Superficial Masseter Muscles Research Articles

The impact of measurement technique and sampling on estimates of skeletal muscle fibre architecture.

Skeletal muscle fibre architecture provides important insights into performance of vertebrate locomotor and feeding behaviours. Chemical digestion and in situ sectioning of muscle bellies along their lengths to expose fibres, fibre orientation and intramuscular tendon, are two classical methods for estimating architectural variables such as fibre length (Lf) and physiological cross-sectional area (PCSA). It has recently been proposed that Lf estimates are systematically shorter and hence less accurate using in situ sectioning. Here we addressed this hypothesis by comparing Lf estimates between the two methods for the superficial masseter and temporalis muscles in a sample of strepsirrhine and platyrrhine primates. Means or single-specimen Lf estimates using chemical digestion were greater in 17/32 comparisons (53.13%), indicating the probability of achieving longer fibres using chemical digestion is no greater than chance in these taxonomic samples. We further explored the impact of sampling on scaling of Lf and PCSA in platyrrhines applying a bootstrapping approach. We found that sampling-both numbers of individuals within species and representation of species across the clade significantly influence scaling results of Lf and PCSA in platyrrhines. We show that intraspecific and clade sampling strategies can account for differences between previously published platyrrhine scaling studies. We suggest that differences in these two methodological approaches to assessing muscle architecture are relatively less consequential when estimating Lf and PCSA for comparative studies, whereas achieving more reliable estimates within species through larger samples and representation of the full clade space are important considerations in comparative studies of fibre architecture and scaling.

Cranial muscle architecture in wild boar: Does captivity drive ontogenetic trajectories?

The jaw system in mammals is complex and different muscle morphotypes have been documented. Pigs are an interesting group of animals as they are omnivorous and have a bunodont crushing dentition. Moreover, they have interacted with humans for over 10,000 years and grow nearly two orders of magnitude in size. Despite being a model system for studies on cranial form and function, data on the growth of the jaw adductor muscles are scant. Moreover, whether captivity impacts the growth and architecture of the jaw adductors remains unknown. Based on dissection data of the jaw adductors of 45 animals ranging from less than 1 kg to almost 100 kg, we show that muscle masses, muscle fiber lengths, and cross-sectional areas scale as predicted for geometrically similar systems or with slight negative allometry. Only the fiber length of the lateral pterygoid muscle grew with slight positive allometry. Animals raised in captivity in stalls or in an enclosure were overall very similar to wild animals. However, some muscles were larger in captive animals. Interestingly, variation in bite force in captive animals was well predicted by the variation in the size of the superficial masseter muscle relative to the overall jaw adductor mass.

THE CONTRIBUTION OF THE MASTICATORY MUSCLES TO PRODUCTION OF 3D OCCLUSAL LOADS ACROSS THE DENTAL ARCH

Occlusal loading and muscle forces during mastication aids in assessment of dental restorations and implants and jaw implant design; however, three-dimensional bite forces cannot be measured with conventional transducers, which obstruct the native occlusion. The aim of this study was to combine accurate jaw kinematics measurements, together with subject-specific computational modelling, to estimate subject-specific occlusal loading and muscle forces during mastication.Motion experiments were performed on one male participant (age: 39yrs, weight: 82kg) with healthy dentition. Two low-profile magnetic sensors were fixed to the participant's teeth and the two dental arches digitised using an intra-oral scanner. The participant performed ten continuous of chewing on a polyurethane rubber sample of known material properties, followed by maximal compression (clenching). This was repeated at the molars, premolars of both the left and right sides, and central incisors. Jaw motion was simultaneously recorded from the sensors, and finite element modelling used to estimate bite force. Specifically, simulations of chewing and biting were performed by driving the model using the measured kinematics, and bite force magnitude and direction quantified. Muscle forces were then evaluated using a rigid-body musculoskeletal model of the patient's jaw.The first molars generated the largest bite forces during chewing (left: 309 N, right: 311 N) and maximum-force biting (left: 496 N, right: 495 N). The incisors generated the smallest bite forces during chewing (75 N) and maximum-force biting (114 N). The anterior temporalis and superficial masseter muscles had the largest contribution to maximum bite force, followed by the posterior temporalis and medial pterygoid muscles.This study presents a new method for estimating dynamic occlusal loading and muscle forces during mastication. These techniques provide new knowledge of jaw biomechanics, including muscle and occlusal loading, which will be useful in surgical planning and jaw implant design.

