Impression Materials

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<p>Guided by Dr.A. Chandrasekar Prof. and Head</p> <p>Presented by G. Mahalakshmi 1st year PG</p> <p>Introduction Definition Ideal impression material Review of literature Inelastic impression materials - impression compound - zinc oxide eugenol paste - impression waxes Elastic impression materials - Reversible hydrocolloids - Irreversible hydrocolloids</p> <p>- Polysulfide polymers - Condensation silicones - Polyether - Addition silicones - Polyether urethane dimethylacrylate Problems with impression materials - to the patient - to the dentist - to the environmentDisinfection Conclusion References</p> <p> An</p> <p>impression is a negative reproduction of hard and soft tissues. It can serve as a mould toobtain a cast, on which a planned restoration is fabricated</p> <p> Impression</p> <p>materials are used to register or reproduce the form and relationship of the teeth and supporting oral tissues.</p> <p> From</p> <p>the impression, an exact replica of the dental structures of interest is obtained using a cast or die materials.. The replica thus, is a positive reproduction. The positive reproduction is called a model or cast when large areas of oral tissues are involved or a die when a single preparation is recorded</p> <p>Ideal Properties of Impression Materials(1) Non toxic and non irritant (2) Acceptability to the patient: (a)Setting time, (b)Taste, (c)Consistency (a) Surface reproducibility (b) Dimensional stability (a) Ease of mixing (b) Working time (c) Setting time (d) Handling of the material</p> <p>(3) Accuracy : both (4) Use of material :</p> <p>(5) Compatible with model materials (6) Economics of material (a) Cheap (b) Long shelf life (c) Accuracy (save redoing impression)</p> <p>7)readily disinfected without loss of accuracy 8)No release of gases during setting 9)Adequate strength so it will not break or tear on removal from mouth 10)Hydrophilic</p> <p>Impression Materials</p> <p>Non-elastic</p> <p>CLASSIFICATION OF IMPRESSION Compound MATERIALS based on nature of the Waxes materialPlaster</p> <p>ZnO - Eugenol</p> <p>Aqueous Hydrocolloids Elastic</p> <p>Agar (reversible) Alginate (irreversible)</p> <p>Polysulfide Non-aqueous ElastomersSilicones Polyether</p> <p>ACCORDING TO THE MANNER IN WHICH THEY HARDEN(a) set by chemical reaction(irreversible)</p> <p>-plaster of Paris</p> <p>-zinc oxide eugenol -alginate -non aqueous elastomers</p> <p>(b)set </p> <p>by physical change(reversible)-impression compound -agar</p> <p>Mucostatic materials which are initially fluid- less likely to compress soft tissues. (b) Mucocompressive materials which are initially viscous(A)</p> <p>High viscosity Medium viscosity Low viscosity 1)Imp com 1)regular elastomers 1)imp paste 2)Putty elas 2)hydrocolloid 3)light body elas 4)imp plaster</p> <p>Suitable for edentulous jaws: Plaster Impression compound Zinc oxide eugenol paste Irreverisible hydrocolloid B) Suitable for dentulous jaws; Irreversible hydrocolliod Reversible hydrocolloid Elastomers c) Suitable for crown and bridge work Green stick compound Elastomers Reversible hydrocolloidsA)</p> <p> Powder-liquid Paste-liquid Paste-paste Materials</p> <p>softened by heat</p> <p>Used to carry the impression material into the mouth stock trays custom trays special use trays (bite registration trays)</p> <p>Also called as modelling plastic. It is one of the oldest impression material to be used TYPES: 1. TYPE-1: IMPRESSION PURPOSE 2. TYPE-2: TRAY FABRICATION</p> <p>It is a thermoplastic compound i.e. it softens when heated and hardens when cooled. This process does not involve a chemical reaction.</p> <p>Type-1 - used to take impressions of the mouth. Softening temp is 55-600C.Type-2 - used for modifying impression trays. Softening temperature is 700C</p> <p>INGREDIENTSMade up of 1. Resins (e.g. wax) - principal ingredient 2. Filler (e.g. talc or soapstone) improve their physical properties like strength flow and viscosity) 3. Lubricants (stearic acid or stearin, shellac, guttapercha) - plasticizer-reduce brittleness 4. Colouring agent ( appropriate amt )</p> <p>Impression Compound - MANIPULATION1. The compound is completely immersed in a water bath at 55-60 degree Celsius for about 4-5 minutes to ensure complete softening. 2. Gauze is placed at the bottom of the water bath to prevent adherence. 3. If left too long some of the constituents may be leached out into the water bath, altering the properties of the material (it is often the plasticiser stearic acid that is leached out). 4. The compound is loaded on to the tray and firm pressure is used to seat the tray in the mouth.</p> <p>An impression compound impression taken in an upper edentulous stock tray</p> <p> The</p> <p>temperature at which it is placed inside the mouth is 43.5-45 degree celcius</p> <p>Conductivity of heat is low, hence material should be allow to cool completely before removal to avoid distortion and also should be uniformly softened before making the impression. SOFTENING (A)OVEN (B)FLAME (C)HOT WATER Care should be taken not to over heat the impression to avoid boiling/burning/leaching out of low molecular weight ingredients. This will make compound brittle and grainy.