Insights from the skull and postcranial osteometry of the Sardinian pine marten (Martes martes latinorum). Does it obey the island rule?

Comparison of glutamate-evoked pain between the temporalis and masseter muscles in men and women

The masseter acoustic/vestibular evoked myogenic potential (mVEMP) is a recently developed electrophysiological tool used to assess otolithic function. The mVEMP assesses brainstem integrity and is sensitive in detecting brainstem lesions. The masseter muscles are supplied by the mandibular branch of the fifth cranial nerve and help stabilize the jaw in response to high-intensity sound. The temporalis and masseter muscles function together to stabilize the mandible. Both muscles are supplied by the trigeminal nerve. Hence, the study hypothesized that mVEMP could also be recorded from the temporalis muscle. Twenty healthy adults (13 males and seven females; age range: 18-28 years) were recruited for the study. mVEMPs were recorded using a 500-Hz tone burst with 125 dB peSPL for all individuals. Vestibular evoked myogenic potentials (VEMPs) were then recorded in the temporalis muscle of the same individuals. VEMPs from the masseter and temporalis muscles were recorded ipsilaterally, contralaterally, and bilaterally, respectively. A within-subject design was adopted, and purposive sampling was used to assign the subjects. Both VEMPs from the masseter and temporalis muscles elicited a 100% response rate. A paired t test revealed no significant difference (p > .05) in the p11 and n21 latencies for unilateral and bilateral stimulation between masseter and temporalis VEMPs. In addition, a paired t test revealed a significant difference (p < .05) in the p11-n21 rectified amplitude between the masseter and temporalis VEMPs. The rectified amplitude for the temporalis muscle was reduced than masseter muscle. The study found that VEMPs recorded from the temporalis muscle are similar to mVEMPs. This preliminary finding supports that the temporalis serves as an alternate muscle to record mVEMP.

Flautists are at risk of developing muscular and joint pain. While playing the flute muscles of the maxillofacial region do not work physiologically. In addition, the musicians stay in an asymmetrical posture for a long time and often experience stress during performance. All these factors can affect masseter and temporal muscles and consequently lead to temporomandibular joint dysfunction (TMD).&#x0D; The aim of research was to investigate the state of the temporal and masseter muscles of flautists by means of electromyography in comparison to the control group.&#x0D; Electromyography of the temporal and masseter muscles was performed in 30 flautists and 30 control subjects aged 18 to 35 with the BioEMG from the BioPAK complex (BioResearch, USA). Electromyography at rest registered increased bioelectric potential of the temporal and/or masseter muscles in a subgroup of flautists who play more than 3 hours a day in 37.5% of cases. In a clench test both musicians and control subjects showed asymmetrical work of masticatory and temporal muscles, while in the control group, symmetry below 50% was noted only in the work of the temporal muscles. Synergy between temporal and masseter muscles less then 50% was 1.3 times more common in the control group than among flute players though right-sided disorders were more common in flute players.&#x0D; Electromyography of masticatory muscles is an important stage in a comprehensive examination of the TMJ condition, however, this method cannot be used as the single one or decisive one to diagnose the professional pathology of flautists.

Objective: To compare the electromyographic activity of masseter and temporal muscles between bruxers and nonbruxers in adult and adolescent patients. Material and Methods: The samples composed of the surface electromyography (EMG) recordings obtained from the orthodontic patients. Sixty-eight patients who had bruxsim habit (43 female and 25 male) were divided into four groups according to their age and gender. Control groups consisted of 79 patients who had not bruxism habit. EMG of the masseter muscle and anterior temporal muscle were recorded before treatment in clenching at maximum intercuspation. The ratio of temporal and masseter muscle activity (T/M ratio) was compared between bruxers and nonbruxers in adult and adolescent patients. Results: EMG of masseter muscle and temporal muscle were significantly higher in adult male bruxism group than control. T/M ratio in adult male bruxism group was significantly lower than in adult male nonbruxism group. However, there was no significant difference in T/M ratio between adolescent bruxism group and adolescent nonbruxism group. Conclusions: The balance in the activity of the masseter and temporal muscles may not differ between bruxers and nonbruxers during adolescent periods. However, in adult period, the masseter muscle activity against temporal muscle is greater in males with bruxism habit compared to non-bruxer.

