cosmetic dentistry_ beauty & science International Edition

review _ ceramics I previously, restorations milled from blocks tend to have improved density and mechanical properties compared with powder/liquid or pressed restora- tions owing to the standardised manufacturing process (Fig. 16).35, 36 3.1.2Glass/crystal VITABLOCS Mark II are fabricated using fine- grained powders, which produce a nearly pore-free ceramicwithfinecrystals.Thiswasthefirstmaterial specifically produced for the CEREC system and hasanexcellenthistoryofclinicalsuccessforinlays, onlays, and anterior and posterior crowns.36 The restoration may be characterised with external stains or porcelain may be added to produce a lay- eredeffect(Figs.17a&b).Theseblocksareavailable as monochromatic, polychromatic with stacked shadesasinalayercake,andmorerecentlyinaform replicating the hand-fabricated crowns for which anenamelporcelainislayeredondentineporcelain. 3.1.3Glass/leucite IPS Empress CAD is based on the pressable IPS Empress and has the same microstructure, a feldspathic glass with about 45 % leucite crystal. Theseblocksalsohaveafineleucitecrystalstructure (about 5–10 µ) and may be further characterised using external stains or porcelain. IPS Empress CAD is available in monochromatic and polychromatic stacked shades. Its strength properties are similar to that of VITABLOCS Mark II. Common to all of these blocks is a microstructure with a fine particle size that helps resist machining damage, improve mechanical properties and decrease the polishing time of the finished restoration. 3.1.4Lithiumdisilicate The IPS e.max block (lithium disilicate) is not initially fully crystallised. This improves milling time and decreases chipping from milling. The milled restoration is then heat-treated for about 20–30 minutes to crystallise the glass, and produce the final shade and mechanical properties of the restoration. The crystallisation process changes the restoration from a blue colour to a tooth shade. The microstructure and chemical composition are essentially the same as those of IPS e.max Press. The IPS e.max block has several translucency levels, the least translucent used primarily as a framework material and the higher translucency blocks used for full contour restorations. 3.1.5Framework (a)Alumina:Interpenetratingphase orglass-infused VITA In-Ceram blocks are fabricated by pressing the alumina-based powder into a block shape in amannersimilartothatofVITABLOCSMarkII.How- ever,theseblocksareonlyfiredtoabout75%dense. PorousblocksofVITAIn-Cerammaterialsaremilled toproduceaframework.Theblocksaretheninfused with a glass in different shades to produce a 100 % dense material, which is then veneered with porce- lain. Glass infusion only requires about 20 minutes for a coping and 1.5 hours for a three-unit bridge. The microstructure is the same as that of slip-cast alumina. The blocks are available in all three types of VITA In-Ceram. (b)Alumina:Porous Alumina frameworks may be fabricated from porous blocks of material. Pressing the alumina powder with a binder into moulds produces the blocks. The blocks may be partially sintered to im- prove resistance to machining damage or used as pressed in a fully green state (unfired, with binder). The frameworks are milled from the blocks and then sintered to full density at about 1,500 °C for 4–6 hours. The alumina has a fine particle size of about 1 µ and a strength of about 600 MPa, and is designed for anterior and posterior single units, as well as anterior three-unit bridges. Figs. 17a & b_A milled crown. I 33cosmeticdentistry 1_2014 Fig. 17bFig. 17a CDE0114_26-34_McLaren 11.06.14 14:07 Seite 8