Masseter Vestibular evoked myogenic potentials: A new tool to assess the vestibulomasseteric reflex pathway

Purpose: This review article provides the readers with an in-depth insight in understanding and interpreting various research literatures on the masseter vestibular evoked myogenic potentials(mVEMP). The article also reviews the contemporary researches involving the clinical applications of the mVEMP. Conclusions: Masseter VEMP is an evolving yet clinically promising neuro-otology test tool that has recently gained more research interest and is considered an additional tool to diagnose various vestibular disorders. Masseter VEMP assesses the functional integrity of the acoustic-masseteric and vestibulo-masseteric reflex pathways. The mVEMP could be used as a complementary test to evaluate the same peripheral generator as the cervical VEMP but a different central pathway i.e., vestibulo-trigeminal pathway. Various research studies that have experimented on parameters such as the effect of different electrode montages(zygomatic vs mandibular configurations), stimulation rates, filter settings and stimuli used to evoke mVEMP have been discussed in this article that could assist in the optimization of a comprehensive clinical protocol. The latency and the amplitude of mVEMP waveforms serve as significant parameters in differentiating normals from those of the clinical populations. Along with the cVEMPs and oVEMPs, mVEMP might help diagnose brainstem lesions in REM Sleep behaviour disorders, Multiple Sclerosis and Parkinson's disease. However, further studies are required to probe in this area of research.

Preservation of Parotid Masseter Fascia in Preventing Frey's Syndrome

Objective: To compare the functional outcomes of patients who had parotid masseter fascia reserved and unreserved flap elevating scheme in parotidectomy, especially the morbidity of Frey's syndrome. Methods: Twenty-three patients (group A) had parotid masseter fascia reserved in the parotidectomy, 32 patients (group B) had parotid masseter fascia unreserved in the operation. Compare the morbidity of gustatory sweating syndrome of the two groups. Results: Follow-up after 6 months to 2.5 years, gustatory sweating syndrome occurred in 4 patients of group A (17%), 17 patients in group B (57%). Conclusion: Reservation technic of the parotid masseter fascial in parotidectomy could prevent regeneration of parasympathetic nerve and thus prevent Frey's syndrome post-operation.

The effect of EMG magnitude on the masseter vestibular evoked myogenic potential(mVEMP)

Introduction:The masseter vestibular evoked myogenic potential(mVEMP)is a bilaterally generated,electromyographically(EMG)-mediated response innervated by the trigeminal nerve.The purpose of the present investigation was to 1)determine whether subjects could accurately achieve and maintain a range of EMG target levels,2)to examine the effects of varied EMG levels on the latencies and amplitudes of the mVEMP,and 3)to investigate the degree of side-to-side asymmetry and any effects of EMG activation.Methods:Subjects were nine neurologically and otologically normal young adults.A high-intensity tone burst was presented monaurally while subjects were seated upright and asked to match a range of EMG target levels by clenching their teeth.Recordings were made from the ipsilateral and contralateral masseter muscles referenced to the ear being monaurally stimulated.Results:We found that the tonic EMG target had no effect on mVEMP latency.Additionally,although mVEMP amplitudes“scaled”to the EMG target,there was a tendency for the subjects’EMG level to“undershoot”the EMG target levels greater than 50 mV.While some individuals did generate differences in EMG activation between sides,there were no significant differences on average EMG activation between sides.Further,while average corrected amplitude asymmetry was similar across EMG targets,some individuals demonstrated large,corrected amplitude asymmetry ratios.Conclusions:The results of this investigation suggest that,as with cVEMP recordings,the underlying EMG activation may vary between subjects and could impact mVEMP amplitudes,yet could be mitigated by amplitude correction techniques.Further it is important to be aware that even young normal subjects have difficulty maintaining large,tonic EMG activity during the mVEMP recording.

