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Applied Dental Material
Second Year

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  • Elastomeric impression materials are 2-component chemically setting materials that are traditionally delivered as two tubes of pastes. The pastes can be mixed together with (1) mixing pads (manually), (2) auto-mixing guns (by manually expressing the two pastes through a Kenics mixing tip), or (3) mixing equipment (electrically driven pumps for proportioning of materials from larger tubes through a Kenics mixing tip).
    The type of mixing technology depends on the rheological behavior of the mixture. [CLICK] Materials that are Newtonian or dilatant are actually hard to mix through a mixing tip. [CLICK] Silicone and polysulfide elastomers are examples of those situations, respectively. [CLICK] Therefore, they must be mixed manually on a mixing pad. Materials that are shear-thinning (pseudo-plastic) [CLICK] benefit from high shear in a mixing tip on an auto-mix gun or auto-mix equipment. [CLICK] Polyether and polyvinyl siloxane are examples of materials that are shear-thinning. [CLICK]
    A typicial Kenics mixing tip is shown above dissembled to reveal a series of connected mixing paddles (alpha-helixes with alternating rotations) that split and fold the mixing stream to produce mixing. A mixing tip with 8 paddles will split and fold the stream of two components 256 times (2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 2 to the eighth power = 256). [CLICK] The entire mixing event occurs in less than 1 second. Material that is left in the mixing tip will set and so the tip must be discarded. However, before the next mixing event, the tip functions as a cap on the dispensing gun.
  • Transcript

    • 1. Introduction, Non-elastic & Elastic Impression Materials Professor Hala Bahgat 1
    • 2. 2
    • 3. Impression Materials  Definition: Impression materials are materials used to make impressions for the dental arch.[Upper or lower] Impression is an accurate replica of the teeth & oral tissues negative reproduction of the dental arch. 3
    • 4. Impression Materials  Purpose for making impressions: Impression is filled with model material Model [Cast] It is the positive reproduction of the dental arch. 4
    • 5. Impression Materials  Purpose of making models :[Casts] 1.To study the case. 2.To diagnose the case. 3.To plan the line of treatment . 4.To educate the patient about his/her dental need. 5.To construct indirect restorations e.g. Inlay, onlay, crown, bridge, complete or partial denture . 5
    • 6. Impression Materials  Types of dental restorations: 6
    • 7. Impression Materials Types of dental restorations: Direct restorations Indirect restorations 7
    • 8. Impression Materials Procedures for taking impression : 1.Eqiupments: Water Measuring Cup Spatula Alginate Powder & Scoop Mixing Bowl Maxillary Tray Mandibular Tray 8
    • 9. Impression Materials  Procedures for taking impression: 1.Equipments:  Impression tray:[In details]  Definition: It is a device used -To support the impression material in contact with the patient’s oral tissues during taking the impression. -To support the impression material during removal from the patient’s mouth.  Parts of the impression tray:: 9
    • 10. Impression Materials  Procedures for taking impression: 1.Equipments:  Impression trays:[In details]  Types: 10
    • 11. Impression Materials Procedures for taking impression: 1.Equipments: Impression trays:[In details] Types: Stock trays: Metallic/Plastic Full arch/ Quadrant Perforated/Non Dentulous/Edentulous Special tray[Custom tray] 11
    • 12. Impression Materials  Procedures for taking impression: 1.Equipments:  Impression trays:[In details]  Types: 12
    • 13. Impression Materials  Procedures for taking impression: 2. Steps: a. Mixing b. Loading the lower or upper tray c. Insertion while the material is still soft Homogenous mix 13
    • 14. Impression Materials  Procedures for taking impression: 2.Steps: d. Holding the tray in place. Complete hardening of the material. e. Removal of the tray. f. Wash the impression 14
    • 15. Impression Materials  Procedures for impression taking: 2. Steps: g. Disinfect the impression h. Wrapping the impression. i. Insert the wrapped impression in a plastic bag. 15
    • 16. Impression Materials Procedures for pouring the model: [Cast]  Steps: 1 4 2 5 3 6 16
