Assessment of fit accuracy and retentive strength of additively manufactured zirconia crowns luted to Ti-base abutments with different resin cements: An in vitro study.

Purpose: This study investigated the influence of cement gap size on the marginal and internal fit, and cement gap size and type on retention of additively manufactured zirconia (AM-Z) crowns on titanium bases (Ti-base).

Materials and methods: A total of 135 zirconia crowns were designed with three different cement gap sizes: 20 µm, 30 µm, and 40 µm (n = 45 per group). The crowns were additively manufactured using a lithography-based ceramic 3D printer (Cerafab, Lithoz GmbH, Austria) and a zirconia slurry (LithaCon 3Y 210, Lithoz GmbH, Austria). All crowns, Ti-base (RC Variobase, Straumann, Switzerland), and crown-Ti-base assemblies were scanned, and the marginal and internal gaps were measured using specialized software, following the triple scan protocol. Specimens were further divided into three subgroups based on the resin luting agent used for bonding the crowns to the Ti-bases (n = 15 per subgroup): Group PV21 used Panavia 21 (P21) (Kuraray Noritake Dental Inc., Japan), Group PV5 used Panavia V5 (PV5) (Kuraray Noritake Dental Inc., Japan), and Group MHA used Multilink Hybrid Abutment (Ivoclar Vivadent, Liechtenstein). After cementation, specimens were subjected to thermocycling between 5°C and 55°C. Pull-out forces between the additively manufactured zirconia (AM-Z) crowns and Ti-bases were measured using a universal testing machine. Variance analysis was conducted on root mean square (RMS) values for internal and marginal gaps, as well as pull-out forces (α = 0.05).

Results: The one-way analysis of variance test revealed a statistically significant difference in marginal discrepancy values (p < 0.001). A post-hoc Tukey analysis indicated that the marginal (25.9 µm) and internal discrepancy (24.6 µm) values associated with the 30 µm cement gap size were higher than those obtained with other cement gap sizes (p < 0.01). No significant differences were found between the 20 µm and 40 µm cement gap sizes (p = 0.113). The 30 µm cement gap group demonstrated lower discrepancies. Both cement gap size and cement brand significantly influenced the marginal and internal fit, as well as the pull-out resistance of the crowns. The impact of the cement brand, the cement gap size, and their interaction significantly affected the retention between the Ti-bases and crowns (p < 0.01). The use of P21 with a 30 µm gap resulted in significantly higher pull-out values than P21 with a 20 µm gap (p = 0.008) and P21 with a 40 µm gap (p = 0.004). Retention with a 40 µm cement gap was not significantly different from that with a 20 µm cement gap, regardless of the cement brand (p = 0.089). PV5 presented the lowest pull-out values across all cement gap sizes (p = 0.02).

Conclusion: Cement gap size significantly affected the fit, and cement gap size and type significantly impacted the retention between AM-Z crowns and Ti-bases. Cement space of 30 µm and PV21 resin luting agent led to improved adaptation and high bonding strength.