Presentation on theme: "Impression materials أحمد عبد العزيز الحسين"— Presentation transcript:
1 Impression materials أحمد عبد العزيز الحسين أخصائي تركيبات سنيه في وزارة الصحة الأردنيةمحاضر غير متفرغ في جامعة العلوم والتكنولوجيا الأردنيةAhmad Abdul Aziz AlhussienProsthodontist at M.O.HPart time lecturer at J.U.S.TBSc , MSc, Jor. Board/ prosthodontics
2 The function of an impression material is to make a negative copy of the oral tissue … that is poured to produce a positive replica for these tissues
3 Requirement of an impression material Must be a semi-liquid material that will flow and adapt itself around the structure of interest.It must set and harden into a solid ?? that is rigid enough “not too rigid” to be removed from the mouth without becoming deformed.Copy details accuratelyDimensional stability after removal from the mouthAppropriate working time (from the start of mix)Appropriate time to harden in the mouth (setting time)Bio-compatibility/Aesthetic, odor/tasteChemically compatible with material used to pour cast or dies
4 Impression traysUsed to carry the impression material into the oral cavityCan bemetal or plasticPerforated or non perforatedfor edentulous or dentatepre-manufactured (stock trays) or custom-made (made in the lab. From resin).Trays need to be rigid enough to support impression material.For impression material to be retained in tray, tray maybe perforated, and adhesive spray can be used to enhance retention.
11 Inelastic impression materials (rigid) Plaster of Paris (Type I gypsum)Dental compound/impression compoundsSoftened by heat and pressed against tissue before it hardens. Thermoplastic softens at 60°C, remains plastic at 45°C and becomes firm at mouth temperature. Used for primary impressionZOE (Zinc oxide eugenol)Other uses ???Impression waxElastic impression materials (non-rigid)HydrocolloidsElastomers (Rubber)
13 HydrocolloidsThe colloid state represents a highly dispersed phase of fine particles within another phase, some where between solution and a suspension.The colloid can exist as a viscous liquid known as a sol or a solid known as gel.If the particles are suspended in water, the suspension is called a hydrocolloid (hydrosol, hydrogelHydrocolloids come in two forms:Reversible agarIrreversible alginate
14 Agar Composition of agar: Material Percentage purpose Agar (seaweed extract)12-15%Colloidal particles as basis of the gelPotassium sulfate1%Ensures set of gypsum materialsBorax0.2%Strengthens gelAlkyl benzoate0.1%Antifungal agentwater85%Dispersing medium for the colloidal suspension
15 PropertiesFlows well and adapts readily to hard and soft tissue contoursAccurate reproduction (hydrophilic nature), however, the impression need to be poured immediately.Need to be stored in 100% humidity for short period of time if not poured immediatelyDistortion is more likely to occur if impression not poured within an hour.
16 Tear strength is not high. If compressed it might rebound if compression is not too sever otherwise deformation occurs.Material suffers from loss or gain of water:Syneresis: a process by which the gel contracts and some of the liquid is squeezed out, forming an exudate on the surface.Evaporation: loss of water which causes the material to shrink, and impression is distorted.Imbibition: uptake of water, this will swell and distort the impression.
17 Clinical applicationThe use of agar requires special equipment consisting of hydrocolloid conditioner (has 3 water bath chambers) and water -cooled tray connected to a rubber hose that delivers water.Usually used in lab for cast duplicationAgar is supplied in two viscosities, thick and thin (depending on the amount of agar).
