Analysis of the osseous/metal interface of drill free screws and self-tapping screws

Aim: A comparison of metal/osseous interface and bone remodelling after ins ertion of different types of titanium bone screws in vivo, Material: Sample s of five of each of the following bone screw types were inserted into the anterior wail of the frontal sinus of five Gottingen minipigs: self-tapping micro- (1.5 mm) and miniscrews (2.0 mm) or drill free micro- (1.5 mm) and miniscrews (2.0 mm) (Martin Medizintechnik. Tuttlingen, Germany). Screw len gth was 7 mm, Methods: Sequential intraperitoneal injections of fluorochrom es were performed between the second and ninth postoperative week, After 6 months the pigs were sacrificed, the screw-bone-blocks resected, and micror adiographic, histological and fluorescence microscopical examinations were carried out, Results: Using drill free screws, mean screw/bone contact was 88.4% (miniscrews), or 93.8% (microscrews), With self-tapping miniscrews it was 54.9%, but in microscrews 81%; the differences were statistically sign ificant (t-test: p < 0.05). By fluorescence microscopy, the amount of bone remodelling (ratio of residual us. newly formed bone) was measured. Signifi cantly more of the residual bone was found in the region of the screw threa ds using drill free screws (miniscrews: mean 71.8%, microscrews: mean 67.9% ) than in the region of screw threads with self-tapping screws (miniscrews: mean 33.1%, microscrews: mean 42.4%), Conclusion: The present data support the view that screw/bone contact with drill free screws was superior to th at of self-tapping screws; the greater amount of original bone in the threa ds of drill free screws demonstrated that the insertion of drill free screw s did not cause harm to the surrounding bone. Both results are important fo r osteosynthesis in regions where thin cortical bone is present, such as th e central midface. (C) 2001 European Association for Cranio-Maxillofacial S urgery.