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Condensation Silicone

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II- Condensation Silicone Polymer: hydroxy-terminated poly (dimethyl siloxane)

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Base Dimethyl siloxane polymer with terminal OH gp Copper carbonate, silica as fillers. Catalyst Stannous octoate + alkyl silicate as Tetra ethyl silicate Reaction silicone rubber + alcohol exothermic 1C Condensation polymerization largest dimensional change. Shrinkage-0.6% Consistencies: only two Lowputty very high Limited shelf life due to oxidation of stannous octoate and ethyl silicate is not stable in presence of tin. +

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Condensation Silicone Base: Polydimethylsiloxanes Fillers (35% to 75%) Accelerator: Stannous octoate Alkyl silicate By-product = ethanol The release of ethanol is greater in the low viscosity materials than the heavy body materials. causes more shrinkage

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SILICONE RUBBER Manipulation and Technique Considerations a. Limited shelf-life: Unstable in tubes. b.Requires mechanical retention or special tray adhesives c.No syneresis or imbibition, but continued polymerization shrinkage. d.Better dimensional stability than RHC but more expensive e.Pouring of models: (1)More flexible so more chance for distortion during removal (2)Wait 20-30 minutes before pour for stress relaxation to occur Has more desirable qualities in comparison to polysulphide: Easy mix & easy to use Better taste and odorless so much more used friendly & much comfortable for the pat ient Shorter setting time (5-7 minutes)

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Addition Silicone

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III- Addition Silicone Base Polymer with silane group * Fillers Catalyst Polymer with vinyl terminal groups *Filler *Chloroplatinic acid

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Reaction: Ionic Polymerization Addition type --- no by products. Addition type --- no by products. If proper balance between two polymers is not maintained 2 ry reaction occurs. Evolution of the hydrogen gas bubbles on surface of impression voids in stone model. bubbles on surface of impression voids in stone model. Manufacturers add finely divided Platinium or palladium to absorb Hydrogen.

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Consistencies: low medium high light regular heavy light regular heavy and a very high (putty). Latex or rubber gloves: containing sulphur cause retarded or no polymerization of addition silicones Use: Vinyl gloves.

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Addition Silicone Polyvinylsiloxane The terminal vinyl groups are crosslinked with hydride groups activated by a platinum salt catalyst.

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POLVINYLSILOXANE Manipulation and Technique Considerations a. BEST impression material for dimensional stability(n0 byproducts): Pouring should be delayed at least 4 hours for H2 out-gassing. Pouring can be delayed up to 7-to-10 days (or indefinitely). b.Stiffness makes removal difficult. c.Most material dispensed using auto-mixing gun and mixing tips d. Expensive material

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Polyether

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IV- Polyethers: Base Polymer with ethylene Imine rings terminal groups. Silica filler plasticizer: glycoether phthalate Catalyst Cross linking agent as dichlorobenzene sulphonate Reaction: Cationic polymerization and opening of the imine rings. Additional polymerization exothermic 4C

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Consistencies: *medium consistency + thinner in a separate tube to viscosity. Recently low and high viscosity. Hydrophilic must not be stored in H 2 O or humid atmosphere. Very short working time 2.5 minutes by thinner Stiff: difficult to remove from the patients mouth and to separate from the cast.

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Polyether Chemistry Aromatic sulfonate ester 2 3 1 Polyether molecule with ethylen imine ring

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POLYETHER RUBBER Manipulation and Technique Considerations a. Excellent impression accuracy and dimensional stability. b.Stiff and therefore difficult to remove without rocking. c.Break seal and rock slightly to prevent tearing: Low tear resistance. d.Negatively affected by H2O, saliva, and blood. (1)Since hydrophobic, moisture increases marginal discrepancy (2)Increased water absorption occurs if use thinning agents e.Can be dispensed from automated extruder and mixer (ESPE PentaMix)

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Properties Setting time Polysulphide: longest S.T 7-10 min. Condensation silicone6-8 min. Addition silicone6-8 min. Polyethers3-4.5 min. W.T and S.T Decreases as viscosity increases from low to high W.T and S.T by in temperature and humidity.

