Ultrasound analysis of the masseter and anterior temporalis muscles in edentulous patients rehabilitated with full-arch fixed implant-supported prostheses.

OBJECTIVES: Total tooth loss is common in the aging population resulting in insufficient chewing function with subsequent weakening of the masticatory muscles. The study aims to evaluate the changes in thicknesses of the masseter and anterior temporal muscle in edentulous patients following the reconstruction of implant-supported fixed prostheses and compare them with the dentate individuals. MATERIALS AND METHODS: The study was designed as a prospective, single-center, controlled clinical trial. A total of 60 participants were included in the present study. The patients were divided into two groups; Group I (Test Group): 30 edentulous patients who received implant-supported fixed prostheses, Group II (Control Group): 30 dentate individuals of an age and sex-matched group. Ultrasonography was used to measure the cross-sectional thickness of the left and right musculus masseter and anterior temporalis immediately after the cementation of the prosthetic rehabilitation (T1), on the 1st (T2) and 6th (T3) months after rehabilitation and at a single time point in the control group. RESULTS: The results showed that there were significant comparison differences in muscle thickness at the baseline measurements between groups while at the end of the 6th month, these differences were not significant. The muscle thicknesses of both the masseter and anterior temporalis muscles increased significantly at T2 and T3 compared to T1 in the test group. The asymmetry index between the left and right muscles in the test group and the asymmetry differences between groups also decreased significantly at the end of the 6th month. CONCLUSION: The implant-supported fixed prostheses significantly increase the thicknesses of the masseter and anterior temporal muscle together with a decrease in the asymmetry between the left and right muscles. At six months, implant-treated patients showed similar muscle thicknesses compared to dentate individuals. CLINICAL RELEVANCE: The findings suggest that implant-supported fixed prostheses can improve the masticatory function and facial symmetry of edentulous patients.

Comparison of ultrasonography-based masticatory muscle thickness between temporomandibular disorders bruxers and temporomandibular disorders non-bruxers.

To compare masticatory muscle thickness in patients with temporomandibular disorders (TMDs) during rest and clenching, and by body position, using ultrasonography. This prospective study included 96 patients with TMD (67 females, 29 males; mean age: 40.41 ± 17.88 years): group 1, comprising 66 patients with TMD without bruxism (TMD_nonbruxer), and group 2, comprising 30 patients with concurrent TMD and bruxism (TMD_bruxer). In patients with TMD, bruxism was correlated with the presence of tinnitus, muscle stiffness, sleep problems, psychological stress, and restricted mouth opening. The masseter muscle significantly thickened during clenching (11.16 ± 3.03 mm vs 14.04 ± 3.47 mm, p < 0.001), whereas the temporalis muscle showed no significant increase in thickness from resting to clenching in an upright position (7.91 ± 1.98 vs 8.39 ± 2.08, p = 0.103). Similarly, during clenching in the supine position, the masseter muscle was significantly thicker compared with rest (11.24 ± 2.42 vs 13.49 ± 3.09, p < 0.001), but no significant difference was observed in temporal muscle thickness (8.21 ± 2.16 vs 8.43 ± 1.94, p = 0.464). In comparison between two groups, the average thickness of the masseter muscle was greater among TMD_bruxers than among TMD_nonbruxers in both the upright and supine positions (all p < 0.05). In the generalized lineal model, female sex (B = - 1.018, 95% confidence interval [CI] - 1.855 to - 0.181, p = 0.017) and bruxism (B = 0.868, 95% CI 0.567 to 1.169, p = 0.048) significantly predicted changes in masseter muscle thickness. Female sex (B = - 0.201, 95% CI - 0.299 to - 0.103, p = 0.011), increased age (B = - 0.003, 95% CI - 0.005 to 0.000, p = 0.038), and muscle stiffness (B = - 1.373, 95% CI - 2.369 to - 0.376, p = 0.007) were linked to decreased temporal muscle thickness. Comparing TMD nonbruxer and bruxer muscle thicknesses in upright and supine positions revealed significant increased thickness in the masseter muscle during clenching but not in the temporalis muscle. Masseter muscle thickness varied significantly by sex, body position, and resting/clenching, notably influenced by bruxism. These findings emphasize the relevance of these factors in clinical examinations of patients with TMD.

