RESORBABLE DOWELS FOR OSTEOSYNTHESIS OF NONCONGRUENT BONE FRAGMENTS

Dowels, in contrast to screws, offer the great advantage in osteosynth esis that no pressure peaks occur by functional loading rectangular to the screw axis; consequently, there is no bone resorption and no loos ening of the fixation because of the even contact of dowel and bony su rface. However, dowels must be made of resorbable materials because th ey cannot be removed. We developed double-spreading dowels with a slot ted tube whose outside is cylindric and the inside conical at both end s. Two conical screws in the core of the dowel moved toward each other cause symmetric expansion of the outer surface. Dowel material consis ted of polylactic acid with an inherent viscosity > 7 dl/g (Resomer 21 4, Bohringer Ingelheim). A model simulating retromolar sagittal split osteotomy was chosen for experimental research because, in this case, noncongruent bone segments have to be osteosynthesized to regenerate i n the sense of distance osteogenesis. Two segments of synthetic materi al were synthesized like proximal and distal segments after retromolar sagittal split osteotomy fixed by two or three dowels without coheren t contact. The synthesized segments underwent a continuous jiggling st ress test comparable with the physiologic stress of a jaw for about 4 weeks. Dowel fixation proved to be nearly as stable as position-screw fixation. Resorbable dowel fixation yields experimentally the required stability for the time needed for bony regeneration.