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Applied Dental Material

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). <br /> 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] <br /> 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. <br />

Impression materials 3 Impression materials 3 Presentation Transcript

  •  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. 1
  • 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. 2
  • 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. 3
  • Rubbers[Elastomers] Types: II-According to consistency: Purpose: To provide different impression techniques for better accuracy. 4
  • 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. 5
  • 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 6
  • 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] 7
  • 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. 8
  • 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. 9
  • 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. 10
  • 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. 11
  • 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. 12
  • 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. 13
  • 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] 14
  • 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. 15
  • 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. 16
  • 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. 17
  • 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. 18
  • 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 19
  • 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 20
  • 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 21
  • 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. 22
  • 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? 23
  • 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. 24
  • Polyether  Shelf life: Excellent more than 2years.  Cost: Very expensive. 25
  • 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. 26
  • 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. 27
  • 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 . 28
  • 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. 29
  • 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 30
  • 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.] 31
  • 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. 32
  • Rubbers[Elastomers]  Properties: 2.Dimensional accuracy during setting: Solutions:[ Polymerization shrinkage] *Use 2 step technique: 33
  • 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. 34
  • 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 35
  • 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. 36
  • 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. 37
  • 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. 38
  • 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. 39
  • 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. 40