To analyze possible correlations between the electrical activity of masseter and temporal muscles, Bite Force (BF), and Morphological Facial Indices (MFI). The study involved 43 young adults, both genders, 18 to 37 years old. The individuals were submitted to: face measurement to calculate MFI; Masseter and Temporal Surface Electromyography (sEMG) and BF measurements on right and left premolars and incisors. The following electromyographic tests were conducted: at rest position; Maximal Voluntary Isometrical Contraction (MVIC) and usual chewing of raisins. Statistical analysis was conducted using the coefficient of Spearman correlation with significance level of 5%. The values at rest in the temporal muscles were significantly higher than those in the masseter muscles. A meaningful correlation was found between MFI and sEMG in the MVIC test for the Left Temporal (rs=36, p=0.017). A significant correlation was observed between FMI and sEMG during BF in incisors for temporal muscles and the Right Masseter. During the force tests, it was possible to observe a meaningful correlation between BF in right premolars and the sEMG of the Left Temporal and Masseters. No correlation was found between the sEMG of temporal and masseter muscles, BF, and FMI in adult individuals based on the tests performed. The SEMG of temporal and masseter muscles seems to be associated only with BF. As a datum of habitual postural characteristic, the electrical activity of temporal muscles is higher than the activity of masseters, also regardless of MFI.

Today, bruxism is a fairly common phenomenon. Bruxism is often defined as the parafunctional activity of the masticatory and facial muscles. Parafunction is called increased inappropriate activity, tension or even spasm of the masticatory and facial muscles, as well as the muscles of the tongue. However, the peculiarity of the work of masticatory muscles during the day in patients with signs of bruxism remains insufficiently studied.&#x0D; The aim of our study was to determine the features of EMG-activity of masticatory muscles in patients with bruxism.&#x0D; Materials and methods of research. We performed a clinical examination and superficial electromyography (EMG) of the masticatory muscles in 13 subjects aged 25 to 43 years. There were 7 women (53.8%), 6 men (46.2%). All examined subjects were somatically healthy, had no bad habits and defects of the dental arches. The mean age of the subjects was 32.5 ± 5.4 years. In the sample of patients, there were clinical signs of bruxism such as pathological abrasion of the hard tissues of the teeth; point dentin exposure; cracks in tooth enamel; hyperesthesia; pain or feeling of tension and discomfort in the masticatory muscles. All patients were performed superficial electromyography of the anterior temporal and masseter muscles using a 4-channel computerized electromyograph, according to the recommendations by Ferrario V., Sforza C. Electrical biopotentials of masticatory muscles were registered in tests lasting 10 s each: maximum bilateral teeth clenching, clenching of teeth on the left side; clenching of teeth on the right side. The data obtained during the EMG were processed using Synapsis software from Neurotech. We analyzed the indicators of maximum amplitude, mean amplitude (μV) of each muscle in every test. For objective evaluation of the results, we performed electromyography of masticatory muscles of 15 subjects comparable in age and sex without clinical signs of bruxism (control group, mean age was 33.4 ± 6.1 years).&#x0D; Research results. We determined the characteristics of EMG-activity of masticatory muscles in the control group in the test of bilateral maximum teeth clenching: symmetrical activity of masseter and temporal muscles on the left and right sides (p&gt; 0.05), the value of maximum amplitude of contractions did not exceed 1200 μV. It was found higher EMG-activity of the masseter and temporal muscles on a working side, compared to a balancing one in the test of unilateral teeth clenching, that was statistically confirmed (p&lt;0,05).&#x0D; In patients with bruxism, the EMG-activity of the masticatory muscles differed from the control group. Thus, the maximum amplitude of muscle contractions in all tests was significantly higher (p &lt;0.05) among people with bruxism. EMG-activity of masseter muscles in the majority of cases (10 subjects – 76.9%) was greater than the temporal. In tests of unilateral teeth clenching, the EMG-activity of the temporal and masseter muscles was slightly higher on the working side, but the difference with the indicators on the balancing side was not statistically confirmed (p&gt; 0.05). We found the peculiarity of the EMG-activity of the masticatory muscles in subjects with bruxism: the presence of pathological rhythmic peaks of activity in the resting phase. Differences in the indicators of EMG-activity between the subjects with bruxism and control group were evaluated using analyses of Student’s paired t-test. The hypotheses were verified at the level of significance p&lt;0,05.&#x0D; Conclusions. Bruxism is a complex problem of the whole human body, characterized by neuromuscular activity. In our study, some features of EMG-activity of masticatory muscles were studied and established. Patients with clinical signs of bruxism had significantly higher values of maximum, mean amplitude, which are 2.3-3.5 times higher than normal. In most cases, the EMG-activity of the masseter muscles was higher than the temporal. Presence of pathological rhythmic peaks of activity in the resting phase was found. In the future, it is planned to study individual changes in EMG-activity of masticatory muscles in patients with bruxism at different stages of total dental rehabilitation.

