Masticatory Muscle Volume Research Articles

Assessment of Masseter Volume and Postoperative Stability After Orthognathic Surgery in Patients With Skeletal Class III Malocclusion With Facial Asymmetry.

This study aimed to evaluate the effect of orthognathic surgery on masseter volume in patients with skeletal Class III malocclusion with facial asymmetry and the effect of masseter volume on stability in orthognathic surgery. This research studied 16 patients with Class III malocclusion with facial asymmetry who received combined orthodontic-orthognathic treatment and underwent craniofacial computed tomography (CT) before (T0), 2 weeks after (T1), and 6 months after (T2) surgery. Three-dimensional (3D) CT images were retrospectively analyzed, using 3D volume reconstruction to obtain the masseter volume and examine the impact of the masseter volume on stability in orthognathic surgery. A statistically significant difference ( P < 0.05) in the volume of the masseter was found up to 6 months after orthognathic surgery compared with the preoperative period, and the reduction in the masticatory muscle volume on the lengthened side is greater than on the shortened side ( P < 0.05). The volume of both masseters differed according to facial asymmetry, and the difference was significantly reduced after orthognathic surgery ( P < 0.05). During the period time (T1-T2), cephalometric maxillary marker points were not significantly different ( P > 0.05), and mandibular marker points were significantly anteriorly shifted ( P < 0.05). There was an association between the masseter volume and anterior shift of point B (R > 0.5, P < 0.05), the upward and anterior shifts of the gonion point differed between the lengthened and shortened sides ( P < 0.05). The size of the masseter becomes smaller 6 months after orthognathic surgery, and orthognathic surgery improves both bone and soft tissue symmetry. A larger sagittal relapse of mandibular setback occurred in patients with greater masseter volume. Considering these alterations may be helpful in planning orthognathic surgery.

Masseter muscle volume measured by MRI correlated with cognitive function in a memory clinic

AbstractBackground“Oral frailty” which indicates a decline in oral function, has been focused on the fact that it can also affect cognitive function in the elderly population. Although Several studies have been attempted for establishing the utility of the cross‐sectional area or volume of masticatory muscles as objective indices reflecting oral frailty, no report has examined the relationship between masticatory muscles volume and cognitive function in detail. In this study, we aimed to clarify the relationship between size of masseter muscle, one of major masticatory muscles, and cognitive function in the elderly.MethodA total of 349 subjects (mean age 77.3 +/‐ 9.2 years, 126 males and 223 females, 58 with subjective cognitive impairment, 88 with mild cognitive impairment, and 203 with dementia), who visited the Memory clinic of Tohoku University Hospital with a chief complaint of forgetfulness by March 2018 were included. Using 3D T1‐weighted images acquired on a 3‐Tesla MRI system, the bilateral masseter muscle cross‐sectional area was automatically calculated for all subjects using a custom deep‐learning image‐processing model trained on a subset of subjects to identify the relevant muscles and consistent section. Then, partial correlations with the MMSE score were conducted, adjusting for age and gender.ResultThe mean left and right masseter muscle cross‐sectional area are 399.3±84.7mm2 in subjective cognitive impairment, 387.9±106.5 mm2 in mild cognitive impairment, and 355.1±88.4 mm2 in dementia, respectively (p &lt; 0.01). Adjusted for age and sex, they showed a significant correlation with MMSE (R = 0.151, p &lt; 0.01). For post‐hoc stratified analysis, there was a significant correlation between mean masseter muscle cross‐sectional area and MMSE with female patients (R = 0.049, p &lt; 0.05), whereas no correlation with male patients after adjusted age (R = 0.025, p &gt; 0.05).ConclusionOur result revealed that the masseter muscle cross‐sectional area obtained from MRI may be related to cognitive function in the patients with complaint of forgetfulness. Therefore the masticatory function may reflect cognitive function in the elderly who are vulnerable in their memory, and the cross‐sectional area of masseter muscle based on MRI could be a potential indicator for predicting dementia risk.

