Effect of treatment of dentofacial deformities on the electromyographic activity of masticatory muscles

Individuals with dentofacial deformities present changes in masticatory muscles. The objective of the present study was to determine the influence of interdisciplinary treatment in cases of class III dentofacial deformities regarding the EMG activity of the temporal (T) and masseter (M) muscles. The study was conducted on 15 patients with class III dentofacial deformities who were submitted to orthodontic, oromyofunctional and surgical treatment and assigned to groups P1 (before surgery) and P2 (6-9 months after surgery). Fifteen individuals with no alterations in facial morphology or dental occlusion and without signs or symptoms of temporomandibular joint dysfunction were used as controls (CG). The T and M muscles were submitted to EMG bilaterally in the situations of mastication and mastication plus biting, with analysis of amplitude interval and root mean square. For all muscles tested, there was a difference between CG, P1 and P2; CG was higher than P2 and P2 higher than P1 in all situations assessed. We conclude that there was an increase in EMG activity in the T and M muscles after surgical correction of the dentofacial deformity accompanied by interdisciplinary treatment, although the values were still lower than those obtained for CG.     

Effect of treatment of dentofacial deformity on masseter muscle thickness

OBJECTIVE: The objective of the present study was to determine the modifications in masseter muscle thickness before and after interdisciplinary orthodontic, oromyofunctional and surgical treatment of class III dentofacial skeletal deformities (DFSD). DESIGN: Fifteen patients with class III DFSD participated in the study, denoted P1 group before the interdisciplinary treatment and P2 group (same patients) 6-8 months after surgery. Fifteen individuals with no DFSD were used as the control group. Bilateral ultrasonography (US) of the masseter muscle under resting and biting conditions was performed in the three groups. RESULTS: There was a significant difference (P<0.01) for all muscles tested between the control, P1 and P2 groups, with greater thickness for controls, intermediate thickness for P2, and the lowest thickness for P1 in all situations evaluated. CONCLUSION: We conclude that there was an increase in masseter muscle thickness after surgical correction of DFSD accompanied by interdisciplinary treatment, although the values were still lower than those observed in the control group.     

Masticatory function in retrognathic patients, before and after mandibular advancement surgery.

PURPOSE: Mandibular retrognathia is a dentofacial deformity that can be surgically corrected. The purpose of this study was to evaluate the influence of orthognathic surgery on masticatory function in a sample of retrognathic patients and to compare these findings with those of controls. PATIENTS AND METHODS: Eleven retrognathic patients were tested before and 1 to 1.5 years after mandibular advancement surgery and compared with 12 controls. The median particle size after chewing a silicon rubber test food, the maximum bite force, and the electromyographic activity (EMG) of the anterior temporalis and the masseter muscles during isometric clenching and during chewing were determined. Patients, before and after treatment, and controls were statistically compared by analysis of variance. RESULTS: Surgical correction of mandibular retrognathia did not change chewing efficiency, maximum bite force, EMG during maximal clenching, EMG during chewing, or the EMG/bite-force relationship. Compared with controls, the chewing efficiency, maximum bite force, EMG during maximal clenching, and EMG during chewing values were lower. No difference for the EMG/bite-force ratio at maximal clenching was found, indicating similar muscle efficiency for patients and controls. However, in the range of 10% to 40% of the maximum bite force, the slope of the EMG/bite-force regression line was steeper for the patients than for the controls, indicating decreased muscle efficiency for patients. CONCLUSIONS: The results of this study suggest that in retrognathic patients, function of the masticatory system is impaired. Oral function was not influenced by mandibular advancement surgery.     

