Metal Ceramic Restoration PDF 2022

Metal-Ceramic Restoration By Dr. Mohammed Hosny Associate Professor of Fixed Prosthodontics Collage of Dentistry Taibah University 3/27/2022 M.Hosny 2 Outline ❖ Definition ❖ Alloy used & alloy requirement ❖ Porcelain requirement ❖ Techniques for construction of metal substructure ❖ Metal prepa...

Metal-Ceramic Restoration By Dr. Mohammed Hosny Associate Professor of Fixed Prosthodontics Collage of Dentistry Taibah University 3/27/2022 M.Hosny 2 Outline ❖ Definition ❖ Alloy used & alloy requirement ❖ Porcelain requirement ❖ Techniques for construction of metal substructure ❖ Metal preparation ❖ Bonding mechanism ❖ Ceramic for MCR ❖ Porcelain buildup ❖ Porcelain labial margin ❖ Failure 3/27/2022 M.Hosny 3 Definition It is a complete coverage cast metal crown veneered with a layer of fused porcelain. 3/27/2022 M.Hosny 4 Metal ceramic restoration Metal substructure (Coping) for strength & accuracy Porcelain veneer for esthetic May be Consists of three porcelain layers Full veneered Labial veneered Opaque Thin copy of metal covered completely with porcelain Recognizable crown with areas to be covered with porcelain Mask the underlying metal 3/27/2022 M.Hosny Dentin Enamel Makes up the bulk Provides the translucency of the restoration of the providing its color restoration and shade 5 Alloys used for metal-ceramic High noble Metal alloys 60% noble metal 40% gold •Au-Pl -Pd •Au –Pd-Ag •Au - Pd 3/27/2022 Noble Metal alloys 25%noble metal •Pd-Ag •Pd-Cu-Ga •Pd-Ga M.Hosny Base Metal alloys Less than 25% noble metal. • Ni-Cr • Co –Cr •Ti 6 Requirements for alloys used with metal ceramic restoration 1. The coefficient of thermal expansion of metal and porcelain should be compatible ( optimum difference 1 x 10-6 °c) to avoid shear stresses during cooling failure of the bond between porcelain and metal 2. The melting range temp. of metal should be higher than the fusing temp. of porcelain by at least 170 – 280 °c (less than 170 3/27/2022 flow and deformation of metal) M.Hosny 7 3. The metal should be rigid enough. Any flexing under occlusal forces shearing of porcelain 4. Alloy should have high sag resistance during porcelain firing cycles. 5. They should be capable of forming a strong bond with porcelain at the interface. 3/27/2022 M.Hosny 8 Requirements for dental porcelain used as veneering material 1- Low fusing temp. (less than metal 170 – 280 °c) 2- High viscosity ( to maintain its basic shape during firing) 3- CTE should be slightly lower than metal by 1 x 10-6 °c to enhance bond strength 4- Should resist vitrification when fired many times thus becoming milky & difficult to glaze. 3/27/2022 M.Hosny 9 Devitrification: is a phenomenon in which the amorphous glass changes into crystalline one and it is associated with an increase in the coefficient of thermal expansion and opacity, and it occurs mainly with multiply firing of the porcelain material. 5) Should be chemically & optically stable over series of 6) firing cycles. Should be able to withstand oral environment & resist stress corrosion. 7) Should not abrade opposing teeth. 3/27/2022 M.Hosny 10 Techniques for construction of metal substructure 3/27/2022 M.Hosny 11 I- Lost wax casting technique 3/27/2022 M.Hosny 12 Lost wax casting technique 3/27/2022 M.Hosny 13 Lost wax casting technique 3/27/2022 M.Hosny 14 II. Alternative techniques to conventional casting for construction of metal substructure in metal- ceramic restorations 3/27/2022 M.Hosny 15 ❑ Electroforming technology e.g., Helioform HF 600 system ➢ Composed of pure 24 K gold deposited directly onto a duplicate die. ➢ Copings are relatively thin (0.2 mm). ➢ highly biocompatible. ➢ High marginal accuracy of 20 microns on average. 