Dental Ceramics Lecture 10 PDF

Dental Ceramics LECTURE 10 Classification and clinical indications Dental ceramics’ classification according to their application, fabrication method or crystalline phase according to Craig’s Dental Materials, 13...

Dental Ceramics LECTURE 10 Classification and clinical indications Dental ceramics’ classification according to their application, fabrication method or crystalline phase according to Craig’s Dental Materials, 13th ed  Used criteria for classification 1. Firing T 2. Composition 3. Laboratory processing 4. Usage domain I. According to sintering T -High - over 13000C -Medium - 1100-13000C -Low - 850-11000C -Ultra low – under 8500C  II. According to composition 1.Silicate ceramics = multi phases: a glassy phase well represented in which are dispersed different crystals − medium and low sintering T −good aesthetics −poor mechanical strength −for plating the metal framework or full ceramic crown 2.Oxide ceramics = monophase (>90% metallic oxides) with a polycrystalline structure −high sintering T −very good mechanical strength −poor aesthetics (they are opaque)  III. According to laboratory processing 1. Sintered 2. Castable 3. Pressed 4. Glass-infiltrated 5. CAD-CAM  III. According to laboratory processing 1. Sintered = burning into successive layers onto: -metallic framework -platinum foil -refractory cast -hydrothermal glass According to laboratory processing 2. Casting = wax pattern, mould, melting ceramic block, casting + ceramization (crystallization) of the cast framework (thermal treatment) -A variant = core casting + veneering 3. Glass-infiltration = a framework from oxide ceramics obtained through CAD-CAM or by the technician + glass- infiltration + veneering  According to laboratory processing 4. Pressed = wax pattern, molten glass ingot and pressed into mould + veneering -Precision wax-up duplicated in ceramic -Consistent pre-blended ceramic ingots -Ingot being pressed  According to laboratory processing 5. CAD-CAM (Computer Aided Design- Computer Aided Manufacturing) = subtractive processes from the ceramic ingot through : -Mechanical milling based on the optical impression -Milling based on a copy -Sonoerosion -Electrophoresis  IV. According to usage domain 1. Prosthetics, for: -veneering the metallic framework or oxide ceramics -single prosthetic restorations-partial or full ceramic (veneers, inlay, post and cores, crowns) -framework of the full ceramic dental bridges -mesostructure for Ti implants 2. Orthodontics  brackets 3. Implantology  ceramic implants 4. Periodontal surgery  for bone defects filling (ceramics based on absorbent hydroxyapatite) 5. Therapy for oro-facial defects  medication support (for Gentamicin) for osteomyelitis treatment 1. Ceramics for metal – ceramic restorations (Metal- bonded ceramics or porcelain-fused-to-metal restorations=PFM restorastions) crowns and mixed dental bridges through sintering Variants: 1.Traditional feldspathic ceramics 2.Feldspathic-ceramics with different addition of components for improving their properties : -Aluminous(Alumina)- reinforced feldspathic ceramic -Spinell- reinforced feldspathic ceramic (with MgO) -Leucite –reinforced feldspathic ceramic  2. Ceramics for all-ceramic restorations 2.1. Silicate ceramics 2.1.a. Feldspathic ceramics - simple ( inlay, veneers, crowns or veneering onto a frame) -sintered over a platinum foil or a refractory cast (e.g. Vitadur) - CAD-CAM (e.g. Vita Blocks, Sirona CEREC Blocks) - leucite (inlay, veneers, crowns or veneering) - sintered (e.g Mirage, Fortress, Optec-HP) - pressed (e.g. Empress I) - CAD-CAM (e.g. Procad) - alumina (for core) - sintered (e.g. Hi-Ceram) - Spinell(magnesium oxide)(for core) - sintered - zirconium (for core) - sintered (e.g. Mirage II)  2. Ceramics for all-ceramic restorations 2.1. Silicate ceramics 2.1.b. Glass ceramics - with leucite (for inlay, veneers, crowns) -sintered - pressed - with fluormica (inlay, veneers, crowns) - castable (e.g. Dicor) - pressed (e.g. HeraCeramPress) - CAD-CAM (e.g. Macor) - with lithium disilicate (for core)(used always together with Hydroxyapatite ceramics) - pressed (e.g. Empress II, IPS e.max Press, IPS e.max ZirPress) - CAD-CAM (ex. IPS e.max CAD) -with