Mandibular elevator muscles: physiology, action, and effect of dental occlusion

Oro-facial function and quality of life in children and adolescents with large horizontal maxillary overjet-A case-control study

BACKGROUND

Large horizontal maxillary overjet (overjet) is associated with reduced bite force (BF) and number of contacts, which influence the chewing effectivity (CE). Oral health, oro-facial function (OF) and malocclusion have great impact on psychological well-being and quality of life (QoL).

OBJECTIVES

The aims of the study were to examine OF, temporomandibular disorders (TMD), BF, CE, QoL and well-being in children and adolescents with large overjet.

METHODS

The study was a case-control study including healthy children with large overjet in the study group compared to a control group of healthy children with neutral occlusion, all 9-14 years old. OF was examined by use of Nordic Orofacial Test-Screening (NOT-S), Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) and registration of morphological and functional occlusion. QoL and well-being were examined using KIDSCREEN-10 and Strengths and Difficulties Questionnaire.

RESULTS

The study and control groups included 37 and 32 participants, respectively. Significantly increased NOT-S score (p < .001) and reduced BF (p = .011), numbers of contacts (p < .001) and CE (p = .005) were found in the study group. BF, numbers of contacts and CE were negatively associated with erupting canines and premolars. No significant difference was found in age, gender, dental eruption, TMD diagnosis or QoL between the groups. Significantly increased emotional symptoms (p = .007), hyperactivity (p = .043) and total difficulties score (p = .009) were found in the study group.

CONCLUSION

The study group showed higher NOT-S score and reduced BF, number of contacts and CE. No difference in QoL were found between the groups, although reduced well-being and increased emotional symptoms, hyperactivity and total difficulties were found in the study group.

A Comparison Between Skeletal Class II and Class III Malocclusion Patients in Terms of the Masticatory Muscles' Activity: A Cross-Sectional Study

Background This study aimed to determine if individuals with skeletal Class II and skeletal Class III malocclusions had different levels of masticatory muscle activity. Materials and methods This cross-sectional study, conducted at the University of Damascus, investigated the myoelectric activity of perioral muscles in patients with Class II and III malocclusions. The sample size of 60 patients was determined according to a prior sample size calculation. Patients were selected based on specific inclusion and exclusion criteria and divided into Class II and III groups. Electromyography was used to monitor the activity of various muscles, including the temporalis, masseter, orbicularis oris, buccinator, mentalis, and digastric muscles. Results The study found similar muscle activity within the same group in the temporalis, masseter, buccinator, digastric, and orbicularis oris muscles. No significant differences were observed between the Class II and III groups for several oral and perioral muscles (P > 0.05). However, the mean activity of the digastric muscle was significantly greater in the Class II group (P < 0.05), whereas the mean activity of the mentalis muscle was smaller in the Class II group (P < 0.05). Conclusions Perioral muscles influence facial complex development and jaw relationship, affecting orthodontic treatment. Digastric muscle activity is greater in Class II patients, while mental muscle activity is smaller in Class III patients. Further studies are needed for older age groups and other skeletal malocclusion types.

Effect of Botulinum Toxin on Masticatory Muscle Pain in Patients with Temporomandibular Disorders: A Randomized, Double-Blind, Placebo-Controlled Pilot Study

This study aimed to evaluate the efficacy of botulinum toxin type A (BoNT/A) in patients with temporomandibular disorders (TMDs) associated with masticatory muscle pain (MMP) and headaches. This randomized, double-blind, placebo-controlled pilot study is the first clinical trial to evaluate both disorders simultaneously. Twenty-one patients with myogenous TMD were randomly assigned to two groups. The experimental and control groups received injections of either BoNT/A or saline into the sites showing tenderness after palpation of a total of 16 muscle areas, including each masseter, a temporalis, splenius capitis, sternocleidomastoid, and trapezius muscle. During each visit, the clinical effects, based on the intensity of orofacial pain (OVAS), headache (HVAS), number of tender points (TPs), maximum mouth opening (MMO), and headache frequency (HF), were evaluated at four time points, namely, pre-injection and 4, 8, and 12 weeks after the injection, in both groups. Friedman and Mann-Whitney tests were used for the analyses. In the experimental group, the reductions in OVAS, TP, HVAS, and HF showed significant differences over time, excluding MMO, whereas there was no significant difference in any of the variables in the control group. In addition, the decline in TPs was significantly different between the experimental and control groups at all time points, especially after 4 and 12 weeks, compared to that during pre-injection. In conclusion, treatment with BoNT/A was relatively effective for masticatory muscle pain caused by TMDs and headache compared to the saline placebo.

