Influence of dental rotary instruments on the roughness and wettability of human dentin surfaces.

STATEMENT OF PROBLEM

Although it is known that different dental rotary instrument types produce distinct surface roughness of the axial walls which may contribute to the clinical performance of a cast restoration, the ideal roughness that produces optimum wetting at the adhesive interface is unclear.

PURPOSE

The purpose of this study was to characterize the surface roughness and its influence on wettability of teeth prepared for complete veneer crowns with different dental rotary instruments.

MATERIAL AND METHODS

Sixty standardized tooth preparations for complete crowns were completed using a modified milling machine on extracted human teeth with diamond, tungsten carbide finishing, and cross-cut carbide rotary instruments of similar shape (n=20). Morphological changes obtained were investigated with a surface texture analyzer. Two additional specimens from each group were treated and prepared for scanning electron microscopy. The contact angle of a drop of distilled water on each of the prepared surfaces was used as the measure of wettability with a goniometer microscope. The data were analyzed with 1-way ANOVA and Tukey's Honestly Significant Difference (HSD) test (alpha=.05).

RESULTS

Surface preparation resulted in significant differences for surface topography and wettability (P<.001). The carbide burs had significantly higher mean roughness readings (SD) for all parameters: Ra (8.6 (1.9) microm), Rq (10.9 (2.2) microm), and Ry (41.1 (2.1) microm), except for the mean Rz (12.1 (3.1) microm) value, which was recorded for diamonds. The other roughness parameters for the diamond rotary instruments were intermediate. Teeth completed with carbide finishing burs produced a smoother surface Ra (1.2 (0.5) microm), Rq (1.6 (0.6) microm), Ry (6.4 (2.6) microm), and Rz (1.9 (0.6) microm). The highest mean contact angle (SD), 81.5 (9.1) degrees, was associated with diamond rotary instruments, and the lowest (75.3 (5.9) degrees) was recorded for finishing burs. The contact angle for teeth prepared with tungsten carbide burs was intermediate: 76.1 (5.9) degrees.

CONCLUSIONS

The selection of dental rotary instruments for tooth preparation significantly affects surface roughness and wettability of dentin, which may influence the retention of cast restorations.