Impression Trays Stock Impression Trays



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CUSTOM TRAYS 302B
WEEK 5
INTRODUCTION:
The topics covered today are:



IMPRESSION TRAY
A RECEPTACLE OR DEVICE USED TO CARRY THE IMPRESSION MATERIAL TO THE MOUTH, CONFINE THE MATERIAL IN APPOSITION TO THE SURFACES TO BE RECORDED, AND CONTROL THE IMPRESSION MATERIAL WHILE IT SETS TO FORM THE IMPRESSION.

THERE ARE TWO TYPES OF IMPRESSION TRAYS:




  1. STOCK IMPRESSION TRAY




  1. “CUSTOM” IMPRESSION TRAY

“CUSTOM” IMPRESSION TRAYS MAY ALSO BE CALLED “SPECIAL” OR “INDIVIDUAL” TRAYS.

STOCK IMPRESSION TRAYS
STOCK TRAYS COME IN A VARIETY OF DESIGNS AND SIZES. THESE TRAYS FALL INTO THREE MAIN TYPES:
FULL DENTATE TRAYS

PARTIALLY DENTATE TRAYS



EDENTULOUS TRAYS
THERE ARE A VARIETY OF SIZES TO SUIT MOST PATIENTS. STOCK TRAYS CAN BE MADE OF METAL (NOT DISPOSABLE) OR PLASTIC. THE PLASTIC TRAYS ARE INTENDED TO BE DISPOSABLE.
ADVANTAGES (METAL STOCK TRAYS)


  • DESIGNED TO BE USED MANY TIMES

  • MUST BE ABLE TO BE SRERILISED

  • USED TO TAKE FIRST IMPRESSION FOR THE PRODUCTION OF THE PRIMARY CAST


DISADVANTAGES


  • THE PROBLEM IN USING STOCK TRAYS IS THAT THE IMPRESSION MATERIAL IS OF VARIOUS THICKNESS WHICH CAN LEAD TO DISTORTION

  • THE FLOW OF THE IMPRESSION MATERIAL CANNOT BE GUARANTEED TO COVER ALL THE AREAS OF THE TEETH OR TISSUES REQUIRED

  • PRESSURE POINTS CAN OCCUR WHEN USING A STOCK TRAY. THE PATIENT CAN EXPERIENCE DISCOMFORT DURING IMPRESSION TAKING DUE TO THE LARGE AMOUNT OF IMPRESSION MATERIAL USED IN THE TRAY. IN ORDER TO OVERCOME THESE PROBLEMS, SPECIAL TRAY SHOULD BE CONSTRUCTED.

CUSTOM IMPRESSION TRAYS
MADE BY A TECHNICIAN FOR AN INDIVIDUAL PATIENT AND ONLY USED FOR THAT PATIENT.
CUSTOM TRAYS ARE CONSTRUCTED BY THE TECHNICIAN ON A PRELIMINARY MODEL. THE MATERIALS WHICH CAN BE USED FOR THE CONSTRUCTION OF A CUSTOM TRAY ARE AS FOLLOWS:
1. THERMOPLASTIC IMPRESSION COMPOUNDS
2. ACRYLIC RESIN – ‘SELF CURE’ OR ‘HEAT CURE’
3. PRESSURE OR VACUUM FORMED THEMOPLASTIC COMPOUNDS
4. LIGHT CURED ACRYLIC

WE WILL BE CONSTRUCTING OUR SPECIAL TRAYS WITH LIGHT CURED ACRYLIC. THIS IS BECAUSE IT IS RELATIVELY CHEAP, SAFE (NO MIXING REQUIRED) AND EASY TO ADAPT TO A MODEL. IT ALSO HAS A RELATIVELY LONG WORKING TIME.


ADVANTAGES OF CUSTOM TRAYS


  1. Even thickness of impression material.




  1. Controlled distortion of tissues.




    • Muco-static: pertaining to the normal, relaxed condition of mucosal tissues covering alveolar ridges and denture related surfaces.

    • Muco-compressive: pertaining to pressure on mucosal tissues covering alveolar ridges and denture related surfaces.




  1. Even support of the impression material.




  1. Control over the flow of the impression material.




  1. Reduced discomfort for the patient.




  1. Economic use of the impression material.




  1. Reduced distortion during pouring of model due to support of impression material.


PRIMARY IMPRESSION
Is an impression which is taken with a stock tray, it is not an accurate representation of the patient. Once the impression is poured a primary model is produced.


PRIMARY MODEL
Is an inaccurate copy of a patient’s mouth which is used to assess and decide on a treatment plan. A primary models purpose is also to construct a custom tray on it.


SECONDARY IMPRESSION
Is an impression which is taken with a custom tray, it is an accurate representation of the patient. Once the impression is poured a secondary model is produced.


SECONDARY OR MASTER MODEL
This model is an accurate copy of the patient’s mouth, it is this model which is used to begin the steps in constructing an appliance or denture.




HANDLE DIMENSIONS AND POSITION




20 – 25mm


20mm

10 mm

4mm 4mm


The handle must be placed so that it will not interfere with any movements of the patients’ lips during the impression taking, it should be placed where the teeth once were. The handle should be shaped so that it is:



OUTCOME:
You should now be able to know the following:


  • What is an Impression Tray

  • What are Stock Impression Trays

  • The Advantages of Stock Impression Trays

  • The Disadvantages of Stock Impression Trays

  • What are Custom Impression Trays

  • The Advantages of Custom Impression Trays

  • The types of Impressions and Models

  • Flow Chart of Impression Trays

  • Handle Dimensions and Position


Stage 1
Custom Trays 302B – Week 5 Page of


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