hydroxyapatite (used always together with Li disilicate ceramics) - sintered (for veneering the core of Li disilicate) - castable (e.g. Cerapearl)  2. Ceramics for all-ceramic restorations 2.2. Oxide ceramics (for core) 2.2.a. Glass infiltrated ceramics - with alumina or spinell or zirconia(zirconium) - core made by the tehnician (e.g. In-Ceram Alumina, In-Ceram Spinell, In-Ceram Zirconia) -core through CAD-CAM milling or electrophoresis (e.g. In-Ceram Alumina, In-Ceram Spinell, In-Ceram Zirconia, Vita Celay) 2.2.b. Sintered oxide ceramics (sintered at high pressures) - with pure alumina core - pressed and sintered (e.g. Procera Alumina, Procera Zirconia, Techceram) -with zirconia core -CAD-CAM (e.g. 3M Espe LAVA Frame, Sirona inCoris ZI, KaVo Everest HPC-Blank, KaVo Everest ZS-Blank, VITA In-Ceram YZ) 2.2.c. Zirconium oxide isostatic sintered - CAD-CAM (e.g. DC-Zirkon, DigiZon HIP, KaVo Everest ZH-blank, Zirkon)  1. Metal-bonded ceramic restorations/ Porcelain-fused- to-metal restorations (PFM) A major requirement: compatibility alloy -ceramic -1962 – Weinstein and Weinstein – first veneered feldspathic ceramic -Ceramics’ disadvantage = lack of fracture toughness, micro-cracks on the inner surface -appliance of the ceramics onto the metal framework – a stopper in the way of micro-cracks’ propagation -Fragile zone = interface metal - ceramics Metal – ceramic bonding - Imposed conditions for Metal-Ceramic Alloy – see MCA lecture no.8 + CTEceramic < CTEalloy/metal -solidus T of MCA > with min.150-2000C than sintering T of the ceramics (850-11000C) -CTE ceramics for full ceramic restorations= 7-8 ppm/0C -CTE alloys = 14-16 ppm/0C a. CTEc > CTEmetal b. CTEc = CTEm c. CTEc < CTEm Tensile loads will have to get out ceramics firstly under compression and after that they will get in action Effects of the differences between the CTEs over the residual stress accumulated into metal and ceramics  CTEc > CTEmetal Ceramics will shrink more than the metal; but the metal won’t let ceramics to shrink  tension within ceramics and compression within metal  tensile forces on the ceramic’s surface => cracks over the ceramic’s surface  CTEc = CTEm The 2 materials will equally shrink : => no internal stresses CTEc < CTEm The metal will tend to shrink more than ceramics :  compressive forces over the ceramics   reduced risk of cracks within ceramics   CTEc < CTEm, but with minimal differences (0.5-1 ppm/0C)  -BUT big differences, CTEc give a similar fluorescence with that of natural teeth - excellent aesthetics, strongly influenced by the size of crystals and differences in the refractive indices of the crystalline phase and the glass phase.  Fluormica Glass-Ceramics - ceramization (ceraming process) through formation and growing of some crystals of tetrasilicate of mica in the glassy phase,with a needle-like shape, can stop the propagation of the micro-cracks through the material - flexural strength 120-150 Mpa - Adhesive cementation= increase the strength of material - used also for posterior crowns - Process technology: - casting (Dicor)- eliminated - pressure (HeraCeramPres) - CAD-CAM (Macor). 2.2.b. Glass-Ceramics Lithium disilicate and Hydroxyapatite Glass- Ceramics (inlay, veneers, crowns for any tooth and 3-unit bridge) -Very good flexural strength (350-450 MPa) and fracture toughness -Can be lightly opaque, or too translucent used as core material, and then veneered with aesthetic ceramics  Lithium disilicate and Hydroxyapatite Glass- Ceramics - CTE of Li disilicate glass-ceramics = over 10 ppm/0C - aren’t compatible with traditional veneered feldspathic ceramics (CTE ~ 7-8 ppm/0C)  new glass-ceramics developed => hydroxyapatite glass- ceramics (Ca10(PO4)6·2OH) - Process technology: -pressure (Empress II) -CAD-CAM. The pros of the used ceramics: - ideal chromatics– natural look (stability, gloss/polish, translucency) -biocompatibility - reduced thermal conductivity -chemical resistance -compressive strength - high surface density and polish/gloss The cons of the used ceramics: - decreased tensile strength, bending, flexural - impossible ulterior workings, surfaces become rough -hardness isn’t anymore a problem - external and internal cracks – fractures - high price