Masseter Activity , Arch Width and Facial Type

Dr. (Mrs.) Chandralekha .B, MDS Former Head of the Department of Orthodontics, Government Dental College & Hospital, Fort, Bangalore 560 001. Ph: 09448-091115 The present study investigated the effect of masseter muscle thickness on maxillary dental arch width and growth pattern of face. Sample comprised of 40 patients, (20 females, 20 males) between 18 to 23 years. They were subdivided according to molar relation (10 Class I, 10 Class II). Masseter muscle thickness was measured by Ultrasonography. Maxillary dental arch width was measured on dental casts, using calipers, between the palatal surfaces of first permanent molars. The growth pattern of face was assessed by lateral cephalograms. Results: The masseter muscle thickness was more in males and Class II groups compared to females and Class I groups respectively. In all the subgroups masseter muscle thickness had a positive linear correlation with maxillary dental arch width, midfacial length and corpus length (r0.5) and a negative linear correlation with ramal height, mandibular ratio and sum of angles (r-0.7). Conclusions: An increase in masseter muscle thickness widens the maxillary dental arch. Masseter muscle increases the sagittal growth, while limiting the vertical growth of jaws. It tends to make the face grow in a more horizontal pattern. INTRODUCTION: with intergonial width and bizygomatic facial width. 3 Among the masticatory muscles, masseter has been shown to have significant relation with bite force magnitude and craniofacia l morphology.4 In adu lts, corre lations have been found between facial dimensions and masseter muscle thickness. 3.4 Since there is an association between masseter muscle thickness and craniofacial width, a similar association might be expected to exist regarding dental arch width, particularly in regions with molars under eruption.2 Maxillary intermolar width showed a direct, significant association with masseter thickness both durin g contraction and relaxation, i.e. individuals with thicker masseter muscles had a wider maxillary dental arch. ' It is widely accepted that an interaction exists between masticatory muscle function and craniofacial growth. Studies have shown an association between the functional capacity of the masticatory muscles and craniofacial morphology. Individuals with a short facial configuration have high electromyographic activity/ bite force or vice versa.' Masticatory muscle function was found to influence the transverse growth of the skull at areas under direct muscle infl.uence.2 Muscle thickness had a Significantly negative relation with anterior facial height and mandibular length, and a significantly positive relation