Indian Journal of Dental Research

ORIGINAL RESEARCH
Year
: 2010  |  Volume : 21  |  Issue : 3  |  Page : 402--407

Masseter muscle thickness in different skeletal morphology: An ultrasonographic study


Sushma Rani, MS Ravi 
 Department of Orthodontics, A.B. Shetty Memorial Institute of Dental Sciences, Mangalore, India

Correspondence Address:
M S Ravi
Department of Orthodontics, A.B. Shetty Memorial Institute of Dental Sciences, Mangalore
India

Abstract

Background: The thickness of the masseter muscle during relaxation and contraction states was measured by ultrasonography. Subjects were classified according to their sagittal skeletal relationships. The association between muscle thickness and facial morphology was studied. Context: Masseter muscle thickness influences the skeletal patterns. Aim: To measure and compare the thickness of the masseter muscle in individuals with skeletal class I occlusion and skeletal class II malocclusions and to correlate its relationship with craniofacial morphology. Settings and Design: The study was conducted in a hospital setup and was designed to study the thickness of the masseter muscle in different skeletal morphologies. Materials and Methods: Seventy two individuals between the ages of 18 and 25 years were divided into Group I, Group IIA and Group IIB according to their skeletal relationships. Masseter muscle thickness was measured by ultrasonography. Eight linear and six angular cephalometric measurements were assessed. Statistical Analysis Used: Analysis of variance and Pearson«SQ»s correlation analysis. Results: There was a statistically significant difference in muscle thickness between subjects of different skeletal patterns. Significant positive correlation between masseter muscle thickness and posterior total face height, jarabak ratio, ramus height, mandibular length and significant negative correlations with mandibular plane angle, gonial angle and PP-MP angle were observed. Conclusion: This study indicates the strong association between the masseter muscle and skeletal morphology.



How to cite this article:
Rani S, Ravi M S. Masseter muscle thickness in different skeletal morphology: An ultrasonographic study.Indian J Dent Res 2010;21:402-407


How to cite this URL:
Rani S, Ravi M S. Masseter muscle thickness in different skeletal morphology: An ultrasonographic study. Indian J Dent Res [serial online] 2010 [cited 2014 Oct 30 ];21:402-407
Available from: http://www.ijdr.in/text.asp?2010/21/3/402/70812


Full Text

The effects of muscle thickness on bone morphology can be explained by Wolff's law. This law states that the internal structure and the shape of the bone are closely related to the bone's function and it also defines a relationship between the bone's shape and muscle function. In order to describe facial morphology, the structure of the facial muscles should be thoroughly investigated to determine the pattern of interaction of the skeleton and the muscles. [1]

Recently, muscle thickness has been considered as one of the indicators of jaw muscle function. [2] This report indicated that muscle thickness was significantly correlated with maxillofacial morphology. [2] The influence of masticatory muscle function on craniofacial growth has been recorded in a series of experimental animal and clinical studies. [1],[2],[3],[4] The common characteristic of these investigations is that the elevator muscles of the mandible influence the transverse and the vertical dimensions of the face.

Masseter muscle thickness has been measured by various imaging techniques, including ultrasound scanning, computerized tomography (CT) and magnetic resonance imaging (MRI). [5] In recent years, the development of ultrasonography has proven to be a reproducible, simple and inexpensive method for accurately measuring muscle thickness. [5] This study was carried out with the aim of measuring the thickness of the masseter muscle in individuals with skeletal class I occlusions and comparing it with skeletal class II individuals using ultrasonography.

 Materials and Methods



Seventy-two individuals between the ages of 18 and 25 years were divided into Group I, Group IIA and Group IIB according to skeletal relationships as measured by lateral cephalometric parameters, SNA, SNB, ANB, NA and NB.

Each group consisted of 24 individuals with a 1:1 male-female ratio [Table 1].{Table 1}

Ultrasound procedures

All scans were performed using a LOGIQ 400 PROSERIES scanner (GE Medical systems,Milwaulkee, USA)using a multifrequency 7.5-11.0 MHZ broadband transducer. A water-based gel was applied to the probe before the imaging procedure. During imaging, the transducer was held perpendicular to the surface of the skin and care was taken to avoid excessive pressure. The imaging and measurements were performed bilaterally with the subjects in a supine position under two different conditions:



When teeth are occluding gently with muscle in a relaxed position [Figure 1]During maximal clenching with the masseter muscle contracted [Figure 2]{Figure 1}{Figure 2}

The measurements were made directly from the image at the time of scanning.

Measurements on lateral cephalometric radiographs

All lateral cephalograms were obtained under standardized conditions using a Planmeca PM 2002 cc Proline machine.(Planmeca OY, Helsinki, Finland). The cephalograms were traced onto an acetate paper. Angular and linear measurements were made up to an accuracy of 0.5 0 and 1 mm, respectively.

Six angular measurements and eight linear measurements were analyzed [Table 2]; [Figure 3] and [Figure 4].{Table 2}{Figure 3}{Figure 4}

Statistical measurement

Data obtained were statistically evaluated using analysis of variance and Pearson's correlation analysis.

