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Types of impressions: Previous Final

Imprints, their classification, method of receipt. Classification of materials of imprint. Clinical, physical and chemical descriptions of materials for imprint. Impression is a negative (reverse) reflection of any organ of the dentomaxillar system: teeth, alveolar sprout or part, palate, nose,

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Types of impressions: Previous Final

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  1. Imprints, their classification, method of receipt. Classification of materials of imprint. Clinical, physical and chemical descriptions of materials for imprint

  2. Impression is a negative (reverse) reflection of any organ of the dentomaxillar system: teeth, alveolar sprout or part, palate, nose, ear and others like that. Impression is a negative (reverse) reflection of hard and soft tissues, placed in the area of dental prosthesis and it’s borders which Is being taken by means of the special impression materials

  3. Types of impressions: Previous Final

  4. Final impressions: Anatomical Functional

  5. Types ofimpressions Single layer Double layer Combined

  6. Types ofimpressions Anatomical (orientation)– take with standard or individual tray in the state of calmness of tissues of prosthetic bed and tissues, which are placed on a border with them. Functional - take with individual tray by means of the special functional tests, in the case of making of removable constructions of dentures : compression - in the case of pressing of buffer areas of prosthetic bed, by masticatory pressure or by the hand of doctor; decompression - in the case of minimum pressure on the tissues of prosthetic bed

  7. Double layer – an exact reflection of gingival edge is taken by means of impression materials of the same group (previous layer + correction layer) Combined– is taken by means of impression materials of different groups (previous layer + correction layer) Occlusal–for taking impression in position of central occlusion

  8. Impression trays Standard:made factory - On maxillae different sizes - On mandible different sizes Individual:made in dental laboratory By material: plastic metallic waxen Presence of retentin points perforated unperforated

  9. Impression trays for taking impression at the same time

  10. Placing of impression tray in oral cavity

  11. Impression of maxillae

  12. Double layer impression

  13. Impression Materials • Non-elastic • Elastic • Aqueous hydrocolloids • Agar • Alginate • Non-aqueous elastomers • Polysulfide • Silicones • Condensation • Addition • Polyether

  14. Indications • Diagnostic casts • preliminary • opposing • Indirect reconstruction • fixed • removable • Bite registration

  15. Elastomeric Impression Materials • Viscoelastic • physical properties vary • rate of loading • Rapidly remove • decreases permanent deformation • chains recoil from a recoverable distance • increases tear strength

  16. Plaster Compound Waxes ZnO - Eugenol Polysulfide Silicones Polyether Non-elastic Impression Materials Agar (reversible) Aqueous Hydrocolloids Alginate (irreversible) Elastic Condensation Non-aqueous Elastomers Addition

  17. Aqueous Hydrocolloids • Colloidal suspensions • chains align to form fibrils • traps water in interstices • Two forms • sol • viscous liquid • gel • elastic solid • Placed intra-orally as sol • converts to gel • thermal or chemical process

  18. Aqueous Hydrocolloids • Semi-permeable membranes • poor dimensional stability • Evaporation • Syneresis • fibril cross linking continues • contracts with time • exudes water • Imbibition • water absorption • swells

  19. Agar (reversible) Aqueous Hydrocolloids Alginate (irreversible) Elastic Polysulfide Condensation Non-aqueous Elastomers Silicones Addition Polyether

  20. Reversible Hydrocolloid (Agar) • Indications • crown and bridge • high accuracy • Example • Slate Hydrocolloid (Van R)

  21. Agar complex polysaccharide seaweed gelling agent Borax strength Potassium sulfate improves gypsum surface Water (85%) cool to 43ºC agar hydrocolloid (hot) agar hydrocolloid (cold) (sol)(gel) heat to 100ºC Composition

  22. Manipulation • Gel in tubes • syringe and tray material

  23. Manipulation • 3-chamber conditioning unit • (1) liquefy at 100°C for 10 minutes • converts gel to sol • (2) store at 65°C • place in tray • (3) temper at 46°C for 3 minutes • seat tray • cool with water at 13°C for 3 minutes • converts sol to gel

  24. Advantages • Dimensionally accurate • Hydrophilic • displaces moisture, blood, fluids • Inexpensive • after initial equipment • No custom tray or adhesives • Pleasant flavor • No mixing required

  25. Disadvantages • Initial expense • special equipment • Material must be prepared in advanced • Tears easily • Dimensionally unstable • Must be poured immediately • Can only be used for a single cast • Difficult to disinfect

  26. Agar (reversible) Aqueous Hydrocolloids Alginate (irreversible) Elastic Polysulfide Condensation Non-aqueous Elastomers Silicones Addition Polyether

  27. Irreversible Hydrocolloid (Alginate) • Most widely used impression material • Indications • study models • removable fixed partial dentures • framework • Examples • Jeltrate (Dentsply/Caulk) • Coe Alginate (GC America)

