Denture Processing PDF

Dr. Emad Amin Azmy Lecturer of Prosthodontic, BDs, MDs, DDs. (Cairo University) Faculty of Dentistry, Nahda University If dentist and patient are satisfied with all aspects of the trial denture; denture is completed in the laboratory.  Denture Processing...

Dr. Emad Amin Azmy Lecturer of Prosthodontic, BDs, MDs, DDs. (Cairo University) Faculty of Dentistry, Nahda University If dentist and patient are satisfied with all aspects of the trial denture; denture is completed in the laboratory.  Denture Processing Processing involves replacing the trial base and waxed portions with the final denture material (Heat cured acrylic resin material).  Denture Processing 1. Waxing up 2. Flasking 3. Wax elimination 4. Packing a) Injection method b) Open flask method 5. Curing of acrylic resin a) Long curing cycle b) Short curing cycle c) Rapid curing method 6. Cooling 7. Deflasking 8. Finishing and polishing Waxing up  Definition Waxing-up is the contouring of trial denture bases by adding or carving wax → to produce a pleasing natural appearance by reproducing the original form of tissues in the dentulous mouth.  Importance Proper form of polished surfaces and location of artificial teeth play a major role in: 1. Denture stability and retention. 2. Esthetics and phonetics. 3. Proper support for cheeks, lips and tongue.  Technique of waxing-up ❖Shaping of wax surface falls into two parts: First part General form. Second part concerned with appearance of labial surfaces to reproduce the natural gingivae.  Upper denture 1. Peripheries must be: ⚫ Extended to maximum depth. ⚫ Fully rounded. ⚫ Highly polished. 2. Proper thickness of labial flange for Lip support and restore lost facial contour. 3. Concavity of buccal contouring for denture stability. 4. Palatal festooning of maxillary anteriors for phonetics. 5. Cusped eminence should be provided. 6. Gingival crests should be trimmed exactly to the finished line. 7. Stippling of the facial surface. 8. Even thickness of the palate (2.5 mm).  Gingival contour Normal gingival contour in Gingival recession in young. elderly. Sharp interdental papillae. Round interdental papillae.  Lower denture 1. Lower labial flange shouldn't be thick to avoid displacement by pressure of lower lip. 2. The peripheries are: ⚫ Fully rounded. ⚫ Highly polished. 3. Proper thickness & slight concavity of the Lingual flanges in the middle of the flange; so that the tongue does not raise the denture. 4. The wax should be extended to cover the maximum area possible in the retromolar region. FLASKING FLASKING  Flasking It is the process by which the cast and trial denture is surrounded by stone or plaster in a metal flask. To produce a mold of the waxed-up denture for packing and processing of acrylic material.  Flask Flask is a metal case used to make a mold for processing acrylic resin during fabrication of dentures and other prosthetic appliances. Flask should be larger enough than the casts.  Procedures Seal the trial denture by wax to the cast. Paint inner walls of flask and bases of casts by separating medium to facilitate their removal. Plaster or dental stone is used (stone is stronger, more accurate than plaster). Place the cast in the flask. Seal the waxed denture base to Soak casts and mounts the cast using base plate wax to facilitate removal Centralize the waxed denture in plaster with the occlusal surface parallel to the base Paint separating medium (to facilitate deflasking) except occlusal surfaces of teeth and pour the third mix of stone to fill the flask and cover with its cover lid. a. Holes to allow excess material to come out. b. Clean flasks, ready for wax removal  Wax elimination  Boil-out & Wax elimination After setting of flasking stone, place flask in boiling water for 3-5 minutes (not more) to soften the wax then flask removed from the water and opened. Not more than 5 min otherwise molten wax will penetrate the flasking plaster.  Boil-out & Wax elimination Carefully open the flask; wax and record base are completely warmed and removed. Both flask halves are thoroughly cleaned by rinsing with boiling water. Ensure that; wax is completely removed → a detergent may be used.  Packing the mold with acrylic resin Open flask method. Injection method. Open flask method  Heat-cured acrylic resin Powder: Polymethylemethacrylate (PMMA). Liquid: Methyl methacrylate (MMA). ❖Insufficient wetting of polymer weaker and granular denture is obtained. ❖Increased monomer increase polymerization shrinkage and porosity.  Packing of Acrylic resin Apply separating medium on stone surface only  Mixing acrylic resin according to the manufacturer’s instructions and packed in the dough stage into cold flask halves.  Polymer/monomer mixture stages 1. Sandy stage. 2. Sticky stage (thread phase). 3. Dough stage (soft but not stick to the gar). 4. Rubber stage. 5. Stiff stage. a) If packed in sandy or sticky stages (high fluidity) and will flow out of the flask denture porosity. b) If packed in rubbery or stiff stage; not flow under pressure and result in dentures without details with moved or fracture teeth.  Application of separator in the mold Before closing the flask apply Tin foil of 0.003 inch thickness as a separator. Functions of separator: 1. To prevent the passage of water from plaster to resin. 2. To minimize the passage of monomer to the plaster. 3. To facilitate the separation of the flask.  