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Impression materials

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Impression materials

  1. 1. Impression materials<br /> by <br />Bibinbhaskaran<br />
  2. 2. Impression materials<br /> Definition :- (GPT): <br />A negative likeness or copy in reverse of the surface or object.<br />2) An imprint of the teeth and adjacent structures for use in dentistry<br />
  3. 3. Impression material:-<br /> Any substance or combination of substances used for making an impression or negative reproduction.<br />Impression technique:-<br /> A method and manner used in making a negative likeness.<br />
  4. 4. classification<br />
  5. 5.
  6. 6. Classification <br />Based on rigidity : Rigid <br />egPlaster,Zincoxideeugenol<br /> impression compound<br /> Elastic<br />egAlginate,polyether,silicone<br />Based on setting of the material: 1.) Chemical reaction(irreversible)<br />eg plaster of paris,zincoxideeugenol<br />alginate,additon and condensation silicones <br /> 2 ) Physical change of state(reversible)<br />eg agar<br />
  7. 7. Based on viscosity : Mucostatic<br />eg impression plaster,agar,<br /> light body elastomer<br />Mucocompressive<br />eg Impression compound,alginates<br />Pseudoplastic<br />eg addition silicones<br />
  8. 8. Based on interaction with saliva <br /> and water : Hydrophobic<br />eg polysulfide ,condensation <br /> silicones <br />Hydrophilic<br />egputty,impression plaster<br />Based on use : <br /> Primary <br /> impression material<br />eg impression compound,alginate<br /> Secondary <br /> Impression material<br />egZoe,medium bodied elastomers<br /> Duplicating<br /> material <br />eg agar <br />
  9. 9. Based on <br />Chemical composition : impression plaster<br /> impression compound<br /> metal oxide(zinc oxide eugenol)<br /> pastes<br /> agar hydrocolloid<br /> alginate hydrocolloid<br />polysulfides<br /> condensation silicones<br /> addition silicones<br />polythers<br /> light curing polyether <br /> (urethane dimethacrylate) <br />
  10. 10. Desirable qualities<br />Pleasant odor taste and color<br />Absence of toxic irritants<br />Adequate shelf life<br />Economical <br />Easy to use<br />Setting that meet clinical requirements<br />Satisfactory consistency<br />
  11. 11. Readily wet oral tissues<br />Elastic <br />Adequate strenght<br />Dimensional stability<br />Compatiblity with cast and die materials<br />Accuracy <br />Disinfection <br />
  12. 12. Impression plaster<br />
  13. 13. Impression plaster <br />The impressions are very accurate<br />Being hydrophilic it has got intimate contact with oral tissues by absorbing surface moisture<br />
  14. 14. Impression compound<br />
  15. 15. Impression compound <br />Fusion temperature of impression compound is 43.5 degree celesius<br />
  16. 16. Zinc oxide eugenol impression material<br />
  17. 17. Zincoxideeugenol impression material<br />Non eugenol pastes-<br />One of the chief disadvantages of Zoe pastes is the possible burning sensation caused by eugenol.orthoethoxybenzoic acid (EBA) is a valuable substitute for eugenol in this regard.<br />
  18. 18. Alginate <br />
  19. 19. Alginate <br />Gelation reaction-<br /> 2Na3P04 + 3CaSo4----- Ca3(Po4)2+3 Na2SO4<br />
  20. 20. Recent advances in alginates<br />Dust free alginates-<br /> De-dusting agent (glycerin or glycol)<br />Siliconized alginates- <br /> silicon polymers are added to strengthen the material<br />Alginates containing disinfectants-<br />eg quaternary ammonium salts or chlorohexamine are added to alginate powder.<br /> Hard and soft set alginates-<br /> by adjusting the amount of fillers<br />
  21. 21. Reversible hydrocolloid-AGAR<br />
  22. 22. Agar <br />Gelation-<br />Gelation is accomplished by circulating cold water of approximately 18-23 degree for not less than 5 min.<br />
  23. 23. Elastomeric impression materials<br />Classification :-<br />Based on viscosity-<br />Class 1 heavy body heavy viscosity<br />Class 2 regular body or medium body<br />Class 3 light body or low viscosity<br />Based on chemistry-<br />Polysulfides<br />Condensation silicones<br />Additional slilicones<br />Polythers<br />Visible light curable polyether<br />
  24. 24. POLYSULFIDES<br />
