Superficial Masseter Research Articles

Biomechanical effects of different mandibular movements and torque compensations during mandibular advancement with clear aligners: a finite element analysis

IntroductionThis study aimed to evaluate the biomechanical effects of different mandibular movements and torque compensations during mandibular advancement with clear aligners using finite element analysis.MethodsModels were constructed to include the mandible, teeth, periodontal ligament (PDL), and clear aligners with buccal wings. Five oral muscles (superficial masseter, deep masseter, medial temporalis, posterior temporalis, and medial pterygoid) were represented as springs. Muscle values were measured and applied during different mandibular movements, including advancement distances (1–7 mm) and occlusal opening distances (2–4 mm). Different torque compensation angles (0°, 1°, 2°, and 3°) were applied to the mandibular central incisor.ResultsWhen the mandibular advancement was equal to or slightly excessed the occlusal opening distance, stress on the posterior PDL decreased and became more evenly distributed. Increasing the occlusal opening distance significantly raised stress on the posterior PDL and caused grater labial inclination of the mandibular anterior teeth. As the torque compensation increased, the labial inclination of the mandibular central incisor decreased, but stress on the PDL increased. Nearly complete bodily movement of the lower central incisor was achieved with torque compensation angles of approximately 15°, 19°, and 20° in models M1-2, M2-3, and M3-4, respectively.ConclusionTo maintain periodontal health during mandibular advancement, it is recommended that the mandibular advancement distance be equal to or slightly excessed the occlusal opening distance. Excessive occlusal opening distance increases stress on the posterior PDL and the labial inclination of mandibular anterior teeth, requiring careful control. Additionally, proper torque control of the mandibular interior teeth is crucial for optimal outcomes.

Acrylated Hyaluronic-Acid Based Hydrogel for the Treatment of Craniofacial Volumetric Muscle Loss.

Current treatment options for craniofacial volumetric muscle loss (VML) have disadvantages and cannot fully restore normal function. Bio-inspired semisynthetic acrylated hyaluronic acid (AcHyA) hydrogel, which fills irregularly shaped defects, resembles an extracellular matrix, and induces a minimal inflammatory response, has shown promise in experimental studies of extremity VML. We therefore sought to study AcHyA hydrogel in the treatment of craniofacial VML. For this, we used a novel model of masseter VML in the rat. Following the creation of a 5 mm × 5 mm injury to the superficial masseter and administration of AcHyA to the wound, masseters were explanted between 2 and 16 weeks postoperatively and were analyzed for evidence of muscle regeneration including fibrosis, defect size, and fiber cross-sectional area (FCSA). At 8 and 16 weeks, masseters treated with AcHyA showed significantly less fibrosis than nonrepaired controls and a smaller decrease in defect size. The mean FCSA among fibers near the defect was significantly greater among hydrogel-repaired than control masseters at 8 weeks, 12 weeks, and 16 weeks. These results show that the hydrogel mitigates the fibrotic healing response and wound contracture. Our findings also suggest that hydrogel-based treatments have potential use as a treatment for the regeneration of craniofacial VML and demonstrate a system for evaluating subsequent iterations of materials in VML injuries. Impact Statement Craniofacial volumetric muscle loss (VML) is a debilitating condition for which current treatment options are unable to restore normal appearance, or function. Tissue engineering approaches, such as hydrogel implants, may be an effective strategy to fill the volumetric defects and promote de novo muscle regeneration. In this study, we describe a novel rodent model for the study of craniofacial VML and a hyaluronic acid-based hydrogel that can be used as a treatment for the regeneration of craniofacial VML.

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.

Masticatory myology of the llama (Lama glama, Camelidae) andcomparisons with other camelids and euungulates.

