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B2 ◊Page B1 LAB TRIBUNE Dental Tribune Middle East & Africa Edition | 3/2018 similar to IPS Empress but with a fi ner particle size; this material was designed to be use with the CEREC system (Sirona Dental) and was available in different shades.2 More recently, the introduction of IPS Empress CAD (Ivoclar Vivadent) and Paradigm C that according to the manufacturer (3M ESPE) is a 30 to 45 percent leucite reinforced glass ce- ramic with a fi ne particle size.10 To overcome esthetic problems of most CAD/CAM blocks having a monochromatic restoration, a dif- ferent version was developed as a multicoloured ceramic block, which was called VITA TriLuxe (Vident) and also IPS Empress CAD Multiblock; the base of the block is a dark opaque layer, while the outer layer is more translucent; the CAD software allows the clinician to position or align the restoration into the block for the de- sired outcome of the restoration.11,12 Fig. 1: Number of steps comparison between traditional methods of all-ceramic resto- rations and CAD/CAM restorations. Fig. 2: Vita Mark II block. Fig. 3: In-house milled crown from an E-max block. Fig. 4: Full arch implant supported prosthesis milled from a partially sintered sintered (green state) zirconia puck. Fig. 5: STL fi le of an intraoral scan. ing restorations’ fi t, quality, accu- racy, short and long-term prognosis.1 The purpose of this document is to provide a review of the literature re- garding the different materials and systems available up until 2015 in the USA. CAD/CAM materials Glass ceramics The fi rst in-offi ce ceramic mate- rial was Vitablock Mark I (Vident); it was a feldspathic-based ceramic compressed into a block that was milled into a dental restoration. Af- ter the invention of the Mark I block, the next generation of materials for CAD/CAM milling fabrication of all-ceramic restorations were Vita Mark II (Vident) and Celay, which replaced the original Mark I in 1987 for fi ne feldspathic porcelains pri- marily composed of silica oxide and aluminum oxide.2,3 Mark II blocks are fabricated from feldspathic por- celain particles embedded in a glass matrix and used for single unit res- torations available in polychromatic blanks nowadays. On the other hand, Celay ceramic inlays have been con- sidered clinically acceptable by tradi- tional criteria for marginal fi t evalu- ation.4 Dicor-MGC was a glass ceramic ma- terial composed of 70 percent tetra- silicic fl uormica crystals precipitated in a glass matrix; but this material is no longer available on the mar- ket.[5] Studies from Isenberg et al. suggested that inlays of this type of ceramics were judged as clinically successful in a range from 3–5 years of clinical service.6-8 In 1997, Para- digma MZ100 blocks (3M ESPE) were introduced as a highly fi lled ultrafi ne silica ceramic particles embedded in a resin matrix; the main advantage of this material is that it can be use as a milled dense composite that was free of polymerisation shrinkage but cannot be sintered or glazed.9 In 2014, the Enamic (VITA) material was released as a ceramic network infi ltrated with a reinforcing poly- mer network that has the benefi ts of a ceramic and resin in one material, but no clinical data are available.14 Alumina-based ceramics Alumina blocks (Vitablocs In-Ceram Alumina, VITA) are available for mill- ing with the CEREC system (Sirona Dental) and now compatible with other milling machines as well. Due to the opacity of alumina- based ce- ramic materials, the In-Ceram Spi- nell (VITA) blocks were developed as an alternative for anterior aes- thetic restorations; it is a mixture of alumina and magnesia. Its fl exural strength is less than In-Ceram Alu- mina, but veneering with feldspathic porcelain for a more esthetic result could follow it after the milling pro- cess.14,15 In early 1998, IPS ProCAD (Ivoclar Vivadent) was introduced as a leu- cite reinforced ceramic, which was Nobel Biocare developed Procera material; for its fabrication high pu- rity aluminum oxide is compacted Anterior Material thickness 1.2 Staining technique 1.2 Cut-back technique Layering technique 0.8 Values are expressed in millimetres Premolar 1.5 1.5 0.8 Molar 1.5 1.5 – Veneers 0.6 0.6 – Table 1: Recommended dimensions for E-max CAD by Ivoclar Vivadent. onto an enlarged die that is fabri- cated from the scanned data.[16] The enlarged fabricated core shrinks to the dimensions of the working die when sintered at 1,550 °C; this material offers a very high strength core for all-ceramic restorations; the crown is fi nished with the applica- tion of feldspathic porcelain.17 More recently, In-Coris AL (Sirona Den- tal) has been introduced as a high- strength aluminum oxide block with similar mechanical properties as Procera.18 Lithium disilicate Lithium disilicate is composed of quartz, lithium dioxide, phosphor oxide, alumina, potassium oxide and other components. According to Saint-Jean (2014) the crystallization of lithium disilicate is heterogenous and can be achieved through a two or three stage process depending if the glass ceramic is intended to be used as a mill block (e-max CAD) or as a press ingot (e-max press). Lithium disilicate blocks (Fig. 3) are partially sintered and relatively soft; they are easier to mill and form to the desired restoration compared to fully sin- tered blocks; after this process the material is usually heated to 850 °C for 20 to 30 minutes to precipitate the fi nal phase. This crystallization step is usually