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1.  Masseter and medial pterygoid muscle hypertrophy 
BMJ Case Reports  2011;2011:bcr0720114557.
Hypertrophy refers to an enlargement caused by an increase in the size but not in the number of cells. Generalised masticatory muscle hypertrophy may affect the temporalis muscle, masseters and medial pterygoids in a variety of combinations. Masseteric hypertrophy may present as either unilateral or bilateral painless swelling of unknown origin in the region of angle of mandible. It is a relatively rare condition and presents a diagnostic dilemma. While the history and clinical examination are important in differentiating this benign condition from parotid or dental pathology, they cannot necessarily exclude rare malignant lesion within the muscle. Advanced imaging modalities like CT and MRI are essential to confirm the diagnosis. Here the authors are reporting a unique case of masseter muscle hypertrophy along with medial pterygoid hypertrophy which was missed clinically but confirmed using CT and MRI.
PMCID: PMC3185404  PMID: 22679271
2.  Presumptive Intramuscular Hemangioma of the Masseter Muscle 
Patient: Male, 34
Final Diagnosis: Intramuscular hemangioma of the masseter muscle
Symptoms: Swelling over parotid region
Medication: —
Clinical Procedure: Clinical-Radiological work-up
Specialty: Radiology
Rare disease
Hemangioma is a benign vascular proliferation. Intramuscular hemangiomas are rare, accounting for less than 1% of all hemangiomas, and occur normally in the trunk and extremities. Approximately 10–20% of intramuscular hemangiomas are found in the head and neck region, most often in the masseter muscles. The typical clinical characteristic is a painful soft tissue mass without cutaneous changes. Currently, MRI is the standard imaging technique for diagnosing soft-tissue hemangioma. The optimal management is the surgical resection.
Case Report:
We report a case of 34-year-old male patient consulted for a swelling of 1 year evolution, around the parotid region. On physical examination, a soft, well-contoured lesion of about 2 cm on its long axis was found. MRI showed a space-occupying lesion in the left masseter muscle, with intermediate signal intensity on T1-weighted images and hyperignal intensity on T2-weighted images, containing nodular hypointense foci corresponding to calcification. The presumptive diagnosis of an intramasseteric hemangioma with phlebolith was made based on these findings. The patient was informed about her condition, and treatment options were discussed; however, the patient elected to forgo treatment at that time.
The possibility of an IMH should be included in the differential diagnosis of any intra-masseteric lesion. The appropriate radiologic examinations especially MRI can enhance accurate preoperative diagnosis; the treatment of choice should be individualized in view of the clinical status of the patient.
PMCID: PMC4298281  PMID: 25590509
Diagnostic Imaging; Hemangioma; Magnetic Resonance Imaging
3.  BOTOX: Broadening the Horizon of Dentistry 
Botox has been primarily used in cosmetic treatment for lines and wrinkles on the face, but the botulinum toxin that Botox is derived from has a long history of medically therapeutic uses. For nearly 13 years, until the introduction of Botox Cosmetic in 2002, the only FDA-approved uses of Botox were for crossed eyes (strabismus) and abnormal muscle spasms of the eyelids (blepharospasm). Since then botulinum A, and the seven other forms of the botulinum toxin, have been continuously researched and tested. Botox is a neurotoxin derived from bacterium clostridium botulinm. The toxin inhibits the release of acetylcholine (ACH), a neurotransmitter responsible for the activation of muscle contraction and glandular secretion, and its administration results in reduction of tone in the injected muscle. The use of Botox is a minimally invasive procedure and is showing quite promising results in management of muscle-generated dental diseases like Temporomandibular disorders, bruxism, clenching, masseter hypertrophy and used to treat functional or esthetic dental conditions like deep nasolabial folds, radial lip lines, high lip line and black triangles between teeth.
PMCID: PMC4316364  PMID: 25654058
Black triangles; Botulinum toxin A; Bruxism; Gummy smile; Hyperfunction
4.  Surgical management of masseteric hypertrophy and mandibular retrognathism 
Masseter hypertrophy is a rare condition. It is mostly idiopathic with no known cause. It is recognized as an enlargement of one or both masseter muscles. Most patients complain of facial asymmetry; however, symptoms such as trismus, protrusion, and bruxism may also occur. This article reports a case of bilateral masseter hypertrophy with retrognathic mandible in which comprehensive treatment was rendered to the patient by using a combination approach.
PMCID: PMC3304221  PMID: 22442621
Masseteric hypertrophy; orthognathic surgery; sagittal split osteotomy
5.  Botulinum toxin in masticatory muscles: Short- and long-term effects on muscle, bone, and craniofacial function in adult rabbits 
Bone  2011;50(3):651-662.