18 Preparing the material for impression: Gel heated to °C, becomes liquid (sol)Tray and agar syringe are liquefied in 8-12 minutes in boiling water in 1st chamber2nd chamber is used to store the agar at 60-66°C.3rd camber kept at 45-47°C to temper agar before use to prevent burns.Agar exhibits hysteresis, melting at 85 °C and solidifying from °C
19 Alginate Common uses: Inexpensive Easy to manipulate Requires no special equipmentReasonably accurateCommon uses:Diagnostic cast (study model)Preliminary impression for complete denturePartial denture frameworkCustom trays for fluoride or bleaching
20 Composition/setting rxn/ working time MaterialPercentagepurposeNa, K alginate15-20%Basis of the gelCa sulfate dihydrate14-20%Creates irreversible gel with alginatePotassium sulfate10%ensures set of gypsumTrisodium sulfate2%Retarder to control settingDiatomaceous earth55-60%Filler to increase thickness and strength
21 Setting rxn/working time Setting rxn occurs when the powder is mixed with water:Ca sulfate dihydrate + NaAlginate Ca alginateWorking time: total time from start of mixing to the final time at which an impression tray can be fully seated without distortionRegular set: 2-3 minutesFast-set: minutesSetting time: elapsed time from the start of mixing until impression material becomes firm enough to resist permanent deformation.Regular set: 2-5 minutes, Fast set: 1-2 minutes
22 Setting rxn/working time Controlling water temperature shortens or lengthens setting timeChanging P:L has adverse effect on materials property and strengthAllow extra 1-2 minutes, tear strength increases, and rebound from undercuts w/out deformation improves
23 Important considerations to ensure accurate impression 2-4 mm bulk material in traySnap action removal from mouthAllow extra 1-2 minutes after setting to improve tear strengthStored in a moist environment to avoid loss of water and deformationDisinfect in less than 10 minutes to avoid dimensional instability
24 Impression making Fluff powder, wait 30 seconds for the dust to settle Measure powder and water according to manufacturer instructionUse spatula to stir water into powder to mixStir vigorously to create homogenous mix (45 seconds for regular, 30 seconds for fast setting alginate)
25 Tray should cover all anatomical features Utility wax can be added on tray borders to extend its coverageAdhesive spray is used to prevent separation of alginate from tray.Tray is loaded from posterior towards anteriorMoisten and smooth alginatePosterior part of tray is seated first then anterior.*tips to control gag reflex*
28 ElastomersOften called rubber materials since they have properties similar to rubber.Clinical uses:BridgesImplantsPartial dentures complete denturesIndirect esthetic restorations
29 Polymerization reaction Involves formation of long-chain polymers and cross-linking of chainsGeneral properties:Not as sensitive to water as hydrocolloidsHave a certain amount of rebound, the highest is for addition silicon and polyethers, medium for condensation silicon and poorest for PolysulfidesNot wet well by water (hydrophobic) possible solution: surfactants
30 Polysulphides Dispensing & Composition Supplied in two tubes as base and catalyst, equal lengths are mixed. Light, regular, heavy viscositiesChemical composition of base:80% low-molecular-weight organic polymer containing mercaptan reactive groups (-SH), and 20% reinforcing agents: titanium dioxide, silica, zinc sulfideChemical composition of catalyst:Lead dioxide or copper hydroxide
31 Setting reaction Mercaptan + lead dioxide polysulfide+H2O The reaction is sensitive to temperature and moisture so increase in any will accelerate the setting.Also sensitive to correct mixing ratio
32 Uses Crown and bridge impressions Partial and complete denture impressionsClinical considerations when usedUsed with custom traysAllow 2mm thicknessUse tray adhesiveDry field
33 Properties of clinical interest Setting time: 8-14 minutesHigher tear strength than hydrocolloidsAccuracy improves if impression is poured within 30 minutesvery unpleasant taste and odorMessy (orange solvent to remove stains)Can be irritant to oral mucosaFor all these reasons, Polysulfides have been largely replaced by other rubber materials
35 Condensation silicon Developed as alternative to Polysulfides Has more desirable qualities in comparison:Easy mixBetter taste and odorlessShorter setting time (5-7 minutes)
36 Dispensing & Composition Two pastes, base and catalyst.Comes as light, medium, or heavy viscosityBase: dimethylsiloxane + filler (silica)Catalyst: suspension of stannous octoate + alkyl silicate
37 Setting rxnCondensation reaction that produces ethyl alcohol as by product. The alcohol evaporates which causes dimensional instability.The material continues to contract with time, so needs to be poured within minutes.
