Masticatory muscle activity in children and adults with different facial types

Evaluation of morphological and morphometric characteristics of the temporomandibular joint in children with different skeletal models in the sagittal and vertical direction

OBJECTIVE

This study aims to evaluate differences in the morphological and morphometric features of hard tissue components of the temporomandibular joint (TMJ) in the cone beam computed tomography (CBCT) images of children with different skeletal models in the sagittal and vertical plane.

METHODS

Condyle dimensions, horizontal condylar angle, the distance of the condyle center to the midsagittal plane, condyle position, eminence height, eminence inclination, condyle, and fossa shape and symmetry were evaluated in CBCT images in 190 TMJs in 95 pediatric patients. Patients were classified as Class 1-2-3 in the sagittal direction, as hypodivergent, normodivergent, and hyperdivergent in the vertical direction. Children were divided into 10-13 and 14-17 age groups.

RESULTS

The left superior joint space in children with a different skeletal model in the sagittal plane was lower and found to be statistically significant in Class 3 children (p < 0.05). A statistically significant difference was found lower in the left articular eminence inclination and height in Class 3 children (p < 0.05). The most common oval fossa form was seen in Classes 2-3 children (p < 0.05). It was determined that the anterior joint space was lower in hyperdivergent children and the condyle was located more anteriorly. The mediolateral length of the condyle and the height of the articular eminence were positively correlated with age.

CONCLUSIONS

The results revealed that the difference in skeletal models seen in sagittal and vertical planes in children may cause morphological and morphometric changes in the hard tissue components of TMJ.

Total arch extrusion with skeletal anchorage to improve inadequate maxillary incisor display in a case of vertical maxillary deficiency

Inadequate maxillary incisor display can negatively impact facial esthetics. Various treatment options exist depending on the underlying cause and severity of the condition. Skeletal anchorage was used to extrude the maxillary dentition and rotate the mandible backward, enhancing visibility of the maxillary incisors. An extrusion assembly was introduced to achieve orthodontic extrusion. Use of bite raisers and interarch elastics was also discussed. Treatment results demonstrated successful achievement of the treatment goals. In addition to optimal occlusion, the patient's facial profile improved with increased lip fullness. There was an increase in vertical facial height, and maxillary incisor display was significantly improved, resulting in a more pleasant smile. Two-year postretention records evidenced the stability of total arch extrusion to improve maxillary incisor display.

Orthodontic considerations in hypodivergent craniofacial patterns

This article examines the characteristics of hypodivergent craniofacial patterns and explores treatment modalities in response to these features. It discusses the impact of robust masticatory muscles, which produce heavy occlusal forces. In addition, it examines the use of Botox or splints to reduce gonial angles in individuals with a square face. A nonextraction treatment approach supported by temporary skeletal anchorage devices is recommended; however, if anatomical limitations persist, extraction may be necessary when arch expansion, molar distalization, incisor proclination, or interproximal reduction cannot create the necessary space. In hypodivergent cases where a nonextraction approach is impractical, a single-arch extraction strategy may be considered to prevent a reduction in the vertical dimension. Emphasizing esthetics, particularly maxillary incisor display, a protocol of total arch extrusion of the maxillary dentition assisted with temporary skeletal anchorage device, bite raisers, and interarch elastics is suggested.

The effect of passive clear aligners on masticatory muscle activity in adults with different levels of oral parafunction

BACKGROUND

There is limited knowledge of the possible side-effects of clear aligners on jaw function.

OBJECTIVES

To determine the short-term effect of passive clear aligners (PCAs) on masticatory muscle activity (MMA), occlusal discomfort (OD) and temporomandibular disorder (TMD) symptoms in adults with different levels of self-reported oral parafunction.

MATERIALS AND METHODS

Participants were screened for oral parafunctional behaviours using the oral behavioural checklist. Respondents in ≥85th and ≤15th percentiles were invited to participate and allocated to a high (HPF: N = 15) or low (lower parafunction [LPF]: N = 16) parafunction group. Participants underwent a TMD clinical examination; somatisation and somatosensory amplification were assessed by questionnaires; OD and stress were assessed by visual analogue scales. While wearing PCAs, awake-time MMA was assessed three times over 9 days using a wearable electromyography device, along with OD, stress and TMD symptoms.

RESULTS

The wearing of PCAs was associated with a significant decrease in mean contraction episode amplitude in both groups (p = 0.003). OD levels increased and remained raised in all participants after insertion of the PCAs (p < 0.001), more so in the HPF group (p = 0.048). The HPF group had higher somatisation scores (p = 0.006) and reported more TMD symptoms at all time points (p ≤ 0.004). No significant changes in stress or TMD symptoms were found in either group during the study period.

