Strain-related bone remodeling in distraction osteogenesis of the mandible

Distraction osteogenesis has become a mainstay in craniofacial surgery. How ever, there are several unresolved problems concerning the biology of bone regeneration. We investigated the biomechanical effects of mandibular lengt hening in 32 rabbits on a cellular and histologic level. The mandible was s ubjected to a corticotomy, held in a neutral position for 4 days, and then lengthened at various strain rates and frequencies for 10 days. Radiographi c, histologic, and electron microscopic examinations shelved a strain-relat ed bone regeneration. Application of physiologic strain rates (2000 microst rains or 0.2 percent) led to a bridging of the artificial fracture exhibiti ng woven ossification, whereas at 20,000 microstrains trabecular bone forma tion was demonstrated, In contrast, hyperphysiologic strain magnitudes (200 ,000 microstrains and 300,000 microstrains) showed a fibrous tissue formati on. Multiple strain applications (10 cycles/day versus 1 cycle/day) increas ed the width of the distraction gap without changing the stage of bone rege neration. The gradual distraction of bone in physiologic magnitudes at high er frequencies seems to be desirable for a bony differentiation and may hel p to improve clinical applications.