Correlation of masticatory muscle activity and occlusal function with craniofacial morphology: a prospective cohort study

OBJECTIVES

Masticatory function, including masticatory muscle activity and occlusal function, can be affected by craniofacial morphology. This study aimed to investigate the relationship between craniofacial morphology and masticatory function in participants who had completed orthodontic treatment at least two years before and had stable occlusion.

MATERIALS AND METHODS

Fourty-two healthy participants were prospectively enrolled and divided into three vertical cephalometric groups according to the mandibular plane angle. Masticatory muscle activity (MMA) in the masseter and anterior temporalis muscles was assessed using surface electromyography. The occlusal contact area (OCA) and occlusal force (OF), defined as occlusal function in this study, were evaluated using occlusal pressure mapping system. Masticatory muscle efficiency (MME) was calculated by dividing MMA by OF. The craniofacial morphology was analyzed using a lateral cephalogram. The masticatory function was compared using one-way analysis of variance. Pearson correlations were used to assess relationships between craniofacial morphology and masticatory function.

RESULTS

The hypodivergent group had the lowest MMAand the highest MME in the masseter (167.32 ± 74.92 µV and 0.14 ± 0.06 µV/N, respectively) and anterior temporalis muscles (0.18 ± 0.08 µV/N, p < 0.05). MMA in the masseter showed a positive relationship with mandibular plane angle (r = 0.358), whereas OCA (r = -0.422) and OF (r = -0.383) demonstrated a negative relationship (p < 0.05). The anterior temporalis muscle activity negatively correlated with ramus height (r = -0.364, p < 0.05).

CONCLUSIONS

Vertical craniofacial morphology was related to masticatory function. Hypodivergent individuals may have low MMA and high occlusal function, resulting in good masticatory muscle efficiency.

CLINICAL RELEVANCE

Hypodivergent individuals require careful consideration in orthodontic diagnosis and prosthetic treatment planning.

A Contemporary Approach to Non-Invasive 3D Determination of Individual Masticatory Muscle Forces: A Proof of Concept

Over the past decade, the demand for three-dimensional (3D) patient-specific (PS) modelling and simulations has increased considerably; they are now widely available and generally accepted as part of patient care. However, the patient specificity of current PS designs is often limited to this patient-matched fit and lacks individual mechanical aspects, or parameters, that conform to the specific patient’s needs in terms of biomechanical acceptance. Most biomechanical models of the mandible, e.g., finite element analyses (FEA), often used to design reconstructive implants or total joint replacement devices for the temporomandibular joint (TMJ), make use of a literature-based (mean) simplified muscular model of the masticatory muscles. A muscle’s cross-section seems proportionally related to its maximum contractile force and can be multiplied by an intrinsic strength constant, which previously has been calculated to be a constant of 37 [N/cm2]. Here, we propose a contemporary method to determine the patient-specific intrinsic strength value of the elevator mouth-closing muscles. The hypothesis is that patient-specific individual mandible elevator muscle forces can be approximated in a non-invasive manner. MRI muscle delineation was combined with bite force measurements and 3D-FEA to determine PS intrinsic strength values. The subject-specific intrinsic strength values were 40.6 [N/cm2] and 25.6 [N/cm2] for the 29- and 56-year-old subjects, respectively. Despite using a small cohort in this proof of concept study, we show that there is great variation between our subjects’ individual muscular intrinsic strength. This variation, together with the difference between our individual results and those presented in the literature, emphasises the value of our patient-specific muscle modelling and intrinsic strength determination protocol to ensure accurate biomechanical analyses and simulations. Furthermore, it suggests that average muscular models may only be sufficiently accurate for biomechanical analyses at a macro-scale level. A future larger cohort study will put the patient-specific intrinsic strength values in perspective.

