Remodeling along the bone-screw interface.

Objective: The stability of cortical miniscrews depends on the contact between bone and implant. The aim of this study was to compare bone remodeling along the contact surface between the screw and bone with and without pre-drilling.

Materials And Methods: Twenty-four FAMI miniscrews (length 10 mm, diameter 2 mm) were inserted into the mandibular alveolar process apical to the premolars of four miniature pigs. Each pig received six screws, three on the one side with pre-drilling, three on the other side without pre-drilling. Polychrome fluorescent labels were used to assess the bone remodeling. After 12 weeks of osseointegration, all 24 screws and surrounding bone were removed. Microsections were prepared and analyzed histomorphometrically and under fluorescent microscopy. Differences between the groups were determined using the t test with a significance level of 5%.

Results: All the screws osseointegrated without any complications. Those without pre-drilling revealed a bone-screw contact of 64 +/- 11%, and those subjected to pre-drilling 63 +/- 12%. This difference was not significant. The mineral apposition rate, 1.6 +/- 0.4 microm/d and 1.7 +/- 0.4 microm/d, respectively, also failed to demonstrate any significant differences between the groups, while the portion of newly-formed bone in the pre-drilled group was significantly higher (59 +/- 9% vs. 27 +/- 6%).

Conclusion: Significant differences in the bone-to-screw contact between the two groups are no longer in evidence after three months due to new bone formation. The minor extent of bone remodeling in the not pre-drilled group rules out substantial bone damage, which might have occurred during screw placement as a result of "cracks" or an excessive increase in pressure along the interface. The similar rate of new bone formation in both groups speaks against a stimulating effect of pre-drilling. Despite the absence of quantitative differences, it remains unclear whether the mechanical quality of the newly-formed bone resembles that of preexisting bone. Our findings seem to be applicable to the human mandible, however, its thinner cortical layer means less screw-to-bone contact is likely. We must reckon with less bone contact in the maxilla for the same reason.