Fixed Prosthodontics All Ceramic Preparation PDF

Fixed Prosthodontics All Ceramic Preparation Professor Name : Dr. Amr Hussein Aziz Professor title at MSA: Lecturer of Fixed Prosthodontics Dr. Amr Aziz BUT !! Metal shadow Gingivitis Dr. Amr Aziz  Nowadays All Ceramic restorations are now fabrica...

Fixed Prosthodontics All Ceramic Preparation Professor Name : Dr. Amr Hussein Aziz Professor title at MSA: Lecturer of Fixed Prosthodontics Dr. Amr Aziz BUT !! Metal shadow Gingivitis Dr. Amr Aziz  Nowadays All Ceramic restorations are now fabricated using a special types & special techniques of porcelain that overcome most of all ceramic disadvantages without metal substructure All ceramic crown is one of the most esthetically pleasing prosthodontic restoration They can resemble natural tooth structure in terms of color and Three-unit all-ceramic posterior bridge translucency better than any other restorative options Dr. Amr Aziz Success of All ceramic restoration requires : 1- careful patient selection 2- proper tooth preparation 3- proper restoration construction 4- Favorable occlusion with centric contact limited to the middle third of the lingual surface Dr. Amr Aziz Definition: A non-metallic (ceramic or resin) extracoronal restoration covering the prepared clinical crown and restoring aesthetics, anatomy and function. Dr. Amr Aziz Indications: Where superior aesthetics is demanded: As a single crown or bridge retainer in short span bridges in case of high strength ceramics e.g. Inceram, Empress II. Dr. Amr Aziz As an individual crown in the following cases: 1. Fractured anterior teeth. Dr. Amr Aziz As an individual crown in the following cases: 2. Discolored anterior teeth. a. generalised discoloration as in tetracycline. Dr. Amr Aziz b. localised discoloration following root canal Dr. Amr Aziz 3. Mottled, pitted and hypoplastic teeth. 4. Bilateral proximal decay. 5. To realign malposed or rotated teeth. 6. To correct malformed teeth to correct contour e.g. Peg shaped, diastema, microdontia, amelogenesis imperfecta, fluorosis. 7. Restore root canal teeth in need of highly aesthetic requirement. Dr. Amr Aziz Dr. Amr Aziz Contraindications: Dr. Amr Aziz  Contraindications: 1. Unfavourable load distribution. Deep Bite and edge-to-edge relationship. When opposing teeth occlude on the cervical third of the lingual surface , this will produce tensile stress resulting a characteristic Half Moon Fracture 2. Short clinical crowns, either naturally or due attrition, as these offer inadequate tooth prepartion resulting in stress concentration lead to its Fracture. 3. Young patients due to large pulp and fear of exposure. Dr. Amr Aziz  Contraindications: 4. When a more conservative restoration can be used 5. Persons with high risk of fractures such as contact sport athletes. 6. Patients with parafunctional habits such as clenching and bruxism. 7. Periodontally compromised teeth with root exposure due to inadequate margin support 8. Thin teeth labio-lingually due to aggressive shoulder preparation Dr. Amr Aziz 0.7-1.2 mm Advantages: 1.Excellent aesthetics due to ability to reproduce natural color and translucency. 2. Good resistance and retention due to full coverage. 3. Biocomatibility :good tissue response even in case of subgingival margins. 4. Reduction facially is more conservative than veneered restorations as there is no need to mask the metal and create translucency. 5- Low thermal conductivity Dr. Amr Aziz Disadvantages: 1.Brittle restorations liable to fracture. 2) Pulp vitality cannot be tested. 3) Recurrent caries under the restoration cannot be detected. Dr. Amr Aziz Preparation Parameters Dr. Amr Aziz Preparation Parameters Biological Mechanical Esthetical Dr. Amr Aziz Armamentarium End cutting Finishing bur stone Dr. Amr Aziz Anterior All Ceramic Index Fabrication Facial Index Mid-sagittal index Dr. Amr Aziz Aim of the preparation Dr. Amr Aziz  1. Labially Two sets of depth orientation grooves are made cervically and incisally in a two plane reduction using a tapered with flat end diamond stone instrument of known diameter. The tooth structure in between the grooves is removed. Dr. Amr Aziz  The labial surface is reduced uniformly in two planes to correspond to the two geometric planes of a natural tooth. Two sets of depth orientation grooves are made cervically and incisally in a two plane reduction using a tapered with flat end diamond stone instrument of known diameter. The lingual half of the tooth is reduced 1 mm and a shoulder finish line is developed, 1 mm in width. Dr. Amr Aziz Dr. Amr Aziz Steps of Reduction: 1.Labial Reduction: 2 plane reduction. depth of (( 1 -1.5 mm )) to avoid opaque or over-contoured restorations Depth cuts: Cervical 1/3 Incisal 2/3 Dr. Amr Aziz Dr. Amr Aziz Dr. Amr Aziz 2.Incisal Reduction: Direction: Inclined 45 to the long axis of the tooth Depth → 2 mm at least to provide enough space for translucency. Never exceed 1/3 the total inciso-gingival length Instrument: Tapered with flat or round end stone Wheel stone. Dr. Amr Aziz 3. Proximal Reduction Initially for access Tapered Needle stone Followed by Tapered with round end stone Dr. Amr Aziz  4.Palatal Reduction : Cingulum Should be parallel to the proposed path of insertion and to the labial cervical 1/3 Tapered with flat end Round tapered stone Palatal Fossa : It`s concavity should be followed to allow the maximum clearance needed Wheel stone Football Dr. Amr Aziz Finish lines of all-ceramic crown maybe: Dr. Amr Aziz  Finish lines of all-ceramic crown maybe: Shoulder a) 90 rounded shoulder 1 mm is preferred to provide support. b) Heavy chamfer , less favourable. Dr. Amr Aziz Finish lines of all-ceramic crown maybe: Dr. Amr Aziz  5.Finishing the preparation Torpedo or tapered finishing bur Roundation of all line & point angles Shoulder F.L. Dr. Amr Aziz Checking incisal or occlusal clearance: 1-Indexing using rubber base. 2-Using modeling wax. 3-Using adjacent tooth as a guide. 4-Using reduction gauge. 