| 1257 Subcellular Response of the Masseter Muscle to Stretch | ||
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F. URIBE1, B.A. HAVENS1, L.J. KREBS1, and E.-K. PAE2, 1 University of Connecticut Health Center, Farmington, USA, 2 UCLA, Los Angeles, CA, USA Objectives: Functional orthodontic appliances have been used to correct malocclusions. Functional appliances stretch the jaw closing muscles during function. We assume that functioning of the jaw closers cause mechanical stress to the bone that in turn adapts structurally. We hypothesize that composition of the muscle fibers in the masseter muscle change when stretched and that this fiber type change is associated with the effectiveness of the functional appliance. Methods: Eight New Zealand rabbits were divided into control (n = 3) and experimental groups (n = 5). Experimental animals received a prefabricated curved inclined plane (3 mm thick) cemented to the upper central incisors with a glass ionomer cement to achieve protrusion of the mandible as the lower incisors glide forward along the inclined plane while the control animals received no intra-oral appliance. In addition, both groups received a cast on one of the hind legs that stretched the extensor digitorum longus muscle (EDL). Animals were sacrificed a week later and tissue harvested from the masseter, lateral pterygoid, and EDL muscles. Tissue was prepared for immuno-histochemistry study to evaluate changes in fiber composition. Results: Slow fibers type-1 in the stretched EDL increased 118% suggesting fast to slow muscle phenotype transition. The EDL muscle also showed a significant increase (P < 0.001) in the percentage of developmental fibers suggesting a reprogramming effect. However, no significant change in muscle fiber type was found in the masticatory muscles despite some increase in the number of neonatal fibers. Conclusions: The results suggest that rabbit masticatory muscles may respond differently from limb muscles to stretch. We conclude that no statistically significant changes are detected in the masticatory muscles to explain the craniofacial changes during functional appliance therapy. (This study was supported by AAOF grant category 1 to Dr. E. Pae) | ||
| Seq #134 - Craniofacial Development and Growth; Molecular Biology 9:00 AM-11:00 AM, Friday, 27 June 2003 Svenska Massan A6 | ||
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