Paralysis of the masticatory muscles using botulinum toxin (BTX) is a common treatment for cosmetic reduction of the masseters as well as for conditions involving muscle spasm and pain. The effects of this treatment on mastication have not been evaluated, and claims that the treatment unloads the jaw joint and mandible have not been validated. If BTX treatment does decrease mandibular loading, osteopenia might ensue as an adverse result. Rabbits received a single dose of BTX or saline into one randomly chosen masseter muscle and were followed for 4 or 12 weeks. Masticatory muscle activity was assessed weekly, and incisor bite force elicited by stimulation of each masseter was measured periodically. At the endpoint, strain gages were installed on the neck of the mandibular condyle and on the molar area of the mandible for in vivo bone strain recording during mastication and muscle stimulation. After termination, muscles were weighed and mandibular segments were scanned with micro CT. BTX paralysis of one masseter did not alter chewing side or rate, in part because of compensation by the medial pterygoid muscle. Masseter-induced bite force was dramatically decreased. Analysis of bone strain data suggested that at 4 weeks, the mandibular condyle of the BTX-injected side was underloaded, as were both sides of the molar area. Bone quantity and quality were severely decreased specifically at these underloaded locations, especially the injection-side condylar head. At 12 weeks, most functional parameters were near their pre-injection levels, but the injected masseter still exhibited atrophy and percent bone area was still low in the condylar head. In conclusion, although the performance of mastication was only minimally harmed by BTX paralysis of the masseter, the resulting underloading was sufficient to cause notable and persistent bone loss, particularly at the temporomandibular joint.
PMCID: PMC3278508  PMID: 22155510
Botulinum neurotoxin; masseter; mastication; mandibular bone strain; bone microarchitecture; temporomandibular joint
6.  Effects of massage therapy and occlusal splint therapy on electromyographic activity and the intensity of signs and symptoms in individuals with temporomandibular disorder and sleep bruxism: a randomized clinical trial 
Temporomandibular disorder (TDM) is the most common source of orofacial pain of a non-dental origin. Sleep bruxism is characterized by clenching and/or grinding the teeth during sleep and is involved in the perpetuation of TMD. The aim of the present study was to investigate the effects of massage therapy, conventional occlusal splint therapy and silicone occlusal splint therapy on electromyographic activity in the masseter and anterior temporal muscles and the intensity of signs and symptoms in individuals with severe TMD and sleep bruxism.
Sixty individuals with severe TMD and sleep bruxism were randomly distributed into four treatment groups: 1) massage group, 2) conventional occlusal splint group, 3) massage + conventional occlusal splint group and 4) silicone occlusal splint group. Block randomization was employed and sealed opaque envelopes were used to conceal the allocation. Groups 2, 3 and 4 wore an occlusal splint for four weeks. Groups 1 and 3 received three weekly massage sessions for four weeks. All groups were evaluated before and after treatment through electromyographic analysis of the masseter and anterior temporal muscles and the Fonseca Patient History Index. The Wilcoxon test was used to compare the effects of the different treatments and repeated-measures ANOVA was used to determine the intensity of TMD.
The inter-group analysis of variance revealed no statistically significant differences in median frequency among the groups prior to treatment. In the intra-group analysis, no statistically significant differences were found between pre-treatment and post-treatment evaluations in any of the groups. Group 3 demonstrated a greater improvement in the intensity of TMD in comparison to the other groups.
Massage therapy and the use of an occlusal splint had no significant influence on electromyographic activity of the masseter or anterior temporal muscles. However, the combination of therapies led to a reduction in the intensity of signs and symptoms among individuals with severe TMD and sleep bruxism.
Trial registration
This study is registered in August, 2014 in the (NCT01874041).
Electronic supplementary material
The online version of this article (doi:10.1186/s12998-014-0043-6) contains supplementary material, which is available to authorized users.
PMCID: PMC4266206  PMID: 25512839
Physical therapy modalities; Temporomandibular joint disorders; Massage therapy; Occlusal splint
7.  Masticatory Muscle Sleep Background EMG Activity is Elevated in Myofascial TMD Patients 
Journal of oral rehabilitation  2013;40(12):883-891.