5-Flexible clearance tabs. Dr. Amr Aziz  Clearance tabs *www.kerrlab.com Dr. Amr Aziz Dr. Amr Aziz TOOTH PREPARATION ERRORS IN ALL-CERAMIC RESTORATIONS Dr. Amr Aziz Tooth preparation done following the principles or guidelines of tooth preparation forms the foundation for clinical success in all-ceramic restorations. The following are the most commonly seen errors during tooth preparation for all-ceramic restorations and precautions to be taken to rectify them. a. Sharp Line Angles b. Margins c. Over shortening of the Preparation d. Excess Taper of the Prepared Tooth e. Over reduction of Tooth Structure f. Inadequate Preparation of Axial Walls g. Inadequate Occlusal Reduction h. Lack of Uniform Anatomic Reduction Dr. Amr Aziz  a. Sharp Line Angles Problem : Leaving behind sharp line angles and point angles in the preparation can lead to major fit problems and time consuming appointment at the time of cementation. Sharp line angles form potential sites for fracture stimulation of all-ceramic restoration Solving: Rounding off all the sharp line angles and point angles at the time of tooth preparation Dr. Amr Aziz  b. Margins 1. Feather Finish Lines problem restoration has high chances of failure during seating in the form of chipping or bulk fracture. Solving shoulder is required for strength at the margins because marginal area bears much support of the crown in function Dr. Amr Aziz b. Margins 2. Rough Shoulder problem: Rough shoulders are not just difficult to record but also difficult for the technician to work on. They contribute to unnecessary build-up of stresses at the margins. Solving: A smooth shoulder ensures an excellent fit, minimal cement line and good esthetics. Also, under stress at the margins arising from rough shoulder is avoided. Dr. Amr Aziz b. Margins 3. J Margin: Problem: This happens when the operator goes deeper than the width of the head of diamond creating a groove. Such a margin is difficult to scan for a CAD-CAM procedure. A “J” margin is not acceptable as it leads to thin ceramics at the margin, which is susceptible to fracture also undermined enamel could be fractured leaving mieroleakage after crown cementation solving: One should be cautious as to not go deeper than the head of diamond while preparing the margins. Dr. Amr Aziz b. Margins 4.Incomplete and Non uniform Shoulder: Problem: If the width of the shoulder varies from one region to another, it can vary the ceramic thickness with a potential for premature fracture during fabrication, seating or cementation. This can also cause an undesirable esthetic failure. Solving: one must prepare a uniform shoulder of 1 mm all around the tooth. Dr. Amr Aziz c.Ove rshortening of the Preparation In a full veneer crown, whenever load is applied from a lingual direction, the labial marginal ceramic is placed under compression. This compressive stress can be resisted only by adequate length of abutment. Hence, we should be cautious not to over-shorten the crown. Ideally incisal edge should be reduced by 2 mm or 1/3rd the length of the crown. Incisal edge should not be made thin, rather it should be prepared flat and placed at right angle to the direction of forces. Dr. Amr Aziz  d. Inadequate Preparation of Axial Walls Some dentists use small, round-ended, tapered or flame-shaped diamonds for reduction of the medial, distal, lingual, and even facial walls of tooth preparations for crowns. This results in minimal reduction of tooth structure and creation of featheredge margins. Although this type of preparation is adequate for all metal restorations, it is not acceptable for metal ceramic and all-ceramic crowns because it leaves inadequate thickness for both substructure and veneering ceramic. Inadequate axial tooth preparation forces technician to make overcontoured crowns and compromises both esthetics and biologic. Dr. Amr Aziz e. Excess Taper of the Prepared Tooth Increase axial taper will affects tooth biological in which Pulp preparation distance will decreased as well as retention of the crown will be affected. Dr. Amr Aziz f. Over reduction of Tooth Structure It makes the laboratory work easier and allows optimum esthetics and strength of the restoration, but the damage caused to the dental pulp is unpardonable. The rule of thumb should be to remove only as much tooth structure as required. Dr. Amr Aziz g. Inadequate Occlusal Reduction Inadequate occlusal reduction will provide insufficient space for the bulk of ceramic leading to weak areas prone to fracture. Dr. Amr Aziz h. Lack of Uniform Anatomic Reduction Dr. Amr Aziz  Fixed Prosthodontics All Ceramic Restorations Professor Name : Dr. Amr Hussein Aziz Professor title at MSA: Lecturer of Fixed Prosthodontics This is our Aim.. & Our Problem  Biological Mechanical Esthetical Dr. Amr Aziz Dr. Amr Aziz  Dental Ceramics -- The word ceramic is derived from the Greek word "keramikos" which means burnt stuff. -- Ceramic materials are inorganic compounds formed of: metallic or semi-metallic and non-metallic elements, which are subjected to high heat treatment ((firing )) for a period of time to achieve desirable properties. Dr. Amr Aziz -- Dental Ceramics are nonmetallic inorganic materials, however their compounds are formed of : metallic and nonmetallic elements Eg: zirconia ZrO2, as zirconium (Zr) is the metallic element. & oxygen (O) is the non-metallic element. --Dental porcelain refers to a specific compositional range of ceramic materials originally made by : mixing feldspars (potassium and sodium aluminosilicates), quartz (silica), kaolin (hydrated aluminosilicate). Dr. Amr Aziz ** Ceramics Application in dentistry : 1. Metal – Ceramic restorations ( Crowns & Bridges ). 2. All-ceramic crowns, inlays, onlays , veneers crowns & Bridges 3. Ceramic denture teeth ** All ceramics : Ceramic cores : High strength ceramics >>> Poor esthetics Veneering material : Low strength ceramics >>>> Good esthetics (((( Strongest – non esthetic core materials )))) Dr. Amr Aziz General composition 1- Vitreous phase or Glassy phase: ((amorphous in structure )) - Called feldspar as represents the matrix that holds other components - Responsible for esthetics and translucency. - It is formed by vitrification. ((as the molten glass has been cooled without crystallization)). ---- composed of an-hydrated potassium aluminum silicate (K2O – Al2O3 – 6SiO2). Potash (orthoclase) and Soda (albides) 2- Crystalline phase: ((crystalline in structure )) - This phase responsible for strength and hardness. - It is formed by devitrification , ( as the crystallization of glass occurs at high temperature in the presence of nucleating agents ).Dr. Amr Aziz After -firing, -- Dental ceramics are composed of two phases: a glassy (or vitreous) phase surrounding a crystalline phase -- Increasing the amount of glassy phase : lowers the resistance to crack propagation but increases translucency -- Increasing the amount of crystalline phase (Crystalline Reinforcement ): increasing the resistance to crack propagation but decrease translucency & increase opacity -- Materials for all-ceramic restorations have increased amounts of crystalline phase (between 35% and 90%) for better mechanical properties Dr. Amr Aziz  Glass Ceramic Polycrystalline Ceramic (more esthetic than strength) (more strength than eshtatic) *Ceramics in Dentistry by R. Narasimha Raghavan Dr. Amr Aziz  Glass Ceramic Polycrystalline Ceramic (more esthetic than strength) (more strength than eshtatic) *Ceramics in Dentistry by R. Narasimha Raghavan Dr. Amr Aziz  The revolution has been Started with discovering a Material Which Provides >> The best Esthetic Restoration Dr. Amr Aziz  Dental Porcelain The first porcelain tooth material was patented in 1789 by a French dentist deChemant in collaboration with a French pharmacist Duchateau. The first commercial porcelain was developed by Vita Zahnfabrik in about 1963 Dr. Amr Aziz  Glass Ceramic Polycrystalline Ceramic (more esthetic than strength) (more strength than eshtatic) *Ceramics in Dentistry by R. Narasimha Raghavan Dr. Amr Aziz Definition: >> is a vitreous ceramic based on silica network. Supplied form: >> Powder in different shades mixed with distilled water forming a plastic mass. Carried to the removable die ( which is covered by platinum matrix) & shaped to form the crown. Applications: 1. Denture teeth. 