Assessment of thickness and function of masticatory and cervical muscles in adults with and without temporomandibular disorders

Objective

The aim of this study was to evaluate the maximal bite force (MBF), electromyographic (EMG) activity and thickness of the masseter, anterior part of the temporalis and sternocleidomastoid (SCM) muscles in a group of young adults with and without temporomandibular disorders (TMDs).

Design

Nineteen individuals comprised the TMD group (6 males/13 females, aged 25.4 ± 3.8 years), classified based on the Research Diagnostic Criteria for TMD (RDC/TMD), and 19 comprised the control group (6 males/13 females, aged 24.1 ± 3.6 years). The MBF was determined with a transducer placed between the dental arches at the first molars level (N). The muscles were evaluated bilaterally at rest and during maximal voluntary clenching (MVC) by assessing EMG activity and performing ultrasonography (USG). The mean values of these measures for both sides of the mouth were used. The normality of the distributions was assessed by the Shapiro–Wilks test. Variables between groups and genders were compared using two-way factorial ANOVA test and correlated using the Spearman coefficient (α = 0.05). Unpaired t test was used to compare variables between TMD subgroups. Logistic regression analysis was used to identify the variables associated with the presence of TMD.

Results

MBF, EMG and USG data were similar among clinical groups and among TMD subgroups. The thickness of masseter and SCM muscles in the relaxed and clenching states were significantly higher in males than females. On the other hand, the EMG of the temporalis muscle in the rest state was significantly higher in females than males. Additionally, the MBF was positively correlated with the USG characteristics of masseter and SCM muscles, as well as with the EMG activity of masseter and temporalis muscles in the TMD group. In this group, there was also a positive correlation between the thickness of the masseter muscle and its activity. On the other hand, the thickness of the SCM muscle was negatively correlated with its activity. A lower MBF was independently associated with the presence of TMD.

Conclusions

Subjects with TMD exhibited similar values of MBF, thickness and electrical activity of masticatory and cervical muscles when compared with controls; positive correlations observed between these variables may suggest a muscular alteration in TMD patients and a co-activation of masticatory and cervical muscles during mandibular movement. This fact may also be confirmed by the negative association between bite forces and presence of TMD.     

Occlusal force, electromyographic activity of masticatory muscles and mandibular flexure of subjects with different facial types

Objective

The aim of this study was to evaluate whether vertical facial patterns influence maximal occlusal force (MOF), masticatory muscle electromyographic (EMG) activity, and medial mandibular flexure (MMF).

Material and Methods

Seventy-eight dentate subjects were divided into 3 groups by Ricketts''s analysis: brachyfacial, mesofacial and dolychofacial. Maximum occlusal force in the molar region was bilaterally measured with a force transducer. The electromyographic activities of the masseter and anterior temporal muscles were recorded during maximal voluntary clenching. Medial mandibular flexure was calculated by subtracting the intermolar distance of maximum opening or protrusion from the distance in the rest position. The data were analyzed using ANOVA followed by Tukey''s HSD test. The significance level was set at 5%.

Results

Data on maximum occlusal force showed that shorter faces had higher occlusal forces (P<0.0001). Brachyfacial subjects presented higher levels of masseter electromyographic activity and medial mandibular flexure, followed by the mesofacial and dolychofacial groups. Additionally, dolychofacial subjects showed significantly lower electromyographic temporalis activities (P<0.05).

Conclusion

Within the limitations of the study, it may be concluded that maximum occlusal force, masticatory muscle activity and medial mandibular flexure were influenced by the vertical facial pattern.     

Effect of capsaicin-evoked jaw-muscle pain on intramuscular blood-flow

Aim

To investigate effect of capsaicin-evoked masseter-muscle pain on intramuscular blood-flow (BF) at rest and during contractions.

Methods

Eight healthy men (22-31 years) participated. BF was measured with Laser Doppler (Moor Instruments, UK) using a single-fibre probe inserted into the right masseter. Three BF probes were attached to the skin above right and left masseter and the right-middle finger. Subjects performed 30 s isometric contractions at 5%, 15%, and 25% of maximal voluntary contraction. After the contractions, capsaicin (0.1 mL, 100 μg/mL) was injected into the right masseter close to the fibre probe. When the pain sensation had disappeared, the series of submaximal contractions were repeated. BF data were sampled continuously, processed in 10 s bins, and analyzed with repeated-measures ANOVAs.