Musculoaponeurotic architecture of the human masseter muscle: an in vivo ultrasonographic study of architectural changes during mandibular protrusion and lateral excursions.

OBJECTIVE: The present study evaluated the in vivo musculoaponeurotic architecture of the superficial head (SH) of the masseter muscle (MM) of asymptomatic participants in excursive mandibular movements compared to the relaxed state as examined with ultrasonography. It was hypothesized that the mean fiber bundle length (FBL) and mean height of the aponeurosis (HA) of the laminae of the SH would differ significantly between the relaxed state and protrusion, ipsilateral excursion, and contralateral excursion. STUDY DESIGN: The MM was studied volumetrically in 12 female and 12 male asymptomatic participants bilaterally by using ultrasound imaging. Mean FBL and HA in protrusion and ipsilateral and contralateral excursion were compared to these values in the relaxed state using paired t tests (P < .05). The intraclass correlation coefficient was used to assess intraexaminer reliability. RESULTS: The SH exhibited multiple laminae. Fiber bundles were found to attach to bone and the superior and inferior aponeuroses. Mean FBL was significantly shorter and mean HA significantly longer in protrusion and the excursions than in the relaxed state although the pattern of altered laminae and aponeuroses differed among the mandibular movements. Intraexaminer reliability was excellent. CONCLUSION: Specific changes in mean FBL and mean HA suggest differential contraction of the SH of the MM based on laminar morphology. These findings provide a baseline to investigate musculoaponeurotic changes in patients with myogenic masseter muscle pain.

MR sialographic assessment of the masseter muscle and the ductal kinking in patients with recurrent parotitis.

Dysfunction of the masseter muscle may cause pathological kinking of the parotid duct leading to parotitis; MR sialography is a non-invasive radiological examination that allows to evaluate dynamically the ductal system of the parotid glands. In the present study we aimed to assess the relationships between Stensen's duct and masseter muscle and their implications in the aetiopathogenesis of recurrent parotitis secondary to masseter muscle dysfunction. Forty-one patients with recurrent unilateral parotitis and nine with bilateral recurrent parotitis, all with a clinical suspicious of masseter muscle hypertrophy due to bruxism were enrolled. They underwent ultrasonography as a first line examination and then MR sialography and sialendoscopy. Different anatomical features were studied. Involved parotid glands had a wider duct compared to contralateral unaffected parotid glands of patients with recurrent parotitis (p = 0.00134); male subjects with parotitis had a longer duct compared to the salivary glands of healthy patients (p = 0.00943 for affected glands and p = 0.00629 for the contralateral). A concordance between the evidence of an acute duct angle during sialendoscopy and a wider duct in patients with parotitis was observed although not statistically significant. These initial findings suggest that the masticatory muscle dysfunction related to bruxism seems to condition alteration of parotid duct course and anatomy thus favouring the occurrence of recurrent parotitis. A specific diagnostic iter based on clinical evaluation, dynamic ultrasonography and MR sialography, is therefore, mandatory to confirm the relationship between masseter muscle anatomy and parotid duct anomalies; this is the premise for an adequate therapeutic approach to underlying masticatory muscle disorder.

Automated evaluation of masseter muscle volume: deep learning prognostic approach in oral cancer.

BACKGROUND: Sarcopenia has been identified as a potential negative prognostic factor in cancer patients. In this study, our objective was to investigate the relationship between the assessment method for sarcopenia using the masseter muscle volume measured on computed tomography (CT) images and the life expectancy of patients with oral cancer. We also developed a learning model using deep learning to automatically extract the masseter muscle volume and investigated its association with the life expectancy of oral cancer patients. METHODS: To develop the learning model for masseter muscle volume, we used manually extracted data from CT images of 277 patients. We established the association between manually extracted masseter muscle volume and the life expectancy of oral cancer patients. Additionally, we compared the correlation between the groups of manual and automatic extraction in the masseter muscle volume learning model. RESULTS: Our findings revealed a significant association between manually extracted masseter muscle volume on CT images and the life expectancy of patients with oral cancer. Notably, the manual and automatic extraction groups in the masseter muscle volume learning model showed a high correlation. Furthermore, the masseter muscle volume automatically extracted using the developed learning model exhibited a strong association with life expectancy. CONCLUSIONS: The sarcopenia assessment method is useful for predicting the life expectancy of patients with oral cancer. In the future, it is crucial to validate and analyze various factors within the oral surgery field, extending beyond cancer patients.

