Effect of veneering technique on the fracture resistance of zirconia fixed dental prostheses

To compare the fracture resistance of zirconia 3-unit posterior fixed dental prostheses (FDPs) frameworks veneered with different veneering materials and techniques before and after artificial ageing. Forty-eight zirconia 3-unit FDPs, representing a missing first molar, were adhesively cemented on human teeth. The zirconia frameworks were randomly distributed according to the veneering materials and techniques into three groups, each containing 16 samples: group LV (layering technique/Vintage ZR), group LZ (layering technique/ZIROX) and group PP (CAD/CAM and press-over techniques/PressXZr). Half of each group was artificially aged through dynamic loading and thermocycling to simulate 5 years of clinical service. Afterwards, all specimens were tested for fracture resistance using compressive load. An analysis of variance (anova) was used to assess the effect of veneering ceramic and artificial ageing on fracture resistance (P < 0.05). Except for one minor cohesive chipping in group LV1, all specimens survived artificial ageing. The mean fracture resistance values (in Newton) of different non-aged (+/- s.d.)/aged (+/- s.d.) groups were as follows: LV0 2034 (+/- 401)/LV1 1625 (+/- 291); LZ0 2373 (+/- 718)/LZ1 1769 (+/- 136); and PP0 1959 (+/- 453)/PP1 1897 (+/- 329). Artificial ageing significantly reduced the fracture resistance in groups veneered with the layering technique (P < 0.05), whereas no significant effect was found in specimens veneered with the CAD/CAM and press-over techniques. All tested systems have the potential to withstand occlusal forces applied in the posterior region. The combination of the CAD/CAM and press-over techniques for the veneering process improved the overall stability after artificial ageing, relative to the layering technique.