A rationale method for evaluating unscrewing torque values of prosthetic screws in dental implants

Objectives

Previous studies that evaluated the torque needed for removing dental implantscrews have not considered the manner of transfer of the occlusal loads inclinical settings. Instead, the torque used for removal was applied directly tothe screw, and most of them omitted the possibility that the hexagon could limitthe action of the occlusal load in the loosening of the screws. The present studyproposes a method for evaluating the screw removal torque in an anti-rotationaldevice independent way, creating an unscrewing load transfer to the entireassembly, not only to the screw.

Material and methods

Twenty hexagonal abutments without the hexagon in their bases were fixed with ascrew to 20 dental implants. They were divided into two groups: Group 1 usedtitanium screws and Group 2 used titanium screws covered with a solid lubricant. Atorque of 32 Ncm was applied to the screw and then a custom-made wrench was usedfor rotating the abutment counterclockwise, to loosen the screw. A digital torquemeter recorded the torque required to loosen the abutment.

Results

There was a significant difference between the means of Group 1 (38.62±6.43Ncm) and Group 2 (48.47±5.04 Ncm), with p=0.001.

Conclusion

This methodology was effective in comparing unscrewing torque values of theimplant-abutment junction even with a limited sample size. It confirmed apreviously shown significant difference between two types of screws.