Biomechanical analysis of the effect of mesenchymal stem cells on mandibular distraction osteogenesis.

Background: The purpose of this study was to investigate the effects of bone marrow-derived stem cells on consolidation period by using a new biomechanical testing method on sheep mandible model.

Methods: Eight sheep underwent bilateral mandibular osteotomies. After latency period, bone distraction was activated. Mesenchymal stem cells were transplanted into the gap of the left mandibular distracted callus on the first day of consolidation period. The sheep were then randomly divided into 2 groups (group A = 4, group B = 4). Group A and group B animals were killed on the third and sixth weeks of consolidation, respectively. Fracture pattern and localization, bone regeneration ratio and density, and stress distribution of 16 distracted hemimandibles were evaluated by computed tomography and biomechanical analysis.

Results: Two different fracture patterns were observed in the 2 groups. The left halves of mandibles exhibited horizontal fracture out of the distraction zone, and the cross-sectional area was compact bone [H (-) C], whereas the fracture patterns of control sides were oblique, which passed through the distraction zone with a propensity of trabecular bone [O (+) T]. Stress distribution at the critical cross-section of distraction region was not different in halves of mandibles. However, bone regeneration ratios and regenerated bone densities were significantly higher in left sides (P < 0.05).

Conclusions: Transplantation of mesenchymal stem cells promotes maturity of the distracted callus. The new experimental model, which allowed to test the mandible as a system by simulating in vivo loading conditions, revealed differences in the mechanical behavior of the halves of mandible.