    • 17. Impression Materials  Requirements: I. Factors affecting accuracy: 1. High flow to record the dental arch accurately . a. The material is able to wet &to adapt to the oral tissues. [i.e. Hydrophilic ] b. The material is of low viscosity. 17
    • 18. Impression Materials Requirements: I. Factors affecting accuracy: 18
    • 19. Impression Materials  Requirements: I. Factors affecting accuracy: 2.Dimensional accurate during setting to retain the recorded dimensions. [i.e. No expansion or contraction] 3.Flexible after setting to be removed easily from the mouth. 4. Adhesive to the tray upon removal after setting. 5.Able to record the undercut area without distortion or fracture on removal after setting.[i.e. Elastic] Distortion[Warpage] Fracture 19
    • 20. Impression Materials Requirements: I. Factors affecting accuracy: 5. After removal[Ideal] Slow removal Rapid snap removal .·.Better accuracy 20
    • 21. Impression Materials  Requirements: I. Factors affecting accuracy: 6.Resistant to tearing or fracture upon removal from the patient’s mouth. 7. Can be disinfected without loss of accuracy. 8.Dimensional stable during storage until pouring the model. 9. Compatible with model materials: a. The model material is able to wet the impression to fill it completely. b. No retarding effect of the impression on the model during its setting otherwise one will obtain a model with poor surface quality. c. No mechanical interlocking between the impression & model otherwise there is need for separating medium. d. Able to be electroplated to produce metallic die. [Positive reproduction of a single tooth.] 21
    • 22. Impression Materials  Requirements: II. Other factors: 1.Acceptable for the patient: - Non toxic , non irritant, tasteless & odorless. - Suitable setting time 5-7 minutes. 2. Good handling property: -Easy to mix or prepare with minimum equipment. -Viscous enough in order not to flow out of the tray.[Thixotropic] -Adequate working time for loading & insertion the tray with the impression material. 5.Adequate shelf life. 6. Reasonable cost. 22
    • 23. Impression Materials  Requirements: No impression material fulfills all the requirements. The selection of the impression material best suited for a particular clinical case is the responsibility of the dentist. 23
    • 24. Impression Materials  Classification: The impression materials can be classified according to: 1.Applications. 2.Setting mechanism. 3.Behavior after setting upon removal from the undercut. 24
    • 25. Impression Materials  Classification: 1. According to applications: 25
    • 26. Impression Materials  Classification: 2. According to setting mechanism: 26
    • 27. Impression Materials  Classification: 3. According to behavior after setting on removal from the undercut: 27
    • 28. 28
    • 29. Nonelastic Impression Materials  Definition: They are impression materials which fracture or distort upon removal from the undercut area after setting. They can’t record the undercut area. Better to use them in completely edentulous patients.  Types: 1. Impression wax.[Historical] 2. Impression compound. 3. Plaster. 4. Zinc oxide & eugenol. 29
    • 30. Impression Compound  Supplied form: -Sheets -Cakes -Sticks -Cones 30
    • 31. Impression Compound  Composition: 1.Thermoplastic waxes & resins Thermoplastic polymers 2.Fillers body. 3.Gum adhesive to the tray. 4. Plasticizers. 5. Pigments.  Setting reaction: Being thermoplastic, it sets by physical setting reaction.[Reversible] Impression compound[Hard] ~45ºC Impression compound ~37ºC [Soft] 31
    • 32. Impression Compound Types: 32
    • 33. Impression Compound  Manipulation: 1.As impression compound is of low thermal conductivity, [Type of bonding] adequate time should be given for uniform heating Flow during impression taking.  Soaking in warm water-bath .[Sheets or cakes]  Over a flame.[Sticks]  Dry kneading with fingers. 33
    • 34. Impression Materials  Manipulation:  Application as 1ry impression material + stock tray. Single impression + copper band. Peripheral seal. Tray material for 2ndry impression. 2. As impression compound is of low thermal conductivity, adequate time should be given for uniform cooling. Distortion on removal from the mouth. 34
    • 35. Impression Compound Manipulation: 1.Kneading 2.Filling the stock tray 3.Insertion into completely edentulous patient 4.Lower impression after 35