A dental revolution: The association between occlusion and chewing behaviour

Dentistry is confronted with the functional and aesthetic consequences that result from an increased prevalence of misaligned and discrepant dental occlusal relations in modern industrialised societies. Previous studies have indicated that a reduction in jaw size in response to softer and more heavily processed foods during and following the Industrial Revolution (1,700 CE to present) was an important factor in increased levels of poor dental occlusion. The functional demands placed on the masticatory system play a crucial role in jaw ontogenetic development; however, the way in which chewing behaviours changed in response to the consumption of softer foods during this period remains poorly understood. Here we show that eating more heavily processed food has radically transformed occlusal power stroke kinematics. Results of virtual 3D analysis of the dental macrowear patterns of molars in 104 individuals dating to the Industrial Revolution (1,700-1,900 CE), and 130 of their medieval and early post-medieval antecedents (1,100-1,700 CE) revealed changes in masticatory behaviour that occurred during the early stages of the transition towards eating more heavily processed foods. The industrial-era groups examined chewed with a reduced transverse component of jaw movement. These results show a diminished sequence of occlusal contacts indicating that a dental revolution has taken place in modern times, involving a dramatic shift in the way in which teeth occlude and wear during mastication. Molar macrowear suggests a close connection between progressive changes in chewing since the industrialization of food production and an increase in the prevalence of poor dental occlusion in modern societies.

The influence of cervical spine rehabilitation on bioelectrical activity (sEMG) of cervical and masticatory system muscles

Background

Coexistence of temporomandibular joint discomfort along with cervical spine disorders is quite common, and is associated with many limitations and adverse symptoms for the patient. Both diagnostics and treatment of these ailments are difficult, and in many cases, the effects of therapy are not satisfactory. This study assessed the impact of a 3-week neck-only rehabilitation programme without direct intervention in the craniofacial area on the bioelectric activity of both the cervical spine and muscles in the craniofacial area among patients with idiopathic neck pain who do not report TMJ pain.

Design

A parallel group trial with follow-up; Setting: Rehabilitation Clinic.

Methods

Twenty five patients experiencing idiopathic neck pain underwent the 3-week rehabilitation programme. Thirty five age-matched subjects with no cervical spine and temporomandibular joint (TMJ) dysfunctions were control group. At baseline and after 3 weeks the cervical and craniofacial area muscles’ bioelectrical activity (sEMG) was evaluated.

Results

In the experimental group during cervical flexion, a significant decrease of sEMG amplitude was noted in the right (mean 25.1 μV; 95% CI: 21.5–28.6 vs mean 16.8 μV; 95% CI: 13.8–19.7) and left (mean 25.9 μV; 95% CI: 21.7–30.0 vs mean 17.2 μV; 95% CI: 13.6–20.7) Sternocleidomastoid as well as a significant increase in sEMG amplitude of the right (mean 11.1 μV; 95% CI: 7.9–14.2 vs mean 15.7 μV; 95% CI: 12.1–19.2) and left (mean 15.3 μV; 95% CI: 11.9–18.6 vs mean 20.2 μV; 95% CI: 15.7–24.2) Upper Trapezius muscles. In the experimental group, after therapy right and left Sternocleidomastoid, Temporalis Anterior and Masseter muscles presented lower fatigue levels.

Conclusions

Three weeks of rehabilitation without any therapeutic intervention in temporomandibular joint significantly decreased the bioelectrical activity of the neck and craniofacial muscles while improving the muscle pattern of coactivation in participants with idiopathic neck pain who do not report temporomandibular joint pain. These observations could be helpful in the physiotherapeutic treatment of neck and craniofacial area dysfunctions.

Trial registration

ID ISRCTN14511735—retrospectively registered.

