impression materials in dentistry class presentation

in detail explanation of impression materials

1. IMPRESSION MATERIALS

2. INTRODUCTION: Dentists must understand the maxillary and mandibular tissues as they relate to maintaining support, stability, and retention of the dentures. Dentures contact mucosa with a continum of compressibility and movement that varies between each arch, among areas within the arch, and among patients. Contact and extension of the static intaglio and cameo surfaces of the dentures is a composite of the adjacent tissues at rest and in function. Short-term and long-term health of the contacting tissues is influenced by the methods used to capture these tissues and the final adaptation of the denture bases in function.

3. TERMINOLOGIES : Impression : a negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structure for use in dentistry. – GPT 10 Impression material : any substance or combination of substance or combination of substance used for making an impression or negative reproduction. - GPT 10

4. OBJECTIVES OF IMPRESSION MAKING To provide retention, support, stability, esthetics and preservation of the ridge for the denture. An impression also will act as a foundation for improved appearance of the lips and, at the same time, should maintain the health of the oral tissues. It should record all the potential denture- bearing surfaces available. It should record the depth and the width of the vestibule, otherwise the denture will lack retention. I mpression techniques, methods, and materials vary and should be selected on the basis of biological factors.

5. PRINCIPLES OF IMPRESSION MAKING 1. The tissues of the mouth must be healthy. 2. The impression should extend to include all of the basal seat within the limits of the functions of the supporting and limiting tissues. 3. The border must be in harmony with the anatomical and physiological limitations of the oral structures. 4. Proper space for the selected impression material should be provided within the impression tray.

6. 5 . The impression must be removed from the mouth without damage to the mucous membrane of the residual ridges. 6 . A guiding mechanism should be provided for correct positioning of the impression tray in the mouth. 7 . The tray and the impression material should be made of dimensionally stable materials. 8 . The external shape of the impression must be similar to the external form of the prostheses.

7. IDEAL REQUIREMENTS :

8. CLASSIFICATION : According to elastic properties and thermal type : Polysulphide Silicones polyether Synthetic elastomers Reversible (agar) Irreversible (alginate)

9. According to impression techniques 1. Mucostatic - produce minimal displacement of the tissue during impression. (Ex.) ZOE Paste, Impression Plaster 2. Muco Compressive - are more viscous and displace the tissues while recording them. (Ex.) Impression Compound

10. IMPRESSION COMPOUND Rigid. Thermoplastic. Muco -compressive .

11. Composition : COMPONENT FUNCTION W axes (Beeswax, colophany ) Soften on heating . Thermoplastic resins (Rosin, Shellac, Copal resin) Primarily responsible for transition from solid to liquid state. Filler (Chalk, talk, Limestone) Increases viscosity at temp above mouth temp. Increases rigidity at room temp. Plastcizers ( Guttapercha Stearic acid, Shellac) Improve s plasticty and workability.

12. Types: According to ADA Specification No. 3 Type Flow at Use 37ºC 45ºC Type 1 Impression compound Less than 6% More than 85% Preliminary impressions of edentulous patients. Peripheral seal materials. Impression of single crowns for copper band impressions. Type 11 Tray compound Less than 2% 70-85% Primarily used as tray materials that are sufficiently rigid to support other impression materials.

13. Manipulation : Treated in thermostatically controlled water bath at 55–60 C. Compound added to the water in small pieces. It must be immersed in a water bath for sufficient time to ensure complete softening . However, if it is left too long, some of the constituents may be washed out, thereby altering the properties.

14. Wet Kneading If kneaded in water, water will become incorporated in the material and acts as a plasticizer. By kneading for 1-3 minutes, the flow of compound may be more than doubled. Construction of Cast Gypsum product with in one hour. Disinfection of impression: Rinse to remove blood, debris & saliva. 10 to 30 minutes immersion in Gluteraldehyde or Iodophor.

15. Advantages Rigid when set. Inexpensive. Non toxic. Disadvantages Due to pressure while making impression, tissues will be compressed. Distorts easily leading to poor dimensional stability. Cannot be removed from undercuts. High thermal expansion. Does not reproduce fine surface details.

16. METALLIC OXIDE PASTE Relining distal extension bases Not to be used with stock trays Not to be used- remaining natural teeth Have a set setting time -after which border moulding is not effective

17. COMPOSITION: Base Paste : Zinc Oxide Fixed Veg / Mineral Oil Accelerator Paste : Oil of cloves / eugenol Gum / polymerised rosin Filler Lanolin Resinous balsam Accelerator & colour

18. ADVANTAGES: Good dimensional stability Good detail reproduction Impression can be modified by adding in deficient areas Easy to manipulate Sufficiently long working time DISADVANTAGES: Burning sensation Sticks to skin & instruments Rigid

19. IMPRESSION WAXES Mouth temperature waxes E.g. Iowa and Korrecta No. 4 wax Functional impression/ relining It has the ability to flow in the mouth which permits equalization of pressure and prevent displacement of tissues. Allows rebound of tissues Establish border-width Correctable

20. CONCLUSION Recording impressions is an important aspect for fabricating successful dental prosthesis. Incorrect impression leads to inaccurate casts which causes ill fitting frameworks. An operator should have knowledge about the various techniques and materials. It is advisable to repeat an impression when in doubt rather than making gross adjustments later.