Impression - RPD


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Impression - RPD

  1. 1. IMPRESSION MATERIALS & PROCEDURES FOR R.P.D Presented by Jean Michael Final Year Part 2
  2. 2. INTRODUCTION• An impression is defined as a negative likeness of the teeth and/or edentulous areas where the teeth have been removed, made in a plastic material which becomes relatively hard while in contact with these tissues
  3. 3. CLASSIFICATION OF IMPRESSION MATERIALSRIGID MATERIALSPlaster of ParisMetallic Oxide PasteTHERMOPLASTIC MATERIALSModeling plasticImpression Waxes & Natural Resins
  4. 4. ELASTIC MATERIALSReversible HydrocolloidsIrreversible hydrocolloidsMercaptan Rubber-base materialsPolyether Impression MaterialSilicone Impression Materials Condensation SIM Addition SIM
  5. 5. IRREVERSIBLE HYDROCOLLOIDS (ALGINATE)Indicated for diagnostic casts,orthodontic treatment casts &master casts for R.P.D.Can be used in presence of salivaHydrophilicPleasant taste and smellNontoxic, nonstaining & inexpensive
  6. 6. Can be disinfected with 2% GluteraldehydeShould be stored in 100% moisture & poured within1 HourLow tear strengthSurface details - less than elastomeric impressionmaterialsDimensional stability – less than elastomericimpression materials
  7. 7. POLYSULFIDE IMPRESSION MATERIALS High tear strength Long working and setting time (8 to 10 minutes) Can be disinfected Cast poured will have smoother texture & will be harder as they do not retard or etch the surface of the setting stone Should have a uniform thickness that does not exceed 3mm
  8. 8. Medium and heavy body should not be used in caseof large/multiple undercutsLong term dimensional stability is poor due towater loss after settingShould be held still during the impression makingprocedureAllow to rebound for 7 to 15 minutes after removalfrom mouth and pour immediatelyUnpleasant odor & Stains clothes
  9. 9. POLYETHER IMPRESSION MATERIALS Good surface details Hydrophilic – good wettability for easy cast forming Shorter working and setting time Flow characteristics and flow - lowest among others Stiffness – cast breakage of while removal from tray
  10. 10. Unpleasant tasteAbsorbs waterCannot be immersed in disinfecting solutionsPour within 2 hours for better results
  11. 11. CONDENSATION SILICONESModerate working time (5 to 7 minutes)Pleasant odorGood tear strengthExcellent recovery from deformationCan be disinfected with disinfecting solutions withoutany alternation in accuracyHydrophobicIdeally pored within 1 hour
  12. 12. ADDITION SILICONESMost accurate among elasticimpression materialsLow polymerization shrinkage &distortionFast recovery from distortionGood tear strengthWorking time – 3 to 5 minutes
  13. 13. Both hydrophilic & hydrophobic forms are availableAvailable in automixing devicesPouring can be delayed up to 1 weekStable in sterilizing solutionsSulfur in latex gloves – retards the setting reaction
  14. 14. IMPRESSION OF PARTIALLY EDENTULOUS ARCHElastic impression materials are used for makingimpression of partially edentulous archThis is due to the presence of undercuts in thepartially edentulous mouth
  15. 15. MATERIALS AVAILABLE FOR MAKING IMPRESSIONReversible hydrocolloids (agar-agar)Irreversible hydrocolloids (Alginate)Elastomeric impression materials
  16. 16. STEPS IN IMPRESSION MAKINGPosition of patient & dentistTray selectionMixing the material & loading into the trayImpression making & removalInspecting, cleaning & disinfecting the impression
  17. 17. POSITION OF PATIENT & DENTISTDentist should stand & patient should sit uprightOcclusal plane should be parallel to the floorMAXILLARY IMPRESSION- dentist should stand atthe right rear of the patientMANDIBULAR IMPRESSION- dentist should stand atthe right front of the patient
  18. 18. IMPRESSION TRAY SELECTIONStock trays for dentulous & partially edentulousarches are of 3 types: Rimlock trays Perforated metal trays Plastic disposable trays
  19. 19. CHECKING MAXILLARY TRAY SIZEThere should be a clearance of 5-7mm between theinner flanges of the tray & facial surface of teeth &edentulous ridgeTray should cover the desired anatomic areasToo large a tray may be difficult to insert & mayinterfere with the coronoid process of mandible
  20. 20. CHECKING MANDIBULAR TRAY SIZE There should be a clearance of 5-7mm between the tray and tooth surface and ridge If the tray extends too far in the lingually, there is a tendency to trap the tongue or floor of the mouth. Tray is held in the right hand Left thumb & index fingers are used to manipulate the right corner of the mouth
  21. 21. As the right flange of tray is rotated towardmouth, depress the lower lip & stretch the rightcorner of mouth with the left thumb & index finger
  22. 22. EXTENDING AN IMPRESSION TRAYSome times impressiontray of adequate widthmay not cover thedesired impression areaIn such cases, the tray islengthened usingmodeling wax
  24. 24. LOADING IMPRESSION TRAYPlace impression material in small amounts.Tray should be filled in level with the flangesOverfilling should be avoided
  25. 25. Mandibular Impression Technique Inject some material over occlusal surface of teeth, into vestibular areas & alveolo-lingual sulcus Then tray is rotated into mouth & is carefully seated The patient is asked to keep the tip of tongue in contact with the upper surface of tray during gelation Maintain the position of tray by placing the forefinger of each hand on top of tray on premolar area & thumb under patient’s chin
  26. 26. Maxillary Impression TechniqueInject alginate into occlusal surface & vestibular areas& wipe some amount on the palateTray must be centered & properly aligned & verify theposition by looking at the patient’s face from aboveIt should protrude straight from the center of themouth.After this, the tray is seated by using fingers of bothhands over the premolar areas & stabilize the tray