Response of masticatory muscles to treatment with orthodontic aligners: a preliminary prospective longitudinal study

The emergence of orthodontic aligners has provided an aesthetic and comfortable option for orthodontic treatment. However, the encapsulated design of the aligners can influence the masticatory muscles, and might compromise safe treatment. This preliminary longitudinal study aimed to investigate whether the use of orthodontic aligners affects the biting force and myoelectric activity of the superficial masseter and anterior temporal muscles. Ten subjects participated in the study and underwent treatment during an 8-month follow-up period. The root mean square (RMS), the median power frequency (MPF) of the surface electromyography (sEMG) signals, and the biting force (kgf) were recorded and normalized relative to the pretreatment condition. The data were analyzed by repeated-measure analysis of variance (ANOVA), with the significance level set at 5%. Both the superficial masseter and the anterior temporal muscles presented an increase in sEMG signal activity during the treatment, with a marked increase in the latter compared to the former (p<0.05). Moreover, a significant decrease in bite force was evidenced (p<0.05). This preliminary study observed that the orthodontic aligners affected the muscle recruitment pattern of masticatory muscles, and reduced biting performance during the 8-month follow-up period.

Effect of osteopathic techniques on human resting muscle tone in healthy subjects using myotonometry: a factorial randomized trial

Musculoskeletal disorders (MSDs) are highly prevalent, burdensome, and putatively associated with an altered human resting muscle tone (HRMT). Osteopathic manipulative treatment (OMT) is commonly and effectively applied to treat MSDs and reputedly influences the HRMT. Arguably, OMT may modulate alterations in HRMT underlying MSDs. However, there is sparse evidence even for the effect of OMT on HRMT in healthy subjects. A 3 × 3 factorial randomised trial was performed to investigate the effect of myofascial release (MRT), muscle energy (MET), and soft tissue techniques (STT) on the HRMT of the corrugator supercilii (CS), superficial masseter (SM), and upper trapezius muscles (UT) in healthy subjects in Hamburg, Germany. Participants were randomised into three groups (1:1:1 allocation ratio) receiving treatment, according to different muscle-technique pairings, over the course of three sessions with one-week washout periods. We assessed the effect of osteopathic techniques on muscle tone (F), biomechanical (S, D), and viscoelastic properties (R, C) from baseline to follow-up (primary objective) and tested if specific muscle-technique pairs modulate the effect pre- to post-intervention (secondary objective) using the MyotonPRO (at rest). Ancillary, we investigate if these putative effects may differ between the sexes. Data were analysed using descriptive (mean, standard deviation, and quantiles) and inductive statistics (Bayesian ANOVA). 59 healthy participants were randomised into three groups and two subjects dropped out from one group (n = 20; n = 20; n = 19–2). The CS produced frequent measurement errors and was excluded from analysis. OMT significantly changed F (−0.163 [0.060]; p = 0.008), S (−3.060 [1.563]; p = 0.048), R (0.594 [0.141]; p < 0.001), and C (0.038 [0.017]; p = 0.028) but not D (0.011 [0.017]; p = 0.527). The effect was not significantly modulated by muscle-technique pairings (p > 0.05). Subgroup analysis revealed a significant sex-specific difference for F from baseline to follow-up. No adverse events were reported. OMT modified the HRMT in healthy subjects which may inform future research on MSDs. In detail, MRT, MET, and STT reduced the muscle tone (F), decreased biomechanical (S not D), and increased viscoelastic properties (R and C) of the SM and UT (CS was not measurable). However, the effect on HRMT was not modulated by muscle–technique interaction and showed sex-specific differences only for F.Trial registration German Clinical Trial Register (DRKS00020393).

Comparative study of surface electromyography of masticatory muscles in patients with different types of bruxism.

