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5.Lab procedures for cd after try-in.pptx

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5.Lab procedures for cd after try-in.pptx

  4. 4. INTRODUCTION  The Glossary of Prosthodontic terms defines a complete denture as a removable dental prosthesis that replaces the entire dentition and associated structures of the maxilla or mandible.  Processing converts the trial denture into a denture in its final form.  Success of complete denture is completely dependent on the quality of processing.
  5. 5. ACRYLIC RESINS  Since the mid-1940s, the majority of denture bases have been fabricated using poly (methyl methacrylate) resins.  Such resins are resilient plastics formed by joining multiple methyl methacrylate molecules or “mers”.  Poly methyl methacrylate denture base material usually is supplied as a powder-liquid system.
  6. 6. Based on the method used for activation or curing types of resins are-  Chemically activated denture base resin.  Light activated denture base resin.  Heat activated denture base resin.
  7. 7. Chemically activated denture base resin  chemical activators used to induce the polymerization or curing of denture base resin.  referred to as cold curing, self curing or autopolymerizing resins.
  8. 8. Light activated denture base resin activator initiator  This material has been described as a composite having a matrix of urethane dimethacrylate, microfine silica, and acrylic resin monomers. Visible light camphoroquinone
  9. 9. Heat activated denture base resin activator Water bath/micro-oven  As previously noted, denture base resin contain benzoyl peroxide.  When heated above 60 degree, molecules of benzoyl peroxide decompose to yield free radicals. Thermal energy
  10. 10. COMPOSITION  HEAT ACTIVATED PMMA-  POWDER-  Polymethyl methacrylate  Benzoyl peroxide – Initiator(0.5%)  Pigments and dyed synthetic fibers  LIQUID-  Methyl Methacylate  Hydroquinone- Inhibitor(traces)  Glycol dimethacrylate- Cross-linking agent(10%)
  11. 11.  CHEMICALLY ACTIVATED RESIN-  POWDER-  Polymethyl methacrylate  Benzoyl peroxide – Initiator(0.5%)  Pigments and dyed synthetic fibers  LIQUID-  Methyl Methacylate  Hydroquinone- Inhibitor(traces)  Glycol dimethacrylate- Cross-linking agent(10%)  NN-dimethyl-p-toluidine-Activator
  12. 12.  LIGHT ACTIVATED RESINS  Single component, premixed composite sheets and ropes  Matrix- Urethane dimethacrylate  Filler- Methacrylate resin beads, microfine silica  Photoinitiator- Camphoroquinone
  13. 13. DENTURE PROCESSING TECHNIQUES-  Compression moulding technique  Injection moulding technique
  14. 14. Compression moulding technique  Compression molding is a molding process during which resin is placed between two dies of a mold and subjected to pressure and heat to create a finished part.
  15. 15. Injection moulding technique  It is a complicated procedure requiring special flask and equipment. In this technique the wax pattern is sprued and the material is injected into the mold. This process allows injection of further material during polymerization to compensate for the polymerization shrinkage.
  16. 16. COMPRESSION MOULDING TECHNIQUE  The most commonly used technique for acrylic resins-  1.Preparation of the trial denture  2. Disarticulation  3. Flasking produce  4. Dewaxing ( Boil out )  5. Application of the separation medium
  17. 17.  6. Mixing of powder and liquid  7. Packing  8. Curing  9. Deflasking  10. Finishing and Polishing
  18. 18. PREPARATION OF TRIAL DENTURE  After try-in, the trial dentures are placed on the cast and sealed to the cast using additional wax.  This is done so that the relationship of the trial denture and the cast is not altered during disarticulation.
  19. 19. DISARTICULATION  The junction between the mounting plaster and the cast is split with the help of a wax knife and a plastic mallet.
  20. 20. FLASKING  Flask: Is a metal case or tube used in investing procedures.  Flasking: The process of investing the cast and a waxed denture in a flask to make a sectional mould used to form the acrylic resin denture base.
  21. 21.  The flask is made of 3 major parts,  (1) lower half (which contains the cast),  (2) upper half and  (3) the cover or lid.  The lower half may have a round plate, covering a round hole in the base of the lower half.
  22. 22. Steps in flasking  The waxed maxillary denture on its wetted cast is placed in the bottom part of a denture flask that has been partially filled with plaster.  It is forced into the plaster until the land of the cast is relatively level with the brass sides.  The wet plaster is then smoothened from the brass edge toward the land of the cast so that no undercuts exist, and all plaster is wiped from the edge of the flask.
  23. 23.  When the plaster has set, a film of separating medium is painted on the plaster and the land of cast. This medium will separate this layer from the next.  The upper half of the flask is now placed in position making certain that it is completely seated on the lower half.  The remaining part of the investment may be totally of stone or totally of plaster.