CONCLUSIONS

PCAs were associated with a decrease in MMA in all participants. HPF individuals had greater somatisation and reported greater discomfort when wearing PCAs than LPF individuals.

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.

Wearables for personalized monitoring of masticatory muscle activity - opportunities, challenges, and the future

Wearable devices are worn on or remain in close proximity of the human body. The use of wearable devices specific to the orofacial region is steadily increasing. Orofacial applications of wearable devices include supplementing diagnosis, tracking treatment progress, monitoring patient compliance, and understanding oral parafunctional behaviours. In this short communication, the role of wearable devices in advancing personalized dental medicine are highlighted with a specific focus on masticatory muscle activity monitoring in naturalistic settings. Additionally, challenges, opportunities, as well as future research areas for successful use of wearable devices for precise, personalized care of muscle disorders are discussed.

Effects of sagittal split osteotomy on brainstem reflexes

OBJECTIVES

This prospective study was designed to assess whether patients with skeletal deformities show characteristic masseter inhibitory reflex (MIR) and blink reflex (BR) patterns. A secondary aim was to investigate whether these reflexes change following bilateral sagittal split osteotomy (BSSO).

MATERIALS AND METHODS

Fourteen consecutive patients who underwent single-jaw BSSO and 14 class I subjects who constituted the control group were enrolled into the study. MIR and BR, obtained by the stimulation of supraorbital (SBR) and mental nerves (MBR), were electrophysiologically recorded. Sensory impairment in the mental nerve distribution was clinically tested. Three evaluation periods were specified as immediately before (T0), 1 month (T1) and 6 months (T2) after surgery.

RESULTS

MIR early silent period duration was significantly shorter in the patients at T0 (p < 0.001). Sensory deficits developed on 23 sides after BSSO, of which, 17 recovered after 6 months. At T1, MBR was inelicitable bilaterally in 3 patients and unilaterally in 2 patients. These responses were still unrecordable bilaterally in 1 patient, and unilaterally in 4 patients at T2. MIR were unrecordable on 18 sides at T1 and recovered on 11 sides at T2. There were no parallels between the clinical sensory deficits and the abnormal results of the reflexes.

CONCLUSIONS

Shorter MIR in patients with dentofacial abnormalities may be a reflection of an adapted trigeminal reflex mechanism. Although MBR and MIR abnormalities do not develop parallel to the clinical sensory deficits, their course might provide insights into the disturbed trigeminal reflex pathways.

Geometric morphometric analysis of mandibular symphysis in Class III skeletal base

This study aimed to investigate the general mandibular symphysis (MS) shape variation among Class III skeletal base, using geometric morphometric analysis. Pre-treatment lateral cephalometric radiographs of 254 patients aged 11-40 years old, with Class III skeletal base (ANB <1°) and lower incisor angle (<99°) were included. Nine-landmarks with x and y coordinates were identified on MS using TPSDig2 software, then exported into Morpho J for shape and statistical analysis. Principal component analysis showed that three main shape dimensions with a total variance of 74.6% represented the majority variation of samples. Procrustes Anova showed the shape of MS in Class III skeletal base to be mainly influenced by gonial angle, incisor inclination and sex (P<0.0001). Canonical variate analysis showed that high gonial angle groups had significantly narrower and elongated MS whereas low gonial angle groups had wider, bulbous and rounded MS (P<0.0001). The ratio of alveolar part to basal part was 1:5 in low gonial angle and 2:3 in high gonial angle. Males had significantly taller MS with narrower B point area compared to females (P<0.0001). Retroclined incisors exhibited taller and retroclined alveolar parts (P<0.0001). The shape of MS in Class III skeletal base varied at the alveolar part, basal part or both and it is influenced by gonial angle, incisor inclination and sex. Hence, understanding the shape variation of MS is important to aid orthodontic treatment planning.

The relationship of masseter muscle thickness with face morphology and parafunctional habits: an ultrasound study

OBJECTIVE

The aim of this study was to determine the normal range of masseter muscle thickness by ultrasonographic measurement in individuals over 15 years of age, and to evaluate its relationship with age, gender, facial morphology, body mass index and parafunctional habits.

METHODS

The study was conducted on 115 volunteers whose lateral cephalometric radiography was performed within the indication in Gazi University Faculty of Dentistry, Department of Dentomaxillofacial Radiology. The participants in the study were asked questions about their parafunctional habits, age, height and weight. Individuals were grouped as hypodivergent (n = 28), normdivergent (n = 55), or hyperdivergent (n = 32) according to vertical face morphology by making measurements on lateral cephalometric films. Right and left masseter muscle thicknesses of individuals were measured by ultrasonography while at rest and in contraction.

