Skeletal effects of the alteration of masseter muscle function

To investigate the effects of muscle denervation and the introduction of the β2-adrenoceptor agonist, formoterol, on the relationship between muscles and underlying skeletal growth.

Thirty-one (4-week-old) male Sprague-Dawley rats were assigned to four groups: Surgical Sham; Denervated; Denervated + β2-agonist; and β2-agonist only. The Surgical Sham group had the left masseteric nerve exposed but not sectioned. Both of the denervated groups had the left masseteric nerve exposed and sectioned. The groups receiving the β2-agonist had formoterol directly injected into the left masseter muscle every three days for eight weeks. Sixteen angular and linear skeletal measurements were assessed in the overall craniofacial region and the mandible via standardised digital radiography in three views: lateral head, submento-vertex and right and left disarticulated hemi-mandibles.

The findings indicated that, following surgical denervation of the masseter muscle, there were significant changes in the muscle and in the subsequent development of the underlying skeletal structures. The post-surgical changes were largely offset by the administration of a β2-agonist, formoterol, which attenuated muscle atrophy. However, the administration of the β2-agonist only, without surgical denervation, did not lead to changes in skeletal facial form.

Denervation atrophy of the masseter muscle results in statistically significant changes in the development of the underlying skeleton. The changes, however, are localised to areas of muscle attachment. The administration of the β2-agonist, formoterol, despite its effect on muscle anabolism, does not have a significant effect on underlying skeletal growth.