    • 36. Impression Compound  Properties: 1. Flow: Viscous material Low flow.[Mucocompressive technique] .·.It can not record the fine details. 2. Dimensional accuracy during setting: High coefficient of thermal expansion & contraction.[Due to weak intermolecular 2ndry bonds] Contraction during cooling from mouth-to room temperature 0.30.4%. 3. Flexibility for ease of removal from undercut: Rigid material. .·.It is used only in minimum undercut.[Completely edentulous patient] 4. Adhesion to the tray: Self adhesive to the tray. 36
    • 37. Impression Compound  Properties: 4. Adhesion to the tray: Self adhesive to the tray. 5. Elasticity: Non-elastic on removal from undercut distortion. 6. Disinfection without loosing accuracy: Can be disinfected by immersion. 7. Dimensional stability during storage: Not dimensional stable during storage due to release of internal stresses Time + Temperature distortion. .·. Immediate pouring of the model is recommended. 37
    • 38. Impression Compound  Properties: 8. Compatible with the model material: a. The gypsum mix can adapt & fill the impression. b. No separating medium is required. c. Being thermoplastic ,the assembly[Tray + impression + model] is immersed in warm water-bath to soften the impression compound for easy separation from the model. d. The single impression can be copper electroplated. 38
    • 39. Zinc Oxide & Eugenol  Supplied form: Two pastes of contrast colors in metallic collapsible tubes. 39
    • 40. Zinc Oxide & Eugenol Composition: Catalyst paste: It is of characteristic odor. Base paste:  Zinc oxide.  Inert oil - Plasticizers. - Retarders.  Eugenol or oil of cloves.  Fillers.  Gum.  Accelerators MgCl2. Moisture. 40
    • 41. Zinc Oxide & Eugenol  Types: 1. Eugenol free impression material for sensitive patients: Chlorothymol or lauric acid instead of eugenol. 2. Regarding setting time:[According to the amount of Type I Hard Type II Soft accelerators & retarders] S.T. 10 minutes. S.T.15 minutes. 41
    • 42. Zinc Oxide & Eugenol  Setting reaction:  It is acid base reaction. Zinc oxide + water Zinc hydroxide +2 Eugenol Zinc hydroxide Zinc eugenolate +H2O Chelate [Salt] 42
    • 43. Zinc Oxide & Eugenol  Setting reaction:  Chelation reaction: It is the attachment of molecule or ion to metal ion at more than one point. The term Chelation is derived from the Greek word meaning crab’s claw indicating2 projecting attachments. A central zinc atom is held by 2adjacent eugenol. 43
    • 44. Zinc Oxide & Eugenol  Manipulation:  Armamentarium: - Oil resistant paper pad or glass slab & Stainless Steel spatula. - Special tray.  Steps: 1. Two equal lengths of the two pastes. 2. Mix until homogeneous mix without streaks is obtained. 3. Factors affecting setting time: High temperature & humidity accelerate the setting time. .·. It sets faster inside the patient’s mouth. Cool glass slab[Not below the dew point] & spatula retard the setting time. 44
    • 45. Zinc Oxide & Eugenol  Manipulation:  Application: 2ndry impression for completely edentulous patient + Special tray. 3 1 2 4 45
    • 46. Zinc Oxide & Eugenol  Properties: 1. Flow: Low viscosity High flow Record the fine details. [Mucostatic technique] 2. Dimensional accuracy during setting: Slight contraction during setting.[0.1%] 3. Flexibility for ease of removal from undercut: Rigid Use in minimum undercut.[completely edentulous patient] 4. Adhesion to the tray: Self adhesive to the tray. 46
    • 47. Zinc Oxide & Eugenol  Properties: 5. Elasticity: Non-elastic Can not record the undercut area. .·. Distortion on removal. 6. Disinfection without loosing accuracy: Can be disinfected by immersion. 7. Dimensional stability during storage: Dimensional stable during storage. 8. Compatibility with model materials: a. The gypsum mix can adapt & fill the impression. b. No separating medium is required. c. Immerse the assembly in warm water-bath for easy separation. d. Can not be electroplated. 47
    • 48. 48
    • 49. Elastic Impression Materials  Definition: Elastic impression materials are able to record the undercut area in the dental arch on removal from the patient’s mouth. They are able after setting to compress at the undercut area facilitating their removal from the patient’s mouth. This is known as flexibility. Then they return back to the original recorded dimensions. This is known as elasticity. But these materials are not purely elastic, they are viscoelastic. 49
    • 50. Elastic Impression Materials What is viscoelasticity? Viscoelasticity is a strain time relationship. It is a combination of : 50
