In vitro comparison of the holding power of 1.2 mm, 1.5 mm, and 2.0 mm orthopaedic screws in canine radii

The holding power of miniscrews in canine bone has not been investigated. The report compares the holding power of four different miniscrew types. The screw types tested were: 1.2 mm self-tapping screws, 1.5 mm tapped screws, 2.0 mm self-tapping screws and 2.0 mm tapped screws. They were randomly allocated to canine radius screw sites and screw pull-out strength was determined using a Mechanical Testing System (MTS) machine. The 1.2 mm self-tapping screw has a significantly weaker holding power than the other three screw types. Based upon these findings, the use of the 1.2 mm self-tapping screw cannot be recommended for use in thick cortical bone. There were not any significant differences in holding power of the other three screw types. The performance of the 1.5 mm tapped screws, versus the 2.0 mm tapped screws, was comparable and suggests that the 1.5 mm tapped screw can provide adequate holding power in miniscrew applications. The results were consistent with a linear relationship between the external thread diameter and the holding power. Hypothesis. The hypothesis of this study is that there are not any significant differences in the holding power of different miniscrews. We hypothesized that the effects of tapping prior to screw insertion, or using miniscrews of greater external thread diameter, would not provide any increase in the holding power of the screw.