RESULTS

The mean value of masseter muscle thickness was found to be 13.57 ± 2.57 mm. The rest and contracted muscle thicknesses were significantly higher in males than in females for the right and left masseter muscles (p < 0.05). When the masseter muscle was at rest and contracted, its thickness was higher in individuals with hypodivergent facial morphology, than in the other groups. No statistically significant difference was found in terms of masseter muscle thickness between individuals having parafunctional habits and those who did not have parafunctional habits (p > 0.05).

CONCLUSION

Although masseter muscle thickness varied according to vertical facial morphology, this was not the case for parafunctional habits.

Chewing Patterns and Muscular Activation in Deep Bite Malocclusion

Background: Deep bite, a frequent malocclusion with a high relapse rate, is associated with craniofacial features that need to be considered in the course of orthodontic treatment. Methods: This study included 81 patients with deep bite malocclusion (11.4 ± 1.1 [yr.mo]; M = 32 and F = 49), and 14 age- and gender-matched controls (9.11 ± 1 [yr.mo]; M = 5 and F = 9). The patients with deep bite malocclusion were treated with functional therapy. The chewing cycles and masticatory muscle EMG activity were recorded concomitantly before treatment in both groups (n = 95). Following correction of the malocclusion, a second recording took place (n = 25). Results: The kinematic variables showed the same dependency on bolus hardness in those with deep bite and in the controls. The masticatory muscle EMG activity was increased in those with deep bite, but decreased as a result of functional treatment. The chewing patterns showed a tendency towards a reduced lateral component, which significantly increased after treatment, indicating that functional therapy impacts the neuromuscular coordination of mastication, as well as dental positioning. Conclusions: Deep bite is a complex malocclusion, involving alterations in chewing and masticatory muscle activity. Orthognathodontic treatment should not only consider and correct the teeth position, but should also address muscular hyperactivity.

Digital Photoelastic Analysis of TAD-Supported Maxillary Arch Distalization

The objective of this study was to determine whether the distribution of compressional and tensional stress around tooth roots is influenced by the position of a temporary anchorage device and the length of the retraction hook during the distalization of the maxillary dentition. A photoelastic orthodontic model was made of photoelastic epoxy resin. Six combinations of three retraction hook lengths and two posterior Temporary skeletal anchorage devices (TAD) positions were established. Stress was applied through an elastic chain for each of the combinations. Digital photoelastic stress analysis measured the compression, tensional stress, and direction around the tooth root. Using this novel photoelastic model, we found that the distribution of compressional and tensional stress during the retraction of the maxillary dentition was significantly influenced by the position of the TAD and the length of the retraction hook.

Morphological variations of the condylar head among children aged 4-15 years: A panoramic study

BACKGROUND

Growth and development of dentocraniofacial complex occurs during various stage of development of dentition with TMJ as one of its centres of growth. The condition of temporomandibular joint can be visible from its condylar head form; therefore, it is crucial to recognize the normal morphology of condylar head during different stages of development of dentition.

AIMS

The aim of the study is to view the morphological appearance of condylar head during primary dentition, mixed dentition and permenant dentition.

SUBJECT AND METHODS

400 panoramic images of 194 boys and 296 girls were collected and were divided into three groups bases on the stage of dentition. Shape of the condylar head were determined by tracing the print out of the panoramic image on an X ray viewer.

RESULTS

The study showed that during primary dentition stage shape of the conylar head was dominated by round shape and as growth and development occurs the condylar head shape changes to convex.

CONCLUSION

The study describes the normal morphology of mandibular condyles in a child population attending The dentition status as well as growth of craniofacial has a significant role in determining condylar morphology.

Relationships between craniofacial morphology and masticatory muscle activity during isometric contraction at different interocclusal distances

OBJECTIVE

The aim was to investigate relationships amongst interocclusal distances, masticatory muscle electromyographic (EMG) activity during isometric contraction of masticatory muscles, and craniofacial morphology.

DESIGN

Twenty-eight women and 12 men (25.3 ± 3.8 years old) participated. After measuring maximal voluntary occlusal bite force (MVOBF) between the right-first premolars, the participants were asked to bite at submaximal levels of 0 (= holding the bite force transducer), 15, 22.5, and 30% MVOBF with the use of visual feedback. The thickness of a bite force transducer was set at 10, 12, 13, 14, 16, 17, 18, 19, 20, 22, and 24 mm (= interocclusal distance: IOD). Nine soft tissue craniofacial factors were assessed through digital photograph: face height, middle face height, lower face height, face width, inter-pupil distance and mandibular plane angle, lower face height / face height ratio, inter-pupil distance / facial width ratio and face width / face height ratio.