    • 51. Elastic Impression Materials Strain Permanent deformation Time Strain rate sensitive material Rate = Quickly Time Permanent Deformation Rate = Slowly Time Permanent Deformation 51
    • 52. Elastic Impression Materials  What is the influence of viscoelasticity on the impression material?  Don’t exert pressure on the tray after insertion.  Don’t move the tray.  Rapid snap removal of the impression in a direction as nearly // as possible to the long axes of the teeth. - Permanent deformation. - Tear strength.  Time is required to allow for the gradual recovery of the anelastic recovery 20-30 minutes before pouring the model.  Types: 1. Hydrocolloids.[Aqueous elastic impression materials] 2. Rubbers [Elastomers][ Non aqueous elastic impression materials] 52
    • 53. 53
    • 54. Hydrocolloids[Aqueous Elastic Impression Materials]  Definition:  Hydrocolloids are considered type of 2 phase system. -Dispersed phase [Solute] & Dispersion medium.[Solvent] Water Hydrocolloids  Difference between : 54
    • 55. Hydrocolloids [Aqueous Elastic Impression Materials]  States of hydrocolloids: Sol [Viscous liquid] Gelation Gel [Jelly like material]  Types of hydrocolloids: Reduction in temperature Chemical reaction Agar [Reversible hydrocolloid] Alginate [Irreversible hydrocolloid] Both are introduced in the sol form intra-orally. They are removed in the gel form from the patient’s mouth. 55
    • 56. Hydrocolloids[Aqueous Elastic Impression Materials]  Structure of hydrocolloid gel: Gelation occurs by the agglomeration of the dispersed phase [Solute] to form fibrils in a network pattern enclosing water in-between.[Brush heap structure] This is accompanied by: - slight shrinkage. -Exudation of water. Filler H2O Fibrils 56
    • 57. Hydrocolloids [Aqueous Elastic Impression Materials]  Factors affecting gel strength: 1. Concentration of fibrils. 2. Concentration of fillers. 3. Temperature.  N.B. Hydrocolloids are of poor tear strength. .·. - Use in thick section.[4-6mm] - Rapid snap removal. 57
    • 58. Hydrocolloids [Aqueous Elastic Impression Materials]  Dimensional stability:  Being hydrocolloid Poor dimensional stability 58
    • 59. Agar[Reversible]  Supplied form:[Gel] 1. Sealed container. 2. Metallic collapsible tubes. [ High viscosity 3. Syringe material.[ Low viscosity Flow] Flow] It is packaged -In plastic or glass cartridges that fit a syringe. - Preloaded syringe. 59
    • 60. Agar[Reversible]  Composition: The gel is composed of:  Agar 12% Dispersed phase.[Natural polymer]  Water 8o% Dispersion medium. Viscosity.  Borax Filler to control Strength. but acts as retarder for the setting of gypsum model.  Potassium sulfate Accelerator for the setting of gypsum model. 60
    • 61. Agar[Reversible]  Gelation reaction:  It is a physical reaction.[Reversible] Sol 70 - 100ºC Gel. 37 -45ºC  Hysteresis: It is the temperature lag between the liquefaction & gelation temperature, otherwise - Gelation will be rapid. - There will be thermal injury to the patient’s tissues. 61
    • 62. Agar[Reversible]  Manipulation:  Agar needs special armamentarium. 1.Heating & Conditioning Bath: 1st Compartment:[Boiling] Gel Sol. 2nd Compartment:[Storage] Store agar in the sol state until use. 3rd Compartment:[Tempering] Temper agar to avoid thermal injury of the patient. 62
    • 63. Agar[Reversible]  Manipulation: 2. Use of water cooling system tray with means of retention. [Perforated] 3. Avoid - Iced water Concentration of stresses. -Exerting pressure on the tray after insertion. - Moving the tray during gelation.  Application as -Full & quadrant impression for partially or completely edentulous patients. - Duplication material. 63
    • 64. Alginate[Irreversible]  Supplied form: Powder in -Bulk container. -Preweighed package for individual impression.  N.B. Preweighed package is preferable than large container, because alginate is very sensitive to storage temperature & moisture contamination.[Poor shelf life]  Precautions during storage: 1. Stock only for 1 year. 2. Store in cool dry place. 64
    • 65. Alginate[Irreversible] Composition : Action:  Sodium or Potassium alginate  Soluble salt.[Natural polymer] 12%  Calcium sulfate dihydrate 12%  To release Ca++ to react with alginate. [Reactor]  Trisodium phosphate 2%  Retarder .  Filler Viscosity  To control Strength  Fluoride  Accelerator for the setting of gypsum model.  Glycol  Decrease dust formation.  Chemical indicators  To indicate the pH changes during manipulation. 65