Strategic Use of CAD-CAM Interim Restoration for the Recovery of the Vertical Dimension of Occlusion in the Posterior Partially Edentulous Jaw

Occlusal contact loss occasionally occurs following the placement of implant-supported fixed dental prostheses in the posterior region. This complication is caused by the change in the vertical dimension of occlusion after the recovery of mastication. The change is probably related to the prosthesis sinking phenomenon and previous mandibular dislocation. The use of interim prostheses could help re-establish the vertical dimension of occlusion. The definitive prostheses can then be accurately fabricated using digital techniques in the newly established vertical dimension. In this case report, we introduce a protocol incorporating a computer-aided design and computer-aided manufacturing (CAD-CAM) interim prosthesis and digital techniques to minimize the occurrence of unexpected initial occlusal changes in the prosthetic treatment of implant-supported prostheses in the posterior region.

Computer-Based 3D Simulation Method in Dental Occlusion Education: Student Response and Learning Effect

Occlusion is a fundamental subject in dental education, and occlusal adjustment is clinically essential in daily dental practices. This study aimed to assess the effects of computer-based 3D simulations on learner responses and learning effect on the principles of occlusal adjustment in undergraduate dental students in comparison with the traditional approach. Two teaching methods, i.e., paper-based 2D presentation and computer-based 3D simulation, were used for teaching the occlusal adjustment concepts. Sixty dental students were divided into two groups using a pair-matching randomization method. In the 2D presentation group, a textbook with 2D illustrations was used. 3D graphic dental models and computer design software were applied in the 3D simulation group. After the course, an attitudinal survey and examination were conducted to evaluate the participants’ feedback and the learning effects resulting from the teaching methods. The independent t test was used to compare the test scores between groups (with α = 0.5). Pearson’s correlation coefficient was calculated to investigate the agreement between the survey data and test scores. Most of the students’ feedback indicated that the 3D simulation method would be effective in acquiring knowledge on occlusion and jaw movement. The examination scores were significantly higher in the 3D simulation group compared with those in the 2D presentation group in the questions for centric relation (P = 0.034). Conversely, the scores were insignificant in the questions for eccentric relation (P = 0.403). There was no correlation observed between the survey data and the actual examination score. Computer-based 3D simulation could increase the participants’ expectations and learning effects in dental occlusion education. Further studies in diversified learning environments are required on the efficacy of digital educational modality.

The Maximum Bite Force for Treatment Evaluation in Severely Affected Adult SMA Patients-Protocol for a Longitudinal Study

Spinal muscular atrophy (SMA) is a severe neuromuscular disorder characterized by the degeneration of motor neurons in the spinal cord, and comprises a broad clinical spectrum. With the advent of new therapies (e.g., Nusinersen) for patients of all ages and disease stages, sensitive clinical measures are needed to detect slight changes in muscle force even in immobilized, severely affected patients often unable to move limbs. As for these patients, well-established outcome scales set out to evaluate motor function do not work properly, we propose measurement of maximum bite force which is able to detect subtle changes of bulbar function. Requirements for this approach are mentioned, challenges are discussed, and first insights from a pilot study are presented. Finally, a study design is proposed to evaluate the measurement of maximum bite force during the follow up of SMA patients with and without a disease modifying therapy.

Indexes of jaw muscle function in asymptomatic individuals with different occlusal features

This study aims to assess the correlation between indexes of jaw muscle function and dento-skeletal morphology. A sample of 35 temporomandibular disorders-free healthy individuals (10 males, mean age 26.7 ± 9.8 years) underwent surface electromyographic (sEMG) assessment of bilateral masseter and temporalis muscles, to evaluate sEMG activity during maximum voluntary clenching (MVC) with a dedicated device (Easymyo®, T.F.R. Technology, Udine, Italy). Four outcome parameters were assessed for each individual: MCV on cotton rolls; MVC on teeth; chewing on right and left sides; clench/relax test. Electromyographic recordings were assessed based on five standardized indexes of muscle function, to evaluate the degree of muscle asymmetry during static and dynamic function (i.e., percentage overlapping coefficient [POC], Impact, Asymmetry, Activation, and Torque). For each individual, the presence of a number of occlusal and skeletal features was assessed: asymmetry of molar class; deviated incisor midline; deep bite; open bite; and crossbite. Skeletal class and vertical dimension of occlusion were also evaluated. Based on normality distribution of data, t test and analysis of variance, when needed, were used to compare muscle function indexes between individuals with and without the different dento-skeletal features. None of the muscle function indexes (POC, Impact, Asymmetry, Activation, and Torque) was significantly different between individuals with or without the various dental and skeletal features. Gender differences were also not significant (p > 0.05). Despite some minor differences were observed, none of them was significant. Thus, the interaction between form and function is too complex for hypothesizing a simple one-to-one relationship between interarch tooth relationship and muscle function patterns.