Results

Intramuscular BF significantly increased immediately after capsaicin injection (P < 0.050) and rapidly (30 s) decreased to pre-injection values. A significant increase in cutaneous BF above the right masseter was observed (P < 0.050) and lasted for 10 min, while a significant BF decrease in the finger (P < 0.050) was observed. The contractions were associated with increases in intramuscular BF before and after the injection (P < 0.022) and the contraction levels were also associated with increase in intramuscular BF before injection (P = 0.008) but not after injection (P = 0.314).

Conclusions

This study demonstrated BF increased by muscle contraction but failed to show effects of contraction levels on BF in a muscle exposed to nociceptive stimuli. Neurogenic inflammation in muscles could possibly be mediated via antidromical effects and local release of vasoactive substances. The decreased BF in the finger could be due to involvement of central regulatory mechanisms.     

功能性矫治器打开大鼠下颌对咀嚼肌生物力学特性的影响

目的探讨功能性矫治器对咀嚼肌生物力学特性的影响及其临床意义。方法选用３０只生长期Ｗｉｓｔａｒ雄性大鼠，戴功能性上颌平面导板活动矫治器４周后，应用力学的测试方法对其嚼肌、二腹肌前腹及翼外肌生物力学特性的改变进行定量分析。结果咀嚼肌收缩性质发生了明显变化：嚼肌收缩速度加快，收缩张力增强；二腹肌前腹收缩速度变慢，收缩张力增强；翼外肌的收缩张力明显减弱。结论本项实验表明，功能性矫治器是通过改变咀嚼肌及二腹肌的生物力学特性来促进颌骨的生长改建，达到功能性颌骨矫形目的     

肌电图在偏侧咀嚼研究中的应用

目的 使用肌电仪研究偏侧咀嚼对咀嚼肌功能的影响.方法 选择20名女性受试者,分为两组,实验组10名右侧咀嚼和对照组10名正常咀嚼者,引导她们分别在牙间交错位(ICP)进行牙列轻接触和最大咬合,用肌电图仪记录下嚼肌和颞肌前束的肌电信号数据,进行统计学分析.结果 最大咬合时,实验组的右嚼肌的肌电电位明显小于对照组(P＜0.05).结论 右侧咀嚼的患者有侧嚼肌的活动较双侧咀嚼者明显减少.     

早接触与肌电图分析

目的：研究在实验性早期接触状态下咀嚼肌肌电活动的变化,为临床预防、诊断、治疗因早接触引起的肌功能紊乱,颞下颌关节疾患提供参考。方法：测定10名志愿者在正中He;左右两侧下颌第一双尖牙,第一磨牙,第二磨牙实验性早接触状态下,嚼肌、颞肌前束及二腹肌前腹肌电活动的积分值与频谱值。结果：早接触与正常情况下正中咬合时比较,颞肌前束肌电信号明显减弱（P＜0．01）,嚼肌肌电信号减弱（P＜0．05）,二腹肌前腹肌电活动无显著差异（P＞0．05）,结论：早接触可导致咀嚼肌功能减少,两侧肌张力不平衡,破坏咀嚼肌群的协调性,中枢控制咀嚼肌收缩能力大小主要由抑制闭口肌的收缩来完成,而作为闭口肌的拮抗肌、二腹肌前腹的作用有待于进一步研究。     

Heterogeneous activation of the medial pterygoid muscle during simulated clenching

The aim of this study was to investigate whether the medial pterygoid muscle shows differential activation under experimental conditions simulating force generation during jaw clenching. To answer this question, the electromyographic activity of the right medial pterygoid was recorded with two intramuscular electrodes placed in an anterior and posterior muscle region, respectively. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with strain gauges. The activity distribution in the muscle was recorded in a central mandibular position during generation of eight different force vectors at a constant amount of force (F=150 N). The investigated muscle regions showed different amounts of EMG activity. The relative intensity of the activation in the two regions changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for various motor tasks. The results indicate a heterogeneous activation of the medial pterygoid muscle under test conditions simulating force generation during clenching. This muscle behaviour might offer an explanatory model for the therapeutic effects of oral splints.     

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.     

Bite force in children with bruxism

The bite force of 51 twelve-year-old bruxists was compared with that of a control group of the same age, in order to establish whether bruxism affects bite force and whether there is any connection between the degree of tooth abrasion and bite force. Criteria for bruxism were bruxo facets in the bite and, in the same children, teeth-grinding at the time of examination. No differences in bite force values for bruxists and non-bruxists were found for either very light bite or maximum bite. One group with dentine facets had a higher bite force value for very light bite than the children with enamel facets. Otherwise there was no difference between the various facet groups regarding the bite force produced.     