Evaluation of masticatory muscles in temporomandibular joint disorder patients using quantitative MRI fat fraction analysis-Could it be a biomarker?

Temporomandibular joint disorders (TMDs) are closely related to the masticatory muscles, but objective and quantitative methods to evaluate muscle are lacking. IDEAL-IQ, a type of chemical shift-encoded magnetic resonance imaging (CSE-MRI), can quantify the fat fraction (FF). The purpose of this study was to develop an MR IDEAL-IQ-based method for quantitative muscle diagnosis in TMD patients. A total of 65 patients who underwent 3 T MRI scans, including CSE-MRI sequences, were retrospectively included. MRI diagnoses and clinical data were reviewed. There were 19 patients in the normal group and 46 patients in the TMD group with unilateral disc displacement. The TMD group was subdivided into those with and without clenching. The right and left FF values of the masseter, medial, and lateral pterygoid muscles were measured twice by two oral radiologists on CSE-MRI, and the average value was used. FF measurements using CSE-MRI showed excellent intra- and inter-observer agreement (ICC > 0.889 for both). There were no statistically significant differences between the right and left FF values in the masseter, medial pterygoid, and lateral pterygoid of the normal group (p > 0.05). A statistically significant difference was found in the TMD group without clenching, in which the masseter muscle had a statistically significantly lower FF value on the disc displacement side (3.94 ± 1.61) than on the normal side (4.52 ± 2.24) (p < 0.05). CSE-MRI, which can reproducibly quantify muscle FF values, is expected to be a biomarker for objective muscle evaluation in TMD patients. The masseter muscle is expected to be particularly useful compared to other masticatory muscles, but further research is needed.

Determination of masseter and temporal muscle thickness by ultrasound and muscle hardness by shear wave elastography in healthy adults as reference values.

OBJECTIVES: The purpose of this study is to prospectively investigate the reference values of masseter and temporal muscle thicknesses by ultrasonography and muscle hardness values by shear wave elastography in healthy adults. METHODS: The sample of the study consisted of a total of 160 healthy individuals aged between 18 and 59, including 80 women and 80 men. By examining the right and left sides of each participant, thickness and hardness values were obtained for 320 masseter muscles and 320 temporal muscles in total. RESULTS: The mean masseter muscle thickness was found to be 1.09 cm at rest and 1.40 cm in contraction. The mean temporal muscle thickness was found to be 0.88 cm at rest and 0.98 cm in contraction. The thickness values of the masseter and temporal muscles were significantly greater in the male participants than in the female participants (P < .001). While there were significant differences between the right and left masseter muscle thickness values at rest and in contraction, the values of the temporal muscles did not show a significant difference between the sides. While the resting hardness (rSWE) of the masseter muscle was transversally 6.91 kPa and longitudinally 8.49 kPa, these values in contraction (cSWE) were found, respectively, 31.40 and 35.65 kPa. The median temporal muscle hardness values were 8.84 kPa at rest and 20.43 kPa in contraction. Masseter and temporal muscle hardness values at rest and in contraction were significantly higher among the male participants compared to the female participants (P < .001). CONCLUSION: In this study, reference values for the thickness and hardness of the masseter and temporal muscles are reported. Knowing these values will make it easier to assess pain in the masseter and temporal muscles and determine the diagnosis and prognosis of masticatory muscle pathologies by allowing the morphological and functional assessments of these muscles, and it will identify ranges for reference parameters.

Do repetitive botulinum neurotoxin injections induce muscle fibrosis? Sonographic observation of the masseter muscle.

