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rigid impression materials dental material

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rigid impression materials dental material

Text of rigid impression materials dental material

  • 1. Impression Materials

2. Making an imprint 3. Impression and Cast Impression: -ve replica of the oral hard and soft tissues Cast: +ve replica of the oral hard and soft tissues Die: Metal cast or any cast for single tooth 4. Impression Trays Container used to carry the impression material into or out from the patients mouth Stock trays Special trays 5. Under cut Areas under the inclined planes 6. Ideal requirements of Impression materials Biologically Non- toxic and non-irritant Interfacially Compatible with different model and die materials Chemically 1. Have long shelf life 2. Dimensionally stable in storage Stable in storage 7. Ideal requirements of Impression materials Mechanically 1. When set they should behave elastically 2. Have sufficient mechanical properties ie. tear strength to resist tearing during impression removal from the undercuts 3. Have sufficient flow under pressure that helps in recording the fine details of the oral structure Practicability 1. Inexpensive 2. Easy manipulated 3. Have reasonable working and setting times 8. Classification of Impression Materials I. According to the mechanical behavior A. Elastic materials Used for both edentulous and dentate patients having undercuts 1. Hydrocolloids Reversible hydrocolloid (Agar) Irreversible hydrocolloid (Alginate) 2. Elastomeric Materials Polysulfide Silicones (Condensation-polymerizing & addition- polymerizing) Polyether 3. Gutta Percha 9. I. According to the mechanical behavior B. Inelastic (Rigid) materials Used only with edentulous patients having no or shallow under cuts 1. Plaster of Paris 2. Impression compound 3. Zinc oxide Pastes 4. Impression waxes Classification of Impression Materials 10. II. According to the setting mechanism A. Chemically-set materials Because of the irreversible reaction, they are used only for one time 1. Plaster of Paris 2. Zinc oxide pastes 3. Alginate hydrocolloid 4. Elastomeric materials Classification of Impression materials 11. II. According to the setting mechanism B. Physically-set materials Because of the reversible reaction they are able to be reused 1. Impression compound 2. Agar hydrocolloid 3. Impression waxes 4. Gutta percha Classification of Impression materials 12. III. According to the usage A. Materials for making 1ry impression Used in stock trays, thick consistency, record poor details 1. Impression compound (Complete denture) 2. Alginate hydrocolloid (Removable and fixed prosthesis) 3. Putty and heavy consistencies of rubber impression materials (Removable and fixed prosthesis) Classification of Impression materials 13. III. According to the usage B. Materials for making 2ry impression Used in special trays, thin consistency, record fine details 1. Plaster of Paris (Complete denture) 2. Zinc oxide pastes (Complete denture) 3. Impression waxes (Complete denture) 4. Agar hydrocolloid (Removable and fixed prosthesis) 5. Medium and light consistencies of rubber impression materials (Removable and fixed prosthesis) Classification of Impression materials 14. RIGIDRIGID IMPRESSIONIMPRESSION MATERIALSMATERIALS 1.Impression plaster 2. Impression compound 3. Zinc oxide pastes Manipulation of these materials will be handled in the lab classes 15. 1. IMPRESSION PLASTER1. IMPRESSION PLASTER It is a rigid impression material, used in shellac special trays to make 2ry impressions for edentulous patient has no or shallow undercuts. It is one of the gypsum products that based on - Ca2 So4. H2O (-calcium sulfate hemihydrate) 16. PresentationPresentation The material is presented as powder to be mixed with water to form a slurry (soft creamy mix) 17. Composition of the powderComposition of the powder -calcium sulfate hemihydrate.basic constitute Potassium sulfate.anti expansion and accelerator Boraxretarder Coloring agent Alizarine red Flavoring agent.Ment Starch.Facilitate the removal of stone cast -calcium sulfate hemihydrate 18. Setting reactionSetting reaction The material sets via chemical reaction named crystallization The reaction is characterized by heat generation and setting expansion The reaction could be influenced by; P/L ratio, Mixing rate (time and speed), Particle size, Temperature, Additives (Acc. & Ret.) 19. The calcium sulfate hemihydrate gets some water and changes into inter-meashed calcium sulfate dihydrate crystals 20. PropertiesProperties 1. Biological properties Non toxic and non-irritant Cause dehydration to oral soft tissues 2. Interfacial properties Requires separating medium before pouring of gypsum cast and die materials 3. Mechanical properties Rigid after setting and should not be used in patients with sever undercuts Brittle after setting and could be fractured in clean cut lines during impression removal from shallow undercuts (i.e. fractured parts could be assembled). 