Impressions for fixed partial dentures /certified fixed orthodontic courses by Indian dental academy


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Impressions for fixed partial dentures /certified fixed orthodontic courses by Indian dental academy

  2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
  4. 4.    To obtain an impression is the first step necessary for the indirect fabrication of a prosthesis. Fixed prosthodontics is practiced as indirect restorations. Well-fitting indirect restorations can only be made if there are accurate casts of the oral tissues available, made from high quality impressions. A good quality impression is only obtained when we have a thorough knowledge of materials, their properties, and techniques for their best manipulation.
  6. 6. IMPRESSION : A negative likeliness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry – G.P.T-8 IMPRESSION TRAY : A receptacle into which suitable impression material is placed to make a negative likeliness (or) a device that is used to carry, confine, and control impression material while making impression– G.P.T-8
  7. 7. IMPRESSION MATERIAL: Any substance or combination of substances used for making an impression or negative reproduction. – G.P.T8 IMPRESSION TECHNIQUE : A method and manner used in making a negative likeness. – G.P.T-8
  8. 8. History     Philip Ptaff-1756  First described taking impression with softened wax Christopher Francois Delabarre-1820  Introduced the metal impression tray Chapin Haris-1853  First used Plaster of Paris for making impressions Charles Stent-1857  Introduced the first impression compound
  9. 9.     Sears-1937  First used agar hydrocolloids for recording crown impressions. United States-1945  Introduced alginate during World War II. SL Pearson-1955  Developed synthetic rubber base impression materials Polysulfide- Late 1950’S  First developed as an industrial sealant.
  10. 10.     Condensation Silicone- Early 1960’s Addition Silicone-1970’s Polyether- Late 1970’s Polyether Urethane Dimethacrylate - Late 1980’s
  11. 11. Properties Of An Ideal Impression 1) Complete plasticity before cure 2) Sufficient fluidity to record fine detail. 3) The ability to wet the oral tissues. 4) Dimensional accuracy. 5) Dimensional stability. 6) Complete elasticity after cure. 7) Optimal stiffness.
  12. 12. Impression Materials Used In F.P.D 1)Hydrocolloid impression material a) Reversible hydrocolloid b) Irreversible hydrocolloid 2)Elastomeric impression materials a) Polysulfide b) Addition silicone c) Condensation silicone d) Polyether Dimethacrylate
  13. 13. Impression Techniques       1. Stock tray technique - Double mix - Single mix 2. Custom tray technique - Single mix 3. Closed bite double arch technique 4. Copper band technique 5. Reversible hydrocolloid technique - Laminate Technique - Wet Field Technique 6. The matrix system
  14. 14. STOCK TRAY IMPRESSION TECHNIQUE (Putty wash technique): Mixing method: Double mix and single mix Procedure :     Place patient in supine position. Operator is positioned at nine o clock and assistant is positioned at 3 o’clock position. Select tray type based on relative need for retention and personal preference. Select tray shape and size based on patients arch shape and size.
  15. 15.     Coat the tray with adhesive on the inside and rim. Mix the high viscosity putty impression material according to manufacturer’s instructions. Roll putty into elongated cylinder. Insert into the stock impression tray.
  16. 16.  Cover putty with the manufacturer’s spacer (a sheet of polyethylene)  Insert and seat the tray with a rocking motion. Hold and wait until initial set. Remove from the mouth with minimal sideward movement. Wait and test for final set with the clinical final set, which is when a finer nail impression rebounds completely. Peel off the spacer. Remove excess impression material with a sharp knife.     
  17. 17. SINGLE MIX TECHNIQUE: MAKING FINAL IMPRESSION:   Choose a large mixing pad approximately six by eight inches. Choose a spatula that is long enough to pick up the mixed impression material, yet sufficiently pliable to mix the material against the pad.
  18. 18.    Mix the low-viscosity, impression material according to manufacturer’s instructions. First use a circular motion, joining the two strands. Then a figure eight motion to blend and flatten the mixture onto the mixing pad. While flattening the mixture, limit the number of times of lifting the spatula from the pad, this reduces the number of voids in the mixture.
  19. 19.       Load the low viscosity impression material on to a syringe . Syringe in the inaccessible area first eg disto lingual line angle. Seat the tray . Wait for the final set. Remove the tray parallel to the preparation path of withdrawal. The impression is evaluated for the finish lines and for any distortion and tear.