Despite theoretical speculation and strong clinical belief, recent research using laboratory polysomnographic (PSG) recording has provided new evidence that frequency of sleep bruxism (SB) masseter muscle events, including grinding or clenching of the teeth during sleep, is not increased for women with chronic myofascial temporomandibular disorder (TMD). The current case-control study compares a large sample of women suffering from chronic myofascial TMD (n=124) with a demographically matched control group without TMD (n=46) on sleep background electromyography (EMG) during a laboratory PSG study. Background EMG activity was measured as EMG root mean square (RMS) from the right masseter muscle after lights out. Sleep background EMG activity was defined as EMG RMS remaining after activity attributable to SB, other orofacial activity, other oromotor activity and movement artifacts were removed. Results indicated that median background EMG during these non SB-event periods was significantly higher (p<.01) for women with myofascial TMD (median=3.31 μV and mean=4.98 μV) than for control women (median=2.83 μV and mean=3.88 μV) with median activity in 72% of cases exceeding control activity. Moreover, for TMD cases, background EMG was positively associated and SB event-related EMG was negatively associated with pain intensity ratings (0–10 numerical scale) on post sleep waking. These data provide the foundation for a new focus on small, but persistent, elevations in sleep EMG activity over the course of the night as a mechanism of pain induction or maintenance.
PMCID: PMC3889636  PMID: 24237356
myofascial pain; temporomandibular disorders; TMD; sleep; bruxism; sleep bruxism; muscle tone; EMG; polysomnography
8.  The Electrical Activity of the Temporal and Masseter Muscles in Patients with TMD and Unilateral Posterior Crossbite 
BioMed Research International  2015;2015:259372.
The aim of this study was to assess the influence of unilateral posterior crossbite on the electrical activity of the temporal and masseter muscles in patients with subjective symptoms of temporomandibular dysfunctions (TMD). The sample consisted of 50 patients (22 female and 28 male) aged 18.4 to 26.3 years (mean 20.84, SD 1.14) with subjective symptoms of TMD and unilateral posterior crossbite malocclusion and 100 patients without subjective symptoms of TMD and malocclusion (54 female and 46 male) aged between 18.4 and 28.7 years (mean 21.42, SD 1.06). The anamnestic interviews were conducted according to a three-point anamnestic index of temporomandibular dysfunction (Ai). Electromyographical (EMG) recordings were performed using a DAB-Bluetooth Instrument (Zebris Medical GmbH, Germany). Recordings were carried out in the mandibular rest position and during maximum voluntary contraction (MVC). Analysis of the results of the EMG recordings confirmed the influence of unilateral posterior crossbite on variations in spontaneous muscle activity in the mandibular rest position and maximum voluntary contraction. In addition, there was a significant increase in the Asymmetry Index (As) and Torque Coefficient (Tc), responsible for a laterodeviating effect on the mandible caused by unbalanced right and left masseter and temporal muscles.
PMCID: PMC4391315  PMID: 25883948
9.  Botulinum toxin type A combined with cervical spine manual therapy for masseteric hypertrophy in a patient with Alzheimer-type dementia: a case report 
Journal of Chiropractic Medicine  2012;11(4):280-285.
The purpose of this case study is to present the findings of combining botulinum toxin type A (BoNT-A) and cervical spine manual therapy to address masseter muscle spasticity in a patient with Alzheimer-type dementia.
Case Report
A 78-year-old woman with bilateral spasticity of the masseteric regions for 2 years was referred for physiotherapy. She had trismus and bruxism, and could neither close nor open her mouth normally; thus, she was unable to be fed orally in a normal manner.
Intervention and Outcome
The patient underwent combined treatment with BoNT-A and cervical spine manual therapy. A medical physician (neurologist) performed the BoNT-A injections into 2 points at the center of the lower third of the masseter muscle. A physical therapist performed manual therapy interventions targeted at the cervical spine. Manual therapy started the day after the BoNT-A injection and continued for 5 sessions per week for a total period of 2 weeks. Clinical outcomes were measured including spasticity (Modified Ashworth Scale), functionality (Barthel Index), and jaw opening. Outcomes were conducted at baseline, 2 weeks after treatment, and at 2-month follow-up session after finishing the treatment. The patient improved in all of the outcomes at the end of treatment, and these results were maintained during the follow-up. After treatment, the patient was able to feed with minimal caregiver dependency because oral feeding was possible.
The patient in this study responded positively to a combination of BoNT-A and manual therapy, resulting in decreased masseter muscles spasticity and improved trismus and bruxism.
PMCID: PMC3706701  PMID: 23843761
Botulinum toxin type A; Stroke; Physiotherapy; Muscle spasticity; Masseter muscle, cervical spine; Alzheimer disease
10.  To Evaluate the Feasibility of Neurotisation of Facial Nerve Branches with Ipsilateral Masseteric Nerve: An Anatomic Study 
Context: Facial palsy is a common problem encountered in clinical practice. These patients suffer serious functional, cosmetic & psychological problems with impaired ability to communicate. Functional problems around the eye are usually a first priority for the patient with facial palsy.The nerve to masseter as a direct nerve transfer to the zygomatic branch of facial nerve to reinnervate viable facial muscles within a year after the onset of paralysis has been scarcely reported. This study was contemplated to evaluate the feasibility of neurotisation of zygomatic branch of facial nerve with masseteric nerve branch of the trigeminal nerve
Objectives: Establishing the anatomic relationship of masseteric nerve to masseteric muscle, determining feasibility of neurotisation of zygomatic branch of facial nerve using the nerve to the masseter and establishing fascicular correlation of the donor and the recipient nerves.
