Elastomeric impression materials are used to reproduce very accurate impressions where all the little details are also captured in the impression and reproduced in the cast produced.
Classification of Elastomeric Impression materials:
Elastomeric impression materials are divided into 3 types based on their composition
1. Polyether
2. Polysulfide
3. Silicone:
- Addition
- Condensation
Failures in Elastomeric impression materials is mostly due to presence of Technical errors rather than Faulty material.
Types of Defects in Elastomeric Impression materials and their Respective causes:
Type of Defect: Rough and Uneven surface of Impression:
- Improper proportioning of base of catalyst particularly condensation silicones
- Incomplete polymerization caused by premature removal from the oral cavity
- Rapid polymerization due to high ambient temperatures
- Inhibition of Polymerization by accidental incorporation of impurities as in case of Addition Silicones
Type of Defect: Rough of Chalky Cast:
- Inadequate cleaning of the impression
- Excessive surfactant or water left on the impression
- Improper manipulation of stone
- Premature removal of cast before setting
Type Defect: Distortion:
- Excessive bulk of the material
- Improve adhesion between tray and material
- Movement of tray during polymerization
- Improper removal i.e slower rate of removal from the mouth
Saw your post :). Just wanted to add some more impression defects. 1. Voids caused by air entrapment. 2. Cuspal trails caused by improper use of high viscosity (heavy body) impression material.