Structure and function of masticatory muscles in a case of muscular dystrophy

Histologic examination of muscle biopsies and functional examination comprising electromyography and force measurements in a 19-yr-old boy with muscular dystrophy showed different wasting patterns of mandibular elevator and depressor muscles. Pronounced histopathologic changes were present in the masseter muscle, whereas pathologic findings in the anterior digastric muscle were limited to increased number of cells in slightly enlarged interfiber connective tissue. The masticatory pattern was distorted, and strength of mandibular elevator muscles was less than one third of the norm, whereas depressor strength corresponded more to reference values. This difference of muscular wasting might be caused by protective enzymes in the digastric muscle and/or functionally induced damage of the masseter. As affection from muscular dystrophy may vary greatly between the masticatory muscles, structural and functional examination should be used routinely to clarify prognosis before initiation of treatment procedures.     

An electromyographic evaluation of bilateral symmetry of masticatory, neck and trunk muscles activity in patients wearing a positioner

Summary  This study was designed to investigate the attitude of a positioner (Finition^©) or an Hawley's retention appliance to create a symmetric function of the masticatory, neck and trunk muscles during the orthodontic retention phase. Sixteen patients (18·5 ± 2·2 years) were included in the sample. All the patients received an orthodontic therapy for the treatment of an Angle's class I malocclusion and skeletal class I, for a period of 2 years. After removal of orthodontic brackets, eight patients wore a teeth positioner (group I) as retention appliance and eight subjects wore an Hawley's appliance as upper retention (group II). Surface electromyographic (sEMG) activity was recorded from the bilateral anterior temporal, posterior temporal, masseter, sternocleidomastoid (SCM), upper and lower trapezius and cervical muscles at mandibular rest position and during maximal voluntary clenching (MVC) at T0, i.e. soon after the removal of orthodontic brackets and at T1, i.e. after 3 months of retention treatment. No significant difference was observed between the two groups at T0. At T1, at mandibular rest position, the group I showed a significantly lower sEMG activity of anterior temporal and SCM muscles compared with the group II. During MVC, at T1, the group I showed a significantly lower sEMG activity of the SCM and posterior cervicals, compared with the group II. The positioner seems to show a relevant effect on the sEMG activity of masticatory, neck and trunk muscles.     

持续性高正加速度对咀嚼肌纤维酶组织化学特性的影响

目的：观察持续性高正加速度重复作用对大鼠咀嚼肌纤维酶组织化学特性的影响。方法：雄性Wistar大鼠20只随机分成对照组和实验组。对照组固定于离心机转臂上，俯卧位，头向轴心， 1Gz离心5min。实验组体位同对照组， 10Gz离心30s，间隔时 1Gz离心60s，连续每天5次，每周4天，共3周。进行咬肌和颞肌肌纤维烟酰胺腺嘌呤二核苷酸四唑还原酶(NADH-TR)和腺苷三磷酸酶(ATP酶)染色分析。结果：与对照组相比，实验组咬肌和颞肌Ⅱ型纤维横截面积减小，Ⅱ型纤维百分构成比下降。结论：持续性高正加速度重复作用导致的咬肌和颞肌损伤可能具有Ⅱ型肌纤维横截面积减小的特点。     

Ageing and surface EMG activity patterns of masticatory muscles

Summary The purpose of this study was to evaluate the influence of age on the electromyographic activity of masticatory muscles. All volunteers were Brazilian, fully dentate (except for Group I – mixed dentition), Caucasian, aged 7–80, and divided into five groups: I (7–12 years), II (13–20 years), III (21–40 years), IV (41–60 years) and V (61–80 years). Except for Group V, which comprised nine women and eight men, all groups were equally divided with respect to gender (20 M/20 F). Surface electromyographic records of masticatory muscles were obtained at rest and during maximal voluntary contraction, right and left laterality, maximal jaw protrusion and maximal clenching in the intercuspal position. Statistically significant differences (P < 0·05) were found in all clinical conditions among the different age groups. Considerably different patterns of muscle activation were found across ages, with greater electromyographic activity in children and youth, and decreasing from adults to aged people.     