Closing the flasks and make sure that intimate metal to metal contact Trial Packing  Denture Curing Curing Procedures (polymerization): ❖ The heat necessary for curing can be supplied by: Hot water bath. Dry heat. Microwave:  Curing cycles 1. Short Curing Cycle: Flask placed in water at 160 ºF (70ºC) for two hours and then held at 212 ºF (100 ºC) for one hour. 2. Long (slow) curing cycle: Flask placed in water at 160º F (70 ºC) for 9 hours (overnight). Recommended for thick dentures, as it reduces the chance of porosity caused by boiling of the monomer. 3. Rapid cycle: To Save time, laboratories will frequently use rapid heating in boiling water for 20 minutes. (cleaner and faster).  Advantages of long cycle over short cycle 1. Less dimensional changes → Less time for occlusal correction in remounting procedures. 2. Less residual monomer → allergic reaction in sensitive individuals). 3. Better adaptation to the cast. 4. Decreased porosity. Indicated for thick acrylic appliances.  Avoid rising curing temp. suddenly to 100 ºC Why? Evaporation of monomer Porosity. Avoid Under curing: (less time and/or temperature) high residual monomer (irritant to tissues and weaker resin). Avoid Over curing: (more time and/or temperature) vaporization of monomer (porosity).  Microwave curing Microwave oven. Used with non-metallic (Fiber reinforced plastic) flask. Advantages: 1. Superior denture base adaptation results from homogenous heating of investing plaster. 2. Reduced curing time. 3. Clean method of curing.  Cooling The flask is removed from the curing chamber and allowed to cool slowly to room temperature (bench cooling) to reduce the risk of distortion.  Deflasking Means: Removing the flasking stone. The flask is opened carefully, stone around the casts and dentures is carefully removed. Dentures are kept on their casts for laboratory remounting. The investing plaster is separated The cast with the processed dentures should be returned to the articulator using V-shaped notches (split cast technique). Why?  Selective Grinding 1. Grinding to obtain balance in centric occlusion. 2. Grinding to obtain balance in lateral movements. 3. Grinding to obtain balance in protrusive movement. Checking CR Correction of Centric Contacts Checking eccentric relations lateral movement (right and left) and protrusive movement. After laboratory remount; denture separated from the cast for finishing and polishing  Finishing and Polishing Excess stone is removed by abrasive stone. Roundation of peripheries, frenal notches and sharp edges. Remove any stone remnants on fitting surface. Polishing with brush wheel and wet pumice. Place dentures in fresh water for few hours (leaching out of free monomer). Finishing and Polishing Injection method  Injection method Fluid resin is used with this technique to be easily injectable. Spruing waxed up denture, in suitable Resin is constantly fed into the mold flask during processing by the pneumatic injection  THE END Best Wishes…. NOW *****  References 1-Allen AA, Heath JR, Mc Cord: Complete Prosthodontics; Problems, Diagnosis and Management. Mosby-Wolf, London, 1995. ◼ 2- Beresin, V.E. and Schiesser, F. J.: The neutral zone in complete and partial dentures. 2nd ed. St. Louis, The C.V. Mosby Company: 1978. 3- Coleman, R. D. and kaiser, W. B.: The Scientific Bases of Dentistry. Philadelphia, W. B. Sounders; 1966. ◼ 4- Craig, R.G.: Restorative Dental Materials. 8th ed. St. Louis, C. V. Mosby Company. ◼ 5-Fenn, H.R.B.; Liddelow, K.P. and Gemson, A.B.: Clinical Dental Prosthetics. 2 ed. London, Staples; 1974. ◼ 6- Geering AH, Kundert M , Kelesy C: Complete denture and overdenture Prosthetics. Theme medical publication Inc. New ◼ York, 1993. 7-Grant AR, Heath JR, Mc Cord JF: Complete Prosthodontics; Problems, Diagnosis and Management. Mosby-Wolf, London, ◼ 1996. 8- Heartwell, C.M. and Rhan, A.G.: Syllabus of Complete Dentures. 3rd ed. Philadelphia, Lea and Febiger; 1986. 9- Sharry, J.J.: Complete denture prosthodontics. 3rd ed. NewYork, McGraw-Hill; 1974. ◼ 10- Sowter, J.B.: Dental laboratory technology: prosthodontic techniques. Chapel Hill, University of North Carolina; 1968. ◼ 11-Watt, D.M. and Mac Gregor, A.R.: Designing complete dentures. Philadelphia, W.B. Sounders; 1976. 12-Winkler, S.: Essential of complete Denture Prosthodontics. 2nd ed. PSG Publishing Company; 1988. ◼ 13- Zarb, G.A.; Bolender, C.L.; HicKey, J.C. and carlesson, G.E.: Boucher's Prothodontic Treatment for Edentulous Patients. 7th. Ed. ◼ St-Louis, The C.V.Mosby Company; 1990. N, B. All pictures in these slides are copied from the above references and from the internet. ◼  Common laboratory Errors Porosity a. Packed at sticky stage. b. Rapid rise in temperature. c. Lack of metal to metal contact Crazing a. Contamination. b. Rapid rise in temperature. c. Rapid cooling. Sandy a. Dry mix. appearance b. Evaporation of monomer. c. Delayed curing. Denture base with nodules a. Air bubbles within the stone Cracked or a. Improper flasking or deflasking. fractured teeth b. Rapid curing or cooling. Tooth a. Plaster instead of stone. movement b. Not enough time for plaster setting. c. Late packing or overpacking. d. Incomplete flask closure. e. Teeth not retained.  Denture base and teeth breakage during deflasking Causes: 1. Knife blade hit teeth when removing stone. 2. Hammer used to tap denture out of the flask.  Stone adhere to the surface of denture Causes: 1. Insufficient separating medium on the mold before packing. 2. Contamination of separating medium with stone. 3. Incomplete elimination of wax during washing out thus rendering separating medium ineffective.