The objective is to develop an animal model in the rapidly growing mammal, the rabbit, which is adapting to a mediolateral shift in the mandibular resting posture. The purpose is to determine the effect of the asymmetric rest position on the growth of the cranioskeleton and mandible, the remodeling of this system and the complementary changes in the neuromuscular system. The resting posture of the mandible will be altered mediolaterally by placing similar pole magnets at inclines on the mandibular and maxillary incisors to produce a consistent lateral shift. The first specific aim will determine the effects of changing the mandibular resting position on the contour of bone density within the cranioskeleton. Cranioskeletal changes will be determined by studying bone density distributions assessed with computed tomography in which the density contour of the bone is graphically outlined and quantified, the distribution of density parameters as measured in computed tomography numbers (CT) is displayed and the axial slices are reformatted to compare left and right sides. The second specific aim will determine the effects of changing mandibular resting posture on the growth patterns of this rapidly growing mammal. Growth patterns will be determined radiographically by digitizing and measuring changes in angles and lengths of anatomical sites and metal implanted markers from lateral and postero-anterior cephalograms. This approach will require establishing the techniques of metal implants and assessing mandibular and maxillary changes with techniques similar to those previously used in the primate. The third specific aim will determine the effect of changing the mandibular resting posture on the resting EMG level and the masticatory patterns of the temporalis, medial and lateral pterygoids and masseter muscles. Fine wire electrodes will be placed in the mandibular muscles of the awake, gently restrained rabbit. Statistical analyses of the computer tomography, cephalometric and muscle activity data will be carried out by comparing the same measurement for a given side between the control and experimental animals, as well as evaluating the change in the measurement during the early growth period.