Relation between masseter muscle volumes and mandibular body lengths in skeletal Class III adult female cases without severe mandibular asymmetry

ABSTRACT Objective As reported in our pilot study using skeletal Class III adult female cases without severe mandibular asymmetry (Kawajiri A, et al, Jpn J Jaw Deform. 2019;29:31-41), cranial vaults with unilateral posterior deformation had posteriorly positioned mandibular fossae on the same side, and the longer mandibular bodies were seen with more posteriorly-positioned mandibular fossae. These findings suggest that mandibular body length compensated the A-P position of the mandibular fossa to prevent facial asymmetry. However, the used subjects in our pilot study were selected by two-dimensional P-A cephalograms. Thus, as the first purpose, three-dimensional case selection was performed, and craniofacial structure was examined in subjects. As the second purpose, the relation between the mandibular body lengths and the masticatory muscle volume was examined. Materials and Methods CT images of 32 adult female patients with skeletal mandibular protrusion were used in this study. The lateral deviation of Pog was less than 3 mm in all cases. The 3D analysis was performed on CT images. The cranial vault shape, the position of the mandibular fossae and the length of the mandibular bodies were analyzed. The masseter and medial pterygoid muscles were reconstructed and analyzed. Results The present findings reproduced the results in our previous pilot study. The volume of the masseter muscles, but not the medial pterygoid muscles, had a significant positive correlation with the mandibular body lengths. Conclusion A novel mechanism for preventing mandibular asymmetry was proposed. Both hard and soft craniofacial tissues are likely to be involved in this mechanism.

How to Make a Vampire: Part II. Getting Ready to Feed

The mammalian feeding system is made up of multiple components that influence facial variation, including the masticatory muscles, bony jaw apparatus, and teeth. However, it is not fully understood how the development of these components are coordinated and are impacted by life history and diet.Bats are the only mammals that continue to nurse until they are almost adult size, and often after they become volant. Common vampire bats (Desmodus rotundus) have a relatively prolonged juvenile period among bats, can nurse up to nine months, and later solely subsist off of blood. Feeding system maturity may therefore be delayed in bats, and particularly delayed in Desmodus, as a result of their lengthy juvenile period and liquid diet. In this study, we examine the developmental maturity of the cranium and feeding apparatus in the late fetus of a common vampire bat (Desmodus rotundus) relative to an adult (its mother).The heads of each specimen were microCT scanned twice. Conventional microCT was used to image mineralized tissues. Diffusible iodine‐based contrast‐enhanced CT (diceCT) imaging was used to image soft tissues. Cranial length and palate length measurements were acquired from unstained scans to evaluate size and jaw apparatus development. Masticatory muscles (e.g., medial pterygoid, zygomaticomandibularis) and permanent tooth crypt volumes were acquired from stained tissue scans to evaluate masticatory muscle and tooth development. Developmental maturity of these structures was assessed by calculating a percentage of the growth completed (i.e., [fetal muscle volume/adult muscle volume]*100).In the fetus, permanent tooth crypt volume is already comparable to the adult condition despite cranial length and palate length being &lt;75% of adult size. Masticatory muscle volume maturity is highest in the lateral pterygoid muscle (~35%), whereas other masticatory muscles are far less developed (e.g., medial pterygoid volume maturity, ~20%; temporalis profundus volume maturity, ~20%; temporalis medius volume maturity, ~6%).These results reveal highly precocious permanent tooth development in Desmodus. Although this may facilitate transition to hematophagy, Desmodus do not fly until eight to ten weeks, so the precocious incisors may primarily aid the infant to grip its mother’s skin. Differential development of the masticatory muscles may also be influenced by the need for young bats to use their mouths to help anchor themselves to their mother early in life. This may explain the advanced maturity of the lateral pterygoid muscle, which would protrude the jaw and help to facilitate a more secure grip.

The Effect of Orthognathic Surgery on Changes in Masticatory Muscle Volume in Patients With Facial Asymmetry.

