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Study Objectives: To investigate the effects of botulinum toxin type A (BoNT-A) injection on jaw motor episodes during sleep in patients with or without orofacial pain who did not respond to oral splint treatment. Methods: Twenty subjects with a clinical diagnosis of SB completed this study. Ten subjects received bilateral BoNT-A injections (25 U per muscle) into the masseter muscles only (group A), and the other 10 received the injections into both the masseter and temporalis muscles (group B). Video-polysomnographic (vPSG) recordings were made before and at 4 weeks after injection. Rhythmic masticatory muscle activity (RMMA) and orofacial activity (OFA) were scored and analyzed for several parameters (e.g., frequency of episodes, bursts per episode, episode duration). The peak amplitude of electromyographic (EMG) activity in the two muscles was also measured. Results: BoNT-A injection did not reduce the frequency, number of bursts, or duration for RMMA episodes in the two groups. The injection decreased the peak amplitude of EMG burst of RMMA episodes in the injected muscles (p < 0.001, repeated measure ANOVA) in both groups. At 4 weeks after injection, 9 subjects self-reported reduction of tooth grinding and 18 subjects self-reported reduction of morning jaw stiffness. Conclusions: A single BoNT-A injection is an effective strategy for controlling SB for at least a month. It reduces the intensity rather than the generation of the contraction in jaw-closing muscles. Future investigations on the efficacy and safety in larger samples over a longer follow-up period are needed before establishing management strategies for SB with BoNT–A. Citation: Shim YJ; Lee MK; Kato T; Park HU; Heo K; Kim ST. Effects of botulinum toxin on jaw motor events during sleep in sleep bruxism patients: a polysomnographic evaluation. J Clin Sleep Med 2014;10(3):291–298.

Background Impaired function of masticatory muscles will lead to trismus. Routine delineation of these muscles during planning may improve dose tracking and facilitate dose reduction resulting in decreased radiation-related trismus. This study aimed to compare a deep learning model with a commercial atlas-based model for fast auto-segmentation of the masticatory muscles on head and neck computed tomography (CT) images. Material and methods Paired masseter (M), temporalis (T), medial and lateral pterygoid (MP, LP) muscles were manually segmented on 56 CT images. CT images were randomly divided into training ( n  = 27) and validation ( n  = 29) cohorts. Two methods were used for automatic delineation of masticatory muscles (MMs): Deep learning auto-segmentation (DLAS) and atlas-based auto-segmentation (ABAS). The automatic algorithms were evaluated using Dice similarity coefficient (DSC), recall, precision, Hausdorff distance (HD), HD95, and mean surface distance (MSD). A consolidated score was calculated by normalizing the metrics against interobserver variability and averaging over all patients. Differences in dose (∆Dose) to MMs for DLAS and ABAS segmentations were assessed. A paired t-test was used to compare the geometric and dosimetric difference between DLAS and ABAS methods. Results DLAS outperformed ABAS in delineating all MMs ( p  < 0.05). The DLAS mean DSC for M, T, MP, and LP ranged from 0.83 ± 0.03 to 0.89 ± 0.02, the ABAS mean DSC ranged from 0.79 ± 0.05 to 0.85 ± 0.04. The mean value for recall, HD, HD95, MSD also improved with DLAS for auto-segmentation. Interobserver variation revealed the highest variability in DSC and MSD for both T and MP, and the highest scores were achieved for T by both automatic algorithms. With few exceptions, the mean ∆D98%, ∆D95%, ∆D50%, and ∆D2% for all structures were below 10% for DLAS and ABAS and had no detectable statistical difference ( P  > 0.05). DLAS based contours had dose endpoints more closely matched with that of the manually segmented when compared with ABAS. Conclusions DLAS auto-segmentation of masticatory muscles for the head and neck radiotherapy had improved segmentation accuracy compared with ABAS with no qualitative difference in dosimetric endpoints compared to manually segmented contours.