17β-雌二醇对大鼠咀嚼肌成肌细胞内钙离子影响的实验研究

目的观察17β- 雌二醇对体外培养的大鼠咀嚼肌成肌细胞胞浆中钙离子（ Ca2+）的影响。方法体外培养1周龄雌性SD大鼠的咀嚼肌成肌细胞，以酸刺激模拟咀嚼肌疲劳状态，以Fluo- 4- AM对细胞内Ca2+染色，通过激光共聚焦显微镜动态观察一段时间内正常pH值条件下以及酸性刺激下17β- 雌二醇对咀嚼肌成肌细胞胞浆中Ca2+浓度的影响。结果正常pH值条件下，加入浓度为10- 9、10- 8、10- 7 mol/L的17β- 雌二醇后，细胞内Ca2+浓度迅速升高，随后迅速下降并在与正常pH值时胞浆Ca2+浓度相当的水平上重新形成动态平衡。酸性刺激条件下，加入浓度为10-9、10-8、10- 7 mol/L的17β- 雌二醇后，细胞内Ca2+浓度迅速降低，并在比原来低的水平上形成新的动态平衡。结论本实验观察到一定浓度的雌激素能够使酸性刺激下咀嚼肌成肌细胞胞浆内Ca2+浓度维持在较低的水平，从而减少胞浆Ca2+的超载，维持咀嚼肌正常的功能。     

头颈部放射治疗对咀嚼肌神经电生理的影响

目的:探讨放疗后开口受限的发病机制,为临床放射治疗后开口受限的预防和治疗提供一定的实验依据.方法:以接受头颈部放射治疗后的7例患者为研究对象.分别对患者健、患侧咬肌、翼内肌与翼外肌进行同心圆针肌电图(EMG)检查,同时测量患者开口度.对受照射侧与未受照射侧咀嚼肌静息状态下出现失神经电位情况进行统计分析.结果:放射区域涉及咬肌有4例患者:肌肉静息状态下2例患者患侧咬肌出现失神经电位;肌肉大力收缩状态下2例患者患侧咬肌无募集电位;该4例患者开口度分别为16mm、31mm、15mm和9mm.放射区域涉及咬肌、翼内肌与翼外肌的有3例患者:肌肉静息状态下1例患者患侧翼外肌、咬肌出现失神经电位,1例患者患侧咬肌、翼内肌与翼外肌均出现失神经电位;肌肉大力收缩状态下,1例患者患侧咬肌、翼内肌与翼外肌均无募集电位.该3例患者开口度为39mm、17mm、5mm.受照射侧与未受照射侧出现失神经电位咀嚼肌数差异有统计学意义(p＜0.01).结论:头颈部放射治疗可引起放射区域咀嚼肌神经电生理异常改变,造成放射性周围神经病理性损伤;咀嚼肌神经肌肉系统的放射损伤是放射治疗后开口受限的发生因素之一.     

头位左倾和右倾变化对咀嚼肌肌电的影响

目的：研究不同的头位变化对咀嚼肌肌电活动的影响。方法：以30例健康正常[牙合]受试者为研究对象，通过肌电图仪（EMG）测试下颌姿势位和牙尖交错位最大紧咬时，5种头位姿势的颞肌前束（TA）、颞肌后束（TP）、咬肌（MM）、二腹肌前腹（DA）的肌电幅值，并对结果进行统计学分析。结果：下颌姿势位和紧咬位时，与正中头位相比，头左倾和右倾状态时咀嚼肌的肌电值变化无显著性差异（P〉0．05）。结论：咀嚼肌在头位左倾和右倾变化过程中所受影响不大。     

下颌前突患者胸锁乳突肌和咀嚼肌的肌电研究

目的 探讨下颌前突患者在下颌运动和姿势位时,双侧颞肌前束(TA)、咬肌(MM)、二腹肌前腹(DA)和胸锁乳突肌(SCM)的肌电活动情况,为临床进行正颌手术提供参考数据.方法 选取于中国医科大学口腔医院颌面外科就诊的下颌前突患者32名为研究对象,运用美国BioEMG Ⅱ八道表面肌电仪和BioFLEX带状双极表面电极记录患...     

