To study and compare the stress distribution and displacement of the abutments and prostheses as well as the dislocation-resistance force of resin-bonded fixed bridges with four different retention form designs.

Four groups of resin-boned bridges teeth preparation were made according to the standard of each design on the right first mandibular molar missing arch models, namely traditional lingual flank wingplate retention group (Group A) , D-shaped retention group (Group B) , stress interrupt retention group (Group C) and occlusal rest retention group (Group D) . Prostheses were fabricated with cobalt-chromium alloy and bonded with resin cement on the models, six for each group. Three-dimensional finite element models were established for each group with the aids of Micro-CT scanning technology and Mimics software. The grid partition, boundary condition and load were introduced into Ansys software. 100 N load was applied on the pontic of the resin-bonded bridges vertically and 45-degree obliquely. The stress distribution and displacement of the abutments and prostheses were observed and calculated on the universal testing machine. Tensile test was carried out by pulling out the prosthesis from the abutments. The dislocation resistance values were calculated and analyzed statistically.

With vertical load, the minimum stress of prosthesis (37.45 MPa, P<0.05) and the minimum abutments displacement (3.72 μm, P<0.05) were found in group C; the minimum stress of abutments (14.54 MPa, P<0.05) and the minimum prosthesis displacement (3.80 μm, P<0.05) were found in group A. With oblique load, the minimum stress of prosthesis and abutments was observed in group C (74.30, 19.84 MPa, P<0.05) ; the minimum prosthesis and abutments displacement was observed in group D (1.69, 1.62 μm, P<0.05) . The comparison of von Mises stress was significant different (P<0.05) while the displacement was not (P>0.05) . The dislocation force value was 393.16, 427.62, 339.62, 449.84 N, respectively. There was significant difference among the four groups (F=25.840, P<0.001) , but no statistically significant difference was observed between Group B and D.

The resin-bonded bridge with stress-interruption design may effectively reduce the stress of prosthesis and abutment, but the dislocation resistance capability was lower than that of the other groups. The design of D-shaped retention and occlusion rest retention of resin-bonded bridge can distribute the vertical or oblique stress to prosthesis and abutment, and the dislocation resistance value was higher than those of the rest.