Mandibular mechanics after osteotomy and distraction appliance placement I: Postoperative mobility of the osteotomy site.
OBJECTIVE
Fixation at the osteotomy site for mandibular distraction osteogenesis (DO) is probably not rigid, especially during mastication. Micromotion may affect the course of DO. This study aimed to measure the mobility of the fresh distractor-fixed osteotomy site in response to mastication and masticatory muscle stimulation.


METHODS
Twenty-eight domestic pigs, 6 to 8 weeks old, underwent osteotomy of the right mandible and placement of a distractor appliance. Immediately after surgery, displacement at 3 different locations (superior-lateral, inferior-lateral, and inferior-medial) of the osteotomy site was assessed using ultrasound piezoelectric crystals or differential variable reluctance transducers (DVRTs). The amount of lengthening or shortening at each location was measured during mastication and muscle stimulation. Displacement was also measured for bilateral osteotomy during muscle stimulation from a subgroup of 12 pigs.


RESULTS
The osteotomy site demonstrated significant mobility during power strokes of mastication with an average magnitude of 0.3 to 0.4 mm. Distinct patterns of displacement were associated with different locations, and the patterns varied between chewing sides. The most common pattern was lengthening at the superior-lateral and shortening at both inferior sites. Similar amounts of displacement were observed during the stimulation of jaw-closers (masseter and medial pterygoid), but the patterns produced by these muscles did not completely explain the masticatory pattern. Opening the osteotomy to 1.5 mm did not alter the displacements observed during muscle stimulation. Bilateral osteotomy tended to decrease displacement.


CONCLUSIONS
The study demonstrates that during mastication and masticatory muscle stimulation, an acute mandibular osteotomy site is mobile despite fixation by a distractor appliance.
Department of Oral Biology, University of Washington, Seattle, WA 98195, USA.
Zongyang
Z
Sun
Katherine L
KL
Rafferty
Mark A
MA
Egbert
Susan W
SW
Herring
D000704:Analysis of Variance; D000818:Animals; D001732:Bite Force; D003799:Dental Stress Analysis; D004568:Electrodiagnosis / Q000295:instrumentation; D016268:Internal Fixators; D019248:Jaw Fixation Techniques / Q000295:instrumentation*; D008334:Mandible / Q000000981:diagnostic imaging / Q000502:physiology* / Q000601:surgery*; D008409:Mastication; D008410:Masticatory Muscles / Q000502:physiology; D009068:Movement; D019857:Osteogenesis, Distraction / Q000295:instrumentation*; D010027:Osteotomy / Q000009:adverse effects; D011184:Postoperative Period; D013314:Stress, Mechanical; D034421:Sus scrofa; D013552:Swine; D014463:Ultrasonography