Reliability of electromyographic activity vs. bite-force from human masticatory muscles

The reproducibility of electromyographic (EMG) activity in relation to static bite-force from masticatory muscles for a given biting situation is largely unknown. Our aim was to evaluate the reliability of EMG activity in relation to static bite-force in humans. Eighty-four subjects produced five unilateral static bites of different forces at different biting positions on molars and incisors, at two separate sessions, and the surface EMG activities were recorded from temporalis, masseter, and suprahyoid muscles bilaterally. Intraclass correlation coefficients (ICCs) were determined, and an ICC of ≥ 0.60 indicated good reliability of these slopes. The ICCs for jaw-closing muscles during molar biting were: temporalis muscles, ipsilateral 0.58-0.93 and contralateral 0.88-0.91; and masseter muscles, ipsilateral 0.75-0.86 and contralateral 0.69-0.88. The ICCs for jaw-closing muscles during incisor biting were: temporalis muscles, ipsilateral 0.56-0.81 and contralateral 0.34-0.86; and masseter muscles, ipsilateral 0.65-0.78 and contralateral 0.59-0.80. For the suprahyoid muscles the 95% CIs were mostly wide and most included zero. The slopes of the EMG activity vs. bite-force for a given biting situation were reliable for temporalis and masseter muscles. These results support the use of these outcome measurements for the estimation and validation of mechanical models of the masticatory system.     

Activity patterns of the masticatory muscles during feedback-controlled simulated clenching activities

In 10 normal subjects, the electromyographic (EMG) activities of the masseter, anterior and posterior temporalis, medial pterygoid, inferior lateral pterygoid, as well as the anterior digastric, were bilaterally recorded during clenching with various resulting force vectors. The intraoral force transfer was achieved with a three-component force transducer. The direction and magnitude of the force vectors were controlled by visual feedback. The goal of the study was to investigate how various clenching directions at constant magnitude of force influence the EMG activity in the masticatory muscles during gradual increase of the horizontal force component. Depending on the force direction and the individual muscle, an increase or decrease of activity was observed during clenching with increasing horizontal force components at constant magnitude of force. The inferior lateral pterygoid exhibited the highest activation (about 80% of maximal voluntary clenching) of all masticatory muscles. The medial pterygoid showed the greatest range of variation in activation behavior, and it was the most active muscle in relation to all clenching directions. In conclusion, the results show that with growing horizontal force components at constant magnitude of force, all muscles demonstrated an increase or decrease of activity in several clenching directions.     

Regression analysis of electromyographic activity of masticatory muscles versus bite force

Electromyographic (EMG) activity of the superficial masseter and the anterior temporal muscles versus the bite force was studied in 10 young women. They were fully dentate and had no dysfunction of the stomatognathic system. The descending part of the trapezius muscle was also chosen for EMG registration. The average bite force between the first molars was 396 N (Newton). Steeper slopes for the EMG versus force regression curve at high contraction levels than at low contraction levels for the superficial masseter muscle may indicate that this muscle has a recruitment pattern that differs from that of the anterior temporal muscle. In the case of the anterior temporal muscle there was no difference between the slopes for the EMG-force regression at low and high contraction levels. There was significantly increased activity in the descending part of the trapezius muscle mainly during high bite force levels in half the subjects.     