2. Crown & bridge. 3. Inlays. 4. Onlays. 5. Laminate veneer. Composition: >> Main components: Feldspars – Quartz – Kaolin. >> Other Components: Glass modifier –Flux – Sugar & Starch – Pigments. Dr. Amr Aziz  Main composition : 1- Feldspar : ( 75% - 85 % ) Basic Glass Former - It is an-hydrated potassium & aluminum silicate. ( K2O,AL2O3,6Sio2 ) - On heating ,,at about 1290 C ,,, the mixture of (potassium feldspar & various metal-oxides ) fuse & form leucite and a glass phase that will soften and flow slightly ,That`s allow the porcelain powder particles to coalesce together this process is called “Liquid - Phase Sintering”, a process controlled by diffusion between particles at a temperature sufficiently high to form a dense solid (unless overheated), retains its form without rounding. >> potassium aluminum silicate ∆ treatment Leucite + Glassy phase -leucite [Crystalline structure] change the properties of Porcelain: * Increase strength. * Increase hardness. * Increase α. * Decrease aesthetics Dr. Amr Aziz 2-Silica(Quartz): ( 12% - 20% ) Filler - Pure Silicon oxide(SiO2). - Provides stiffness & hardness. - It gives translucency. 3-Kaolin: ( 3% - 5% ) Binder - It is a hydrated aluminium silicate (AL2O3,2Sio2,2H2O ) - Gives porcelain its properties of opaqueness. - It gives density ,Consistency & strength to the mix to form a workable mass Dr. Amr Aziz 3-Color Frits: ( 1% ) shade They are coloring pigments added to the porcelain mixture. to obtain the delicate shades necessary to imitate natural teeth >>> Metallic pigments: * Titanium oxide – yellow brown shade * Manganese oxide – lavender * Iron oxide –Brown * Nickel oxide – Brown * Cobalt oxide – Blue (useful for producing enamel shades) * Copper or chromium oxide – Green * Chromium – tin or chrome – alumina – Pink * Iron oxide or platinum -- Grey Dr. Amr Aziz Characters Of Dental Porcelain Of Dental Ceramics: 1. Biological Properties: Inert has no interaction with surrounding soft tissue (biocompatible) 2. Interfacial Properties: Not adhere chemically to dental cements 3. Chemical properties: Not soluble in oral fluids and resist acid attach Both hydrofluoric acid and stannous fluoride can cause an increase in surface roughness 4. Mechanical Properties: Brittle Low DTS and fracture toughness Hard, can cause wearing of opposing dentition 5. Thermal Properties: Low thermal diffusivity Coefficient Of thermal expansion similar to that of enamel and dentine 6. Esthetic properties: Excellent esthetic, and color matching Difficult to be stained 7. Practicability: Sensitive manipulation technique, Dr. AmrRequiring Aziz skilled operator and Special equipments Firing shrinkage is always, So operator should build up the restoration to a bigger size that allows shrinkage Types of dental porcelains: According to their fusion temperature, dental porcelains maybe divided into 3 types: 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. Dr. Amr Aziz Jacket crown: A non-metallic (ceramic or acrylic resin) extracoronal restoration covering the prepared clinical crown and restoring esthetics, anatomy and function. beautiful all porcelain crowns Dr. Amr Aziz  Method Of Fabrication Of Jacket crown Powder slurry condensation (free-hand layering technique) Platinum foil technique Refractory die technique Dr. Amr Aziz Platinum foil technique: - This technique involves fabrication on either : >> single platinum foil >> double platinum foil. - Steps : impression Cast itching of the die apply of platinum foil Matrix (0.01 inch) applying porcelain Proper condensation Put in Furnace Firing Finishing & Glazing Removing the Platinum foil - Dr. Amr Aziz - Fabrication on single platinum foil: A pure platinum foil is swaged directly to the model then the porcelain is built up. - Later after the completion as the firing cycles the platinum is peeled off. - The fit of the crown is secured leaving enough space for the cement. Dr. Amr Aziz - Fabrication using a double foil matrix technique: Here a second layer of platinum foil is swaged on the first and cut back by at least 0.5 mm from the gingival shoulder. The second layer is sand basted and cleaned with caustic soda and citric acid to improve impurities this is followed by electroplating, oxidization and finally build up of the porcelain. Later after the procedure is accomplished the inner layer is removed allowing space for the placement of the cement Dr. Amr Aziz Dr. Amr Aziz Dr. Amr Aziz Dr. Amr Aziz Dr. Amr Aziz Dr. Amr Aziz - Disadvantages : >> Less margin adaptation due to the foil matrix. >> Difficulty in margin finishing especially in margin Veneer Restoration Margin chipping >> In ability to do further adjustment firing of the crown after removal of the foil. Dr. Amr Aziz Refractory Die Technique : - Impression Normal working Cast Dies ditching & trimming Duplication those dies into Refractory die apply the creamy mix on the refractory die directly Carry them inside the furnace Firing ,Finishing Dr. Amr Aziz NB: -Refractory die Material : is an absorbable porous material may absorb excess water from the Porcelain mass. So >> refractory die should be place for some time in water before porcelain application. - After glazing ,, Removing the refractory material by sandblasting with glass beads (50 um) to avoid affecting the fitting surface of the ceramic Restoration. - Proper condensation should be done to remove the excess water. Otherwise >>> VOIDS within Porcelain which lead to - Decrease strength ( voids allow crack propagation ) - Bad optical results Dr. Amr Aziz  But We can`t Ignore that it has inherent weakness due to : Their ionic atomic bond which imparts Brittleness (Low tensile strength & low fracture toughness) Of the material. Their Firing shrinkage Which lead to Formation & Propagation Of flaws & Microcracks with subsequent Fracture of Porcelain. Dr. Amr Aziz strengthening mechanisms Dr. Amr Aziz 1- Fusing Porcelain with METAL … ( PFM ) To resist the initiation & Propagation of Microcracks * used for many years but still has a lot of critical problems such as : Dr. Amr Aziz 2- Bilayered restorations ( dispersion strengthening: crystals are added to arrest / inhibit crack propagation ) ❑One method utilises two ceramic materials to fabricate the restoration: ❑a high strength non-aesthetic aluminous ceramic core is constructed which is ❑veneered with a CTE compatible lower strength but translucent porcelain veneer, i.e. Same principle of the metal ceramic crown but the colour of the ceramic core is easier to mask so less thicknesses are required Dr. Amr Aziz Bilayered ceramic: firing of aluminous opaque core on PT foil Porcelain Ceramic Furnace Jacket Crown Dr. Amr Aziz Dr. Amr Aziz bilayered unit Dr. Amr Aziz Bilayered bridge restoration: framework and compatible veneering material Dr. Amr Aziz Usees of Feldspathic porcelain: 1. Inlay 2. Occlusal veneer 3. Onlay 4. Laminate Veneer 5. Veneering metal or opaque frameworks Dr. Amr Aziz Basic requirements of dental porcelain: 1. Low fusion temperature. 2. Resistance to pyroplastic flow , ie it is required to retain its form during firing. 3. Resistance to devitrification. 4. High viscosity. Dr. Amr Aziz Porcelain build up: 1) Aluminous core: (50% by weight alumina) Powder and liquid are mixed and applied to the foil incrementally with a brush until a full core is built and fired. This core is opaque. 2) Veneer porcelain: Veneer porcelain with matching thermal expansion to the core is used to build dentine and enamel parts after which the restoration is fired and glazed. 46 Porcelain firing: Porcelain is fired in special furnaces with controlled temperatures and environment. Most thermo-chemical reactions between porcelain components are completed during manufacturing. Sintering: A process where glass bridges flow and form between unfused particles to produce a continuous mass. This is accompanied by a 30% volumetric shrinkage after firing. Cause of shrinkage: 1. Loss of water. 2. Densification through sintering. Dr. Amr Aziz 47  Stages of Porcelain Firing: 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. Dr. Amr Aziz 48 1. Mixing: Dental porcelain is presented in powder form of different shades. The porcelain powder in the selected colour is mixed with a binder to form a creamy paste (mixing is carried on a glass slab). The types of the binders may be: Distilled water or a water-based glycerine containing liquid; which is the most popular binder for dentin and enamel powders. Propylene glycol; is used with the powder of aluminous core build-up. 2. Application: The porcelain creamy paste is applied to the Pt foil, refractory die or coping using either a brush or spatula. Building is done incrementally in layers with the continuous removal of excess water from the initial mix. Dr. Amr Aziz 3. Condensation: It is the procedure of removal of excess water from the porcelain working mass after its application and moulding to the desired form. Purpose of condensation: 1. Excess water is removed to decrease firing shrinkage. 2. The paste is adapted to the required form. 3. Closely packed particles increase strength of porcelain 4. Porosity is decreased. Dr. Amr Aziz Condensation Advantages: 1. Less porosity. 2. Increases density and adaptation. 3. Less shrinkage during firing. 4. Better surface texture. Dr. Amr Aziz Dr. Amr Aziz Dr. Amr Aziz  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. Brush or capillary attraction: This technique depends on the action of dry porcelain powder to remove the excess water by capillary attraction. The dry powder is applied with a brush to a small area of the wet porcelain mass, and as the water is withdrawn towards the dry area, the wet particles are pulled closely together. Dr. Amr Aziz 4. Gravitation method: The porcelain mix is applied; using a brush, then, water is added. This addition of water is thought to agitate the powder particles so that they will be settled down at the base in a more compact manner, leaving excess water at the surface. The excess water is then drawn off using any absorbent medium, e.g. blotting paper or tissue “linen gauze”. N.B: It should be emphasised that the less the amount of water present initially before porcelain firing, the less will be the firing shrinkage. Dr. Amr Aziz Porcelain powder condensation & absorbent paper Manual condensation Dr. Amr Aziz Even well condensed porcelain shrinks when fired !!!!!!!!!!!!!!!!! due to: Loss of water. Densification through sintering. Dr. Amr Aziz Ceramic adjustment & Corrective addition Dr. Amr Aziz Glaze: A final glaze is obtained to eliminate all flaws from the surface. A final smooth surface is formed after final adjustments using a surface or autoglaze. Any intraoral later adjustments need finishing with special kits and diamond paste or reglazing. Dr. Amr Aziz Finished glazed crown Dr. Amr Aziz Glaze: 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): Following final contouring additional firing in air is done without adding any glaze material and maintained for a time before cooling Pyroplastic flow occurs and a vitreous layer or surface glaze is formed. Dr. Amr Aziz  Nowadays Ceramic material which improved technique of construction + modified Structure To overcome the disadvantages of (conventional porcelain) & (Metal Ceramic Restoration) Dr. Amr Aziz  Glass Ceramic Polycrystalline Ceramic (more esthetic than strength) (more strength than eshtatic) *Ceramics in Dentistry by R. Narasimha Raghavan Dr. Amr Aziz IPS e.max Cad IPS e.max Press ingots used in used in milling machine heart pressing furnace Dr. Amr Aziz  (( IPS e.max Press ingots )) polychromatic Multi ingots monochromatic ingots ( one size ) ( two sizes ) Five levels of translucency IPS e.max Press Multi HT (High Translucency) T MT(Medium Translucency) (Low Translucency) O MO (Medium Opacity) HO (High Opacity) Impulse Dr. Amr Aziz Zirconia Dr. Amr Aziz Zirconia: polycrystalline Dr. Amr Aziz Stress induced transformation Dr. Amr Aziz Tetragonal 3mol%Y- TZP Dr. Amr Aziz Dr. Amr Aziz Platinum foil technique Centrifugal Casting ex: (Castable ceramics) 1-feldspathic porcelain ex: DICOR 2-aluminous porcelain Heat pressed casting Refractory die ex: technique Hand- 1- Empress 1 ex: Hi-ceram stacked Lost- 2- Empress 2 (Powder wax Slurry ) Glass Machined infiltrated ex: ex: 1- In-ceram spinell 1-CAD/CAM 2-In-ceram Alumina 3-In-ceram zirconia * zirconia blockes *Empress 2 blockes 2-Celay System Dr. Amr Aziz Heat pressed casting : Used for fabrication of e.max crowns & Bridges using e.max ingots Dr. Amr Aziz ** IPS Empress II ( e-max ingot ) : For the reason of esthetics have to mention to the processing technique (which add on the external characterization to the ceramic restoration) But ** It