The antegonial notch (AGN) is a structure that has been variably described across studies, with diverse findings regarding its role and association with craniofacial morphology, which is attributed to differing methodologies and the lack of control for sex and size. This study aimed to elucidate the variability of the AGN and examine its association with facial types, skeletal and muscular parameters. This study was carried out using the CT scans of 311 individuals aged 18–95 years. Facial type, skeletal and muscular measurements were recorded. Mann–Whitney and Kruskal–Wallis tests were conducted to examine AGN area differences between the sexes and facial types. Spearman correlation was used to explore the relationships between AGN and the skeletal and muscular parameters. AGN was found to be sex dependent: it was absent in 22.7% of males and 35.1% of females; its size was larger in males than in females (55 mm 2 vs. 31 mm 2 ) ( p  < 0.001). The AGN area did not vary between the facial types ( p  > 0.073). Its size showed weak correlations with skeletal parameters and no associations with masticatory muscles ( p  > 0.375). Our findings indicate that the AGN is more prevalent and pronounced in males, and that there was no evidence of a functional relationship.

Until now, no study has investigated the effects of masticatory muscle training on chewing function in people with dementia. This study aimed to investigate whether physiotherapeutic exercises for the masticatory muscles have an influence on chewing efficiency and bite force in people with dementia. In a clinical trial with stratified randomization subjects were assigned to three groups based on the Mini Mental State Examination (MMSE: group 1—28–30, group 2—25–27, group 3—18–24). Each group was divided into an experimental (ExpG, intervention) and control group (ConG, no intervention). As intervention a Masticatory Muscle Training (MaMuT) (part 1: three physiotherapeutic treatments and daily home exercises, part 2: daily home exercises only) was carried out. Chewing efficiency and bite force were recorded. The MaMuT influenced the masticatory performance regardless of the cognitive state. Bite force increased in ExpG 1 and 2. Without further training, however, the effect disappeared. Chewing efficiency increased in all ExpG. After completion of the training, the ExpG 2 and 3 showed a decrease to initial values. Subjects of ExpG 1 showed a training effect at the final examination, but a tendency toward the initial values was observed. ExpG 3 seemed to benefit most from the physiotherapeutic exercises in terms of improving chewing efficiency by the end of the intervention phase. ExpG 1 showed the greatest gain in bite force. The MaMuT program is a potential method of improving masticatory performance in people with cognitive impairment or dementia when used on a daily basis.

Background Diffusion spectral imaging (DSI) could overcome the inherent limitation of diffusion tensor imaging (DTI), but its outcomes in masticatory muscle fiber-tracking have not been well-established. Therefore, the objective of this prospective study conducted in China was to evaluate and compare the performance of DTI and DSI in human masticatory muscles. Methods The differences and reproducibility of architecture characteristics and diffusion properties derived from DTI and DSI were evaluated in the masticatory muscles of healthy volunteers ( n  = 25). The quality of tracked fiber was analyzed based on anatomical information. To assess the sensitivity of DTI and DSI to muscular microenvironment changes, the architecture characteristics and diffusion properties of the masticatory muscles in patients with temporomandibular joint disorders (TMDs) ( n  = 25) between different subgroups according to the course of diseases were explored. The paired-samples t -test or Wilcoxon signed-rank test, Student’s t-test or Mann-Whitney U test, one-way ANOVA or the Kruskal-Wallis test, and the post-hoc multiple comparisons with false discovery rate adjustment were performed. Bland-Altman plots, within-subject coefficient of variation (CV), and relative absolute difference (RAD) were used to evaluate the reproducibility. Results In the healthy group, DSI generated significantly more fibers in all masticatory muscles (all P  < 0.001) and fewer low-quality fibers in most masticatory muscles ( P <  0.050) than DTI did. Moreover, higher values of mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were found in DSI (all P  < 0.001). Satisfactory coefficient of variation (< 10%), relative absolute difference (< 10%), and agreement exhibited by the Bland-Altman analysis were found between two scans in both DTI and DSI. Compared with DTI, DSI found additional significant changes in the masticatory muscles of TMDs patients. Conclusions Although both DTI and DSI allowed reproducible assessment of masticatory muscles, significant differences existed between them. DSI was more sensitive to the microenvironment changes of the masticatory muscles in TMDs patients.