RESULTS

In the masseter muscle, EMG activity decreased with increased IODs. The participants with higher mandibular plane angle had more negative slope coefficients of IOD-EMG graphs at 0% MVOBF especially in male temporalis and female masseter and temporalis muscles, suggesting that a greater mandibular plane angle is associated with lower EMG activity at longer IOD.

CONCLUSIONS

Overall the findings support the notion that craniofacial morphology is associated with differences in neuromuscular activity of the masticatory muscles, and suggest that the neuromuscular effects of oral appliances may be dependent on patients' craniofacial morphology and the thickness of the device. (247/250 words).

Evaluation of masseter muscles in relation to treatment with removable bite-blocks in dolichofacial growing subjects: A prospective controlled study

INTRODUCTION

The aim of this prospective study was to evaluate the effects of posterior bite-blocks on masseter muscles and on facial growth in prepubertal dolichofacial subjects.

METHODS

The treatment group comprised 21 consecutive prepubertal dolichofacial patients treated with rapid maxillary expansion followed by mandibular removable bite-blocks. Lateral cephalograms and ultrasonographic scans of the masseter muscles were made before (T1) and after (T2) treatment with bite-blocks. The treatment group was compared with a control group of 21 subjects matched for sex, age, and skeletal vertical pattern. An independent samples t test was used to compare the T1 to T2 changes in ultrasonographic scan measurements between the treatment group and the control group, and the T1 to T2 cephalometric changes in the treatment group. Regression analysis was performed to investigate associations between masseter muscle thickness and cephalometric treatment outcomes.

RESULTS

Masseter muscle thickness showed a statistically significant decrease (-0.7 mm) in the treatment group compared with an increase (+0.6 mm) in the control group. A significant anterior rotation of the mandibular plane was observed in the treatment group as well as significant increases in overbite (1.8 mm) and total posterior facial height (1.5 mm). No significant associations were found between masseter muscle thickness and treatment outcomes apart from a tendency for overbite to increase more in subjects with thicker muscles.

CONCLUSIONS

Treatment with removable bite-blocks produced a decrease in masseter muscle thickness and a reduction in vertical facial dimensions due to upward and forward rotation of the mandible. No significant correlation was found between the pretreatment masseter muscle thickness and the T1 to T2 cephalometric changes in the treatment group.

Self-reported oral behaviour habits in hyperdivergent and normodivergent facial types

The relationship between facial morphology and jaw function remains controversial. The purpose of this study was to investigate differences in self-reported oral behaviour habits between individuals with normodivergent and hyperdivergent facial types. Some 80 cases and controls were individually matched on age, sex ethnicity and treatment stage. The participants were recruited from an orthodontic clinic, and included both adolescents and adults. Habitual oral activity was assessed using the Oral Behaviour Checklist (OBC) based on their experiences in the past 4 weeks. Univariate and bivariate analyses were performed. The sample had a mean age of 17·2 years (SD = 4·6; range = 12-49 years), and was predominantly female (65·0%) and of New Zealand European origin (91·3%). The prevalence of reporting one or more frequently performed habitual muscular behaviour in either study group was over 85% (P > 0·05). There was no difference in total OBC score between the hyperdivergent (25·6; SD: 9·0) and normodivergent group (25·3; SD: 9·9). Moreover, there was no difference in the prevalence of either nocturnal or daytime oral behaviours between the two groups. While this study did not include any objective measures of functional or habitual activity, we found no differences in self-reported oral behaviour habits between normodivergent and hyperdivergent individuals. The findings do not support an association between vertical facial form and habitual muscular activity.

Relationship of Anterior Alveolar Dimensions with Mandibular Divergence in Class I Malocclusion - A Cephalometric Study

INTRODUCTION

One of the major limiting factors in retraction of proclined teeth is the width of the alveolus both in maxilla and mandible.

AIM

The objective of this study was to assess the maxillary and mandibular anterior alveolar dimensions and to correlate with mandibular divergence in Class I bi-dento-alveolar protrusion patients.

MATERIALS AND METHODS

Pretreatment lateral cephalograms (n=88) were analysed using a composite analysis with cephalometric software. Both maxillary and mandibular anterior alveolar widths and heights were measured and correlated with mandibular divergence. One-way analysis (ANOVA) and Pearson correlation test were used to compare and establish the significance between groups.

RESULTS

Segregation of the data based on variation in the bi-cortical widths and heights showed that lesser alveolar widths and greater alveolar heights were associated with the high angled subjects and greater alveolar widths and lesser heights were associated with low angled subjects.

