Impression - RPD

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<ul><li>1.IMPRESSION MATERIALS&amp; PROCEDURES FOR R.P.D Presented by Jean MichaelFinal Year Part 2</li></ul> <p>2. INTRODUCTION An impression is defined as a negative likenessof the teeth and/or edentulous areas wherethe teeth have been removed, made in aplastic material which becomes relatively hardwhile in contact with these tissues 3. CLASSIFICATION OF IMPRESSIONMATERIALSRIGID MATERIALSPlaster of ParisMetallic Oxide PasteTHERMOPLASTIC MATERIALSModeling plasticImpression Waxes &amp; Natural Resins 4. ELASTIC MATERIALSReversible HydrocolloidsIrreversible hydrocolloidsMercaptan Rubber-base materialsPolyether Impression MaterialSilicone Impression MaterialsCondensation SIMAddition SIM 5. IRREVERSIBLE HYDROCOLLOIDS(ALGINATE)Indicated for diagnostic casts,orthodontic treatment casts &amp;master casts for R.P.D.Can be used in presence of salivaHydrophilicPleasant taste and smellNontoxic, nonstaining &amp; inexpensive 6. Can be disinfected with 2% GluteraldehydeShould be stored in 100% moisture &amp; poured within1 HourLow tear strengthSurface details - less than elastomeric impressionmaterialsDimensional stability less than elastomericimpression materials 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 &amp; 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. 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 &amp; Stains clothes 9. POLYETHER IMPRESSION MATERIALSGood surface detailsHydrophilic good wettability for easy cast formingShorter working and setting timeFlow characteristics and flow - lowest among othersStiffness cast breakage of while removal from tray 10. Unpleasant tasteAbsorbs waterCannot be immersed in disinfecting solutionsPour within 2 hours for better results 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. ADDITION SILICONESMost accurate among elasticimpression materialsLow polymerization shrinkage &amp;distortionFast recovery from distortionGood tear strengthWorking time 3 to 5 minutes 13. Both hydrophilic &amp; 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. IMPRESSION OF PARTIALLYEDENTULOUS ARCHElastic impression materials are used for makingimpression of partially edentulous archThis is due to the presence of undercuts in thepartially edentulous mouth 15. MATERIALS AVAILABLE FOR MAKINGIMPRESSIONReversible hydrocolloids (agar-agar)Irreversible hydrocolloids (Alginate)Elastomeric impression materials 16. STEPS IN IMPRESSION MAKINGPosition of patient &amp; dentistTray selectionMixing the material &amp; loading into the trayImpression making &amp; removalInspecting, cleaning &amp; disinfecting the impression 17. POSITION OF PATIENT &amp; DENTISTDentist should stand &amp; 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. IMPRESSION TRAY SELECTIONStock trays for dentulous &amp; partially edentulousarches are of 3 types:Rimlock traysPerforated metal traysPlastic disposable trays 19. CHECKING MAXILLARY TRAY SIZEThere should be a clearance of 5-7mm between theinner flanges of the tray &amp; facial surface of teeth &amp;edentulous ridgeTray should cover the desired anatomic areasToo large a tray may be difficult to insert &amp; mayinterfere with the coronoid process of mandible 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 &amp; index fingers are used to manipulate the right corner of the mouth 21. As the right flange of tray is rotated towardmouth, depress the lower lip &amp; stretch the rightcorner of mouth with the left thumb &amp; index finger 22. EXTENDING AN IMPRESSION TRAYSome times impressiontray of adequate widthmay not cover thedesired impression areaIn such cases, the tray islengthened usingmodeling wax 23. MIXING IMPRESSION MATERIAL 24. LOADING IMPRESSION TRAYPlace impression material in small amounts.Tray should be filled in level with the flangesOverfilling should be avoided 25. Mandibular Impression Technique Inject some material over occlusal surface of teeth, into vestibular areas &amp; alveolo-lingual sulcus Then tray is rotated into mouth &amp; 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 &amp; thumb under patients chin 26. Maxillary Impression TechniqueInject alginate into occlusal surface &amp; vestibular areas&amp; wipe some amount on the palateTray must be centered &amp; properly aligned &amp; verify theposition by looking at the patients 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 &amp; stabilize the tray 27. Removal of Impression From Mouth Clinically the initial set of alginate is determined by loss of surface tackiness Release seal by retracting lips &amp; cheek Then impression is removed by a sudden jerk 28. INSPECT THE IMPRESSION FOR DEFECTS 29. CLEAN &amp; DISINFECT THE IMPRESSION 30. Preparation Of Custom Tray 31. Marking the outline on the cast 32. Wax spacer adaptation 33. Self Cure Acrylic 34. Apply self cure acrylic over wax spacer 35. Attaching the Handle and polishing 36. Wax spacer scraped and tray perforated 37. Secondary Impression Same as that for diagnostic impression. In this procedure paint or inject impressionmaterial in critical areas: Rest preparation Hard palate Peripheral extensions 38. SPECIAL IMPRESSION PROCEDURES 39. Anatomic and Functional Form of Ridge 40. Anatomical form of Ridge The anatomic form is the surface contour of the ridge when it is not supporting an occlusal load 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. SPECIAL IMPRESSION PROCEDURES1. Physiologic or functional impression techniqueFunctional Relining methodMc Leans and Hindels methodsFluid Wax method2. Selected Pressure technique 43. Mc LEANS 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 its functional position with finger pressure 44. HINDELS MODIFICATIONMain difference of this with Mc Leans 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. Disadvantages of these methodsConstantly compressed residual ridge is prone toexcessive bone resorption.If the clasp do not hold the partial denture, thedenture will be pushed slightly occlusally by thetissue causing premature contacts (TISSUEREBOUND) 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. 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 &amp; seated in patientsmouth. 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. AdvantagesThe amount of soft tissue displacement is controlledby the amount of relief given to the modeling plasticbefore final impression is madeGreater the relief, the less will be the tissuedisplacement.Tissue surface of metal frame work can be relinedafter insertionDisadvantageSince open mouth technique is used it is difficult tomaintain the previous occlusal contact 50. FLUID WAX FUNCTIONAL IMPRESSION Make an anatomic impression of the arch usingalginate Fabricate a refractory cast using this impression Fabricate the partial denture framework over therefractory cast 51. Draw the outline of the denture baseCast is coated with separating mediumWax Spacer is adapted over the crest of theedentulous ridge 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. 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. 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. SELECTIVED PRESSURE IMPRESSION More force are applied to areas that can absorb stress without adverse response &amp; protect that areas that is least able to absorb force Stress bearing areas are the buccal shelf area &amp; the lingual slopes of residual ridge stress bearing areas The denture base made from this impression will be closely adapted to &amp; in firm contact with the tissues in buccal shelf area 56. Custom Trays 57. The tissue surface if the tray is trimmed with burs toprovide adequate relief 58. Impression material is loaded on the preparedspecial tray and inserted into the patients mouthImpression is made with the patient with his mouthopen under finger pressureOnly the stress bearing areas will be compressedduring impression making 59. Materials used for Secondary ImpressionZinc Oxide Eugenol impression pasteRubber base material 60. Altering The Master CastThis procedure is done to obtain a Hybrid Castwhich records the edentulous areas in the functionalform and the dentulous areas in the anatomic form 61. Conclusion An accurate impression is vital for the successof a cast partial denture. So proper selectionof material, impression technique and the skillof the dentist plays a key role in the success ofthe overall treatment. 62. REFERENCEMc Crackens Removable Partial ProsthodonticsClinical Removable Partial Prosthodontics </p>