[In vivo studies of screw-bone contact of drill-free screws and conventional self-tapping screws].

Screw-bone contact (SBC) and bone remodeling of titanium drill-free screws or self-tapping screws should be compared. Each 10 titanium self-tapping miniscrews or microscrews, and each 10 titanium drill-free miniscrews or microscrews were inserted into the anterior wall of the frontal sinus of 5 Göttingen minipigs. Intraperitoneal injections of fluochromes (Xylenol, Calcein, Alizarincomplexon and Tetrazyklin) were performed between the 2nd and 9th postoperative week. The pigs were sacrificed after 6 months, the screw-bone blocks were resected and microradiographic, histologic and fluorescence microscopic examinations were carried out. In drill-free screws mean SBC was 88.4 (miniscrews) or 93.8% (microscrews). In self-tapping miniscrews mean SBC was 54.9, in microscrews 81%; the differences were significant in statistical analysis (t-test: p < 0.05). In fluorescence microscopy the amount of bone remodeling (ratio of residual versus newly formed bone) was measured. Significantly more of the residual bone was found in the region of the screw threads of drill-free screws (miniscrews: mean 71.8, microscrews: mean 67.9%) than in the region of screw threads of self-tapping screws (miniscrews: mean 33.1, microscrews: mean 42.4%; t-test: p < 0.05). The superior SBC of drill free screws in comparison to SBC of self-tapping screws and the higher amount of original bone in the threads of drill free screws explain the sufficient holding strength of drill free screws in clinical tests. Both results are important for osteosynthesis in regions where thin cortical bone is present, as in the central midface.