不同牙合型人群咀嚼肌肌电活动的研究

目的:利用肌电图仪测量不同牙合型人群咀嚼肌肌电活动,分析比较各组人群的咀嚼肌肌电特点和差异。方法:1)选取符合实验标准的自愿者33人,平均年龄21.71岁。分组,正常对照组10人,安氏Ⅰ类错牙合组10人,安氏Ⅱ类错牙合组8人,安氏Ⅲ类错牙合组5人;2)用肌电图仪测量各组人群的测量不同牙合型的咀嚼肌肌电活动;3)用SPSS17.0软件进行统计学分析,得出各组人群的咀嚼肌肌电特点和差异。结果:1)静息状态下,显著性>0.05,各组人群咀嚼肌的电位变化没有显著性差异;2)咀嚼过程中,安氏Ⅲ类错牙合畸形组,与正常对照组、安氏Ⅰ类错牙合畸形组、安氏Ⅱ类错牙合畸形组相比,咬肌的电位值显著性<0.05,存在显著性差异;3)吞咽时,①安氏Ⅱ类错牙合畸形组人群,与正常对照组间咬肌的电位比较,显著性<0.05,存在显著性差异;②安氏Ⅲ类错牙合畸形组人群,与正常对照组、安氏Ⅰ类错牙合畸形组咬肌的电位相比较,显著性<0.05,存在显著性差异;③安氏Ⅲ类错牙合畸形组与其余3组二腹肌电位相比较,显著性<0.05,存在显著性差异。4)不同状态时各组人群两侧咀嚼肌肌电变化不同,存在相关性与差异性。结论:不同牙合型人群在咀嚼和吞咽过程中,咀嚼肌肌电活动有所不同,推断错牙合畸形可影响咀嚼肌的正常功能运动。     

肉毒杆菌毒素对兔颞下颌关节骨关节病咀嚼肌肌电的影响

目的：研究肉毒杆菌毒素对颞下颌关节骨关节病咀嚼肌功能的影响,为应用肉毒杆菌毒素治疗该病提供依据.方法：30只兔作咀嚼肌肌电图检查,其结果作为肌电正常值,并应用胶原酶注射法制成颞下颌关节骨关节病动物模型,随机分为2组.实验组兔双侧嚼肌、颞肌注射肉毒杆菌毒素,对照组仅为骨关节病状态.分别于4、8、12周末对2组兔作咀嚼肌肌电图检查,分析对比2组兔肌电电位的变化.所得资料用SPSS11.0软件行团体t检验.结果：姿势位时,对照组各时间点肌电电位显著高于正常;实验组在4周、8周末低于正常,12周末与正常相比无显著差异（P＞0.05）.牙尖交错最大紧咬状态下,对照组各时间点肌电电位显著低于正常;实验组在4周、8周末略低于正常,12周末与正常相比无显著差异（P＞0.05）.结论：肉毒杆菌毒素能改变颞下颌关节骨关节病咀嚼肌的功能状态,促进肌功能恢复正常.     

Masticatory muscle activity and hyoid bone behavior during cyclic jaw movements in man. A synchronized electromyographic and videofluorographic study

Synchronized electromyography (EMG) and videofluorography were used to relate the EMG activity from the suprahyoid and masseter muscles and the movement of the hyoid bone to different phases of the jaw open-close-clench cycle. The subjects investigated comprised 19 adult males with normal dentofacial appearances. Five subjects were excluded from the analyses because of a uniform suprahyoid EMG pattern during cyclic jaw movements. The results from the remaining fourteen subjects revealed that mandibular opening was preceded by suprahyoid EMG activity and movement of the hyoid bone in an upward-forward direction. During jaw opening and the first half of the jaw-open phase, EMG activity was registered exclusively from the suprahyoid muscles. The hyoid bone was moved downward-backward during jaw opening. Mandibular closing was preceded by masseter EMG activity and movement of the hyoid bone in a further downward-backward direction. During jaw closing the hyoid bone moved upward and forward. Discrete EMG bursts from the suprahyoid muscles were occasionally registered simultaneously with the masseter EMG activity during jaw closing. No absolute reciprocity existed between suprahyoid and masseter muscle activity during cyclic jaw movements. A period of no EMG activity from either the suprahyoid muscle group or the masseter muscle was noted during the jaw-open phase and the occlusal phase.     

