Bone response to unloaded bicortical screw implant in dog femur model: an experimental study

ABSTRACT

A dog model for study of bone formation around bicortically stabilized screw implants is described. Twelve young adult domestic dogs were used. In each animal, the femur was exposed and after preparing the implant site, a bicortical self -cutting screw [Oraltronics Implant Technology, Germany] of diameter 35 mms and length 25 mms was inserted The animals were equally subdivided into three observation groups [four dogs in each group] and sacrificed with an overdose of thiopentone sodium. The first group was killed 2 weeks, the second 4 weeks, and the third 12 weeks post implantation. Specimens were prepared for histologic examination using Haematoxylin and Eo-sin and Trichrome stains after 2, 4 and 12 weeks of healing. Analysis of the results was qualitative. At 2 weeks, a provisional matrix could be detected that was rich in collagen fibrils and sprouting vascular structures. At 4 weeks, the newly formed bone included woven bone often combined with both parallel-fibered and lamellar bone. At 12 weeks post implantation, marked signs of remodeling could be seen in the bone tissue and all implants were histologically osseointegrated without any signs of inflammation or connective tissue interposition at the bone-implant interface. There was a high bone to implant contact [BIC] in the areas of high bone content i.e. in the areas where the cortical plates were engaged. A continuous line of newly formed bone was often noted surrounding major parts of the implant apex. The current findings indicate clearly that osseointegration represents a dynamic process both during its establishment and its maintenance and that high bone to implant contact [BIC] and initial primary stability, both provided by this implant model, play a major role in osseointegration. Accordingly, this experimental model may prove useful for future studies on the use of various procedures that hypothetically may enhance bone formation