3/27/2022 M.Hosny 16 ❑ Capillary technology e.g., Captek system ➢ It’s an advanced metallurgic system that was developed to combine optimal natural esthetics of dental porcelain with the strength of ceramometal. ➢ Captek alloys are composed of two major components. ▪ The first component, when heated, forms a microscopic three- dimensional network of capillaries. ▪ The second, when melted, flows to fill these capillaries. This microscopic process works by the forces of capillary attraction. 3/27/2022 M.Hosny 17 ❑ CAD/CAM technology 3/27/2022 M.Hosny e.g., Procera system 18 3/27/2022 M.Hosny 19 Metal preparation 1. Metal substructure design (Shape) 2. Investment removal 3. Oxide removal 4. Metal finishing 5. Cleaning 6. oxidizing 3/27/2022 M.Hosny 20 Basic principles of metal substructure design (Shape) 1) No sharp or acute angles. 2) The veneering surface should be smooth to facilitate wetting of the framework by the porcelain slurry. 3/27/2022 M.Hosny 21 Basic principles of metal substructure design 3) The intended metal-ceramic junction should be as definite (90-degree angle) and as smooth as possible to make finishing the veneer easier 3/27/2022 M.Hosny 22 Basic principles of metal substructure design 4) Facilitate the porcelain wrap-around effect. 3/27/2022 M.Hosny 23 Basic principles of metal substructure design 5) Compensate deficiencies in correct form of prepared teeth to provide adequate support to porcelain veneer. 3/27/2022 M.Hosny 24 Basic principles of metal substructure design 6) Metal thickness should provide adequate rigidity. Verification of thickness with a caliper 0.3 – 0.5 mm … Noble 0.2 – 0.3 mm … Base metal 3/27/2022 M.Hosny 25 Basic principles of metal substructure design 7) Occlusal and proximal contacts. A- Occlusal contacts either located on metal or porcelain. Why???????? 1- Prefer on metal ➢ Less wear of natural ➢ Easily reproduced on wax pattern rather than on porcelain 3/27/2022 M.Hosny 26 2- Contact should be away from porcelain-metal junction (1 -1.5 mm) at Maximum intercuspation. 3/27/2022 M.Hosny 27 3/27/2022 M.Hosny 28 B ) Proximal contacts Anterior teeth: on porcelain for better esthetic and translucency If on metal 3/27/2022 block light transmission M.Hosny poor esthetic 29 Metal preparation to receive a ceramic material 2- Investment removal 3- Metal Finishing (Why & how) ➢ To remove all surface imperfections and to increase surface roughness which aid in retention of ceramic by micromechanical interlocking. ➢ Finishing the surface in one direction with light pressure to avoid trapping debris between folds of the metal ➢ Grinding in different directions projections of metal over each other trap air and guiding debris between the metal folds contamination of the porcelain stress concentration and fracture. 3/27/2022 M.Hosny 30 Metal Finishing 3/27/2022 M.Hosny 31 ➢ Surface finishing with ceramic-bound stones, because conventional rotary instruments produce organic binders which is a source of contamination. ➢ Tungsten carbide burs also may be used safely. 3/27/2022 M.Hosny 32 ➢ After grinding, the surface is air abraded with Aluminum oxide to give satin finish on the veneering surface that is easily wettable by the porcelain slurry. ➢ The margins should be protected by soft wax during air abraded. 3/27/2022 M.Hosny 33 3/27/2022 M.Hosny 34 Metal Finishing 4- Cleaning in ultra sonic cleaner for 5 minutes 5- Oxidizing ➢To establish the chemical bond between metal and porcelain, a controlled oxide layer must be created on the metal surface. ➢The oxide layer is typically obtained by placing the substructure on a firing tray, inserting it into the muffle of a porcelain furnace, and raising the temperature to a specified level that sufficiently exceeds the firing temperature of the porcelain. 