[Efficiency and margin quality in the computer-assisted molding and grinding of ceramic inlays]

The life of diamond-coated discs during CAD/CAM machining of ceramic inlays was evaluated using the standard hydro-drive (H) and an electric drive (E) as a part of the Cerec 3rd generation unit. E-drive discs (40 mm diameter, 0.5 mm thickness) with four experimental diamond coatings, i.e. different grain sizes, E126 (106-125 microns), E64 (53-63 microns), E46-3 (38-45 microns; triple coating), E46-1 (38-45 microns; single coating) were used. The standard H-drive disc (30 mm diameter, 0.3 mm thickness) and H126 (106-125 microns) coating were used as a control. The same standard mesio-occluso-distal molar inlay was machined from blocks (size 1-8) of Dicor MGC light glass-ceramic and of Vita MkII feldspathic fine porcelain as many times as possible with one disc in each group and the number of machined inlays per disc was counted. Additionally the edge roughness (Ra) of the machined inlays was measured using a Talysurf 50 instrument. The numbers of inlays machined with H126 were 21 porcelain/12 glass-ceramic inlays. The numbers of inlays machined from porcelain/glass-ceramic with the E-drive test discs were E126: 180/68; E64: 93/29; E46-3: 80/21 and E46-1 (current limited to 2.5 ampere): 44/19 inlays. The edge roughness of porcelain/glass-ceramic inlays machined with the E-drive discs was significantly lower than the roughness of inlays machined using the H-drive. E126: 16% (p < 0.05)/43% (p < 0.001); E64: 49%/66%; E46-1: 62%/73%; E46-3: 83%/87% (all differences p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)