The relationship of masseter muscle thickness with face morphology and parafunctional habits: Study of ultrasound

It is widely accepted that there is a relationship between the activities of the masticatory muscles and the development of the craniofacial structure. Chewing muscles have functional and parafunctional activities. Hyperactivity occurs in the muscles as a result of parafunctional activities. It is suggested that due to this increase in activity, the masseter muscle, one of the muscles of the masticatory system, exhibits adaptive changes and affects facial morphology. Although the activity of chewing muscles is determined by electromyography, recently muscle thickness has been accepted as an indicator of jaw muscle activity. Masseter muscle can be viewed by ultrasonography and its thickness can be measured. Ultrasonography is an easily applicable, repeatable, noninvasive imaging method. The aim of this study was to determine the normal range of masseter muscle thickness by ultrasonographic measurement in individuals over 15 years of age, and to evaluate its relationship with age, gender, facial morphology, body mass index and parafunctional habits. The study was conducted on 115 volunteers over 15 years old, whose lateral cephalometric radiography was performed within the indication and who had not received any orthodontic treatment before, had no hereditary or acquired syndrome, had no trauma and surgical operation in the head and neck region, except for the third molar without posterior tooth deficiency, in Gazi University Faculty of Dentistry, Department of Oral and Maxillofacial Radiology. The participants in the study were asked questions about their parafunctional habits, age, height and weight. Individuals were grouped as hypodivergent (n=28), normdivergent (n=55) or hyperdivergent (n=32) according to vertical face morphology by making measurements on lateral cephalometric films. Right and left masseter muscle thicknesses of individuals were measured by ultrasonography while at rest and in contraction. The mean value of masseter muscle thickness was found to be 13.57 ± 2.57 mm. The rest and contracted muscle thicknesses was significantly higher in men than in women for the right and left masseter muscles (p<0,05). It was found that when the masseter muscle was at rest or contracted, there was a similar but weak relationship between muscle thickness and age and body mass index. When the masseter muscle was at rest and contracted, its thickness was higher in individuals with hypodivergent facial morphology, than in the other groups. No statistically significant difference was found in terms of masseter muscle thickness between individuals having parafunctional habits and those didn't have parafunctional habits (p>0,05). According to the results of the study, while masseter muscle thickness varied according to vertical facial morphology, parafunctional habits didn't cause any difference.