A dental impression is defined as the negative record of thetissues of the mouth . It is used to reproduce the form of theteeth and surrounding tissues.
Have pleasant taste, odor and esthetic color. Not contain any toxic or irritating ingredients. Be economical. Have adequate shelf life for storage and distribution. Be easy to use with minimum equipments. Exhibit dimensional stability. Have adequate strength so that it will not break or tear whileremoving from the mouth. Posses elastic properties with freedom from permanentdeformation after strain. Be able to be electroplated Be compatible with die and cast materials
There are several classification. According to philips scienceof dental materials impression materials are classified on thebasis of setting and elasticity.Mode of setting rigid ElasticSet by chemicalreaction(irreversible)Impression plaster,zinc oxide eugenol.Alginate,polysulfide,polyether, silicone,Set by temperaturechange(reversible)Compound, waxes Agar hydrocolloid.
Impression compound isrigid,reversible impression materialsets by physical change. It softens on heating and hardens oncooling. ADA specification no 3 Supplied as sheets,sticks,cakes andcones.
Making preliminary impression of edentulous mouth. For individual tooth impression. To make a special tray. Border moulding. To check undercuts in inlay preparations.Composition:INGREDIENTS PARTSresin 30Copal resin 30Carnauba wax 10Stearic acid 5Talc 75
Glass transitional temperature =39 degree centigrade. Fusin temperature=43.5 degree centigrade. They are poor conductors of heat. Coefficient of Linear Expansion is high. Good dimensional stability. Good flow. Fine reproduction of detail.
Material can be reused several times. Inaccurate portions can be remade without having to remakethe entire impression. Accuracy can be improved by flaming surface material.Disadvantages: Distortion due to poor dimensional stability. Compress soft tissue while making impression. Difficult to remove if there are undercuts. Difficult to record details because of high viscosity.
Applications: Cementing and insulating medium. Temporary filling. Root canal filling material. Bite registration paste. Impression material for edentulouspatients. Temporary relining material fordentures.
Setting reaction is an acid base reaction to form a chelate. This reaction is also known as chelation and the product iscalled zinc eugenolate. Zno + H2O Zn(OH)2 Zn(OH)2 +2HE ZnE2 +2H2O(Base) (Acid) ( Salt)Setting time;Initial settingtimeFinal settingtimeType 1 3-6 min 10 minType 11 3-6 min 15 min
Particle size of zinc oxide powder. Longer mixing time, shortens setting time. High atmospheric temperature and humidity acceleratesetting. Setting can be delayed by cooling mixing slab, spatula oradding small amount of retarder or oils or waxes.Properties: Good consistency and flow. Detail reproduction. Rigid and having good strength. Good dimensional stability.
Mixing is done on an oil-impervious paper or glass slab. Two ropes of paste of same length and width, are squeezedon mixing slab. A flexible stainless steel spatula is used for mixing. Two ropes are combined until a uniform colour is obtained. Mechanical rotary mixing are also used. Mixing time is one minute
It has enough working time to complete border moulding. It can be checked in mouth repeatedly without deforming. It registers accurate surface details. It is dimensionally stable. Does not require separating media since it does not stick tocast material. Minor defects can be corrected.Disadvantages: Requires special tray for impression making. Sticky in nature and adheres to tissues. Burning sensation of eugenol causes tissue irritation. Highly inelastic in nature.
NON-EUGENOL PASTE aredeveloped to overcome the burningsensation caused by eugenol. Bactericides and other medicamentsare also incorporated. Used in eugenol irritant patients.
Agar hydrocolloid was the first successfulimpression material to be used in dentistry. It is an organic hydrocolloid extracted fromcertain types of seaweeds. Agar is a reversible hydrocolloid. Since it is reversible can be reused.
As tissue conditioner. For full mouth impression without deep undercuts. Used extensively for crown and bridge impression beforeelastomers came to the market. Widely used at present for cast duplication. Supplied as; Gel in collapsible tube(for impression) A number of cylinders in a glass jar(syringe material). In bulk containers(for duplication)
INGREDIENTS PERCENTAGE BY WEIGHTAgar 13-17%Borates 0.2-0.5%Potassium sulphate 1-2%wax, hard 0.5-1%Thixotropic material 0.3-0.5%Alkylbenzoates 0.1%water Around 84%Coloring and flavoring agents Traces
Rim lock trays with water circulatingdevices are used (water cooled rimlock tray). Rim lock has a beading on theinside edge of the tray which helpto retain the material within thetray. It also has an inlet and outlet forconnecting water tubes. The tray should allow a space of3mm occlusally and laterally andextend distally to cover all teeth.
