An impression material is substance used totake negetive replica of the teeth and tissuesof the oral cavity. Impression is then used to make positivereplica. The positive reproduction of tooth iscalled A “DIE” , and of several teeth orwhole tissue then called“CAST “ or “MODEL”. These casts help in saving clinical time.
Desireable Properties Of anImpression Material Initially it must posses soft gel state to flow in undercuts easily to record them. Possess elastic nature to avoid distortion during removal. Possess sufficientworking time andsetting time. Must be dimensionally stable. Should posses retention property Must be non-toxic, non-irritant, non-allergic . Have pleasant taste and odor. Economical. Capable of being decontaminate.
CLASSIFICATION There are several ways of classifying impression materials.1. According to mode of setting and elasticity.2. According to tissue displacement.3. According to their use in dentistry.
CLASSIFICATION1. According To Mode Of Setting And ElasticityMode of setting Rigid ElasticSet by chemical reaction(irreversible)PlasterZinc oxide eugenolAlginate andElastomerseg. Poly sulfide,Silicone, PolyetherSet by tempreturechange( reversible)Impression compo:WaxesAgar
CLASSIFICATION2. According to tissue displacement.A . MucostaticThese material produce minimal displacement of tissue duringimpression.eg. Plaster, ZOE, low viscosity alginates and elastomers.B. MucocompressiveThese materials are more viscous and displace the tissue whilerecording them.eg. Impression compound, high viscous alginates and elastomers.
CLASSIFICATION3. According to their use in dentistryA. Used for Complete Denture ProsthesisPlaster , Impression compound and Impression paste set to rigid mass and hencecannot be removed from undercuts without distortion.Therefore these are used for Edentulous patients.B. Used for Dentulous patientsAlginates and Rubber base Impressions are elastic and suitable for impressionsof Dentulous mouths.
Classes OfImpression MaterialsThere are 2 classes :1. Elastic2. Non-Elastic or Rigid
Elastic Impression Materials The material that transforms from a semisolid , non-elastic stateto a highly elastic solid state . This material changes its shape when pressure is applied and is restoredwhen pressure is removed. More important than Non-Elastic impression materials.ClassificationHydrocolloid ElastomerOr Rubber Base1. Reversible = Agar 1. PolySulphide2. Irreversible = Alginate 2.Poly Ether3. Silicone
Non Elastic Impression Materials These materials are rigid and therefore exhibit little or no elasticity. Any significant deformation produces a permanent deformation. They are used where there are no undercuts and are mainly used foredentulous patient cases.Classification1. Plaster2. Zinc oxide eugenol3. Tissue conditioner materials4. Impression wax5. Impression compoundA. high fusingB. low fusing