21. PropertiesProperties 4. Chemical properties Little degree of dimensional changes due to the presence of anti-expansion additives. Materials powder should be stored in dry, tightly closed containers to elongate the shelf life 5. Practicability Easy manipulation Resenable setting time Somewhate short working time 22. 2. IMPRESSION COMPOUND2. IMPRESSION COMPOUND It is a rigid thermoplastic impression material, used in stock trays to make 1ry impressions for edentulous patient has no or shallow undercuts. Types 1. Low fusing (True impression material, ..softening temp. 45-60o C) 1. High fusing (Tray compound, .. softening temp. 70-130o C) 23. PresentationPresentation L.F. Cakes for full impression H.F. Cakes for making special trays L.F. Green sticks for border tracing L.F. Cones for copper ring impressions 24. CompositionComposition Thermoplastic resins gives thermoplastic behavior Waxes Flow, stickiness, and give thermoplastic behavior Filler (Talc, chalk) consistency, stickiness Plasticizer (Stearic acid) moldability (plasticity) and facilitate the flow Coloring agent 25. Setting ReactionSetting Reaction Thermoplastic material changes its Physical state by temperature change On Heating Hard Soft On Cooling Soft Hard The material is bad thermal conductor, so sufficient heating is required for homogenous softening. Sufficient cooling is also required for proper hardening 26. PropertiesProperties 1. Biological properties Non toxic and non-irritant Overheated material could burn the soft tissue 2. Interfacial properties Does not require separating medium before pouring the gypsum cast 3. Mechanical properties Rigid after cooling and should not be used in patients with sever undercuts 27. PropertiesProperties 4. Chemical properties Thermoplastic material Little degree of dimensional changes due to thermal change and release of stresses Overheating evaporates the plasticizer Moldability 5. Practicability Easy manipulation, Reasonable W.&S. Times The material could be reused Impression should be disinfected before pouring in gypsum and sterilized before reusing 28. 2. ZINC OXIDE PASTES2. ZINC OXIDE PASTES It is a rigid impression material, used in acrylic special trays with border tracing to make 2ry impressions for edentulous patient has no or shallow undercuts. Uses of Zinc oxide pasteUses of Zinc oxide paste 1. Impression material 2. Bite registration 3. Surgical pack 29. TypesTypes 1. ZOE paste..contains eugenol in its formulation 2. Eugenol-free paste.. contains carboxylic acid derivative instead of eugenol The eugenol-free material overcomesThe eugenol-free material overcomes the drawbacks of the eugenol;the drawbacks of the eugenol; 1. Eugenol taste could be unaccepted by some patients 2. Eugenol could irritate the soft tissue 3. Leaching of the eugenol out of the material could cause gastric troubles 30. Both types areBoth types are presented aspresented as two-paste systemstwo-paste systems (Base and Catalyst)(Base and Catalyst) Base Catalyst ZOE white paste red paste E-free white paste blue paste PresentationPresentation 31. CompositionComposition Base paste Catalyst paste 1.Zinc oxide 2.Oils (olive oils) 3.Resins 4.Accelerator (Zinc acetate ) Eugenol- containing materials 1.Eugenol (Oil of clove) 2.Fillers (Kaoline, talc) 3.Accelerator (Zinc acetate) 4.Moisture Eugenol-free materials 1. Carboxylic acid drevative [e.g. EBA] 2. Ethyl alcohol as vehicle 32. Setting ReactionSetting Reaction ZOE sets through chemical reaction named chelation (1).ZnO + H2O Zn(OH)2 (2). Zn(OH)2 + Eugenol (2HE) ZnE2 + H2O The reaction could also be accelerated in presence of higher temperatures, little amount of moisture, 1ry alcohol Eugenol-free material sets through chemical reaction named saponification ZnO + 2RCOOH (RCOO)2 Zn + H2O 33. PropertiesProperties 1. Biological properties Non toxic and non-irritant Eugenol could irritate the soft tissue 2. Interfacial properties Does not require separating medium because of its oil content 3. Mechanical properties Rigid after setting and should not be used in patients with sever undercuts 34. PropertiesProperties 4. Chemical properties Impression inaccuracy could result from the warpage of acrylic trays Dimensionally stable on storage 5. Practicability Easy manipulation, Reasonable W.&S. Times Impression should be disinfected before pouring in gypsum, however long term immersion could cause erosion of impression surface

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