Engaging Abutment Position Effect in Implant Retained Fixed Cantilevered Prostheses

Objective: To investigate the effects of internally connected engaging component position in screw-retained fixed cantilevered prostheses.

Materials and Methods: Twenty-one identical 3-unit FPDs were cast in high palladium alloy (Advantage, Jensen Industries) in three groups. In group A, engaging components were incorporated into distal units; proximal units received non-engaging components. In group B, these positions were reversed. Control specimens were fabricated using non-engaging components. Samples were attached to internally connected 3.5x13mm implants (Replace Select, Nobel Biocare), torqued to 32Ncm, embedded into epoxy resin (Epoxycure, Beuhler). Samples were tested with a 2 Hz sine wave and 0.1 min/max load ratio. Load amplitude started at 1.8 N and increased by 1.8 N every 60 cycles until fracture. Log rank statistic was utilized to evaluate level of statistical significance between survival curves using one-way ANOVA.

Results: In the control group, the mean number of cycles to fracture was 31205 (SD=2639). Mean axial force at fracture was 932N (SD=78N). In group A, these numbers were 38160 (SD=4292), 1138N (SD=128N), and in group B, 31810 (SD=3408), 949N (SD=101N). Statistical significance levels were: Control vs. group “A” p=0.0117, and groups “A” vs. “B” p=0.0156 (statistically significant). Control vs. group B p=0.357 (not statistically significant). Log rank statistic for the survival curves is greater that would be expected by chance; there was a statistically significant difference between survival curves (P = 0.012).

Conclusions: Position of engaging component had a significant effect on the results. The location and mode of failure was noteworthy (always in the distal screw). Rotational orientation of tri-lobe may play a role with regard to fracture pattern. Within the limitations of this investigation, it may be prudent to engage the implant furthest from the mesial cantilever when designing a 3-unit screw retained cantilever FPD. This study was partially supported by a GNYAP Student Grant.