Anatomical Characteristics of the Masseter Muscle in Mandibular Prognathism

Round 1

Reviewer 1 Report

Interesting research upon the masseter morphology in relation to the mandibular structure in patients affected by mandibular prognathism.

In Materials and Methods it could be useful to specify whether patients with a normally developed mandible and maxillary retrusion are considered as affected by mandibular prognathism; please, also indicate the number of patients in these groups.

In this case, it should be indicated whether results differ as per the studied elements between one type of patients and the other.

Potentially, whether considered opportune, provide an explanation of the results obtained between groups.

Some minor English reviews are suggested (at line 198 perhaps 'prognostic' is used instead of prognathic).

Author Response

Interesting research upon the masseter morphology in relation to the mandibular structure in patients affected by mandibular prognathism.

In Materials and Methods it could be useful to specify whether patients with a normally developed mandible and maxillary retrusion are considered as affected by mandibular prognathism; please, also indicate the number of patients in these groups.

In this case, it should be indicated whether results differ as per the studied elements between one type of patients and the other.

Potentially, whether considered opportune, provide an explanation of the results obtained between groups.

Answer) As this study was to find difference between normal group and prognathic group, we didn’t include pseudo-prognathic patients who have normally developed mandible and maxillary retrusion. Patients who were categorized in true prognathism with both Steiner’s analysis and Delaire’s analysis were included. To clarify this, we changed and complemented material and methods part.

Group classification The participants were divided into two groups according to the Steiner’s analysis and the Delaire’s analysis. In Steiner’s analysis, we calculated the sella-nasion-A point angle (SNA), sella-nasion-B point angle (SNB), and the A point-nasion-B point angle (ANB). In Delaire’s analysis, we calculated the angle between C1 plane, which is a constructed horizontal reference plane, and Me-based F1 plane, which is a naso-fronto-maxillary point to menton point [18]. These values were calculated on the midsagittal plane of the 3D CT image. The participants with normal SNB value and normal C1-Me-based F1 angle were classified into the normal group (n= 30, 15 males and 15 females) and participants with high SNB values and high C1-Me-based F1 angle were classified as the prognathic group (n= 30, 15 males and 15 females). Normal group showed 78.42 ± 0.76° of SNB, 86.82 ± 0.99° of C1-Me-based F1 in average, and prognathic group showed 83.59 ± 1.07° of SNB and 92.63 ± 1.07° of C1-Me-based F1 in average (mean ± standard deviation). The age range of the normal group participants was 18 to 29 years (mean age 22.4 ± 3.4) while that for the prognathic group was 18 to 27 years (mean age 21.0 ± 2.7).

Some minor English reviews are suggested (at line 198 perhaps 'prognostic' is used instead of prognathic).

Answer) Thank you for the comment. We corrected the word.

Comparison of the normal group and prognathic group masseter muscle ratio There was a significant difference in masseter size between normal and prognathic individuals.

 

Author Response File: Author Response.docx

Reviewer 2 Report

In my opinion, the work is interesting, but not necessarily innovative (see: 1). The research methodology was new, as CT was used, while the results were predictable and consistent with earlier studies. Moreover, the authors did not specify the selection of patients in terms of vertical dimensions of the face, which has a significant impact on the results. I also have doubts about counting patients with decreased SNA angle (when it comes to the combination of decreased SNA with increased SNB), because it is called pseudo-prognathism (see: 2).

1. 2020: Correlation between mandibular morphology and masticatory muscle thickness in normal occlusion and mandibular prognathism. Tae-Ho Kim, Chul-Hwan Kim. Conclusion: The results suggest a positive correlation of the thickness of masticatory muscles with both horizontal and vertical dimensions of the mandible. However, thickness of the masseter was found to decrease in patients with increasing severity of mandibular prognathism.)
2. Edlira Zere,Prabhat Kumar Chaudhari, Jitendra Sharan,Kunaal Dhingra, Nitesh Tiwari. Developing Class III malocclusions: challenges and solutions: Further, Charles Henry Tweed classified Class III malocclusions as a pseudo Class III malocclusion with normal mandible and underdevelopment of maxilla (category A) and skeletal Class III malocclusion with prognathic mandible or an underdevelopment of maxilla (category B).

Author Response

In my opinion, the work is interesting, but not necessarily innovative (see: 1). The research methodology was new, as CT was used, while the results were predictable and consistent with earlier studies. Moreover, the authors did not specify the selection of patients in terms of vertical dimensions of the face, which has a significant impact on the results.

