Myosin Content in Rat Immobilised M. Latissimus Dorsi

Aims: Eschlerxs functional therapeutic method utilizes the functional forces from the muscles of the face and the jaw to correct the bite. By displacing the lower jaw forwards e.g., the functional appliance activates the muscles of the face and jaw, which gently and gradually correct the bite. Muscles adapt to stress or hyperfunction by changing of fiber types and mRNA content. Aim of this study was to detect changes of Myosin mRNA content of rat m. latissimus dorsi after immobilised by P3HB scaffolds. Material and Methods: Parts of m. latissimus dorsi of 12 Wistar-King rats were immobilised by intramuscular implantation of P3HB scaffolds. For localisation of the implants a statistical randomisation was used, implantation periods were 49 and 98 days. Six rats were killed and implants and surrounding tissues were prepared for genetic evaluation. Eight rats without any implants served as a control group. After homogenisation of muscle tissue RNA was extracted using phenole-chloroform. Changes in mRNA content were measured by Real-Time PCR using specific primers for type I MyHC, IIa, IIb and IIx muscle fibers. Results: Compared to the control group the mRNA level of fibers type I of immobilized muscles were significantly decreased (p<0,05). Further, immobilized muscles showed a significant increase in fibers type IIb mRNA compared to the controls. The mRNA amount of fibers IIa and IIx in both groups showed no significant changes (p<0,05). Conclusion: Muscle immobilisation can lead to uncontrolled changes in affected and not affected muscle structures. These changes can cause a new muscle dysbalance. It should be discussed and proved how these results from m. latissimus dorsi could be transferred to other muscles in the body e.g. chewing muscles after functional orthodontic treatment.