|Year : 2016 | Volume
| Issue : 4 | Page : 207-214
Influence of masseter muscle thickness on buccal corridor space and craniofacial morphology: A correlative study
Harneet Kaur1, Tulika Tripathi2, Priyank Rai3, Anju Garg4, Anup Kanase5
1 Asst. Prof., Department of Orthodontics, Faculty of Dentistry, Jamia Millia Islamia, New Delhi, India
2 Prof. and Head, Department of Orthodontics and Dentofacial Orthopaedics, Maulana Azad Institute of Dental Sciences, New Delhi, India
3 Prof., Department of Orthodontics and Dentofacial Orthopaedics, Maulana Azad Institute of Dental Sciences, New Delhi, India
4 Director Prof. Deparment of Radiodiagnosis, Maulana Azad Medical College, New Delhi, India
5 Prof., Dentofacial Orthopaedics, Faculty of Dentistry, Jamia Millia Islamia, New Delhi, India
|Date of Submission||23-May-2016|
|Date of Acceptance||04-Jul-2016|
|Date of Web Publication||19-Oct-2016|
Department of Orthodontics and Dentofacial Orthopaedics, Maulana Azad Institute of Dental Sciences, New Delhi
Source of Support: None, Conflict of Interest: None
Purpose: The present study was designed to evaluate the influence of masseter muscle thickness on buccal corridor space and underlying craniofacial morphology. Materials and Methods: Forty-six young adults (23 males and 23 females) in the age group of 18–23 years having intact dentitions and Class I molar relationship were included in the study. Masseter muscle thickness was measured using ultrasonography in relaxed, smiling, and contracted states. Posed smile photographs were taken to measure the buccal corridor space. Standardized frontal and lateral cephalograms were taken to determine craniofacial morphology in all three dimensions. Results: The mean masseter muscle thickness was 10.54 (±1.92) mm, 12.00 (±2.06) mm, and 14.04 (±1.99) mm in relaxed, smiling, and contracted states, respectively. Statistically significant correlation also was noted between masseter muscle thickness, during contracted state and buccal corridor width ratio. There was a strong association of masseter muscle thickness on both vertical as well as transverse craniofacial morphologies. Conclusions: Masseter muscle thickness is positively correlated with the buccal corridor width and influences both vertical as well as transverse facial dimensions.
Keywords: Buccal corridor space, craniofacial morphology, masseter muscle thickness, posed smile, ultrasonography
|How to cite this article:|
Kaur H, Tripathi T, Rai P, Garg A, Kanase A. Influence of masseter muscle thickness on buccal corridor space and craniofacial morphology: A correlative study. J Indian Orthod Soc 2016;50:207-14
|How to cite this URL:|
Kaur H, Tripathi T, Rai P, Garg A, Kanase A. Influence of masseter muscle thickness on buccal corridor space and craniofacial morphology: A correlative study. J Indian Orthod Soc [serial online] 2016 [cited 2018 Aug 16];50:207-14. Available from: http://www.jios.in/text.asp?2016/50/4/207/192607
| Introduction|| |
Physical attractiveness plays an important role in how we view ourselves and how we are viewed by others. Dentofacial attractiveness is a major determinant of overall physical attractiveness. Individuals mainly focus on other people's eyes and mouths during the interpersonal interaction, with little time spent on other facial features. In the mind of the general public, the smile ranks second only to the eyes as the most important feature in facial attractiveness.
One of the more controversial aspects of smile attractiveness pertains to buccal corridor size, defined variably as the space between the buccal surfaces of the maxillary teeth and the corners of the mouth during a smile. Assuming that small buccal corridors make a smile more attractive, orthodontic expansion has been proposed to improve smile attractiveness.
Recently, muscle thickness has been considered as one of the indicators of jaw muscle function. Among the group of masticatory muscles, the masseter seems to represent the functional capacity of the masticatory apparatus.,,,,,, Moreover, the superficial position of the masseter allows easy access for application of quantitative measurements, such as ultrasonography.
In recent years, ultrasonography has spread throughout different fields of medicine. For clinical evaluations, ultrasonography has several advantages over computed tomography (CT) and magnetic resonance imaging (MRI). The equipment is portable and can be handled easily. It is rapid, inexpensive, noninvasive technique, and has no cumulative biological effect. Several studies have shown that this method of measuring muscle thickness is as accurate as CT and MRI.,,
By far, no study so far correlates masseter muscle thickness with buccal corridor space. Since masseter muscle has an effect on craniofacial morphology, which in turn has been shown to influence buccal corridor space area, it was hypothesized that increase in masseter muscle thickness has some influence on buccal corridor space and hence smile esthetics.
