Increased tooth mobility because of loss of alveolar bone support: a hazard for zirconia two-unit cantilever resin-bonded FDPs in vitro?

This study evaluates in vitro the impact of increased abutment tooth mobility on survival of zirconia-based two-unit cantilever resin-bonded fixed dental prosthesis (RB-FDP) by long-term dynamic loading in a chewing simulator. Human maxillary central incisors (n = 32) were endodontically treated and alveolar bone loss was simulated: 0% (group B), 25% (group C), and 50% (group D). RB-FDPs were adhesively luted. Zirconia full crown two-unit FDPs served as control (group A). Specimens were exposed to simulated clinical function by two subsequent sequences of thermal-cycling (2 × 3.000) parallel to mechanical loading (1.2 × 10(6) load cycles) (TCML; first sequence: load 1-25 N; second sequence: load 1-50 N). Tooth mobility increased significantly as the simulated bone level decreased (p < 0.001). Log-rank tests revealed no significant differences between experimental groups (p = 0.479). The results support the assumption that zirconia-based two-unit cantilever RB-FDPs may be an appropriate treatment option, even if abutment tooth mobility increase because of alveolar bone loss. However, debonding of zirconia-based two-unit RB-FDPs will be a likely event, whereas fatal failures of the abutment teeth may not occur.