Electromyographic Activity Changes of Jaw-Closing Muscles in Patients with Different Occlusion Schemes after Fixed Prosthetic Restoration

Background/Aim: To investigate the electromyographic (EMG) activity changes of jaw-closing muscles in patients with different occlusion schemes and posterior edentulous span, after the placement of teeth-supported fixed partial denture (FPD).

Material and Methods: The study sample consisted of 20 patients (10 men and 10 women, the mean age being 50 years) with a posterior edentulous area that includes two missing premolars or one premolar and one molar. The participants were divided into two groups with different occlusion schemes: canine-guided occlusion (CGO) and group function occlusion (GFO). The metal-ceramic FPD were fabricated according to the clinic-standardized protocol. EMG activities of masseter and anterior temporalis patients’ muscles were recorded with bipolar surface electrodes during maximal voluntary clenching. EMG evaluation was repeated twice: (T1) before the fabrication of FPD (T2) after eight weeks of FPD cementation and intraoral functioning of restoration. The data were subjected to Analysis of Variance–ANOVA within the methodological framework of the General Linear Models with Repeated Measures. The Bonferroni test was used to compare multiple mean measures. Statistical analysis was conducted with SPSS ver. 11.5. The level of significance was predefined at a=0.05.

Results: Group 1 with CGO presented significantly higher levels of masseter (mean maximum EMG average before 79.36μV and 139.68μV after) and temporalis (mean maximum EMG average before 79.07μV and 149.37μV after) EMG activity after FPD placement. Group 2 with GFO also showed significantly higher levels of masseter (mean maximum EMG average before 61.57μV and 165.30μV after) and temporalis (mean maximum EMG average before 56.94μV and 133.08μV after) EMG activity after the prosthetic restoration.

Conclusions: It may be concluded that fixed prosthetic restoration, in both patients with canine-guided and group function occlusion, results in increased EMG jaw-muscle activity.

A study on the evaluation of bite force, prosthetic and nutritional status in adult cleft patients in Kolkata

CONTEXT

Altered orofacial morphology and poor dental status affects the dietary intake of cleft patient, making susceptible to nutritional imbalance. Oral health care planning for this population is impossible without the evaluation of stomatognathic functional status as well as prosthetic and nutritional status and need.

AIMS

The aim of this study was to evaluate prosthetic status and prosthetic treatment need, bite force and nutritional status, in adult cleft patients and to compare them with the adult noncleft population of similar definition.

SETTINGS AND DESIGN

Cleft (n = 250) and noncleft (n = 250) individuals of either sex, aged 18 years or above, excluding severe medically compromised and differently abled, were examined and individual biteforce was measured after obtaining written consent and ethical clearance from the two institutions in Kolkata.

SUBJECTS AND METHODS

A "raw data sheet" was prepared according to the parameters of the "Oral Health Surveys: Basic methods," World Health Organization (1997) for evaluation of prosthetic status and need, dentition status and Mini-Nutritional Assessment, Nestlé (1994) for the evaluation nutritional status. A Gnathodynamometer was used to record bite force.

STATISTICAL ANALYSIS USED

Statistical analysis was performed using SPSS 20.0.1, Graph Pad Prism version 5, Student's t-test, and Chi-square test.

RESULTS

The mean bite force of frontal area in cleft group (3.4356 ± 0.9457 kgf) was found to be significantly lower (P < 0.0001) than in noncleft (22.8749 ± 5.3644 kgf) group. The difference of mean bite force in the right side (2.4576 ± 0.6131 kgf) and left side (1.2708 ± 0.1036 kgf) in cleft group was found to be statistically significant (P < 0.0001). Prosthetic need in maxillary arch was found to be significantly (χ2: 490.0000; P < 0.0001) higher in cleft than in noncleft group. Nutritional status was observed to be significantly (χ2: 179.4049; P < 0.0001) higher "at risk" in cleft than in noncleft group.

