Hunt, Nigel Peter; (1992) Musculo-Skeletal Adaptation to Disturbances of the Cranio-Facial Complex. Doctoral thesis (Ph.D), University of London.

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Abstract

This study has addressed the possible relationships between the structure and function of the masseter and temporalis muscles and the skeletal morphology of the human face and jaws. Furthermore, it has noted how these muscles respond to surgical correction of facial deformities, and whether this has any relevance regarding surgical stability. 42 patients scheduled for surgical correction of vertical facial deformities were subjected to investigations designed to record the structure and function of masseter muscle, and the function of temporalis muscle. These were repeated over a one year review period. Muscle structure was investigated using ATPase histochemical techniques, whilst muscle function was recorded through electromyography, mandibular kinesiography and occlusal force measurement. Skeletal and dental form was measured from digitized lateral skull cephalometeric radiographs. Where appropriate the results were compared to those from a matched control group (20 patients) with normal skeletal facial morphology. The results showed a significant reduction in the size of type II fibres in patients with a long face morphology and this was reflected in the reduced occlusal force generated by such individuals. Canonical correlation analysis showed that a reduced type II fibre contribution to the relative fibre cross- sectional area influenced the anterior vertical relationship of the mandible to the cranial base ( p ≤ 0.001), but no other aspect of facial form. Facial morphology did not significantly influence muscle structure. Surgery resulted in a reduction in Intermediate fibre incidence and vertical surgical stability correlated with the incidence of Intermediate fibres prior to operation (r =-0.94, p ≤ 0.001). Muscle adaptation was observed over the review period ranging from almost immediate adaptation in the clinical rest position of the mandible relative to the maxilla, through to more gradual adaptation in the physiological rest position and range of mandibular mobility extending over a 12 month period. The measures of muscle function indicated reciprocal activity between masseter and anterior temporalis in maintenance of mandibular rest position. Non-invasive studies of muscle function showed good correlation with type II fibre size and percentage total cross-sectional area but gave little information regarding type I fibres, the sub-groups of type II or Intermediate fibres.

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