Objectives: The aim of the study was to assess the influence of pretreating enamel by different rotary instruments on shear-bond strength of composite to enamel after the acid etch technique.
Methods: Ninety human enamel specimens with transversely and longitudinally sectioned prisms were ground flat, and half of the enamel area of each specimen was prepared with one of the eight different rotary instruments: a 120 microns diamond bur, three finishing diamonds (30, 15 and 8 microns), two tungsten carbide finishing instruments (8- and 30-fluted) and two stones (Dura green and Dura white). The other half of the enamel area was left untreated. Enamel roughness was measured by laser-stylus profilometry. Two cylinders filled with the hybrid composite Pertac were adhesively fixed on each enamel surface, one on the prepared side and the other on the untreated side. After seven days of water storage, shear-bond strength was measured with a Universal testing machine.
Results: Rz values of the treated enamel surfaces were between 4.14 and 17.75 microns. The shear-bond strength data varied between 16.8 and 29.4 MPa and were similar for transversely and longitudinally orientated prisms. The different roughness data had no significant influence on shear-bond strength of composite to enamel. Additional SEM investigation showed that the surface geometry caused by the rotary instruments largely persisted after acid etching.
Significance: With regard to shear-bond strength, there was no advantage in using a special bur for finishing enamel surfaces prior to the acid etch technique. Burs causing extreme roughness should not be used for this purpose.