OBJECTIVE: In the esthetic field, the masseter muscle is commonly targeted by botulinum neurotoxin for facial contouring. However, multiple botulinum neurotoxin injections have been reported to cause muscle fibrosis. Ultrasonography can be useful for clinical consideration in such cases. MATERIALS AND METHODS: This study presents nine cases of masseteric fibrosis caused by repeated botulinum neurotoxin injections with ultrasonographic analysis of full and partial masseteric fibrosis. RESULTS: Repetitive botulinum neurotoxin injections resulted in reduced masseter muscle volume, which frequently appeared hyperechoic on ultrasonography. The hyperechoic region was mostly located in the deep and posterior portions; however, in some cases, it was observed throughout the muscle, including the superficial, deep, or both areas. CONCLUSION: The fibrotic masseter muscles appear hyperechoic, and ultrasonography is necessary to analyze the degree and location of fibrosis. Predictions can be made for cases in which botulinum neurotoxin injections may have less of an effect after ultrasonography. Because muscle fibrosis can be localized, it is necessary to confirm the degree and location of fibrosis before determining the effective area of injection. In clinical practice, muscle fibrosis may be visible in a specific area where blind injections are administered.

Influence of botulinum toxin A in pain perception and condyle-fossa relationship after the management of temporomandibular dysfunction: a randomized controlled clinical trial.

OBJECTIVES: To investigate the pain perception (PP) and condyle-fossa relationship (CFR) after botulinum toxin A (BoNTA) injection in the masseter muscles of painful muscular temporomandibular dysfunction (TMD) patients. MATERIALS AND METHODS: Fourteen women (aged 29.7 ± 5.4 years) diagnosed with myogenic TMD were randomized in the BoNTA-treated group (TG) and control group (CG). TG masseter muscles (n = 7) were bilaterally injected with 30 U. The CG (n = 7) were injected with saline injections. Condyle-fossa relationship (CFR) spaces were measured in sagittal (SP) and frontal planes (FP) of images of cone-beam computed tomography (CBCT) done before (T0) and after 30 days' interventions (T1). Visual analogue scale (VAS) measured the patients' TMD pain perception (PP). Data were compared by generalized linear models considering the results over time (α = .05). RESULTS: There were no statistical differences in CFR in the SP or FP for TG and CG over time (p ˃ .05), except for frontal lateral space CFR (p < .05). In both groups, the condyle was positioned medially after interventions. Frontal lateral space increased in TG for both, left and right sides, over time (p < .05), as well as PP decreased over time (p < .05) for TG and CG. CONCLUSIONS: The results depicted that there was no significant association with BoNTA injection in TMD masseter muscles in PP and CFR, except considering the frontal lateral space of CFR. CLINICAL RELEVANCE: BoNTA injection in the masseter muscles may not promote clinically significant shifts in the condyle-fossa relationships of muscular TMD patients.

Biomechanical properties of masseter muscle assessed through myotonometry in patients with temporomandibular disorder treated with ultrasound therapy: a randomized comparative study.

BACKGROUND: The aim of the study was to make an objective quantitative assessment of effectiveness of procedures with the use of a therapeutic dose of ultrasounds in this nosological entity, in connection with improved biomechanical properties and alleviation of pain experienced in masseter muscles. METHODS: The study included 40 patients with temporomandibular disorder. In group 1 (N.=20) ultrasound therapy (1.2 W/cm2) was carried out, while in group 2 (N.=20) sham therapy was applied. A total of 10 procedures were performed. Myotonometric measurements and assessment of pain intensity were carried out before treatment and after the completion of procedures. RESULTS: The analysis revealed a significant difference (P=0.011) between the values of decrement (D) measured on day 0 (2.08±0.45 [log]) and day 4 (1.80±0.55 [log]) in group 1. In group 2 no statistically significant differences were noted between the results obtained on consecutive days of the therapeutic cycle. A statistically significant difference in values of decrement (D) between group 1 (1.80±0.55 [log]) and group 2 (2.23±0.51 [log]) was noted on day 4 of the experiment (P=0.021). Both in group 1 and in group 2, a statistically significant reduction of pain intensity (VAS Scale) was obtained. CONCLUSIONS: The masseter muscle was more elastic during ultrasound therapy. However, the effect was transient. The analgesic effect was also observed in the control group; therefore, a placebo effect cannot be excluded.

Fractal analysis of the effects on mandibular bone of botulinum toxin therapy of the masseter muscle in patients with bruxism.