CONCLUSION

Patients with hyperdivergent mandible exhibited thin anterior alveolar width and greater alveolar height whereas low angled subjects had wider alveolar width and lesser alveolar height. Orthodontic treatment plan for retraction of anterior teeth must be based on these differences caused by variations in mandibular divergence.

Avaliação clínica e eletromiográfica da mastigação nos diferentes padrões de crescimento facial

RESUMO Objetivo: analisar a função mastigatória nos diferentes padrões faciais de crescimento por meio da avaliação clínica e eletromiográfica dos músculos masseteres e temporais anteriores. Métodos: foram selecionadas 65 crianças entre seis e 12 anos de idade, de ambos os sexos, que se adequaram aos critérios do estudo. Foi realizada avaliação clínica da mastigação tendo por base o protocolo MBGR e a avaliação eletromiográfica dos músculos masseteres e temporais anteriores, mediante mastigação contínua direcionada. Os dados foram analisados considerando nível de significância de 5%. Resultados: na avaliação clínica da mastigação, não foi observada diferença significante entre os três padrões faciais estudados, apenas tendência à significância para as contrações musculares não esperadas, sendo observada maior ocorrência nos dolicofaciais (66,67%), seguido dos mesofaciais (46,67%) e braquifaciais (26,83%). Na avaliação eletromiográfica da mastigação, não foi observada diferença significante entre os três grupos estudados. Ao comparar os músculos para cada padrão facial, verificou-se nas crianças braquifaciais maior atividade elétrica do músculo masseter direito em relação ao temporal direito e maior atividade elétrica do músculo temporal esquerdo em relação ao músculo temporal direito (p=0,049). Conclusão: os resultados das avaliações clínica e eletromiográfica da mastigação não se diferiram nos padrões faciais, sugerindo que o padrão por si só não é determinante nas modificações da função mastigatória e que estas podem estar relacionadas a outras variáveis não consideradas neste estudo.

Association between facial growth pattern and facial muscle activity: A prospective cross-sectional study

OBJECTIVE

To evaluate the relationship between facial growth pattern and electromyography (EMG) of facial muscles: anterior temporalis, masseter, buccinators, orbicularis oris, mentalis and anterior digastric.

PATIENTS AND METHODS

The sample consisted of 77 subjects aged between 18-28 years (mean age 21.10±2.03), with dental Class I relationship, normal overjet and overbite, balanced facial profile, no signs of temporomandibular disorders, and no previous orthodontic treatment. Facial growth pattern was determined on the lateral cephalograms according to the Björk sum (sum of the N-S-Ar, S-Ar-Go, and Ar-Go-Me angles) dividing the sample into three groups: horizontal facial pattern group (24 subjects), normal facial pattern group (41 subjects), and vertical facial pattern group (12 subjects). The EMG of anterior temporalis, masseter, buccinator, orbicularis oris, mentalis and anterior digastric muscles were examined for each patient in the rest position and in functional positions (central maximum intercuspation, chewing on right side, chewing on left side and swallowing). Mean values and standard deviation of EMG were obtained and compared between the three groups.

RESULTS

At rest, the EMG of the masseter, orbicularis oris and anterior digastric were higher in the vertical facial pattern group compared with the other two groups, with a moderate positive correlation between the EMG of these muscles and the Björk sum (P<.01). In contrast, during central maximum intercuspation, the activity of the anterior temporalis, masseter and buccinator was significantly lower in the vertical facial pattern group compared with the two other groups, with a moderate negative correlation between the Björk sum and EMG in the maximum central intercuspation position of these muscles (P<.01).

CONCLUSIONS

A significant relationship was found between facial muscle activity and facial growth pattern. The findings suggest that the activity of masticatory and perioral muscles could play a role in the direction of the facial growth.

Functional and morphological correlates of mandibular symphyseal form in a living human sample

Variation in recent human mandibular form is often thought to reflect differences in masticatory behavior associated with variation in food preparation and subsistence strategies. Nevertheless, while mandibular variation in some human comparisons appear to reflect differences in functional loading, other comparisons indicate that this relationship is not universal. This suggests that morphological variation in the mandible is influenced by other factors that may obscure the effects of loading on mandibular form. It is likely that highly strained mandibular regions, including the corpus, are influenced by well-established patterns of lower facial skeletal integration. As such, it is unclear to what degree mandibular form reflects localized stresses incurred during mastication vs. a larger set of correlated features that may influence bone distribution patterns. In this study, we examine the relationship between mandibular symphyseal bone distribution (i.e., second moments of area, cortical bone area) and masticatory force production (i.e., in vivo maximal bite force magnitude and estimated symphyseal bending forces) along with lower facial shape variation in a sample of n = 20 living human male subjects. Our results indicate that while some aspects of symphyseal form (e.g., wishboning resistance) are significantly correlated with estimates of symphyseal bending force magnitude, others (i.e., vertical bending resistance) are more closely tied to variation in lower facial shape. This suggests that while the symphysis reflects variation in some variables related to functional loading, the complex and multifactorial influences on symphyseal form underscores the importance of exercising caution when inferring function from the mandible especially in narrow taxonomic comparisons.