Boiling section or liquefaction section Ten minutes inboiling water at100 degreeStorage section 65-68 degreeis idealTempering section 46 degree fortwo minuteswith materialloaded in tray
Syneresis and imbibition; The hydrocolloid gel may loose water by exuding of fluid. andthis process is known as synersis. Imbibition is the process of gaining of water when immersedin water. Importance-both the phenomenon can cause dimensionalchanges and produce inaccurate casts. To avoid thisimpressions should be poured immediately.Flow;The material is sufficient fluid to record fine details.
Material is sufficiently fluid to record details.Flexibility; Material is highly flexible.Hysteresis;Temperature lag between liquefaction and gelation.Elasticity and elastic recovery; Highly elastic in nature. Elastic recovery occurs to the extentof 98.8%Fine reproduction of detail;Accuracy and dimensional change They expand when stored in water or 100% relative humidityWorking and setting time Working time- 7 to 15 min Setting time – 5 min
Main disinfectants used include iodophor,bleach orglutaraldehyde.ADVANTAGES Accurate die can be prepared, if material is properly handled Has good elastic properties. Good recovery from distortion Palatable and well tolerated by patient Cheap
Not flow well compared to newly available material It cannot be electroplated Tears relatively easily Only one model can be poured
Its an irreversible elastichydrocolloid It is a mucous extract yieldedfrom certain brown sea weeds Types type 1 – fast setting type 2- normal setting Applications Used for impression making; when there are undercuts in mouth with excessive flow ofsaliva For impression to make studymodels and working casts For making preliminaryimpression
INGREDIENTS FUNCTIONSSodium or pottasium alginate-15% React with calcium ionCalcium sulphate(reactor) - 16% React with potassium alginateZinc oxide - 4% Acts as fillerPotasium titanium flouride -3% Gypsum hardenerDiatomacous earth -60% Acts as fillerSodium phosphate(retarder) -2% React with calcium sulphateColouring and flavouring agents Wintergreen, orange etc.
Two main reaction occur 2Na3Po4 + 3CaSo4 Ca3 (PO4)2+3Na2So4 Here firstly the retarder is completely getreacted to delay the reaction time. Sodium alginate + CaSo4+H2O calciumalginate +Na2So4
Alginate has pleasant taste and smell It is highly flexible Good elasticity and elastic recovery Fine reproduction of tissue detail Compressive strength – ranges from 0343-70mpa Tear strength- 350-700gm/cm2 Dimensionally stable Poorly adheres to the tray Biological properties- inhalation of silica particlescause health hazards.
steps in manipulation fluff or aerate the powder byinvesting can several times. for mixing a clean flexibleplastic bowl and clean widebladed stiff metal spatula isbeing used. proper water powder ratiospecified by the manufacturershould be used(1 measure waterwith two level scoops of powder) mixing is started with a stirringmotion. vigorous figure 8 motioncan also be used.
Mixing time fast setting - 45 sec normal setting- 60sec Working time – fast setting – 1min normal setting – 2 min Gelation time fast setting - 1 to 2min normal - 2 to 4.5 min
Easy to mix and manipulate Low cost Comfortable to patient Hygienic Good surface detail even in presence of saliva Accuracy if properly handled Minimum requirement of equipment
Cannot be electroplated It cannot be corrected Poor dimension stability Poor tear strength Distortion may occur if not properly handled
Classification A) according to chemistry 1) polysulfide 2) condensation polymerizing silicones 3) addition polymerizing silicon 4) polyether B) according to viscosity 1) light bodied(syringe consistency) 2) medium(regular) 3) heavy body(tray consistency) 4) very heavy(putty consistency)
A) Base paste liquid polysulfide polymer – 80-85% inert fillers - 16-18%B) reactor paste lead dioxide -60-68% dibutyl phthalate -30-35% sulphur -3% retarders like magnesium stearate
Base and accelaration paste are mixedtogether which undergoes chemichal reactionto form polymer The reaction is exothermic – 3-4 degreeCelsius rise in temperature Mercaptan+lead oxide polysulfide+water
Unpleasant order and colour Material is extremely viscous and sticky andexhibits pseudoplasticity Long setting time of 12.5min High tear strength Good flexibility Excellent reproduction of surface detail
Types; 1-condensation silicones 2-addition silicones Condensation silicones; Also known as conventional silicones. Available in three viscosities namelylight,medium bodied and heavy.Composition;Base 1-polydimethyl siloxane. 2-colloidal silica Color pigments.AcceleratorStannous octoate
Dimethyl siloxane+orthoethyl silicate silicone inpresence of stannous octoate.Addition siliconeComposition;Base paste and catalyst paste;Setting reaction;Vinyl siloxane+silane siloxane silicone rubber
◦ Good mechanical and compressivestrength comparing otherelastomers.◦ Available in three viscosities.◦ Consist of base paste and catalyst.