Evaluation of prosthetic screw loosening in all-on-four implant-supported restorations with two different connection...

STATEMENT OF PROBLEM: The OT BRIDGE connection system can be an alternative to multiunit abutments (MUA) for patients with all-on-four implant-supported restorations. However, the amount of prosthetic screw loosening of the OT BRIDGE in comparison with the MUA used in all-on-four implant restorations is unclear.

The purpose of this in vitro study was to compare the loss of removal torque in the absence of load and after dynamic cyclic loading between the 2 different connection systems: OT BRIDGE attachment and MUA used in all-on-four implant-supported restorations.

Four dummy implants (Neobiotech Co Ltd) were inserted into an edentulous mandibular model according to the all-on-four concept. Sixteen screw-retained restorations were digitally fabricated and assigned to 2 groups: the OT BRIDGE group received 8 restorations connected with OT BRIDGE (Rhein 83 srl); the MUA group received 8 restorations connected with MUA (Neobiotech Co Ltd). Restorations were tightened to the abutments according to the manufacturers' recommendations by using a digital torque gauge. The removal torque value (RTV) was measured with the same digital torque gauge. After retightening, dynamic cyclic loading was applied by using a pneumatic custom cyclic loading machine. RTV after loading was measured with the same torque gauge. From the RTVs measured, the ratios of removal torque loss (RTL) before and after loading and the difference between before and after loading were calculated. Data were analyzed by using the independent samples t test, paired samples t test, and mixed model analysis of variance (α=.05).

The OT BRIDGE showed significantly higher RTL before loading ratio (%) than the MUA in anterior abutments (P=.002) and posterior abutments (P=.003), as well as significantly higher RTL after loading ratio (%) in anterior abutments (P=.02). The MUA showed significantly higher RTL difference between before and after loading ratio (%) than the OT BRIDGE in both anterior (P=.001) and posterior abutments (P<.001). In both systems, posterior abutments showed significantly higher RTL after loading ratio (%) than anterior abutments (P<.001).

Posterior abutments showed more prosthetic screw loosening than anterior ones in both systems. The OT BRIDGE showed higher total prosthetic screw loosening than the MUA, although this was not significant in posterior abutments after loading. However, the OT BRIDGE was less affected by cyclic loading than the MUA.