Effect of different preparation finishing procedures on the marginal and internal fit of CAD-CAM-produced restorations: A microcomputed tomography evaluation

Statement of problem. Accurate fit is an important factor for the longevity of computer-aided design and computer-aided manufacturing (CAD-CAM) ceramic restorations. Few studies have compared how restoration finishing procedures affect the marginal and internal fit of these restorations by using microcomputed tomography (mu CT).Purpose. The purpose of this in vitro study was to evaluate the preparations with different surface finishing procedures for the fit of CAD-CAM restorations by using mu CT.Material and methods. A total of 28 anatomic contour monolithic feldspathic ceramic crowns were produced for 4 typodont teeth prepared according to the different surface finishing procedures (n=7). The generated experimental groups were finishing with extra-coarse (181 mu m) diamond rotary instruments (EC), finishing with fine (40 mu m) diamond rotary instruments after extra-coarse diamond rotary instruments (F), finishing with very fine (20 mu m) diamond rotary instruments after extra-coarse and fine diamond rotary instruments (VF), and finishing with extra-coarse, fine, and very fine diamond rotary instruments followed by polishing rubber points (P). mu CT scans were obtained to measure the gaps between the typodont teeth and the crowns. Reference points such as the margin, chamfer (the deepest point), cusp tips, and central fossa were determined, and 196 measurements were made. Data were analyzed by using 2-way analyses of variance and the Tukey HSD test (a=.05).Results. The highest gap values in all sections were observed in the finishing with extra-coarse (181 mu m) diamond rotary instruments group. The lowest gap value in the marginal point was observed in the P group (P<.05). In total, the gap values of the reference points were in the order of margin, chamfer, cusp, and central fossa.Conclusions. mu CT evaluation showed that tooth preparation finishing procedure with finer grit rotary instruments yielded better marginal fit for monolithic feldspathic CAD-CAM restorations. The internal gap values of all groups were also in the range of clinically acceptable values, important for mechanical properties.