Effect of different grit sizes of diamond rotary instruments for tooth preparation on the retention and adaptation of complete coverage restorations.

STATEMENT OF PROBLEM Internal adaptation and retention are important factors for the longevity of crown restorations. However, how tooth surface roughness associated with diamond rotary cutting instruments affects the retention and internal adaptation of complete coverage restorations remains unknown. PURPOSE This study evaluated the relationship between the surface roughness of prepared teeth and the internal adaptation and retention of complete coverage restorations after preparation with diamond rotary cutting instruments of different grit sizes. MATERIAL AND METHODS Ninety-two extracted human teeth were divided into 4 groups and assigned to different final grit sizes of the diamond rotary instruments used for preparation following a grit decreasing sequence from coarse (125 to 150 μm), to medium (106 to 125 μm), to fine (53 to 63 μm), to extra fine (20 to 30 μm). After preparation, the surface roughness of 32 teeth was measured with a profilometer. The other 60 teeth were prepared as abutments, with 28 of these teeth used to measure microleakage and cement thickness. The remaining 32 teeth were used to test the retention between teeth and nickel-chromium alloy crowns with a universal testing machine. The data were analyzed with a 1-way ANOVA and Fisher's LSD post hoc multiple comparison tests to determine significant intergroup differences in surface roughness and retention force (α=.05). Microleakage scores and cement thickness were analyzed with the Kruskal-Wallis rank sum test; these were also conducted as multiple comparison tests (α=.05). RESULTS The teeth prepared with the coarsest diamond rotary cutting instruments showed the highest mean surface roughness (SD) (4.8 (0.4) μm), and those prepared with the finest diamond rotary instruments had the lowest mean cement thickness (0.5 (1.2) μm; P<.001 when compared to teeth in the coarse group). The finer surfaces showed less microleakage (P =.03). However, no significant differences in retention were found (P=.19) across the groups. CONCLUSIONS Teeth prepared with the finer grit rotary instruments have smoother tooth surfaces and crown restorations with better internal adaptation. The grit size of the diamond rotary cutting instruments does not affect the removal force between the complete coverage crown and the prepared tooth.