Natural head position and growth of the facial part of the skull

The aim of this study was to determine any correlation between natural head position and cranio-cervical growth direction and if natural head position influences facial growth direction. One hundred sixty (160) cephalometric radiographs were examined and cranio-cervical inclinations determined (angles: NS-Ver, NS-OPT, NS-CVT). On the basis of the NS-ML angle, radiographs were divided into two groups: mandibular anteriorotation and posteriorotation. On the basis of the SGo/NMe index, two groups were formed: short-faced and long-faced subjects. The angles NS-Ver, NS-OPT, and NS-CVT describe cranio-cervical inclination. Subjects with anterior mandible growth do position their heads more vertically and have a shorter face, and those with posterior mandible growth tilt their heads more backwards and have a longer face. An adaptive head position can be a factor in altering the direction of facial growth. Determination of head position and mandible growth direction can be an important indicator in patients with TMD treatment.

Surface electromyography in orthodontics - a literature review

Electromyography is the most objective and reliable technique for evaluating muscle function and efficiency by detecting their electrical potentials. It makes it possible to assess the extent and duration of muscle activity. The main aim of surface electromyography is to detect signals from many muscle fibers in the area of the detecting surface electrodes. These signals consist of a weighted summation of the spatial and temporal activity of many motor units. Hence, the analysis of the recordings is restricted to an assessment of general muscle activity, the cooperation of different muscles, and the variability of their activity over time.

This study presents the main assumptions in the assessment of electrical muscle activity through the use of surface electromyography, along with its limitations and possibilities for further use in many areas of orthodontics. The main clinical uses of sEMG include the diagnostics and therapy of temporomandibular joint disorders, an assessment of the extent of stomatognathic system dysfunctions in subjects with malocclusion, and the monitoring of orthodontic therapies.

Morphological and Functional Parameters in Patients with Tooth Wear before and after Treatment

Advanced tooth wear often results in lost vertical dimension and impacts facial aesthetics. Complex restorative treatment can replace the lost tooth structure and improve functional occlusal and facial skeleton parameters.

PURPOSE

The aim of the study is to assess changes in the morphological and functional occlusal parameters of the facial skeleton after prosthetic rehabilitation that increased lost occlusal vertical dimension.

MATERIAL AND METHODOLOGY

50 patients with advanced tooth wear were clinically examined, to assess the degree of wear. Each subject underwent cephalometric analysis, digital occlusal analysis, and electromyographic analysis, of the anterior temporalis, superficial masetter, anterior digastric, and the sternocleidomastoid muscles. Prosthodontic treatment was performed to restore the occlusal vertical dimension of each subject's occlusion, which was followed by repeating the pretreatment analyses. Pre and post treatment parameters were statistically compared.

RESULTS

Pre-treatment cephalometric analysis showed that lost vertical dimension reduced anterior facial height and resulted in small angular skeletal parameters. Post treatment anterior facial height increased from the increased occlusal vertical dimension. The mean value of functional electrical activity during clenching post treatment, increased compared to pretreatment.

CONCLUSION

Increasing the vertical dimension of occlusion improved facial aesthetics by positively affecting facial skeletal angles. The restored occlusal surface morphology changed the pre treatment flat broad occlusal contacts into more point contacts. The increased vertical dimension of occlusion after treatment also increased muscle activity levels over the pretreatment levels after three months period of adaptation.