Materials and Methods: Ninteen hemi-faces in ten fresh cadavers (6 Male and 4 Female)were dissected in a forensic morgue and access was by a standard preauricular incision and anterior skin flap is elevated in a subcutaneous plane. Facial nerve and its two main divisions are dissected in its full A*/extratemporal course. Zygomatic branch dissected upto zygomatic arch and the nerve to the masseter is identified within the masseter muscle, dissected proximodistally to isolate it. Feasibility of transfer of this masseteric nerve to the zygomatic branch without using nerve graft is determined. At the completion of dissection, the ends of both nerves are sent for HPE analysis to determine fascicular anatomy and count.
Results: The dissection of massteric nerve was done taking into consideration of 3 axes, that is anteroposterior (x), vertical (y) axes and mediolateral(z) for locating the nerve and for standardization of the dissection. The nerve was cut and stored in glutaraldehyde solution and subjected to histopathologic examination after fixing and staining with Haematoxilin-eosin stain. Donor masseter neve has 7-10 fascicles. Recipient zygomatic branch has 2-3 fascicles. And the buccal branch has 5-6 fascicles.
Conclusion: The use of the nerve to masseter offers a simpler ipsilateral alternative for neurotisation of the facial nerve branches in patients who have an early facial nerve paralysis.
PMCID: PMC4064881  PMID: 24959474
Facial palsy; Masseter nerve; Orbicularis oculi; Nerve grafting
11.  Effect of voluntary contraction of the masseter and other muscles upon the masseteric reflex in man 
Experiments were carried out on seven adult subjects in order to establish the relationship between the magnitude of the masseteric reflex and the amount of voluntary activity present in the muscle at the time the reflex was evoked. At the same time, an effort was made to determine whether the magnitude of the reflex could be enhanced by the simultaneous voluntary contraction of muscles other than that being tested (the Jendrassik manoeuvre). The reflex was evoked by applying controlled downward thrusts to the mandible so as to produce a constant displacement in each case, and the response of the masseter muscle was recorded by means of small bipolar surface electrodes attached to the skin over the muscle. These responses were averaged by a computer in the presence of various static loads supported by the mandible. It was found that in all subjects the amplitude of the masseteric reflex appeared to increase as the weight supported by the mandible increased, and that in the majority of subjects it was possible to demonstrate Jendrassik facilitation by simultaneous contraction of the muscles of the upper limbs. The results of the experiments suggest that the enhancement of the masseteric reflex by voluntary contraction of the jaw-closing muscles may be due to autogenetic factors, synergistic factors, or both, and that at least two processes contribute to the amplitude of the masseteric reflex evoked by tooth contact during mastication—namely, the stimulation of muscle spindles by the impact of opposing teeth and facilitation caused by voluntary activity in the jaw-closing muscles before tooth contact.
PMCID: PMC493970  PMID: 5026012
12.  A Case of Painful Hemimasticatory Spasm with Masseter Muscle Hypertrophy Responsive to Botulinum Toxin 
Journal of Movement Disorders  2009;2(2):95-97.
Hemimasticatory spasm (HMS) is a rare disorder of the trigeminal nerve characterized by paroxysmal involuntary contractions of the unilateral jaw-closing muscles. HMS has been frequently described in association with facial hemiatrophy or localized scleroderma. A 42-year-old female presented with involuntary paroxysmal spasms of the left face, of 6 months duration. Her lower face on the left was markedly hypertrophied without skin lesions. An electrophysiological study indicated that the masseter reflexes and masseteric silent period were attenuated on the affected side. Surface electromyography demonstrated irregular bursts of motor unit potentials at high frequencies up to 200 Hz. Magnetic resonance imaging of the head showed marked hypertrophy of the left masseter muscle. Biopsy of the hypertrophied masseter muscle was normal. Repeated local injections of botulinum toxin noticeably reduced the size of the hypertrophied muscle as well as improved the patient’s symptoms.
PMCID: PMC4027721  PMID: 24868368
Hemimasticatory spasm; Masseter hypertrophy
13.  Intramuscular hemangioma of the masseter muscle: a case report 
Cases Journal  2009;2:7459.
Intramuscular hemangiomas are uncommon neoplasm's arising most frequently in the masseter and trapezius muscle. Due to it's location it is often mistaken for a parotid swelling and rarely is an accurate pre-operative diagnosis achieved clinically. The intra masseteric location also poses special problem in terms of proximity to the facial nerve and the post operative flattening following excision of the masseter muscle. A case of intramuscular hemangioma in a 17 year old girl is presented. Inadequacy of computed tomography scan and cytology in achieving a pre-operative diagnosis and also the treatment modalities are reviewed here. An estrogen receptor and progesterone receptor study has been done to verify the hormonal basis of this tumour.