OBJECTIVE: We examined changes in the mandibular angle, ramus, and condylar neck of patients with bruxism after botulinum toxin-A (BTX-A) injection into the masseter muscle as calculated with fractal analysis (FA) on panoramic radiographs (PRs). METHODS: We examined the PRs of 3 groups of 22 patients each (n = 66) obtained upon presentation and 6 months later. One group included healthy controls without bruxism, one group included patients with untreated bruxism, and one group included patients with bruxism who had undergone BTX-A injection into the masseter muscle. We performed FA of the bilateral angle, ramus, and condylar neck of the PRs to calculate fractal dimension (FD). RESULTS: The FD values of the angle on the second PRs of the untreated bruxism group were significantly higher than those of the other groups (P = .026), specifically when compared to the BTX-A injection group (P = .017). The FD values in the angle and ramus of the bruxism group were significantly higher on the second PRs (P ≤..005)) Conversely, the FD values in the angle of the BTX-A injection group were significantly lower on the second PR (P = .039). CONCLUSIONS: Masseter muscle hyperactivity due to bruxism increases bone density in masseter muscle attachment regions. BTX-A injection restricts muscle activity, thereby chnging bone structure and decreasing FD.

Assessing thickness and stiffness of superficial/deep masticatory muscles in orofacial pain: an ultrasound and shear wave elastography study.

INTRODUCTION: Sonoelastography has been increasingly used for non-invasive evaluation of the mechanical features of human tissues. The interplay between orofacial pain and regional muscle activity appears clinically paramount, although only few imaging studies have investigated this association. Using shear wave sonoelastography (SWS), this study ascertained whether orofacial pain induced alterations in the stiffness of superficial and deep masticatory muscles. METHODS: All participants were systematically evaluated for oral/facial-related conditions, including the area and intensity of pain. SWS was applied to measure the stiffness of the bilateral masseter, temporalis, and lateral pterygoid muscles. The association between orofacial pain and muscle stiffness/thickness was investigated using a generalized estimating equation for adjusting the influence of age, sex, laterality, and body mass index on muscle thickness/stiffness. RESULTS: A total of 98 participants were included in the present study: 48 asymptomatic controls, 13 patients with unilateral pain, and 37 patients with bilateral orofacial pain. The reliability, quantified by the intraclass correlation coefficient for muscle stiffness measurement, ranged from 0.745 to 0.893. Orofacial pain at the individual muscle level was significantly associated with masseter muscle stiffness. A trend of increased stiffness (p = 0.06) was also observed in relation to the painful side of the temporalis muscle. No significant correlation was identified between the numeric rating scales for pain and stiffness measurements. CONCLUSIONS: SWS provides reliable stiffness measurements for the superficial and deep masticatory muscles. The ipsilateral masseter and temporalis muscles might be stiffer than those on the side without orofacial pain. Future studies using the present sonoelasotography protocol can be designed to investigate the stiffness changes in the target muscles after interventions.

Shear wave sonoelastography (SWS) can reliably assess the stiffness of masticatory muscles.Orofacial pain, particularly affecting the ipsilateral masseter muscles, exhibited increased stiffness, with a similar trend observed in the temporalis muscle as revealed by SWS. However, the stiffness of the lateral pterygoid muscle appeared to remain unaffected.These findings establish a foundational framework for the objective and quantitative assessment of orofacial pain and indicate the potential utility of SWS as a tool for evaluating treatment outcomes.

Functional reconstruction of the masseter muscle by microvascular free gracilis muscle transfer: technique and outcome.

Microvascular reconstruction of the cheek is most often performed using fasciocutaneous flaps and without functional reconstruction of the masseter muscle. This article reports a technique of masseter muscle resection, dissection of the masseteric nerve, and masseter muscle reconstruction with a functional gracilis muscle flap. The technique was applied in a 38-year-old man with recurrent intramuscular lipoma of the right masseter muscle. The flap was highly stable in form and showed good function. Bite force, electromyography results, and the radiological appearance of the gracilis muscle were similar to those of the contralateral masseter muscle at 12 months after surgery. In conclusion, full rehabilitation of masseter muscle function and good facial aesthetics were achieved by functional gracilis muscle reconstruction of the masseter muscle in a case of total resection.

Ultrasonographic evaluation of changes in the thickness, width, elasticity index and echogenic pattern of the masseter muscle after mandibular set-back surgery.

