Prognosis of multi-unit implant supported and combined tooth-implant supported fixed dental prostheses: a retrospective cohort study with a mean observation period of 4.27 years.

Objectives: The objective of this retrospective cohort study was to evaluate survival of multi-unit FDPs in comparison to 3-unit fixed dental prostheses (FDPs).

Materials and methods: 434 FDPs placed in 326 patients were selected from a prospective clinical long-term study. 213 FDPs were solely implant-supported, 154 FDPs tooth-implant supported, and 67 FDPs were cantilever FDPs. The most FDPs had 3-units (n = 315), 95 FDPs had 4-units, and 24 FDPs had more than 4 units. The most FDPs had a unit/abutment relation of ≤ 1.5 (n = 336), and 98 FDPs had a relation of > 1.5. Kaplan-Meier curves were used to estimate the survival probability of the FDPs for the variables type of FDP support, number of units and loading factor. Univariate log-rank tests were used to test for differences between groups within variables.

Results: The mean observation period was 4.27 years. In the observation period of up to 12.6 years 17 FDPs failed mainly through technical complications. The underlying causes were implant loss (n = 6), abutment tooth loss (n = 5), loosening of the abutment screw (n = 1), and extensive chipping (n = 5). Survival probability of all FDPs was ≥ 89,6% after 10 years. Log-rank tests revealed no significant differences between groups for all variables (support, number of units, and loading factor (p ≥ .339).

Conclusions: Because of their promising prognosis 4-unit FDPs placed on implants or a combination of tooth and implant can be recommended as an alternative to 3-unit FDPs. A higher number of implants in relation to FDP units does not improve the prognosis of FDPs.

Clinical relevance: Support, number of units and the loading factor do not influence the survival of FDPs. Therefore, 4-unit FDPs placed on implants or a combination of tooth and implant are a valuable treatment alternative to 3-unit FDPs.