Facial reanimation with interposition nerve graft or masseter nerve transfer:a comparative retrospective study

Both interposition nerve grafts and masseter nerve transfers have been successfully used for facial reanimation after irreversible injuries to the cranial portion of the facial nerve.However,no comparative study of these two procedures has yet been reported.In this two-site,twoarm,retrospective case review study,32 patients were included.Of these,17 patients(eight men and nine women,mean age 42.1 years)underwent interposition nerve graft after tumor extirpation or trauma between 2003 and 2006 in the Ear Institute,School of Medicine,Shanghai Jiao Tong University,China,and 15 patients(six men and nine women,mean age 40.6 years)underwent masseter-to-facial nerve transfer after tumor extirpation or trauma between November 2010 and February 2016 in Shanghai Ninth People's Hospital,China.More patients achieved House-Brackmann III recovery after masseter nerve repair than interposition nerve graft repair(15/15 vs.12/17).The mean oral commissure excursion ratio was also higher in patients who underwent masseter nerve transfer than in patients subjected to an interposition nerve graft.These findings suggest that masseter nerve transfer results in strong oral commissure excursion,avoiding obvious synkinesis,while an interposition nerve graft provides better resting symmetry.This study was approved by the Institutional Ethics Committee,Shanghai Ninth People's Hospital,China(approval No.SH9 H-2019-T332-1)on December 12,2019.

Sarcopenia diagnosed using masseter muscle area predictive of early mortality following severe traumatic brain injury

Traumatic brain injury（TBI）represents a global pandemic and is currently a leading cause of injury related death worldwide.Unfortunately,those who survive initial injury often suffer devastating functional,social,and economic consequences.

Changes following denervation to the masseter muscle

BACKGROUND： Masseter muscle nerve is often injured in mandible osteotomy. What changes in food intake and masseter muscle will be brought after masseter muscle nerve injury？ OBJECTIVE： This study was designed to selectively establish animal models of denervated masseter muscle and investigate the effects of severing masseter muscular nerve on masseter muscle and animal＇s food intake. DESIGN, TIME AND SETTING： A randomized controlled animal experiment was performed at the Laboratory Animal Center, Nanfang Hospital, Southern Medical University from September to November 2005. MATERIALS： A total of 50 healthy, adult, SPF-grade, New Zealand rabbits, of both genders, were used to develop an animal model of selectively denervated masseter muscle. METHODS： Five rabbits were randomly selected as normal controls. According to various mutilation methods, the remaining animals were randomly divided into 3 experimental groups, with 15 rabbits in each group： masseter muscular neural stem denervated, masseter muscular neural superior branch-denervated, and masseter muscular neural inferior brancb-denervated groups. Self-control comparison was performed on each animal. The right masseter muscle served as the experimental side, and the left masseter muscle served as the control side. In each group, 3 time points （2, 8, and 24 weeks post-surgery） were allotted for observation. MAIN OUTCOME MEASURES： At the pre-set time points, masseter muscular thickness was measured with a Logic 500 color Doppler ultrasonic diagnostic apparatus. Masseter muscle tissue was resected for hematoxylin eosin staining. Masseter muscular fiber diameter and area were measured with an optical microscope. Masseter muscle tissue was sectioned and nicotinamide adenine dinucleotide tetrazolium oxidoreductase （NADH-TR） and adenosine triphosphatase staining were performed. Following staining, the sections were quantitatively analyzed using an IBAS200 image analyzer. RESULTS： Post-surgery food intake： No abnormal food intake was found after surgery among the three groups. Intragroup comparison： In each experimental group, following denervation, masseter muscular thickness was decreased （P 〈 0.05） and masseter muscular fiber cross-section area was reduced in the experimental side compared to the control side （P 〈 0.05）. Inter-group comparison： There was a significant difference in masseter muscular thickness and masseter fiber cross-section area among the three experimental groups （P 〈 0.05）. There was no significant difference in masseter fiber type between the control side of the three experimental groups and the normal control group （P 〉 0.05）. CONCLUSION： Following various methods of masseter muscle denervation, masseter muscle thickness and masseter fiber cross-section area was reduced by varying degrees. Denervated masseter muscle did not influence food intake of experimental animals or alter masseter muscle fiber ratio.