A computed tomography-based comparative cephalometric analysis of the Italian craniofacial pattern through 2,700 years

The aim of our study was to define the changes in morphovolumetric features of neurocranium, basicranium and splanchnocranium in the population of Campania, southern Italy, over the last 2,700 years. This was a very intense period for this region from both historical and evolutionary perspectives and was marked by the succession of colonisations, dominations and invasions by several European and non-European peoples, events that profoundly influenced the original genetic heritage, which subsequently became more complex. Unlike most previous authors, we based our craniometric comparative analysis on multidetector computed tomography (MDCT) studies of contemporary and ancient series dating to between the seventh and fifth centuries B.C. of skulls found in the Etruscan necropolis of Pompei and Pontecagnano. MDCT is extremely reliable in identifying landmarks and measuring linear and angular indices through the use of multiplanar and tridimensional reformations. While highlighting a remarkable stability of 22/32 of the indices considered, as an effect of the role of the genetic heritage in preserving morphovolumetric features in a given population, statistical analysis showed some interesting results: the main changes concerned the splanchnocranium and the occlusion, indicating a higher sensitivity of these districts to environmental factors, mainly related to diet. Conversely, neurobasicranial complex morphovolumetric features remained amazingly intact. In particular, the neurocranium increased in overall capacity in response to the growing brain and changed shape with a progressive shift to a dolichocranic, flattened frontal pattern; the basicranium shape was preserved, as indicated by the stability of the cranial base (NSBa) angle over time. The splanchnocranium, on the contrary, has undergone a dramatic involution, even conditioning gnathic structures with changes in palatal shape (more acute) and in the relationship between the jaws on the sagittal plane, resulting in increased prevalence of Angle's class I and III malocclusions.

Chewing pattern and muscular activation in open bite patients

Different studies have indicated, in open bite patients, that masticatory muscles tend to generate a small maximum bite force and to show a reduced cross-sectional area with a lower EMG activity. The aim of this study was to evaluate the kinematics parameters of the chewing cycles and the activation of masseters and anterior temporalis muscles of patients with anterior dental open bite malocclusion. There have been no previous reports evaluating both kinematic values and EMG activity of patients with anterior open bite during chewing. Fifty-two young patients (23 boys and 29 girls; mean age±SD 11.5±1.2 and 10.2±1.6years, respectively) with anterior open bite malocclusion and 21 subjects with normal occlusion were selected for the study. Kinematics parameters and surface electromyography (EMG) were simultaneously recorded during chewing a hard bolus with a kinesiograph K7-I Myotronics-Usa. The results showed a statistically significant difference between the open bite patients and the control group for a narrower chewing pattern, a shorter total and closing duration of the chewing pattern, a lower peak of both the anterior temporalis and the masseter of the bolus side. In this study, it has been observed that open bite patients, lacking the inputs from the anterior guidance, that are considered important information for establishing the motor scheme of the chewing pattern, show narrower chewing pattern, shorter lasting chewing cycles and lower muscular activation with respect to the control group.

Longitudinal changes in muscle activity of masseter and anterior temporalis before and after Lefort I osteotomies, An EMG study

AIMS

The aim of this study was to compare the levels of electromyography (EMG) activity of masseter and anterior temporalis present presurgically with changes in the intensity of muscle activity that took place post surgically for a period of 6 months follow up.

SETTINGS AND DESIGN

Ten patients with vertical maxillary excess were selected from the department of Oral and Maxillofacial surgery at Saveetha Dental College and Hospitals, Chennai.

MATERIALS AND METHODS

Electromyography was used as a kinesiology tool to study muscle function of Masseter and Anterior Temporalis of all ten subjects pre surgically and post surgically with a 6 month follow up.

STATISTICAL ANALYSIS USED

The statistical package SPSSPC+ (Statistical Package for Social Science, Version 4.0.1) was used for statistical analysis. Mean and standard deviation were estimated from the sample. The tests that were used for the statistical analysis were one way ANOVA and student's T test.

RESULTS

The final inference elucidates that the muscular activity of masseter and temporalis are improved during chewing and clenching in the postoperative 6 months period when compared to preoperative values. The duration was constant at 7 milliseconds for both the positions.

CONCLUSIONS

From this study, it can be concluded that there is a strong correlation between vertical maxillary excess and associated weak musculature. Electromyography has been used as an important tool to demonstrate improved muscle activity after surgical correction of vertical maxillary excess and improvement in functional deficits associated with this dentofacial deformity. From this study it can be concluded that surgical correction of vertical maxillary excess improves occlusion, leading to increased eccentric tooth contacts, increased mean amplitude and increased mean power frequency of the muscles all of which translate into improved muscle activity.

Mastication, EMG activity and occlusal contact area in subjects with different facial types

Dentofacial morphology may affect orofacial functions, therefore the aim of the current study was to evaluate the influence of craniofacial morphology on masticatory function, occlusal contact area (OCA), and masticatory muscles activity. Seventy-eight (78) subjects were divided into three groups according to vertical facial pattern: 1. mesofacial; 2. brachyfacial; and 3. dolichofacial. Artificial material and the sieving method were used to access masticatory efficiency (ME). OCA was determined by registration of posterior teeth. Electromyographic (EMG) activity of the masseter and anterior temporal (AT) muscles was accessed bilaterally at rest and at maximal vertical clenching (MVC). ME (%) was significantly higher in brachyfacial and lower in dolichofacial subjects. Brachyfacials presented the highest OCA (mm2) followed by meso and dolichofacial subjects. The EMG of the masseter and AT at rest and at MVC showed that dolichofacial subjects presented the lowest activity values, while brachyfacial subjects presented significantly higher measurements. Craniofacial morphology affected masticatory function, OCA, and EMG activity of the masticatory muscles.

