Translucent zirconia crown retention - effect of preparation, bonding and aging protocol.

OBJECTIVE: To obtain the retention strength of translucent zirconia crowns on human tooth abutments and evaluate effects of specimen preparation, bonding protocol, and comparing aging in two different chewing simulators. MATERIALS AND METHODS: Translucent zirconia crowns were bonded to prepared human teeth using two resin composite luting materials: Panavia V5 (PV5) and RelyX Universal (with primer [RUV] and without primer [RUO]). Specimens were fabricated at two sites (B and M) and the retention strength was determined before and after aging in two different chewing simulators (N = 216, n = 12) using 1.2 million cycles, 50 N, 1.5 Hz and 6000 thermal cycles. Data were analyzed with 3-way ANOVA and Bonferroni post-hoc test (alpha = 0.05). RESULTS: Higher retention strength values were observed for specimens produced at site M (7.1 +/- 2.6 MPa) compared to B (5.5 +/- 2.7 MPa). Overall, highest values were obtained with PV5 (7.0 +/- 2.1 MPa) and RUV (7.0 +/- 2.7 MPa), while retention strength with RUO was lower (4.9 +/- 2.9 MPa). The highest values overall were determined before aging (8.1 +/- 1.8 MPa), followed by aging in the industrially available simulator using weight-loading (6.1 +/- 2.4 MPa) and the custom-built hydraulic simulator (4.8 +/- 2.9 MPa) enhancing aging effects. CONCLUSIONS: The specimen production affected retention strength values. Bonding protocols PV5 and RUV revealed similar results, while lower values were obtained using the self-adhesive approach RUO. Aging in the hydraulic simulator was more pronounced, despite identical settings. CLINICAL RELEVANCE: Differences in retention strength may occur between operators, despite strict bonding protocol adherence. An adhesive bonding protocol using the respective primer is recommended over self-adhesive bonding of translucent zirconia crowns on human teeth.