38 Addition silicon (PVS) Desirable clinical qualities:Dimensional stabilityAccuracyCleanEasy to mixNo foul odor or tastethe most expensive
39 Dispensing & composition Light, regular and heavy viscosities and also puttyDispensed as cartridge with 2 chambers (pastes), or two putty- systemBase: low-molecular-weight silicon with vinyl groups (paste system), or low-molecular-weight silicon with silane hydrogens (putty) + silica fillerCatalyst: chloroplatinic acid
40 Setting rxnPolymerization rxn of chain lengthening and cross-linking with reactive vinyl groups, producing a stable silicon rubber.No ethyl-alcohol by productSome addition silicons produce hydrogen as by product, manufacturers incorporated palladium powder that absorbs hydrogensetting time: 3-7 minutes
41 Impression making techniques Putty/wash techniqueOne stepTwo step
42 PolyethersAlso used for crown and bridge work since they are very accurate and also more hydrophilic than other silicons
43 Dispensing & composition Dispensing same as other rubber materials (2 tubes)In addition it’s supplied in pouches of base and catalyst placed in mechanical mixer.Composition:Base: low- molecular-weight polyether with cation reactive groupCatalyst: aromatic sulfonic acid*clinical tip: mix well to avoid irritation from unmixed catalyst.
44 Properties Stiff, difficult to remove from undercuts Short working and setting timesSetting time 3-5 minutesSensitive to moisture and temperatureMore hydrophilic (must not be stored in water or disinfectant)accurate
46 Impression compound:Impression compound: softens with heat, hardens in the mouth.2 main forms:Cakes (sheets) /low fusingSticks /high fusingClinical uses:Sheets:Primary impression in metal traysTo make custom traysSticks are used for border molding
47 Composition & properties Thermoplastic resin and waxesFillers to reduce flowPlasticizersOrganic acids or oilsPigmentsPropertiesSoftened at 60°C, remains plastic at 45°C, firm at 37°CHeated in water not by flameShould be poured ASAP to avoid distortionFlame used to heat sticks
48 Impression plaster Impression plaster: seldom used Composed of plaster gypsum (Ca hemihydrae)Used for primary impression (high P:L)Scored with a knife in the mouth then removed and reassembled in the lab (distortion?)Wash impressionEasy to useInexpensiveDisadvantages?
49 ZNO eugenolSecondary impression for complete dentures, or wash impression (mucostatic impression)2 tube paste system, different colorsZinc oxide (80%) and fillers, eugenol (15%) with oils, resin, fillers. In addition to chemical accelerator (zinc acetate)Dispensed in 2 equal lengths and mixed to homogenous color forming zinc eugenolateInitial set:3-6 minutes, final set:10 minutesTo accelerate the setting, a drop of water or zinc acetate is added.
50 Properties Brittle, so not suitable for areas with undercut Flows readilyAccurateEugenol can be irritant (burning sensation)Once set, dimensionally stable
51 Impression wax Clinical uses: Preliminary impression for edentulous patientsBite registrationBaseplate wax used to be used for provisional crown and bridge workMelted to correct voids in gypsum casts
52 Disinfection of impressions The disinfectant should be compatible with the impression materials.After taking the impression, it should be rinsed with water, excess water shaken off, and disinfectant sprayed or impression immersed in disinfectantProtective gloves should be wornRinse after disinfection is complete
53 Disinfecting castsMaybe necessary if impression was not properly disinfected, or if immersion of impression adversely affects the impressionCasts should be set and stored for 24 hours before disinfection.Solution used: Na hypochlorite, iodophors.
54 Sterilizing trays Trays should be properly sterilized before use Disposable trays are recommended if appropriateSterilization can be achieved by heated steam, dry heat, chemical vapors
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