differentiates into (3 Tech.)depending on the type of the ingot used: Dr. Amr Aziz 1- Staining Technique : - Building wax Pattern to the full contour To gain a pressed full Restoration - The pressed restoration are completed by the application of : Stains (IPS e.max ceramic shade ,Essence) Glazing material( IPS e.max ceram glazing Paste or Powder ) Dr. Amr Aziz 2- Cut-Back Technique : - Building wax Pattern to the full contour then cut back of the incisal &/or occlusal area. To gain a pressed Partial Restoration. - then completing the anatomical shape & achieving the esthetic appearance BY applying : [ IPS e.max ceram layering materials (Impulse ,transpa , transpa incisal) ] Dr. Amr Aziz 3- Layering technique : - Building wax Pattern to form the Framework of the restoration. To Gain a Pressed Core Restoration. - then completing the anatomical shape & achieving the esthetic appearance BY applying : [ IPS e.max ceram layering materials(dentin ,deep dentin , margin ,..) ] - Use IPSe.max ceram build-up Liquids allround or soft to Mix the Layering Material. Dr. Amr Aziz Platinum foil technique Centrifugal Casting ex: (Castable ceramics) 1-feldspathic porcelain ex: DICOR 2-aluminous porcelain Heat pressed casting Refractory die ex: technique Hand- 1- Empress 1 ex: Hi-ceram stacked Lost- 2- Empress 2 (Powder wax Slurry ) Glass Machined infiltrated ex: ex: 1- In-ceram spinell 1-CAD/CAM 2-In-ceram Alumina 3-In-ceram zirconia * zirconia blockes *Empress 2 blockes 2-Celay System Dr. Amr Aziz  Machined ceramics Dr. Amr Aziz CAI CAD CAM  Computer Aided Impression  Computer Aided Designing  Computer Aided Manufacturing Dr. Amr Aziz  Classification of CAD/CAM systems Direct chair side In-Direct Inlab Integrated chair Full system Full system side and inlab system In-office scanning -In-lab scanning -In-office scanning -In-office designing -In-lab designing -In-lab designing -In-office Milling -In-lab Milling -In-lab Milling  A) Chairside production The current existing in-office systems with chair- side milling machines are the CEREC, E4D and KaVo CAD / CAM Dr. Amr Aziz  b) Laboratory production Cerec inlab Glidewell Laboratories: BruxZir Mill Creo Dental Systems: Arum 5Axis Milling Machine AmannGirrbach GmbH: Ceramill Motion 2 Milling Datron Dynamics: D5 Dental Mill Roland DGA Corporation: DWX-4 Compact Dental Mill Dr. Amr Aziz  Dry milling Used for fabrication of zirconia crowns & Bridges Advantages:  Pressurized air, vacuum,  Easier in cleaning  Decreased shrinkage after firing  Less time & cost Dr. Amr Aziz  Wet milling Used for fabrication of e.max crowns & Bridges using IPS e.max Cad  It continuously bathes the cutting tool and milling stock, keeping both the tool and material cool, and helps to remove material from the milling disk or block.  the milling diamond or carbide cutter is protected by a spray of cool liquid  This kind of processing is necessary for all metals and glass ceramic material  Wet processing is recommended, if zirconium oxide ceramic with a higher degree of pre-sintering  A higher degree of pre-sintering results in a reduction of shrinkage factor and enables less sinter distortion.  Burs of longer life time  Need more cleaning time and nearly weekly Dr. Amr Aziz  Acrylic Jacket Crown Acrylic resin is used for temporary jacket crown construction. Advantages: 1. Easy construction. 2. Inexpensive. 3. Maybe used for young age patients. Disadvantages: 1. Low wear resistance. 2. Low abrasion resistance. 3. Discoloration. Steps of construction: Impression → cast → die → tin matrix → wax pattern → flasking of wax pattern→ wax elimination → packing (wet or dry) → flasking → curing →cooling →deflasking → finishing & polishing. Dr. Amr Aziz  Wax pattern is made from ivory wax to avoid any discoloration of the acrylic resin from coloured wax. Wax pattern is built to proper form, contour, proximal contact and occlusion. Acrylic resin crown flask is made of 2 parts: upper and lower compartment. Fill the fitting surface of the wax pattern with plaster and the bottom ½ of the flask. Flasking the wax pattern: Upper compartment Lower compartment Dr. Amr Aziz  Wax pattern is positioned so that: Its lingual and proximal surfaces are covered by plaster while the labial, labioproximal and incisal angles are left uncovered. When the plaster sets lubricate the plaster with separating medium. The upper part of the flask is filled with plaster and after closing the flask parts together it is kept under a press while the plaster hardens. Dr. Amr Aziz  Wax elimination: Wax is eliminated by immersing the flask in hot water for 5 minutes then the flask is opened and flushed with hot water to eliminate wax. After the flask cools, cold water is applied to act as separating medium to the acrylic resin. Dr. Amr Aziz Acrylic Resin Packing: I. Wet pack technique: 3 shades of acrylic resin (gingival, body and incisal) are mixed in 3 dappen dishes. When the resin reaches the dough stage gingival colour resin is packed and the flask is closed after putting a wet cellophane paper over it and pressed. The flask is then opened and excess is removed with an incline to allow gradual colour change. The above step is repeated for body and incisal colour. Finally the cellophane paper is removed and the flask is closed for processing. Dr. Amr Aziz II. Dry pack technique: Gingival resin powder is applied cervically, then saturated with monomer and the flask is bench tapped (vibrated). Wet cellophane paper is applied, then excess is removed. Body and incisal resin are applied and adapted then the flask is finally closed for processing. Dr. Amr Aziz Wet Pack Technique Dry Pack Technique 1. Waste material No waste material 2. Harder technique Easier technique 3. Fine details are not reproduced Fine details and colour shades. 4. Better P : L proportioning Dr. Amr Aziz Acrylic Resin Processing: Flask is closed and pressed then placed in a hot water bath. Temperature is gradually brought to boiling in 30 minutes. Flask is left for 30 minutes then bench cooled to room temperature. Deflasking, finishing and polishing: 1. Flask is opened and the crown is retrieved. 2. A sharp instrument is used to clean away the plaster. 3. A tweezer is used to remove the tin foil. 4. Resin flashes are trimmed using a small acrylic stone followed by a sand paper disc, pumice and rubber cup. 5. Polishing is done using a felt wheel. 