cosmetic dentistry_ beauty & science International Edition

I review _ ceramics owing to the glassy phase. Initial clinical data for single restorations with this material is excellent, especially if it is bonded.20 3.Category3:Interpenetratingphaseceramic VITA In-Ceram (VITA Zahnfabrik) consists of a family of all-ceramic restorative materials based on the same principle introduced in 1988. The family includes a range of strengths, translucencies and fabrication methodologies designed to cover the wide scope of all-ceramic restorations, includ- ing veneers, inlays, onlays, anterior and posterior crowns, and bridges. VITA In-Ceram SPINELL (alu- mina and magnesia matrix) is the most translucent, of a moderately high strength and used for anterior crowns. VITA In-Ceram ALUMINA (alumina matrix) is of high strength and moderate translucency, and is used for anterior and posterior crowns. VITA In-Ceram ZIRCONIA (alumina and zirconia matrix) hasaveryhighstrengthandlowertranslucency,and is used primarily for three-unit posterior bridges. Additionally, these materials are supplied in a block form for producing milled restorations using a variety of machining systems. VITA In-Ceram belongs to a class of materials known as interpenetrating phase composites.21 They consist of at least two phases that are inter- twined and extend continuously from the internal to the external surface (Fig. 9). These materials pos- sess improved mechanical and physical properties relative to the individual components owing to the geometrical and physical constraints that are placedonthepaththatacrackmustfollowtocause a fracture. A tortuous route through alternating layers of both components is required to break these materials. Interpenetrating phase materials are generally fabricated by first creating a porous matrix, in the case of VITA In-Ceram a ceramic sponge. The pores are then filled by a second-phase material, a lanthanum aluminosilicate glass, using capillary action to draw a liquid or molten glass into all the pores to produce the dense interpenetrating material. The system was developed as an alternative to conventional metal–ceramic restorations and has met with great clinical success.22, 23 The system utilises a sintered crystalline matrix of a high- modulus material (85 % of the volume), in which there is a junction of the particles in the crystalline phase. This is very different from glasses or glass- ceramicmaterials,inthattheseceramicsconsistof a glass matrix with or without a crystalline filler in which there is no junction of particles (crystals). Slip casting24 may be used to fabricate the ceramic matrix or it can be milled from a pre-sintered block.25 Flexural strength ranges from 350 MPa for VITAIn-CeramSPINELL,450MPaforVITAIn-Ceram ALUMINA and up to 650 MPa for VITA In-Ceram ZIRCONIA. Several clinical studies support the use VITA In-Ceram ALUMINA for single units anywhere in the mouth. In those studies, VITA In-Ceram ALUMINA had the same survival rate as porcelain fused to metal up to the first molar, with a slightly higher failure rate for the second molar.26–28 VITA In-Ceram ZIRCONIA should only be used on molars owing to its very high opacity, which is not ideal for anterior aesthetics. For an- terior teeth, VITA In-Ceram SPINELL is ideal, owing to its higher translucency (Figs. 10 a–c). 4.Category4:Polycrystallinesolids Solid sintered monophase ceramics are materi- als formed by directly sintering crystals together without any intervening matrix to form a dense, air-free, glass-free polycrystalline structure. There are several different processing techniques that allow the fabrication of solid sintered alumina or zirconia frameworks. The first fully dense polycrys- talline material for dental applications was Procera AllCeram alumina (Nobel Biocare) with a strength of about 600 MPa.29 The alumina powder is pressed and milled on a die, and sintered at about 1,600 °C, leading to a dense coping but with about 20 % shrinkage (Figs. 11, 12a & b). The use of what is commonly referred to as zirconia in dentistry has increased rapidly over the past few years. This is not pure zirconia; it is partially stabilised by the addition of small Fig. 11_A scanning electron micrograph of the microstructure of an alumina ceramic. Figs. 12a & b_Alumina anterior crowns. 30 I cosmeticdentistry 1_2014 Fig. 12a Fig. 12bFig. 11 CDE0114_26-34_McLaren 11.06.14 14:06 Seite 5