INTRODUCTION: The masseter muscle is one of the structures that undergoes significant changes following jaw movements in orthognathic surgery. This study aims to investigate the effects of mandibular setback surgery, performed in patients with skeletal class III deformity, on the thickness, width, elasticity index, and echogenic pattern of the masseter muscle. MATERIAL AND METHODS: This prospective case-control study enrolled patients with class III deformity who underwent mandibular setback surgery, while the control group consisted of class I patients. The predictor variable was the time measured at two different points: preoperative (T1) and postoperative 6 months (T2). The primary outcome variable focused on changes in the internal echogenic pattern of the masseter muscle. Secondary, tertiary, and quaternary outcome variables included changes in the thickness, width, and elasticity index of the masseter muscle, respectively. Gender, age, type of operation, and amount of movement were considered as covariates. Ultrasonography was employed to evaluate the outcome variables. RESULTS: The study group comprised 31 patients, including 17 females (mean age 22.24 ± 3.52 years) and 14 males (mean age 23.14 ± 2.65 years). The control group consisted of 16 females (mean age 23.34 ± 1.22 years) and 15 males (mean age 23.12 ± 1.76 years). Masseter muscle thickness increased significantly after mandibular setback surgery (p = 0.015). However, there was no statistically significant difference in masseter muscle width before and after surgery (p = 0.627), nor in the elasticity index (p = 0.588). Furthermore, a statistically significant transformation from Type I to Type II was observed in the internal echogenic pattern of the muscle (p = 0.039). Additionally, there was no statistically significant correlation between the amount of mandibular movement performed and the changes in the masseter muscle. CONCLUSIONS: Mandibular setback surgery leads to changes in both the physical and structural properties of the masseter muscle.

Clinical investigation of botulinum toxin (prabotulinumtoxin A) for bruxism related to masseter muscle hypertrophy: A prospective study.

This study aims to confirm the effectiveness and safety of a prabotulinumtoxin type A (praBTX-A) injection in patients with bruxism and masseter hypertrophy. The study included patients who ground or clenched their teeth while sleeping and had computed tomography (CT) scans that showed a maximum thickness of the masseter muscle of 15 mm or more. The praBTX-A was administered bilaterally into the masseter muscles; 15 U/side for group 1, 25 U/side for group 2, and 35 U/side for group 3. CT scans and bruxism questionnaires were conducted before and eight weeks after the injection. Thirty-seven patients were enrolled, but three dropped out due to loss of follow-up. After injection, masseter thickness decreased to 15.1 ± 2.0 mm for group 1, 14.3 ± 2.9 mm for group 2, and 13.4 ± 1.8 mm for group 3 (p = 0.043). Group 3 showed a statistically significant lower masseter thickness compared to group 1 (p = 0.039). Both subjective and objective frequencies of bruxism decreased for all groups, but there were no significant differences in either subjective (p = 0.396) or objective frequencies (p = 0.87) between the groups after the injection. The results of this study suggest that praBTX-A injection is a safe and effective treatment for bruxism and masseter hypertrophy. A dosage of 35 IU/side can effectively decrease masseter thickness and relieve bruxism symptoms. Even the minimum dosage of 15 IU/side can contribute to improvements in bruxism symptoms. This investigation provides valuable information for managing bruxism that is associated with hypertrophic masseter muscles.

Evaluation of the thickness and internal structure of the masseter muscle with ultrasonography in female bruxism patients.

OBJECTIVES: The aim of this study was to evaluate the differences in the thickness and internal structure of the masseter muscle in individuals with and without bruxism by ultrasonography. MATERIALS AND METHODS: A total of 60 female patients with and without bruxism whose ages were ranging between 20 and 35 were included in the study. The masseter muscle thickness was measured during rest and maximum bite position. Ultrasonographic internal structure of the masseter muscle is classified according to the visibility of echogenic bands. In addition, the echogenic internal structure of the masseter muscle was evaluated with quantitative muscle ultrasound. RESULTS: The masseter muscle thickness was significantly higher in both positions in patients with bruxism (p < 0.05). There was no significant difference between two groups in the evaluation of echogenicity (p > 0.05). CONCLUSIONS: Ultrasonography is a useful and important diagnostic method for evaluating masseter muscle without using radiation.

Long-term evaluation of masseter muscle activity, dimensions, and elasticity after orthognathic surgery in skeletal class III patients.

