Correlations between connector geometry and strength of zirconia-based fixed partial dentures

The purposes of this study are: to assess the correlation between connectors’ geometry and the strength of 3-unit zirconia dental infrastructures, to highlight the zirconia surface modifications generated by its processing (distilled water immersion, grinding) and to evaluate the possible connections between zirconia processing and its fracture resistance. Eight sintered zirconia samples were obtained by using CAD/CAM technology, representing infrastructures for lateral mandible 3-unit fixed partial dentures, replacing the first right lower molar, with connectors having different cross-sectional shapes and areas (circular or elliptical shapes; 5 mm2 or 9 mm2 area). The infrastructures were divided into two groups, one containing sintered samples and the second one containing sintered but processed samples (distilled water immersed, grinded). Flexural tests were performed on zirconia infrastructures by employing a servo-hydraulic testing machine; the morphology of the fracture sites was analyzed by scanning electron microscopy. Two cuboid zirconia sintered samples (10 × 10 × 2mm) were obtained in the same manner as the infrastructure groups, for analyzing surface wettability (contact angle measurements), surface morphology and roughness (using atomic force microscopy). The results showed that the zirconia infrastructures with elliptical 9 mm2 cross-sectional area connector were the strongest; processing the samples resulted in an increased roughness, a higher contact angle and lower strength. •Zirconia restoration connector shape and size are important for strength.•Restorations with elliptical and circular connectors were custom tested in flexure.•An elliptical cross section increases restoration strength.•Water immersion and grinding decrease restoration strength.•Personalized zirconia copings increase infrastructure strength.