The aim of the present study was to find out in a group of young individuals, the correlation between masseter muscle thickness and buccal corridor space.
| Materials and Methods|| |
The study was conducted on 46 young adults (23 males and 23 females) within the age group of 18–23 years. All subjects had Angle's Class I molar relationship intact dentitions with all permanent teeth present up to the second molars and no history of previous orthodontic treatment. None of them had any congenital/acquired facial anomaly or marked facial asymmetry, determined clinically or radiographically.
The thickness of masseter muscle was measured by the single operator using a real-time ultrasound scanner (Philips Envisor, Philips Medical Systems) with a high-resolution 12 MHz linear array transducer (L12-3). The imaging and measurements were performed bilaterally with the subjects seated in upright position and Frankfort horizontal plane parallel to the floor. The site of measurement was the thickest part of masseter close to the level of occlusal plane, ensuring that the transducer is oriented perpendicular to the mandibular ramus. Scanning the masseter obliquely would increase the thickness of the muscle. A generous amount of gel was applied under the transducer to avoid compression of the tissues [Figure 1]. The measurements were taken under three different conditions: Muscle in relaxation, muscle in posed smile, and muscle during maximal contraction (clenching) [Figure 2]. Measurements were done with at least 5 min interval between the two recordings. The measurements were taken directly from the image at the time of scanning with a read-out distance nearest to 0.01 mm.
|Figure 2: Masseter muscle thickness recorded with ultrasonography. (a) Masseter muscle thickness in relaxed state thickness = 0.89 mm. (b) Masseter muscle thickness in smiling state thickness = 1.18 mm. (c) Masseter muscle thickness in contracted state thickness = 1.31 mm|
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Standardized lateral and frontal cephalograms were obtained for all subjects. Using a sharp 3H pencil, the radiographs were traced by a single operator (H.K.) on a mat 36 μ acetate paper. On lateral cephalograms, various linear and angular measurements [Figure 3] were taken to study craniofacial morphology in vertical and sagittal dimensions. On frontal cephalograms, linear measurements [Figure 4] were taken to study craniofacial morphology in transverse dimensions. Standardized posed smile photographs were taken using Canon EOS 500D DSLR camera. The subjects were positioned with Frankfort horizontal plane parallel to the floor. The imaginary center of the subjects' face was aligned to the vertical line of the view finder, and both sides of the subjects' ears were showing to the same amount to prevent transverse rotation. Since the buccal corridor can be seen differently according to different light conditions, all photographs were under standardized light conditions to get actual buccal corridor area. The camera was positioned at a standard distance of 2 feet from the subject. Full frontal facial photographs of the subjects were taken. The photographs were transferred to the computer. Using Adobe Photoshop 7.0 Software (Adobe systems, California, United States), the mouth area of the photographs was cropped using 3 × 5 inch grids with the smile remaining within vertical (nose tip to soft tissue pogonion) and transverse (perpendiculars drawn from zygomatic prominences on both sides) limits. These photographs were then enlarged to the standard resolution of 300 pixels for measurement of buccal corridor space.
For calculation of buccal corridor, following measurements were taken in 0.01 mm units with the linear measuring tool in Adobe Photoshop 7.0 software.
- Buccal corridor linear ratio (BCLR) [Figure 5]: This was calculated as follows:
- Buccal corridor width ratio (BCWR) [Figure 6]: This was calculated as follows:
Descriptive statistical analysis including arithmetic mean and standard deviation was calculated for masseter muscle thickness (in relaxed, smiling, and contracted states), craniofacial morphology (in vertical, sagittal, and transverse dimensions), and buccal corridor space (BCLR and BCWR). Differences among the means of masseter muscle thickness in relaxed (MMTr), masseter muscle thickness in smiling (MMTs), and masseter muscle thickness in contracted states (MMTc) were measured by analysis of variance (ANOVA) test followed by Bonferroni post hoc tests. The difference between the sexes for the MMTr, MMTs, and MMTc as well as for the variables for buccal corridor space was measured using t-test. Association between MMTr, MMTs, MMTc, craniofacial morphology (in vertical, sagittal, and transverse dimensions), and buccal corridor space (BCLR and BCWR) was observed by Pearson's correlation coefficient. P < 0.05 was considered a statistically significant level.
| Results|| |
The mean masseter muscle thickness in all subjects was 10.54 (±1.92) mm, 12.00 (±2.06) mm, and 14.04 (±1.99) mm in relaxed, smiling, and contracted states, respectively. The mean masseter muscle thicknesses were found to be least in relaxed state, higher in smiling, and maximum in contracted state [Table 1] and [Graph 1 [Additional file 1]].
