Stress Analysis On Different Retainer Designs Of Two-unit Cantilever Resin-bonded Fixed Partial Dentures

PURPOSE:To evaluate the influence of different retainer designs on resistance value and failure modes of two-unit cantilever resin-bonded fixed partial dentures.METHODS:Fifty-four maxillary first premolars were randomly divided into3groups: control C group (traditional retainer design), D group (traditional retainer design+occlusal bar) and L group (traditional retainer design+lingual cusp coverage). After abutments preparation54nickel-chromium alloy two-unit cantilever resin-bonded fixed partial dentures were made and cemented with PANAVIA F.24hours later the subgroups of9specimens were loaded to fracture under vertical and45°lingual direction respectively in a universal testing machine. Resistance value and failure modes (prosthesis debonding, prosthesis fracture, abutment fracture) were determined for three designs.RESULTS:①When loaded under vertical direction, both D group(689.11±197.56N) and L group (704.19±194.37N) showed a significantly higher (F=28.059,q=6.390、6.580, P <0.01) resistance value than C group (183.84±87.13N). The difference between D group and L group was not significant (P>0.05). The distribution of failure modes was significantly different between three groups (P<0.001).②When loaded under45°lingual direction, both D group (263.76±69.78N) and L group (347.19±153.29N) showed a significantly higher (F=17.066, q=3.907、5.715,P<0.01) resistance value than C group (82.83±24.17N). The difference between D group and L group was not significant (P>0.05). The distribution of failure modes was significantly different between three groups (P <0.001).③The difference between vertical loaded group and45°lingual loaded group in all three groups was significant (t=3.351-6.090,P<0.01). The distribution of failure modes between vertical group and45°lingual loaded group in all three groups was not significantly different (P>0.05).CONCLUSION:Both retainer designs and loading directions affected the resistance value of two-unit cantilever resin-bonded fixed partial dentures. The failure modes of two-unit cantilever resin-bonded fixed partial dentures were affected by retainer designs, but not affected by loading directions. D and L retainer designs were more effective to improve resistance value of two-unit cantilever resin-bonded fixed partial dentures than conventional C retainer design. Force in oblique directions was more harmful than axial force to two-unit cantilever resin-bonded fixed partial dentures.