Partial-retainer design considerations for zirconia restorations

Objective: Bond strength limitations of adhesive zirconia restorations have stood as a barrier against their widespread use. Selective infiltration etching is a new surface treatment that enhances bonding to zirconia-based materials. Beside bond strength, the performance of adhesive zirconia restorations could be affected by other variables. The aim of this study was to evaluate the influence of partial-retainer design on the failure load of selective infiltration-etched zirconia restorations. Method and Materials: Cantilever selective infiltration- etched zirconia restorations consisting of a pontic, a connector, and a single partial retainer were bonded to resin teeth (Filtek Z250, 3M ESPE). Four designs were tested: lingual, mesiolingual, buccal, and inlay retainers. A full-crown retainer was used as a control. The inner surface of each retainer received selective infiltration-etching surface treatment, and the specimens were bonded using a resin cement (Panavia F 2.0, Kuraray). Half of the cemented restorations were subjected to an artificial aging program (n = 10). The failure load and type of the bonded restorations were evaluated by applying axial load to the pontic. Two-way ANOVA and Tukey S post hoc tests were used to analyze the data (α = 0.05). Results: The partial-retainer design had a significant influence on the failure load of the tested restorations (F = 19.24, P .001), with the lingual design being the weakest. No significant difference was found between the full-crown, inlay, and buccal retainers. Artificial aging did not influence failure load of the tested restorations. SEM examination revealed that all specimens failed cohesively by fracture of the supporting tooth. The lingual design and the full-crown restorations were associated with complete coronal fracture of the supporting tooth, while minor coronal fractures were observed for the other three partial-retainer designs. Conclusions: The design of the partial retainer significantly influences the failure load and type of selective infiltration-etched zirconia restorations. The design of the partial retainer could affect the clinical performance of these restorations. Keywords: partial retainer, selective infiltration etching, zirconia restorations