The masseter muscle changes remarkably with orthognathic surgery and has a marked influence on the contours of the lower face. If the postoperative volume change of masticatory muscles, including the masseter muscles, can be predicted, it will facilitate preoperative planning and outcome prediction. This study investigated the association of masticatory muscle volume according to the presence or absence of facial asymmetry, and evaluated whether the volume of masticatory muscles, including that of the masseter muscle, changes after orthognathic surgery in facial asymmetry patients.Twenty patients who underwent LeFort I osteotomy and bilateral sagittal segmentation ramus osteotomy (BSSRO) with facial asymmetry between 2011 and 2017 were assigned to the asymmetric group. Additionally, 207 patients with a simple nasal fracture between 2016 and 2019 were included as the common group. Threedimensional computed tomography images were retrospectively analyzed and compared between the asymmetric group and common group.The volume of both temporal and masseter muscles differed according to facial asymmetry, with the asymmetry in the muscle volume increasing in proportion to the degree of facial asymmetry. The difference in masseter volume on the shortened and lengthened sides was significantly reduced after orthognathic surgery, but a difference of about 1 cm 3 remained. Additionally, the masticatory muscle volume on the lengthened side tended to be decreased more than that on the shortened side.Consideration of the postoperative change in the volume of the masticatory muscles may be helpful in planning orthognathic surgery in facial asymmetry patients.

Cranial shape variation in mink: Separating two highly similar species.

European and American minks (Mustela lutreola and Neovison vison, respectively) are very similar in their ecology, behavior, and morphology. However, the American mink is a generalist predator and seems to adapt better to anthropized environments, allowing it to outcompete the European mink in areas where it has been introduced, threatening the survival of the native species. To assess whether morphological differences may be contributing to the success of the American mink relative to the European mink, we analyzed shape variation in the cranium of both species using 3D geometric morphometrics. A set of 38 landmarks and 107 semilandmarks was used to study shape variation between and within species, and to assess how differences in size factored into that variation. Sexual dimorphism in both size and shape was also studied. Significant differences between species were found in cranial shape, but not in size. Relative to American mink, European mink have a shorter facial region with a rounder forehead and wider orbits, a longer neurocranium with less developed crests and processes, and an antero‐medially placed tympanic bullae with an anteriorly expanded cranial border. Within species, size‐related sexual dimorphism is highly significant, but sexual dimorphism in shape is only significant in American mink, not in European mink. Additionally, two trends common to both species were discovered, one related to allometric changes and another to sexual size dimorphism. Shape changes related to increasing size can be subdivided into two, probably related, groups: increased muscle force and growth. The first group somewhat parallels the differences between both mink species, while the second group of traits includes an anterodorsal expansion of the face, and the neurocranium shifting from a globous shape in small individuals to a dorsoventrally flattened ellipse in the largest ones. Finally, the sexual dimorphism trend, while also accounting for differences in muscle force, seems to be related to the observed dietary differences between males and females. Overall, differences between species and sexes, and shape changes with increasing size, seem to mainly relate to differences in masticatory‐muscle volume and therefore muscle force and bite force, which, in turn, relate to a wider range of potential prey (bigger prey, tougher shells). Thus, muscle force (and dietary range) would be larger in American mink than in European mink, in males than in females, and in larger individuals than in smaller ones.

Does sleep bruxism affect masticatory muscles volume and occlusal force distribution in young subjects? A preliminary study

Objective To compare the differences in masticatory muscle volume and occlusal force distribution between patients with sleep bruxism (SB) and healthy individuals.Methods The study was performed on 14 SB patients and 12 controls aged between 20 and 27 years. Magnetic resonance images from a previous clinical trial were used for volumetric measurements of masticatory muscles. Distribution of bite forces was recorded using T-Scan® II. T-tests were used for data comparison.Results The mean age of the subjects was 23 ± 1.85 years. The mean muscle volumes of patients with SB and healthy subjects were 177.3 and 185.9 cm3, respectively. The mean occlusal force areas were 72.4 pixels and 89.8 pixels for patients with SB and healthy subjects, respectively. There was no significant difference in measurements between groups (p > 0.05).Conclusion There was no significant difference in the distribution of masticatory muscles and occlusal force between young patients with SB and healthy subjects.

