Surface topography and bond strength of CAD–CAM milled zirconia ceramic luted onto human dentin: effect of surface treatments before and after sintering

The purpose of this study was to investigate whether different surface treatments, executed before and after the sintering process, affect the surface characteristics (roughness and morphology) and shear bond strength of computer-aided design–computer-aided manufacturing (CAD–CAM) milled zirconia luted with self-adhesive resin cement onto human dentin. Sixty-four rectangular zirconia slabs (6?×?8.5?×?2.3?mm thickness) were prepared using the CAD–CAM system and randomly distributed into two groups according to the moment of treatment, before and after sintering, and four subgroups according to the surface treatment (n?=?8): C (untreated; control), AO (aluminum oxide air abrasion), GB (glass beads air abrasion), and HA (etching with hydrofluoric acid). The samples were evaluated using a confocal laser microscope to assess the surface roughness and morphology. For the shear bond strength test, the milled zirconia was cemented onto dentin slabs using self-adhesive resin cement and submitted to the test in a universal testing machine. Data were submitted to a two-way ANOVA and Tukey test (p?<?0.05). The surface roughness was always higher for the samples treated before sintering (highest roughness in the GB group). When treatment was employed after sintering, there was no difference between the subgroups. The shear bond strength analysis showed that the adhesion was greater when the treatment was employed after sintering, where groups AO, HA, and GB showed similar bond strength, higher than group C. Thus, it is concluded that regardless of the treatment performed, the bond strength is greater when zirconia is treated after sintering, while the surface roughness is greater before sintering.