Malignant or benign but locally destructive tumors of the mandible can have a substantial impact on the quality of life of affected dogs.1,2 Therefore, it is generally accepted that when possible, mandibular tumors should be promptly removed by means of mandibulectomy.1–3 Other treatment modalities such as radiation therapy and intralesional chemotherapy may also be used, either to complement mandibulectomy or as a sole treatment, depending on the tumor type.4 However, the excision of bone and soft tissue structures of the mandible, as occurs with mandibulectomy, disrupts continuity of the mandible, and the associated critical-size bone defect severely compromises mobility of the remaining mandibular segments.2,5
The intact support of the TMJ and the masticatory forces on the unaffected side in dogs undergoing mandibulectomy result in the intact mandible typically drifting away from the median plane and toward the excised side without deliberate muscular guidance. The nature of such mandibular drift is typically dependent on the site of mandibulectomy.1,2,5,6 Specifically, unilateral segmental and bilateral rostral mandibulectomy result in mandibular instability and drift and may result in difficulty in eating and drinking. Moreover, the drift and instability of the mandible may result in stress on the muscles of mastication and the TMJ as the dog attempts to reposition the jaw to its normal position.7,8 In the long term, mandibular drift may result in irreversible changes such as TMJ osteoarthrosis.9
Over the past decade, a regenerative approach to mandibular reconstruction in companion dogs has been reported by our group and others.6,10–14 The main goals of mandibular reconstruction in dogs are the restoration of dental occlusion, mandibular stability, and normal function, which includes physiologic mouth opening and closing and minimal lateral movement (ie, laterotrusion).6,10,15 People undergoing mandibular reconstruction after mandibular tumor excision have superior function, aesthetics, and quality of life, compared with those who do not undergo mandibular reconstruction,16–20 and our experience performing mandibular reconstruction suggests that results are similar for dogs.
An understanding of normal jaw motion and the effects of mandibulectomy on that motion can provide clinically relevant insight into the complex masticatory changes that occur after mandibulectomy.20–22 To our knowledge, no studies have been reported regarding mandibular kinematics in dogs, the effects of mandibulectomy on those kinematics, or the kinematic outcome of restoring mandibular stability in dogs by means of internal fixation. Therefore, the purpose of the study reported here was to evaluate the motion of intact canine mandibles, the kinematic behavior of mandibles treated with unilateral segmental or bilateral rostral mandibulectomy, and the kinematic behavior of mandibles treated with unilateral segmental or bilateral rostral reconstruction. We hypothesized that mandibular kinematics in dogs would be adversely affected (ie, significant deviation from the motions of the intact mandible) by unilateral segmental or bilateral rostral mandibulectomy. We further hypothesized that reconstructive surgery, which restores the continuity after mandibulectomy, would restore normal mandibular kinematics. We believed the findings would allow evaluation of the kinematic benefits of mandibular reconstruction to enhance surgical techniques.
Funded by the Companion Animal Memorial Fund, administered by the Center for Companion Animal Health, University of California-Davis. DePuy Synthes Vet, a division of DePuy Orthopedics Inc, donated the plates and screws used in this study.
The authors declare that there were no conflicts of interest regarding any of the materials or manufacturers used in the study.
The authors thank Dr. C. Toupadakis Skouritakis for assistance with the illustrations.
IMEX Veterinary Inc, Longview, Tex.
S-PRI, AOS Technologies AG, Baden, Switzerland.
VPT4120.24, DePuy Synthes Vet, a division of DePuy Orthopaedics Inc, West Chester, Pa.
VST311.014, DePuy Synthes Vet, a division of DePuy Orthopaedics Inc, West Chester, Pa.
Motus 10, Contemplas, Kempten, Germany.
PROC MIXED, SAS, version 9.4, SAS Institute Inc, Cary, NC.
PROC UNIVARIATE, SAS, version 9.4, SAS Institute Inc, Cary, NC.
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