Lateral preference in mastication: an electromyographic study

To study concurrence of specific electromyographic chewing patterns and the side of mastication, twelve subjects chewed gum for 15, 20 and 25 s. Gum bolus placement on the right or left side of the dentition was estimated by three series of visual inspections. Contraction patterns of the chewing and non-chewing side masseter muscles were appraised by integrated and cumulative surface electromyography. Consistent and predominant gum bolus placement on the right side of the dentition could be predicted fairly reliably from comparative electromyographic observations. This was also the case in instances of consistent left-sided gum bolus placement, but not in predominant left-sided bolus placement. The latter phenomenon was explained by deviant observations made in two subjects only. Agreement between a presumed chewing side and a predictive contractility pattern was established in 78% of observations (P less than 0.001).     

腭裂咽成形术后患者异常语音的发音特点研究

目的：对腭裂咽成形术后患者的发音特点和发生机制进行探讨。方法：本组病例82例(男46，女36)，年龄4～31岁(平均13.44岁)。采用汉语语音清晰度测试表(包含音节、词、词组、短句)对患者录音，并对其语音清晰度、异常语音、代偿性发音进行分析比较。结果：在82例患者巾，以腭咽闭合不全型为持点的代偿性语音71例：声门塞音60例、咽摩擦音11例；以腭咽闭合良好型为特点的代偿性语音11例：腭化音6例、腭化 侧化音2例、侧化音3例．清晰度：声门塞音46.27％、咽摩擦音57.19％、腭化音67．17％、腭化 侧化音74．67％、侧化音77．50％．异常辅音多见于塞音、擦音、塞擦音，辅音的弱化以送气音p66．67％(8／12)、t78.95％(15／19)、s60％(39／64)、sh60％(39／64)、c66％(43／65)、ch66％(43／65)、x62％(39／63)、q67％(43／64)、k76％(31／41)、b73％(43／59)所占比例较多；辅音的脱落则以不送气音z81％(56／69)、zh81％(56／69)、i80％(56／70)、g84％(48／57)所占比例较多。结论：咽成形术后仍以腭咽闭合不全型为特点的代偿性语音为主，主要表现为辅音的脱落与弱化。产生弱化的辅音多见于送气音，产生脱落的辅音则多见于不送气音．     

不同功能运动时翼外肌上下头的肌电研究

目的 探讨翼外肌上下头在不同功能运动中的肌电变化规律，以期深入了解翼外肌上下头的功能特征。方法 检测了16例健康青年男性在牙尖交错位(intercuspal position，ICP)紧咬及小张口(约10mm)、中度张口(约25mm)状态下，翼外肌上下头的肌电活动。结果 翼外肌上头在小张口时电位(0．10mv)低于ICP紧咬时的电位(0．21mv)，而中度张口时电位(0．17mv)接近于ICP紧咬时的电位；翼外肌下头在ICP紧咬、小张口、中度张口时电位(0．14mv、0．24mv、0．34mv)递增。结论 翼外肌上下头均参与张口运动，共同将髁状突、关节盘拉向前下方。而在ICP紧咬时，翼外肌上头亦收缩，其作用是维持生理状态下关节盘相对于髁状突、关节结节的稳定关系。     

The reproducibility of electromyographic recordings of the masseter muscle in humans

An investigation was undertaken into the reproducibility of electromyograms of masseter muscles in five human subjects. Under standardized conditions, integrated electromyographic recordings were taken during three sessions on each of 5 days. Analysis of variance showed that at the 0-05 probability level the results were reproducible for each subject not only during the same day but also between days.     

Role of the soft palate in respiration: an electromyographic study in the dog

The present study investigates the nature of tensor veli palatini muscle (TVP) and levator veli palatini muscle (LVP) as accessory respiratory muscles. In the first part of the study, the relation between the muscles' activities as revealed by EMG activities and respiration rhythm was analysed under various combinations of partial pressures of O2 and CO2 in the arterial blood. Furthermore, the effect of sodium cyanide (NaCN) perfused through the carotid sinus was examined. During resting breathing, no EMG activity was recorded from either muscle. In hypercapnic or hypoxemic conditions produced by rebreathing, TVP exhibited a phasic EMG activity during inspiration. LVP showed a phasic EMG activity during expiration in hypoxic conditions (PaO2 less than 40 mmHg). NaCN perfused bilaterally through the carotid sinus induced the phasic EMG activities similar to those observed in hypercapnia and/or hypoxemia. TVP was more sensitive to NaCN than LVP. The second part of the study examined specific roles of the muscles in altered states of breathing. At the time of onset of LVP activity induced by rebreathing, the oral proportion of airflow markedly increased. On the other hand, TVP activity greatly increased in amplitude when negative pressure was applied to the upper airway. The results suggest that both muscles are accessory respiratory muscles and are regulated by chemogenic inputs including those from the carotid body; TVP is an accessory inspiratory muscle that contributes to the maintenance of upper airway patency, and LVP is an accessory expiratory muscle that increases the portion of expiratory airflow through the oral cavity.     

