[Influence of retention-form design on the retention of resin-bonded fixed partial dentures]

To evaluate the influence of retention-form design of resin bonded fixed partial dentures (RBFPDs).

Forty-five metal replicas of posterior metal RBFPDs were divided into 3 groups(n=15):C shape(control group), C shape + axial groove, C shape + pin hole. All the replicas were luted with Panavia F cement and subgroup of 5 specimens were subject to 70 N compressive load cycling for 0 cycles, 240,000 cycles , and 1,200,000 cycles respectively .Half of the cycles was on the central fossa of the pontics and half on the buccal inclined surface of the lingual cusp. Forces for dislodgment of the specimens were applied along the long axis of the abutment at a cross head speed of 1.0 mm /min. The separation forces were recorded as maximum retention force at the time of dislodgement.

Separation forces of the C shape group (566.82+/-71.59 N)0.05). After 1,200,000 cycles, the retention force of the RBFPDs decreased significantly (P<0.001).

To compare with axial groove, the design of pinhole retention form was conduced to the improvement of the retention force and durability of RBFPDs.