6. Store the jacket crown in water. Dr. Amr Aziz Dr. Amr Aziz  Heat cured resin Bis-Gma :Protemp & Systemp Dr. Amr Aziz Causes of cracks and flaws in ceramics 1. They are made of several components each has its own CTE 2. They have porosity, 3. They have surface defects (during recontouring and shaping) 4. They undergo static ( moisture+ water )and dynamic fatigue 5. Brittle material, cannot undergo any deformation Dr. Amr Aziz  Fixed Prosthodontics Metal Ceramic restorations Professor Name : Dr Sohaila Ali M Sahel Professor title at MSA: Lecturer of Fixed Prosthodontics Definition It is a complete coverage cast metal crown veneered with a layer of fused porcelain. Full veneered Labial veneered ALLOYS USED IN CERAMO-METALLIC RESTORATION Are classified by the American Dental Association (ADA) according to their noble metal content into: I- High noble: Gold content > 40 wt % and noble content > 60 wt %. II- Noble: Noble metal content > 25 wt %. III- Base metal: Noble metal content < 25 wt %.  Dental Alloys fused to porcelain High noble Noble Base Metal alloys Metal alloys Metal alloys 60% noble metal 25%noble metal Less than 25% noble 40% gold and no gold metal. Au-Pl -Pd Pd-Ag Ni-Cr Au –Pd-Ag Pd-Cu-Ga Co –Cr Au - Pd Pd-Ga Ti Requirements of alloys used for metal-ceramic restorations: 1- The difference of coefficient of thermal expansion of porcelain and metal should be not greater than 1 10-6 0C. to avoid production of shear stress due to the difference in their cooling rates thus leading to failure of the bond between them. 8  2- The melting range temperature of the metal should be higher than the fusing temperature of the porcelain by at least 170-280 0C ………otherwise the metal coping may undergo flow or creep and deformation. 3- High yield strength to decrease coping thickness. 4- High modulus of elasticity to avoid bending in long span bridges. 5- High sag resistance to avoid thermal distortion. 9 6- A metal ceramic alloy must be able to produce surface oxides for chemical bonding with dental porcelain. Base metal alloys possess a natural tendency to oxidize when subjected to the elevated temperature of a porcelain furnace. Noble alloys, on the other hand, do not oxidize. So trace amounts of base elements are added for oxidation to take place. Indium (In), Tin (Sn), Gallium (Ga), Iron (Fe) Hardens the alloy and Provides oxides for ceramic bonding Facial view of the porcelain-bearing area of the finished substructure 11 Cleaning procedures: Air-abrasion of the veneering area. The margins have been protected by soft wax. The completed substructure ready for oxidizing 12  -- 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. 13 Oxidizing: Metal-ceramic substructure after cleaning and before oxidizing in the porcelain furnace. 14 Basic requirements needed for dental porcelain used as veneering material: 1. Low fusing temperatures, less than the melting range of the cast metal substrate by about 170-280 oC. 2. Should be of high viscosity high resistance to slumping to maintain their basic shapes during firing 3. Must be chemically & optically stable over a series of firing cycles. 16  3. Should resist devitrification :. if porcelain fired many times it becomes milky (cloudy) & difficult to glaze 4. Coefficient of thermal expansion should be lower than that of metal by 1 × 10 -6 0C to enhance bond strength & avoid crack formation. 17  Principles of metal substructure design  1- No sharp or acute angles: 📫 Rounded convex metal surface with no sharp angles is important to * eliminate areas of stress concentration * Distribute occlusal forces evenly * Facilitates wetting of metal with porcelain so enhancing bonding 20 ▪ The metal substructure ‘d have a distinct margin for finishing the veneer. {Rounded angles } 21 2- Adequate support to porcelain: Otherwise fracture of brittle porcelain. thick porcelain as layers away from metal is under tension subsurface porosity 22 A and C, Cross section through a metal-ceramic restoration. Ideal porcelain thickness is ensured by waxing to the full anatomic contour and cutting back. B and D, Incorrect framework design has insufficient support for the incisal porcelain. This can lead to fracture. 23 Unsupported thick porcelain. Sub-surface porosity increased with thickness of porcelain 24 3- No occlusal contacts on porcelain/metal interface: otherwise porcelain fracture * Junction ‘d be away from all centric occlusal contacts by at least 1-1.5 mm to avoid metal flow and subsequent 25 Occlusal contact away from the metal-ceramic junction. 26  4- Proximal contacts: 📫 For anterior teeth be on porcelain for better esthetics & translucency If on metal … block light transmission & poor esthetics 27 Cutback for proximal contact in porcelain. 28 Proximal contact in metal 29 5- Facilitates the wrap around effect : Metal is designed to allow porcelain to wrap around the metal to a- porcelain resistance against splitting b- better translucency & esthetics 30 Wrap around of porcelain veneer Porcelain covering part of the lingual surface 31 6- Compensate deficiencies in correct form of prepared teeth: - Deficiencies in the incisal edges or buccal or lingual cusps ‘d be compensated for with extra-metal thickness , not in porcelain thus …having even, minimal thickness of porcelain 32 ▪ Thin porcelain of uniform thickness ( which doesn’t impair esthetics ) supported by rigid metal ‘s stronger than thick porcelain. ▪ Minimum thickness of porcelain 0.7 mm ▪ Optimum thickness 1.0 mm ▪ Maximum 1.5 mm 33 7- Metal thickness to provide adequate rigidity: as … Flexing or bending during a) seating or b)under occlusal forces porcelain fracture 34 ▪ Minimal metal thickness noble metal alloys base metal alloys 0.3-0.5 mm 0.2-0.3 mm can be finished to these thin sections, withstand distortion as - Melting range - Yield strength -Modulus of elasticity 35 Porcelain and metal thickness. 36 ❑Metal finishing: The metal caliper should be used to measure the thickness of metal before any adjustments are made. Hold the gauge securely and allow the movable area to close on the casting. The thickness of metal will be indicated on the scale at the base of the gauge 37 Finishing the surface in one direction with light pressure helps avoid trapping debris between folds of the metal. 38 Some of the irregularities may retain debris that can later contaminate the porcelain 39 Finish the metal in one direction. Unidirectional finishing should leave the metal surface smooth and free of debris. 40 1) No sharp or acute angles. Convex surfaces and rounded contours of metal surfaces should be created. 