Camelids are the only living representatives of the Suborder Tylopoda, and present a unique set of osteo-myological masticatory features, differing from all other extant euungulates. They combine selenodont dentition and rumination with a fused symphysis, and roughly plesiomorphic muscle proportions. Despite its potential relevance as an euungulate model in comparative anatomy studies, the available data is strikingly scarce. The present study represents the first description of the masticatory muscles of a Lamini, analyzing the functional morphology of Lama glama and other camelids in a comparative framework. Both sides of the head of three adult specimens from Argentinean Puna were dissected. Descriptions, illustrations, muscular maps, and weighing of all masticatory muscles were performed. Some facial muscles are also described. The myology of llamas confirms that camelids possess relatively large temporalis muscles, with Lama being less extreme than Camelus. This plesiomorphic feature is also recorded in suines and some basal euungulates. Conversely, the direction of the fibers of the M. temporalis is mainly horizontal, resembling grinding euungulates such as equids, pecorans, and some derived suines. Although the M. masseter of camelids and equids do not reach the particularly modified configuration of pecorans, in which it is rostrally extended and arranged horizontally, the posterior sectors of Mm. masseter superficialis and pterygoideus medialis have acquired relatively horizontal disposition in the former lineages, suitable for protraction. The pterygoidei complex presents several bundles, and its relative size is intermediate between suines and derived grinding euungulates. The whole masticatory muscles are relatively light when compared to jaw weight. The evolution of the masticatory muscles and chewing of camelids implied that grinding abilities were reached with less extreme modifications of the topography and/or proportions than pecoran ruminants and equids. A relatively large M. temporalis recruited as a powerful retractor during the power stroke is a key feature of camelids. The relaxed pressure on chewing derived from the acquisition of rumination explains the slenderer build masticatory musculature of camelids compared to other euungulates except ruminants.

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.

Using the quad helix to treat bruxism in children: a clinical case

Objective: To present a treatment for bruxism in children using quad helix as an intraoral device based on a clinical case. Methodology: A case report. Results: At the end of the treatment, the presence of the quad helix afforded enough space for the eruption of the permanent teeth, as well as had changed the child’s occlusal pattern, deprogrammed the parafunctional habit, cultivated a functional muscle pattern, reduced hyperactivity, and completely relieved all painful symptomatology. Conclusion: The use of quad helix for 4 months, along with achieving its orthodontic function, proved capable of increasing the patient’s proprioception by enhancing the non-visible recognition of the spatial location of the mandible, deprogramming the child’s bruxism, and consequently eliminating all pain in the temporal and superficial masseter masticatory muscles.

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.

The Difference in Electromyographic Activity While Wearing a Medical Mask in Women with and without Temporomandibular Disorders

Wearing a medical mask influences resting activity of the temporalis anterior and masseter muscles in healthy young women. However, no studies link medical mask-wearing with masticatory muscle activity in patients with temporomandibular disorders (TMDs). Therefore, this study aims to compare electromyographic patterns while wearing a medical mask between women with and without temporomandibular disorders. Based on the Research Diagnostic Criteria for Temporomandibular Disorders, 115 adult women qualified for the study. Participants were divided into the following two groups: diagnosed TMDs (n = 55; mean age: 23.5 ± 2.3 years) and healthy women (n = 60; mean age: 23.7 ± 2.6 years). Examinations of the resting and functional electromyographic activity of the temporalis anterior (TA), superficial masseter (MM), anterior bellies of the digastric muscle (DA), and the middle part of the sternocleidomastoid muscle (SCM) were carried out using the BioEMG III™. Both groups showed statistically significant decreases in resting masticatory muscle activity during medical mask examination compared to no mask measurement. The significant differences in no mask measurement between both groups were noted regarding resting masticatory activity, clenching in the intercuspal position, and clenching on dental cotton rollers. During medical mask examination, women with TMDs showed differences in resting masticatory activity and clenching on dental cotton rollers compared to the healthy group. In all analyzed variables, both groups showed similar electromyographic patterns in the maximum mouth opening measurement during medical mask and no mask examination. A medical mask influences the resting bioelectric activity of the masticatory muscles in women with temporomandibular disorders and healthy women. We observed differences and some similarities in resting and functional electromyographic patterns within masticatory and neck muscles in both groups during medical mask and no mask examination.

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).

The effect of tooth cusp morphology and grinding direction on TMJ loading during bruxism

Increased mechanical loading of the temporomandibular joint (TMJ) is often connected with the onset and progression of temporomandibular joint disorders (TMD). The potential role of occlusal factors and sleep bruxism in the onset of TMD are a highly debated topic in literature, but ethical considerations limit in vivo examinations of this problem. The study aims to use an innovative in silico modeling approach to thoroughly investigate the connection between morphological parameters, bruxing direction and TMJ stress. A forward-dynamics tracking approach was used to simulate laterotrusive and mediotrusive tooth grinding for 3 tooth positions, 5 lateral inclination angles, 5 sagittal tilt angles and 3 force levels, giving a total of 450 simulations. Muscle activation patterns, TMJ disc von Mises stress as well as correlations between mean muscle activations and TMJ disc stress are reported. Computed muscle activation patterns agree well with previous literature. The results suggest that tooth inclination and grinding position, to a smaller degree, have an effect on TMJ loading. Mediotrusive bruxing computed higher loads compared to laterotrusive simulations. The strongest correlation was found for TMJ stress and mean activation of the superficial masseter. Overall, our results provide in silico evidence that TMJ disc stress is related to tooth morphology.