BACKGROUNDBruxism is a rhythmic masticatory muscle activity that occurs involuntarily in a non-physiologically functional state. There is a lack of research classifying the functional status of masticatory muscles in patients with different mandibular movement types (centric clenching or eccentric grinding) of bruxism.AIMTo assess the differences of the masticatory muscle activity in patients with different types of bruxism.METHODSA total of 21 subjects with centric bruxism (CB) and 21 subjects with eccentric bruxism (ECB) were screened from college students according to a questionnaire and their tooth wear features. Sixteen subjects with no bruxism were also recruited. The surface electromyography (EMG) signals of the temporalis anterior (TA) and superficial masseter muscle (MM) were measured in different mandibular positions and during the chewing task. The EMG amplitude and chewing cycle duration parameters were then analyzed.RESULTSThe CB group showed fewer muscle maximal motor units, with the MM being more pronounced, a higher proportion of muscle contractions to be recruited for the same load of chewing activity, and a longer chewing cycle. The ECB group showed more TA maximal motor units and higher MM activity on the non-working side in unilateral chewing.CONCLUSIONCB mainly affects the MM, and patients with CB show reduced masticatory muscle contraction efficiency and chewing cycle efficiency. ECB mainly affects the TA, and patients with ECB show enhanced contraction of non-functional lateral muscle bundles.

The effects of unilateral posterior crossbite toward the superficial masseter and anterior temporalis on muscle activity during mastication: A surface electromyographic study

Background: Adapted patterns of mastication caused by unilateral posterior crossbite require early orthodontic treatment to prevent permanent muscle change. Stable orthodontic results depend on the harmonious contraction of the occlusion and masticatory muscles. Purpose: Using surface electromyography, this study aimed to analyse the effects of unilateral posterior crossbite on the superficial masseter as well as anterior temporalis muscle activity on the crossbite and non-crossbite sides during chewing soft and hard foods. Methods: A cross-sectional study was conducted on 20 subjects with at least two posterior teeth who had a unilateral posterior crossbite without mandible shifting. Surface electromyography was used to measure activity amplitudes for the superficial masseter and the anterior temporalis muscles while chewing soft and hard foods. An independent t-test was used to determine the mean difference between chewing soft and hard foods through the superficial masseter and anterior temporalis muscles. Results: Results showed a significant difference in amplitude mean between crossbite and non-crossbite sides of the superficial masseter and anterior temporalis muscles with both soft and hard food chewing (p &lt; 0.05). The study also revealed a decrease in the activities of superficial masseter and anterior temporalis muscles when masticating soft and hard foods on the crossbite sides as compared to the non-crossbite sides. Conclusion: A unilateral posterior crossbite results in a decrease in the superficial masseter and the anterior temporalis muscle activity when masticating both soft and hard foods on the crossbite side.

Sex differences in masticatory muscle activity in healthy young adults

Abstract Introduction. Several studies analyzed the gender differences in masticatory muscle activity. Previous scientific reports indicate the predominance of the masseter muscle activity in male subjects and the predominance of the temporalis anterior in women. However, there is a lack of studies analyzing the differences in the activity of the mandibular abduction muscles between men and women. Aim. The presented study evaluated the sex differences in activity within temporalis anterior, masseter, and digastric muscle in healthy young adults. Material and methods. Thirty-six healthy young adults aged 20 to 29 years (mean 22±2.6 years) were qualified for the presented study. The subjects were divided into two equal groups (n=18) in terms of gender. The masticatory muscle activity was recorded within the temporalis anterior (TA), the superficial masseter muscle (MM), and the anterior bellies of the digastric muscle (DA). Electromyographic activity was recorded in three conditions: at rest, during maximum voluntary clenching at the intercuspal position, and during maximum voluntary clenching with cotton rolls between teeth. Results. Significant differences in electromyographic activity between the male and female group were observed within resting activity for the TA-R (Women: 1.98 µV vs. Men: 1.26 µV; p=0.000), TA-L (Women: 2.13 µV vs. Men: 1.33 µV; p=0.000), DA-R (Women: 2.17 µV vs. Men: 1.29 µV; p=0.001), DA-L (Women: 2.13 µV vs. Men: 1.37 µV; p=0.005). Moreover, significant difference in resting activity index was observed within left side (Women: -9.89 % vs. Men: 10.39%; p=0.037), and within right side during clenching with cotton rolls between teeth (Women: 9.83% vs. Men: 25.59%; p=0.016). Conclusions. Women represent higher resting sEMG activity within the temporalis anterior and digastric muscles than men. Electromyographic patterns may be influenced by gender at rest and during clenching tasks.