Masticatory muscle function after unilateral condylar fractures: a prospective and quantitative electromyographic study

Electromyographic (EMG) recording of masticatory muscle activity was performed in 9 adult men with unilateral condylar fracture immediately after conservative treatment of the condylar fracture (TO) and 4 (T1) and 8 (T2) months after the trauma. From TO to T2, maximal voluntary contraction of the anterior and posterior temporal muscles and of the masseter muscle opposite the fracture side (contralateral) increased significantly. Activity in the anterior temporal muscles also rose significantly during natural chewing, whereas the masseter muscles remained at the same level, but activity consistently tended to be strongest contralaterally to the condylar fracture. In addition, there was a tendency from T1 to T2 for natural chewing to take place predominantly on the contralateral side. The most obvious overall changes during the follow-up were shorter and stronger contractions in all muscles during chewing, on the side of the impaired joint. The increase of activity in the anterior temporal muscles during maximal bite and natural chewing, and the occurrence of stronger and shorter contractions during ipsilateral chewing, were interpreted as signs of improved function due to healing and relief of pain from the impaired joint. On the other hand, there was a specific rise of maximal activity only in the contralateral masseter. and during natural chewing, activity was constantly stronger in the same muscle in combination with the tendency of increasing predominance of contralateral strokes. These traits specificly related to the masseter muscles were considered an indication of a permanent functional distortion due to reflex suppression on the fracture side as an after-effect of the injury.     

Anatomical and electromyographic studies of the digastric muscle

The techniques and sites for EMG recordings from the digastric muscles are controversial. To re-evaluate old techniques for recording from the digastric muscles, especially the posterior bellies, the morphology of the muscles was studied by conventional dissections and by examination of specimens sectioned in the frontal and the horizontal planes. Based on these anatomical findings, recording sites and approaches to them were developed for the anterior and posterior bellies of the digastric muscles. EMG recordings from the two bellies of the muscle were obtained from five healthy subjects. The EMG recordings were ranked according to muscle activity level and the activity within single muscles and between muscles compared using the Wilcoxon signed rank test. The anterior and posterior bellies had synchronized activity in all mandibular movements but were silent or had negligible activity with the mandible in the rest position, when the head was rotated, and while clenching. Both bellies had marked to very marked activity during jaw opening, and moderate to marked activity during protrusion, retrusion and lateral movements. During swallowing the anterior and posterior bellies had patterns characterized by bursts of activity of high amplitude and short duration. The two bellies were not, however, always synchronously active.     

Anatomical and electromyographic studies of the lateral pterygoid muscle

The relationships of the lateral pterygoid muscle within the infratemporal fossa were observed by conventional dissections and by examination of specimens sectioned in the horizontal and frontal planes. The following less well-known features were noted. At the origins of the superior and inferior heads there are regions in which the fibres are interlaced or closely overlapped by fibres of either the temporalis muscle or the medial pterygoid muscle. Fibres of the superior head insert not only into the meniscus of the temporomandibular joint, but also into the pterygoid fovea at the neck of the mandibular condyle. Specimens sectioned through the origin of the inferior head of the muscle show internal tendon lamellae consistent with a pennate structure. Electromyographic (EMG) activity was recorded in five healthy subjects using concentric needle and fine-wire electrodes. Strong to very strong activity was consistently observed in the superior head during clenching and tooth gnashing. The inferior heads were silent or had negligible to slight activity most of the time during ipsilateral movements or clenching, but were co-activated bilaterally, with strong to very strong activity during jaw opening, protrusion, swallowing, tooth gnashing and during passive retrusion. They showed marked activity unilaterally during contralateral movements.     

The validity of the masseteric post-stimulus electromyographic complex: a twin study.

The twin model was used to assess the validity of an electromyographically recorded, masseter muscle reflex by measuring the sensitivity and specificity. Results were satisfying, implying that in future studies this reflex could be used to calculate heritability estimates between monozygotic and dizygotic twins.     

