Evaluation of four surface coating treatments for resin to zirconia bonding

Objectives: To compare the effects of four surface coating methods on resin to zirconia shear bond strength.

Material and methods: Eighty pre-sintered zirconia discs were prepared and randomly divided into five study groups according to the corresponding methods of surface treatments as follows: group C (control group, fully sintered without any surface treatment), group S (fully sintered and then sandblasted with silica coated alumina powder), group G (fully sintered and then coated with glazing porcelain followed by acid etching), group Si (pre-coated with silica slurry then fully sintered), and group Z (coated with zirconia particles and then fully sintered). The observation of surface morphology and elemental composition analysis were conducted by SEM and EDX. Self-adhesive resin cement stubs (diameter 3.6mm and height 3mm) were then bonded on the zirconia discs with a cylindrical shape. Both initial and artificial aged (including 30-day water storage, thermal cycling for 3000 and 6000 cycles) shear bond strengths were then evaluated.

Results: All the tested coating methods showed significantly higher shear bond strengths than the control group, in both dry and aged conditions. Group S produced the strongest initial zirconia/resin bonding (19.7MPa) and the control group had the lowest value (8.8MPa). However, after thermal cycling, group Z exhibited the highest mean value. All the samples in the control group failed in the thermal cycling. Both different coating methods (p<0.001) and various aging treatments (p<0.001) produced significant influence on resin-zirconia shear bond strength.

Conclusions: A reliable and durable resin zirconia bonding is vital for the longevity of dental restorations. Silica coating might be a reliable way in enhancing adhesion between resin and zirconia.