Purpose: This study investigated the influence of placing implant-supported crowns on the torque loss of the abutment screw before and after loading.
Material and methods: Twenty implant-abutment assemblies were randomly assigned to two groups. The first group was consisted of abutments with abutment-level finishing line (abutment-level), and in the second group the crown margin was placed on the implant shoulder (implant-level). Initial torque loss was recorded for all specimens. After 500000 cyclic load of 75 N and frequency of 2 Hz, post loading torque loss was recorded. Finite element model of each group was also modeled and screw energy, and stress were analyzed and compared between two groups.
Results: ANOVA for repeated measurements showed that the torque loss did not change significantly after cyclic loading (P=0.73). Crown margin also had no significant effect on the torque loss (P=0.56). However, the energy and stress of screw in abutment-level model (4.49 mJ and 22.74 MPa) was higher than implant-level model (3.52 mJ and 20.81 MPa).
Conclusions: Although embracing the implant with crown produced less stress and energy in the abutment-implant screw, it did not have any significant influence on the torque loss of the screw.
Keywords: Dental Implant; Ferrule Effect; Screw Loosening.
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