  27. 27. Removal of Impression From Mouth Clinically the initial set of alginate is determined by loss of surface tackiness Release seal by retracting lips & cheek Then impression is removed by a sudden jerk
  30. 30. Preparation Of Custom Tray
  31. 31. Marking the outline on the cast
  32. 32. Wax spacer adaptation
  33. 33. Self Cure Acrylic
  34. 34. Apply self cure acrylic over wax spacer
  35. 35. Attaching the Handle and polishing
  36. 36. Wax spacer scraped and tray perforated
  37. 37. Secondary Impression• Same as that for diagnostic impression.• In this procedure paint or inject impression material in critical areas: Rest preparation Hard palate Peripheral extensions
  39. 39. Anatomic and Functional Form of Ridge
  40. 40. Anatomical form of Ridge The anatomic form is the surface contour of the ridge when it is not supporting an occlusal load
  41. 41. Functional form of Ridge The functional form of the residual ridge is the surface contour of the ridge when it is supporting a functional load
  42. 42. SPECIAL IMPRESSION PROCEDURES1. Physiologic or functional impression technique Functional Relining method Mc Lean’s and Hindel’s methods Fluid Wax method2. Selected Pressure technique
  43. 43. Mc LEAN’S PHYSIOLOGIC IMPRESSIONProcedure A custom impression tray is constructed over a preliminary cast Functional impression of distal extension ridge is made. Patient applies some biting force with occlusion rims Then an Alginate impression is made with the 1st impression held in it’s functional position with finger pressure
  44. 44. HINDEL’S MODIFICATIONMain difference of this with Mc Lean’s is thatimpression of edentulous ridge is not made underpressure but is an anatomic impression made at restwith ZOE paste.As the hydrocolloid impression was being madefinger pressure was applied through holes in the trayto the anatomic impression.
  45. 45. Disadvantages of these methods Constantly compressed residual ridge is prone to excessive bone resorption. If the clasp do not hold the partial denture, the denture will be pushed slightly occlusally by the tissue causing premature contacts (TISSUE REBOUND)
  46. 46. FUNCTIONAL RELINING METHODHere a new surface is added into the inner, or tissueside of the denture baseThe partial denture is made from a cast made fromimpression made with alginateA space is provided by adapting a metal spacer overthe ridge on the cast before processing the denturebase.A functional impression of the edentulous area ismade using the cast partial denture framework.
  47. 47. The patient must maintain the mouth in a partiallyopened positionBorder moulding is carried out.Then a low fusing modeling plastic/green stickcompound is allowed to flow over the tissue side ofthe denture base.It is tempered in water bath & seated in patient’smouth.
  48. 48. To provide space for the impressionmaterial, modeling plastic is scraped to a depth of1mmThe modeling plastic serves a s a tray material for thesecondary impression materialThe final impression is made with a Zinc OxideEugenol impression pasteIf undercuts are present, light bodied rubber basedimpression materials can be used
  49. 49. Advantages The amount of soft tissue displacement is controlled by the amount of relief given to the modeling plastic before final impression is made Greater the relief, the less will be the tissue displacement. Tissue surface of metal frame work can be relined after insertionDisadvantage Since open mouth technique is used it is difficult to maintain the previous occlusal contact
  50. 50. FLUID WAX FUNCTIONAL IMPRESSION• Make an anatomic impression of the arch using alginate• Fabricate a refractory cast using this impression• Fabricate the partial denture framework over the refractory cast
  51. 51. Draw the outline of the denture baseCast is coated with separating mediumWax Spacer is adapted over the crest of theedentulous ridge
  52. 52. Framework is placed over the spacerAuto-polymerizing resin is mixed to doughstage and is adapted and contoured over theframework along the length of the ridgeBorders of the tray are trimmed
  53. 53. Impression ProcedureWax is softened at 51 ̊ to 54 ̊Softened wax is painted on the tissue surface with abrushWax is painted in excess near the border to recordthe sulcusTray is seated and held in positionIt takes at least 5 minutes for the wax to set
  54. 54. The tray is removed and the impression is examinedThe wax surface that has contacted soft tissueappears glossy and the other areas that has notcontacted the tissues will appear dullThe impression should be placed in the mouth finallyfor 12 minutes
  55. 55. SELECTIVED PRESSURE IMPRESSION More force are applied to areas that can absorb stress without adverse response & protect that areas that is least able to absorb force Stress bearing areas are the buccal shelf area & the lingual slopes of residual ridge stress bearing areas The denture base made from this impression will be closely adapted to & in firm contact with the tissues in buccal shelf area
  56. 56. Custom Trays
  57. 57. The tissue surface if the tray is trimmed with burs toprovide adequate relief
  58. 58. Impression material is loaded on the preparedspecial tray and inserted into the patient’s mouthImpression is made with the patient with his mouthopen under finger pressureOnly the stress bearing areas will be compressedduring impression making
  59. 59. Materials used for Secondary Impression Zinc Oxide Eugenol impression paste Rubber base material
  60. 60. Altering The Master CastThis procedure is done to obtain a ‘Hybrid Cast’which records the edentulous areas in the functionalform and the dentulous areas in the anatomic form
  61. 61. Conclusion• An accurate impression is vital for the success of a cast partial denture. So proper selection of material, impression technique and the skill of the dentist plays a key role in the success of the overall treatment.
  62. 62. REFERENCEMc Cracken’s Removable Partial ProsthodonticsClinical Removable Partial Prosthodontics