing B. Static automixing: For low-viscosity(Light &Medium) Internal spirals in the mixing tip is static. Advantages Greater uniformity in proportioning and mixing. Fewer voids in the mix. Less mixing time. Fewer possibilities for contamination of material. Less of material waste. Mixing system Static automixing  I- Mixing C- Dynamic Mechanical Mixing for high viscosity Internal spirals in mixing tips is Motor driven Advantages Easy to use High speed of mixing Accurate mixing Disadvantage: Waste of material Mixing system Dynamic mechanical mixing  II-Impression Techniques 1.Multiple mix technique (simultaneous dual-viscosity tech): Two viscosities (light and heavy), single step. 2.Monophase technique: One viscosity(medium),single step. 3.Putty-wash technique. a.Two-stage (reline) technique:Two viscosities(light and putty), two steps. b. Single-stage technique:Two viscosities (light and putty), single step.  II-Impression Techniques 1. Multiple mix technique (dual-viscosity technique) Two mixes are made and inserted simultaneously in the mouth. Equal lengths of pastes are mixed with separate spatulas on two separate paper pads, one for the syringe type (light body) and the other for the custom tray type (heavy body) till homogenous mix with no colored streaks of base and catalyst are seen. Disadvantage: Higher viscosity material may displace the more fluid low viscosity material II-Impression Techniques  II-Impression Techniques 2. Monophase technique (Single viscosity technique) The Medium Body Polyether or Additional Silicone is used for this technique. Single mixture is used Part of it is placed in syringe and its extrusion out of syringe tip reduces its viscosity (pseudoplasticity) which is placed around the prepared tooth. Remaining material in the tray retains its medium viscosity and forces the light body in the patient 's mouth.  II-Impression Techniques 3. Putty wash technique: (used to reduce the effect of polymerization shrinkage.) A- In the two steps technique: The putty is placed in a stock tray to make a primary impression, so it acts as a custom tray for a light body. A space for wash material (light body) is done by: Cut away part of the putty in the tray. OR Putting polyethylene sheet between prepared teeth and putty during primary impression taking. Wash material is injected around the prepared tooth and applied over the putty.  II-Impression Techniques B- In one step technique: The wash material is injected around the preparation. Then, putty in the tray is immediately seated over the wash material. Disadvantage: this approach risks displacing too much wash material by the putty.