|Table 1: Mean and standard deviation for masseter muscle thickness for all subjects in relaxed, smiling, and contracted states|
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There is statistically significant difference among the means of MMTr, MMTs, and MMTc as shown by ANOVA test with F being 28.402, P < 0.001 [Table 2]. Comparison between the groups was done by Bonferroni post hoc test [Table 3].
|Table 2: Difference between mean masseter muscle thickness in relaxed, smiling, and contracted states (n=46)|
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|Table 3: Bonferroni post hoc test performed for comparison between masseter muscle thickness in relaxed, smiling, and contracted states (n=46)|
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The mean masseter muscle thickness in females was 9.7 (±1.3) mm, 11.2 (±1.4) mm, and 13.0 (±1.4) mm in relaxed, smiling, and contracted states, respectively [Graph 2 [Additional file 2]]. The mean masseter muscle thickness in males was 11.7 (±2.1) mm, 12.8 (±2.3) mm, and 15.1 (±2.0) mm in relaxed, smiling, and contracted states, respectively. Masseter muscle thicknesses in all states were higher in males than females in each state. Furthermore, there is statistically significant difference between the sexes for the MMTr, MMTs, and MMTc as shown by the t-test [Table 4].
|Table 4: Mean, standard deviation, and t-test between sexes for mean masseter muscle thickness in relaxed, smiling, and contracted states|
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The mean linear vertical craniofacial morphology (total anterior facial height [TAFH], total posterior facial height [TPFH], and lower anterior facial height [LAFH]) and transverse craniofacial morphology was more in males as compared to females. The angular values for vertical craniofacial morphology (Frankfort-mandibular plane angle [FMA], Gonial angle [GA]) were lesser in males showing that males have lesser divergence of the mandible and are more horizontal growers. The mean values for sagittal craniofacial morphology (ANB) show an average Class I skeletal pattern among the subjects [Table 5].
|Table 5: Mean and standard deviation for craniofacial morphology in vertical, sagittal, and transverse dimensions for n=46 (23 females and 23 males)|
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The mean value for BCLR in all subjects was 61.40 ± 4.60%, and the mean value for BCWR was 17.85 ± 3.79%. The mean values for BCLR were 62.35 ± 4.53% in females and 60.73 ± 4.29% in males. The mean values for BCWR were 16.88 ± 3.40% in females and 18.50 ± 3.65% in males. The mean values for BCLR were higher in females than males while those for BCWR were more in males. These values suggest more amount of buccal corridor space in males as compared to females. However, there is no statistically significant difference among sexes for the variables for buccal corridor space as shown by t-test [Table 6] and [Graph 3 [Additional file 3]].
|Table 6: Mean, standard deviation, and t-test between sexes for buccal corridor linear ratio and buccal corridor width ratio|
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The MMTr, MMTs, and MMTc correlated significantly and positively with linear measurements for vertical craniofacial morphology (TAFH, TPFH, and LAFH), as well as with measurements for transverse craniofacial morphology bizygomatic width (Za-Za), maxillary width (J-J), and mandibular width (Ag-Ag) as shown by the Pearson rank correlation tests. However, the correlation between MMTr, MMTs, and MMTc and angular measurements for vertical craniofacial morphology (FMA, GA) was negative but statistically not significant. Furthermore, no significant correlation was observed between the masseter muscle thickness in any state and sagittal craniofacial morphology (ANB) [Table 7].
|Table 7: Pearson rank correlation (two-tailed) of masseter muscle thickness (in relaxed, smiling, and contracted states) with craniofacial morphology (in vertical, sagittal, and transverse dimensions)|
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The Pearson rank correlation tests showed that there was a significant positive correlation between the BCWR and mandibular width. Furthermore, there was significant correlation observed between the BCWR and bizygomatic width (Za-Za) and maxillary width (J-J), but only in females. No significant correlation was observed between the BCLR and masseter muscle thickness in any state. There was no significant correlation between BCLR and vertical or sagittal craniofacial morphology [Table 8].
|Table 8: Pearson rank correlation of buccal corridor space (buccal corridor linear ratio and buccal corridor width ratio) with masseter muscle thickness (in relaxed, smiling, and contracted states) and craniofacial morphology (in vertical, sagittal, and transverse dimensions)|
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| Discussion|| |
The contemporary orthodontic practice involves techniques based on many biomechanical principles that effect favorable changes in the dentofacial complex. However, it also requires an awareness of craniofacial muscle environment of each patient and how this musculature affects the etiology, treatment, and stability after treatment of malocclusions and jaw deformities. Hence, the present study was undertaken with the aim of determining the correlation between the masseter muscle thickness and buccal corridor space.
