PFM 2(1) PDF - Porcelain Fused To Metal Restorations

PORCELAIN FUSED TO METAL RESTORATIONS: LAB TECHNIQUES II Dr. MOHAMED El HALAWANI  Ceramics What are ceramics? “Ceramic” derived from Greek words “Keramikos” = Earthen “Keramos” = Burnt stuff Defined as; inorganic, non- metallic materials made by man by...

PORCELAIN FUSED TO METAL RESTORATIONS: LAB TECHNIQUES II Dr. MOHAMED El HALAWANI  Ceramics What are ceramics? “Ceramic” derived from Greek words “Keramikos” = Earthen “Keramos” = Burnt stuff Defined as; inorganic, non- metallic materials made by man by the heating of raw minerals at high temperature*. * Rosenblum MA, Schulman A. A review of all ceramic restorations, J Am Dent Assoc 1997;128:297-307.  Dental Ceramics contain a glassy matrix reinforced by various dispersed phases consisting of crystalline structures such as Lucite, alumina & mica*. The term ‘glass ceramic’ has been introduced to classify ceramics where one or more crystalline phases have been precipitated from a glassy phase*. Ceramics and glasses are brittle, which means that they display a high compressive strength but low tensile strength and may be fractured under very low strain (0.1%, 0.2%)**. * Kelly JR. Dental ceramics: what is this stuff anyway?. JADA 2008;139(suppl 4):4S-7S ** Shenoy A, Shenoy N. Dental ceramics: An update. J Conserv Dent 2010;13:195-203 Classification of Ceramics Based on firing temperature Ultra-low fusing < 870oC Low fusing 870oC - 1070oC Medium fusing 1090oC - 1260oC High fusing > 1290oC Ceramics in PFM restorations range between 950oC to 1020oC Rosenstiel L, Fujimoto. Contemporary Fixed Prosthodontics. 4th ed. St. Louis, Missouri: Mosby Inc; 2006.  Classification of Ceramics Microstructurally Predominantly Glass Best mimic the optical properties of enamel and dentin. Have a high glass content. Used in veneering ceramics (including PFM). Particle-filled Glass Improved mechanical properties. These fillers usually are crystalline, but they also can be particles of high-melting glasses that are stable at the firing temperatures of the ceramic. Polycrystalline Ceramics Contains no glass, all of the atoms are packed into regular crystalline arrays through which it is much more difficult to drive a crack. Generally are much tougher and stronger. Kelly JR. Dental ceramics: current thinking and trends. Dent Clin North Am 2004;48(2):viii, 513-530.  Glass Ceramics A glass ceramic is a multiphase solid containing a residual glass phase with a finely dispersed crystalline phase. The controlled crystallisation of the glass results in the formation of tiny crystals that are evenly distributed throughout the glass. The number of crystals, their growth rate and thus their size are regulated by the time and temperature of the ceraming heat treatment. Shenoy A, Shenoy N. Dental ceramics: An update. J Conserv Dent 2010;13:195-203  What is Ceraming? It is a conversion process from a glass to a partially crystalline glass. Divided into 2 phases; 1. Nucleation Glass is heated up to a temperature where nuclei form (750°- 850°C), and this temperature is kept for a period of time ranging from 1 to 6 h so that crystalline nuclei form in the glass. 2. Crystallization The temperature is increased to the crystallization point (1000°- 1150°C) and this temperature is maintained for a period ranging from 1 to 6 h until the desired level of glazing is obtained Adair PJ. Glass ceramic dental products. 1982. US Patent 4,431,420, 1984 - Google Patents.  Composition of Glass Ceramics Main Components: Feldspar - Basic Glass former (potassium aluminum silicate - K2O.Al2O3.6SiO2) - Reduces fluidity of molten materials - Helps maintain form of porcelain buildup - Adds translucent qualities after firing Glass Modifiers - Fluxes (potassium, calcium and sodium oxides) - Increase coefficient of thermal expansion by breaking up oxygen cross-linking. Silica - Filler (Quartz or Flint - SiO2) - Responsible for forming glass matrix - Framework for other ingredients —> Stability - Strengthening of porcelain Kaolin - Binder (Clay - Al2O3-2SiO22H2O) - Opaqueness - Mouldability - sticky when mixed with water forming workable mass - Maintains shape during firing in furnace - Shrinks during firing Alumina (Al2O3) - Adds strength to porcelain - acts as crack stopper  Composition of Glass Ceramics Its composition is as follows: 45-70% SiO2 8-20% MgO 8-15% MgF2 5-35% R2O + RO - R2O has a range between 5-25% and is composed of at least one of the following oxides: 0-20% K2O, 0-23% Rb2O and 0-25% Cs2O to improve translucency - RO has a range between 0-20%, and is composed of at least one of the following oxides: SrO, BaO and CdO. Additional components may account for up to 10% of Sb2O5 and/or up to 5% of traditional glassy colorants. Adair PJ. Glass ceramic dental products. 