1. 2020: Correlation between mandibular morphology and masticatory muscle thickness in normal occlusion and mandibular prognathism. Tae-Ho Kim, Chul-Hwan Kim. Conclusion: The results suggest a positive correlation of the thickness of masticatory muscles with both horizontal and vertical dimensions of the mandible. However, thickness of the masseter was found to decrease in patients with increasing severity of mandibular prognathism.)

Answer) It is true that vertical dimension is one of the important topics. There are many studies on the relationship between vertical dimension and mandibular morphology or surrounding soft tissues. However, in this study, we tried to focus on the difference on masseter muscle between normal group and prognathic group, following our previous study. (Mun, S.H.; Park, M.; Lee, J.; Lim, H.J.; Kim, B.C. Volumetric characteristics of prognathic mandible revealed by skeletal unit analysis. Annals of anatomy = Anatomischer Anzeiger : official organ of the Anatomische Gesellschaft 2019, 226, 3-9.) Thereby, we added a paragraph about the vertical dimension in discussion section.

There are many studies on whether vertical dimension affects the mandibular morphology and masticatory muscles. Kim et al. showed a positive correlation between the thickness of masticatory muscle and vertical dimension of the mandible [36]. Choi et al. suggested that the patients with higher mandibular plane angle showed an increase in the thickness of the soft tissue pogonion after bimaxillary surgery [37]. On the other hand, Lee et al. showed that the vertical facial types do not cause any differences in relapse after mandibular setback surgery [38]. Like this, vertical dimension is one of the important topics in this field. However, in our study, we focused on the difference on masseter muscle between normal and prognathic group, following our previous study [15]. Further studies considering vertical dimension would be needed.

 

I also have doubts about counting patients with decreased SNA angle (when it comes to the combination of decreased SNA with increased SNB), because it is called pseudo-prognathism (see: 2).

2. Edlira Zere,Prabhat Kumar Chaudhari, Jitendra Sharan,Kunaal Dhingra, Nitesh Tiwari. Developing Class III malocclusions: challenges and solutions: Further, Charles Henry Tweed classified Class III malocclusions as a pseudo Class III malocclusion with normal mandible and underdevelopment of maxilla (category A) and skeletal Class III malocclusion with prognathic mandible or an underdevelopment of maxilla (category B).

Answer) As the aim of this study was to find the difference between normal group and prognathic group, we actually didn’t include pseudo-prognathic cases. However, we had an error in writing the group classification part. We only chose patients who met the criteria of true prognathism of both Delaire’s analysis and Steiner’s analysis. Thereby, we changed and complemented our material and methods part.

Group classification The participants were divided into two groups according to the Steiner’s analysis and the Delaire’s analysis. In Steiner’s analysis, we calculated the sella-nasion-A point angle (SNA), sella-nasion-B point angle (SNB), and the A point-nasion-B point angle (ANB). In Delaire’s analysis, we calculated the angle between C1 plane, which is a constructed horizontal reference plane, and Me-based F1 plane, which is a naso-fronto-maxillary point to menton point [18]. These values were calculated on the midsagittal plane of the 3D CT image. The participants with normal SNB value and normal C1-Me-based F1 angle were classified into the normal group (n= 30, 15 males and 15 females) and participants with high SNB values and high C1-Me-based F1 angle were classified as the prognathic group (n= 30, 15 males and 15 females). Normal group showed 78.42 ± 0.76° of SNB, 86.82 ± 0.99° of C1-Me-based F1 in average, and prognathic group showed 83.59 ± 1.07° of SNB and 92.63 ± 1.07° of C1-Me-based F1 in average (mean ± standard deviation). The age range of the normal group participants was 18 to 29 years (mean age 22.4 ± 3.4) while that for the prognathic group was 18 to 27 years (mean age 21.0 ± 2.7).

 

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript is coherent and concise. It is divided properly into the standard sections (introduction, material and methods, results, discussion and conclusions). The number of references is relevant to the subject of research.

The originality of the study should be appreciated because it likely sheds a light on the interdependence between mandibular development and the function of masticatory muscles.

 I suggest publication after the authors have considered the comments above and the following minor remarks:

Abstract

The abstract summarizes the main aspects of the manuscript and precisely indicates the aim of the study. In line 24 should include “head of the masseter ” after mentioning superficial and deep (parts of the whole muscle).

Introduction

 

Line 39-40: I recommend to rewrite that sentence:

 “All the units are influenced by  the surrounding functional matrix; the soft tissue such as the masseter muscle and the lateral pterygoid muscle” - are the muscles the only part of functional matrix? And  what the term “functional matrix” actually mean?

