Elastomeric Impression Materials

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    23-Nov-2014

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<p>Elastomeric Impression MaterialsSeminar by Dr. Anuradha .G.MohiteGuided by Dr. Smita Athavale1ontents W lnLroducLlonW ueflnlLlon ob[ecLlves Cf lmpresslon MaklnaW ClasslflcaLlon of uenLal lmpresslon MaLerlalsW ldeal requlremenLs of lmpresslon maLerlalsW 1vpes of LlasLomerlclmpresslon MaLerlalsW varlous ConslsLencles Cf LlasLomerlc lmpresslon MaLerlalsW Making Impressions with Elastomeric materials.2ontents W ompositions and Reactions oI Elastomeric materials.W Properties oI Elastomeric materials.W DisinIection OI impressions. W Failures In impressions Making.W onclusion W ReIerences 3IntroductionElastomers reIer to a group oI rubberypolymers, which are chemically or physically cross-linked. They can be easily stretched and rapidly recover their original dimensions when applied stress is released.4ImpressionW DeIinition : Impressions are negative reproduction oI oral structures.3Obiectives oI impression makingW To providea. support,b. retention,c. stability,d. Ioundation oI improved appearance oI lips,e. maintain the health oI tissues.W The impression should record all the potential denture-bearing surIaces available6lassiIication oI dental impression materials.By elasticity and useInelastic or rigid ElasticMaterial use MaterialUse By setting Mechanismhemicalreaction (irreversible)Plaster oI parisZinc oxide eugenolEdentulous ridgeInteroccusalrecords.Alginate,Nonaqueouselastomers. Teeth and soIttissues.Thermallyinduced physical reaction (reversible) ompound wax Preliminary impressionAgarTeeth and soIttissues.7Ideal Requirements oI impression materials 1. Adequate Ilow properties,2. Ease oI manipulation,3. Appropriate working and setting times,4. SuIIicient mechanical strength,5. Good dimensional accuracy,6. Acceptability by the patient,7. Biocompatible,8. ost-eIIective.8Types oI Elastomeric Materials W PolysulIides (1950) : 1stmaterial introducedW ondensation Silicones (1955)W Polyether (1965)W Addition Silicones (1975)9onsistencies W Light body : used with a syringe and placed directly on hard and soIt tissues,W Medium body : preparation oI custom tray required to support this material,W Heavy body : placed in the tray to support the light-body material,W Putty : useIul Ior materials that exhibit signiIicant polymerization shrinkage.10onsistencies Elastomeric material are supplied in several consistencies.W PolysulIides :a. low/light ( syringe or wash )b. medium ( regular )c. high/heavy ( tray )11onsistencies W ondensation Silicones :a. low/lightb. putty/heavyW Addition Silicones : a. plus extra lowb. monophasec. putty (extra high)12onsistencies W Polyether : Previously available as medium but now available as, a. low/lightb. mediumc. high/heavy13Making an impression with elastomeric materialW 5 steps are included in Iabricating models, casts and dies Irom elastomeric materials.1. Preparing a tray,2. Preparing the material,3. Making an impression,4. Removing the impression,5. Preparing stone, casts and dies.14Preparing a tray The use oI a custom tray reduce the quantity oI the materials used tomake impressions,any dimensional changes oI the materialscan be minimized.W Particularly true Ior PolysulIides.W Adhesion oI impression material to the tray is essential.13Preparing a tray W The use oI custom trays not so critical Ior addition silicone &amp; polyether as thesematerials arestiIIer and have lesspolymerization shrinkage.W Disposable stock trays works satisIactory.W Tray adhesives is also needed Ior stock trays.16Preparing the materialMixing systems:W 3 systems available Ior mixing atalyst and Base paste:1. Hand mixing,2. Static automixing,3. Dynamic mechanical mixing.17Preparing the materialW Hand mixing: Equal lengths oI catalyst and base, Initial mixing circular motion, Final mixbroad strokes, Mixing completed in 45 seconds. Hand mixing is available Ior all 4 types oI elastomeric materials.18Hand mixingW ManlpulaLlon 8ase AcceleraLor on mlxlna padMlxlna of Lhe base AcceleraLor wlLh a Lapered sLlff bladed spaLulaPreparing the materialW Two putty system variation in hand mixing. Available with condensation and addition silicone. Scoops available Ior dispensing, Putties kneaded with Iingers until Iree Irom streaks.20Preparing the materialW Static automixing: Base and atalyst supplied in separate cylinders oI the plastic cartridge. artridge placed in mixing gun containing 2 plungers advanced by ratchet mechanism to extrude equal quantities oI base and catalyst. UniIorm mix is obtained21Preparing the materialW Static automixing:W Advantage : 1. Fewer voids than hand mixing,2. 