Impression Materials Classification and Requirements PDF

IMPRESSION MATERIALS CLASSIFICATION AND REQUIREMENTS PREPARED BY: DR.BELA SHAH IMPRESSION MATERIAL: DEFINITION: A negative imprint of an oral structure used to produce a positive replica of the structure to be used as a permanent record or in the prod...

IMPRESSION MATERIALS CLASSIFICATION AND REQUIREMENTS PREPARED BY: DR.BELA SHAH IMPRESSION MATERIAL: DEFINITION: A negative imprint of an oral structure used to produce a positive replica of the structure to be used as a permanent record or in the production of a dental restoration or prosthesis. There are wide variety of impression materials available each with their own properties, advantages and disadvantages. DESIRABLE PROPERTIES OF IMPRESSION MATERIALS. A. COMPATIBILITY WITH PATIENT: 1.pleasant odor. 2.pleasant taste. 3.non-toxic. 4.non-irritant. 5.decreased setting time. 6.esthetic color. B. EASE OF MANIPULATION: - 1. Minimum equipment. 2. Consistency & satisfactory texture. 3. Adequate flow property. 4. Readily wets oral tissues. 5. Clinically satisfactory setting characteristics & time. 6. Dimensional accuracy. 7. Adequate mechanical strength to resist tearing. DEFINITION: Impression is a negative replica of oral hard and soft tissue from which positive reproduction can be formed. MUCOSTATIC IMPRESSION MATERIALS: Materials which is initially very fluid because they are less likely to compress soft tissue ex: impression plaster MUCOCOMPRESSIVE IMPRESSION MATERIALS: Material which are initially more viscous ex: impression compound Pseudoplasticity: (PSEUDOPLASTIC MATERIALS) The tendency of a material to become less viscous as the shear rate increases and to recover viscosity immediately upon the elimination of shear stress. Ex: addition silicon and polyethers Viscocity decreases with increase in strain rate till it reaches constant value Classification of impression materials by viscosity :  IMPRESSION COMPOUND: *CAKE FORM: *STICK FORM  PUTTY ELASTOMERS: REGULAR ELASTOMERS :  IMPRESSION PLASTER:  IRREVERSIBLE HYDROCOLLOID  REVERSIBLE HYDROCOLLOID  LIGHT BODY ELASTOMERS: classification according to elastic properties: REQUIREMENTS OF IMPRESSION MATERIALS 1) Factor which affect the accuracy of the impression. 2) Dimensional stability of the impression. 3) Manipulative variables. 4) Additional factors. ACCURACY 1) Material should be fluid on insertion into the patient’s mouth. 2) Material interacts with saliva is an other factor affecting fine details reproduction. 3) Fine details recorded in an impression will only be transferred to the gypsum cast  4) A low contact angle is favourable as it indicate good wetting Wetting Dewetting 5) Material which expand during setting results in under size dies/cast. 6) The effect on the accuracy of fit of the restoration depends on the type of restoration and complexity of the shape involved. 7) It is important that impression material remain attached to impression tray during recording of impression 8)Additional retention achieved by perforated tray. 9) Materials used for recording under cut a) Material’s elastic properties b)Adequate tear resistant  10) Degree of distortion depends upon severity of under cut 11) On removing elastic impression materials from undecut areas they are often put under a considerable tensile stress. DIMENSIONAL STABILITY The way in which accuracy of impression changes during this period is a measure of its dimensional stability. An ideal impression material would have perfect dimensional stability Manipulative variables: Many methods of dispensation used for impression materials. Some involve mixing of p/w ,others p/l , other two pastes and some requires no mixing.  some materials , generally require warming in water bath , flame or other heat sources to soften them Two paste supplied in tooth paste like tubes Advantages?????  If mixing is incomplete, certain part o f impression remain unset. Setting characteristics of material have important effect on ease of handling.  What is WORKING TIME?? SETTING TIME? HOW BOTH ARE DETERMINED? CLINICAL CONSIDERATIONS: 1) CHOICE OF IMPRESSION MATERIAL 2)IMPRESSION TRAY 3)TISSUE MANAGEMENT 4) IMPRESSION TECHNIQUE. 5)CROSS INFECTION CONTROL CHOICE OF IMPRESSION MATERIALS Choice of I.M is b/w rigid and elastomeric products Rigid material used when underut not present Exception is impression plaster Rigid impression material can be used in edentulous arch where compressible undercuts present. Impression tray Purpose of impression tray is to give rigid support to impression materials. Tray can be custom made / stock. Custom tray produced on study cast of patient’s mouth Custom Tray: STOCK TRAY:  Properties of custom tray: Rigid Optimal spacing b/w tray & tissue Appropriate extensions in all directions.  Stock tray produced in variety of shapes & size Such tray is either too short or too long(over/under extension) Modification of extension of tray achieved by cutting it back or by extending periphery using rigid thermoplastic material ( green stick) Methods for retaining impression material attached to tray: Mechanical interlocks. Wire attached to base of tray. Use of adhesives. MECHANICAL METHOD: ADHESIVE : PANASIL ADHESIVE Compatible Impression Material: Silicone Based Materials VINYAL ADHESIVE Compatible Impression Material: Vinyl Polysiloxane Impression Tissue management For fixed / removal appliance it is imp not only to record tooth surface but also relationship between teeth & soft tissues surrounding them. Syringing impression materials in those areas which may be recorded badly.  For fixed prosthesis the preparations on teeth commonly extend up to / beneath the gingival margin It is necessary , to displace gingival tissue away from the preparation.  Displacement achieved either by packing retraction cord or by widening the crevice temporarily using either electrosurgical unit or soft tissue laser.  Whats the complication of retraction cord ????????????? Retraction cord often use with haemostatic agent to assist moisture control. Agents,like epinephrine,aluminium, ferric chlorides. Impression technique: Specific technique used for each material will vary from product to product. For Greatest accuracy teeth need to be clean & dry. How to isolate tooth?  Isolation by means of  In additional cured silicone rubber dam is not being used because the plasticizers in the rubber dam will poison the platinum catalyst in the impression material, inhibiting its setting. Cross infection control Cross infection control It is important that impression are disinfected prior to sent to lab for manufacture of models/prosthesis/appliances To protect laboratory staff from transmission of infection from patients.  Disinfectant of impression by immersing them in sodium hypochlorite solution for 10 min. Recently developed disinfectants like sodium peroxymonosulphate likely to overcome many of handling & storage problem of sod.hypochloride.  Greater efforts need to be made to sterilize rather than to disinfect impressions , like in case of HIV/AIDS pts. Cold sterilization involves immersion in 2% gluteraldehyde under acidic,neutral,alkaline condition for 10 hours.  The disinfectant should be compatible with the impression materials. Protective gloves should be worn. Rinse after disinfection is complete. QUICK REVIEW :  Q1) Define impression and types of impression ? along with examples  Q2)Classify impression by means of viscosity?  Q3)What is the function of retraction cords?  Q4)Classify impression materials by means of elastic property?  Q5) What is the significance of low contact angle?  Q6)What is the property of custom tray?  Q7)What is the difference b/w custom tray and stock tray?  Q8)What is the complication of retraction cords?