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Fig.1:Numberofstepscomparisonbetween traditionalmethodsofall-ceramicresto- rationsandCAD/CAMrestorations. Fig.2:VitaMarkIIblock. Fig.3:In-housemilledcrownfromanE-maxblock. Fig.4:Fullarchimplant supportedprosthesismilledfroma partiallysinteredsintered(greenstate)zirconiapuck. Fig.5:STLfileofanintraoralscan. LAB TRIBUNE Dental Tribune Middle East & Africa Edition | 1/2017 B2 torations and information that is saved in a computer and constitutes an extraordinary communication toolforevaluation. The incorporation of dental tech- nology has not only brought a new range of manufacturing methods and material options, but also some concernsabouttheprocessesinvolv- ing restorations’ fit, quality, accura- cy,shortandlong-termprognosis.[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 theUSA. CAD/CAMmaterials Glassceramics The first in-office 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 fine 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 blanksnowadays.Ontheotherhand, Celay ceramic inlays have been con- sideredclinicallyacceptablebytradi- tional criteria for marginal fit evalu- ation.[4] Dicor-MGC was a glass ceramic ma- terial composed of 70 percent tetra- silicic fluormica 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 introducedasahighlyfilledultrafine silica ceramic particles embedded in a resin matrix; the main advantage of this material is that it can be use asamilleddensecompositethatwas freeofpolymerisationshrinkagebut cannotbesinteredorglazed.[9] In early 1998, IPS ProCAD (Ivoclar Vivadent) was introduced as a leu- cite reinforced ceramic, which was similar to IPS Empress but with a finer 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 ceramicwithafineparticlesize.[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; thebaseoftheblockisadarkopaque layer, while the outer layer is more translucent; the CAD software al- lowsthecliniciantopositionoralign the restoration into the block for the desired outcome of the restoration. [11,12] In 2014, the Enamic (VITA) material was released as a ceramic network infiltrated with a reinforcing poly- mer network that has the benefits of a ceramic and resin in one material, butnoclinicaldataareavailable.[14] Alumina-basedceramics Alumina blocks (Vitablocs In-Ceram Alumina,VITA)areavailableformill- 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 flexural strength is less than In-Ceram Alu- mina,butveneeringwithfeldspathic porcelain for a more esthetic result could follow it after the milling pro- cess.[14,15] Nobel Biocare developed Procera material; for its fabrication high pu- rity aluminum oxide is compacted onto an enlarged die that is fabricat- edfromthescanneddata.[16]Theen- larged fabricated core shrinks to the dimensions of the working die when sintered at 1,550 °C; this material of- fers a very high strength core for all- ceramic restorations; the crown is finished with the application of feld- spathic porcelain.[17] More recently, In-Coris AL (Sirona Dental) has been introduced as a high-strength alu- minumoxideblockwithsimilarme- chanicalpropertiesasProcera.[18] Lithiumdisilicate Lithium disilicate is composed of quartz, lithium dioxide, phosphor oxide, alumina, potassium oxide andothercomponents.Accordingto Saint-Jean (2014) the crystallization of lithium disilicate is heterogenous andcanbeachievedthroughatwoor 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 easiertomillandformtothedesired 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 final 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-office 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] Accordingtothemanufacturerspec- ifications, 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 (TableI). 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 first 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- rialwithaflexuralstrengthof360to 400 MPa (two to three times strong- erthanglassceramics);theblocksare blue in the partially crystallised state butitachievesthefinalshadeafterit issubmittedtothefiringprocessina porcelain oven for 20 to 25 minutes to complete the crystallisation; the final result is a glass-ceramic with a fine grain size of approximately 1.5 µm and 70 percent crystal volume incorporatedinaglassmatrix.[20] In 2014, Vident released Suprinity; the first 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 asabiomaterialforcrownandbridge 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 interocclusalspace.[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- atedwithvolumeexpansion’.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 fit or passiveness of the restorations. [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 inordertominimizethiseffect.[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 tipofthecrackconstitutesanenergy 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 expansionofaround3.5percentthat increases the energy that opposes thecrackpropagation.[4] Zirconia restorations can be fabri- cated from fully sintered zirconium oxideorpartiallysinteredzirconium oxide blanks (green-state). Propo- nent of milling fully sintered zirco- nia claim that fitness 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 fastertomillandproponentsofmill- 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;thismicrodefectsorsurfaceflaws can affect the final strength of the fi- nal restoration and could potentially chip the marginal areas; however furtherresearchisneededaboutthis topic.[10] Oneofthefirstsystemsthatusedzir- coniawasIn-CeramZirconia(Vident), whichisamodificationoftheIn-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 workflow 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 highesthetics.[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 Table1:RecommendeddimensionsforE-maxCADbyIvoclarVivadent. Materialthickness Anterior Premolar Molar Veneers Stainingtechnique 1.2 1.5 1.5 0.6 Cut-backtechnique 1.2 1.5 1.5 0.6 Layeringtechnique 0.8 0.8 – – Valuesareexpressedinmillimetres ÿPageB3 ◊PageB1 Stainingtechnique 1.21.51.50.6 Cut-backtechnique 1.21.51.50.6 Layeringtechnique 0.80.8 – –