Relationship Between Mandibular Ramus Height and Masticatory Muscle Function in Patients With Unilateral Hemifacial Microsomia.

To clarify the relationship between mandibular ramus height and function of masticatory muscles in patients with hemifacial microsomia. Retrospective study of imaging and physiological data. Images and physiological data were obtained from the records of Sapporo Medical University Hospital. A total of 29 patients with hemifacial microsomia who showed Pruzansky grades I, II deformity. Mandibular ramus height and masticatory muscle volume were evaluated with multi-detector row computed tomography. The electromyographic value was measured by the K7 Evaluation System. The hemifacial microsomia patients were classified into three groups based on the mandibular ramus height ratio of the affected and unaffected sides: group 0, >1.00; group 1, 1.00 to 0.85; group 2, <0.85. The Tukey-Kramer method and Games-Howell method were used to determine correlations between parameters. Decreased mandibular ramus height was significantly correlated with both reduced electromyographic values of the masseter muscle (P < .05) and the amount of mandibular lateral deviation at the time of maximum opening (P < .05) on the affected side. These differences were prominent in unilateral hemifacial microsomia patients classified as group 2. Decreased mandibular ramus height may cause dysfunction of the masseter muscles but not the temporal muscle on the affected side in patients with hemifacial microsomia.

Prolonging the duration of masseter muscle reduction by adjusting the masticatory movements after the treatment of masseter muscle hypertrophy with botulinum toxin type a injection.

Botulinum toxin type A (BTX-A) is widely used for the clinical treatment of masseteric hypertrophy. Until now, few reports have discussed how to prolong the duration of its effectiveness. This study evaluated that purposely adjusting the masticatory movements is possible of postponing the masseter muscle rehypertrophy. Ninety-eight patients were randomly and equally divided into 2 groups, and 35 U BTX-A per side was injected into the masseters. The thickness and volume of the masticatory muscles were measured by ultrasound and computerized tomography, respectively. Patients in Group 1 were instructed to strengthen their masticatory effort during the denervated atrophic stage of the masseter (the interval was evaluated by real-time ultrasound monitoring), whereas patients in Group 2 were not given this instruction. When the masseter muscle began to recover, patients in both groups were instructed to reduce their chewing. The duration of the masseter muscle rehypertrophy was significantly prolonged in Group 1 patients. The thickness and the volume of the other masticatory muscles were significantly increased in Group 1 but were either slightly decreased or insignificantly different in Group 2. Purposely strengthening masticatory muscle movement during the denervated atrophic stage of the masseter can prolong the duration of masseter rehypertrophy.

Quantitative analysis of human masticatory muscles using magnetic resonance imaging

The objective of this study was to quantitatively evaluate the correlation between left and right masticatory muscle volumes in normal subjects. Contiguous 1 mm MR scans were obtained of 12 normal adult subjects aged 20-25 years using a Siemens 1.5 T MR scanner. The volumes of the human masticatory muscles (masseter, lateral and medial pterygoid) were measured from the scans using our previously proposed method. To test for inter- and intraobserver reproducibility, measurements were performed by two users on two separate occasions, with a span of 2 weeks between them and with the previous results blinded. Good inter- and intraobserver reproducibility was achieved in our study. The mean volumes for left and right masseters, and lateral and medial pterygoids were 29.54 cm3, 29.65 cm3, 9.47 cm3, 10.23 cm3, 8.69 cm3 and 8.92 cm3, respectively. The Pearson correlation coefficients between the volumes of the left and right masseters, lateral and medial pterygoids are 0.969, 0.906 and 0.924, respectively. The computed volumes of the masticatory muscles show a strong correlation between the volumes of the left and right masseters, and lateral and medial pterygoids for normal adult subjects. The total masticatory muscle volume on the left and right sides of normal subjects is similar.