An electromyographic evaluation of the bilateral symmetry and nature of masticatory muscle activity in jaw deformity patients during normal daily activities

This study was designed to investigate the nature of masticatory muscle activity and the balance in the bilateral symmetry of the masticatory muscle activity in jaw deformity patients. Fifteen patients (19.9 +/- 5.3 years) with lateral shift of the mandible caused by transverse craniofacial deformity and 15 controls (28.6 +/- 1.9 years) were used as the subjects in this study. Surface electromyographic (EMG) activities were recorded from the bilateral masseter and anterior temporal muscles during daytime (142 min, including mealtime) and sleep (142 min). The averaged rectified EMG values were normalized with reference to the EMG amplitude induced by a 98-N bite force. Bilateral symmetry of masseter and anterior temporal muscle activities was examined using an asymmetry index (AI) for both the controls and the patients. The normalized activities of the masseter and anterior temporal muscles during normal daily activities were lower in patients than in the controls. Asymmetry indices in patients were significantly greater during usual daytime activities and sleep for the anterior temporal muscle and significantly smaller during sleep for the masseter muscle as compared with the controls. The results show that masticatory muscle activity is lower in these jaw deformity patients in association with more prominent asymmetry of anterior temporal muscle activity than in the controls. It is suggested that these findings are highly relevant to occlusal interference and instability because of malocclusion and lateral mandibular deviation.     

Implant-supported prosthesis following Brånemark protocol on electromyography of masticatory muscles

Summary This research evaluated the effects of Brånemark protocol on electromyography of the masseter and temporal muscles. The patients were divided into two groups: Group I: patients who wore an implant‐supported prosthesis in the mandibular arch following Brånemark protocol, and maxillary removable complete dentures; Group II: dentate individuals (control). Electromyography was carried out at rest, right (RL) and left (LL) laterality, protrusion and maximum voluntary contraction (MVC). Data were compared by t‐test. At rest, a higher electromyographic (EMG) activity was observed in Group I, and the values were significant in the right masseter and left temporal muscles. In RL, there were statistically significant differences for right masseter (P < 0·01), left masseter and temporal muscles and for the left temporal muscle in LL (P < 0·05). In protrusion, Group I presented a higher EMG activity, and there was a statistically significant difference for the right masseter muscle (RM) (P < 0·05). In MVC, the EMG values were higher in Group II (control), but significant just for the right temporal muscle (P < 0·05). In conclusion, individuals with mandibular fixed dentures supported according to the Brånemark protocol and maxillary removable complete dentures showed a higher activity of masticatory muscles during the mandibular postural clinical conditions examined; however, in the MVC, Group I presented lower values when compared to dentate group. Despite presenting different EMG values in all of the clinical conditions, both groups showed similar EMG patterns of muscle activation which demonstrates that the proposed treatment can be considered as a good option for oral rehabilitation.     

Influnece of an occlusal splint on integrated electromyography of the masseter muscles

In order to examine the effect of an occlusal splint on the integrated electromyography (EMG) of the masticatory muscles, EMG of bilateral masseter muscles of 23 patients with temporomandibular joint disturbance syndrome (TMJDS), with and without an occlusal splint, was measured and integrated on line during maximum clenching. It was found that the integrated myoelectrical value of the masseter muscle on the involved and non-involved side was reduced with the occlusal splint. The absolute difference between integrated myoelectrical values in the left and right masseter muscles was reduced with an occlusal splint, but the relative difference remained virtually unchanged. These results indicate that the occlusal splint can decrease masseter muscle activity and thus exert a therapeutic effect.     

Masseter muscle thickness three years after surgical correction of class III dentofacial deformity

Objective

To analyse the effect of integrated orthodontic treatment, orthognathic surgery and orofacial myofunctional therapy on masseter muscle thickness in patients with class III dentofacial deformity three years after orthognathic surgery.

