Effect of Botulinum Toxin Type A on Mandibular Fracture Healing: An Experimental Study in Rabbits

Purpose The effect of botulinum toxin type A (BTX-A) on fracture healing of the long bones is controversial, and no controlled clinical or experimental study has investigated the effect of BTX-A on mandibular fractures. The purpose of this study was to investigate whether BTX-A injection into the masseter muscles affects bone healing by reducing the displacing forces in an unfavorable mandibular fracture model. Materials and Methods Forty-eight male New Zealand white rabbits were used. Ten units of BTX-A was injected into each masseter muscle in the animals in the BTX-A group, whereas saline solution was injected in the animals in the control group. A unilateral osteotomy and fixation with a microplate were performed. Bone healing was evaluated by radiodensitometric, biomechanical, histologic, and histomorphometric methods after 21 days. Results The mean bone mineral density in the fracture area was significantly higher in the BTX-A group (P = .038). The mean failure load and bending modulus values were significantly higher in the BTX-A group than in the control group (P = .032 and P = .005, respectively). The mean histologic bone healing scores, bone volume–total volume values, and trabecular diameter values were significantly higher in the BTX-A group than in the control group (P = .001, P = .001, and P = .026, respectively). Conclusions BTX-A application into the masseter muscles improves bone healing of a unilateral mandibular fracture in rabbits. The effect of botulinum toxin type A (BTX-A) on fracture healing of the long bones is controversial, and no controlled clinical or experimental study has investigated the effect of BTX-A on mandibular fractures. The purpose of this study was to investigate whether BTX-A injection into the masseter muscles affects bone healing by reducing the displacing forces in an unfavorable mandibular fracture model. Forty-eight male New Zealand white rabbits were used. Ten units of BTX-A was injected into each masseter muscle in the animals in the BTX-A group, whereas saline solution was injected in the animals in the control group. A unilateral osteotomy and fixation with a microplate were performed. Bone healing was evaluated by radiodensitometric, biomechanical, histologic, and histomorphometric methods after 21 days. The mean bone mineral density in the fracture area was significantly higher in the BTX-A group (P = .038). The mean failure load and bending modulus values were significantly higher in the BTX-A group than in the control group (P = .032 and P = .005, respectively). The mean histologic bone healing scores, bone volume–total volume values, and trabecular diameter values were significantly higher in the BTX-A group than in the control group (P = .001, P = .001, and P = .026, respectively). BTX-A application into the masseter muscles improves bone healing of a unilateral mandibular fracture in rabbits.