3/27/2022 M.Hosny 35 Oxidizing ➢ Base metal alloy does not need oxidation because it contain elements undergoes continuous oxide formation. ➢ Noble alloys (iron, tin, indium, and gallium )are incorporated in the alloy content for oxide formation. 3/27/2022 M.Hosny 36 ➢ High-gold content ceramic alloys usually are held at the oxidizing temperature for several minutes. ➢ Lower-gold content alloys contain more base elements, which can result in a thicker oxide layer. So it does not need to be held at the oxidizing temperature for any length of time. 3/27/2022 M.Hosny 37 3/27/2022 M.Hosny 38 Porcelain-Metal Bonding 3/27/2022 M.Hosny 39 Porcelain-metal bonding Mechanism 1) Mechanical retention 2) Compressive bonding 3) Chemical bonding 4) Vander waal’s force 3/27/2022 M.Hosny 40 Porcelain-metal bonding Mechanism 1) Mechanical retention ➢ Roughness created by burs OR air-borne particle abrasion 1. Increase wettability by porcelain slurry. 2. Increase surface area. ➢ Excessive roughness drawbacks in porcelain/metal bond . Why???????? a) Stress concentration at metal/ceramic interface. b) Deep interface angles incomplete wetting voids at metal/ceramic interface. 3/27/2022 M.Hosny 41 3/27/2022 M.Hosny 42 Porcelain-metal bonding Mechanism 2) Compression bonding CTE of porcelain is slightly lower than metal by 0.5-1 x 10-6 ºc compressive stresses at the porcelain surface. 3/27/2022 M.Hosny 43 Porcelain-metal bonding Mechanism 3) Chemical bonding ❖ Plays the major role in the bond ❖ Due to the formation of an oxide layer on the metal surface Which forms chemical bond (covalent or ionic) to similar oxides in the opaque porcelain layer across the interface. ❖ Base metal alloys all elements are oxidizable. So, at Ni-Cr alloys added elements to control thickness of oxide layer. ❖ Gold alloys oxide forming by added trace elements (tin, indum, gallium) which migrate to the interface and oxidized. 3/27/2022 M.Hosny 44 ❖ Contamination or excessive oxide on coping surface will result in failure of bonding. 3/27/2022 M.Hosny 45 Porcelain-metal bonding Mechanism 5) van der Waal’s forces Molecular attraction with no actual exchange of electrons. … … minimal contribution 3/27/2022 M.Hosny 46 Ceramics for metal-ceramic restoration 3/27/2022 M.Hosny 47 Feldspathic ceramic Traditional dental porcelain is a vitreous ceramic based on silica network and feldspar. Other additives like pigments, opacifiers and glasses are added in smaller concentrations Composition of traditional dental porcelain Feldspar (Potassium and sodium aluminosilicate) Quartz (Silica) Clay/Kaolin (Hydrated aluminosilicate) act as a binder 3/27/2022 M.Hosny 49 Types of dental porcelain According to their fusion temperature: High fusing : 1290C-1370C for porcelain denture teeth. Medium fusing : 1090C-1260C for jacket crowns. Low fusing : 870-1065C for metal ceramic veneering. Ultra low fusing : less than 8700C for veneering titanium and titanium alloys. 3/27/2022 M.Hosny 50 Porcelain build-up 3/27/2022 M.Hosny 51 Spatula Brushes Hemostat 3/27/2022 M.Hosny Porcelain furnace •Manual •Automatic •Programmable 52 Three layers of porcelain cover the metal coping ❑ Opaque porcelain: A layer of 0.3 mm is condensed and fired first. Function of Opaque: ❖ Establishes the porcelain to metal bond. ❖ Masks the color of the metal substructure. ❖ Initiates the development of the selected shade. ❑ Dentine (body) porcelain: Makes up the bulk of the restoration. It provides most of shade & most of the tooth form is built from it. 3/27/2022 M.Hosny 53 ❑ Incisal (Enamel) Provides the translucency of the incisal portion of the restoration. 