  24. 24.  A combination of plaster and stone is recommended. The stone is painted with a brush into the interproximal spaces and around the gingival spaces; it is then poured to the level of the incisal and occlusal surfaces of the teeth.  The remaining space is filled with plaster.
  25. 25. DEWAXING  When the flasking materials have set, the flask should be heated in boiling water for 4 minutes.  The object is to soften the wax, not to melt it.  If the wax is properly softened, it can be easily lifted from the teeth, almost in one piece with the trial base, and discarded.
  26. 26. APPLICATION OF THE SEPARATION MEDIUM  The flask is now allowed to cool to a point where it can be held in the hand, and separating medium is applied to separate the denture base material from the investing stone or plaster.  All the gypsum mold surfaces must be painted.
  27. 27.  Various types of separating media used are-  Tin foil  Cellulose lacquers  Solution of alginated compounds  Calcium oleate  Soft soaps  Sodium sillicate  Starches
  28. 28.  Sodium alginate solution- It is commonly known as “Cold mould Seal” and is the widely used separating media because of it’s effective and easy manipulation.  Composition-  Sodium alginate solution  Sodium phosphate  Glycerine  Alcohol  Preservatives
  29. 29. MIXING AND PACKING  The monomer and polymer are mixed according to the instructions supplied by the manufacturer.  The ratio is 1 part monomer to 3 part polymer by volume or 1 part to 2 parts by weight.  When the powder and liquid components are mixed in the proper proportions, a doughlike mass results.
  30. 30. POLYMER-MONOMER INTERACTION  Sandy stage  Stringy stage  Doughlike stage  Rubbery Stage/elastic stage  Stiff stage
  31. 31.  DOUGH- FORMING TIME- The time required for the resin mixture to reach a doughlike stage is termed the dough-forming time.  WORKING TIME- Working time may be defined as the time that a denture base material remains in the doughlike stage.
  32. 32. PACKING  The placement and adaptation of denture base resin within the mold cavity is termed packing.  The placement of too much material, that is overpacking leads to a denture base that exhibits excessive thickness and resultant malpositioning of prosthetic teeth.  The use of too little material, that is underpacking leads to denture base porosity.
  33. 33.  The packing process should be performed while the denture base resin is in a doughlike stage.  The resin form is bent into a horseshoe shape and placed into the portion of the flask that houses the prosthetic teeth.
  34. 34.  Then a polyethelene(nylon sheet) is placed over the dough in the upper half and then the two halves of the flask are closed until they are almost in approximation, this is done to spread the dough evenly throughout the mold.  Then the two halves of the flask are separated, the excess material at the borders of the denture is removed by a wax knife, and additional resin is added at any places that are deficient.  At least two trial closures are done and before the final closure the polyethelene sheet is removed and then the two halves of the flask are closed under pressure by bench press.
  35. 35. CURING  After the final closure of the flask in the compress, they should remain at room temperature for a minimum of 1 hour or as much as 4 hours.  This is termed as bench curing.
  36. 36.  It offers several advantages- -it provide longer flow period, thus permitting an equalization of pressures throughout the mold. -it allows time for a more uniform dispersion of monomer throughout the mass of dough, -it also provides longer exposure of resin teeth, to the monomer in the dough.
  37. 37.  Curing is polymerization of the heat cure acrylic, to produce the final denture.  The material is cured by heating in a water bath.  pressure is applied during curing for the following reasons: 1- To decrease the effect of thermal expansion. 2- To decrease the polymerization shrinkage.
  38. 38. Curing cycle  The heating process used to control polymerization is termed the polymerization cycle or curing cycle.  Types of curing cycles for heat cure acrylic:  1- Short curing cycle .  2- Long curing cycle  3- Ultra short curing cycle
  39. 39. 1- Short curing cycle: rapid processing  Submerge the closed flask in water at 71o C for one and half hour followed by boiling for one hour.
  40. 40. 2- Long curing cycle: slow processing:-  9 hours at a constant 71o C is considered adequate for the average denture.  If boiling also is desired in the slow cure, the temperature should be held at 71oC for 9 hrs and then raised to 100o C for 30 minutes.
  41. 41.  The amount of heat must be controlled while processing acrylic resin, as the reaction is exothermic and becomes very rapid at temperature between 60o and 71oC.  Once polymerization has begun , the temperature of the resin may be considerably higher than the temperature of water bath.
  42. 42.  For this reason, the temperature of the water should be maintained at ,or below , 71oC for at least 1 and ½ hrs so that the exothermic heat can be conducted away from the resin.  The boiling point of monomer is 100.8oC. If the heat is not controlled, the exothermic reaction will cause the monomer to boil and result in area of porosity.