3 to 4 times less material wasted than hand mixing,3. Less air incorporated in mix,4. Mixing time is reduced,5. less contamination oI the material 22Preparing the materialW Automixing guns and mixing tips available Ior all consistencies except putty.W Addition silicone, condensation silicone and polyethers available with this type oI mixing.23Automatic mixing gunPreparing the materialW Dynamic mechanical mixing: atalyst and base supplied inlarge plastic bags housed in a cartridge which is inserted into the top oI the mixing machine. When button is depressed, parallel plungers push against collapsible bags thereby opening the bags and Iorcing material into the dynamic mixing tip. mixing is accomplanished by rotation plus Iorward motion oI the material since internal spiral is motor driven.23Preparing the materialW Dynamic mechanical mixing:W Advantages: ease oI use, speed, thoroughness oI mixing and higher viscosity materials can be mixed with ease.W Disadvantage : costly and more material wasted than automixing but less than hand mixing.W Polyether and Addition silicone available with this system.26Impression making Impression techniques: W 3 common methods Ior impression making:1. Simultaneous, dual-viscosity technique,2. Single-viscosity or monophase technique,3. Putty-wash technique.27Impression making W Simultaneous, dual viscosity technique: Low consistency material is iniected with a syringe into critical areas. High consistency material is mixed, placed in an impression tray and inserted in the mouth The more viscous tray material Iorces the lower viscosity material to Ilow into Iine aspects The materials ioin, bond and set together 28Impression making W Single viscosity or monophase technique: Impression taken with medium viscosity material. Addition silicone and polyether can be used with this technique because they have a capacity Ior shear-thinning. When medium viscosity material is Iorced through impression syringe, the viscosity is reduced, whereas viscosity oI material in tray is unaIIected.29Impression making W Putty wash technique: Two approaches used-- two stage and one stage procedures.Two stage procedure: Preliminary impression taken in putty consistency material beIore the preparing the teeth. Space is provided Ior low consistency material in the impression. Low consistency material is syringed into the impression and the preliminary impression is re-inserted.30Impression making W Putty wash technique:Single stage procedure: Wash material is syringed into place Unset putty is seated over the light body material Occlusal stops are provided in the tray to avoid pushing through the wash material when seating putty mass.31Impression making W Low and high consistency material bond and aIter the low consistency material sets, impression is removed.W Putty consistency and this technique was developed Ior condensation silicone to minimize eIIects oI dimensional change during polymerization.W It can also be used Ior addition silicone.32Removing the impressionW Impression should not be removed until curing has progressed to the extent to provide adequate elasticity so that distortion will not occur.W Typically, impression should be ready Ior within atleast 10 mins Irom time oI mixing, allowing 6 to 8 mins Ior the impression to remain in the mouth.W All elastomeric materials are viscoelastic and it is necessary to use a quick snap to minimize plastic deIormation oI the impression during removal. 33Preparing stone casts and diesW All elastomeric materials are compatible with all types oI gypsum products.W The excellent dimensional stability oI addition silicone and polyether materials makes it possible to construct 2 or 3 casts or dies Irom these materials but time interval should not be greater than 30 mins.34PolysulIideW PolysulIides: First rubber impression materials.W Available in 3 consistencies:1.low(syringe orwash),2. medium(regular), 3.high(tray)33ComposlLlon Base paste: 1.PolysulIide polymer,2. Filler (e.g,lithoponeor titanium dioxide)- Ior strength,3. Plasticizer-appropriate viscosity to paste,4. SulIur (0.5)-AcceleratorW atalyst paste:1. Lead oxide,2. Same Iiller andplasticizer as basepaste, 3. Alongwith oleic acid or stearic acid-- retarder.361vpes of polvsulphlde maLerlalsllahLreaular heavv bodledPolysulIideW Setting reaction: Main component: MultiIunctional Mercaptan(--SH) or polysulIide polymer. Lead dioxide ( oxidizing agent)PolysulIide Water( byproduct )38PolysulIideW The reaction results in a rapid increase in the molecular weight , converting the mixed paste to a polysulIide rubber.W The reaction is slightly exothermic- increase in temperature oI 3 to 4 degree.W Lead dioxide- gives characteristic Brown color.39Mechanical properties W Elastic recovery 96 , W Flow 0.4 to 1.9 , indicating tendency to distortW Least stiII W High Ilexibility, advantage over silicones and polyether is that removal Irom undercuts is easier40PolysulIideW Advantages:1. Long working time,2. High tear strength,3. High Ilexibility Ior easier removal Irom undercuts,4. Good Ilow beIore setting,5. Good reproduction oI surIace detailW Disadvantages:1. Requires custom tray due to greater chance oI distortion,2. Stretching leads to distortion,3. Obnoxious odor,4. Pour within 1 hour,41ondensation SiliconeW ondensation Silicones are supplied as1. Low2. PuttyThe catalyst oI the ondensation Silicone