Line 43 – what is exactly the association between the shape of mandible and the muscle force?

Line 46  I suggest that “the vertical craniofacial morphology” should be developed by mentioning the terms such as brachyfacial, mesofacial or dolichofacial types of vertical pattern.

Line 56 – it should be mentioned that all of the masticatory muscles are bilateral (so actually there are 8 of them)

Line 62- what the words “the former” and the “the latter” refer to?

 

Material and methods

• The methodology of 3D digital measurements in performed well. However the question arises how the patients were actually selected? The authors clearly explained the including and excluding criteria, however:

-why the age between 18-29 was chosen?

-what does the “normal mandible” actually mean ?– it was based on clinical examination and standard 2D cephalograms? Which cephalometric measurements were taken into consideration? And after that first selection the most “representative” participants were chosen? The same question I see according to the control group – participants with prognathic mandible and their qualification to the study.

• Line 88: While the anterio-posterior measurements according to Steiner analysis (SNA, SNB)  are widespread and well-known, the measurement “C1-Me-based F1” from 3D  Delarie’s cephalometric analysis should be better explained
• Line 93 why participants with high SNB values participants with low SNA values were classified to the same group meaning “the mandibular prognathism:? Low SNA value is not the indicator of mandibular prognathism, but suggests the retrognathic maxilla. Are these “low SNA” patients exhibit high SNB values?
• The average cephalometric findings in each of the group should be presented
• Line 97 and line 111 unnecessary space and dot between  3 . D

 

Discussion

Line 253 should be “we analyzed”

Line 266 what the term “small jaw angled” means? It should be written more precisely

Conclusions

Line 309 should be superficial and deep head of the masseter

 

To sum up suggest publication after the authors have considered the comments above.

 

Author Response

The manuscript is coherent and concise. It is divided properly into the standard sections (introduction, material and methods, results, discussion and conclusions). The number of references is relevant to the subject of research.

The originality of the study should be appreciated because it likely sheds a light on the interdependence between mandibular development and the function of masticatory muscles.

 I suggest publication after the authors have considered the comments above and the following minor remarks:

Abstract

The abstract summarizes the main aspects of the manuscript and precisely indicates the aim of the study. In line 24 should include “head of the masseter” after mentioning superficial and deep (parts of the whole muscle).

Answer) Thank you for the comment. We added the words.

In addition, the orientation of both superficial and deep head of the masseter of the participants in the normal group was more vertical with respect to the mandibular plane than that of the prognathic group (p < 0.05).

 

Introduction

 

Line 39-40: I recommend to rewrite that sentence:

 “All the units are influenced by the surrounding functional matrix; the soft tissue such as the masseter muscle and the lateral pterygoid muscle” - are the muscles the only part of functional matrix? And what the term “functional matrix” actually mean?

Answer) Functional matrix a concept proposed by Moss. It includes all the soft tissues surrounding the bone. Moss suggested that the growth of bone is regulated by this surrounding soft tissues.

To clarify this, we rewrote the sentences

In 1968, Moss first described the functional units of the mandible to be composed of symphysis, body, angle, coronoid, and dentoalveolus [5]. He proposed the concept of functional matrix, which is the soft tissue surrounding the bone, and that functional matrix regulates the growth of bone [6].

 

Line 43 – what is exactly the association between the shape of mandible and the muscle force?

Answer) Sella-Tunis et al. showed that wider mandibular shape is associated with larger masticatory muscle force.

To clarify, we complemented the sentence.

Sella-Tunis et al. showed that wider mandibular shape is associated with larger masticatory muscle force

 

Line 46  I suggest that “the vertical craniofacial morphology” should be developed by mentioning the terms such as brachyfacial, mesofacial or dolichofacial types of vertical pattern.

Answer) Thank you for the comment. We changed the terms.

Gionhaku and Kiliaridis described the relationship between brachycephalic morphology and large masticatory muscles

 

Line 56 – it should be mentioned that all of the masticatory muscles are bilateral (so actually there are 8 of them)

Answer) Thank you for the comment. We changed the sentence.

There are four bilateral masticatory muscles, and the masseter muscle is one of them.

 

Line 62- what the words “the former” and the “the latter” refer to?

Answer) As the force has magnitude and direction, we investigated volume/length ratio to estimate the magnitude and orientation to estimate the direction. The former refers to volume/length ratio of the muscle and the latter refers to the orientation of the muscle.

