All about Impression Materials in Dentistry | Dentalkart

IMPRESSION MATERIALS IN DENTISTRY Impression materials are used to copy the teeth and surrounding oral structures by creating a dental impression poured with dental plaster to fabricate a dental cast. This procedure provides a 3-dimentional and accurate mouth replica, allowing dental work even in the absence of the patient. HISTORY OF IMPRESSION MATERIALS: Until mid-19th century, wax was the only impression material. In 1857, thermoplastic modelling compound was made that showed similarities to today’s impression compound. Then agar a reversible hydrocolloid manufactured from algae, was introduced in dentistry. During the second world war, Americans used another elastic impression material known as alginate. Alginate and Agar have disadvantages, like dimensional instability and low tear strength, which led to the manufacture of elastomeric (also known as rubber-based) impression materials. First came polysulfide, then condensation silicone followed by polyether, and then addition silicone. CLASSIFICATION The following classification is based on materials rigidity and elasticity. 1. Rigid - i) impression compound ii) impression waxes iii) zinc oxide eugenol paste iv) impression plaster 2. Elastic - Aqueous hydrocolloids – i) agar & ii) alginate Non- aqueous elastomers – i) Polysulphur ii) Polyethers iii) silicones- condensation silicone and additional silicone RIGID IMPRESSION MATERIALS- Rigid impression materials include impression compound, waxes, plaster and zinc oxide-eugenol; however, these materials cannot engage undercuts that may be present on the teeth or the bone. Therefore, their use is restricted to edentulous patients without bony undercuts. Impression Compound: Impression compound is a muco-compressive, thermoplastic and rigid impression material. Impression Plaster: Impression plaster is similar in composition to the dental plaster used to construct models and dies. Not so widely used nowadays. Patient complains about a very dry sensation after the impression is recorded. Impression Waxes: It is a thermoplastic material and does not set by chemical reaction. It is used for correcting small imperfections in other impressions. Cast has to be poured immediately to avoid distortion. Zinc Oxide Eugenol Impression Paste: Zinc Oxide Eugenol impression paste is created by the combination of zinc oxide and Eugenol contained in oil of cloves. An acid-base reaction takes place with the formation of zinc eugenolate chelate. Useful for edentulous cases and in relining / remodelling techniques with individual tray for uniform support. ELASTIC IMPRESSION MATERIALS- Elastic impression materials are those that remain in an elastic or flexible state after they have been removed from the mouth. 1. Agar Impression Material: Was used for Cast duplication, full mouth impressions without deep undercuts, as tissue conditioner, was used extensively for crown & bridge impressions before elastomers 2. Alginate: Word alginate from “algin” –brown sea-weed (algae). It was used as substitute of agar, when it became scarce during world war-II. More popular than agar because of simpler usage. NON- AQUEOUS ELASTOMERS- These include: polysulphides, polyethers and silicones (addition and condensation). 1. Polysulphides Supplied as a base and catalyst paste. It causes condensation polymerisation reaction, which releases H20 (water is the byproduct). 2. POLYETHER These are the most hydrophilic of the synthetic elastomer impression materials. Therefore, we often use them when moisture control is difficult. They are dimensionally stable, provide good accuracy and have adequate tear resistance 3. Addition silicone It is the most widely used impression material in dentistry. Also called as, PVS (polyvinyl siloxane) or VPS (Vinly poly siloxane) This material undergoes an addition polymerisation reaction that has no by-products which makes it dimensionally stable and increases the accuracy of the material enabling the impression to remain unchanged for a long period of time. It also has good detail reproduction, excellent dimensional stability, fast setting, high patient acceptance and has better dimensional stability compared to condensation silicone. 4. Condensation silicone It derives its name from a reaction that occurs during its setting known as condensation reaction. This reaction results in the production of ethyl alcohol. The loss of this by-product leads to shrinkage of the impression. It has high accuracy, high patient acceptance, is easy to use and be used in cases with deep undercuts. However, it has unreliable dimensional stability, is hydrophobic, causes marked shrinkage on setting with release of by-product. Follow us WhatsApp Channel: https://www.whatsapp.com/channel/0029... Instagram:   / dentalkart   Twitter:   / dentalkart   Facebook: https://www.facebook.com/search/top/?... LinkedIn:   / dentalkart