PMCID: PMC2740236  PMID: 19829968
14.  Association Between Self-Reported Bruxism and Malocclusion in University Students: A Cross-Sectional Study 
Journal of Epidemiology  2015;25(6):423-430.
Bruxism can result in temporomandibular disorders, oral pain, and tooth wear. However, it is unclear whether bruxism affects malocclusion. The aim of this study was to examine the association between self-reported bruxism and malocclusion in university students.
Students (n = 1503; 896 men and 607 women) aged 18 and 19 years were examined. Malocclusion was defined using a modified version of the Index of Orthodontic Treatment Need. The presence of buccal mucosa ridging, tooth wear, dental impression on the tongue, palatal/mandibular torus, and the number of teeth present were recorded, as well as body mass index (BMI). Additional information regarding gender, awareness of bruxism, orthodontic treatment, and oral habits was collected via questionnaire.
The proportion of students with malocclusion was 32% (n = 481). The awareness of clenching in males with malocclusion was significantly higher than in those with normal occlusion (chi square test, P < 0.01). According to logistic regression analysis, the probability of malocclusion was significantly associated with awareness of clenching (odds ratio [OR] 2.19; 95% confidence interval [CI], 1.22–3.93) and underweight (BMI <18.5 kg/m2) (OR 1.89; 95% CI, 1.31–2.71) in males but not in females. In subgroup analyses, the probability of crowding was also significantly associated with awareness of clenching and underweight (P < 0.01) in males.
Awareness of clenching and underweight were related to malocclusion (crowding) in university male students.
PMCID: PMC4444496  PMID: 25865057
bruxism; malocclusion; young adult; cross-sectional studies
15.  Joint Use of Skull Base Surgery in a Case of Pediatric Parotid Gland Carcinoma 
Case Reports in Otolaryngology  2014;2014:158451.
Parotid gland carcinoma is extremely rare in children. We report a case of pediatric parotid gland carcinoma with extensive infiltration into surrounding tissues including the skin and temporomandibular joint capsule at initial examination. Total resection of the parotid gland was conducted together with skull base surgery and mandibular dissection. The patient was a 14-year-old girl. In addition to the skin and temporomandibular joint, infiltration into the anterior wall of the external auditory meatus and masseter muscle was also seen, and T4N0M0 stage IV parotid carcinoma was diagnosed. Skin was resected together with the pinna, and temporal craniotomy and skull base surgery were performed to resect the temporomandibular joint capsule and external auditory meatus en bloc, and mandible dissection was conducted. Facial nerves were resected at the same time. Level I to level IV neck dissection was also conducted. A latissimus dorsi myocutaneous flap was used for reconstruction. The postoperative permanent pathology diagnosis was high-grade mucoepidermoid carcinoma with a low-grade component. Postoperatively, radiotherapy at 50 Gy alone has been conducted, with no recurrence or metastasis observed for over 4 years.
PMCID: PMC4037578  PMID: 24949210
16.  Injection of Adjuvant but not Acidic Saline into Craniofacial Muscle Evokes Nociceptive Behaviors and Neuropeptide Expression 
Neuroscience  2007;149(3):650-659.
Craniofacial muscle pain including muscular temporomandibular disorders accounts for a substantial portion of all pain perceived in the head and neck region. In spite of its high clinical prevalence, the mechanisms of chronic craniofacial muscle pain are not well understood. Injection of acidic saline into rodent hindlimb muscles produces pathologies which resemble muscular pathologies in chronic pain patients. Here we investigated whether analogous transformations occur following repeated injections of acidic saline into the rat masseter muscle. Injection of acidic saline (pH 4) into the masseter muscle transiently lowered intramuscular pH to levels comparable to those reported for rodent hindlimb muscles. Nevertheless, repeated unilateral or bilateral injections of acidic saline (pH 4) into the masseter muscle failed to alter nociceptive behavioral responses as occurs in the hindlimb. Changing the pH of injected saline to pH 3.0 or 5.0 also did not evoke nocifensive behavior. ASIC3 receptors, which are implicated in transformations following acidification of hindlimb muscles, were found on trigeminal ganglion muscle afferent neurons via combined neuronal tracing and immunocytochemistry. In contrast to the acidic saline, injection of complete Freund’s adjuvant (CFA) into the masseter muscle induced mechanical allodynia for three weeks, thermal hyperalgesia for one week and an increase in the number of CGRP-immunoreactive muscle afferent neurons in the trigeminal ganglion. Although pH may alter CGRP release in primary afferent neurons, the number of CGRP-muscle afferent neurons did not change following intramuscular injection of acidic saline. Further, there was no change in ganglionic iCGRP levels at one, four or twelve days after intramuscular injection of acidic saline. While these findings extend our earlier reports that CFA-induced muscle inflammation results in behavioral and neuropeptide changes they further suggest that intramuscular acidification in craniofacial muscle evokes different responses than in hindlimb muscle and imply that disparate proton sensing mechanisms underlie these discrepancies.