Design

A longitudinal study was conducted on 13 patients with class III dentofacial deformities, denoted here as group P1 (before surgery) and group P3 (same patients 3 years to 3 years and 8 months after surgery). Fifteen individuals with no changes in facial morphology or dental occlusion were assigned to the control group (CG). Masseter muscle ultrasonography was performed in the resting and biting situations in the three groups. Data were analysed statistically by a mixed-effects linear model considering a level of significance of P < 0.05.

Results

Significantly higher values (P < 0.01) of masseter muscle thickness (cm) were detected in group P3 (right rest: 0.82 ± 0.16, left rest: 0.87 ± 0.21, right bite: 1 ± 0.22, left bite: 1.04 ± 0.28) compared to group P1 (right rest: 0.63 ± 0.19, left rest: 0.64 ± 0.15, right bite: 0.87 ± 0.16, left bite: 0.88 ± 0.14). Between P3 and CG (right rest: 1.02 ± 0.19, left rest: 1 ± 0.19, right bite: 1.18 ± 0.22, left bite: 1.16 ± 0.22) there was a significant difference on the right side of the muscle (P < 0.05) in both situations and on the left side at rest.

Conclusion

The proposed treatment resulted in improved masseter muscle thickness in patients with class III dentofacial deformity.     

A preliminary study of maximum voluntary bite force and jaw muscle efficiency in pre-orthognathic surgery patients.

The functional state of dentofacial deformity patients before orthognathic surgery has received relatively little study. In this study, the ability to generate occlusal force was compared between 84 patients before treatment for various dentofacial deformities and 57 controls. Maximal and submaximal bite forces were measured at the incisor and right and left first molar bite positions. Electromyographic activity (EMG) was recorded bilaterally from the anterior temporalis, posterior temporalis, and masseter muscles during each bite. An efficiency ratio was calculated for the jaw muscles by dividing the level of EMG by the occlusal force. There was a reduced ability to generate occlusal forces in the patients before surgery, especially among female patients. The reductions in maximal occlusal force were correlated with reduced efficiency of the jaw muscles.     

Masseter muscle changes following orthognathic surgery

Abstract Objective: To evaluate the long-term changes of masseter muscle morphology in skeletal Class III patients with facial asymmetry following two-jaw orthognathic surgery (Le Fort I osteotomy + intraoral vertical ramus osteotomy). Materials and Methods: Using computed tomography (CT), a longitudinal study was conducted on 17 skeletal Class III patients with facial asymmetry. Measurements from the reconstructed three-dimensional (3D) CT images were compared from T1 (before surgery), T2 (1?year after surgery), and T3 (4?years after surgery). The maximum cross-sectional area (CSA), orientation, thickness, and width of the masseter muscle were measured on both the deviated and nondeviated sides. The control group included 17 volunteers with skeletal and dental Class I relationships without dentofacial deformities. Results: At T1, there were no significant differences in CSA, thickness, or width of masseter muscle between the deviated and nondeviated sides. Masseter muscle orientation was significantly more vertical on the nondeviated side than on the deviated side at T1 (P < .01); no significant bilateral differences were noted at T2 and T3. At T1, masseter muscle measurements were significantly lower than controls (P < .01). During T1-T3, a significant increase was noted in CSA, thickness, and width (P < .01) of masseter muscle. At T3, no significant difference was noted between the study and control groups. Conclusion: After surgery, the masseter muscle measurements of skeletal Class III asymmetry patients showed no significant differences compared with the control group within the 4-year follow-up period, indicating adaptation to the new skeletal environments and increased functional demand.     