 

Material and methods

• The methodology of 3D digital measurements in performed well. However the question arises how the patients were actually selected? The authors clearly explained the including and excluding criteria, however:

-why the age between 18-29 was chosen?

Answer) We wanted to analyze patients after growth period as this study is to see how the surrounding muscles affected the growth of mandible. However, because other factors such as environment will affect overtime, we set the maximum of 29 years old.

-what does the “normal mandible” actually mean? – it was based on clinical examination and standard 2D cephalograms? Which cephalometric measurements were taken into consideration? And after that first selection the most “representative” participants were chosen? The same question I see according to the control group – participants with prognathic mandible and their qualification to the study.

Answer) We didn’t intentionally choose the patients. We just set our criteria according to 3D analysis based on Delaire’s and Steiner’s analysis, and collected the CT images of visiting patients. However, as the effects of the gender was so obvious, we at least tried to match the gender ratio. 

• Line 88: While the anterio-posterior measurements according to Steiner analysis (SNA, SNB) are widespread and well-known, the measurement “C1-Me-based F1” from 3D Delarie’s cephalometric analysis should be better explained

 

Answer) Thank you for the comment. We changed and added sentences about the Delarie’s analysis.

The participants were divided into two groups according to the Steiner’s analysis and the Delaire’s analysis. In Steiner’s analysis, we calculated the sella-nasion-A point angle (SNA), sella-nasion-B point angle (SNB), and the A point-nasion-B point angle (ANB). In Delaire’s analysis, we calculated the angle between C1 plane, which is a constructed horizontal reference plane, and Me-based F1 plane, which is a naso-fronto-maxillary point to menton point [18].

 

• Line 93 why participants with high SNB values participants with low SNA values were classified to the same group meaning “the mandibular prognathism:? Low SNA value is not the indicator of mandibular prognathism, but suggests the retrognathic maxilla. Are these “low SNA” patients exhibit high SNB values?

 

Answer) As our goal was to compare the masseter muscle between normal group and prognathic group, we only included patients with true mandibular prognathism, not the pseudo-prognathism. However, we had an error in writing the group classification section. We corrected the sentence as below.

 

These values were calculated on the midsagittal plane of the 3D CT image. The participants with normal SNB value and normal C1-Me-based F1 angle were classified into the normal group (n= 30, 15 males and 15 females) and participants with high SNB values and high C1-Me-based F1 angle were classified as the prognathic group (n= 30, 15 males and 15 females).

 

• The average cephalometric findings in each of the group should be presented

 

Answer) As we used CT images to classify patients, our data was based on CT images using Steiner’s analysis and Delaire’s analysis. In result, normal group showed 2.35 ± 0.55 of ANB, 78.42 ± 0.76 of SNB, 86.82 ± 0.99 of C1-Me-based F1, and prognathic group showed -2.48 ± 0.60 of ANB, 83.59 ± 1.07 of SNB and 92.63 ± 1.07 of C1-Me-based F1.

We added those result to the Group classification section, however only SNB and C1-Me-based F1 data to avoid confusion on pseudo-prognathism.

 

Normal group showed 78.42 ± 0.76° of SNB, 86.82 ± 0.99° of C1-Me-based F1 in average, and prognathic group showed 83.59 ± 1.07° of SNB and 92.63 ± 1.07° of C1-Me-based F1 in average (mean ± standard deviation).

• Line 97 and line 111 unnecessary space and dot between 3 . D

 

 Answer) Thank you for the comment. We corrected the words.

3D CT and Segmentation 3D image reconstruction and revision

 

Discussion

Line 253 should be “we analyzed”

 Answer) We wanted to refer our previous study, that we analyzed the skeletal unit differences between normal group and prognathic group. (Mun, S.H.; Park, M.; Lee, J.; Lim, H.J.; Kim, B.C. Volumetric characteristics of prognathic mandible revealed by skeletal unit analysis. Annals of anatomy = Anatomischer Anzeiger : official organ of the Anatomische Gesellschaft 2019, 226, 3-9.)

Line 266 what the term “small jaw angled” means? It should be written more precisely

 Answer) Thank you for the comment. We changed the words to clarify.

This result corresponds to other studies that have elucidated that the masseter muscle is large in brachycephalic, short- faced, and narrow mandibular angled participants [27,28].

 

Conclusions

Line 309 should be superficial and deep head of the masseter

 Answer) Thank you for the comment. We added the words

The orientation of both superficial and deep head of the masseter of the participants in the normal group was more vertical with respect to the mandibular plane than that of the prognathic group.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear Authors,

Thank you for making the necessary corrections.