Abstract
This study evaluated the influence of retorque on loosening torque (Lt) of prosthetic screws in implant-supported dentures with different fit levels. Ten mandibular implant-supported dentures were fabricated and then 20 cast models were then prepared using prosthetic structures to create 2 fit levels: passive fit (Pf) and misfit (Mf). Two tightening techniques were also evaluated: initial torque only (T1); and initial torque and retorque after 10 min (T2). Gold or titanium screws were used, resulting in 4 groups to each one: Pf/T1, Pf/T2, Mf/T1, Mf/T2. The Lt was measured 24 h after the tightening torque using digital torque meter. Data were analyzed statistically by two-way ANOVA and Tukey's test (alpha=0.05), separately for each screw material. For titanium screws, no significant difference (p>0.05) was found between Pf/T1 and Pf/T2, or between Pf/T2 and Mf/T2. However, statistically significant difference (p<0.05) was found between Pf/T1 and Mf/T1, and between Mf/T1 and Mf/T2. Mf reduced the Lt using T1, while and T2 increased the Lt for Mf. Retorque and fit were shown to have no significant influence on the Lt of the gold screws. Retorque application made insignificant the misfit effect on the Lt of the titanium screws, suggesting that this procedure should be performed routinely during the screw tightening in multi-unit dentures.
Highlights
Lack of passivity of implant-supported dentures may cause biologic complications of the surrounding tissues, or mechanical failures of the dentures and implant systems
The screws used in dentures with misfit presented lower loosening torque than those used in dentures with passive fit, when retorque was not applied (p=0.005)
This misfit had no significant influence on the loosening torque, when the retorque was applied on the titanium screws (p=0.857)
Summary
Lack of passivity of implant-supported dentures may cause biologic complications of the surrounding tissues, or mechanical failures of the dentures and implant systems. Mechanical complications may include loosening of the prosthetic and abutment screws or fracture of various components in the system [1]. There is very limited information about the effects of retightening some time after settling of the prosthetic screws on the joint stability in multiunit dentures. The aim of this in vitro study was to evaluate the effect of retightening the screws 10 min after the initial tightening torque (retorque) on the loosening torque of prosthetic screws at 2 levels of fit (passive fit and vertical misfit) in mandibular implant-supported dentures. A master cast was fabricated using a splinted impression technique to allow the waxing of ten pros-
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