Malocclusion with posterior unilateral crossbite affects superficial masseter and anterior temporal muscle activity during mastication

Background: Mastication patterns due to malocclusion with unilateral posterior crossbite may permanently change. Purpose: This study aimed to examine the effect of malocclusion with unilateral posterior crossbite of the superficial masseter and anterior temporal muscles on the crossbite and non-crossbite sides during mastication. Methods: Thirty subjects (8 males and 22 females) between the ages of 17 and 30 years who were students of the 2017–2019 Dentistry and Dental Hygiene Study Program, Faculty of Dentistry, UGM and who had at least two posterior teeth with unilateral posterior crossbite were divided into 10 subjects with Angle’s class I, 10 subjects with class II and 10 subjects with class III malocclusions. The amplitude of the superficial masseter and temporal anterior muscles was performed during mastication using surface electromyography (sEMG). The mean difference between the groups of malocclusion on the crossbite and non-crossbite sides of the superficial masseter and temporal anterior was analysed by a two-way analysis of variance (ANOVA). Results: The results indicated a difference in amplitude mean between the malocclusion types on the crossbite sides and non-crossbite sides of the superficial masseter and temporal anterior muscles (p&lt;0.05). This study confirmed there was a decrease in superficial masseter and anterior temporal muscle activity on the crossbite side rather than in the non-crossbite side in Angle’s class I and class II. However, there was an increase in activity of the superficial masseter and anterior temporal muscles on the crossbite side for class III. Conclusion: Malocclusion with unilateral posterior crossbite affects masticatory activity of the superficial masseter and temporal anterior muscles on the crossbite side.

Comparative biomechanics of the Pan and Macaca mandibles during mastication: finite element modelling of loading, deformation and strain regimes.

The mechanical behaviour of the mandibles of Pan and Macaca during mastication was compared using finite element modelling. Muscle forces were calculated using species-specific measures of physiological cross-sectional area and scaled using electromyographic estimates of muscle recruitment in Macaca. Loading regimes were compared using moments acting on the mandible and strain regimes were qualitatively compared using maps of principal, shear and axial strains. The enlarged and more vertically oriented temporalis and superficial masseter muscles of Pan result in larger sagittal and transverse bending moments on both working and balancing sides, and larger anteroposterior twisting moments on the working side. The mandible of Pan experiences higher principal strain magnitudes in the ramus and mandibular prominence, higher transverse shear strains in the top of the symphyseal region and working-side corpus, and a predominance of sagittal bending-related strains in the balancing-side mandible. This study lays the foundation for a broader comparative study of Hominidae mandibular mechanics in extant and fossil hominids using finite element modelling. Pan's larger and more vertical masseter and temporalis may make it a more suitable model for hominid mandibular biomechanics than Macaca.

English

Considering the large number of fixed functional appliances, choosing the best device for your patient is not an easy task. To describe the development of fixed functional appliances as well as our 20-year experience working with them. Fixed functional appliances are grouped into flexible, rigid and hybrid. They are different appliances, whose action is described here. Four clinical cases will be reported with a view in illustrating the different appliances. Rigid fixed functional appliances provide better skeletal results than flexible and hybrid ones. Flexible and hybrid appliances have similar effects to those produced by class II elastics. They ultimately correct class II with dentoalveolar changes. From a biomechanical standpoint, fixed functional appliances are more recommended to treat class II in dolichofacial patients, in comparison to class II elastics. The electromyographic (EMG) activity of masticatory muscles was monitored longitudinally with chronically implanted EMG electrodes to determine whether functional appliances produce a change in postural EMG activity of the muscles. Pre-appliance and post-appliance EMG levels in four experiments that had been fitted with functional appliances were compared against the background of EMG levels in controls without appliances. The insertion of two types of functional appliance to induce mandibular protrusion was associated with a decrease in postural EMG activity of the superior and inferior heads of the lateral pterygoid, superficial masseter, and anterior digastric muscles; the decrease in the first three muscles was statistically significant. This decreased postural EMG activity persisted for approximately 6 weeks, with a gradual return towards pre-appliance levels during a subsequent 6-week period of observation. Progressive mandibular advancement of 1.5 to 2 mm every 10 to 15 days did not prevent the decrease in postural EMG activity. KEY WORDS Orthodontics, Class II Malocclusion, Fixed Functional Appliance.