  20. 20. DOUBLE MIX TECHNIQUE       For the stock tray double mix insert the low viscosity impression material into the tray without overfilling it. Spread the cheeks one at a time, first with the tray and then with an index finger. Position the tray over the arch. Seat from posterior to anterior, allowing the excess to extrude anteriorly. Apply force in a vertical direction until further seating is impossible. Evaluate final position and adjust tray quickly if necessary.
  21. 21. EVALUATING FINAL IMPRESSION     Elastomeric material should be present 0.5 mm beyond visible finish line. Note presence of bur marks, the junction of smooth root surface, and continuous finish line. There should be no shiny smooth areas; if present, they suggest moisture contamination. There should be no tray showthough in any areas of the impression except at tissue stops.
  22. 22.   There must be no voids present, they suggest mixing problems or contamination. There should be no thin areas leaving the finish line unsupported. These areas distort under the weight of the stone.
  23. 23. Custom Tray Fabrication For Elastomeric Impression 1)Mark the border of the tray on the diagnostic cast with a pencil approximately 5mm apically to crest of the free gingiva.
  24. 24. 2)Adapt a wax spacer to the diagnostic cast two layers for 2.5mm thickness approximately.
  25. 25. Tray Stops
  26. 26. 3)Apply a layer of tinfoil over the wax. 4)Mix autopolymerizing acrylic resin according to manufacturers recommendation 5)Adapt the resin to the cast when in dough stage.
  27. 27. Tray handle is made Borders are trimmed and the tray is polished
  28. 28. Lateral wings can be made which will help in easy removal of the tray
  29. 29. Thermoplastic Tray Thermoplastic custom tray material Material is softened in hot water Material being adapted to spaced cast
  30. 30. 2-3 mm thick hard splint material is softened and adapted using vacuum adaptation machine.
  31. 31. Visible light – polymerized custom tray Visible light-polymerized custom tray material Material adapted to the spaced cast The assembly is placed on the turntable of a special curing unit and exposed to intense light
  32. 32. Prepare syringe:    Lubricate the syringe lightly. Trim tip. Open orifice to increase rate of flow or close orifice to decrease rate of flow. Measure arch length of tray to guide in dispensing the amount of elastomer. (Dispense one time the length of the tray for the low viscosity elastomer).
  33. 33. Making the final impression. Medium or high viscosity is used in the tray and low viscosity in the syringe. The syringe is loaded with the low viscosity material and syringed in the prepared site. The high viscosity material is placed in the custom tray and seated in the mouth.
  34. 34. The impression is removed and evaluated.
  35. 35. Close Bite Double Arch Method synonyms :dual quad tray, double arch , triple arch , accu -bite ,closed mouth impression. Requirements The articulator must have a vertical dimension holding stop such as an incisal pin or other metal-to-metal contact. There should be sufficient space distal to the terminal tooth in the arch to allow tray approximation.
  36. 36. Technique Evaluate the fit of the tray in the patients mouth. Observe the complete bilateral closure and the patients comfort.
  37. 37. Making the final impression      Mix the low viscosity material and load the syringe The high viscosity material is used in the tray. After the low viscosity material is syringed the tray is positioned on the arch. Instruct the patient to close the mouth and observe for the interdigitation on the opposite arch. Wait for the material to set .
  38. 38. Instruct the patient to open the mouth remove the tray by applying equal pressure bilaterally. Evaluate the impression.
  39. 39. Advantages The physical deformation of the mandible is minimal The shifting of teeth occurring during maximum intercuspation is captured. Less impression material is needed. Less gagging may occur. Disadvantages The tray is not rigid . Limited to one casting per quadrant . The distribution of impression material is not uniform
  40. 40. Copper Band or Tube Method The copper band is used to salvage an impression of multiple preparation where there is only vague margins on one or two preparation that are not adequately replicated in the impression. Fitting of the copper band to preparation A copper band is selected and annealed by heating on a flame and quenching in alcohol. Mark the finish line with the explorer and round off the edges. evaluate the fit and cut orientation hole in top one fifth of the facial surface .
  41. 41. Copper band with orientation holes
  42. 42. Copper band contoured
  43. 43. Evaluating the fit of the copper band The circumference of the copper band must be such that it will fit over the preparation and still project into the gingival crevice. An oversize band should not be used since it will impinge on the gingival tissues.
