Effects of pilot hole size and bone density on miniscrew implants' stability.
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PROBLEM: How does pilot hole size and bone density affect the primary stability of miniscrew implants (MSIs)? METHODS: Using 120 MSIs divided equally into six groups, this 2 3 factorial design evaluated the effects of synthetic bone density (0.64 g/cc vs 0.8 g/cc cortices) and pilot hole size (no pilot hole, 1.0 mm pilot hole, and 1.4 mm pilot hole) on maximum insertion torque and pullout strength. The maximum placement torque was measured as the last thread of the MSIs was inserted. The pullout strength test applied a vertical force at 10 mm/min until failure. RESULTS: The insertion torque and pullout strength values were significantly (p .05) greater for the MSIs placed in high-density than in low-density cortical bone. The insertion torque and pullout strength decreased as pilot hole size increased, with significant (p .05) differences between all three subgroups. Insertion torque and pullout strength were significantly intercorrelated for all subgroupings, with stronger correlations in denser bone having smaller or no pilot holes. CONCLUSION: Depending on bone density, pilot holes of limited size can be used to optimize primary stability by decreasing insertion torque while maintaining the pullout strength of bone.
