Contribution of the periosteum to mandibular distraction.

Mandibular distraction is a surgical process that progressively lengthens bone. To improve the distraction procedure and devices, the load of distraction and the mechanical strain of soft tissues during the process must be determined. We tested the assumption that it could be the periosteum primarily opposing distraction. Therefore we assessed the mechanical properties of the human mandibular periosteum and compared the stress-strain data with the torque measured on the activator during a cadaveric mandibular distraction. A 20 mm horizontal mandibular distraction was performed in 7 cadavers using standard distractors. Torque was measured with a torquemeter placed on the activation rods of the devices, providing a load (Lt) for each millimeter of distraction. In parallel, 18 periosteum samples were harvested from 9 cadaver mandibles. Uniaxial tensile tests were performed on the specimens and an estimated load (Lc) was calculated using periosteal stress-strain data and mandibular dimensions. During the distraction process, we observed an increase of the load Lt from 11.6 to 50.6 N. The periosteum exhibited a nonlinear viscoelastic stress-strain relationship, typical of biological tissues composed of collagen and elastin. The median Lc and Lt were not significantly different for the first millimeter of distraction. We demonstrated the periosteum is primarily responsible for opposing the distraction load.