  44. 44. Making the compound plug The red stick compound is heated over the Bunsen flame . Insert the warm compound mass to fill approximately the top third of the copper band. Seat and orient on to preparation and compress excess in to the band. The compound should just touch the occlusal surface . Remove and evaluate the impression, only the occlusal surface should be impressed. Remove 0.2mm of the compound to create space for the heavy body poly vinyl silicone. Drill a hole through the centre of the compound plug.
  45. 45. Making the impression. Make 4 to 5 holes evenly distributed above the bottom of the copper tube for the retention of the impression material. Coat the internal surface sparingly with adhesive . Clean and isolate the preparation. Mix heavy viscosity material and inject in to the band and position it on the tooth. Wait the material to set remove the band and inspect the impression
  46. 46. Copper band with the final impression
  47. 47. Reversible hydrocolloid technique This impression technique requires a special conditioning unit which consists of 3 thermostatically controlled water baths. 1. A liquefaction bath . 2.A storage bath . 3.A tempering bath.
  48. 48. Rimlock trays
  49. 49. Procedure Select the correct size of water cooled impression trays. Place small modeling compound or prefabricated stops in the tray to prevent over seating . Fill the impression tray with heavy bodied material from the storage bath and place it in the tempering bath Load the syringe material in the syringe and replace it in the storage bath. Carefully remove the retraction cord and flood the tooth with water.
  50. 50. Inject the syringe material on the tooth cover the entire tooth. Remove the impression tray from the bath wipe with the gauze and place it in the mouth. After seating cold water is circulated through the tray until the impression material is set. Remove the impression with a rapid motion, wash with cold water ,evaluate for accuracy.
  51. 51. Laminate Technique (or) Agar Alginate Combination Technique   After injecting the syringe agar on to the area to be recorded, an impression tray containing a mix of chilled alginate that will bond with the syringe agar is positioned on it. The alginate gels by a chemical reaction, whereas the agar gels by means of contact with the cool alginate rather than the water circulating through the tray.
  52. 52. Advantages 1. Less air bubbles 2. Water cooled trays are not required 3. It sets faster than the regular agar technique.
  53. 53. Wet Field Technique    This is relatively new technique which has become popular.the areas to be recorded are actually flooded with warm water. Then the syringe material is introduced quickly, liberally and in bulk to cover the occlusal and/or incisal areas only. while the syringe material is still liquid, the tray material is seated.
  54. 54.  The hydraulic pressure of the viscous tray materials forces the fluid syringe hydrocolloid down into the areas to be recorded.  This motion displaces the syringe materials as well as blood and debris throughout the sulcus
  55. 55. The matrix impression system This system uses three impression materials  Matrix impression material  Tray impression material  Matrix forming material
  56. 56. Matrix impression material :    This material is used to fill the matrix and generate the critical portion of the impression. It would be a high viscosity material to facilitate the displacement of the gingiva and to effectively flush the debris out of the sulcus. High viscosity polyether is preferable for this procedure.
  57. 57. Tray impression material:   The impression material that is placed in the stock tray should be compatible with and bond to the matrix forming material and the impression material lining the matrix. The viscosity of the tray material should be considerably less than that of the matrix material to facilitate impression removal because the matrix manages the critical portion of the impression removal ; a stock tray is used to incorporate the matrix and the remaining teeth in the arch.
  58. 58. Matrix forming material :    On setting this impression material needs to provide a semi rigid matrix . The matrix forming material should register details equal to the best impression materials Matrix forming materials should be rapid setting and compatible with matrix impression and tray impression materials.
  59. 59. Immediately after tooth preparation and before any retraction procedures Clear plastic carrier selected from assortment of premade forms. Matrix is made in carrier with polyvinyl siloxane material before soft tissue is retracted.
  60. 60.  Slender bur or knife edged rubber wheel used to enlarge interproximal embrasures. Black Lines Indicate Sulcular extension . Thick red line indicates crest of gingiva. Two black marks point out proximal contacts that must be relieved. Matrix should extend one half to two thirds of tooth beyond prepared teeth and close to gingival crest.
  61. 61. Impression syringe is used to fill matrix with high viscosity impression material. Matrix impression is seated with light pressure. Stock tray filled with medium viscosity impression material is seated over matrix impression before matrix material polymerizes.