正颌手术后咀嚼肌改变的研究进展

正颌手术通过打破原有的颌骨系统,重建咬合平衡来达到改善面型和咀嚼功能的目的。随着现代医学的发展和人们观念的进步,正颌外科被越来越多的患者所接受,其疗效和安全性也得到了学术界的肯定,但是也有少部分术后恢复不佳甚至治疗失败的病例存在。颌面部解剖结构复杂,影响预后的因素较多,尤其正颌术后颌面部软组织的变化难以动态观察,至今其变化过程及机制尚不明确。本文就近年来正颌术后咀嚼肌改变的研究进展作一综述。     

Electromyographic activity of the masticatory and cervical muscles during resisted jaw opening movement

One of the relaxation techniques that have been used by physical therapists when treating patients with temporomandibular disorders, is the agonist contract-antagonist relax technique (AC). When the AC technique is applied, a submaximal resistance to the jaw opening movement is necessary to cause relaxation of the masticatory muscles. No information about the effect of this technique on masticatory or cervical muscles has been found in the literature. Thus, the aim of this study was to evaluate the electromyographic activity of the masseter and anterior temporalis and the upper trapezius and splenius capitis during resisted jaw opening movement. A convenience sample of 30 students was used. Electromyography activity of the superficial masseter, anterior temporalis, upper trapezius and splenius capitis was registered before, during and after the application of this resistive movement to jaw opening. A two-way anova with repeated measures analysis was used to analyse data. The level of significance was at alpha = 0.05. The EMG activity of both the masticatory muscles and the cervical muscles increased during and after the application of resisted jaw opening (P < 0.05). Based on the results obtained from this study, the behaviour of all muscles analysed (masseter, anterior temporalis, splenius capitis and upper trapezius) was similar. All muscles increased their activity when the resistance to the jaw opening movement was applied. Complex muscular interactions of the supra- and infrahyoid muscles (jaw openers), masticatory muscles, and cervical muscles may exist to stabilize the craniomandibular system during resisted jaw opening.     

Effects of a functional appliance on masticatory muscles of young adults suffering from muscle-related temporomandibular disorders

The aim of this study was to investigate the effects of an original orthodontic functional appliance [function generating bite for deep bite correction (FGB-D)] on masticatory muscle activity in subjects suffering from muscle-related temporomandibular disorders (TMD). Electromyographic (EMG) analysis was performed on 33 young adults (nine men, 24 women) to evaluate the contractile symmetry of the right and left masseter and anterior temporalis muscles. The subjects were divided into three groups: a muscle-related TMD group requiring orthodontic treatment for deep bite correction (three men, eight women) and treated with FGB-D; a muscle-related TMD group not requiring orthodontic treatment (three men, eight women) and treated with a Michigan occlusal splint; and a TMD-free group (three men, eight women) as a control group. Records were made by surface EMG of maximum voluntary teeth clenching, with and without the functional appliance or occlusal splint in place, before and after 12 months of therapy. A torque index was derived from the surface EMG recordings to estimate lateral displacement of the mandible. The results show that the FGB-D corrects the torque index and thus the lateral displacement of the mandible.     

Co‐contraction behaviour of masticatory and neck muscles during tooth grinding

The objective of this study was to analyse the co‐contraction behaviour of jaw and neck muscles during force‐controlled experimental grinding in the supine position. Twelve symptom‐free subjects were enrolled in the experimental study. Electromyographic (EMG) activity of semispinalis capitis, splenius capitis and levator scapulae muscles was recorded bilaterally with intramuscular fine‐wire electrodes, whereas that of sternocleidomastoideus, infrahyoidal, suprahyoidal, masseter and anterior temporalis muscles were registered with surface electrodes. EMG and force measurements were performed during tasks simulating tooth grinding on custom‐made intraoral metal splints. The mean EMG activity normalised by maximum voluntary contraction (% MVC) of each of the neck muscles studied during grinding was analysed and compared with previous data from jaw clenching at identical force (100 N) and (supine) position. The occurrence of low‐level, long‐lasting tonic activation (LLTA) of motor units was also documented. The mean three‐dimensional force vector of the grinding forces was 106 ± 74 N. In the frontal plane, the incline to the midsagittal plane ranged between 10° and 15°. In the midsagittal plane, the incline to the frontal plane was negligibly small. Posterior neck muscle activity during grinding ranged between 4.5% and 12% MVC and during clenching with 100 N between 1.8% and 9.9% MVC. Masticatory muscle activity during grinding ranged between 17% and 21% MVC for contralateral masseter and ipsilateral temporalis and between 4% and 6.5% for ipsilateral masseter and contralateral temporalis. LLTA had an average duration of 195 ± 10 seconds. The findings from this study do not support pathophysiological muscle chain theories postulating simple biomechanical coupling of neck and jaw muscles. Co‐contractions of neck and masticatory muscles may instead occur as a result of complex neurophysiological interactions.     