PMCID: PMC2196131  PMID: 17928159
pain; trigeminal; pH; chronic; deep tissue; TMD
17.  A comparative study of the efficacy and safety of radiofrequency ablation and botulinum toxin A in treating masseteric hypertrophy 
The aim of the present study was to evaluate the effects of two treatments for masseteric hypertrophy. In total, 24 patients with masseteric hypertrophy were enrolled in this study. Patients were randomly divided into two groups: 12 individuals were treated with radiofrequency (RF) ablation and 12 patients received an injection of botulinum toxin A. The thickness of the masseter muscle under tension was measured using ultrasound and clinical photographs were captured prior to treatment and at 6 and 12 months following treatment. Complications were observed during 12-month follow-up. In the group injected with botulinum toxin A, masseteric muscle thickness decreased to the lowest point 6 months after the injections but increased until 12 months after injection. However, in the group treated with RF ablation, muscle thickness decreased steadily over the 12 months following surgery. Therefore, the results of the present study indicated that the effect of RF ablation on the thickness of the masseter muscle may be much larger than that obtained following injection with botulinum toxin A.
PMCID: PMC3991521  PMID: 24940412
masseteric hypertrophy; botulinum toxin A; radiofrequency ablation
18.  Gender Difference in Prevalence of Signs and Symptoms of Temporomandibular Joint Disorders: A Retrospective Study on 243 Consecutive Patients 
Background: This study evaluated the prevalence of the signs and symptoms of temporomandibular joint disorder (TMD) among patients with TMD symptoms. Methods: Between September 2011 and December 2011, 243 consecutive patients (171 females, 72 males, mean age 41 years) who were referred to the Department of Prosthodontics, Faculty of Dentistry, Karadeniz Technical University, Trabzon were examined physically and completed a questionnaire regarding age, gender, social status, general health, antidepressant drug usage, dental status, limited mouth opening, temporomandibular joint (TMJ) sounds, and parafunctions (bruxism, clenching). The data were analyzed using the chi-square test and binary logistic regression model (alpha = 0.05). Results: With a frequency of 92%, pain in the temporal muscle was the most common symptom, followed by pain during mouth opening (89%) in both genders. TMJ pain at rest, pain in the masseter muscle, clicking, grinding, and anti-depressant use were significantly more frequent in females than males. Age (p=0.006; odds ratio 0.954; 95% CI 0.922-0.987) and missing teeth (p=0.003; odds ratio 3.753; 95% CI 1.589-8.863) had significant effects on the prevalence of TMD. Conclusion: Females had TMD signs and symptoms more frequently than males in the study population. The most common problem in both genders was pain.
PMCID: PMC3444974  PMID: 22991492
temporomandibular joint dysfunction; orofacial pain; epidemiology; oral parafunctions; dental health.
19.  Longitudinal evaluation of jaw muscle activity and mandibular kinematics in young patients with Class II malocclusion treated with the Teuscher activator 
Objectives: A longitudinal study was performed to evaluate the jaw muscle activity and mandibular kinematics after Teuscher activator treatment and at 2 years after orthodontic treatment completion. Material and Methods: Twenty-seven children with Class II division 1 malocclusion were evaluated before treatment (T0; mean: 11.6 years), after functional treatment (T1; mean: 12.8 years), and 2 years after orthodontic treatment (T2; mean: 18 years). Bilateral surface electromyographic activities of the anterior temporalis, posterior temporalis, masseter, and suprahyoid muscle areas were analyzed at rest and during clenching, swallowing, and mastication. Kinematic recordings of the mandibular maximum opening, lateral shift, right and left lateral excursions, and protrusion were evaluated. Results: Compared to T0, the left masseter activity during clenching was decreased at T1 but increased at T2, similar to the other evaluated muscles. The suprahyoid activity during swallowing was increased at T1 but decreased at T2. The masseter activity during mastication was increased at T1 and further increased at T2. The left and right lateral excursions and protrusion did not show significant changes throughout the experiment. Conclusions: Teuscher activator and subsequent fixed orthodontic treatment improved jaw muscle function; however, a long period was needed to attain complete neuromuscular adaptation.
Key words:Class II malocclusion, jaw muscles, mandibular kinematics, sEMG, Teuscher activator.