Masseter muscle thickness
Ultrasonography is used for the measurement of muscle thickness in experimental and clinical studies and is confirmed to be a reliable procedure., In the present study, a strict protocol was followed regarding the methodology of ultrasound. The subjects were made to sit in an upright position with their heads in a natural position or their Frankfort horizontal plane parallel to the floor.,, Recording the ultrasonography in sitting position, minimized the variability between postures during the posed smile while taking ultrasonography as well as photographs. The masseter muscle ultrasonography was carried out in each state as described by Kubota et al., with a light feather-like pressure applied during measurement, so that the applied pressure may not reduce the thickness of muscle. Furthermore, a generous amount of gel was used under the probe to avoid tissue compression. In this study, the ultrasonographic recordings were made while orienting the transducer perpendicular to the ramus angle of scanning was altered until the best echo of mandibular ramus was achieved. Scanning the masseter obliquely would have increased the thickness of the muscle. The site of measurement was in the thickest part of masseter muscle close to the occlusal plane, half-way between zygomatic arch and GA, approximately at the center of the mediolateral distance of the ramus; this method was consistent with many studies.,,
In the present study, the mean masseter muscle thicknesses were found to be least in relaxed state (10.54 ± 1.92 mm), higher in smiling (12.00 ± 2.06 mm), and maximum in contracted state (14.04 ± 1.99 mm). When a muscle is contracted, there is sliding of the muscle fibers and increase in fiber diameter that causes thickening. This change can be observed concomitant with the start of contraction and it shows a large value. Another cause of increase in muscle size while contracting for long periods would be an edematous change of muscle. Thus, an increase in muscle thickness during smiling suggests some amount of masseter muscle activity during smiling.
The thickness of masseter muscle in male adults was found to be greater than females, in all the three states. This is in accordance with previous studies.,,, The observed difference may be due to the result of natural sexual dimorphism, differences in total muscle mass, creatinine excretion, numbers of muscle nuclei, and limb muscle size, males having slightly higher values than females. Furthermore, these differences may be accentuated by the difference in facial morphology between the sexes in the study. Males had more tendencies to shorter (lower mandibular plane angle, FMA) and broader (more bizygomatic width, Za-Za) face than females.
Buccal corridor space, masseter muscle thickness, and craniofacial morphology
The buccal corridor is an important feature in smile esthetics. It is the space between the most visible maxillary posterior teeth and the lip commissure when the patient is smiling.,
The mean values for BCLR were more in females (62.35 ± 4.53%) than males (60.73 ± 4.29%) while those for BCWR were more in males (18.50 ± 3.65%) as compared to 16.88 ± 3.40% in females. These values implied that there is more buccal corridor space in males as compared to females although the difference was not statistically significant. This is in accordance with those observed by Ritter et al. who found more amount of buccal corridor space in males as compared to females.
Significant negative correlation was noted between the BCWR and transverse dimensions of arch width suggesting a decrease in buccal corridor space with an increase in arch width. However, this correlation was significantly more in females than males.
Since masseter muscle has an effect on craniofacial morphology, which in turn has been shown to have some influence on buccal corridor space, there may be some association between the masseter muscle thickness and buccal corridor space. By far, no study so far tries to find out this association. The present study shows a positive correlation between BCWR and masseter muscle thickness in contracted state. This corresponds to the earlier findings in the study where masseter muscle thickness increased during smiling state.
However, the further scope of this investigation is to conduct a study on a larger sample preferably selected on the basis of skeletal features.
| Conclusions|| |
The results of the present study suggest that:
- The difference between the MMTr, MMTs, and MMTc was significant with the thickness being least in relaxed state, increased during smiling, and maximum when contracted
- There was a strong influence of masseter muscle thickness on both vertical as well as transverse craniofacial morphologies
- Males showed a statistically larger buccal corridor than females, yet the percentage difference was not significant
- Statistically significant correlation was noted between masseter muscle thickness during contracted state and buccal corridor width.
Clinical relevance of the study
In our present investigation, correlations were observed between masseter muscle thickness, arch width, and buccal corridor space. This is important in assessing the amount of buccal corridors that can be utilized on during arch expansion, especially in dolichofacial patients who have thin masseter muscles. Thin masseter muscle does not provide adequate contraction thereby reducing the buccal corridor. Hence, overexpansion in canine-premolar regions in these patients might lead to “denture smile” which appears unaesthetic, especially in young individuals.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]