Masticatory Functional Load Increases the mRNA Expression Levels of ACTN2 and ACTN3 and the Protein Expression of α-Actinin-2 in Rat Masseter Muscle.

α-actinins play structural and regulatory roles in cytoskeletal organization. They form a lattice structure that secures actin in thin filaments, which generate and transmit muscle contractile forces. The morphological and biochemical characteristics of rat masseter muscles are known to change reactions to masticatory functional loads, but their effect on α-actinins remains unknown. This study aimed to determine the response of α-actinins to masticatory functional loads. Twenty-four male Wistar rats aged 3 weeks were divided randomly into 3 groups of liquid diet (LD), soft diet, and hard diet (HD). The rats were then sacrificed at the end of 8 weeks. The middle part of superficial masseter muscles was examined to investigate the masticatory effect of functional load on the mRNA expression levels of ACTN2 and ACTN3 and the protein expression levels of α-actinin-2 and α-actinin-3. The mRNA expression levels of ACTN2 and ACTN3 and the protein expression levels of α-actinin-2 of the HD group were significantly higher than those of the LD group, which served as the control group. Masticatory functional load organizes the mRNA expression levels of ACTN2 and ACTN3 and the protein expression levels of α-actinin-2 in rat masseter muscles through stimuli during muscle physiological adaptation.

Impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency.

Whether precise orthodontic detailing of occlusion impacts masticatory function is unknown. In this study, we aimed to assess the impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency. Fifty-four adults who completed orthodontic treatment were categorized into two groups using the American Board of Orthodontics (ABO) model grading system: one meeting ABO standards (ABO, N = 29), the other failing to meet them (non-ABO, N = 25). The electromyographic (EMG) signals of the anterior temporalis (AT) and superficial masseter muscles were recorded bilaterally during static (clenching) and dynamic (gum chewing) tests. Chewing efficiency was measured by calculating the median particle size (MPS) and broadness of particle distribution (BPD) after five chewing trials of experimental silicone food at a standardized chewing rate. Participants of the ABO group had a slightly more symmetric activation of the AT muscles during clenching (P = 0.016) and chewed a gum at a slower rate (P = 0.030). During the standardized chewing test with silicone food, ABO subjects had slightly greater EMG potentials at all muscle locations than non-ABO individuals (all P < 0.05). MPS and BDP did not differ significantly between groups (all P > 0.05). The severity of the initial malocclusion of the study participants was not in the statistical model as a potential confounder on the outcome measures. Meeting ABO standards contributes to a slightly more balanced activation of the temporalis muscles during clenching and more efficient muscle recruitment during chewing but does not improve chewing efficiency.

Comparative evaluation of the masticatory muscleS activity with CAD/CAM versus conventional complete denture using electromyography

Purpose: To evaluate in-vivo the effect of CAD/CAM constructed dentures on the masticatory muscles activity using electromyography in comparison to conventionally constructed dentures.Materials and Methods: Fourteen completely edentulous patients were randomly allocated to two equal groups. Patients in the first group received conventionally constructed complete dentures and patients in the second group received complete dentures constructed using CAD/CAM technology. After 30 days of denture use the anterior temporalis and superficial masseter muscles activity were measured by EMG. A cross over was performed for patients with conventional denture to CAD/CAM and vice versa and the dentures were used for further 30 days, after which measurements of anterior temporalis and superficial masseter muscles activity were taken using EMG. Electromyographic data was recorded and analyzed, mean values were compared by independent t-test to compare between the two groups as regard to muscle activity. Results: There was a significant difference in the activity of the masseter muscles and the anterior temporalis muscles for the patients received CAD/CAM denture in comparison to those received the conventional denture, after 30 days of denture use (p < 0.05). Conclusion: CAD/CAM constructed complete dentures produced higher muscle activity if compared to conventionally constructed complete dentures.