Nonlinear characteristics and functional analysis of masseter electromyography

The C-C method was adopted to analyze the nonlinear characteristics of masseter electromyography （EMG） signals and the chaotic degree by the largest Lyapunov exponent （LLE） of different genders and sides. First, the embedding dimension and the delay time were obtained through this method, then the phase space was reconstructed to resume the chaotie attractor and determine the LLE. The result shows that the trajectory of attractor is denser than Chen＇s attractor, and the LLE is positive, which means that not only the signal has the character of chaos, but also the chaotic degree of masseter EMG is relatively high. According to the value of the LLE, the chaotic degree of men＇s masseter EMG is higher than that of women＇s; when the dentition is normal, the chaotic degree of two sides is almost the same. Then, a conclusion can be deduced that if the LLE of both sides are in great difference, the unilateral mastication is likely to exist, which means that the nonlinear characteristics of masseter EMG can be applied to predict the unilateral mastication.

Alterations in blink and masseter reflex latencies in older adults with neurocognitive disorder and/or diabetes mellitus

BACKGROUND Blink and masseter reflexes provide reliable,quantifiable data on the function of the central nervous system:Delayed latencies have been found in patients with neurocognitive disorder(ND)and type 2 diabetes mellitus(T2DM),but this has not been studied in patients with both pathologies.AIM To investigate if older adults with ND plus T2DM have prolonged latencies of blink and masseter-reflex and if they were associated with disease progression.METHODS This cross-sectional study included 227 older adults(>60 years)from Colima,Mexico.Neurocognitive disorder was identified by a neuropsychological battery test,and T2DM identified by medical history,fasting glucose,and glycosylated hemoglobin.Latencies in the early reflex(R1),ipsilateral late(R2),and contralateral late(R2c)components of the blink reflex were analyzed for all subjects,and 183 subjects were analyzed for latency of the masseter reflex.RESULTS In 20.7%of participants,ND was detected.In 37%,T2DM was detected.Latencies in R1,R2,and R2c were significantly prolonged for groups with ND plus T2DM,ND,and T2DM,compared with the control group(P<0.0001).The masseter reflex was only prolonged in older adults(regardless of T2DM status)with ND vs controls(P=0.030).In older adults with ND and without T2DM,the more the cognitive impairment progressed,the more prolonged latencies in R2 and R2c presented(P<0.01).CONCLUSION These findings suggest that blink and masseter reflexes could be used to evaluate possible changes in brainstem circuits in older adults with ND and T2DM.

Quantitative Analysis of Relationships between Masseter Activity during Chewing and Textural Properties of Foods

The aim of this study was to quantify the relationships between four physiological parameters of masseter activity during chewing and properties related to the sizes and textures of the six representative test foods. The physiological parameters analyzed were the number of chewing cycles, chewing time, masseter amplitude, and cycle duration, which were obtained from masseter surface electromyography recorded in ten (seven male and three female) healthy, young participants. The six test foods differed in size dimensions (length, width, and height) and in textural properties (hardness, fracturability, and adhesiveness). The quantitative relationships were examined using linear regression. Nine statistically significant regression coefficients were found between the four physiological parameters and the textural properties, but not the height, of the test foods. From the regression coefficients, contributions of the food properties to the physiological parameters were estimated. Individual relationships between the physiological parameters and textural properties of the test foods are discussed in relation to their physiological implications.

The Effect of Masseter Activity Patterns during Chewing on Suprahyoid Activity in Subsequent Chewing Cycles

Few studies have evaluated the effects of activity patterns of the jaw closing muscles assessed by specific parameters on jaw opening in subsequent cycles during the chewing of food. The objective of this study was to quantitatively analyze the effect of the masseter (jaw closer) activity patterns on suprahyoid (jaw opener) activity during subsequent cycles. The assessments were performed while participants naturally chewed six test foods that differed in size dimensions and textural properties. Surface electromyograms of the masseter (on the habitual working side) and suprahyoid muscles were recorded in ten healthy young adults, each of whom randomly received one of the six test foods. The activity patterns were assessed using three parameters specifically developed for their quantification. Changes in suprahyoid activity during each of the subsequent chewing cycles were examined by three amplitudinal (minimum, maximum, and net values of the integrated suprahyoid electromyogram) parameters and one durational (active duration) parameter. The main finding was that two of the three activity pattern parameters had a statistically significant effect only on the three amplitudinal parameters in three of the six test foods. These results suggest that masseter activity patterns partially affect suprahyoid activity during subsequent chewing cycles and that the effect is food dependent. A possible neural mechanism responsible for this effect is presented.