牙齿重度磨耗患者咀嚼肌肌电的实验研究

目的 :研究重度牙齿磨耗 (TW )患者咀嚼肌的肌电活动 ,探讨不同类型牙合磨耗患者咀嚼肌受损的肌电表现。方法 :以 15例中老年重度牙齿磨耗患者为研究对象 ,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颞肌前束 (TA)、咬肌 (MM )、二腹肌前腹 (DA )的肌电幅值 ;并以 8例正常牙合患者的咀嚼肌肌电幅值作为对照。结果 :姿势位时 ,磨耗Ⅰ、Ⅱ、Ⅲ组患者TA、MM、DA的平均肌电幅值高于对照组 ,TA、MM的肌电幅值增高显著大于对照组 (P <0 .0 1) ;ICP最大紧咬时 ,Ⅰ、Ⅱ、Ⅲ组患者TA、MM、DA平均肌电幅值降低 ,MM、DA肌电幅值与对照组比较有显著性差异 (分别为P <0 .0 1,P <0 .0 5 )。结论 :牙齿磨耗患者有肌紧张存在 ,Ⅲ型磨耗导致的不均匀接触对咬肌的损伤较大     

Patterns of masseter muscle activities during sleep in guinea pigs

Basic neurophysiological mechanisms for sleep bruxism remain unknown. Analyses of masseter muscle activity during sleep in guinea pigs have shown that the duration and activity of masseter bursts differ between non-rapid eye movement (NREM) and rapid eye movement (REM) sleep and that some repetitive burst episodes do occur. Furthermore, masseter bursts occurred in association with a transient heart rate increase. These results suggest that various patterns of masseter bursts occur in association with transient arousal activity during sleep in guinea pigs.     

全口义齿患者咀嚼功能与人工牙硬度关系的实验研究

目的 研究不同材料的人工牙修复对全口义齿患者咀嚼功能的影响。方法 选择15例颌关系正常、无口颌系统疾病的无牙颌受试者，为每位受试者制作三副全口义齿，测定每副义齿的咀嚼效率和最大咬合力。结果 戴不同人工牙的全口义齿患者的咀嚼效率和最大咬合力均无统计学差异，而同种义齿性别间存在显著性差异。结论 全口义齿患者咀嚼功能与人工牙的硬度无密切关系，而受其年龄、性别、口颌系统健康状况及义齿支持组织条件等因素影响。     

Test–retest reliability of electromyographic variables of masseter and temporal muscles in patients with cerebral palsy

IntroductionThe aim of this study was to evaluate the reliability of surface electromyography of the masticatory muscles in patients with cerebral palsy.MethodsSurface electromyography was performed over the masseter and temporal muscles in 15 patients with cerebral palsy with the mandible at rest and during maximum clenching effort in two sessions. The data were analyzed using the root mean square amplitude, mean frequency, median frequency, zero crossings and approximate entropy.ResultsIn the within-day evaluations, intraclass correlation coefficients were higher (0.80–0.98) for the all electromyography variables and muscles during maximum clenching effort. In the resting position, the coefficients revealed good to excellent reliability (0.61–0.95) for root mean square, mean frequency, median frequency and zero crossings and fair to good reliability (0.53–0.74) for approximate entropy. In the between-day evaluations, the coefficients revealed good to excellent reliability (0.60–0.86) for mean frequency, median frequency, zero crossings and approximate entropy. In the resting position, the coefficients revealed poor to fair reliability (0.23–0.57) for all electromyography variables studied. The root mean square had the highest standard errors during maximum clenching effort (2.37–5.91) and at rest (1.47–6.86).ConclusionMean frequency, median frequency and approximate entropy are the most reliable variables of surface electromyography signals of the masseter and temporal muscles during maximum clenching effort in individuals with cerebral palsy. These measures can be used to evaluate the function and behaviour of the masticatory muscles in this population following oral rehabilitation and surgical oral procedures as well as for the study the physiology of these muscles.     

Co-activation of jaw and neck muscles during submaximum clenching in the supine position

Objective

The purpose of this study was to test the hypothesis that jaw clenching induces co-contraction and low-level long-lasting tonic activation (LLTA) of neck muscles in the supine position.

Design

Ten healthy subjects developed various feedback-controlled submaximum bite forces in different bite-force directions in supine position. The electromyographic (EMG) activity of the semispinalis capitis, semispinalis cervicis, multifidi, splenius capitis, levator scapulae, trapezius, sternocleidomastoideus, masseter and infra/supra-hyoidal muscles was recorded. For normalization of EMG data, maximum-effort tasks of the neck muscles were performed.