 Results



Statistically significant difference in the masseter muscle thickness (both in relaxed and contracted state) was observed between Group I and Group IIB subjects [Table 3]. Males in skeletal class I and skeletal class II groups had thicker masseter muscle compared to females [Table 4].{Table 3}{Table 4}

In Group I subjects, there was a significant positive correlation between masseter muscle thickness (both in relaxed and contracted state) and posterior total face height (P=0.001, 0.005), ramus height (P = 0.0005, <0.0005) and mandibular length (P=0.001, 0.021) [Table 5]. There was a significant negative correlation between muscle thickness in the contracted state and mandibular plane angle (P=0.090, 0.007) [Table 6].{Table 5}{Table 6}

In Group IIA subjects, there was a significant positive correlation between muscle thickness (both in the relaxed and the contracted state) and posterior total face height(P = 0.0005, <0.0005), jarabak ratio, (P = 0.0005, <0.0005), ramus height (P = 0.0005, <0.0005), maxillary length(P=0.004, 0.005) and mandibular length (P=0.001, 0.001) [Table 7]. Significant negative correlations were noted between muscle thickness and mandibular plane angle(P= 0.001, <0.0005), lower gonial angle (P = 0.0005, <0.0005) and PP-MP angle (P = 0.0005, <0.0005) [Table 8].{Table 7}{Table 8}

In Group IIB subjects, there was a significant positive correlation between muscle thickness (both in the relaxed and in the contracted state) and ramus height(P=0.001,<0.0005) [Table 9]. Significant negative correlations were noted between muscle thickness (both in the relaxed and the contracted state) and mandibular plane angle (P=0.007, 0.001) as well as PP-MP angle (P=0.013, 0.004) [Table 10].{Table 9}{Table 10}

Pearson's correlation analysis for the entire sample revealed significant positive correlation between muscle thickness (both in the relaxed and the contracted state) and posteriortotal face height (P=0.001, 0.002), jarabak ratio (P = 0.0005, <0.0005), ramus height (P = 0.0005, <0.0005) and mandibular length (P = 0.0005, 0.002) [Table 11]. Significant negative correlations were observed with mandibular plane angle(P = 0.0005, <0.0005), lower gonial angle (P = 0.0005, <0.0005) and basal plane angle (P = 0.0005, <0.0005)[Table 12].{Table 11}{Table 12}

 Discussion



The results of the present study show variation in masseter muscle thickness during relaxation and contraction among individuals with different skeletal morphology. Individuals with skeletal class I jaw relationship had thicker muscles when compared to the skeletal class II subjects. Among skeletal class II subjects, those with maxillary excess had thicker masseter muscles compared to the subjects with mandibular deficiency.

Muscle thickness has been considererd as an indicator of jaw muscle function. [2] The significance of masticatory muscle function with regard to craniofacial growth has been proven by numerous clinical and experimental studies. They have suggested that bone shape and structure are closely related to the attached muscle activity. [2],[3]

The results of the present study suggest that the thickness of masseter muscle should be considerd as one of the factors affecting facial morphology. Similar findings were also reported by Weijs and Hillen, [4] Kiliaridis and Kalebo, [2] Benington et al., [6] Raadsheer et al. [7] and Satiroglu et al., [1] who observed a strong correlation between facial morphology and masseter muscle thickness. Masseter muscle thickness was found to be significantly correlated with vertical facial pattern and body mass index, showing that individuals with thicker masseter had a vertically shorter facial pattern. [1]

The entire sample of subjects in the present study had significant positive correlation between muscle thickness and posterior total face height, jarabak ratio, ramus height and mandibular length whereas these subjects had significant negative correlation between muscle thickness and mandibular plane angle, gonial angle and basal plane angle. Many studies have found a positive correlation between muscle thickness and ramus height and a negative correlation with mandibular plane angle. [3],[4],[7],[8],[9],[10]

The present study indicates that the thickness of the masseter muscle varies among individuals with different skeletal morphologies. These variations will have implications during treatment planning for orthodontic and orthognathic surgical cases. The variation in muscle thickness may also play a vital role in the retention and steability of the results obtained. Further studies in this regard are required.

Further studies are also required to investigate the association between other muscles of mastication and facial morphology.

 Conclusion



The ultrasonographic study has revealed variations in masseter muscle thickness among individuals with different skeletal morphologies. Significant positive correlations were also observed between masseter muscle thickness and various craniofacial parameters.

 Acknowledgment



The authors would like to thank Prof. Dr. U.S. Krishna Nayak, HOD, Department of Orthodontics and Dean (Academics), A.B.Shetty Memorial Institute of Dental Sciences, Mangalore and Prof. Dr. Rabindra Prabhu, HOD, Department of Radiology, K.S. Hegde Medical Academy, Mangalore for their support during the study. The authors would also like to thank the Indian Council of Medical Research (ICMR) for the financial support extended for the study.

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