    • 66. Alginate[Irreversible]  Gelation reaction: It occurs by chemical reaction.[Irreversible] It occurs in 2 steps: - Retardation reaction:[To prolong the working time] Trisodium phosphate + Calcium sulphate dihydrate +H2O Calcium phosphate + Sodium sulphate. - Gelation reaction: Potassium alginate + Calcium sulphate dihydrate Calcium alginate [gel] +H2O + Potassium sulphate 66
    • 67. Alginate[Irreversible]  The gel structure: The final structure sodium alginate cross-linked with calcium ions.  Types: Cross-linking of Sodium alginate According to the amount of Trisodium phosphate [Retarder] -Regular set -Fast set [Less amount of retarder] 67
    • 68. Alginate[Irreversible]  Manipulation:  Armamentarium: -Rubber bowl & stiff wide bladed Stainless Steel spatula. - Perforated stock tray for retention.  Steps: 1. Proportioning for powder & water. 2. Vigorous mixing against the sides of the rubber bowl [Sol] Mixing time: 1 minute [Regular set] 45 seconds [Fast set] 3. Gelation time: 1.5-5 minutes from the start of the mix till the material looses tackiness.[Sol Gel] 4. Avoid -Iced water for mixing. -Exerting pressure on the tray after mixing. -Moving the tray during gelation. 68
    • 69. Alginate [Irreversible] Manipulation:  The pH changes during gelation 69
    • 70. Alginate [Irreversible]  Manipulation:  Application: 1. 2. 3. 4. 5. Alginate is the most frequently used impression material: Easy to use & to mix. Does not require special equipment. Fast setting. Acceptable by the patient. Low price. 70
    • 71. Agar & Alginate  Properties: 1. Flow: Hydrophilic. Since the dispersion medium is water, they are High flow. .·. Excellent in recording fine details. 2. Dimensional accuracy during setting: Slight shrinkage during gelation due to agglomeration of the dispersed phase. 3. Adhesion to the tray Not adhesive to the tray. Need for mechanical retention. e.g. Perforations. 4. Flexibility for ease of removal from undercut: Flexible Agar< Alginate [Most flexible elastic impression material] 71
    • 72. Agar & Alginate  Properties: 5. Elasticity: Viscoelastic. Record the undercut. .·. No torque or twist during removal of the impression. Rapid snap removal Permanent deformation [Agar<Alginate] Allow for gradual recovery 20-30 minutes before pouring the model. 6. Tear strength: Low tear strength. .·. –Use thick section. [4-6mm] - Rapid snap removal. 72
    • 73. Agar & Alginate  Properties: 7. Disinfection without loosing accuracy: Can be disinfected only by spraying for <10 minutes due to their hydrophilic nature .[Otherwise imbibition will occur] 8. Dimensional stability during storage: During storage they are subjected to synersis & imbibition. .·.- Pour the model as soon as possible.[ After the anelastic recovery] - Keep the impression in a humidor .[100%relative humidity] - Wrap the impression in wet paper towel. 73
    • 74. Agar & Alginate  Properties: 9. Compatibility with model materials: a. Being hydrophilic , the gypsum model can be poured without air pockets. b. Compatible No need for separating medium. .·. Easy separation if the impression is not left overnight. c. Retarding effect on the model surface Chalky soft surface. .·. Accelerator for the setting of the gypsum model is included in the material. d. Can not be electroplated due to their hydrophilic nature.[Otherwise imbibition will occur] 74
    • 75. 75
    • 76. Rubbers[Elastomers]  Definition: Synthetic rubbers are introduced in dentistry after World War II, due to scarce in natural sources. They are coiled slightly crosslinked polymer chains above their glass transition temperature.  Behavior: On stretching , the chains uncoil. On stress removal, they snap back to their original coiled condition. .·. High elastic recovery. 76
    • 77. Rubbers[Elastomers]  Delivery system: Rubbers are two component chemically setting materials. They are delivered as two pastes.  Types: I- According to chemistry: 1. Polysulphide. 2. Silicones[Condensation &Addition] 3. Polyether. 77
    • 78. Rubbers[Elastomers]  Types: II- According to consistency: Each material can be supplied in different consistencies according to % of filler: 1. Light body or syringe consistency. 2. Medium body or regular consistency.[Special tray + Adhesive] 3. Heavy body or tray consistency. Perforated stock tray. 4. Very heavy body or putty consistency. 5. Mono-phase: It is associated with shear thinning .[Pseudo-plasticity] It can be used both as syringe & tray material. There is * Low viscosity with high shear stress.[mixing or syringing] *High viscosity at low stress as when inserted in the tray. 78