Classification of Masseter Activity Patterns during Chewing in Healthy Young Adults: The Effect of Taste Signals

This study examined the effects of the textural properties and chemical components of foods on masseter activity patterns. Ten healthy young participants (seven men and three women) were asked to chew four gummy candies with different flavors while their masseter activities were recorded by a surface electromyogram. The masseter activity patterns during chewing were analyzed quantitatively using a TP technique, generating three TP values (T25, T50 and T75). The textural analysis included four representative properties, and six sugars and four organic acids were tested in the chemical analysis. The hierarchical cluster analysis classified the T25 and T75 values into four subclusters and classified the T50 values into three subclusters. Two T75 subclusters differed significantly in the combined amounts of the two predominant sugars (sucrose and maltose);however, these T75 subclusters did not differ in their organic acid contents or textural properties. Therefore, sucrose and maltose affect masseter activity patterns during chewing, particularly in the later stage of masseter activity.

Effect of Botubinum toxin type A injection into the masseter muscle on mandibular development in rats

Objective To investigate the effect of Botulinum toxin type A(Botox)injection into the masseter muscle on mandibular development in rats.Methods 1228-day-old Wistar rats were divided into two groups as Botox group(n=6)and control group(n=6)

Abnormalities of masseter inhibitory reflex in patients with episodic tension-type headache

Objective： To investigate the masseter inhibitory tension-type headache （TTH）. Methods： MIR was studied in 21 sex matched to the study cohort. Median age of patients was reflex （MIR） and its eventual changes in patients with episodic patients with episodic TTH and 30 healthy subjects, with age and 17.0 years （ranged 16-49 years）, median duration of disease 12 months （1-5 years）, and median frequency of headache 7.5 d per month. Results： The second period of suppression （$2） of MIR was reduced in intensity and duration in 10% of controls and 66.7% （confidence interval （CI） 45.3%-85%; P〈0.05） of patients with episodic TTH （X2=74.9; P〈0.001）. In 3 （14.3%） of patients with episodic TTH, S2 was completely absent. No significant correlation between the duration of disease and headache frequency was found. Conclusion： Our results confirm the link between episodic TTH and reduction or absence of S2. Teenage patients with episodic TTH may exhibit marked pathological changes in S2 in contrast to older individuals.

不同方法治疗后咬肌厚度减少的比较研究

目的通过比较三种方法处理后的咬肌厚度的变化,评价不同方法在减小咬肌厚度中的应用价值。方法对单纯下颌角截骨术患者5例,下颌角截骨术+咬肌部分切除术患者4例,下颌角截骨术+咬肌注射A型肉毒毒素患者4例,应用B超对患者手术前后12、24周咬肌厚度进行测量,比较其术后咬肌厚度减小程度。结果单纯下颌角截骨术、下颌角截骨术+咬肌部分切除术及下颌角截骨术+咬肌注射A型肉毒毒素组于术后12周咬肌厚度平均减少(4.876±5.270)%,(32.939±2.900)%,(14.006±4.866)%;术后24周分别减少(2.637±4.806)%,(30.286±3.644)%,(36.878±4.702)%。结论从远期效果观察,下颌角截骨联合咬肌注射A型肉毒毒素与下颌角截骨联合咬肌部分切除或单纯下颌角截骨手术比较,能更有效地减少咬肌厚度。

A型肉毒毒素治疗良性咬肌肥大远期疗效观察

目的:评价A型肉毒毒素治疗咬肌肥大的远期疗效。方法:对18例(34侧)咬肌肥大患者进行A型肉毒毒素肌肉注射治疗。其中16例双侧咬肌肥大就医者每侧注射剂量为50U/1ml,2例单侧咬肌肥就医者每侧注射剂量为60U/1ml。观察治疗前后不同时期就医者咬肌厚度变化情况及不良反应和并发症发生情况。结果:治疗后不同时期的咬肌厚度均较治疗前减小(P<0.001),药物注射后4～12周咬肌厚度减小最明显。平均随访时间78.5±18.8个月,患者总体满意率为83%,无严重并发症发生。结论:A型肉毒毒素可以替代手术治疗咬肌肥大。

