impression compound

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  1. 1. IMPRESSION COMPOUND Dr. Anjana Maharjan
  2. 2. CONTENT Introduction Composition Type Properties Dimensional Stability Precaution Advantage/Disadvantage
  3. 3. INTRODUCTION Impression compounds are thermoplastic materials softened to their working consistency by immersion in hot water or by warming over the flame. Rigid after setting and has poor elastic properties
  4. 4. COMPOSITION Ingredients Parts Rosin 30 Copal resin 30 Carnauba wax 10 Stearic acid 5 Talc 25 (75) Coloring agent Appropriate Amount
  5. 5. TYPE 1. Lower Fusing - Impression Compound 2. Higher Fusing Tray Compound
  6. 6. TYPE I Available as sheets, sticks, cylinders and cones Should flow readily at just above mouth temperature Should be capable of recording sharp grooves 0.2-4 mm wide into the surface of metal test block Most viscous of impression material i.e 4000 (pas) thus characterized as mucocompressive
  7. 7. TYPE I Low Fusing - Green stick compound- 54 C Medium Fusing Impression compound -
  8. 8. TYPE I SHEETS Recording Impression of edentulous ridge Manipulation: Compound softened in water bath kneaded with finger to improve qualities Temperature of water bath 55-60C is ideal for 4-5 mins to ensure complete softening
  9. 9. Conti.. Gauze is placed at bottom of water bath to prevent adherence Soften by heat, inserted in an impression tray and placed against tissue before it cools to a rigid mass
  10. 10. TYPE I - STICKS Soften with flame Skill and experience is required Material is tempered in a water bath before placing in the patients mouth Used to refine /modify peripheral extent of special tray for CD or edentulous region of RPD Used for securing rubberdam retainer and occlusal registration plate Recording single crown preparation
  11. 11. STICKS - COPPER RING TECHNIQUE Recording a single tooth preparation using stick Hollow open ended copper tube used as a tray
  12. 12. Conti A separate locating impression is also recorded of the prepared tooth The die is inserted into this impression and a stone working model is made by pouring a stone This technique is superseded by the use of rubber base Still used where moisture control is a problem
  13. 13. STICKS - MANIPULATION For adequate border seal for retention of CD Trimming special tray until it is short of lines of movement of mucosa Tray periphery is coated with soften greenstick and tray replaced in mouth Cheeks are manipulated to stimulate functional movement to produce dynamically generated shape
  14. 14. Conti.. Care should be taken not to burn patient Used in distal extent of palatal coverage of upper denture for border seal
  15. 15. TYPE II Also k/a tray compound Making impression tray Not distorted at mouth temperature Used for corrective wash impression by adapting soften compound on study model and border of denture area trimmed Tray compound lacks dimensional stability and strength Thus replaced by acrylics and plastics
  16. 16. PROPERTIES Glass transition temperature Temperature at which material losses its hardness i.e. 39C or brittleness At this stage it is not plastic or soft enough for making impression Forms a rigid mass upon cooling
  17. 17. PROPERTIES Fusion Temperature: Indicates definite reduction in plasticity of materials during cooling Heating at approximately 43.5C material soften to plastic mass that can be manipulated Above this temperature soften material remains plastic while impression being made
  18. 18. PROPERTIES Fusion Temperature: Once the impression tray is seated, it should be held gently(passively) in position until the impression cools below the fusion temperature Impression should not be removed until it reaches oral temperature
  19. 19. THERMAL PROPERTIES Coefficient of thermal expansion 0.3% is acceptable conductivity is very low thus need extended time to achieve thorough heating and cooling The materials should be uniformly soft at the time it is placed on the tray and thoroughly cooled in the tray before the impression is withdrawn from the mouth
  20. 20. THERMAL PROPERTIES Cold water can be sprayed on the tray while it is in the mouth until the compound is thoroughly hardened prior to removal of impression tray from mouth Low thermal conductivity influences cooling Outerside cools rapidly and innerside remains soft thus adequate time is required for cooling
  21. 21. SOFTENING AND FLOW Soften at point just above mouth temperature and exhibit adequate flow to adapt closely to tissue and register details Hardens at mouth temperature and exhibit minimum flow to reduce danger of distortion on removal
  22. 22. SOFTENING AND FLOW
  23. 23. VISCOSITY Most viscous of impression material i.e. 4000(pas) 70 times greater than impression plaster 100 times greater than light body elastomers
  24. 24. VISCOSITY Significance 1. Limits degree of fine detail which can be recorded in impression 2. Characterizes compound as a mucocompressive impression material
  25. 25. VISCOSITY Advantage 1. Recording impression of some edentulous patient for recording full depth of sulcus so that a denture with adequate retention can be designed 2. Able to displace the lingual and buccal soft tissue sufficiently
  26. 26. DIMENSIONAL STABILITY Relaxation can occur in short time period with increased temperature Relaxation causes warpage or distortion of impression
  27. 27. DIMENSIONAL STABILITY To reduce distortion one has to allow the thorough cooling of impression before removal from mouth Construct cast or die as soon as possible (within 1 hr)
  28. 28. PRECAUTIONS Prolong heating /immersion in water bath cause compound to be brittle and grainy due to leaching out of low molecular weight ingredients e.g. stearic acid Compound should not be allowed to boil or inginite so that the constituents are volatized while using flame
  29. 29. PRECAUTIONS Incorporation of water acts as plasticizer Wet kneading causes incorporation of water in compound causes increased flow at mouth temperature causing distortion on removal Reheating also causes increased flow
  30. 30. ADVANTAGES Cheap and reusable Does not produce irritation to patient Can be remodify and resoften again till the accurate impression is obtain Compatible with die and model materials Easily electroplated to form accurate and abrasion resistant dies
  31. 31. DISADVANTAGES Difficult to record details because of high viscosity Mucocompressive Distortion due to poor dimensional stability Difficult to remove from severe undercuts Does not have pleasant taste
  32. 32. DISINFECTION In 2% alkaline glutaraldehyde solution impression is immersed for 10 minutes , rinsed and poured
  33. 33. ADA specification 3 for impression compound 1. Requires to be homogenous 2. Should be smooth and glossy in appearance after passed through flame 3. Must be firm and smooth while trimming with sharp knife at room temperature 4. Manufactures must indicate: Method of softening Working temperature Data/curve showing shrinkage from 40-20C
  34. 34. REFERENCES Applied Dental Materials - 9th edition-Jhon F.McCabe and Angus W.G.Walls Restorative Dental Material Craige Phillips Science of Dental Materials 11th edition - Knneth J Anusavice Dental Material Science, Mannippalli Dental Materials and Their Selection, 3rd edition, William J OBrein
  35. 35. Thank you