Relationships between facial morphology and activity of orofacial muscles in patients with a complete upper and a...

In a sample of 30 partially edentulous subjects, provided with an immediate complete upper denture and a partial lower denture and followed for 2 years, a correlation analysis was performed between facial morphology, as measured by lateral head films, and EMG peak mean voltages of the anterior temporal and masseter muscles when clenched and during swallowing and chewing, and of the lip muscles during swallowing. At the pre-treatment stage, when the patients occluded on a residual anterior dentition, correlations between facial morphologic characteristics and peak mean voltages of the jaw closing muscles indicated stronger muscle activity in individuals with a square facial type. No significant associations were observed between muscle activity and the age of the subjects, which ranged from 36 to 71 years. After placement and use of the dentures a significant forward-upward rotation of the mandible with a decrease in overbite occurred, as a result of resorption of the edentulous maxillary ridge. At the 1 year stage of denture use, the elevator activity showed no significant correlations with facial morphology. On the other hand, negative correlations were observed especially between the anterior temporal activity and anterior overbite. Similar negative correlations were observed for the lip activity during swallowing, especially of the upper lip. These findings suggest occlusal contact between the incisors during the various functions in subjects with a small overbite. The findings further suggest that the anterior temporal and the upper lip muscles are sensitive to changes in anterior occlusal relations of the dentures.