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Double mix technique-single impression Syringe or light bodied material is injected in and around preparation. Heavy body is mixed, inserted in tray and placed over syringed material. Two materials bond, set at about the same time.

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Relining or Putty wash techniques- Double Impression 1 st heavy body is mixed and impression is made before preparation in a stock tray (set alone). Impression is removed from patients mouth. Heavy body act as special tray. Light body is mixed, placed over heavy body, reinserted in patients mouth to record fine details. Impression is placed twice in patients mouth.

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POLYSULFIDE Vs SILICONE Vs POLYETHER

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Dimensional Changes on Setting Addition silicone: smallest change -0.15% Polyethers-0.2% Polysulphides-0.4% Condensation silicone: largest change -0.6%

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Elastic Recovery from Deformation: Addition silicone: shows the best recovery from deformation Condensation silicone. Polyethers Polysulfies shows greatest deformation i.e., poorest recovery. Visco elastic Mechanical properties are time dependent, higher rate of deformation higher tear strength (sudden pull).

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Detail Reproduction: All reproduce 0.02mm wide line except the very high viscosity 0.075mm line. Compatible with gypsum.

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Strain in compression Measure of flexibility. Low consistency more flexible than high consistency. Polyethers highest stiffness Addition silicone Condensation silicone Polysulfides lowest Lowest strain (flexibility) Highest strain

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Shore A Hardness Highest: polyethers. Lowest: polysulfides Hardness and flexibility (strain) affect the force necessary for removal of impression from mouth.

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Tear strength: Tear strength: withstand tearing in thin interproximal areas. Much higher than hydrocolloids 350-700 g/cm. Elastomers: Elastomers: 2000-4000g/cm. Polysulfides: Polysulfides: shows the highest tear strength. But due to high permanent deformation inaccurate impression

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1- Automatic mixing systems (mixing gun).

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Advantages Uniform dispensing of catalyst and base. Fewer bubbles. Less waste than in hand mixed.

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2- Hydrophilic Addition Silicone: Hydrophobic materials has poor wettability: high contact angle: casts with voids (water repellent). In hydrophilic: surfactants (wetting agents) added contact angle, improve wettability, simplify pouring of gypsum models.

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Disadvantage: cannot be electroplated as metallizing powder does not adhere to surface of hydrophilic silicone. 3-Addition Silicone Containing Hydrogen Absorbers So that dies can be poured as soon as desired without bubbles.

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4- Single viscosity (Monophase) addition silicone with sufficient shear thinning qualities So they can be used as both syringe and tray material. Decrease in viscosity at high shear stress as during syringing or mixing, high viscosity at low stress as when inserted in the tray.

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Disinfection of Elastomeric Impression Materials Done by: Immersion Spraying Solutions used : Chlorine: harmful to skin,eye, unpleaseant odour, bleach clothes Aldehyde solutions 2%: suffocating odour irritating to skin Iodine (iodophors 1%) Phenols

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Disinfection of Elastomeric Impression Materials Polysulphide : can be disinfected by immersion up to 30 mins Polyether :should be sprayed < 10min not immersed due to swelling Cond. And Addition silicone are more dimensionally stable even if immersed for long periods

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Impression During setting shrinkage, distortion of impression is toward tray. Dies tend to be oversize and so the casting is oversize. ELASTOMERIC IMPRESSIONS Management of Shrinkage Impression Impression Tray Use 2-step techniques: (a) Light-Heavy Body, OR (b) Wash-Putty Load tray with heavy-bodied IM Cover prep with light-bodied IM from syringe

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Impression Impression Tray IMPRESSION MATERIALS Key Properties Accuracy a.Accuracy = ability to replicate the intraoral surface details. Dimensional Stability b.Dimensional Stability = ability to retain its absolute dimensional size over time. Tear Resistance c.Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.