  62. 62. REVIEW OF LITERATURE  Nachum Samet DMD, Michael Shohat DMD, Alon Livny DMD and Ervin I. Weiss DMD: A clinical evaluation of fixed partial denture impressions; J Prosthet Dent, volume 94, issue 2, August 2005, pages 112 – 117: This study evaluated the quality of impressions sent to commercial laboratories for the fabrication of fixed partial dentures (FPD) by describing the frequency of clinically detectable errors and by analyzing correlations between the various factors involved. Within the limitations of this study, impressions made with polyethers had the most detectable errors, followed by condensation-type silicones. The high frequency of detectable errors found in impressions sent for FPD fabrication is of concern.
  63. 63.  Hung SH, Purk JH, Tira DE, Eick JD : Accuracy of one-step versus two-step putty wash addition silicone impression technique; J Prosthet Dent. 1992 May; 67(5):583-9: This study compared the accuracy of one-step putty wash with two-step putty wash impression techniques. Five addition silicone impression materials-Mirror 3 (MR), Mirror 3 Extrude (ME), Express (E), Permagum (P), and Absolute (A)-were tested. A stainless steel model containing two full-crown abutment preparations was used as the positive control. Five replications for one-step and two-step putty wash impressions of the master model were made for each test material. Accuracy of the materials was assessed by measuring six dimensions on stone dies poured from impressions of the master model. Accuracy of addition silicone impression material is affected more by material than technique. Accuracy of the putty wash one-step impression technique was not different from the putty wash two-step impression technique except at one of the six dimensions where one-step was more accurate than two-step. Mirror 3 putty wash two-step impression presented less distortion than Mirror 3 Extrude putty wash one-step or two-step impression.
  64. 64.  Ciesco JN, Malone WF, Sandrik JL, Mazur B : Comparison of elastomeric impression materials used in fixed prosthodontics; J Prosthet Dent. 1981 Jan; 45(1):89-94: Five elastomeric impression materials were evaluated: two polysulfides (one lead-cure and one nonlead cure), two silicones (one condensation polymerization and one addition polymerization), and one polyether. These materials were subjected to simulated clinical conditions. Two techniques were evaluated. All materials were evaluated initially with use of a custom tray and manufacturers' adhesive. A second evaluation was performed without using the tray system. Both techniques were subjected to statistical comparison. Conclusions of the research were as follows: 1. All impression materials that were poured immediately and evaluated using a custom tray and adhesive consistently demonstrated superior results in comparison to those tested without the custom tray. 2. Polyether material consistently yielded superior results with or without a custom tray when compared to the other impression materials. The additional polymerization silicone ranked second, followed by the leadcure polysulfide and the condensation polymerization silicone, respectively.
  65. 65.  Nissan J, Laufer BZ, Brosh T, Assif D : Accuracy of three polyvinyl siloxane putty-wash impression techniques; J Prosthet Dent. 2000 Feb; 83(2):161-5; This study assessed the accuracy of 3 putty-wash impression techniques (1) 1-step (putty and wash impression materials used simultaneously); (2) 2-step with 2-mm relief (putty first as a preliminary impression to create 2-mm wash space with prefabricated copings. In the second step, the wash stage was carried out); and (3) 2-step technique with a polyethylene spacer (plastic spacer used with the putty impression first and then the wash stage). using the same impression material (polyvinyl siloxane) in a laboratory model. For each technique, 15 impressions were made of a stainless steel master model that contained 3 complete crown abutment preparations, which were used as the positive control. Accuracy was assessed by measuring 6 dimensions (intraabutment and interabutment) on stone dies poured from impressions of the master model. CONCLUSION: The polyvinyl siloxane 2-step, 2-mm, relief putty-wash impression technique was the most accurate for fabricating stone dies.
  66. 66. Summary A good impression is an exact replica of each prepared tooth and should include adequate amount of the unprepared surfaces adjacent to the margin. Impression technique and material should be selected on the basis of biologic factor dictated by the anatomy and the physiology of the mouth dictated by the orofacial tissues. Even though there are innumerable techniques and procedure for impression making ,it is the responsibility of the dentist to select the best possible procedure based on sound knowledge , for achieving the best possible result for the patient.
  67. 67. Thank you Leader in continuing dental education