</p> <p> According</p> <p>to ADA specification , impression compound should have maximum flow not less than 85% at safe temperature 45 degree celcius. And should have minimum flow at 37 degree celcius (mouth temperature) not more than 6%.</p> <p>PROPERTIES1.Poor surface detail 2.High coefficient of thermal expansion (contraction of up to 0.3% when removed from mouth to room temperature) 3. Distorts when removed over undercut areas 4. Mucocodisplacive</p> <p>5. Poor dimensional stability6. Can be modified by re-heating 7. Non toxic and non irritant 8. Good shelf life 9. Can be sterilized in autoclave for 10 minutes</p> <p>INDICATIONS FOR USE: To make an impression of completely edentulous ridge In operative dentistry impression of single tooth -tube impression(with the help of cylindrical copper band or matrix band) construction of custum trays tray compound border moulding of acrylic custum tray</p> <p>ADVANTAGES: 1. Non irritant and non toxic 2. Reusable 3. Can be reheated and readapted 4. Can support other materials for wash impressions 5. Mucocompressive 6. Beading and boxing can be done</p> <p>DISADVANTAGES: 1. Poor dimensional stability- relaxation of stresses 2. Poor surface detail 3. Expansion coefficient 4. Will distort if removed from undercuts 5. Not suitable for dentulous cases</p> <p> Zinc</p> <p>oxide and eugenol react and yield a relatively hard mass which possess certain medicinal advantages as well as mechanical benefits in certain dental operations.</p> <p>Dispensed as two separate pastes (base and catalyst pastes) TUBE NO 1: Zinc oxide - main ingredient 87% Fixed vegetable or mineral oil - plasticizer - 13% (offsets the action of eugenol)</p> <p>TUBE NO 2: contains Oil of cloves or Eugenol 12% Gum or polymerised rosin 50% (facilitates reaction speed and helps in yielding a smoother and homogenous mix) Filler(silica) 20% Resinous balsam 10% (improve mixing properties and flow) Accelerator(calcium chloride,zinc acetate, glacial acetic acid) 5% Lanolin 3%</p> <p>ZnO +H2o</p> <p>Zn(oH)2</p> <p>22</p> <p> Zn(oH)2 +eugenol</p> <p>ZnE +2H o AUTOCATALYTIC REACTION So the reaction proceeds faster in humid environment</p> <p> Oil-</p> <p>impervious paper or glass slab is used Squeeze 2 strips of paste in equal length Flexible stain less spatula is used to mix Two strips are combined with first sweep of spatula and mixing continued for 1 minute. Uniform color should be obtained.</p> <p> Initial</p> <p>setting time 3-6 mins - includes time of mixing, filling into the tray and seating the impression in mouth</p> <p> Final</p> <p>setting time: is the time at which the material is hard enough to resist penetration under a load Type 1 paste(hard) - 10 mins Type 2 paste(soft) - 15 mins When the final set occurs the impression can be withdrawn from the mouth</p> <p> Adding</p> <p>accelerator or a drop of water to the eugenol paste Cooling the spatula and mixing slab prolong setting time Adding olive oil, mineral oil, and petrolatum prolong setting time this reduces rigidity and gives inhomogenous mix Altering ratio of two pastes Longer the mixing time , shorter the setting time</p> <p> Accelerating</p> <p>action of body temperature and saliva on the surface of tissues cause the adjacent surface of the impression to harden first Impression should be removed after complete hardening of the material</p> <p>less flow shorter working time Rigidity and strength: same or superior that of compound . Dimensional stability good Flow:</p> <p>Disadvantage with eugenol is stingy and produce burning sensation ZOE reaction is never completed so free eugenol may leach out Disagreeable tasteSo, carboxylic acid can be used in place of eugenol. Orthoethoxybenzoic acid (EBA) is used Bactericides and medicaments can also be incorporated</p> <p> Impression</p> <p>material for edentulous ridges - wash impression(paste is spreaded over compound) Surgical dressing- soft pastes are used Bite registration paste offers less resistance to closure of the mandible and also gives a stable record Temporary relining material for dentures</p> <p>WAXES: 1)pattern waxes 2) impression waxes corrective wax biteplate wax 3) processing waxes BITE REGISTRATION WAX: used for occlusal registration. formulated from bees wax or hydrocarbon waxes and contain few metal particles</p> <p>CORRECTIVE IMPRESSION WAX: for edentulous impressions. used as wax veneer over an original impression to contact and register the detail of the soft tissue formulated from hydrocarbon waxes (such as paraffin, ceresin) and beeswax and may few metal particles flow at 37 degrees is 100%.</p> <p>Material susceptible to being stretched compressed or distorted and then tending to resume the original shape. Elastic impression materials are capable of accurately reproducing both the hard and the soft structures of the mouth including the undercut areas and interproximal spaces</p> <p>can be used in both dentulous and edentulous cases with undercuts. The distortion when removed from an undercut is minimal.