Relationship Between the Masticatory Muscles and Mandibular Skeleton in Mandibular Prognathism With and Without Asymmetry

The purpose of the present study was to evaluate the relationship between masticatory muscle volume and mandibular skeletal measurements in patients with and without facial asymmetry. This was done in order to determine whether asymmetric mandibular prognathism is related to masticatory muscle asymmetry. The study was conducted with 40 adult patients with mandibular prognathism composed of 2 groups, the asymmetry group (n = 20) and the nonasymmetry group (n = 20). Using 3-dimensional reformatted computed tomography (CT) images, the volume of masticatory muscle (masseter, temporal, medial, and lateral pterygoid muscles) and various skeletal measurements (hemimandibular volume, ramal height, body length, mandibular length, gonial angle) were evaluated and compared. The right-left difference was expressed by an asymmetry index {(right-left)/left, %}. The results showed that in the asymmetry group, the longer mandibular side (contralateral side of chin deviation) exhibited longer ramal and body length, a wider gonial angle, and more hemimandibular volume with less medial pterygoid volume, whereas the nonasymmetry group did not show a statistical bilateral difference between the skeletal and muscular measurements. The correlation analysis showed that patients with facial asymmetry did not have similar patterns of muscle-bone relation as compared with the symmetrical subjects. In patients with mandibular prognathism, the bilateral difference in muscle volume would reflect the difference in the spatial anatomy of a skeletal structure and could not predict mandibular skeletal asymmetry.

Masticatory muscle right-left differences in controls and hemifacial microsomia patients.

One aim of this study was to assess right-left differences in the volume of masticatory muscles in controls so as to be able to distinguish between normal variations and pathological differences. The other aim was to compare the masticatory muscle volume of the nonaffected side of hemifacial microsomia patients with the smaller side of controls so as to test the compensation hypothesis. The study group consisted of 39 children with hemifacial microsomia and the control group of 52 children. Computed tomography scans were made using a Philips Tomoscan 350 and a Pro Speed S Fast Spiral General Electric scanner. The normal right-left differences in volume of the masticatory muscle of the controls, calculated as a percentage of the total, demonstrated small mean differences of 2.57% to 2.88% (SD:1.98-2.74). For hemifacial microsomia patients, the relative difference was about 10 times the difference for controls. For controls, the averages of the right-left differences (%) were all below the generally accepted SEM of 4%. Testing the compensation hypothesis of all effects, only the age effect was multivariately significant (P < 0.001). No overcompensation of the masticatory muscles of the nonaffected side of hemifacial microsomia patients could be demonstrated.

Human masticatory muscle volume and zygomatico-mandibular form in adults with mandibular prognathism.

Although several investigators have reported associations between masticatory muscles and skeletal craniofacial form, there is no agreement on the association. We tested the hypothesis that masticatory muscle volume correlates with the size and form of the adjacent local skeletal sites. For this purpose, we investigated the morphological association of the cross-sectional area and volume of temporal and masseter muscles with zygomatico-mandibular skeletal structures using computerized tomography (CT) in 25 male adults with mandibular prognathism. Muscle variables significantly correlated with widths of the bizygomatic arch and temporal fossa but not with the cranium width. Masseter volume significantly correlated with cross-sectional areas of the zygomatic arch and mandibular ramus. Masseter orientation was almost perpendicular to the zygomatic arch and mandibular antegonial region. The zygomatic arch angle significantly correlated with the antegonial angle. The results of the study suggest that the masticatory muscles exert influence on the adjacent local skeletal sites.

Human Masticatory Muscle Volume and Zygomatico-mandibular Form in Adults with Mandibular Prognathism

Human Masticatory Muscle Volume and Zygomatico-mandibular Form in Adults with Mandibular Prognathism