  43. 43.  3- Ultra short curing cycle- polymerized in 100oC for 20 min immediately after being packed. In hybrid acrylics both chemical and heat activated initiator formulated to allow rapid polymerization without porosity. Hybrid acrylics
  44. 44. Curing cycle according to different manufacturer Acrylic resin Curing cycle Trevalon -immerse flask in boiling water -turn off heat for 20 min. -Re-heat 100oC for 10 min. Triplex -immerse flask in cold water, -heat up to 100oC -& boil for 45 min. Lucitone -90 min in 73oC -then 30 min in boiling water. pyrax -immerse flask in cold water -heat up to 100oC for 30 min -then boil for 30 min. DPI -2 hrs in 74oC -increase the temp up to 100oC & processing for 1 hr.
  45. 45.  At the close of curing cycle, the flasks in their compress are removed from the water and allowed to cool on the bench.  The compress must not be loosened until the operator is certain that the centre of the flask has reached room temperarure,
  46. 46. POLYMERIZATION VIA MICROWAVE ENERGY  Polymethyl methacrylate resin also may be polymerized using microwave energy.  This technique employs a specially formulated resin and a nonmetallic flask.  A conventional microwave oven is used to supply the thermal energy required for polymerization.
  47. 47. DEFLASKING  When deflasking complete dentures, it is best to use a deflasker, which allows retrieval from the flask without damage to the dentures or flask.  The lid of the flask should be removed by prying with wax knife.  The flask is inverted and placed on the deflasker and tightened with a thumbscrew.
  48. 48.  Pribars are inserted laterally to fit on to the slots of the flask. Once these pribars are engaged, they are lifted up , so that they separate the base and the body by lever action. The body or counter will slide out of the investment.  Place a knife blade in contact with the junction between the second and third pour investment. Tap the back of knife blade with plastic mallet to separate the stone cap and to expose the cusp tips and incisal edges of the denture.
  49. 49.  With a saw and spiral blade, cut through the stone that encloses the denture opposite the central incisor teeth.  Place more saw cuts at the distobuccal corners of the flasked denture.  Placing a knife in the anterior and posterior saw cut and gently separate the stone from the buccal and anterior flanges of the denture.
  50. 50. REMOUNTING  The remounting procedure gives the operator the oppourtunity to see the changes that occurred in the teeth during processing and makes it possible to restore the occlusion that existed on the completion of waxing.  The dentures on their casts are seated, by means of the index notches that were cut on the cast bases before they were mounted on the articulator, on the original plaster mountings and attached with plaster that is added to the sides.
  51. 51.  Normally the incisal pin will show a slight opening.  Articulating paper is placed between the teeth, and the articulator opened and closed in the centric position.  The marks made by the paper indicate which areas should be ground.  This is continued until the original vertical dimension has been restored.
  52. 52. FINISHING AND POLISHING  The dentures on their casts are now removed from the articulator, and the casts separated from the dentures.  The borders, as well as all other areas reduced with the arbor bands, then polished using a wet mix of pumice on a wet rag wheel  Highly polished denture surfaces are more resistant to stains, are more easily cleaned by the patient, and are more conductive to tissue health.
  53. 53.  The inside surface of the denture should be examined both by the eye and the finger and all sharp projections smoothed or removed.  The dentures should then be thoroughly cleaned with warm water, soap and a stiff brush and stored in water until they are delivered to the patient.
  54. 54. Effect of different curing temperatures on the distortion at the posterior peripheral seal: An in vitro study Pasam N, Hallikerimath RB, Arora A, Gilra S. Indian J Dent Res 2012;23:301-4  Most of the maxillary complete dentures do not adapt accurately to the cast because of the changes in the resin during polymerization.
  55. 55. Minimum distortion Maximum distortion no significance difference between the denture bases processed from 68 to 72°C. 70°C 80°C
  56. 56.  Amount of distortion increases as the processing temperature increases which was highly significant.  This study carried out on an ideal edentulous maxillary cast to determine the discrepancy incorporated into the posterior aspect of maxillary denture bases by long curing cycle.
  57. 57. CONCLUSION  All these laboratory steps are important for complete denture construction. Esthetics, function and patient satisfaction depend on a skillfully waxed and properly processed prosthesis.
  58. 58. REFERENCES  Sharry J J. Complete denture Prosthodontics. Third edition. A Blakiston publication.  Morrow R M, Rudd K D, Rhoads J E. Dental laboratory procedures Complete dentures. Second edition. C. V. Mosby company .  Anusavice K J. Phillips’Science of dental materials. Eleventh edition. Elsevier Publication.  RangarajanV, Padmanabhan TV. Textbook of Prosthodontics. Elsevier Publication.  Effect of different curing temperatures on the distortion at the posterior peripheral seal: An in vitro study Indian J Dent Res 2012;23:301-4.