  28. Sodium alginate salt of alginic acid mucous extraction of seaweed (algae) Calcium sulfate reactor Sodium phosphate retarder Filler Potassium fluoride improves gypsum surface 2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4 H2O Na alginate + CaSO4 Ca alginate + Na2SO4 (powder) (gel) Composition

  29. Manipulation • Weigh powder • Powder added to water • rubber bowl • vacuum mixer • Mixed for 45 sec to 1 min • Place tray • Remove 2 to 3 minutes • after gelation (loss of tackiness)

  30. Advantages • Inexpensive • Easy to use • Hydrophilic • displace moisture, blood, fluids • Stock trays

  31. Disadvantages • Tears easily • Dimensionally unstable • immediate pour • single cast • Lower detail reproduction • unacceptable for fixed pros • High permanent deformation • Difficult to disinfect

  32. Non-Aqueous Elastomers • Synthetic rubbers • mimic natural rubber • scarce during World War II • Large polymers • some chain lengthening • primarily cross-linking • Viscosity classes • low, medium, high, putty • monophasic

  33. Agar (reversible) Aqueous Hydrocolloids Alginate (irreversible) Elastic Polysulfide Condensation Non-aqueous Elastomers Silicones Addition Polyether

  34. Polysulfide • First dental elastomers • Indications • complete denture • removable fixed partial denture • tissue • crown and bridge • Examples • Permlastic (Kerr) • Omni-Flex (GC America)

  35. Composition • Base • polysulfide polymers • fillers • plasticizers • Catalyst • lead dioxide (or copper) • fillers • By-product • water

  36. O O = = mercaptan + lead dioxide polysulfide rubber + lead oxide + water Pb Pb = = O O Polysulfide Reaction --SH HS---------------------SH HS-- -S-S---------------S-S- S S + 3PbO + H2O H S O = Pb = O H S

  37. Manipulation • Adhesive to tray • Uniform layer • custom tray • Equal lengths of pastes • Mix thoroughly • within one minute • Setting time 8 – 12 minutes • Pour within 1 hour

  38. Advantages • Lower cost • compared to silicones and polyethers • Long working time • High tear strength • High flexibility • Good detail reproduction

  39. Disadvantages • Poor dimensional stability • water by-product • pour within one hour • single pour • Custom trays • Messy • paste-paste mix • bad odor • may stain clothing • Long setting time

  40. Agar (reversible) Aqueous Hydrocolloids Alginate (irreversible) Elastic Polysulfide Condensation Non-aqueous Elastomers Silicones Addition Polyether

  41. Condensation Silicone • Indications • complete dentures • crown and bridge • Examples • Speedex (Coltene/Whaledent) • Primasil (TISS Dental)

  42. Composition • Base • poly(dimethylsiloxane) • tetraethylorthosilicate • filler • Catalyst • metal organic ester • By-product • ethyl alcohol Phillip’s 1996

  43. C2H5O OC2H5 Si C2H5O OC2H5 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 HO – Si – O – Si - O - H HO – Si – O – Si - O - HO – Si – O – Si - O - HO – Si – O – Si - O - H CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 n n n n OC2H5 + 2C2H5OH Si OC2H5 CondensationSilicone Reaction metal organic ester ethanol

  44. Manipulation • Mix thoroughly • paste - paste • paste - liquid • Putty-wash technique • reduces effect of polymerization shrinkage • stock tray • putty placed • thin plastic sheet spacer • preliminary impression • intraoral custom tray • inject wash material

  45. Advantages • Better elastic properties • Clean, pleasant • Stock tray • putty-wash • Good working and setting time

  46. Disadvantages • Poor dimensional stability • high shrinkage • polymerization • evaporation of ethanol • pour immediately • within 30 minutes • Hydrophobic • poor wettability

  47. Agar (reversible) Aqueous Hydrocolloids Alginate (irreversible) Elastic Polysulfide Condensation Non-aqueous Elastomers Silicones Addition Polyether

  48. Addition Silicones • AKA: Vinyl polysiloxane • Indications • crown and bridge • denture • bite registration • Examples • Extrude (Kerr) • Express (3M/ESPE) • Aquasil (Dentsply Caulk) • Genie (Sultan Chemists) • Virtual (Ivoclar Vivadent)

  49. Composition • Improvement over condensation silicones • no by-product • First paste • vinyl poly(dimethylsiloxane)prepolymer • Second paste • siloxane prepolymer • Catalyst • chloroplatinic acid Phillip’s 1996

  50. O O - Si – CH3 H - Si – CH3 CH3 CH3 O O CH = CH2 – Si – O --- CH2 - CH2 – Si – O --- CH3 - Si - H CH3 - Si - CH3 CH3 O O CH3 CH3 ---O – Si – CH = CH2 ---O – Si – CH2 - CH2 CH3 CH3 Addition Silicone Reaction Chloroplatinic Acid Catalyst

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