can be supplied as putty or a liquid 42ondensation SiliconeW Base paste:1.Polydimethyl siloxane(which has reactive terminal -OH groups),2.Orthoalkylsilicate(Ior cross-linking)3.Fillers- calcium carbonate or silica (Irom 35 Ior low consistencies to 75 Ior puttylike consistencies).W atalyst paste:(low viscosity liquid or paste catalyst)1. liquid consisting oI stannous octoatesuspension and alkyl silicate.43CondensaLlon Slllcone havlna low conslsLencles puLLvllke conslsLencvSetting reactionW Reaction produces a 3 dimensional network with the liberation oIEthyl alcohol as a byproduct and exothermic rise in temperature oI about 1 degree.W Polydimethyl siloxane Tetraethyl orthosilicate Stannous octoateSilicone rubber Ethyl alcohol ( byproduct)43ondensation SiliconeW Evaporation oI Ethyl Alcohol (byproduct) causes polymerization shrinkage oI the silicone rubber impression.W This shrinkage was more in low consistency silicone , thereIore, to overcome the large shrinkage a high viscosity material reIerred as'Putty was developed.W These putties have more Iillers and less polymer so they have less shrinkage. 46Mechanical properties W Excellent elastic recovery oI 99W Low Ilow, less than 0.1, thus, less distortion is likely to be caused by light pressure on standing.W StiIIer than polysulIides because oI lower Ilexibility valuesW Greater shrinkage than polysulIide and polyether0.2 to 1 because oI release oI alcohol byproduct.47ondensation SiliconeAdvantages :1. lean and pleasant,2. Putty Ior tray,3. Good working time,4. Highly elastic and the setting time can be controlled with the amount oI accelerator.Disadvantages:1. High polymerization shrinkage,2. Volatile by-product,3. Low tear strength,4. Hydrophobic,5. Pour immediately.48PolyetherW Polyether was introduced in Germany in the late 1960`sW Available in: 1. low2. medium3. heavy 49PolyetherW Base paste:1. Polyether polymer with ethylene-imineterminal groups,2. Filler- colloidal silica,3. Plasticizer -glycolether or phthalate.W atalyst paste:1. Alkyl-aromatic sulIonate,2. Filler,3. Plasticizer.30olveLher MaLerlalsSetting reactionW Polyether Aromatic sulIonate ester(initiator) ross-linked polyether rubber.32PolyetherW The main chain is a copolymer Ethylene oxide and TetrahydroIuran.W The cross linking is produced by polymerization via the imine end groups.33Mechanical propertiesW 0.3 shrinkage in 24 hrs, thus good accuracy but inIerior to addition silicones,W Since polyether absorbs water and changes its dimensions, storage in water is not recommended.W Elastic recovery is between polysulIides and addition silicones 98.5W Flow is very low and thus, contributes to accuracyW Low Ilexibility i.e high stiIIness; it may cause problems in removal oI impression Irom mouth or the die Irom impression. 34PolyetherW Advantages:1. lean,2. Ease oI mixing,3. Good surIace detail reproduction,4. Least hydrophobic,5. Good stability,6. Delay pour.W Disadvantages:1. Short working and setting times,2. High stiIIness aIter setting, 3. Bitter taste,4. Needs to block undercuts,5. Leaches components,6. High cost.33Addition silicone W Frequently called as Polyvinyl siloxane or vinyl polysiloxane impression materialsW Available in : a. extra lowb. low/lightc. medium d. heavye. extra heavy.36omposition W Base paste:1.Polymethyl hydrogen siloxane (low molecular weight polymer) , 2.Hybrid silicone and 3.Fillers.W atalyst paste:1.Divinyl polydimethylsiloxane , 2.Platinium salt activator (chloroplatinic acid)and 3.Fillers (Retarders may also be present.)37Setting reactionW Polymethyl hydrogen siloxane divinylpolydimethyl siloxane platinium salt activatorSilicone rubber. W No reaction by-products.38Addition silicone W However, a secondary reaction between moisture and residual hydrides oI the base polymer can lead to the development oI hydrogen gas that can result in pinpoint voids in the gypsum casts that are poured immediatelyW ThereIore, Platinium or Palladium is added to act as a scavenger Ior the released hydrogen gas or to wait 30 mins or more Ior pouring the impression.39Addition silicone W SulIur contamination Irom latex gloves have been shown to inhibit the setting oI addition silicone. These compounds can contaminate platinium containing catalyst which results in retarded or no polymerization.W Instead Vinyl or Nitrile gloves can be used.60Addition SiliconeW Disadvantage oI this material is their inherent hydrophobic nature.W Distortion at the impression margins is caused by undetected moisture in the area to be replicated.W A Nonionic surIactant is added to make surIace oI impression hydrophilic.W This will allow impressionmaterial to readily wet soIt tissues and capture maximum details.61Mechanical propertiesW Working and setting time Iaster than polysulIides. Retarder is oIten supplied to extend working time.W Excellent elasticity and very low dimensional shrinkage upon storage, thus can be poured up later.W Greater rigidity, hence, diIIicult to remove Irom undercuts as they have lower Ilexibility valuesW Tear strength less than po...</p>