The reproducibility of electromyographic (EMG) activity in relation to static bite-force from masticatory muscles for a given biting situation is largely unknown. Our aim was to evaluate the reliability of EMG activity in relation to static bite-force in humans. Eighty-four subjects produced five unilateral static bites of different forces at different biting positions on molars and incisors, at two separate sessions, and the surface EMG activities were recorded from temporalis, masseter, and suprahyoid muscles bilaterally. Intraclass correlation coefficients (ICCs) were determined, and an ICC of ≥ 0.60 indicated good reliability of these slopes. The ICCs for jaw-closing muscles during molar biting were: temporalis muscles, ipsilateral 0.58-0.93 and contralateral 0.88-0.91; and masseter muscles, ipsilateral 0.75-0.86 and contralateral 0.69-0.88. The ICCs for jaw-closing muscles during incisor biting were: temporalis muscles, ipsilateral 0.56-0.81 and contralateral 0.34-0.86; and masseter muscles, ipsilateral 0.65-0.78 and contralateral 0.59-0.80. For the suprahyoid muscles the 95% CIs were mostly wide and most included zero. The slopes of the EMG activity vs. bite-force for a given biting situation were reliable for temporalis and masseter muscles. These results support the use of these outcome measurements for the estimation and validation of mechanical models of the masticatory system.

The aim of this study was to compare the effects of hard and soft splints on the activity of the anterior temporalis and masseter muscles. Surface EMG recordings were made from these muscles during clenching at 10% of maximum, 50% of maximum and at maximum clench, both before and after insertion of a hard splint. This sequence was then repeated with a soft splint. The relative level of activity in the anterior temporalis and masseter muscles at all three activity levels was quantified by means of an Activity Index, which provides a measure of the balance of activity in the masseter relative to the activity in the anterior temporalis muscle. It was found that hard splints led to a decrease in EMG activity in relation to activity with no splint in both muscles at maximum clench and particularly the anterior temporalis. Soft splints produced a slight increase in activity of both muscles, but particularly the masseter muscle. The Activity Index indicated a shift in the balance of activity away from the anterior temporalis muscles with both splints, particularly at 10% of the maximum clenching level. It is possible that the decrease in activity of the temporalis muscles relative to the masseter muscles may be a factor in the therapeutic effect of both a hard and a soft splint, although the decrease is clearly greater with the hard splint.

The purpose of this study is to prospectively investigate the reference values of masseter and temporal muscle thicknesses by ultrasonography and muscle hardness values by shear wave elastography in healthy adults. The sample of the study consisted of a total of 160 healthy individuals aged between 18 and 59, including 80 women and 80 men. By examining the right and left sides of each participant, thickness and hardness values were obtained for 320 masseter muscles and 320 temporal muscles in total. The mean masseter muscle thickness was found to be 1.09 cm at rest and 1.40 cm in contraction. The mean temporal muscle thickness was found to be 0.88 cm at rest and 0.98 cm in contraction. The thickness values of the masseter and temporal muscles were significantly greater in the male participants than in the female participants (P < .001). While there were significant differences between the right and left masseter muscle thickness values at rest and in contraction, the values of the temporal muscles did not show a significant difference between the sides. While the resting hardness (rSWE) of the masseter muscle was transversally 6.91 kPa and longitudinally 8.49 kPa, these values in contraction (cSWE) were found, respectively, 31.40 and 35.65 kPa. The median temporal muscle hardness values were 8.84 kPa at rest and 20.43 kPa in contraction. Masseter and temporal muscle hardness values at rest and in contraction were significantly higher among the male participants compared to the female participants (P < .001). In this study, reference values for the thickness and hardness of the masseter and temporal muscles are reported. Knowing these values will make it easier to assess pain in the masseter and temporal muscles and determine the diagnosis and prognosis of masticatory muscle pathologies by allowing the morphological and functional assessments of these muscles, and it will identify ranges for reference parameters.

