IM0410

research _ dental surfaces I after a proprietary polishing procedure produces minimal wear of human enamel. When compared directlywithapolishedtypeIVgoldsurface,thezir- conia (both surface finishes) does produce statisti- cally significantly more enamel wear than the con- trol. When comparing the two zirconia surface fin- ishes to each other, the polished zirconia surface produced less enamel wear than the as-delivered surface but the difference was not statistically sig- nificant. Several all-ceramic veneering porcelains were also evaluated in this study. The polished zirconia surface underwent the same polishing procedure as the veneering porcelains allowing a direct com- parison between gold, zirconia and porcelain. This was to determine whether the application of ve- neeringporcelainwouldhaveapositiveornegative impact with regards to the abrasiveness of the restorative surface. Firstly, when the polished porcelain surfaces were compared to the type IV gold control surface all the polished porcelain sur- faces were statistically significantly more abrasive tohumanenamel.Thisresultcorrespondswithear- lier studies.8, 9, 10, 11, 12 Secondly, there was no statis- tically significant difference between the polished zirconia surface and the polishedtype IV gold con- trol surface (p > 0.05) indicating that the polished zirconia surface was equivalent to a polished gold surface in its level of abrasiveness to human enamel. Inthisstudytheapplicationofveneeringporce- lain to the zirconia core material statistically sig- nificantly increased the abrasiveness of the zirco- niasurfacetohumanenamel.Thepolishedzirconia surface was statistically comparable to a polished goldsurfaceinitsdegreeofabrasivenesstohuman enamel indicating that it is beneficial to have pol- ished zirconia forming the occlusal contact sur- faces rather than applying a porcelain veneer. Zirconia has far greater strength than alu- minium oxide when in similar dimension. The pos- sibilitythereforeexiststousezirconiaasacorema- terial in the posterior region of the mouth and in highocclusalloadareaswheretheocclusioncanbe placed directly on the core material (cingulum of upper canines and occlusal surfaces of molars) if the restoration is opposing enamel. The porcelain veneer is then placed mainly for aesthetics. If the restorationisopposinganothercrownthentheap- plication of a porcelain veneer is optional. The use of CAD/CAM technology allows fabrica- tion of customized zirconia cores, abutments and bridgestorestorenaturalteethanddentalimplants with the appropriate reduction for veneering porcelain. This is known as the “dual scan” tech- niquewherethetechnicianuseseithercastingwax or a composite resin to build up the proposed restoration—crown or bridge—to full contour and in occlusion with the opposing arch. The wax or resin pattern is then “cut back” leaving all the cen- tric stops intact and supporting the opposing oc- clusion. This modified pattern is then scanned to produce the customised zirconia framework with all the occlusal loads being borne directly on the core material. The increased thickness of the zirco- nia in these areas improves both the physical and mechanicalpropertiesofthecore.Thisdoesnotim- ply that one can simply rely on the strength of restorative materials to withstand high occlusal loads and simply ignore the underlying causes, such as bruxism and parafunctional habits. Diag- nosis, treatment planning and prescribing the ap- propriaterestorativesurfacesarejustasimportant today as they have been in the past. _Conclusions Within the limitations of this study the follow- ing conclusions can be made: _The type IV gold surface produced the least amount of enamel wear. _The polished zirconia surface produced less enamel wear than the as-manufactured zirconia surface but the result was not statistically signif- icant when compared directly to the type IV gold control surface. _The polished and as-manufactured surfaces pro- duced statistically significantly greater enamel wear than the type IV gold control surface. _Alltheveneeringporcelainsproducedstatistically significantly more enamel wear than the type IV gold control surface. _Whenviewingallthepolishedsurfacedata(zirco- nia, porcelains and type IV gold) the polished zir- conia surface was not statistically significantly more abrasive than the type IV gold control sur- facep>0,05).Alltheporcelainsweresignificantly more abrasive than the type IV gold control sur- face. Editorial note: The literature list can be requested fromtheauthor. I 23implants4_2010 Dr Tussavir Tambra Wolverhampton,UK E-mail:dr.tambra@hotmail.co.uk _contact implants