Dental ceramics Silicate ceramics and oxidceramics Prepared by

Dental ceramics Silicate ceramics and oxidceramics Prepared by: Dental Materials Department Yenepoya Dental College, Yenepoya University, Mangalore.

Images from Ka. Vo Everest CAD/CAM system

Why use ceramics n Biocompatibility n Aesthetics Durability n The biocompatability issue is essential to prevent adverse reactions within the patients The use of dentally coloured glasses can provide replacement structures that can be made to imitate tooth structure in both colour, translucency and response to different lighting sources. Improvements in fracture toughness, wear resistance, machinability, solubility and flexural strength

Ceramics used in dentistry Fillings n Veneering metal frameworks n All ceramic restorations n Denture teeth n Implants n Orthodontic brackets n

Silicate ceramics Oxid ceramics ESTHETICS STRENGTH Feldspathic porcelain Veneering ceramics – sintering n Glass Ceramic Castable glasses-Dicor Pressed leucite system- IPS Empress n n Glass infiltrated Alumina system In-ceram Alumina In-Ceram Spinell In –Ceram Zirconia n Policrystal ceramics: CAD/CAM Cercon Base DC-Zirkon Lava Frame etc.

Basic structure of dental ceramics Two different phases built by metallic (Al, Ca, Mg, K etc) and non-metallic (Si, O, B, F etc. ) elements: (their composition varies in each type of ceramic) Glass matrix + Crystals §An overcooled liquid §Not crystalline, but still ordered structure §Silica tetrahedron network §Glass modifiers built in network Most important crystals: n Leucit n Fluormica n Aluminium n Spinell n Zirconia They determin the physical, optical physical chemical and chemical properties of the ceramics

First ceramic material in dentistry Feldspathic Porcelain: derived from the natural mineral feldspar n 75%feldspar, 22 -25% quartz, 0 -3% kaolin Feldspar: Provides for transparency and influences the flow characteristics of the ceramics. ¨ Quartz (silicon oxide): Provides for adequate strength and also for transparency. ¨ Kaolin: Provides for the necessary opaque properties. ¨ n n n Fritting: -cleaning and mixing raw materials, heating, melting, sudden cooling and grinding to fine powder Sintering: powder mixing with liquid, firing, powder particles stick together Shrinkage: appr. 30 vol% Structure: leucite crystals in silica glass matrix Disadvantage: brittle, hard, rigid

Veneering metal frameworks Image from Bego Virtual Academy

Image from Bego Virtual Academy

Esthetic consideration Metal-ceramic restorations: • Ceramic material is veneered (sintered) onto a metal frame in several firing processes

Veneering ceramics n n n Used for the porcelain-fused-to-metal technique Based on modified feldspathic porcelain Binding oxides for metal-ceramic bond Leucite content: thermal expansion coeff. Fusing temperature 200 -250 C lower than metal framework (low fusing ceramics) Hydrothermal ceramics Synthetic ceramics (metal –ceramics) • tempering and fusing in high pressure §No natural raw materials steam §Made of high purity chemicals §Tempering: guided heating process, to • Hydroxil ions built in glassy matrix • Compact and homogenous structure form certain type, size, amount and • Better fracture toughness and lower dispersion of crystals (micro-leucite hardness crystals • Leucite content allows veneering §Standard physical, chemical and optical frameworks properties • Ultra-low fusing temp. Can be achieved §Standard quality • Pure glass can be used for dental §Low or ultra-low fusing temperature purposes (one and only among dental ceramics)

The bonding of ceramic materials to alloys follows four principles: ¨ Shrinking the ceramic onto the metal frame - coefficient of thermal expansion ¨ Chemical bond The bond is formed by means of oxygen bridges between the silicon atoms of the ceramic and the metal oxides of the alloy. ¨ Mechanical retention is created through finishing and blasting of the frames-surface enlargement also takes place. ¨ Bonding through adhesion takes place via intermolecular forces (VAN DER WAAL forces)

All ceramic restorations

n n driving forces for developments: Public perception that metal-free restorations are more aesthetic Disadvantages of the metal ceramic systems include radiopacity, some questions centring around metal biocompatibility and lack of natural aesthetics Difference in reliability between metal-ceramic systems and all-ceramic systems

All ceramic restorations Laboratory processing n Silicate ceramics Sintering o Casting o Pressing o CAD/CAM o n Oxidceramics o infiltration and /or CAD/CAM technology

§Sintering is a method for making objects from powder, by heating the Sintering material (below its melting point) until its particles adhere to each other The base-material for heating ceramic on: - platinum foil (removable heat-resistant cap platinum foil from the gypsum cast) - Heat resistant investment material made cast - Hydrothermal glass/ Duceram LFC under vacuum to prevent porosities

n Casting (Dicor) Casting is a process by which a Casting material is introduced into a mold while it is liquid, allowed to solidify in the shape inside the mould, and then removed producing a fabricated object Cast using lost-wax investment method followed by heat-treatment to precipitate a crystalline phase § Pressing (Empress) Pressed ceramic technology produces Pressed consistently precise crowns by eliminating shrinkage, porosity and the inconsistency of brush build-ups

Glass Ceramic n n n first a glassy matrix is produced precursors of crystals are in glassy matrix, crystals produced by tempering (heating), “bonded” to the remaining tooth structure using a dental Bis. GMA based composite resin

§Glass infiltration Oxidceramics Glass infiltrated Alumina system In-ceram Alumina In-Ceram Spinell In –Ceram Zirconia n Slip-cast slurry in porous mould-sintered — infiltration by low viscosity glass — veneered with more translucent feldspathic frit Slip-cast slurry: A fine particle ceramic dispersed in an aqueous liquid medium is poured into a porous mould which rapidly extracts the liquid causing the formation of a close-packed but weak ceramic particle structure.

Polycrystal Oxid ceramics High strength underlying core to support veneering porcelain which gives the final shape and aesthetic attributes required for the restoration. n Yttrium stabilized Zirconium -dioxide ceramics: Zr. O 2 95%+ 5% Yttrium n n. More to come: lecture on CAD/CAM

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