单侧后牙缺失对咀嚼肌肌电图的影响

目的:观察单侧后牙缺失对咀嚼肌肌电图的影响,从而探讨单侧后牙缺失在颞下颌关节(temporomandibular joint, TMJ)发病中的作用。方法:对40例单侧上颌后牙缺失患者组成的缺牙组和40例牙列完整的自愿者组成的对照组,进行肌电图检查。结果:缺牙组无论是松弛状态或紧咬时咀嚼肌的电位明显高于对照组(P<0.05),并且缺牙组紧咬时同名肌不对称性活动增加(P<0.05),其中对照组的咬肌肌电活动的对称性明显高于缺牙组(P<0.01),以上变化缺牙侧较非缺牙侧显著(P<0.05)。结论:单侧后牙缺失可以对咀嚼肌肌电图造成影响,可能是颞下颌关节疾病的发病原因之一。     

Electromyographic activity of masticatory, neck and trunk muscles of subjects with different skeletal facial morphology--a cross-sectional evaluation

The electromyographic pattern activity of masticatory, neck and trunk muscles was assessed using surface electromyography (sEMG) in 60 Caucasian adult females (20 subjects in skeletal class I, 20 subjects in skeletal class II and 20 subjects in skeletal class III), classified on the base of their skeletal class (ANB angle), corrected on the base of maxillary and mandibular rotations. The sEMG activity was recorded at mandibular rest position and during maximal voluntary clenching. At mandibular rest position, the sEMG activities of masseter and anterior temporal muscles were significantly higher in class III subjects than in class I and class II subjects, that showed no significant difference between them. Then, the sEMG activities of posterior cervicals and upper trapezius were significantly higher in skeletal class III subjects than in the other two groups. During maximal voluntary clenching, no significant difference was observed in the sEMG activity of masticatory muscles among the three considered groups. However, the sEMG activities of posterior cervicals and upper trapezius were significantly higher in skeletal class III subjects than in the other two groups, which showed no significant difference between them. In conclusion, the skeletal class seems to affect the sEMG pattern activity of masticatory, neck and trunk muscles.     

Effects of delayed‐onset muscle soreness on masticatory function

The aim was to clarify the effects of experimentally provoked delayed‐onset muscle soreness (DOMS) in the jaw‐closing muscles on subjective and objective measures of masticatory function. Twenty‐one dentate female subjects, without pain‐related signs and symptoms of temporomandibular disorders, participated. Delayed‐onset muscle soreness was provoked with eccentric and concentric contractions of the jaw‐closing muscles using a custom‐made apparatus. At baseline, and 24 h and 1 wk after the exercises, data were gathered on the subjective measures of muscle fatigue, muscle pain, and masticatory chewing ability using visual analogue scale (VAS) scores, on the maximum voluntary bite force (MVBF), and on the food Mixing Ability Index (MAI). After 24 h, muscle fatigue and muscle pain had increased and the MAI had decreased. All had returned to baseline levels after 1 wk. There were no significant changes found in the chewing ability VAS scores and in the MVBF over time. After correction for its baseline value, the MAI after 24 h was found to be significantly related to the muscle pain after 24 h. In conclusion, DOMS in the jaw‐closing muscles can cause a decrease in the objectively scored chewing ability, while the subjectively scored chewing ability remained the same.