Bond Strength of Two- and Three-unit Resin Bonded Bridges

Objectives: Cantilever two-unit resin bonded fixed partial dentures (RBFPDs) are said to be as if not more successful than three-unit fixed-fixed counterparts, this is thought to be due to adverse interabutment forces that occur on a fixed-fixed framework when functionally loaded. The aim of this study was to investigate this hypothesis by way of fatigue testing two designs of RBFPD framework with a single pontic.

Methods: using a stone model, a two-unit cantilever and a three-unit fixed-fixed RBFPD were cast in nickel chrome dental alloy (Optimum, Matech, USA) to fit machined stainless steel tooth analogues that had a simulated periodontal ligament by way of orthodontic elastic rings. After cementation with a resin cement (Panavia F 2.0, Kuraray, Japan) they were subjected to controlled force with an oscillating fatigue load of between 20-80N for 12,000 cycles. Two loading points were used, one on the pontic and the other on the tooth analogue afterwhich the bond strength of the framework to the tooth analogue was tested to failure in a universal testing machine.

Results: Control (no loading) 409N(±48); cantilevered 421N(±34); Fixed-fixed loaded 332N(±129), not loaded 333N(± 97). There was no difference in the debonding force between cantilevered and control groups (p<0.05). Both of the fixed-fixed tooth analogues had a lower bond strength than the cantilvered analogue (p<0.05) and the non loaded analogue had a lower bond strength that the control (p<0.05)

Conclusion: Cyclic loading on a three-unit fixed-fixed RBFPD creates interabutment stresses that challenge the cement lute of the framework retainer wings. Two-unit cantilevered RBFPDs are more retentive than three-unit prostheses as they are subjected to less complex stresses.