华西改良腭咽肌瓣和Hogan咽后壁瓣术后腭咽功能及语音的对比研究

目的:通过对比研究华西改良腭咽肌瓣和Hogan咽后壁瓣2种术式在大龄腭裂患者术后腭咽功能和语音状况的变化,为临床大龄患者最佳术式的选择提供参考。方法:选择2009-01～2011-01行Hogan咽后壁瓣咽成形术(PF组,32例)和华西改良腭咽肌瓣咽成形术(P+SP组,49例)的患者,对其术后的腭咽闭合状况、共鸣、鼻漏气及辅音正确率、鼻呼吸通畅度进行分析对比统计。结果:PF组术后21例(62.50%)腭咽闭合完全;6例(18.75%)术后语音完全清晰。P+SP组术后VPC 30例(61.22%)腭咽闭合完全;13例(25.63%)语音完全清晰。PF组术后20例(62.5%)出现打鼾现象,P+SP组术后32例(65.31%)患者出现打鼾现象。PF和P+SP术式对术后腭咽闭合完全率、高鼻音、鼻漏气、辅音正确率以及呼吸的改变无差别。结论:2种术式都能显著提高患者的腭咽闭合率和语音清晰度。     

Replicability of electromyographic recordings of the masseter muscle during mastication

This study evaluates the reliability of a method to duplicate the location of surface electrodes for recording the electromyographic activity of masseter muscles during mastication and quantifying the activity by a microcomputer system. A plastic framework consisting of a bite fork and electrode positioners was used to place the electrodes by relating the positioners to an occlusal index and keeping this relationship constant at subsequent sittings. EMG recordings were repeated on two different days for each of 10 subjects while they performed standardized masticatory performance tests with peanuts and carrots. The muscle activity recorded with hardware integrators was an average of 26.7% of the computerized software integrations but measures derived from the two methods of integration were highly correlated (r = 0.965) and yielded similar results. Significant correlations were found between test sessions for each measure of masticatory performance and integrated EMG activity for ipsilateral and contralateral muscles. For each subject, no significant differences were found between sessions for any masticatory performance or EMG variable. The results indicate that reliable inter session EMG recordings during mastication can be made by using the template for positioning of the electrodes. In addition, the microcomputer data acquisition system provides results comparable to those obtained with conventional hardware integrators, with the added benefit of providing information on each individual stroke and its various components.     

An electromyographic study of masticatory and lip muscle function in patients with complete dentures

The activity of the anterior and posterior portions of the temporal muscle, of the masseter muscle, and of the upper and lower lips was studied with electromyography in 10 individuals with complete dentures. Recordings were made when the patients had old, ill-fitting dentures and 6 months after these were replaced with new dentures. The muscle activity was studied in the postural position of the mandible, during chewing and swallowing of three test foods, and during maximal biting. The maximal tooth tapping rate was also recorded. The postural muscle activity was the same with old and new dentures and comparable with that in patients with natural teeth. The muscle activity during maximal biting was markedly lower than in patients with natural teeth and lower with new than with old dentures. There was no difference in muscle activity between chewing with old and new dentures, but the activity was lower than in patients with natural teeth. This was not compensated for by a longer duration of chewing. The lips were not especially active during chewing in the complete denture wearers.     

External location of the buccinator muscle to facilitate electromyographic analysis

Electromyography is frequently used to measure the activity of masticatory muscles. It requires the precise setting of the electrodes, which demands the accurate location of the muscle to be evaluated. The purpose of this study was to investigate the accuracy of an external method to locate the buccinator muscle. Fifteen human cadavers were evaluated and planes were determined on the face using anatomic landmarks. An angle (a) was obtained at the intersection of these planes on the central point of buccinator muscle and measured with a protractor. The value of the angle allows locating the central point of buccinator muscle based on anatomic landmarks on the face. Statistical analysis of the collected data indicated an angle of 90 masculine with 95% reliability, thus proving the efficacy of the proposed method.     

Cross-sectional characteristics of the masseter muscle: an ultrasonographic study

Cross-sections of the masseter muscle may now be measured non-invasively using ultrasonography. The purpose of the present study was to determine (1) whether the scanning level may affect cross-sectional measurements and (2) whether measurements made at identical levels may be reproducible. The study included 42 asymptomatic volunteers. Unilateral ultrasonographic investigation was performed with a linear (B-scan) 7.5 Mhz small-part transducer to register cross-sections of the masseter muscle on five different levels. Scans were made on the relaxed and contracted muscle. Measurements were made in two sessions with a time interval of at least 5 min. Statistical analysis consisted of univariate analysis of variance for repeated measurements. Data were analysed for reproducibility by using the method error and measurement error. For the ultrsonographic measurements the main effects of the variables 'session' (P=0.0001), 'level' (P=0.0001), and 'condition' (P=0.0001) were significant. Analysis of simple session-within-level effects revealed a significant difference between the repeated measurements for the most upper level (P=0.022), the upper level (P=0.012), and the most lower level (P=0.0001) of the relaxed muscle. An additional significant effect was found for the most lower level of the contracted muscle (P=0.015). Cross-sections evaluated at the middle (method error=0.31 mm; measurement error=2.0%) and lower level (method error=0.32 mm; measurement error=2.4%) of the contracted muscle were the most reproducible. The conclusion is that ultrasonography is a reproducible method for measuring cross-sections at the middle and lower level of the contracted masseter muscle.