保留腮腺咬肌筋膜预防Frey综合征的系统评价与Meta分析

目的通过系统评价和Meta分析的方法评估腮腺切除手术中保留腮腺咬肌筋膜对于预防术后Frey综合征的有效性及安全性。方法采用主题词检索策略,电子检索Pubmed、EMBase、Cochrane临床随机对照试验数据库、中国生物医学文献数据库、中国知网、维普数据库、万方数据库,检索时间截止至2013年3月30日。2位评价员按照Cochrane协作网推荐的方法和标准,对纳入的文献提取数据,并独立进行偏倚风险评价,并进行系统评价。运用Review manager 5.2进行Meta分析。结果共纳入随机对照试验13篇,偏倚风险不清。Meta分析结果显示:保留腮腺咬肌筋膜能够减少81%的主观Frey综合征的发生率(P<0.000 01),能够减少69%的客观Frey综合征的发生率。患者术后复发情况的Meta分析结果显示:两组患者术后复发情况没有统计学差异(P=0.47)。结论保留腮腺咬肌筋膜能够明显降低患者术后Frey综合征的发生,具有良好的有效性和安全性,而且术后复发情况无差异。

口内进路下颌角及咬肌肥大矫正术

为了避免面部留有切口疤痕，寻找出一种简单方便的回内进路手术方式。方法：口内进路、用skruber摆动锯截除肥大的下颌角，来复锯经日内补充截除骨断面下部骨突起及部分骨下绿，再用长柄骨磨头进一步磨改。结果：12例患者面形改善明显。结论：下颌角及咬肌肥大采用正颌外科技术经单纯的日内进路不需作辅加切口即能达到良好的手术效果。

颞部W形小切口除皱术对中下面部提升及瘢痕脱发的影响

目的探讨颞部W形小切口除皱术较传统切口的除皱术在对中下面部提升及术后瘢痕和脱发方面的优越性。方法本组16例患者,随机分为W形小切口除皱术A组(9例)和传统切口的除皱术B组(7例)。A组:于耳上颞部发际内行W形切口,颞浅筋膜悬吊固定,从水平30～90°方向上提升松垂的皮肤,每个V形的一条边与头皮纹平行,点状张力缝合。B组:于耳轮上头皮内行切口,悬吊颞浅筋膜和SMAS筋膜,将切口前缘头皮沿水平30～45°向后上提紧,1-0线缝合。结果随访患者2个月,A组患者的切口愈合佳,且前缘有毛发生长,隐蔽性好,鱼尾纹明显减轻,下垂的外眦角、颧部、下颊部和腮腺咬肌区皮肤有较明显的提升,与B组比较差异有显著意义(P<0.05)。结论颞部W形小切口除皱术是一种简便、安全、有效,且切口隐蔽的除皱方法,值得在临床上推广应用。

A型肉毒毒素治疗咬肌肥大的剂量改良

目的:探索不同剂量A型肉毒毒素(BTX-A)治疗咬肌肥大的效果。方法:根据咬肌在放松位和咬合位的状态,将咬肌肥大分成轻型和重型,分别应用30单位/侧和50单位/侧BTX-A治疗轻、重型患者6例。结果:随访3～5月,所有患者都对面形改变满意,无并发症,无复发。结论:根据咬肌肥大的严重程度采用不同剂量BTX-A治疗,可取得相同效果。

A型肉毒毒素在治疗咬肌肥大中的作用

目的评价A型肉毒毒素在治疗咬肌肥大中的作用。方法 2005年8月至2014年1月,对15例咬肌肥大患者行A型肉毒毒素治疗,并应用B型超声于术前和术后4、12、24周测量咬肌厚度。结果本组患者术后随访6个月,咬肌注射A型肉毒毒素后4、12、24周,咬肌厚度萎缩(15.60±4.96)%、(27.72±9.13)%和(24.32±8.86)%。结论 A型肉毒毒素能有效减少咬肌厚度;B型超声测量能有效地反映咬肌萎缩的程度。