associated with a 0.2 percent shrinkage accounted for the designing software.19 Nowadays, blocks of lithium disilicate are avail- able for both in-offi ce and in-labo- ratory fabrication of all-ceramic res- torations; monolithic blocks require layering or staining to achieve good esthetic results.8 Different in vitro studies that evaluate the marginal accuracy of milled lithium disilicate reveal that these restorations could be as accurate as 56 to 63 microns.20 According to the manufacturer spec- ifi cations, the designing principles for lithium disilicate are produced by default in the designing software, but in full all-ceramic crowns struc- tures the minimum thickness must be applied in the preparation design (Table I). During the crystallisation process, the ceramic is converted from a lithium metasilicate crystal phase to lithium disilicate. Some commercial types of ceramics are Empress CAD (Ivoclar Vivadent) and IPS E-max. The fi rst one is a leucite based glass ceramic with a composition simi- lar to Empress ceramic. IPS E-max was introduced in 2006 as a mate- rial with a fl exural strength of 360 to 400 MPa (two to three times strong- er than glass ceramics); the blocks are blue in the partially crystallised state but it achieves the fi nal shade after it is submitted to the fi ring process in a porcelain oven for 20 to 25 minutes to complete the crystallisation; the fi nal result is a glass-ceramic with a fi ne grain size of approximately 1.5 µm and 70 percent crystal volume incorporated in a glass matrix.20 In 2014, Vident released Suprinity; the fi rst ceramic reinforced with zir- conia (10 percent weight); this mate- rial is a zirconia reinforced lithium silicate ceramic (ZLS) available in a precrystallized or fully crystallized (Suprinity FC) state indicated for all kind of single all-ceramic restora- tions. Zirconia Zirconia has been used in dentistry as a biomaterial for crown and bridge fabrications since 2004; it has been useful in the most posterior areas of the mouth where high occlusal forc- es are applied and there is limited interocclusal space.22 Zirconia is a polymorphic material that can have three different forms depending on the temperature: monoclinic at room temperature, tetragonal above 1,170 °C, and cubic beyond 2,370°C. According to Piconi (1999) ‘the phase transitions are re- versible and free crystals are associ- ated with volume expansion’. Differ- ent authors state that when zirconia is heated to a temperature between 1,470 °C and 2,010 °C and cooled, a volume shrinkage of 25 to 35 percent can occur that could affect marginal fi t or passiveness of the restora- tions.22 This feature limited the use of pure zirconia until 1970 when Rieth and Gupta developed the yttria-te- tragonal zirconia polycrystal (Y-TZP) containing 2 to 3 percent mol-yttria in order to minimize this effect.10 One of the most interesting prop- erties of zirconia is transformation toughening; Kelly (2008) describes it as: ‘A phenomenon that happens when a fracture takes place by the extension of an already existing de- fect in the material structure, with the tetragonal grain size and stabi- lizer, the stress concentration at the tip of the crack constitutes an energy source able to trigger the transfor- mation of tetragonal lattice into the monoclinic phase’. This process dis- sipates part of the elastic energy that promotes progression of cracks in the restoration; there is a localized expansion of around 3.5 percent that increases the energy that opposes the crack propagation.4 Zirconia restorations can be fabri- cated from fully sintered zirconium oxide or partially sintered zirconium oxide blanks (green-state). Propo- nent of milling fully sintered zirco- nia claim that fi tness of restorations is better because it avoid volumetric changes during the fabrication pro- cess. On the other hand, the partially sintered zirconia (Fig. 4) is easier and faster to mill and proponents of mill- ing partially sintered blanks claim that micro cracks can be induced to the restoration during the milling process and it also requires more time and intensive milling process- es; this micro defects or surface fl aws can affect the fi nal strength of the fi - nal restoration and could potentially chip the marginal areas; however further research is needed about this topic.10 One of the fi rst systems that used zir- conia was In-Ceram Zirconia (Vident), which is a modifi cation of the In-Cer- am Alumina but with the addition of partially stabilised zirconia oxide to the composition. Recently many companies have integrated zirconia into their CAD/CAM workfl ow due to its mechanical properties, which are attractive for restorative den- tistry; some of these properties are: high mechanical strength, fracture toughness, radiopacity for marginal integrity evaluation, and relatively high esthetics.13,14 Different manufacturers are using zirconia as one of their main mate- rials such as: Ceramill Zolid (Amann Girbach), Prettau (Zirkonzahn), Cer- con (DENTSPLY), BruxZir (Glidewell Laboratories), IPS ZirCAD (Ivoclar Vi- vadent), Zenostar (Ivoclar Vivadent), inCoris ZI (Sirona Dental), VITA In- Ceram YZ (Vident), among others. Companies have introduced mate- rials that are in combination with zirconia to improve its properties in different clinical situations. Lava Plus, for example, is a combination of zirconia and a nano-ceramic. CAD/CAM systems A number of different manufactur- ers are providing CAD/CAM systems that generally consist of a scanner, ÿPage B3