2) The junction between metal and ceramic as definite (90o degree angle) and as smooth as possible. Is the occlusal contact to be in metal or porcelain? ▪ Occlusion in metal require less tooth reduction 1-1.5 mm. On the other hand ▪ 2 mm of occlusal reduction for posterior teeth and 1-1.5 mm for anterior teeth for porcelain on occluding surfaces. ▪ Metal surface can be more easily adjusted and re polished in chair side without adversely affecting the restoration.. ▪ Metal is potentially less abrasive to opposing natural teeth than dental porcelain. On the other hand removal of the glaze in the metal ceramic restoration in the intra-oral adjustment weaken the porcelain greatly. The transverse strength reduced by ½ compared with porcelain with intact glazed surface 3)No occlusal contact on porcelain metal interface contact at porcelain metal junction leads to porcelain fractures. The metal-ceramic interface must be at least 1.5 mm away from all centric occlusal contacts to avoid metal flow and subsequent ceramic fracture. Occlusal contacts against natural opposing teeth should be wherever possible in metal. The centric occlusal 1.5-2 mm from the porcelain-metal junction. When the anterior teeth contact in the incisal region, it is often necessary to consider a design with the lingual surface in porcelain to avoid functioning on or over the porcelain-metal junction. Do not design the substructure so contact occurs at the porcelain-metal junction. When the anterior teeth occlude in the gingival one half of the maxillary teeth, or when the lingual tooth reduction is less than 1 mm, it is best to design the substructure with the occlusion in metal. 4) Facilitates the porcelain wrap-around effect: as this would result in: a) increasing porcelain resistance against splitting (fracture under mastictary force). b) Better transleucency and good esthetics. 5) Metal thickness should provide adequate rigidity to prevent it distortion during porcelain firing or flexing under occlusal load resulting in porcelain fracture. A minimum thickness noble metal alloys is (03.05 mm) and 0.2-0.3 mm is for base metal. 6) Adequate support to porcelain veneer where lack of metal support results in porcelain fracture due to its brittleness and low flexure a strength. 7) The metal framework should be shaped to allow for a distinct margin. 8) Deficiencies in the incisal edge , buccal or ligual cusps should be compensated for with extra-metal thickness and should never economise on metal by replacing areas of gross destruction of tooth structure with porcelain. Minimal thickness of porcelain is0.7 mm, optimum thickness is 1 mm maximum is 1.5 mm. 9) Proximal contacts occlusal contacts Proximal contacts: should allow light transmission through the porcelain enamel in the proximal area. A natural tooth will always exhibit high tranleucency at its mesial distal and incisal margins. So the lingual metal collar should not encroach into the proximal space by more than needed for strength. Porcelain for metal veneering Dental porcelain is produced from a blend of quartz (SiO2), feldspar (potassium aluminum silicate, sodium aluminum silicate), and other oxides. During manufacture, the materials are heated to high temperature to form a glassy mass and then rapidly cooled by quenching them in water, which causes the glassy mass to fracture. The resulting product is called a frit. 55  Dental porcelain is supplied in powder form of several shades Mixing the powder with water or water-base glycerin containing liquid to form paste which is used to build-up restoration to its proper contour. Building-up using hairbrush , paste condensed onto metal through several condensation techniques ( vibration, spatulation or dry brush technique) 57 A variety of instruments from a porcelain kit includes a large whipping brush, and brushes for porcelain application, metal carving instruments, and a glass mixing rod. 58 A large ceramic slab is recommended for the buildup procedure because you have more working area to accommodate mixes of dentine, enamel, translucent porcelain, and various modifiers. 59 Condensation: To obtain a dense mass by: Vibration technique Spatulation technique Dry brush technique Purpose of porcelain condensation: 1. To remove excess water to firing shrinkage 2. To adapt the paste in adequate form. 3. To porosity. 61 The porcelain layer types: There ‘re three types of porcelain powders: 1. Opaque porcelain 2. Body or dentin porcelain 3. Enamel or incisal porcelain 62 Porcelain powders. 63 1. Opaque porcelain: First porcelain layer applied to the metal substructure. Oxides of titanium , tin or zirconium are added to original porcelain blend to mask the underlying metal color through scattering & reflection of the incident light rather High refractive than transmission index of these metal oxides 64 Role of opaque porcelain: 1. Masks the color of underlying metal. 2. Provides the basis for the total color tone of the crown as it ‘s the background of the overlying porcelain 3. provides chemical bond to the metal through it’s oxides 65 Opaque layer A unform thickness of 0.2 – 0.3 mm generally is regarded as ideal. 67 2. Body (Dentin) porcelain Fired onto the opaque layer together with the enamel porcelain. Contains oxides that aid in matching the proper color as it forms the main bulk of the build -up 68 Body layer 69 3. Enamel (incisal)porcelain Translucent porcelain that imports natural translucency to the final restoration Enamel layer 70 Porcelain Margin: With a vertical-loading porcelain furnace, work is placed on the centre of the ceramic platform and automatically raised into the vertical muffle. 72 The porcelain-metal bonding mechanisms 1.Mechanical 2. Compressive 3. Chemical 4. Van der waals forces 74 1. The mechanical bond The micro-roughness on the metal surface which are produced by finishing the metal surface with: * Non-contaminating stones or discs * Air abrasion ( sand blasting) creates some form of mechanical interlocking between opaque P. and metal. 75  Air abrasion (sand blasting) leads to : 1- Enhances the wettability of metal substrate with porcelain. 2- Mechanical interlocking. 3- surface area for chemical bonding. 76  But excessive micro-roughness leads to: a) Stress concentration at metal-ceramic interface. b) Deep interface angles no complete wetting air entrapment and voids at metal-ceramic interface. 77 2. Compressive stresses: Due to the slightly smaller coefficient of thermal expansion of the porcelain than that of the metal ( 1×10-6 o C) being placed in a state of compression during cooling to room temp. Porcelain in a state of compression at the alloy interface. 78 In a restoration with full-porcelain coverage, the metal is probably under tension (T) and ideally the porcelain is under compression (C). 79 3. Chemical bonding: Plays the major role in metal-ceramic bonding mechanisms ……formation of oxide layer on the metal surface. Oxide forming trace elements such as tin, indium or gallium are added to gold alloys They migrate to the interface where they oxidize & form covalent or ionic bond to similar oxides in the opaque porcelain. 80 On a very basic level, a metal ceramic restoration is made up of a metal substructure, porcelain veneer, and (preferably) an intermediary monomolecular oxide layer. 