    • 79. Rubbers[Elastomers] Types: II-According to consistency: Purpose: To provide different impression techniques for better accuracy. 79
    • 80. Rubbers[Elastomers]  Polymerization reaction: Synthetic liquid prepolymer + Catalyst Condensation Crosslinked Polymer Addition During polymerization there will be: 1. Chain lengthening. 2. Crosslinking. 3. Polymerization shrinkage. 4. Heat evolution. 5. Residual monomer. N.B.: After clinical set of the material; the polymerization reaction continues for 24 hours. 80
    • 81. Rubbers[Elastomers]  Manipulation: Polyether, Polyvinylsiloxane Polysulfide Rubber, Silicone Rubber Mixing Options:  2 Pastes on Mixing Pad  2 Pastes in Mixing Gun  2 Pastes in Mixing Machine Manual mixing Auto-mixing gun by manually expressing the 2 pastes through a kenics mixing tip 2x2x2x2x2x2x2x2 = 256 folds Mixing equipment with electrically driven pumps for proportioning of 2 pastes from larger tubes through a kenics mixing tip 81
    • 82. Rubbers[Elastomers]  Manipulation:  The type of mixing technology depends on the rheological behavior of the mix. 1. Newtonian flow 2. Dilatant flow Polysulphide. Condensation silicone. 3. Pseudo-plastic flow [ Shear thinning] They are hard to mix through mixing tip. .·. They are mixed manually. Addition silicone. Polyether. - A typical kenics mixing tip consists of a series of connected mixing paddles[ Alpha helixes with alternating rotations] that split & fold the mixing stream to get homogenous mix in less than one second. [8 paddles =28 =256 times] 82
    • 83. Rubbers[Elastomers]  Manipulation:  Advantages of automatic mixing: 1. Uniform dispensing of base & catalyst. 2. More homogenous mixing Uniform polymerization Less permanent deformation on removal. 3. Less waste. 83
    • 84. Rubbers[Elastomers]  Applications: 1. 2. 3. 4. They are impression materials for: Fixed partial dentures.[Crown + Bridge] Removable dentures.[Partial + Complete dentures] Impressions for implants. Duplicating materials for refractory casts. 84
    • 85. Polysulphide  Introduction to dentistry: It is introduced ~1950.  Supplied form: -Two pastes of contrast color in equal sized metallic collapsible tubes. - It is present in different consistencies.[Light-Regular-Heavy]  Shelf life: 2 years.  Price: Inexpensive compared to other rubbers. 85
    • 86. Polysulphide  Composition: Base paste: [Offensive odor]  Polysulphide prepolymer with terminal & pendant mercaptan [SH] group.  Filler % according to consistency. Catalyst paste: [Characteristic staining brown color + Toxic]  Lead dioxide.  Or Organic hydro-peroxide to eliminate the staining brown color.[Green mix] Alternative names: Rubber Base. Thiokol. [As it is derived from thiols ,which are sulfur analogues of the alcohol] Mercaptan. 86
    • 87. Polysulfide  Condensation polymerization: Pb S H O H S = = Pb HSO - -S-S---------------S-S- = HS--------------------O SH = --SH O = Pb = O Mercaptan + Lead dioxide O S + 3PbO + H O 2 S Polysulfide rubber + Lead oxide + Water  N.B. : -Exothermic 3-4ºC -.·.Thermal shrinkage -Polymerization shrinkage . -Longest setting time~12minutes among the elastic impression materials.[Patient discomfort] - Sensitive to heat & moisture. 87
    • 88. Polysulphide  Manipulation : 1 2 3 4 -A s polysulphide is dilatant *The mix is viscous. *it is difficult to mix with auto-mix gun or equipment. -Only manual mixing can be performed to be loaded in the syringe or special acrylic resin tray with adhesive. - Single pour is only recommended. 88
    • 89. Silicones  Introduction to dentistry: Silicones overcome the disadvantages of polysulphide: 1. Bad odor. 2. Messy & stains clothes permanently. 3. Effort during mixing. 4. Long setting time. 5. High curing shrinkage. 6. High permanent deformation.  Types: Based on the type of polymerization reaction: -Condensation silicones.[1960] - Addition silicones. [1975] 89
    • 90. Condensation Silicone  Supplied form: - Two pastes of contrast color in unequal sized metallic collapsible tubes. - One paste in jar & liquid.[ Putty form] - It is present in different consistencies: *Light *Very heavy [Putty]  Shelf life: Limited shelf life [1 year] due to unstable nature of the catalyst. [Oxidation]  Cost: Relatively expensive. 90