PMCID: PMC3668879  PMID: 23385506
20.  Influence of temporomandibular disorder on temporal and masseter muscles and occlusal contacts in adolescents: an electromyographic study 
The aim of the present study was to analyse the influence of temporomandibular disorder (TMD) on electromyographic activity in the masseter and temporal muscles of adolescents and investigate a possible association with the number of occlusal contacts.
The Helkimo Index was administered for the diagnosis of TMD and classification of the adolescents into three groups: without TMD; with mild TMD; and with moderate/severe TMD. Carbon paper was used for the determination of occlusal contact points. A standardised electromyographic evaluation was performed on the masticatory muscles at rest, during habitual chewing and during maximum voluntary clenching. The readings were normalised to maximum voluntary clenching. Statistical analysis involved the chi-squared test and Fisher’s exact test. The Kruskal-Wallis test and one-way analysis of variance with Dunn’s post hoc test were used to compare differences between groups. Pearson’s correlation coefficients (r) were calculated for the determination of correlations between the number of occlusal contacts and RMS values.
Electromyography revealed significant differences in the right and left masseter and temporal muscles at rest and during chewing among the three groups. These differences were not observed during maximum voluntary clenching. No statistically significant differences were found between the groups with and without TMD regarding the number of occlusal contacts.
Electromyographic activity in the masseter and temporal muscles was greater among adolescents with moderate to severe TMD.
PMCID: PMC3991888  PMID: 24721559
Temporomandibular joint; Occlusion; Occlusal contacts; Electromyography
21.  Identification of the occurrence and pattern of masseter muscle activities during sleep using EMG and accelerometer systems 
Sleep bruxism has been described as a combination of different orofacial motor activities that include grinding, clenching and tapping, although accurate distribution of the activities still remains to be clarified.
We developed a new system for analyzing sleep bruxism to examine the muscle activities and mandibular movement patterns during sleep bruxism. The system consisted of a 2-axis accelerometer, electroencephalography and electromyography. Nineteen healthy volunteers were recruited and screened to evaluate sleep bruxism in the sleep laboratory.
The new system could easily distinguish the different patterns of bruxism movement of the mandible and the body movement. Results showed that grinding (59.5%) was most common, followed by clenching (35.6%) based on relative activity to maximum voluntary contraction (%MVC), whereas tapping was only (4.9%).
It was concluded that the tapping, clenching, and grinding movement of the mandible could be effectively differentiated by the new system and sleep bruxism was predominantly perceived as clenching and grinding, which varied between individuals.
PMCID: PMC2654433  PMID: 19208264
22.  A relationship between bruxism and orofacial-dystonia? A trigeminal electrophysiological approach in a case report of pineal cavernoma 
In some clinical cases, bruxism may be correlated to central nervous system hyperexcitability, suggesting that bruxism may represent a subclinical form of dystonia. To examine this hypothesis, we performed an electrophysiological evaluation of the excitability of the trigeminal nervous system in a patient affected by pineal cavernoma with pain symptoms in the orofacial region and pronounced bruxism.
Electrophysiological studies included bilateral electrical transcranial stimulation of the trigeminal roots, analysis of the jaw jerk reflex, recovery cycle of masseter inhibitory reflex, and a magnetic resonance imaging study of the brain.
The neuromuscular responses of the left- and right-side bilateral trigeminal motor potentials showed a high degree of symmetry in latency (1.92 ms and 1.96 ms, respectively) and amplitude (11 mV and 11.4 mV, respectively), whereas the jaw jerk reflex amplitude of the right and left masseters was 5.1 mV and 8.9 mV, respectively. The test stimulus for the recovery cycle of masseter inhibitory reflex evoked both silent periods at an interstimulus interval of 150 ms. The duration of the second silent period evoked by the test stimulus was 61 ms and 54 ms on the right and left masseters, respectively, which was greater than that evoked by the conditioning stimulus (39 ms and 35 ms, respectively).
We found evidence of activation and peripheral sensitization of the nociceptive fibers, the primary and secondary nociceptive neurons in the central nervous system, and the endogenous pain control systems (including both the inhibitory and facilitatory processes), in the tested subject. These data suggest that bruxism and central orofacial pain can coexist, but are two independent symptoms, which may explain why numerous experimental and clinical studies fail to reach unequivocal conclusions.
PMCID: PMC3874619  PMID: 24165294
Bruxism; Orofacial pain; Temporomandibular disorders; Dystonia; Oro facial dystonia; Trigeminal electrophysiology; Bilateral Root-MEPs
23.  Effectiveness of botulinum toxin type A treatment of neck pain related to nocturnal bruxism: a case report 
Journal of Chiropractic Medicine  2010;9(3):132-137.
