Surface roughness of two milled CAD/CAM ceramics following polishing

Objectives: The objective of this study was to assess the effects of two polishing techniques on the surface roughness of a commercial and experimental dental ceramic for use in a chairside CAD/CAM system. Methods: An optical impression of a prepared tooth was recorded and 15 Vita Mk II onlays (2M2 C/ I10) and 15 Test onlays (fluormica) were milled using a Cerec 3/3D CAD/CAM at the University of Michigan Dental School. The unused ceramic material that remained on the sample holders after milling was retained and used to assess polishability of the two materials. Five random samples of each were left in the as-machined state, five were polished with Sof-Lex aluminium oxide discs and five polished with diamond impregnated polishing wheels. Four surface roughness parameters (Ra, Rq, Rv and Rp) were measured for each material group using confocal microscopy. Results: For all parameters measured, the as-machined surfaces of both materials were statistically similar. Furthermore, polishing with Sof-Lex discs was effective at reducing surface roughness of both materials. However, whilst the polishing wheels were effective in reducing surface roughness for the commercial material, there was no statistically significant difference in the surface roughness of the experimental material in the as-machined or wheel polished states. Conclusions: Although Sof-Lex discs were effective in reducing surface roughness of the two materials examined in this study, wheel polishing should not be used to reduce surface roughness of the experimental fluormica glass-ceramic material. This would need to be taken into consideration in any future clinical studies of this material.