11-PROCESSING DENTURES.pdf

DENTURES PROCESSING Introduction Denture Processing It involves replacing the base of the waxed portion with final denture base acrylic resin material (heat cure resins) 2 Preparation of dentures for flasking 1 -The teeth waxed securely into place. 2 - The dentures sealed to the casts 3 - The...

DENTURES PROCESSING Introduction Denture Processing It involves replacing the base of the waxed portion with final denture base acrylic resin material (heat cure resins) 2 Preparation of dentures for flasking 1 -The teeth waxed securely into place. 2 - The dentures sealed to the casts 3 - The casts separated from articulator and trimmed (tapered). 3 1 – FLASKING / INVESTING Process by which the trail denture by plaster/ stone in a metal flask. Purpose of flasking: To produce a mould of the waxed-up denture for packing and processing of the acrylic material. 4 Selection of flask  A big flask, allowing at least half an inch between the teeth and the flask edge. 3 Part flask 1 2 3 4 5 Selection of flask The rim of the cast should flush with the bottom half of the flask. The teeth are not too high in relation to the top of the flask. 6 Technique of Flasking FLASKING TWO POUR TECHNIQUE THREE POUR TECHNIQUE 7 Technique of Flasking  Dental plaster /stone is the best material for flasking.  The lower flask is filled with Model plaster and the model is placed in.  Excess plaster is wiped away and smoothed. 8 ➢ Undercuts should not be present. Sharp edges of plaster removed. A separating medium painted over the plaster The top part is placed in position. 9 ➢ A mixture of Modelling Plaster & Dental stone is placed over the teeth and wax surfaces and vibrate for easy flow of material. ➢ A separating medium painted over this Mixture and washed. 10 ➢ The top section is filled with Dental stone for more strength and excess plaster is wiped away and the two sections closed Lid is closed together. ➢ Leave for bench curing and after the plaster sets remove the excess from the flask. 11 Flask is clamped 2. Wax elimination  The flask is placed in boiling water for 5-7mins.  The flasks are opened and taken under hot running water to clean the remnants of wax.  Wash the mold with a mild detergent for complete removal of wax. 12 Wax washing Wax is washed by boiling water Care is taken to avoid loss of teeth Wax washing Upper and lower flask parts after wax washing Upper flask with teeth 13 3 - PACKING OF ACRYLIC RESIN 14 Separating medium application  Tin foil substitutes is applied by brush.  Examples of the separating medium are: – Water glass (sodium silicate 60 per cent in water) – sodium alginate solutions – Vaseline. 15 Mixing of acrylic resin  The hands washed, mixing vessel cleaned.  The polymer to monomer 3.5 to 1 by volume.  6-8 c.c. of monomer is placed in the mixing container.  The polymer added slowly, tapped and stirred.  The vessel covered. 16 Packing of acrylic resin: Packing done when: – The resin has reached dough consistency - The plaster surfaces in the flask are cold – Separating medium is applied. 17 A - The open flask method  Resin is packed into tooth section of flask  Celloid sheet is placed over it and then the flask is closed gradually under bench press upto 3000Psi pressure  Then the flask is opened and excess resin (Flash) is cut with a sharp knife and removed 18  Again the celloid sheet is placed and the The open flask method flask is closed and pressure applied to remove the flash.  This procedure is repeated 3-4 times until all the excess resin is removed  The flask is then closed without celloid sheet and placed in flask press which is firmly closed for 30 minutes before curing. 19 B - The injection method  In this method a sprue arrangement with a suitable flask is used.  Acrylic resin is constantly fed into the mould during processing through a plunger and spring tension system. 20 Sprue placement Sprue for upper denture Sprue for lower denture 21 The injection system 22 4 - Curing of acrylic resin 23 Curing of acrylic resin  The packed flask is heated in an oven or water-bath  The temperature and time of heating must be controlled.  If the material is under-cured the denture have a high residual monomer content. – a) Free monomer irritate the oral tissues. – b) Residual monomer make the resin weaker.| 24  The rate of temperature rise must be gradual.  Monomer boils at 100.3 degree C.  Polymerization reaction is exothermic.  Thus if a large mass of unreacted material is suddenly plunged into boiling water, the temperature of the resin may rise above 100.3 degree C  So vaporizing the monomer occurs.  This causes gaseous porosity. 25 A - Long curing cycle A constant temperature  At 74º C  For 8 hours or 9 hours  With no terminal boil.  No degradation of resin properties occurs. 26 B - Short curing cycle  Heat at 740 c  For 1.5 hours  Boiling for an additional one hour. 27 C - Rapid curing method  Rapid heating in boiling water for 20 minutes. Cooling  The flask is cooled slowly on the bench to room temperature  Slow cooling permits relief of stresses to avoid distortion (warp) of the acrylic. 28 5 - DEFLASKING 29 Deflasking  The investing plaster is removed in one block from the flask. Investing plaster is cut down from the cast.  Then the model is removed from the denture. 30 Deflasked denture; no porosity or contaminations 31 6- FINISHING AND POLISHING 32 Finishing  The excess flush at the periphery is removed with a large stone or bur.  The surfaces are shaped until it is smooth and clean.  Care must be taken particularly to make the peripheries rounded  Small plebes from the fitting surface are removed with a small stone or bur. 33 Finishing 34 Overheating during finishing cause burn mark 35 Polishing  Polish first with pumice  The final polish with: A rag wheel, brush wheel and felt cone with pumice 36 Finished and polished denture with rounded border, festooning and stippling 37 Processing errors of acrylic resins 38 1. Porosity  Porous denture is difficult to clean, esthetically objectionable and weak Large voids 39 A- SHRINKAGE POROSITY It appears as irregular voids throughout the surface of the denture due to under packing. Causes: • Lack of dough in the mold at the time of final closure. • Lack of adequate pressure during polymerization. • Packing the resin in a sticky rather than doughy stage. 40 B - GASEOUS POROSITY It appears as fine uniform bubbles particularly in thick sections of the denture. Cause: • Thick denture bases heated too rapidly 41 2. Tooth movements Causes:  The use of plaster instead of stone in investing the trial denture.  Incomplete closure of the flask.  Excessive and rapid pressure during trial closure.  Over packing of the mold with resin material before final closure. 42 3. Denture base and teeth breakage during deflasking. Causes:  Knife blade hit teeth when removing stone cap.  Hammer used to tap denture out of the flask. 43 4. Crazing of acrylic resin base or acrylic teeth: Causes:  Stresses induced by the contraction of the resin around the tooth by rapid cooling.  The use of solvents to remove wax from the mold before packing. 44 5. Bleaching of acrylic resin Causes:  Undercured acrylic resin.  Incorporation of the tinfoil substitutes with the acrylic resin. 45 6. Color streaks in the resin material Causes:  Improper mixing of the monomer and polymer.  Contamination of the resin mix with dirty hands or instrument.  Adding resin material in layers during packing. 46 Metallic denture base construction 47 Palatal plate wax pattern 48 Spruing the wax pattern Palatal plate sprue Mandibular plate Sprue 49 and casting Investing The wax pattern is invested and cast into chrome cobalt. 50 Completed cast framework 51 Record block on framework 52 Mounting and setting up of teeth 53 Waxed up denture 54 Finished denture 55 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. 56