Background and Objectives: The occlusal angle (OA), influenced by pillow height, may affect muscle tension in the head and neck. However, its optimal range for minimizing muscle activation has not been clearly defined. This study aimed to investigate the effects of OA on the resting muscle activity of masticatory and cervical muscles and to identify an optimal OA range using cluster analysis and linear mixed-effects modeling. Materials and Methods: The resting muscle activities of the masseter (MAS), temporalis (TEM), sternocleidomastoid (SCM), and posterior vertebral muscles (PVM) were measured at OA conditions modulated by pillow heights of 0, 5, and 10 cm at 0, 1, and 5 min in the supine position. Intraclass correlation coefficients (ICCs) assessed measurement reliability. Statistical analyses included ANOVA, ROC curve analysis, k-means clustering, and linear mixed-effects models. Results: MAS and TEM resting muscle activity ratio (RMR) significantly increased with larger OA values (p < 0.001), while SCM showed decreased activation (p = 0.001). An OA range of 105°–111° was identified as the center of a low-activity cluster, and an upper cut-off of 138° was associated with potential muscular overload. ICC values for MAS and SCM ranged from 0.82 to 0.89, indicating excellent test–retest reliability. Conclusions: OA modulated by pillow height is a modifiable factor that influences muscle activity. An OA of 105°–111° may serve as a practical comfort zone, especially for individuals at risk of TMDs.

Study Objectives: Sleep bruxism is characterized by rhythmic masticatory muscle activity (RMMA). This study aimed to determine the number and type of jaw muscles needed for a valid RMMA scoring in individuals with obstructive sleep apnea. Methods: Ten individuals with obstructive sleep apnea (4 males; age, 50.1 ± 8.1 years) were included in this study. RMMA was scored using 1 or more of the following jaw muscles’ electromyography (EMG) traces of polysomnography recordings: bilateral masseter and temporalis (4MT; the reference standard), unilateral masseter (1M), bilateral masseter (2M), unilateral temporalis (1T), bilateral temporalis (2T), unilateral chin EMG (1C), and bilateral chin EMG (2C). Results: 1M, 2M, 1T, and 2T showed excellent agreement with 4MT (intraclass correlation coefficient = 0.751, 0.976, 0.815, and 0.950, respectively), while 1C and 2C presented fair agreement (intraclass correlation coefficient = 0.662 and 0.657). In addition, 2M and 2T displayed good sensitivity (87.8% and 72.0%) and positive predictive value (83.1% and 76.0%). In contrast, 1M and 1T had good sensitivity (88.4% and 87.8%) but fair positive predictive value (60.1% and 53.2%). 1C and 2C showed poor sensitivity (41.1% and 40.3%) and fair positive predictive value (62.9% and 60.6%). Conclusions: Polysomnography with bilateral masseter or temporalis muscle EMG traces is regarded valid in RMMA scoring in individuals with obstructive sleep apnea. In contrast, unilateral masseter or temporalis muscle EMG showed only fair accuracy, and chin EMG had poor accuracy. Consequently, these montages cannot be recommended for RMMA scoring in the presence of obstructive sleep apnea. Clinical Trial Registration: Registry: ClinicalTrials.gov; Name: The Effects of Oral Appliance Therapy on Masseter Muscle Activity in Obstructive Sleep Apnea; URL: https://clinicaltrials.gov/ct2/show/NCT02011425 ; Identifier: NCT02011425. Citation: Li D, Aarab G, Lobbezoo F, Arcache P, Lavigne GJ, Huynh N. Accuracy of sleep bruxism scoring based on electromyography traces of different jaw muscles in individuals with obstructive sleep apnea. J Clin Sleep Med . 2022;18(6):1609–1615.

