Evaluation of three fixation techniques for repair of mandibular fractures in dogs

Abstract

Summary Bilateral midbody hemimandibular osteotomies were performed between premolars 3 and 4 in 18 adult dogs. Hemimandibles were repaired by use of monocortically applied bone plates (n = 6), an interdental fixator composed of an Erich arch bar and acrylic (n = 6), or a type I external skeletal fixator (n = 6). At the immediate postoperative evaluation, hemimandibles stabilized with interdental fixators had an osteotomy gap distance (mean ± SEM, 1.6 ± 0.2 mm) that was significantly (P < 0.05) greater than for hemimandibles stabilized with external skeletal fixators (1.2 ± 0.3 mm). Osteotomy gap distance of hemimandibles stabilized with external skeletal fixators (1.5 ± 0.2 mm) was significantly (P < 0.05) greater at weeks 4 (1.1 ± 0.2 mm) and 8 (0.8 ± 0.3 mm) after surgery than the osteotomy gap distance of hemimandibles stabilized by application of bone plates. By week 16, significant differences in osteotomy gap distance were not detected between groups. Immediately after surgery, mandibular alignment measurements were not significantly different for dogs with bone plates (0.3 ± 0.1 mm), interdental fixators (0.3 ± 0.1 mm), and external skeletal fixators (0.9 ± 0.5 mm). Mandibular alignment scores were not significantly different between treatment groups during the remaining postoperative period. Occlusal measurements were not significantly different between evaluations performed before surgery and 16 weeks after surgery, regardless of treatment group. Radiographic evidence of healing in hemimandibles stabilized with external skeletal fixators was significantly (P < 0.05) less at 4 and 8 weeks, compared with hemimandibles stabilized with bone plates and interdental fixators; however, radiographic evidence of bone healing was not significantly different between fixation groups at 16 weeks. Radiographic evidence of implant loosening was seen in 1 of 12 (8%) hemimandibles receiving bone plates, 1 of 12 (8%) hemimandibles receiving interdental fixators, and 4 of 12 (33%) hemimandibles receiving external skeletal fixators. Periosteotomy callus was radiographically evident in 11 of 18 (61%) hemimandibles at 4 and 8 weeks only, but significant differences in periosteotomy callus surface area were not detected between groups. Of 24 hemimandibles stabilized with interdental and external skeletal fixators, 22 (92%) had callus formation that progressively matured into trabecular bone by 16 weeks. At 4 weeks, bone healing characterization scores of hemimandibles stabilized with bone plates were significantly (P < 0.05) less than (ie, had greater stability) bone healing characterization scores of hemimandibles stabilized with interdental and external skeletal fixators, but at 8 and 16 weeks, bone healing characterization scores between treatment groups were not significantly different. Histopathologic or radiographic evaluation did not reveal evidence of pulp disease or pathologic changes of teeth, which would have been associated with root resection at the osteotomy site, application of acrylic to the crown surface, or placement of external fixator pins and cortical screws. On the basis of the fact that the dogs appeared clinically normal and were able to masticate, analgesics were discontinued by 24 hours after surgery. Analysis of data indicated that an interdental fixator composed of an Erich arch bar and acrylic may be a viable method for fracture repair of mandibles.