In this study, botulinum neurotoxin type A (BoTx/A) was injected into the temporalis and masseter muscles of growing rats to induce masticatory hypoactivity. Sixty, 30-day-old, male Long-Evans rats were randomly divided into four groups. BoTx/A was bilaterally injected in the masseter muscles in group I, in the temporalis muscles in group II, and into both the masseter and the temporalis muscles in group III. Group IV served as the control in which saline was bilaterally injected into both muscles. Forty-five days after the injections, the rats were sacrificed. Observation of cortical bone thickness from bone biopsies of the right halves of the mandibles, evaluation of the volume of masseter and temporalis muscles with a plethysmometer, and scanning of bone mineral density (BMD) of the skull and mandibular bone structure with dual-energy X-ray absorptiometry were performed. One-way analysis of variance was employed to analyse measurements of muscle volume, BMD, and cortical bone thickness among the groups. The least square difference was then used to determine significance. Reduced cortical bone thickness and BMD of the skull and mandibular bone structure were observed. The volumes of the temporalis and masseter muscles injected with BoTx/A were smaller. Masticatory hypofunction affects bone structure during development.

To test the hypothesis that experimental noxious stimulation of the right masseter muscle results in a reorganization of motor unit activity within the right temporalis and right masseter muscles during jaw closing tasks. A total of 20 healthy participants received hypertonic saline (5% sodium chloride) infusion into the right masseter muscle, and pain intensity was maintained at 40-60/100 mm on a visual analog scale. Standardized isometric biting tasks were performed with an intraoral force transducer while single motor units (SMUs) were recorded from the right masseter and temporalis muscles. Tasks were repeated in four blocks: block 1 (baseline 1), block 2 (hypertonic saline [HS] infusion or isotonic saline [IS] infusion), block 3 (infusion of the other solution), and block 4 (baseline 2). The occurrences of SMUs were tabulated across blocks. Statistical significance was considered to be P < .05. There were no significant effects of block on the tasks. A total of 83 SMUs were discriminated in the temporalis and 58 in the masseter. For the comparison between HS and IS across tasks, the occurrences of 74.6% to 82.8% of SMUs were unchanged (70.2% to 94.3% for masseter), while during HS, 10.3% to 17.1% of SMUs were recruited (0% to 12.8%, masseter) and 6.9% to 12.7% were de-recruited (5.7% to 17%, masseter). The present findings suggest that most biting-task-related jaw muscle SMUs remain active during experimental muscle noxious stimulation. There was some evidence in both the anterior temporalis and masseter muscles for motor unit recruitment and de-recruitment consistent with a motor unit reorganization during experimental pain.

A randomized controlled trial. To investigate the immediate effects on pressure pain thresholds over latent trigger points (TrPs) in the masseter and temporalis muscles and active mouth opening following atlanto-occipital joint thrust manipulation or a soft tissue manual intervention targeted to the suboccipital muscles. Previous studies have described hypoalgesic effects of neck manipulative interventions over TrPs in the cervical musculature. There is a lack of studies analyzing these mechanisms over TrPs of muscles innervated by the trigeminal nerve. One hundred twenty-two volunteers, 31 men and 91 women, between the ages of 18 and 30 years, with latent TrPs in the masseter muscle, were randomly divided into 3 groups: a manipulative group who received an atlanto-occipital joint thrust, a soft tissue group who received an inhibition technique over the suboccipital muscles, and a control group who did not receive an intervention. Pressure pain thresholds over latent TrPs in the masseter and temporalis muscles, and active mouth opening were assessed pretreatment and 2 minutes posttreatment by a blinded assessor. Mixed-model analyses of variance (ANOVA) were used to examine the effects of interventions on each outcome, with group as the between-subjects variable and time as the within-subjects variable. The primary analysis was the group-by-time interaction. The 2-by-3 mixed-model ANOVA revealed a significant group-by-time interaction for changes in pressure pain thresholds over masseter (P<.01) and temporalis (P = .003) muscle latent TrPs and also for active mouth opening (P<.001) in favor of the manipulative and soft tissue groups. Between-group effect sizes were small. The application of an atlanto-occipital thrust manipulation or soft tissue technique targeted to the suboccipital muscles led to an immediate increase in pressure pain thresholds over latent TrPs in the masseter and temporalis muscles and an increase in maximum active mouth opening. Nevertheless, the effects of both interventions were small and future studies are required to elucidate the clinical relevance of these changes. Therapy, level 1b.J Orthop Sports Phys Ther 2010;40(5):310-317, Epub 12 April 2010. doi:10.2519/jospt.2010.3257.