Correlation between Changes in the Transverse Relaxation Time and Electromyographic Measurements of the Superficial Masseter and Temporal Muscles.

We analyzed the correlations between the T2 shift and integrated electromyographic (iEMG) values in the masseter and temporal muscles. Six healthy adults engaged in a clenching task over two durations at various bite forces. We evaluated the mean T2 shift per voxel and assessed their correlations with iEMG using a linear mixed model. The regression coefficients were different for each muscle type, similar for the left and right sides, and decreased upon doubling duration.

Biomechanical Analysis of the Forces Exerted during Different Occlusion Conditions following Bilateral Sagittal Split Osteotomy Treatment for Mandibular Deficiency.

The bilateral sagittal split osteotomy (BSSO) technique is commonly used to correct mandibular deficiency. If the patient is exposed to excessive external forces after the procedure, occlusal changes or nonunion may occur. However, previous studies only focused on single external forces on the mandible and did not conduct relevant research on the forces exerted by different occlusion conditions. The main purpose of this study was to use finite element analysis methods to determine the biomechanics of four common occlusion conditions after BSSO surgical treatment. This study constructed a finite element analysis computer model of a miniplate implanted in the lower jaw. The structure of the model consisted of the mandible, miniplate, and screws. In addition, external forces were applied to the superficial masseter, deep masseter, medial pterygoid, anterior temporalis, middle temporalis, and posterior temporalis muscles to simulate the incisal clench, intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function occlusion conditions. Subsequently, this study observed the effects of these conditions on the miniplate, screws, and mandible, including the von Mises stress values. The results showed that all of the different occlusion conditions that this study evaluated placed high stress on the miniplate. In the ICP and RMOL occlusion conditions, the overall mandibular structure experienced very high stress. The screw on the proximal segment near the bone gap experienced high stress, as did the screw on the buccal side. According to the present analysis, although the data were not directly obtained from clinical practice, the finite element analysis could evaluate the trend of results under different external forces. The result of this study recommended that patients without intermaxillary fixation avoid the ICP and RMOL occlusion conditions. It can be used as a pilot study in the future for providing clinicians more information on the biomechanics of implantation.

Correlación entre la actividad muscular masetera y la fuerza máxima de mordida entre varios patrones de divergencia facial

Objective: To comparatively assess electromyographic (EMG) activity of masseter muscle and maximum bite force among various facial divergence pattern. To compare bilateral variation therefore derive the clinical importance changes in masseter EMG activity. Materials and Methods: The sample size comprised of 90 subjects, age ranging from 16-25 years. They were further classified under three subgroups-normodivergent, hypodivergent and hyperdivergennt based on the cephalometric values. Tekscan Flexiforce B201H sensor along with the associated software was used to record the bite force. The EMG of the superficial masseter muscle was recorded using Biotech Neurocare 2000 surface electromyography machine. The muscle activity was recorded bilaterally from the superficial masseter. The data obtained were statistically analyzed using ROC curve at p&lt;0.05. Results: The bite force of the Hypodivergent group (571.83N±36.65) was more than the Normodivergent (387.26±27.20) and Hyperdivergent groups (373.21N±29.23). The EMG recording of masseter muscle activity in Hypodivergent group was significantly higher than Normodivergent and Hyperdivergent groups. (p-value= &lt;0.01). A significant correlation existed between masseter activity and bite force. Conclusion: The bite force of Hypodivergent jaw base individuals is highest followed by Normodivergent and least in Hyperdivergent individuals.The strong correlation between the muscular activity and the bite force is definitely a contributor to the anchorage value during treatment by fixed Orthodontics.

Electromyographic activity of superficial masseter and anterior temporal muscles during unilateral mastication of artificial test foods with different textures in healthy subjects.