1982. US Patent 4,431,420, 1984 - Google Patents. Grossman D. Tetrasilicic mica glassceramic method. 1973. US Patent 3,732,087, 1973 - Google Patents.  Properties of Ceramics Strength of Feldspathic Porcelain: Flexural Strength —> (60 - 100 MPa)* Compressive Strength —>Good CS (331 MPa) Tensile Strength —> Low TS (34 MPa) Factors Affecting Strength: Composition —> amount of fillers Surface integrity and imperfections (cracks or porosities) —> dec. strength Firing procedures —> inadequate firing —> dec strength * Ironside and Swain. Ceramics in dental restorations - a review and critical issues. Journal of the australasian ceramic society. 1998.34;78-91  Properties of Ceramics Surface Hardness Much higher than natural teeth. Wear Resistance More resistant to wear than natural tooth enamel. Chemical Stability Insoluble and impermeable to oral fluids. Can only be etched by HF acid. Excellent esthetics matching tooth translucency and color Very Biocompatible to human tissues. * Ironside and Swain. Ceramics in dental restorations - a review and critical issues. Journal of the australasian ceramic society. 1998.34;78-91  Properties of Ceramics Thermal Coefficient of Expansion: (COTE) - It is the change in length per unit of original length of material when temperature is raised by 1 K. - COTE of veneering porcelain must be compatible with that of metal substructure -> prevent cracking after cooling - Difference of COTE of 0.5 x 10-6 between porcelain and metal causes higher contraction in metal during cooling —> puts ceramic under compressive forces —> improves bond PROJECT BONDING OF PORCELAIN TO METAL SUBSTRUCTURE  Bonding Mechanisms 1. Mechanical Entrapment 2. Compressive Forces 3. Van del Waal’s Forces 4. Chemical Bond H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Bonding Mechanisms 1) Mechanical Entrapment Interlocking ceramic with micro abrasions in surface of metal Enhanced by finishing of the metal with; A. Non contaminating stones or discs B. Air abrasion —> enhances wettability H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Bonding Mechanisms 2) Compressive Forces Produced by the difference in COTE Porcelain should have slightly lower COTE than metal (around 0.5 x 10-6) —> porcelain will draw towards metal coping when restoration cools H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Bonding Mechanisms 3) Van der Waal’s Forces Affinity based on mutual attraction of charged molecules Insignificant on its own Contributes to initiation of chemical bond H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Bonding Mechanisms 4) Chemical Bond Oxides in opaque layer of porcelain bonds to oxide layer formed on the surface of the metal when fired in air. Oxide layer should have optimum thickness - avoid too thick oxide layer Gold alloys: Trace elements such as tin, gallium or iron in gold alloys migrate to surface during firing. Base metals: Readily form chromium oxides. H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Classification of Failure of Bond No oxide layer formed Most common type of Or Contaminated fracture with gold alloys Surface Occurs due to over Common in Base metals production of oxide alloys layer Due to over-production Most unlikely in crowns. of Chromium oxide on Occurs in joint areas in surface bridges Rosenstiel L, Fujimoto. Contemporary Fixed Prosthodontics. 4th ed. St. Louis, Missouri: Mosby Inc; 2006. LABORATORY TECHNIQUES - PORCELAIN BUILD UP  Metal Framework Preparation Sharp angles or pits on the veneering surface of metal-ceramic restoration should be avoided. Convex surfaces and rounded contours should be created so that the porcelain is supported without development of stress concentration. Non-contaminating discs and burs should be used. The metal framework should be sufficiently thick to prevent distortion and flexing during firing (min 0.3 - 0.5 mm for noble metals & 0.2 mm for base metals) H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Metal Framework Preparation The intended metal-ceramic junction should be as definite ( 90 0 ) and as smooth as possible. Occlusal contacts should be placed away from the metal-ceramic junction — > prevent de-lamination. Proximal contacts in anteriors must be placed lingual to contact area; - Better esthetics (depth of porcelain) - Optimum stress distribution H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Metal Framework Preparation Oxidizing: 1) Done to obtain an oxide layer for chemical bonding with porcelain. 