A systematic review was conducted to identify and summarize the available scientific literature addressing pressure pain threshold (PPT) values over the temporalis, masseter, and frontalis muscles in healthy humans, patients with tension-type headache (TTH), and those with migraine both in males and females. Six relevant medical databases for the literature search were included: PubMed, Web of Science, Cochrane, CINAHL, BioMed Central, and Embase. The search strategy was performed applying 15 keywords (eg, pressure pain threshold, temporalis muscle, tension type headache, pressure algometer) and their combinations. A total of 156 articles were identified, and 40 relevant articles were included. The main outcomes of the systematic review were extracted, and it was demonstrated that the PPT values in general were lower in patients compared with healthy subjects, and this was especially noted for temporalis in both females (migraine: 231.2 ± 38.3 kPa < TTH: 248.4 ± 39.3 kPa < healthy: 282.1 ± 70.8 kPa) and males (migraine: 225.5 ± 61.2 kPa < TTH: 264.2 ± 32.5 kPa < healthy: 314.8 ± 63.3 kPa). The masseter muscle seemed to be more sensitive than the other 2 muscles, in both females (healthy: masseter 194.1 ± 62.7 kPa < frontalis 277.5 ± 51.1 kPa < temporalis 282.1 ± 70.8 kPa) and males (healthy: masseter 248.2 ± 48.4 kPa < temporalis 314.8 ± 63.3 < frontalis 388 kPa). Females had lower PPT values than those of males in temporalis, masseter, and frontalis muscles. This work is the first to systematically review the scientific literature addressing PPT values over craniofacial muscles of healthy subjects, patients with TTH, and those with migraine to provide the PPT value ranges. Based on these findings, a set of guidelines was established to assist future studies including PPT assessments over craniofacial muscles.

Histochemical characteristics of masseter and temporalis muscles after 5 weeks of maxillomandibular fixation—An investigation in Macaca mulatta

The purposes of the present study were to elucidate the influences of the deficiency of teeth on masticatory muscles, such as the masseter, temporalis and digastric muscles and compare the influence among masticatory muscles. We analysed the expressions of myosin heavy chain (MyHC) isoform messenger RNA (mRNA) and protein in these muscles in the microphthalmic (mi/mi) mouse, whose teeth cannot erupt because of a mutation in the mitf gene locus. The expression levels of MyHC mRNA and protein in the masseter, temporalis, digastric, tibialis anterior and gastrocnemius muscles of +/+ and mi/mi mice were analysed with real-time polymerase chain reaction and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively. The mi/mi masseter muscle at 8 weeks of age expressed 4.1-fold (p < 0.05) and 3.3-fold (p < 0.01) more MyHC neonatal mRNA and protein than that in the +/+, respectively; the expression level of MyHC neonatal protein was 19% of the total MyHC protein in the masseter muscle of mi/mi mice. In the digastric muscle, the expression levels of MyHC I mRNA and protein in the mi/mi mice were 4.7-fold (p < 0.05) and 5-fold (p < 0.01) higher than those in the +/+ mice. In the temporalis, tibialis anterior and gastrocnemius muscles, there was no significant difference in the expression levels of any MyHC isoform mRNA and protein between +/+ and mi/mi mice. These results indicate associations between the lack of teeth and the expression of MyHC in the masseter and digastric muscles but not such associations in the temporalis muscle, suggesting that the influence of tooth deficiency varies among the masticatory muscles.