This case report describes a patient with nocturnal bruxism and related neck pain treated with botulinum toxin type A (BTX-A).
Clinical Features
The patient was a 27-year-old man with nocturnal bruxism and difficulty in active mouth opening and chewing and neck pain at rest. His numeric pain score was 7 of 10. Surface electromyography of the temporalis and masseter muscles showed typical signs of hyperactivity, characterized by compound muscle action potential amplitude alterations.
Intervention and Outcome
After clinical evaluation, he was treated with BTX-A to reduce masseter and temporalis muscle hyperactivity. After 3 days of treatment with BTX-A, with each masseter muscle injected with a dose of about 40 mouse units with a dilution of 1 mL and with temporal muscle bilaterally injected with 25 mouse units with the same dilution, a decrease in bruxism symptoms was reported. Neck pain also decreased after the first treatment (visual analog scale of 2/10) and then resolved completely. After 4 weeks, electromyography showed the reduction of muscle hyperactivity with a decrease in the amplitude of the motor action potential. The same reduction in signs and symptoms was still present at assessment 3 months posttreatment.
These findings suggest that BTX-A may be a therapeutic option for the treatment of bruxism and related disorders.
PMCID: PMC3188369  PMID: 22027036
EES: bruxism; Neck pain; Botulinum toxin type A
24.  Lower facial remodeling with botulinum toxin type A for the treatment of masseter hypertrophy* 
Anais Brasileiros de Dermatologia  2014;89(6):878-884.
Masseter hypertrophy has been treated with botulinum toxin injections because of esthetic complaints especially in Asians.
The goal of the present study was to evaluate the efficacy of abobotulin toxin use in masseter hipertrophy treatment in Brazilians.
Ten Brazilian female patients with masseter hypertrophy were subjected to injections of 90U of abobotulinum toxin A applied on each side respecting the safety zone stabilished in literature and were followed up for 24 weeks.
When analyzing the coefficients between measures of middle and lower third of the face obtained from standardized photographs, an increase was observed, with statistical significance at 2 weeks (p=0.005) and 12 weeks (p=0.001). The progression of lower third reduction was 3.94%, 5.26%, 11.99%, and 5.47% (2, 4, 12, and 24 weeks respectively). All patients showed improvement in bruxism after treatment. Observed adverse effects were masticatory fatigue, smile limitation, and smile asymmetry.
The use of abobotulinum toxin A for masseter hypertrophy is effective in Brazilians and reached its maximum effect of facial thinning at 12 weeks. Smile limitation had a higher incidence compared to that reported in the literature and may result from risorius muscle blockage caused by toxin dissemination. Despite its side effects, 80% of the patients would like to repeat the treatment.
PMCID: PMC4230655  PMID: 25387491
Botulinum toxins, type A; Face; Masseter muscle
25.  Specific Diurnal EMG Activity Pattern Observed in Occlusal Collapse Patients: Relationship between Diurnal Bruxism and Tooth Loss Progression 
PLoS ONE  2014;9(7):e101882.
The role of parafunctional masticatory muscle activity in tooth loss has not been fully clarified. This study aimed to reveal the characteristic activity of masseter muscles in bite collapse patients while awake and asleep.
Materials and Methods
Six progressive bite collapse patients (PBC group), six age- and gender-matched control subjects (MC group), and six young control subjects (YC group) were enrolled. Electromyograms (EMG) of the masseter muscles were continuously recorded with an ambulatory EMG recorder while patients were awake and asleep. Diurnal and nocturnal parafunctional EMG activity was classified as phasic, tonic, or mixed using an EMG threshold of 20% maximal voluntary clenching.
Highly extended diurnal phasic activity was observed only in the PBC group. The three groups had significantly different mean diurnal phasic episodes per hour, with 13.29±7.18 per hour in the PBC group, 0.95±0.97 per hour in the MC group, and 0.87±0.98 per hour in the YC group (p<0.01). ROC curve analysis suggested that the number of diurnal phasic episodes might be used to predict bite collapsing tooth loss.
Extensive bite loss might be related to diurnal masticatory muscle parafunction but not to parafunction during sleep.
Clinical Relevance: Scientific rationale for study
Although mandibular parafunction has been implicated in stomatognathic system breakdown, a causal relationship has not been established because scientific modalities to evaluate parafunctional activity have been lacking.
Principal findings
This study used a newly developed EMG recording system that evaluates masseter muscle activity throughout the day. Our results challenge the stereotypical idea of nocturnal bruxism as a strong destructive force. We found that diurnal phasic masticatory muscle activity was most characteristic in patients with progressive bite collapse.
Practical implications
The incidence of diurnal phasic contractions could be used for the prognostic evaluation of stomatognathic system stability.
PMCID: PMC4092086  PMID: 25010348

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