Summary
The holding power of miniscrews in canine bone has not been investigated. This 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 (MIS)
machine. The 1.2 mm self-tapping screw had 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 these 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.
Key words Canine - screws - miniscrews - holding power - screw pull-out
