EVALUATION OF 3 FIXATION TECHNIQUES FOR REPAIR OF MANDIBULAR FRACTURES IN DOGS

Bilateral midbody hemimandibular osteotomies were performed between pr emolars 3 and 4 in 18 adult dogs. Hemimandibles were repaired by use o f monocortically applied bone plates (n = 6), an interdental fixator c omposed of an Erich arch bar and acrylic Cn = 6), or a type I external skeletal fixator (n = 6). At the immediate postoperative evaluation, hemimandibles stabilized with interdental fixators had an osteotomy ga p 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 st abilized with external skeletal fixators (1.5 +/- 0.2 mm) was signific antly (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 s tabilized by application of bone plates. By week 16, significant diffe rences in osteotomy gap distance were not detected between groups. Imm ediately after surgery, mandibular alignment measurements were not sig nificantly different for dogs with bone plates (0.3 +/- 0.1 mm), inter dental fixators (0.3 +/- 0.1 mm), and external skeletal fixators (0.9 +/- 0.5 mm). Mandibular alignment scores were not significantly differ ent between treatment groups during the remaining postoperative period . Occlusal measurements were not significantly different between evalu ations performed before surgery and 16 weeks after surgery, regardless of treatment group. Radiographic evidence of healing in hemimandibles stabilized with external skeletal fixators was significant (P < 0.05) less at 4 and 8 weeks, compared with hemimandibles stabilized with bo ne plates and interdental fixators; however, radiographic evidence of bone healing was not significantly different between fixation groups a t 16 weeks. Radiographic evidence of implant loosening was seen in 1 o f 12 (8%) hemimandibles receiving bone plates, 1 of 12 (8%) hemimandib les receiving interdental fixators, and 4 of 12 (33%) hemimandibles re ceiving external skeletal fixators. Periosteotomy callus was radiograp hically 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 inte rdental and external skeletal fixators, 22 (92%) had callus formation that progressively matured into trabecular bone by 16 weeks. At 4 week s, bone healing characterization scores of hemimandibles stabilized wi th bone plates were significantly (P < 0.05) less than (ie, had greate r stability) bone healing characterization scores of hemimandibles sta bilized with interdental and external skeletal fixators, but at 8 and 16 weeks, bone healing characterization scores between treatment group s were not significantly different. Histopathologic or radiographic ev aluation 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 place ment of external fixator pins and cortical screws. On the basis of the fact that the dogs appeared clinically normal and were able to mastic ate, analgesics were discontinued by 24 hours after surgery. Analysis of data indicated that an interdental fixator composed of an Erich arc h bar and acrylic may be a viable method for fracture repair of mandib les.