Several studies have been conducted on this type of implant–abutment connection [23, 34]. Sutter et al. [35] demonstrated reverse torque values of this hybrid implant–abutment connection that were 124% of the initial tightening torque. These authors suggested that cold welding occurred in the conical hybrid implant–abutment connection.

Schmitt et al. [36] compared conical and nonconical implant–abutment connection systems in terms of their in vitro and in vivo performances. In vitro studies indicate that conical and nonconical abutments exhibited sufficient resistance to the maximal bending forces and fatigue loading. However, conical abutments were superior in terms of sealing, microgap formation, torque maintenance, and abutment stability.

According to the results of this study, %RTL increased significantly with increasing collar length and the percentage of removal torque gaining after load with 0° abutments with collar height 4 mm was less than that of 2 mm. This finding matches what was found by Siadat et al. [9] who evaluated the effect of collar length on screw loosening and concluded that an increase in the abutment collar length significantly increase the torque loss of abutment–implant screw after cyclic loading. The abutment collar length acts as vertical cantilever, so increasing abutment collar would lead to an increased vertical cantilever which acts as a force magnifier [8]. Cantilever designs increase bending forces on screws due to the lever effect [17, 18].