This study aimed to examine the electromyographic activity of superficial masseter and anterior temporal muscles during chewing gum and gummy jelly mastication in healthy subjects to reveal the difference of neuromuscular control of jaw-closing muscles, according to the food texture. Electromyographic activity was recorded in 30 adults with Angle Class I occlusion and unimpaired function from the bilateral superficial masseter and anterior temporal muscles during unilateral mastication of two test foods: standardized gummy jelly and color-changeable chewing gum. Differences in normalized electromyographic activity and asymmetry index values between gummy jelly and chewing gum mastication were analyzed during the early, middle, and late phases of mandibular closure. Furthermore, changes among the three closing phases were compared for each test food. High electromyographic activity of both muscles tended to occur bilaterally during the middle and late closing phases during gummy jelly mastication, but increased muscle activity in the late closing phase was not observed during chewing gum mastication. The asymmetry index of the superficial masseter muscle increased significantly from early to late closure, regardless of the food texture, but it tended to decrease for the anterior temporal muscle during gummy jelly mastication. The different aspects of the chewing process between the comminution and mixing test measures are necessary to elicit the different human neuromuscular strategies of chewing for different test foods. These characteristic EMG activities of the superficial masseter and anterior temporalis muscles may be used as supporting diagnostic information during patient assessments and a reference during evaluation of masticatory system disharmony or dysfunction.

Ultrasonographic evaluation of mandibular elevator muscles to assess effects of attrition-type tooth wear on masticatory function

Objectives: Occlusal alterations may result in changes in the functional performance of masticatory muscles. This study was planned to evaluate mandibular elevator muscles of patients with dental attrition by using ultrasonography (USG). Methods: 30 physiologically dental attrition subjects, aged 35–65 years, were clinically examined by tooth wear index (TWI). Patient group (TWI scores of 2–4) and age-matched controls (TWI scores of 0–1) underwent ultrasonographic analysis to assess the thickness of anterior temporalis, superficial masseter muscles, bilaterally, during clench and rest positions. Results: The mean thickness of masseter and temporal muscles for rest and clench positions and the ratio between thickness of clench and rest position (C/R) were evaluated. Muscle thickness had a higher mean value in the tooth wear group. However, the only significant differences were in the C/R ratio for left side of masseter (p=0.04) and temporal muscles (p=0.03). Although, there was a negative correlation between TWI scores and the muscle C/R ratio for the tooth wear group. A significant positive correlation was found between age and TWI in both groups. Conclusion: The contraction capacity of the chewing muscles and the attrition mutually interact. This study showed an associate on between the severity of occlusal tooth wear and the C/R of chewing muscles. Although dental attrition can occur due to increased jaw muscle activation, and it can also cause a reduction in the contraction capacity of mandibular elevator muscles.

Immediate effects of temporary bite-raising with light-cured orthodontic band cement on the electromyographic response of masticatory muscles.

Objective:To assess the immediate effects of temporary bite-raising using light-cured orthodontic band cement on the superficial masseter and anterior temporalis electromyography (EMG) activity in healthy adults.Materials and Methods:Surface EMG signals were recorded bilaterally from the superficial masseter and anterior temporalis muscles of 30 volunteers with a normal occlusion, before and after having temporary bite-raising. The bite-raising was done by adding light-cured orthodontic band cement (3x5x2 mm WxLxH) on the lingual cusps of both upper first molars. The measurements were recorded (i) at rest, (ii) while clenching in centric occluding position and (iii) while chewing on an artificial test food. The EMG activity at rest and during clenching, the maximum voltage, and the duration of the identified EMG signal burst while chewing the artificial test food before and after temporary bite-raising were statistically compared using the paired t-test or the Wilcoxon signed-rank test based on the normality of the variables. The significance level was set at 5%.Results:After temporary bite-raising, we found no significant change in integral EMG activity at rest position for the superficial masseter (mean difference (MD)=7.5 μVs) and for the anterior temporalis muscle (MD=36.8 μVs); however, the integral EMG activity during clenching was significantly reduced for the superficial masseter (MD=201.2 μVs) and for the anterior temporalis muscle (MD=151.8 μVs). During mastication, the maximum voltage of the identified burst was significantly reduced on the preferred chewing side of the superficial masseter and anterior temporalis muscles (MD=127.9 and 47.7 μV, respectively), while no significant change was found for the duration of the identified burst (MD=-34.1 and 3.4 ms, respectively) after temporary bite-raising.Conclusion:The results point to an altered neuromuscular behavior during clenching and chewing immediately after temporary bite-raising with light-cured orthodontic band cement. This information is relevant for orthodontists to inform their patients what will happen to their masticatory muscle activity when this bite-raising method is used.