    • 91. Condensation Silicone  Composition: Base paste:[Large tube] Catalyst:[ Small tube]  Siloxane prepolymer with  Tin octoate. terminal hydroxyl group.  Filler % according to consistency.  Orthoalkyl silicate Cross-linking  Alternative name: Conventional Silicone. 91
    • 92. Condensation Silicone  Condensation polymerization: Ethanol N.B.: -Exothermic 1ºC. .·.Thermal shrinkage. -Polymerization shrinkage. - Less setting time than polysulphide. - Less sensitive than polysulphide to heat & moisture. 92
    • 93. Condensation Silicone  Manipulation: - As condensation silicones is dilatant; .·. Manual mixing is only available. -For the 2 paste system: 2 equal lengths of base & catalyst on oil resistant paper pad…… - For the paste & liquid system: Dispense given volume of paste by scoop with definite amount of drops per scoop…… N.B.: - Direct skin contact should be avoided to prevent allergic reaction. -The difference in the viscosity of base & catalyst may lead to improper proportioning, mixing & polymerization. 93
    • 94. Addition Silicone  Supplied form: -2 pastes of contrast colors in jar &metallic collapsible tube. -2 pastes of contrast colors in unequal-sized metallic collapsible tubes. -2 pastes of contrast colors in equal-sized jars. - 2 pastes of in double barreled cartridges for use in auto-mix gun 94
    • 95. Addition Silicone  Supplied form: The pastes are present in different consistencies: 1. Light body or syringe consistency. 2. Medium body or regular consistency. 3. Heavy body or tray consistency. 4. Very heavy body or putty consistency. 5. Mono-phase: It is associated with shear thinning .[Pseudo-plasticity] It can be used both as syringe & tray material. There is *Low viscosity with high shear stress.[mixing or syringing] * High viscosity at low stress as when inserted in the tray.  Shelf life: 2years.  Cost: Expensive 95
    • 96. Addition Silicone Composition: Base paste: Catalyst paste:  Siloxane prepolymer with  Siloxane prepolymer with silane group.  Filler % according to consistency. vinyl terminal group.  Chloroplatinic acid. Alternative name: Polyvinylsiloxane 96
    • 97. Addition Silicone  Addition polymerization:[No byproducts]  N.B.: - Exothermic 1º C. .·. Thermal shrinkage. - Polymerization shrinkage. - Sulfur compounds ,present in Latex gloves, inhibit the polymerization . .·. Use vinyl gloves. -Ferric & aluminum sulfate in retraction solution inhibit polymerization. .·. Don’t use it. - Short setting time. 97
    • 98. Addition Silicone  Manipulation: 1. Manual mixing. [As mentioned earlier] 2. Mechanical mixing.[As mentioned earlier] N.B.: Multiple pouring is only advisable with addition silicone. Why? 98
    • 99. Polyether  Introduction to dentistry: Polyether is introduced to dentistry in the late 1960s in Germany.  Supplied form: It is supplied as 2pastes of contrast color in unequal sized metallic collapsible tubes. It is present in different consistencies: 1. Light body or syringe consistency. 2. Medium body or regular consistency. 3. Heavy body or tray consistency. 4. Mono-phase: It is associated with shear thinning .[Pseudo-plasticity] It can be used both as syringe & tray material. There is *Low viscosity with high shear stress.[mixing or syringing] * High viscosity at low stress as when inserted in the tray. 99
    • 100. Polyether  Shelf life: Excellent more than 2years.  Cost: Very expensive. 100
    • 101. Polyether  Composition: Base paste [Bitter taste] Catalyst paste  Polyether prepolymer with  Sulphonate ester terminal ethylene imine group.  Filler % according to consistency. It may cause allergic reaction. 101
    • 102. Polyether  Cationic polymerization:[Ring opening polymerization]  N.B.: - Exothermic ~4ºC .·. Thermal shrinkage - Polymerization shrinkage. Ring opening offset some of the polymerization shrinkage. - Shortest setting time among the elastic impression materials. 102
    • 103. Polyether  Manipulation: 1. Manual mixing. [As mentioned previously] 2. Mechanical mixing. [As mentioned previously] N.B.: - As polyether is of low flexibility [Stiff], it is better not indicated for: • Full arch impression. .·. Quadrant arch or single impression is recommended • When FPD is present . 103
    • 104. Rubbers[Elastomers]  Properties: 1. Flow: a. * Polysulphide & condensation silicone are hydrophobic. .·. Dry & clean oral field is recommended to allow for better flow & & adaptation of the impression material. * Addition silicone is extremely hydrophobic. .·. Surfactant should be added contact angle between the impression & the surface. Better wetting. Hydrophilized addition silicone. 104