81  In base metal alloys all metal elements are oxidizable, chromium oxide layer is readily formed that bonds to porcelain. Elements are added in nickel-chromium alloys to control oxide layer thickness prevent premature bond failure through metal oxide or at metal-metal oxide interface. 82 4-Van der waals forces: The attraction between charged atoms that are in intimate contact yet do not actually exchange electrons is derived from van der waals forces. Ceramo-metallic failure Possible modes of failure of alloy-porcelain restorations.  Fixed Prosthodontics Veneered Reduction Professor Name : Dr Sohaila Ali M Sahel Professor title at MSA: Lecturer of Fixed Prosthodontics Definition: It is a full metal cast crown which has all or part of its surfaces veneered with an acrylic or ceramic material i.e. the extent of the veneer may vary. Indications: Indications: 1. Single restoration or a retainer of a bridge 2. Extensive teeth destruction e.g. caries, trauma. 3. In posterior teeth, where esthetics is required. 4. Short teeth where partial coverage would be contraindicated. 5. Correction of minor misalignment, rotated malposed and tilted teeth 6. Cases where aesthetics is needed and jacket crowns are contraindicated e.g. higher stress situations such as deep bite and parafunctional habits ex bruxism, clenching. 7. Patients with high caries index, rampant caries & bad oral hygiene. 8. Non-vital teeth. 9. Veneered restorations may accommodate a rest for removable prosthesis 10.Need for axial tooth recontouring ex for clasp of a partial denture..  Contraindications: 1. Young patients with large pulp due to fear of exposure. 2. Whenever more conservative restorations maybe performed. 3. Small teeth where insufficient bulk exists for reduction Contraindications:  Advantages: 1.Combines good aesthetics and strength. 2.Provides good resistance and retention 3.Corrects misalignment. 4.Correction of axial contour is possible. 5.Preparation is easier than partial coverage restorations. 6.Can be used for fixed bridge work and splinting. Compared with all ceramic crowns : 1. They provides more strength. 2. Longer life span as it is more durable. 3. Better marginal fit due to cast metal coping. 4. Can accommodate cast or soldered connectors. 5. Long span fixed bridges maybe done. 6. Maybe used to correct the occlusal plane. 7. Rests maybe incorporated in the metal coping to accommodate support for removable prosthesis. Disadvantages: 1.Excessive tooth reduction is required.(to accommodate metal casting & ceramic) 2.Pulp vitality cannot be detected. 3.Caries under the restoration cannot be detected clinically or radiographically. 4.Porcelain may fracture and resin may undergo discoloration. 5.All ceramic restorations provide superior aesthetics. 6.Expensive restoration. 7.Difficult shade match. Preparation Parameters Armamentarium Round-ended rotary diamonds (regular grit for bulk reduction, fine grit for finishing) or tungsten carbide burs Football- or wheel-shaped diamond (for lingual reduction of anterior teeth) Flat-ended, tapered diamond (for shoulder margin preparation) Finishing stones Explorer and periodontal probe Anterior Veneered Preparation  1. Labially labial half has greater amount of reduction to provide enough space for the metal and veneering material (1.2 mm in case of using base metal, &1.5 mm for noble metal). This reduction extends proximally and ends lingual to the contact area. Finishing line is shoulder.  The labial surface is reduced uniformly in two planes to correspond to the two geometric planes of a natural tooth. The lingual half of the tooth is reduced 1 mm to receive a metal casting only and a chamfer finish line is developed, 0.5 mm in width. In case of full veneered more reduction is needed.  The lingual half : of the tooth is reduced 1 mm to receive a metal casting only and a chamfer finish line is developed, 0.5 mm in width. In case of full veneered more reduction is needed. The meeting of both reductions results in a half groove (wing) proximally due to the abrupt meeting of different depths of reductions. This wing extends inciso-gingivally and adds some resistance to the preparation. All axial opposing walls should have a taper of approximately (5-10°) Nadia Fahmy 25 Nadia Fahmy 26  In anterior teeth, the palatal fossa is prepared with 1 mm clearance, if the centric contacts are located on the metal. Full veneered restorations need additional clearance. Incisal reduction should be 1.5-2 mm at least for adequate translucency of the final restoration.. The same amount is required as occlusal clearance in intercuspal and all excursions in case of posterior veneered restorations. Nadia Fahmy 27  Steps of Reduction: 1.Labial Reduction: 2 plane reduction. depth of 1.2-1.4mm to avoid opaque or overcontoured restorations Depth cuts: Cervical 1/3 Incisal 2/3 Nadia Fahmy 28 Nadia Fahmy 29 Nadia Fahmy 30 2.Incisal Reduction: Direction: Inclined 45° to the long axis of the tooth Depth 🡪 2 mm at least to provide enough space for translucency. Never exceed 1/3 the total incisogingival length Instrument: Tapered with flat or round end stone Wheel stone. Nadia Fahmy 31 3. Proximal Reduction Initially for access Tapered Needle stone Followed by Tapered with round end stone Nadia Fahmy 32 4.Palatal Reduction : Cingulum Torpedo diamond stone Round tapered stone Palatal Fossa : Wheel stone Football Nadia Fahmy 33 Finish lines of veneered reductions maybe: Shoulder Sloped shoulder Shoulder with bevel Nadia Fahmy 34 5.Finishing the preparation Torpedo or tapered finishing bur Roundation of all line & point angles Chamfer F.L. palatally Shoulder F.L. labially Wing Nadia Fahmy 35 Finished Reduction & Function provided by each part : Nadia Fahmy 36 Nadia Fahmy 37 Finished reduction : incisal view Nadia Fahmy 38 Wingless Reduction : Gradual transition in F.L. thickness from labial to palatal Nadia Fahmy 39 Veneered Premolar Reduction depth: Nadia Fahmy 40 Posterior veneered Preparation: Nadia Fahmy 41 Putty Index Nadia Fahmy 42 Veneered Premolar Preparation Occlusal Reduction Functional cusp bevel Nadia Fahmy 43 Nadia Fahmy 44 Nadia Fahmy 45 Nadia Fahmy 46 Nadia Fahmy 47 1.2-1.4mm to avoid opacity or overcontouring Nadia Fahmy 48 Proximal Reduction: Needle diamond stone Tapered with round end stone Nadia Fahmy 49 Palatal Reduction: Torpedo diamond Stone Tapered with round end stone Finishing Bur Nadia Fahmy 50 Finish line : Shoulder F.L. Shoulder with bevel F.L. Nadia Fahmy 51 Finishing of the preparation Roundation of all line and point angles Labially shoulder and Palatally chamfer Nadia Fahmy 52 Nadia Fahmy 53 Finished Preparation & wing direction Nadia Fahmy 54 Finished Reduction & function provided by each part: Nadia Fahmy 55 Finished Reduction: Nadia Fahmy 56