CONCLUSIONS

Lack of adequate Government concern leading to significantly higher prosthetic need and lower prosthetic status, hence lower bite force resulting lower nutritional status in adult cleft patients in Kolkata.

Preventive orthodontic approach for functional mandibular shift in early mixed dentition: A case report

The case reported here highlights the importance of examination of functional occlusion along with static occlusion. Any undetected malocclusion during early mixed dentition has potency to alter the growth and function of stomatognathic system. Premature contacts in primary canine region is the most prevalent cause of functional mandibular shift and can lead to TMJ problems for the prevalence of self correction of such malocclusion is very low if not intervened. A case of functional mandibular shift due to faulty canine guidance because of premature contacts is discussed here. Selective grinding of premature contacts and myofunctional exercise resulted in well balanced centric occlusion coinciding with centric relation.

Effects of the functional orthopaedic therapy on masticatory muscles activity

Background

The purpose of this study was to examine surface electromyographic (sEMG) activity of masticatory muscles before and after functional orthopaedic therapy with Sander appliance.

Material and Methods

Ten adolescents (5 girls, 5 boys) with an Angle Class II, division I malocclusion, 9-13 years old, were submitted to sEMG before and after functional orthopaedic therapy. To verify the neuromuscular equilibrium, the standardized EMG activities of right and left masseter and anterior temporal muscles were recorded during maximum voluntary clench, and analysed calculating: POC (index of the symmetric distribution of the muscular activity determined by the occlusion); TC (index of presence of mandibular torque) and Ac (index suggesting the position of occlusal barycentre). The total muscular activity was also calculated. Pre- and post- functional therapy data were compared with Wilcoxon Signed-Rank Test.

Results

Before treatment, all subjects had a good neuromuscular equilibrium, which was not altered by treatment.

Conclusions

sEMG evaluations allow to quantify the impact of occlusion on masticatory muscle activity and to control that the functional orthopaedic therapy maintain a good muscular coordination.

Key words:Functional appliance, Sander appliance, electromyography, masticatory muscles.

[The influence of teeth morphology on bioelectrical activity of masticatory muscles]

The aim of the study was to reveal correlation of dental morphology and bioelectric activity of masticatory muscles. The study included 76 young adults (47.4% females and 52.6% males) divided in 3 groups according to dental morphology features: intact teeth (26 patients), dental decay in fissures with intact cusps (25 patients), pronounced dental decay with varying degree of crown destruction (25 patients). Electromyography (EMG) was used to document the bioelectric activity (BEA) of temporal and masticatory muscles. The study showed high level of correlation of destructive teeth changes with BEA of masticatory muscles. Intragroup correlation proved direct link of BEA to the number of decayed teeth. EMG activity differed significantly between groups 2 and 3. There was no statistically significant difference between groups 3 and 1 mostly because of high variability of BEA in group 3. Relative activity of temporal and masticatory muscles increased in groups 2 and 3 by 2 and 4% and 38 and 19%, correspondingly. There was no significant impact of gender or emotional status on masticatory muscles BEA.

The relationship between occlusal support and maxillary development: An animal study

Objective:

To test the hypothesis that maxillary development may be affected by occlusal support.

Materials and Methods:

The sample was composed by Wistar rats (5 weeks old) divided into three groups: Control (n = 10), extraction of mandibular molar teeth – left side (n = 10), extraction mandibular molar teeth – left and right sides (n = 10). The rats were sacrificed 8 weeks postextraction. Cone beam computed tomography scan images were taken for posterior measurement of maxillary length and width. Data were analyzed by one-way analysis of variance (Tukey test as post-hoc test).

Results:

Maxillary length was significantly shorter (P < 0.005) in both groups after tooth extraction. No difference was observed regarding maxillary width and body weight.

Conclusion:

Reduced occlusal support may impair the development of the maxilla in rats.