2) Degassing —> getting rid of Hydrogen gas incorporated in metal during casting IF Left Hydrogen release during firing —> Air bubbles —> Weaker Bond H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Metal Framework Preparation A controlled oxide layer must be formed on the metal surface The oxide layer is obtained by placing the substructure on a firing tray, inserting it into the muffle of a porcelain furnace and raising the temperature to a 300 - 400oC. Noble Alloys - trace elements; tin, gallium, indium and zinc form oxides Base Metal Alloys - readily oxidize —> carefully control oxidation process H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Metal Framework Preparation After oxidation, most alloys require air abrasion with 50μ Al2O3 —> reduce layer of oxide formed. Excess oxide —> weakens bond —> cohesive failure in oxide layer H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997. PORCELAIN APPLICATION  Steps of Porcelain Application 1. Opaque Porcelain Application 2. All-porcelain Margin (Shoulder porcelain) 3. Dentin and Enamel Application 4. Surface Treatment (Glazing)  Opaque Porcelain Application Objectives: A. Mask the metal substructure B. Give the basic shade C. Initiate bond with metal H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Opaque Porcelain Application Composition of Opaque Porcelain: These porcelains are made opaque by the addition of insoluble oxides; Tin oxide (SnO2), titanium oxide (TiO2), zirconium oxide (ZrO2), cerium oxide (CeO2), rubidium oxide, barium oxide and zinc oxide. Such oxides have high refractive indices, so they scatter light. Between 8% and 15% of an opaque powder is composed of metallic oxides, and some particles may be less than 5 um in size.  Opaque Porcelain Application Brush Technique: First Layer A. Opaque porcelain mixed with distilled water or special liquid B. Thin layer wash is applied with brush C. 1st layer is for wetting the metal, does not have to completely mask it H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Opaque Porcelain Application D. Preheating: Coping is dried in front of the muffle of an open preheated porcelain furnace —> prevent rapid formation of steam which can break up the condensed mass. E. Then it is fired under vacuum; A. Powder particles packed together by initial air currents B. Air pressure reduced to 1/10 atmospheric C. Temp rises —> porcelain sinters —> closed voids formed within mass D. Vaccum released and pressure returns to normal —> voids are compressed to 1/10 of their original size.  Opaque Porcelain Application Brush Technique: 2nd layer A. Applied to mask the metal B. Should be as thin as possible (approximately 0.3 mm) C. Coping is gently vibrated to condense porcelain and remove excess water H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Opaque Porcelain Application Glass Rod technique A. Wet the oxidized metal with distilled water or special liquid B. Use pointed end of glass rod to apply the opaquer C. Begin opaquing from the most convex portion and move the opaquer from one inter proximal area to the other  Opaque Porcelain Application Sprayed Opaquers Available in different shades (ex AEROpaque, Enamellite LLC)  All-porcelain Margin Fabrication (Shoulder Porcelain) Direct Lift Technique Facial shoulder finish-line marked with side of red pencil Cyanoacrylate cement applied to seal the die in area of shoulder and excess is blown off Porcelain release agent (lubricant)—> prevent sticking of porcelain to die H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  All-porcelain Margin Fabrication (Shoulder Porcelain) Direct Lift Technique First shoulder porcelain applied to the facial shoulder with a brush - extend 2-3 mm on metal coping Condensed and blotted with tissue Excess removed using spoon excavator or discoid carver H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  All-porcelain Margin Fabrication (Shoulder Porcelain) Direct Lift Technique