Botulinum toxin type A (BoNT-A), a potent neurotoxin, is increasingly used to treat myogenic temporomandibular disorders (TMDs); however, the interplay between muscle atrophy and pain relief remains incompletely understood. This pilot study investigated how masseter and temporalis muscle thickness and pain intensity change over 12 weeks following BoNT-A injections in 15 patients (mean age 51.42 years) with myogenic TMD. Muscle thickness was measured via ultrasonography across multiple anatomical positions under both clenching and resting conditions at baseline and at 2, 4, 8, and 12 weeks post-injection. Significant thinning of both muscles occurred within 2 weeks, lasting until 12 weeks, but became less pronounced after the first month. Pain intensity showed parallel decreases, most notably early on, but these reductions were not consistently statistically significant. Correlation analyses revealed no strong persistent association between muscle thickness and pain except for a moderately positive correlation in the anterior temporalis at two weeks (r = 0.61, p = 0.04). BoNT-A induces rapid masticatory muscle atrophy and modest pain relief; however, these outcomes do not coincide. Pain relief was observed earlier than the full development of muscle atrophy and should be considered during TMD pain management.

Background To evaluate the effect of Low Level Laser (LLL) application at the points of greatest pain in patients with chronic masticatory muscle pain. Methods A total number of 30 (21 women, 9 men, with a mean age of 39.2) were selected after the diagnosis of MPDS according to the Research Diagnostic Criteria for Temporomandibular Disorder (RDC/TMD). The patients were randomly divided into three groups; laser group I ( n  = 10); patients received the LLL at the point of greatest pain, laser group II ( n  = 10); patients received LLL at pre-established points in the effected muscles and placebo group ( n  = 10). LLL and placebo were applied three times per week, for a total of 12 sessions. Mandibular mobility was examined, masticator muscles tenderness were assessed and PPT values were obtained. Subjective pain levels were evaluated using VAS. The measurements performed before the treatment and after the completion of the therapy. Descriptive statistics (mean, standard deviation, and frequency) Student’s t -test, Mann–Whitney U -test and paired-sample t -tests were used for analysis. Results In both laser groups, there was a statically significant reduction in PPT values of the muscles, number of muscles without any pain on palpation increased significantly, mandibular movements’ ranges were improved. Laser group I demonstrated statistically better results than the Laser group II in all of the measured values. Plasebo group did not show any statistically difference in any of the measured values. Conclusions LLLT can be accepted as an alternative treatment modality in the management of masticatory muscle pain and direct irradiation seems to effect better. Trial registration Current Controlled Trials ISRCTN31085 , Date of registration 28/08/20145.

This study investigated the effect of low-level laser therapy (LLLT) on the masticatory performance (MP), pressure pain threshold (PPT), and pain intensity in patients with myofascial pain. Twenty-one subjects, with myofascial pain according to Research Diagnostic Criteria/temporomandibular dysfunction, were divided into laser group ( n  = 12) and placebo group ( n  = 9) to receive laser therapy (active or placebo) two times per week for 4 weeks. The measured variables were: (1) MP by analysis of the geometric mean diameter (GMD) of the chewed particles using Optocal test material, (2) PPT by a pressure algometer, and (3) pain intensity by the visual analog scale (VAS). Measurements of MP and PPT were obtained at three time points: baseline, at the end of treatment with low-level laser and 30 days after (follow-up). VAS was measured at the same times as above and weekly throughout the laser therapy. The Friedman test was used at a significance level of 5 % for data analysis. The study was approved by the Ethics Committee of the Federal University of Sergipe (CAAE: 0025.0.107.000-10). A reduction in the GMD of crushed particles ( p  < 0.01) and an increase in PPT ( p  < 0.05) were seen only in the laser group when comparing the baseline and end-of-treatment values. Both groups showed a decrease in pain intensity at the end of treatment. LLLT promoted an improvement in MP and PPT of the masticatory muscles.