The effects of stretching exercise for upper trapezius on the asymmetric rate of bite force

[Purpose] The purpose of this study was to observe the effects of stretching the upper trapezius muscle on the asymmetric rate of bite force. [Subjects] Forty-seven female university students who had all their original teeth, had no disorders in the temporomandibular joints, and had never worn braces; participated in this study. [Methods] An occlusometer was used to measure biting forces. Subsequently, stretching exercises of the upper trapezius were performed. The subjects were divided into 3 groups at the start of the testing: the asymmetric rate of the first group was less than 10%; the asymmetric rate of the second group was between 10% and 20%; and the asymmetric rate of the third group was more than 20%. The stretching exercises were done on the dominant side of the upper trapezius. [Results] After the stretching exercises of the upper trapezius, the results showed that for the first group, whose asymmetric rate of biting force was less than 10%, there was a significant increase in asymmetric rate (from 5.1% to 10.3%). For the second group, whose asymmetric rate of biting force was measured to be between 10% and 20%, the asymmetric rate decreased from 14.7% to 14.3%, but the change was not statistically significant. For the third group, whose asymmetric rate of biting force was more than 20%, there was a significant decrease in asymmetric rate (from 27.8% to 12.6%). [Conclusion] We concluded that stretching exercises of the upper trapezius muscle had a direct effect on the asymmetric rate of biting force.

Peak torque and average power at flexion/extension of the shoulder and knee when using a mouth guard in adults with mild midline discrepancy

[Purpose] This study was conducted to investigate the changes in torque and power during flexion and extension of the shoulder and the knee joints caused by midline correction using mouth guards made from different materials in adults with mild midline discrepancy. [Subjects] The subjects of this study were males (n=12) in their 20s who showed a 3–5 mm difference between the midlines of the upper and lower teeth but had normal masticatory function. [Methods] The torque and average power of the lower limb and upper limb were measured during flexion and extension according to various types of mouth guard. [Results] There were significant differences in relative torque and average power between three conditions (no mouth guard, soft-type mouth guard, and hard-type mouth guard) at shoulder flexion and extension. There were no significant differences in relative torque and average power between the three conditions at knee flexion and extension. [Conclusions] These results suggest that use of a mouth guard is a method by which people with a mild midline discrepancy can improve the stability of the entire body.

Protective buttressing of the hominin face

When humans fight hand-to-hand the face is usually the primary target and the bones that suffer the highest rates of fracture are the parts of the skull that exhibit the greatest increase in robusticity during the evolution of basal hominins. These bones are also the most sexually dimorphic parts of the skull in both australopiths and humans. In this review, we suggest that many of the facial features that characterize early hominins evolved to protect the face from injury during fighting with fists. Specifically, the trend towards a more orthognathic face; the bunodont form and expansion of the postcanine teeth; the increased robusticity of the orbit; the increased robusticity of the masticatory system, including the mandibular corpus and condyle, zygoma, and anterior pillars of the maxilla; and the enlarged jaw adductor musculature are traits that may represent protective buttressing of the face. If the protective buttressing hypothesis is correct, the primary differences in the face of robust versus gracile australopiths may be more a function of differences in mating system than differences in diet as is generally assumed. In this scenario, the evolution of reduced facial robusticity in Homo is associated with the evolution of reduced strength of the upper body and, therefore, with reduced striking power. The protective buttressing hypothesis provides a functional explanation for the puzzling observation that although humans do not fight by biting our species exhibits pronounced sexual dimorphism in the strength and power of the jaw and neck musculature. The protective buttressing hypothesis is also consistent with observations that modern humans can accurately assess a male's strength and fighting ability from facial shape and voice quality.

Neuromuscular dentistry: Occlusal diseases and posture

Neuromuscular dentistry has been a controversial topic in the field of dentistry and still remains debatable. The issue of good occlusion and sound health has been repeatedly discussed. Sometimes we get complains of sensitive teeth and sometimes of tired facial muscles on getting up in the morning. Owing to the intimate relation of masticatory apparatus with the cranium and cervico-scapular muscular system, the disorders in any system, draw attention from concerned clinicians involved in management, to develop an integrated treatment protocol for the suffering patients. There may be patients reporting to the dental clinics after an occlusal restoration or extraction, having pain in or around the temporomandibular joint, headache or neck pain. Although their esthetic demands must not be undermined during the course of treatment plan, whenever dental treatment of any sort is planned, occlusion/bite should be given prime importance. Very few dentist are able to diagnose the occlusal disease and of those who diagnose many people resort to aggressive treatment modalities. This paper aims to report the signs of occlusal disease, and discuss their association with TMDs and posture.