  25. 25. polysulfides<br />Polysulfide is one of the least stiff or highly flexible of elastomeric material<br /> For accurate polysulfide impressions-<br />The cast should be poured immediately after taking impression<br />Minimise the amount of material used to take impression by using custom made acrylic trays<br />
  26. 26. Condensation silicones(Double mix type)<br />
  27. 27. Condensation silicones<br />It is also called room temperature vulcanising silicones(RTV)<br /> Uses –<br />It is widely used in recording dentulous impressions in preparation of crowns,bridges,inlays,onlays and to some extent for partial dentures<br />It is also used to record edentulous impressions in preparation of complete denture<br />
  28. 28. Putty type<br />Advantages –<br />No custom tray required<br />No special equipment required<br />Moderate strength in deep sulcus<br />Pleasant odor<br />Adequate shelf life<br /> Disadvantages –<br />Should be poured shortly after removal<br />Hydrophobic<br />Difficult to electroplate<br />Easily distorted<br />
  29. 29. Addition silicones(Double mix type)<br />
  30. 30. Addition silicones<br />Addition polysilicones are the most stable of all the existing materials<br />It has an excellent recovery of 99.93%<br />It exhibits pseudoplasticproperties.it can be used both as syringe and tray materials<br />
  31. 31. Putty type<br /> Advantages –<br />No custom tray<br />No special equipment<br />Good shelf life<br />Can be poured more than once<br /> Disadvantages –<br />Extremely hydrophilic<br />More difficult to pour<br />Most expensive<br />
  32. 32. Polyether materials<br />
  33. 33. Polythers<br /> Uses-<br />For recording impression in preparation of crowns and bridges<br />Cavity preparation for inlays and onlays<br />For construction of partial and complete dentures<br />
  34. 34. Visible light cured polyether<br />
  35. 35. Light cured polyether<br />It has excellent elasticity<br />It has infinite working time and short setting time<br />The impression can be stored upto two weeks<br />
  36. 36. Disinfection <br />Most manufacturers recommend a specific<br />disinfectant,such as iodophor,bleach,orglutaldehyde,for disinfection.<br />Certain disinfectants may result in gypsum casts that have a lower surface hardness or diminished surface detail.<br /> The current protocol for disinfecting hydrocolloid impressions recommended by the centre for disease control is to use house hold bleach(1 to 10 dilutions),iodophor or synthetic phenols as disinfectants<br />An alternate disinfection method is by immersion,but this should not exceed 10 min.<br />
  37. 37. Duplicating materials<br />Duplicating is required for two reasons:-<br /> 1, The cast on which the wax pattern of the metal frame work is to be formed must be made from refractory investment because it must withstand the casting temperatures required for gold or base metal alloys<br /> 2, The original cast is needed for checking the accuracy of the metal frame work and for processing the denture base portion of the partial denture<br />The most common duplicating materials are agar hydrocolloid compounds, The primary advantage of agar is their set is reversible.the disadvantage is it is subject to dimensional change.The best storage condition is 100% humidity.<br />
  38. 38. Tissue conditioners<br />Tissue conditoners are soft elastomers used to treat an irritated mucosa supporting a denture.it is used to provide time for healing of soft tissues<br />Tissue conditioners are composed of powder containing poly(ethyl methacrylate)and a liquid containing an aromatic ester – ethyl alcohol.<br />The properties that make tissue conditioners effective are-<br />1,viscous behavior which allows adaptation to irritated denture bearing mucosa<br />2,viscoelastic behavior which cushions the cyclic forces of mastication and bruxism<br />
  39. 39. References <br />Zardiackas.L.D , Dental materials,Dentla clinics of morthamerica,July 2007,vol 51,pg 629-643 .<br />O’Brien.W.J, Dental materials and their selection, 3rd edition, Quintessence publications.<br />Craig.R.G, Dental Materials, 12th edition, Elsevier publications.<br />Anusavice, Phillip’s Science of Dental Materials, 11th edition, Saunders publications. Impression materials.<br />

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