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。     

Masticatory muscle reaction in simulated low-velocity rear-end impacts

AIMS: To evaluate the electromyographic (EMG) activity of masseter and temporalis muscles in relation to impact awareness, gender, impact magnitude, and kinematics of head movement in simulated low-velocity rear-end impacts. METHODS: Twenty-nine individuals (17 men and 12 women) were subjected in random order to 3 rear-end impacts: 2 unexpected impacts (chair accelerations of 4.5 m/s2 and 10.1 m/s2) and 1 expected impact (chair acceleration of 10.1 m/s2). The EMG activity of the deep and superficial masseter muscle was recorded bilaterally. EMG activity was also recorded for the left anterior temporalis muscle. Angular acceleration and angular displacement of the head were also recorded. The temporal relationship between onset of the masticatory muscle activity and maximum peak of the kinematics of head movement was determined. RESULTS: The magnitude of normalized masticatory EMG activity ranged from 1.4 to 1.8 times higher (P < .05) for fast unexpected impacts compared to slow unexpected impacts in all masticatory muscles. The magnitude of normalized anterior temporalis EMG peak response ranged from 1.8 to 2.5 times higher (P < .05) in female subjects than in male subjects for all impacts. No significant differences were identified for impact awareness in the magnitude of normalized EMG activity for any masticatory muscle. No significant differences were identified with respect to timing of masticatory muscle response (P > .05). CONCLUSION: EMG activity increased with increased impact magnitude. Temporal and amplitude awareness of a simulated impact did not produce a difference in the masticatory muscle response. Gender differences were identified in the anterior temporalis muscle response. The onset of the masticatory muscle response occurred after peak angular acceleration of the head but prior to peak angular displacement of the head.     

Influence of pre-orthodontic trainer treatment on the perioral and masticatory muscles in patients with Class II division 1 malocclusion

The aim of this follow-up study was to evaluate the effects of Pre-Orthodontic Trainer (POT) appliance on the anterior temporal, mental, orbicularis oris, and masseter muscles through electromyography (EMG) evaluations in subjects with Class II division 1 malocclusion and incompetent lips. Twenty patients (mean age: 9.8 ± 2.2 years) with a Class II division 1 malocclusion were treated with POT (Myofunctional Research Co., Queensland, Australia). A group of 15 subjects (mean age: 9.2 ± 0.9 years) with untreated Class II division 1 malocclusions was used as a control. EMG recordings of treatment group were taken at the beginning and at the end of the POT therapy (mean treatment period: 7.43 ± 1.06 months). Follow-up records of the control group were taken after 8 months of the first records. Recordings were taken during different oral functions: clenching, sucking, and swallowing. Statistical analyses were undertaken with Wilcoxon and Mann-Whitney U-tests. During the POT treatment, activity of anterior temporal, mental, and masseter muscles was decreased and orbicularis oris activity was increased during clenching and these differences were found statistically significant when compared to control. Orbicularis oris activity during sucking was increased in the treatment group (P < 0.05). In the control group, significant changes were determined for anterior temporal (P < 0.05) and masseter (P < 0.01) muscle at clenching and orbicularis oris (P < 0.05) muscle at swallowing during observation period. Present findings indicated that treatment with POT appliance showed a positive influence on the masticatory and perioral musculature.     

单侧下颌骨发育过度畸形咀嚼肌肌电活性的研究

目的：研究下颌骨发育性不对称畸形患者下颌骨附丽肌的功能状况,探讨该类畸形与咀嚼肌肌电活性的关系。方法：以１０例成年单侧下颌骨过度发育性不对称畸形患者为研究对象,通过肌电图仪测试双侧颞肌、咬肌、二腹肌在功能活动时的肌电变化,进行该类患者双侧咀嚼肌肌电活性比较;并以１０例正常下颌骨双侧咀嚼肌肌电活性作为对照。结果：在单侧下颌骨发育过度性不对称畸形患者中,双侧咀嚼肌的肌电活性具有显著差异,其双侧肌电活性     