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.

Surface electromyography for evaluating patients with oromandibular dystonia

ABSTRACT Objective To investigate myoelectric signals of dystonic activities in oromandibular dystonia (OMD) subjects using surface electromyography (EMG). Methods Twelve OMD subjects were included in this study. Resting myoelectric activities of the superficial masseter, anterior temporalis, and anterior belly of the digastric muscle on both sides were monitored, and dystonic muscle contractions were recorded using surface EMG. Myoelectric signal amplitude, the type of muscle contraction, and contraction rate for phasic activities were evaluated. Results Surface EMG revealed that eight subjects had dystonic muscle activities in the phasic contraction pattern, three subjects had a tonic contraction pattern, and one subject had a mixed pattern. Synchronous contraction of dystonic muscles was frequently observed. Many of the monitored muscles showed high resting amplitudes. Conclusion Surface EMG detects abnormal muscle activities related to oromandibular dystonia. Surface EMG can serve as an objective method for diagnosing oromandibular dystonia.

The Relationship of Myofascial Trigger Points (MTrPs) Pain to Headache: Type, Location, and Intensity of Headache

Headaches are one of the most common nervous system disorders with a major impact on public health. They can be caused by various etiologies, and some of them are symptoms of serious pathology. The location and intensity of the headache are related to the etiology of the headache. In some cases, headaches can be accompanied by pain due to myofascial trigger points (MTrPs), which are small hyper-irritating spots located centrally within bands that have been injured or overworked. The purpose of this study was to determine the relationship between Myofascial Trigger Points (MTrPs) Pain and the Type, Location, and Intensity of Headaches. This type of research is analytic observational with a cross-sectional design. Data were collected in October and December of 2014, and a sample of 50 people was drawn using a consecutive sampling technique.Data were gathered through neurologists' history-taking and physical examinations, as well as interviews using a numerical pain scale (NPS), and then analyzed using Fisher and Mann Whitney.The results showed that MTrPs were positive for M. sternocleidomastoid in 38 people, M. trapezius in 36 people, M. temporalis in 31 people, M. masseter superficialis in 20 people, M. suboccipital in 18 people, M. levator scapulae in 34 people, and M. obliquus superior in 20 people. The highest number of active MTrPs was 4 in 15 people, and referred pain from MTrPs was present in only 5 people. It can be concluded that there is no relationship between Myofascial Trigger Points (MTrPs) pain and the type of headache, but there is a relationship between Myofascial Trigger Points (MTrPs) pain and the location and intensity of the headache.

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.

Novel Functional Indices of Masticatory Muscle Activity.

The aim of the present study was to analyze novel functional indices of masticatory muscle activity and compare them to existing and commonly used indices in patients with temporomandibular disorders (TMDs) and healthy adults. Based on the Research Diagnostic Criteria for Temporomandibular Disorders, 78 adult women qualified for the study. Subjects were divided into two groups: diagnosed TMDs (n = 36; mean age: 23.4 ± 2.6 years) and healthy adults (n = 42; mean age: 22.4 ± 2.3 years). Measurements of the bioelectric activity of the temporalis anterior (TA), superficial masseter (MM), and anterior bellies of the digastric muscle (DA) were carried out using the BioEMG III ™. Functional Clenching (FCI) and Functional Opening (FOI) indices were obtained as the ratio of the difference between the mean muscle root mean square (RMS) potentials during functional activity, including clenching (CL) and opening (MMO), and mean muscle resting (REST) potentials. Next, based on FCI and FOI indices, the Functional Clenching Activity Index (FCAI), Functional Clenching Symmetry Index (FCSI), and Functional Opening Symmetry Index (FOSI) were obtained. The statistical analysis showed significant differences in activity index left-sided (AcIL) and Activity index both-sided (AcItot) between TMDs and healthy women during rest measurements. The significant differences between both groups were noted in terms of all Functional Clenching Indices except Functional Clenching Index for MM right-sided (FCIMM-R). In all analyzed FCI indices, the control group showed higher values compared to the TMDs. Moreover, a significant difference between TMDs and controls was observed within Functional Clenching Activity Index left-sided (FCAIL) (14.56 vs. −0.45, p = 0.01). Both functional indices, and asymmetry (AsI) and activity (AcI) indices seem to be reliable in assessing symmetry and activity within masticatory muscles. Further studies should be performed to verify the effectiveness and suitability of the assessment of masticatory muscles using functional indices.