Smooth the margin with #10 sable condensing brush Carefully tease the coping from die Any visible porcelain on internal aspect —> removed Dry porcelain in front of furnace and fire it under vacuum at a temp 30oC higher than body and enamel porcelain H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  All-porcelain Margin Fabrication (Shoulder Porcelain) Correction of Shoulder Porcelain After firing; inspection of the restoration —> if small opening present at margin — > more shoulder porcelain can be added Die seated firmly after addition of porcelain Excess removed and smoothed H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Dentin and Enamel Build Up Dentin Build Up: Mix dentin porcelain with distilled water H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Dentin and Enamel Build Up Dentin Build Up: Apply over opaquer with stable brush - start gingivo-facially H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997. Dentin and Enamel Build Up Condensation of Ceramic —> Process of packing porcelain powder close together. Methods of Condensation: Vibration —> helps settling of powder Spatulation —>wet porcelain smoothed with spatula to bring excess water out Brush —> dry powder placed on side opposite of wet porcelain —> capillary action of water Ultrasonic Whipping Excess water absorbed with a tissue.  Dentin and Enamel Build Up Dentin Build Up: Develop full contour Vibrate to condense Absorb excess liquid with tissue Carve dentin back to allow placement of enamel H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Dentin and Enamel Build Up Enamel Build Up: Apply enamel porcelain on inciso-facial part to restore full contour (space available after cut back) Condense and blot excess liquid Dry and Fire under vacuum H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Dentin and Enamel Build Up Enamel Build Up: Porcelain exhibits significant linear shrinkage on firing Restoration should be slightly larger incisally to compensate for shrinkage H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Dentin and Enamel Build Up Enamel Build Up: Add porcelain into the proximal area to compensate for shrinkage Remove excess from unveneered metal at the junction Build up dried in front of furnace and fired under vacuum H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Dentin and Enamel Build Up Minor Corrections: After Correction bake, crown may not seat completely —> Adjust with diamond discs, aluminum oxide stones or carborandum stone H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Porcelain Surface Treatment 3 Commonly used treatments 1.Natural autoglaze 2.Applied overglaze 3.Polishing H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Porcelain Surface Treatment 1.Natural (autoglaze) Porcelain has the ability to glaze itself when held at its fusing temp Preserves surface character and texture of porcelain H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Porcelain Surface Treatment 2.Applied Overglaze Porcelain loses ability to self glaze after multiple firings —> overglaze indicated (large restorations) Low-fusing clear porcelain Painted on surface of the restoration H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Porcelain Surface Treatment 2.Applied Overglaze Fired at fusing temp much lower than enamel and dentin porcelain Caution not to overfire —> return to more crystalline state — > milky or cloudy appearance “devitrification” H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997.  Porcelain Surface Treatment 3.Polishing Used on relatively small areas (proximal contacts and limited areas of occlusal contacts) Done by rubberized abrasives and polishing compounds Polished porcelain less destructive to opposing tooth structure than glazed porcelain H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997. McLaughlin G: One hundred second etch technique for etched-metal fixed parcial dentures. J Mich Dent Assoc 1982;64:347-49  Shade Modification (Custom Staining) Lightening dark shade porcelain nearly impossible —> repeat build up Lighter shades can be modified Simulation of fracture lines and areas or discoloration — > more natural appearance H T Shillingburg SH, L Whitsett, R Jacobi, S Bracket. Fundamentals of fixed prosthodontics. 3rd ed. Illinois: Quintessence Publishing Co. Inc; 1997. Before and After Staining  Revision of Steps 1 2 3 4 Revision of Steps 5 6 Thank You Dr. Mohamed Halawani