</p> <p> Colloids</p> <p>are classified as the fourth state of matter , they lie between suspension and solutions. A solid liquid or gaseous substance made up of large molecules or masses of smaller molecules that remain in suspension in a surrounding continuous medium of different matter</p> <p>. TYPES OF COLLOIDSAerosols---- liquids or solids in air Lysosols ------gas or liquid or solid in liquid. Foams---------gases in solid Solid emulsion liquids in solid Solid suspension -- solids in solid</p> <p> The colloidal materials that are dissolved in water are termed</p> <p>hydrocolloids If the change of sol to gel is thermal and reversible reversible hydrocolloid (agar) If the change of sol to gel is chemical and irreversible irreversible hydrocolloid (alginates)</p> <p>A colloid that contains water as the dispersion phase</p> <p>A network of fibrils that form a weak slightly elastic brush heap structure of hydrocolloid</p> <p>If a hydrocolloid contains an adequate concentration of dispersed phase, a sol may change to semisolid material known as gel. In the gel state the dispersed phase agglomerates to form chain of fibrils also called as micelles. The fibrils may branch and intermesh to form a brush heap structure. The dispersed medium is held in the interstices between the fibrils by capillary attraction or adhesion .</p> <p>For agar secondary bonds hold the fibrils together,these bonds break at slightly elevated temperature and become re-established as the hydrocolloid cools to room temperature. This process is reversible. In case of alginate the fibrils are formed by chemical action and the transformation is not reversible.</p> <p>REVERSIBLE HYDROCOLLOID AGAR Introduced by Alphous poller of Vienna in 1925 It was the first successful elastic impression material</p> <p> Agar is an organic hydrophilic colloid extracted from certainSeaweed It is a sulphuric ester of a linear polymer of galactose</p> <p> Though highly accurate, it has been largely replaced byalginates and elastomers due to its cumbersome manipulation</p> <p>Composition:ComponentAgar Borate Pot. Sulfate Wax, ZO, Silica, , etc.</p> <p>FunctionBrush Heap structure Strength Gypsum hardener Filler</p> <p>Composition (%)13 17 0.2 0.5 1.0 2.0 0.5 1.0</p> <p>Thixotropic materialsWater Alkylbenzoates</p> <p>ThickenerReaction medium Perservative</p> <p>0.3 0.5Balance 84% 0.1</p> <p>GELATIONSetting of reversible hydrocolloidTHERE IS A PHASE CHANGE FROM</p> <p>SOL</p> <p>GEL</p> <p>GELATION TEMPERATURE:Gelation temperature - approximately 37C. If the gelation temperature is too high it is possible that injury may result to the oral tissues involved , a severe surface stress may also develop . If the gelation temperature is too low it will be difficult or even impossible to chill the material to a temperature sufficiently low to obtain a firm gel adjacent to the oral tissues . According to ADA specification no. 11 gelation temperature must not be less then 37C or more then 45C.</p> <p>LIQUIFACTION TEMPERATURETemperature at which gel change to sol. (70 -100c)</p> <p>GELATION TEMPERATURETemperature at which sol changes to gel.(37-50c)</p> <p>HYSTERESISThe temperature lag between the liquefaction temperature and the gelation temperature.</p> <p>IMBIBITIONThe process of water sorption i.e. the gel swells when placed in water.</p> <p>SYNERESISExpression of fluid on to the surface of gel structure.</p> <p> Based</p> <p>on viscosity type 1 - high consistency type 2 - medium consistency type 3 - low consistency</p> <p>The Material is supplied as: Gel in collapsible tubes (for impressions) A number of cylinders in a glass jar (syringe material)</p> <p>In bulk containers (for duplication)</p> <p>Available forms:Syringe material Tray material The only difference between the syringe and the tray material is colour and the greater fluidity of the syringe material Manipulation: Agar hydrocolloid requires special equipments Hydro colloid conditioner Water cooled rim lock trays</p> <p>PREPARATION OF THE MATERIAL : First step is to reverse the hydrocolloid gel to the sol form. Usually done at 100C for 10min 3 min should be added to this time whenever the material is being reused. As it becomes difficult to break down the agar brush heap structure. After liquefaction ,material may be stored in sol condition. Storage temperature: 65C to 68C.</p> <p>Conditioner Consists of:a. b. c. Boiling or liquefaction section: 10 mins in boiling water (1000 C). Storage section: 65-680 C is ideal it can be stored till needed</p> <p>Tempering section: 460 C for about 2mins</p> <p>CONDITIONING OF THE MATERIAL:This refers to the cooling of the material (also called as tempering of the material) Tempering is usually done at 43C for 7min. Uses of tempering: It increases the viscosity of the material so that the hydrocolloid does not flow out. It reduces the temperature of the material so that it is not uncomfortable for the patient.</p> <p>WATER COOLED RIM LOCK TRAYS</p> <p>The tray material is seated over the syringe materialExcess water from the surface of the tray material should be removed to facilitate proper union of the tray and the syringe material. Gelation is...</p>