Masticatory muscle activity in myotonic dystrophy patients

summary The aim of the study was to compare the masticatory pattern and the activity of the masticatory muscles of a group of myotonic dystrophy patients with those of a group of healthy individuals. The electromyographic (EMG) activity of the temporal and the masseter muscles was measured in the resting position, during maximal clenching, and while the patient was chewing five peanuts until swallowing. It was found that the patients had approximately 3 times less EMG activity in the masticatory muscles during maximal clenching. During chewing the patients had approximately half the activity in the anterior temporal and the masseter muscles, while the activity of the posterior temporal muscle did not differ significantly from that in healthy individuals. No differences were found in the muscle activity in the resting position or in the speed of chewing between the groups. The patients needed more time and more chewing cycles to bring the five peanuts to the swallowing threshold, but possibly this was an effect of the lower number of antagonizing teeth. Myotonic dystrophy thus influences the masticatory muscles, reducing their activity both at a maximal and a functional level.     

The amplitude distribution of electromyographic activity in painful masseter muscles during unilateral chewing

The aim of this study was to investigate whether the amplitude distribution of electromyographic activity (EMG) in terms of muscular load revealed any differences between patients with painful masseter muscles and referents during the chewing of an almond and of gum. The relative masticatory forces of the masseter muscle and the anterior temporal muscle during chewing were calculated by a transformation of the muscular load levels of EMG activity (microV) to load levels of relative masticatory force (%RVC). This was done by regression in reverse of an isometric reference voluntary contraction (RVC) for EMG versus bite force biting on a bite-force sensor. The maximal bite-force values for patients and referents were similar. The relative masticatory force for chewing an almond was higher than that for gum-chewing. The peaks of the relative masticatory forces were similar for both patients and referents. During the chewing of an almond the relative masticatory forces of the masseter muscle below the peak load were higher for patients than referents. During gum-chewing the patients used higher forces than referents for 70% of the total chewing time analysed. This also applied to the anterior temporal muscle when chewing an almond. Estimates of the peak masticatory forces were calculated in newtons.     

Electromyographic activity of lower lip muscles when chewing with the lips in contact and apart

Masticatory muscle activity is coordinated with perioral muscle during chewing. Subjects with competent lips usually chew with the lips in light contact, whereas subjects with incompetent lips possibly have dysfunctional chewing. In this study, the electromyographic (EMG) activities of the lower lip and masseter muscles were recorded when chewing with the lips in contact and apart. At first, 37 subjects were divided into an incompetent lip group and competent lip group on the basis of EMG activity of the lower lip muscle at rest. The durations of the masseter nonactive phase and total phase when chewing with lips in contact were shorter in the incompetent lip group than in the competent lip group. In the incompetent lip group, when chewing with the lips apart, the EMG activity of lower lip in the masseter nonactive phase was significantly (P < .05) higher than in the competent lip group, but there was no difference in the EMG activity in the masseter active phase between two groups. Our results suggest that subjects with incompetent lips have difficulty chewing while their lips are relaxed. We conclude that the inability of sealing the lips and lip dysfunction could possibly affect masticatory function.     

Controlled study of EMG activity of the jaw closers and openers during mastication in patients with myasthenia gravis

Mastication was evaluated in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in remission who previously suffered from bulbar symptoms, and healthy controls. Bulbar myasthenia gravis may impair mastication due to weakness of the masticatory muscles. The aim of the study was to objectively evaluate the influence of myasthenia gravis on mastication. The subjects chewed a piece of breakfast cake and chewed 1 min on a piece of chewing gum. Surface EMG of the masseter muscle, temporalis muscle and jaw opener muscles was recorded. Statistical analysis revealed that bulbar patients produced significantly less EMG activity in the closing phase of a chewing cycle in both experiments. The EMG of the masseter muscle expressed as percentage of the maximum EMG during maximal clenching showed significantly higher values in the bulbar group than in the other groups. This was not found for the temporalis muscle. It was suggested that bulbar patients use a strategy of limited effort to produce a bolus that can be swallowed. The ocular patients and the patients in remission showed no subclinical impairments in muscle function during chewing.