Fracture Resistance of Crowns Cemented on Titanium and Zirconia Implant Abutments: A Comparison of Monolithic Versus Manually Veneered All-Ceramic Systems

Purpose: To evaluate the fracture resistance of all-ceramic crowns cemented on titanium and zirconia implant abutments. Material and Methods: Customized implant abutments for maxillary right central incisors made of titanium (Ti) and zirconia (Zr) (n = 60, n = 30 per group) were fabricated for an internal connection implant system. All-ceramic crowns were fabricated for their corresponding implant abutments using the following systems (n = 10 per group): (1) monolithic computer-aided design/computer-assisted manufacture (CAD/ CAM) lithium disilicate (MLD); (2) pressed lithium disilicate (PLD); (3) yttrium stabilized tetragonal zirconia polycrystal (YTZP). The frameworks of both PLD and YTZP systems were manually veneered with a fluorapatitebased ceramic. The crowns were adhesively cemented to their implant abutments and loaded to fracture in a universal testing machine (0.5 mm/minute). Data were analyzed using two-way analysis of variance (ANOVA) and Tukey's test (α = 0.05). Results: Both the abutment material (P = .0001) and the ceramic crown system (P = .028) significantly affected the results. Interaction terms were not significant (P = .598). Ti-MLD (558.5 ± 35 N) showed the highest mean fracture resistance among all abutment− crown combinations (340.3 ± 62 − 495.9 ± 53 N) (P .05). Both MLD and veneered ceramic systems in combination with Ti abutments (558.5 ± 35 − 495.9 ± 53 N) presented significantly higher values than with Zr abutments (392.9 ± 55 − 340.3 ± 62 N) (P .05). MLD crown system showed significantly higher mean fracture resistance compared to manually veneered ones on both Ti and Zr abutments (P .05). While Ti-MLD and Ti-PLD abutment-crown combinations failed only in the crowns without abutment fractures, Zr-YTZP combination failed exclusively in the abutment without crown fracture. Zr-MLD and Zr-PLD failed predominantly in both the abutment and the crown. Ti-YTZP showed only implant neck distortion. Conclusions: The highest fracture resistance was obtained with titanium abutments restored with MLD crowns, but the failure type was more favorable with Ti-YTZP combination. Keywords: CAD/CAM, lithium disilicate, monolithic crowns, pressed ceramics, titanium, YTZP