Results

Co-contractions of the posterior neck muscles varied between 2% and 11% of their maximum voluntary contraction. Different bite forces and bite-force directions resulted in significant (p < .05) activity differences between the co-contraction levels of the neck muscles. In addition, LLTA of specific neck muscles, provoked by the jaw clenching tasks, was observed.

Conclusions

This study demonstrated for the first time moderate co-contractions of jaw and neck muscles in the supine position under controlled submaximum jaw clenching forces. LLTA of most neck muscles was observed, outlasting clenching episodes and indicating an additional neuromuscular interaction between the two muscle groups.     

Chewing in patients with severe neurological impairment

OBJECTIVE AND DESIGN: As degenerative disease, infarction and hemorrhage in the CNS may compromise chewing, the aim was to classify and analyse such chewing disturbances. The case series included clinical and electromyographic recordings from 10 patients (ages 12-78 years) with neurological disorders. RESULTS: Classifications were involuntary munching (two women with dystonia which was abolished during mastication), ceased chewing function (three men with impaired volitional motor control and spasticity from locked-in syndrome, restricted chewing range (two men and one woman with reduced jaw opening due to paradoxical activity after brainstem lesions), and distorted chewing pattern (two men with dystonia resulting in blockings during chewing). CONCLUSION: The effect of the neurological impairment illustrated the complex control of mastication and the interaction between central and peripheral mechanisms, and the variation of the chewing disturbances was surprisingly great, even with similar diagnosis.     

Sleep less and bite more: Sleep disorders associated with occlusal loads during sleep

Occlusal overload during sleep is a significant clinical issue that has negative impacts on the maintenance of teeth and the longevity of dental prostheses. Sleep is usually viewed as an ‘out-of-functional’ mode for masticatory muscles. However, orodental structures and prostheses are not free from occlusal loads during sleep since masticatory muscles can be activated at a low level within normal sleep continuity. Thus, an increase in masticatory muscle contractions, by whatever the cause, can be associated with a risk of increased occlusal loads during sleep. Among such conditions, sleep bruxism (SB) is a type of sleep-related movement disorders with potential load challenge to the tooth and orofacial structures. Patients with SB usually report frequent tooth grinding noises during sleep and there is a consecutive increase in number and strength of rhythmic masticatory muscle activity (RMMA). Other types of masticatory muscle contractions can be non-specifically activated during sleep, such as brief contractions with tooth tapping, sleep talking, non-rhythmic contractions related to non-specific body movements, etc.; these occur more frequently in sleep disorders. Studies have shown that clinical signs and symptoms of SB can be found in patients with sleep disorders. In addition, sleep becomes compromised with aging process, and a prevalence of most sleep disorders is high in the elderly populations, in which prosthodontic rehabilitations are more required. Therefore, the recognition and understanding of the role of sleep disorders can provide a comprehensive vision for prosthodontic rehabilitations when prosthodontists manage complex orodental cases needing interdisciplinary collaborations between dentistry and sleep medicine.     

Comparison of immediate complete denture, tooth and implant-supported overdenture on vertical dimension and muscle activity

PURPOSE

To compare the changes in the occlusal vertical dimension, activity of masseter muscles and biting force after insertion of immediate denture constructed with conventional, tooth-supported and Implant-supported immediate mandibular complete denture.

MATERIALS AND METHODS

Patients were selected and treatment was carried out with all the three different concepts i.e, immediate denture constructed with conventional (Group A), tooth-supported (Group B) and Implant-supported (Group C) immediate mandibular complete dentures. Parameters of evaluation and comparison were occlusal vertical dimension measured by radiograph (at three different time intervals), Masseter muscle electromyographic (EMG) measurement by EMG analysis (at three different positions of jaws) and bite force measured by force transducer (at two different time intervals). The obtained data were statistically analyzed by using ANOVA-F test at 5% level of significance. If the F test was significant, Least Significant Difference test was performed to test further significant differences between variables.

RESULTS

Comparison between mean differences in occlusal vertical dimension for tested groups showed that it was only statistically significant at 1 year after immediate dentures insertion. Comparison between mean differences in wavelet packet coefficients of the electromyographic signals of masseter muscles for tested groups was not significant at rest position, but significant at initial contact position and maximum voluntary clench position. Comparison between mean differences in maximum biting force for tested groups was not statistically significant at 5% level of significance.

CONCLUSION

Immediate complete overdentures whether tooth or implant supported prosthesis is recommended than totally mucosal supported prosthesis.