Fluorination of zirconia surfaces impairs bonding to resin cement

The aim of this study was to evaluate the fluorination of a zirconia surface as an alternative treatment for bonding to resin cement; the null hypothesis was that fluorination would not improve adhesion values. Four different surface treatments were performed on the surface of yttria-stabilized tetragonal zirconia polycrystal discs (N = 80): Ctrl (control), no treatment; SB, sandblasting with 50-μm alumina particles; SBS, sandblasting with 30-μm silica-modified alumina particles and application of silane; and SF, fluorination with sulfur hexafluoride-containing plasma. The surface roughness (Ra) of each group was measured after surface treatment. Dual-cure resin cement was inserted into cylindrical matrices, and 2 cylinders (0.7 × 3.0 mm) were cemented to each ceramic disc surface. Half of the specimens were thermocycled, and microshear bond strength tests were performed. The SBS group presented the highest median values of surface roughness, while the Ctrl group presented the lowest values. Without thermocycling, the median bond strength of the SF group was statistically similar to those of the sandblasted groups (SB and SBS). After thermocycling, all specimens from the Ctrl and SF groups presented as failures, and their bond strength was considered null. The SB and SBS groups presented decreased bond strengths. Failures were classified as predominantly mixed at the adhesive interface. The fluorination of the zirconia ceramic surface with sulfur hexafluoride as a source gas did not promote stable bond strengths to resin cement. After aging, adhesion was possible only after sandblasting of the ceramic surface.