OBJECTIVE: To evaluate changes in the masseter muscle after orthognathic surgery using electromyography (EMG), ultrasonography (US), and ultrasound elastography (USE) in individuals with skeletal class III anomaly over long-term follow-up and compare with a control group. MATERIALS AND METHODS: The study group included 29 patients with class III dentofacial deformities scheduled to undergo orthodontic treatment and orthognathic surgery. The control group included 20 individuals with dental class I occlusion. Assessment of the masseter muscles using EMG, US, and USE was performed before orthognathic surgery (T1) and at postoperative 3 months (T2) and 1 year (T3) in the study group, and at a single time point in the control group. All assessments were performed at rest and during maximum clenching. Masseter muscle activity, dimension, and hardness were analyzed. RESULTS: Electromyographic activity of the masseter muscle during maximum clenching was increased at postoperative 1 year but did not reach control group values. On ultrasonography, the masseter muscle showed minimal changes in dimension at postoperative 1 year compared to preoperative values and remained below control group values. The postoperative increase in masseter muscle hardness at rest and during maximum clenching persisted at postoperative 1 year. CONCLUSION: The results of this study suggest that after orthognathic surgery, additional interventions and much longer follow-up are needed to ensure better muscle adaptation to the new occlusion and skeletal morphology. CLINICAL RELEVANCE: All assessment methods are useful for comprehensively evaluating changes in the masticatory muscles after orthognathic surgery.

A Comprehensive Ultrasound Evaluation Approach of Lower Facial Structure Before Masseter Muscle Botulinum Toxin Injection.

BACKGROUND: Masseter reduction by botulinum neurotoxin A (BoNT-A) injection is a popular procedure in East Asia. Inappropriate injection can result in various complications. OBJECTIVES: The aim of this study was to develop an approach for comprehensively evaluating the lower facial structure based on the shape of the mandible angle, the thickness of the masseter, and the thickness of subcutaneous fat. METHODS: Clinical profiles and standard ultrasound images were collected from patients seeking masseter BoNT-A injections. Lower facial structures were evaluated based on 3 aspects: mandible, masseter, and subcutaneous fat and skin. The mandibular angle was classified as extroverted, straight, or introverted. The starting point of the middle part of the masseter was recorded. The thickness of the deep inferior tendon, the superficial and deep belly of the superficial part of the masseter, and their contractility were measured. Overall thickness and the thickness of subcutaneous fat and skin were also measured. RESULTS: Eighty-four masseters from 42 patients were included. Straight mandibular angles were the most common type of angle (48.81%), followed by introverted (26.19%) and extroverted angles (25.00%). The middle part of the masseter starts from 2.33 [0.36] cm (mean [standard deviation]) above the mandible edge, which is above the usual injection points. The superficial belly was thicker than the deep belly in both static and clenching states (P = .048, P = .001) and had greater contractility. The average overall thickness was 1.87 [0.29] cm. CONCLUSIONS: Comprehensive evaluation of the lower facial contour and structure based on ultrasound examination could be a reliable and replicable assessment approach.

Probable bruxism effects on masseter muscle thickness in children: ultrasonographic evaluation.

OBJECTIVE: To compare the masseter muscle thickness (MMT) of patients with probable sleep/awake bruxism and controls without bruxism in mixed dentition as measured with ultrasonography (USG), and to calculate the correlation of MMT with body mass index (BMI). STUDY DESIGN: The diagnosis of probable bruxism was established based on the parents' reports of the children's behavior, habits, and discomfort, and the presence of clinical signs and symptoms such as attrition-type wear on the teeth and the presence of discomfort, fatigue, and/or pain in the jaw muscles on palpation during clinical examination. The bruxist study group and the control group each included 28 children. MMT was measured separately in relaxed and contracted positions in both groups using USG. The height and weight of the patients were recorded in order to calculate BMI. Statistical analysis was performed with significance established at P < .05. RESULTS: MMT was found to be significantly larger in the study patients than in controls on the right and left sides in the relaxed and contracted positions (P < .001). No statistically significant correlation was found between MMT and BMI (P ≥ .134). CONCLUSIONS: MMT as measured with USG can be a beneficial approach in diagnosing bruxism in children. The lack of correlation between MMT and BMI indicates that BMI would not be helpful in diagnosing bruxism.