Skeletal pattern in subjects with temporomandibular joint disorders

INTRODUCTION

To establish the skeletal pattern in subjects with malocclusions and temporomandibular disorders (TMD); to assess the relationship between craniofacial skeletal structures and TMD in subjects with malocclusions.

MATERIAL AND METHODS

Sixty-four subjects with malocclusions, over 18 years of age, were included in the study. Temporomandibular disorders were clinically assessed according to the Helkimo Anamnestic Index. Subjects underwent a lateral cephalogram. Subjects were grouped according to the sagittal skeletal pattern (ANB angle) into class I, II and III. Parametric Student tests with equal or unequal variations were used (variations were previously tested with Levene test).

RESULTS

Twenty-four patients with TMD (experimental sample); 40 patients without TMD (control group); interincisal angle was higher in class I and II (p < 0.05) experimental subjects; overjet was larger in experimental subjects; midline shift and Wits appraisal were broader in the experimental group in all three classes. In class III subjects, the SNB angle was higher in the experimental group (p = 0.01). Joint noises followed by reduced mandible mobility, muscular pain and temporomandibular joint (TMJ) pain were the most frequent symptoms in subjects with TMD and malocclusions.

CONCLUSIONS

Temporomandibular joint status is an important factor to consider when planning orthodontic treatment in patients with severe malocclusions; midline shift, large overjet and deep overbite have been associated with signs and symptoms of TMD.

Surface electromyographic evaluation of jaw muscles in children with unilateral crossbite and lateral shift in the early mixed dentition. Sexual dimorphism

OBJECTIVES

To examine the activity of jaw muscles at rest and during maximal voluntary clenching (MVC) in children with unilateral posterior crossbite (UPXB) and functional lateral shift in the early mixed dentition and to evaluate sex differences.

MATERIAL AND METHODS

The sample included 30 children (15 males, 15 females) aged 6 to 10 years old, with UPXB and functional mandibular lateral shift (≥1.5 mm) in the early mixed dentition. sEMG activity coming from the muscle areas (anterior temporalis [AT], posterior temporalis [PT], masseter [MA] and suprahyoid [SH]) were obtained from both the crossbite (XB) and noncrossbite (NONXB) sides at mandibular rest position. sEMG activity of the bilateral AT and MA muscles sides was obtained during MVC. Asymmetry and activity indexes were calculated for each muscle area at rest and during MVC; the MA/TA ratio during MVC was also determined.

RESULTS

At rest, no differences were found between sexes for any muscle areas or asymmetry and activity indexes. No differences were found between XB and NONXB sides. During MVC, however, significant sex differences were found in AT and MA activity, with higher sEMG values in males than in females, on both XB and NONXB sides. Asymmetry indexes, activity indexes and MA/AT ratios did not show significant differences between the sexes. Activity was symmetric both in males and in females.

CONCLUSIONS

At rest, no sex differences were found, but during MVC males showed higher activity than did females in both XB and NONXB AT and MA muscle areas. Muscular activity was symmetrical at rest and during MVC in both sexes. Sexual dimorphism should be considered in the diagnosis and treatment of UPXB and lateral shift in the early mixed dentition.

Bruxism control in a child with cerebral palsy

Cerebral palsy (CP) is one of the most severe childhood disabilities due to a lesion in the developing brain. Oral conditions often observed in this pathogenic are a tendency for the delayed eruption of permanent molars, higher percentages of malocclusion and parafunctional habits, including bruxism. The significance of oral conditions observed in CP patients demonstrates the need for intensive home and professional care for these individuals. This paper presents a 7-year-old boy, with cerebral palsy, severe mental retardation, who had high abrasion wear of the primary teeth related to bruxism. Dental care was carried out under oxide-induced sedation, and management of the bruxism was achieved after the use of a resin acrylic protective appliance fixed on both sides of the mandibula. The treatment performed offered efficiency advantages, was clinically viable, and should be a valuable option to practitioners considering appliance therapy to control parafunctional behavior.