RESORBABLE DOWELS FOR OSTEOSYNTHESIS OF NONCONGRUENT BONE FRAGMENTS

Dowels, in contrast to screws, offer the great advantage in osteosynthesis that no pressure peaks occur by functional loading rectangular to the screw axis; consequently, there is no bone resorption and no loosening of the fixation because of the even contact of dowel and bony surface. However, dowels must be made of resorbable materials because they cannot be removed. We developed double-spreading dowels with a slotted tube whose outside is cylindric and the inside conical at both ends. Two conical screws in the core of the dowel moved toward each other cause symmetric expansion of the outer surface. Dowel material consisted of polylactic acid with an inherent viscosity > 7 dl/g (Resomer 214, 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 in the sense of distance osteogenesis. Two segments of synthetic material were synthesized like proximal and distal segments after retromolar sagittal split osteotomy fixed by two or three dowels without coherent contact. The synthesized segments underwent a continuous jiggling stress 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.