    • 105. Rubbers[Elastomers]  Properties: 1. F low: a. *Polyether is hydrophilic [As it contains ethylene oxide unit] Better wetting & adaptation. b. Consistency: Light Regular Heavy Very heavy 105
    • 106. Rubbers[Elastomers]  Properties: 2. Dimensional accuracy during setting: All rubbers suffer from polymerization shrinkage. Solutions:[ Polymerization shrinkage] *Proper adhesion of the impression to the tray, as shrinkage will be directed to the tray & not centrally. *Use minimum thickness 2-3mm . [Except hydrophilic addition silicone & polyether.] 106
    • 107. Rubbers[Elastomers]  Properties: 2. Dimensional accuracy during setting: *Use 2 different cosistencies: -Use light consistency material [ Filler Flow Shrinkage] to wet the preparation . -Then use high consistency of the same material [ Filler Flow Shrinkage] in perforated stock tray to make up most of the bulk of the rest of the impression. -Both materials will cure simultaneously during polymerization. 107
    • 108. Rubbers[Elastomers]  Properties: 2.Dimensional accuracy during setting: Solutions:[ Polymerization shrinkage] *Use 2 step technique: 108
    • 109. Rubbers[Elastomers]  Properties: 3. Adhesion to the tray: - All rubbers are not self adhesive to the tray. - .·. Perforations or adhesives are recommended. -The adhesives of the different rubbers should not be used interchangeably. -The adhesive should be - thin. - dry before loading the tray. 4. Flexibility for ease of removal from undercut : -Polysulphide is the most flexible one among the rubbers. -Silicones are less flexible than polysulphide. - Hydrophilic addition silicone & polyether are of low flexibility.[Stiff] .·. Use them in thick section ~4mm to facilitate removal without tearing. 109
    • 110. Rubbers[Elastomers]  Properties: 5. Elasticity: - All rubbers are viscoelastic. They record the undercut with some permanent deformation. The highest elastic recovery in all elastic materials 110
    • 111. Rubbers[Elastomers]  Properties: 5. Elasticity: -.·. No torque or twist during removal of the impression. - Rapid snap removal Permanent deformation - Allow for gradual recovery 20-30 minutes before pouring the model. 6. Tear resistance: -All rubbers have high tear resistance. - Polysulphide>Addition Silicone>Condensation Silicone>Polyether. - However rapid snap removal improves more their tear resistance. 111
    • 112. Rubbers[Elastomers]  Properties: 7. Disinfection without loosing accuracy: - All rubbers except Polyether can be disinfected by immersion for not less than 3o minutes without loosing accuracy. - Polyether should be disinfected by spraying for<10 minutes due to its hydrophilic nature.[Otherwise imbibition will occur] 8. Dimensional stability during storage: -Polymerization reaction is never complete. It continues for at least 24 hours after clinical set More shrinkage. - All rubbers have high coefficient of thermal expansion. .·. They undergo thermal shrinkage. 112
    • 113. Rubbers[Elastomers]  Properties: 8. Dimensional stability during storage: Immediate pouring is recommended after the gradual recovery [within1hour] Most dimensional stable impression material. No definite time for pouring. 113
    • 114. Rubbers[Elastomers]  Properties: 9. Compatibility with model materials: a. Rubbers are compatible with the gypsum model. b. No separating medium is required. c. Since Polysulphide, Condensation Silicone & Addition silicone are hydrophobic, dry clean field is required for proper wetting & adaption of the gypsum mix in the impression. d. It is easier to pour gypsum models in hydrophilized addition silicone & polyether due to their better wet-ability. e. Easy separation. f. Rubbers can be silver electroplated except: - Hydrophilized addition silicone, as metalizing powder can not adhere to its surface. - Polyether, as its hydrophilic nature may cause imbibition. 114
    • 115. Rubbers[Elastomers]  Properties: 9. Compatibility with model materials: g. If proper balance between the two polymers in addition silicone is not maintained ,2ndry reaction will occur Evolution of hydrogen gas. Bubbles on the surface of impression. Pitting of the model Solution: -Wait not less than 1 - 4hours before pouring the model until the evolution of hydrogen gas is finished. - Manufacturer adds Palladium to absorb hydrogen gas. 115
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