Canine mandibular osteotomy model: the effects of fixation on bone healing and nerve regeneration

Osteotomies made between premolar 3 and premolar 4 in the body of the mandible in canine cadaver hemimandibles (n = 48) were stabilized with five interdental fixation apparatuses in a preliminary biomechanical study. Testing in bending determined ultimate strength, stiffness, and yield strength of the interdental fixation apparatuses. Erich arch bar supplemented with acrylic had significantly (P < 0.05) greater ultimate strength, stiffness, and yield strength than Stout loop supplemented with acrylic, Acrylic, Stout loop, and Erich arch bar alone. Due to the combined superior biomechanical strength of Erich arch bar supplemented with acrylic, it was utilized as the interdental fixation apparatus for the in vivo study.

Bilateral osteotomies made between premolar 3 and premolar 4 in the body of the mandible were stabilized with monocortical bone plate (n = 6), interdental (n = 6), and external skeletal fixation (n = 6). None of the dogs showed clinical evidence of pain or discomfort associated with the fixation devices or the development of neuromas. Radiographic signs of bone healing were observed at all osteotomy sites by 16 weeks. Histologic evaluation of bone healing of the mandible with monocortical bone plate, interdental fixation, and external skeletal fixator was not significantly different (P > 0.05) at 8 and 16 weeks postoperatively.

The inferior alveolar nerves were evaluated electrophysiologically pre-operatively and at 4, 8, and 16 weeks postoperatively. Nerves were histologically evaluated at 4, 8, and 16 weeks after injury. Nerve function disappeared immediately postoperatively and returned in 64% (24 of 36) by 4 weeks, in 78% (28 of36) by 8 weeks, and 83% (30 of 36) by 16 weeks. Neuromas developed in 100% (36 of 36) of the nerves.

Using a transverse osteotomy model, results indicate that the type of bone and nerve healing does not significantly differ between fixation groups tested. Therefore, a simpler and more economical fixation device, Erich arch bar-acrylic, should be suitable to repair selected mandibular fractures in the dog.