3/27/2022 M.Hosny 54 Thickness is bout 0.2-0.3 mm 3/27/2022 M.Hosny 55 Body dentin Opaque dentin Enamel + translucent porcelain 3/27/2022 M.Hosny 56 Methods of porcelain condensation 1. Vibration: ➢ The porcelain is applied with a brush or spatula and vibrated gently. ➢ Excess water is then removed with a clean absorbent paper. 2. Spatulation: ➢ This consists of smoothening the wet porcelain with a suitable spatula until the excess water is brought to the surface, where it is absorbed. 3/27/2022 M.Hosny 57 3. Brush or capillary attraction: This technique depends on the action of dry porcelain powder to remove the excess water by capillary attraction. 4. Gravitation method: ➢ The porcelain mix is applied using a brush. ➢ The excess water is then drawn off using any absorbent medium, e.g., blotting paper or tissue “linen gauze”. 3/27/2022 M.Hosny 58 Bisque stages of porcelain maturation (Firing) … … (physical appearance of fired porcelain) Low Bisque Stage: Glass bridges flow between particles. Medium Bisque Stage: More glass bridges flow resulting in more cohesion and shrinkage. High Bisque Stage: Maximum cohesion resulting in dense closely packed mass with no more shrinkage. 3/27/2022 M.Hosny 59 3/27/2022 M.Hosny 60 A final glaze: Is obtained to eliminate all flaws from the surface:❑ Over glaze ( surface glaze): Low fusing ceramic powders painted on the surface of the restoration. Fired at temperatures less than the maturing temperatures of the restoration to produce a glossy transparent layer on the surface. ❑ Self-glazing (auto glaze): Following final contouring additional firing in air is done without adding any glaze material and maintained for a time before cooling. 3/27/2022 M.Hosny 61 3/27/2022 M.Hosny 62 3/27/2022 M.Hosny 63 Porcelain labial margins Shoulder porcelain = Butt margin 3/27/2022 M.Hosny 64 3/27/2022 M.Hosny 65 Methods of fabrication 1- Platinum foil matrix technique: 3/27/2022 M.Hosny 66 2- Direct lift (cyanoacrylate) technique 3/27/2022 M.Hosny 67 3/27/2022 M.Hosny 68 Enamel Dentin 3/27/2022 Dentin modifier M.Hosny 69 Cervical Enamel & translucent 3/27/2022 M.Hosny 70 3/27/2022 M.Hosny 71 Failure Of Metal-ceramic restoration 3/27/2022 M.Hosny 72 1- Porcelain-metal bond failure Causes:➢ Improper thickness of oxide layer ➢ Contamination of the metal Substructure ➢ Excessive air abrasion ➢ Unfired opaque ➢ Stress corrosion 3/27/2022 M.Hosny 73 2- Porcelain cracking Causes:➢ Mismatch in coefficient of thermal expansion ➢ Improper metal finishing ➢ Improper porcelain condensation ➢ Rapid cooling of dental porcelain 3/27/2022 M.Hosny 74 3- Fracture of porcelain veneer ➢ A thin metal substructure can not protect porcelain veneer from fracture. ➢ Flexing of metal substructure under occlusal stresses. 3/27/2022 M.Hosny 75 5- Failure in the metal substructure ➢ Deformation (sag-creep) of the metal substructure due to low melting range of the metal and fusion temperature of the porcelain (less than 170°C). ➢ Metal fracture: it is very rare type of failure in metal ceramic restoration. 3/27/2022 M.Hosny 76 6- Unsatisfactory esthetics 3/27/2022 M.Hosny 77 Six pattern of failure between metal and porcelain in ceramo - metallic restoration. 3/27/2022 M.Hosny 78 Thank You Reference ❑ Contemporary of fixed prosthodontics. Stephen Rosenstiel. {5th edition}. Pages {521-543}{647-671} ❑ Introduction to metal ceramic technology 3/27/2022 M.Hosny 79