Masticatory mechanics of a mandibular distraction osteogenesis site: interfragmentary micromovement.

Micromovement at a fracture or distraction osteogenesis (DO) site may play a significant role in bone formation and healing. Mastication is an important physiological process that can cause substantial micromovement at a mandibular disjunction. The purpose of this study is to characterize and quantify the micromovement caused by mastication. Eighteen pigs, divided into three groups based on duration of consolidation, received a unilateral (right) mandibular angle distraction osteogenesis protocol. Differential variable reluctance transducers (DVRTs) and ultrasound crystals were used to measure the change of gap width as well as interfragmentary movement during mastication. Synchronized chewing video and interfragmentary movement recordings were used to determine the magnitude and direction of micromovement at different phases of the chewing cycle. The magnitude of micromovement did not increase significantly with distraction up to almost 5 mm, but did decrease gradually with consolidation. The average micromovement magnitude during the distraction phase was 0.2-0.3 mm, equaling 50,000-250,000 microstrain (muepsilon) on interfragmentary tissue. The dominant deformation pattern was bending in the sagittal plane. The most common direction of bending at the power stroke of chewing was concave dorsally, i.e., superior shortening and inferior lengthening. These findings elucidate how masticatory mechanics affect a mandibular distraction site, and the measurements may be useful for future simulation studies.