[Effect of rotary instruments on composites for coronal restoration. A proposed evaluation protocol for the effect of rotary instruments and surface conditions].

Numerous core composites are used to reconstruct abutments for fixed partial dentures. The preparation is carried out with various type of burs. The purpose of this study is to facilitate the choice among them. Six chemical composites, one glass ionomer cement and two light cured composites have been selected. Calibrated samples have been made, divided into four series and prepared with six different burs used for fixed partial dentures, three of them as finishing burs. In the first part of the investigation, the samples were examined with a S.E.M., in order to visualize the surface texture. According to the materials used, variations may exist. In the second part of the investigation, a tridimensional study was performed using a mechanical scanner microscope which permitted the quantification of some roughness characteristics, thus, an objective comparison of the surfaces became possible. Due to the complementary nature of the two investigation techniques, a protocol is presented for the study of burs instrumentation and prepared tooth surface.