Mandibular mechanics following osteotomy and appliance placement II: Bone strain on the body and condylar neck.
OBJECTIVE
The purpose of this investigation was to determine if the mechanical environment of the mandible is changed by osteotomy and fixation, as assessed by the measurement of bone strain on the condylar neck and mandibular corpus.


METHODS
Immediately following unilateral mandibular osteotomy and distractor placement, strain gauges were attached directly to the corpus and condylar neck in a sample of domestic pigs. Bone strains were recorded during mastication and muscle stimulation. Comparisons of principal strain magnitudes and orientations were made between sides and between the osteotomy sample and a control database.


RESULTS
The animals preferred to chew on the non-osteotomy side. Corpus strains were higher for osteotomy-side chewing but were comparable to the control database, regardless of chewing side. For the condyle, compared with the control database and the non-osteotomy side, the osteotomy side was underloaded in compression. Furthermore, the orientation of compressive strain was highly variable and more horizontally oriented than that of control and non-osteotomy condyles. Stimulation of the masseter and medial pterygoid loaded the mandible to normal levels.


CONCLUSIONS
Masticatory behavior was altered, probably as a combined result of disruption of the occlusion, changes in muscle recruitment, and probable loss of sensory feedback. However, neither these changes nor damage to the muscles explain the decrease and reorientation of compressive strain on the condylar neck. Alternatively, the modified strain pattern could have arisen from positional instability of the proximal bone fragment.
Department of Orthodontics, University of Washington, Seattle, WA 98195, USA.
Katherine L
KL
Rafferty
Zongyang
Z
Sun
Mark A
MA
Egbert
Emily E
EE
Baird
Susan W
SW
Herring
D000818:Animals; D001732:Bite Force; D019245:Compressive Strength; D003799:Dental Stress Analysis; D004558:Electric Stimulation; D016268:Internal Fixators; D019248:Jaw Fixation Techniques / Q000295:instrumentation*; D008334:Mandible / Q000502:physiology* / Q000601:surgery*; D008335:Mandibular Condyle / Q000502:physiology; D008409:Mastication; D008410:Masticatory Muscles / Q000502:physiology; D019857:Osteogenesis, Distraction / Q000295:instrumentation*; D010027:Osteotomy; D011184:Postoperative Period; D033081:Shear Strength; D013314:Stress, Mechanical; D034421:Sus scrofa; D013552:Swine; D013718:Tensile Strength