Five-year outcomes of zirconia and fiber-reinforced composite cantilever inlay-retained fixed dental prostheses with...

To evaluate and compare the clinical performance of three retainer designs of cantilever inlay-retained fixed dental prostheses (IR-FDPs) fabricated from zirconia and fiber-reinforced composite over 60 months.

This prospective randomized controlled clinical trial included 47 patients with 60 IR-FDPs requiring replacement of mandibular second premolars. Patients were randomly allocated into three groups according to retainer design: inlay ring (IR), lingual coverage (LC), and occlusal coverage (OC) (n = h20 each). Each group was further subdivided based on material into zirconia (Z) and fiber-reinforced composite (FRC) (n = 10). Randomization was performed using a computer-generated sequence with allocation concealment via sealed opaque envelopes. All restorations were adhesively bonded following standardized preparation protocols. Clinical and radiographic evaluations were conducted over 60 months using modified FDI criteria. Monte Carlo tests were used to compare qualitative data between groups as appropriate. Cochran's Q test was used to compare >2 follow-up readings for qualitative data.

No statistically significant differences were observed among the groups (P > 0.05) in clinical performance, with satisfactory esthetic, functional, and biological outcomes according to modified FDI criteria. Five failures requiring replacement were recorded, including two zirconia connector fractures, two debonding-related failures, and one irreversible framework deformation. In addition, six complications were observed, including debonding, plastic deformation, veneering composite delamination, minor veneering chipping, and two cases of secondary caries, all of which were successfully managed without replacement. Zirconia failures tended to occur as connector fractures or loss of retention, whereas FRC restorations showed predominantly repairable complications with occasional progressive deformation. The overall survival rate was 91.7%, while the success rate was 81.7%.

Within the limitations of this randomized controlled clinical trial, zirconia and fiber-reinforced composite cantilever IR-FDPs demonstrated favorable 5-year clinical performance with high survival rates. Apparent differences in failure behavior between materials should be considered exploratory and interpreted cautiously because of the limited number of observed failures.

Cantilever IR-FDPs with different retainer configurations, including the inlay ring design, provide reliable, conservative, and long-term treatment options for posterior tooth replacement.