Framework Fracture of Zirconia Supported Full Arch Implant Rehabilitation: A Retrospective Evaluation of Cantilever Length and Distal Cross‐Sectional Connection Area in 140 Patients Over an Up‐To‐7 Year Follow‐Up Period
Federico Tirone, Stefano Salzano, Erik Rolando, Laura Pozzatti, Donata Rodi
Abstract
PURPOSE: To evaluate the relationship between different dimensional parameters in implant-supported monolithic zirconia fixed complete dental prostheses (IFCDPs) and the incidence of framework fracture in a large sample of cases in vivo. MATERIALS AND METHODS: This retrospective observational study evaluated all patients rehabilitated with screw-retained zirconia IFCDPs between January 2013 and April 2019 at a private practice. The minimum follow-up period was 1 year after occlusal loading. Fractures were classified as: type I-fractures that happened between but not involving the two most posterior screw-access openings (SAOs) and type II-fractures of the distal cantilever. Cantilever length, distal connector cross-sectional area, and screw access opening length were measured using data obtained from digital scans. Logistic regression was performed to evaluate the relationship between types I and II fractures and the independent variables (dimensional parameters). Using the receiver operating characteristic curves, two parameters were identified to be useful for establishing a cut-off and predicting type II fractures. RESULTS: A total of 180 prostheses delivered to 140 patients were analyzed. Five implants failed in three patients: three before delivery of the definitive prostheses and two after. Ten prostheses failed (5.6% prosthetic failure rate): 2 because of implant failures, and 8 because of framework fractures. Five fractures were classified as type I and three as type II. Significant associations were found between cantilever length and type I fractures (Wald = 5.772, df = 1, p = 0.016), distal connector cross-sectional area and type II fractures (Wald = 3.806, df = 1, p = 0.051), and cantilever length and the total number of fractures (Wald = 6.117, df = 1, p = 0.013). CONCLUSION: Zirconia IFCDPs may be reliable medium-term solutions if some dimensional parameters are followed. The ratios between the cantilever length and cross-sectional connector area should be <0.51, while the ratio between the cantilever length and screw access opening length should be <1.48.