impression tray and impression technique
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DESCRIPTIONImpression tray and impression technique. Dr. Nora Sheta. Steps of Complete Denture Construction. IMPRESSION TRAYS AND IMPRESSION TECHNIQUES. IMPRESSION. An impression is a negative record or imprint of the tissues of the oral cavity that forms the basal seat of the denture. - PowerPoint PPT Presentation
Impression tray and impression technique Dr. Nora Sheta
ClinicalLaboratory1. Examination & Diagnosis2. Primary impression Study cast Special tray3. Final impression Boxing and pouring master cast Occlusion blocks4a. Jaw relation registration4b. Selection of artificial teeth Mounting on articulator Setting of artificial teeth and waxing up5. Try inProcessing6. Insertion7. Post insertion care
IMPRESSION TRAYS AND IMPRESSIONTECHNIQUESIMPRESSIONAn impression is a negative record or imprint of the tissues of the oral cavity that forms the basal seat of the denture. Reproduce a positive form and shape of the same oral tissues (Cast) .
IMPRESSION TRAYS A tray is an instrument used to carry the impression material to the mouth , holding it in position against tissues until the material hardens ,it helps in removing the impression from the mouth .Parts 1 . Body2 . HandleBodyBodyHandleHandleDENTULOUS TRAYEDENTULOUS TRAYDentulous TrayEdentulous TrayBodyHandleBodyHandleFloorFlangeFloorFlangeStraightL - ShapeFlatLongRoundShort
Types of Trays
I- Stock trays
II- Custom trays (Special, Individual trays)
Impression tray is composed ofBody: The body consists of a floor and flanges.Handle.
The body and handle are designed to suit different mouths
1-Dentulous mouth cases
2-Edentulous mouth cases
3-Partially edentulous mouth cases.
types Stock tray Perforated or non perforated Metal or plastic
Preliminary ImpressionStudy castUSESAs a study cast to study :1. Ridge shape .2. Palatal Vault shape .3. Denture bearing areas . 4. Areas of undercut .5. Relief areas .6. Posterior palatal seal area .7. Sharp bony edges .8. Depth of the sulcus .9. Inter-ridge space 10. Inter-ridge relations .As a cast on which the final impression tray is fabricated.
SPECIAL OR INDIVIDUAL TRAYS 1. Shellac base plates .
2. Self & light curing acrylic resin .
3. Cast or swaged metal .TYPESAdvantages of Special Trays 1 . Fit more accurately the individual arch of the patient. 2 . Bulk of the impression material is reduced .4 . More accurate border contour 5 . Less impression material is used . 6. More comfortable to the patient .
Types of special trays
1- Shellac base plate special tray 2- Acrylic resin custom (special) trays: a- cold cured b- heat cured c- light cured Both heat and cold cured are used widely now. It is rigid and light in weight, not wrap in the mouth . 3- Cast or swaged metal tray 4- Vacuum formed plastic sheets It needs a pressure forming machine
Comparison between shellac and acrylic resin custom trays
Shellac base plate special trayLow strength.2. Easily distorted by load and temperature.3. Improper adaptation to the cast4. Easily constructed Self-cured acrylic resin special trayHigher strength and rigidity.Not distorted by temperature.
4. Easily constructed
Tray can be 1- with a spacer
2- without a spacer
SHIM OR SPACER One thickness of modeling wax or shellac base plate adapted on the study cast under the special tray
Upper & Lower spacer (Shim)
Custom (Special) trays with spacer (Shim)Steps for fabrication upper tray
Custom Tray With Spacer
Custom (Special) trays with spacer (Shim)Steps for fabrication lower tray
FINAL IMPRESSION TECHNIQUES OR THEORIES 1 . Minimal Pressure Impression Technique (Mucostatic Impression Technique) .2 . Definite Pressure Impression Technique or Mucocompression Impression or Functional Impression Technique .3 . Selective Pressure Impression Technique .
2NDRY IMPRESSION TECHNIQUES
(1) IMPRESSION TECHNIQUEMINIMAL PRESSURE ( MUCOSTATIC)FUNCTIONAL PRESSURE (MUCOCOMPRESSIVE)SELECTIVE PRESSURE(2) PHILOSOPHYALL THE TISSUES ARE UNDER THE LEAST PRESSURE.ALL THE TISSUES ARE UNDER FUNCTIONAL PRESSURE.TISSUES THAT CAN WITHSTAND PRESSURE ARE LOADED. AND TISSUES THAT CAN'T ARE RELIEVED.(3) TRAYPERFORATED + ON SPACER + WITH TISSUE STOPS.WELL ADAPTED + NO SPACER + WAXRIM.STOCK TRAY WITH COMPOUND ,THEN IT IS RELIEVED AND WASHED WITH PLASTER IMPRESSION MATERIAL.(4) PRESSUREFINGER PRESSUREPATIENTS BITING FORCE.FINGER PRESSURE.(5) IMPRESSION MATERIALPLASTER, FLOWY MATERIAL.ZnO/E , HEAVY MATERIALIMPRESSION COMPOUND (HEAVY)+ PLASTER OR ZnO/E(FLOWY)
5 Final Impression .
Upper ImpressionLower Impression
Boxing the impression
An impression is boxed to preserve the borders of the impression so that it will be accurately reproduced in the cast.
Methods for boxing
1- Wax method
2- Plaster and Pumice method
Beading wax for boxing
1- Wax Method
1-wax method Lower impression
2-Plaster and Pumice method Plaster and pumice for boxing
2-Plaster and Pumice methodUpper impression
MASTER CASTSADVANTAGES OF BOXING1 . The borders of the impression are preserved2 . The thickness of the base of the cast can be controlled 3 . Permits vibrating the stone material into the impression 4 . Time is conserved 5 . Material are conserved