Masticatory features, EMG activity and muscle effort of subjects with different facial patterns

It has been suggested that craniofacial morphology plays an important role in masticatory function, however, there are controversies and unsolved questions that still require elucidation. The aims of this study were to evaluate masticatory performance, mandibular movement, electromyographic (EMG) activity and muscle effort of masseter and anterior temporal muscles during mastication. Seventy-eight dentate subjects were selected and divided into three groups according to vertical facial pattern: brachyfacial, mesofacial and dolichofacial. Silicon-based material was used for chewing tests. Masticatory performance was determined by a 10-sieve method, and masticatory movements during mastication were assessed using a 3D mandibular tracking device. Electromyographic activities of masseter and anterior temporal muscles were evaluated during mastication, and muscle effort was calculated by the percentage of activity required for mastication based on maximum muscle effort. Data were analysed using anova and anova on-ranks tests. Dolichofacial subjects presented significantly poorer masticatory performance (6·64±2·04; 4·33±0·70 and 3·67±0·63), slower rate of chewing (1·34±0·27, 1·18±0·22 and 1·21±0·20 cycles per second) and larger posterior displacement during mastication (6·22±2·18; 5·18±1·87 and 5·13±1·89) than meso- and brachyfacial individuals, respectively. No statistical difference was detected among groups for the other masticatory movement parameters. There was no difference in absolute EMG amplitudes of masseter and anterior temporal muscles during mastication among groups, but the relative effort of both muscles was higher in dolichofacial, followed by meso- and brachyfacial subjects (masseter: 39·34± 2·25; 36·87±4·05 and 33·33±4·15; anterior temporal: 38·12±1·61; 38·20±8·01 and 35·75±2·48). It was concluded that the vertical facial pattern influences masticatory performance, mandibular movement during mastication and the effort masticatory muscles required for chewing.

Masticatory muscle activity in children with a skeletal or dentoalveolar open bite

SUMMARY

The aim of this study was to compare the electromyographic (EMG) characteristics of masticatory muscles in children with either a skeletal or dentoalveolar open bite, compared with a control group (CG). Forty-five children (31 boys and 14 girls), aged 6-11 years, were included in the study, 15 with a skeletal anterior open bite (SAOB), 15 with a dentoalveolar anterior open bite (DAOB), and 15 with a normal occlusion (CG), defined by clinical evaluation and lateral cephalograms. EMG recordings of the temporal and masseter muscles were performed under maximal voluntary clenching and during chewing. Analysis of variance was used for inter-group analysis, followed by the Tukey post hoc test. A Student's t-test for paired data was used for intra-group analysis. There were statistically significant differences among the three groups (P < 0.05), with the mean EMG being highest in the CG and lowest in children with a SAOB. The percentage EMG activity during chewing in relation to that during maximal voluntary clenching was more than 100 per cent in the SAOB group. The CG and DAOB groups presented higher EMG activity during clenching compared with chewing (P < 0.001), as well as a greater difference between tasks. In the SAOB group, the neuromuscular system appeared to have a lower capacity to produce EMG activity according to the task, while that in the DAOB group suggests that their functional capacity during growth should also be carefully observed.

Electromyographic activity of masseter and temporal muscles with different facial types

OBJECTIVES

To compare the electromyographic (EMG) activity of the masseter and anterior portion of temporal muscles in different vertical facial types.

MATERIALS AND METHODS

Clinical examination, cephalometric analysis, and electromyographic examination were performed in 44 volunteers ranging from 18 to 35 years old. The volunteers were classified on the basis of their vertical facial characteristics into three groups-brachyfacial, mesofacial, and dolicofacial-by the grouping analysis. The EMG records were obtained with three repetitions during mandibular rest, maximum voluntary contraction in intercuspidation, and simultaneous bilateral isotonic contraction. The Kolmogorov-Smirnov and Levene tests were applied to verify the normality and homogeneity of variance. Analysis of variance and the Kruskal-Wallis test identified statistical differences among groups that did not present normality and homogeneity of distribution, respectively. Significance for all statistical tests was set at P < .05.

RESULTS

At rest, only the right temporal and masseter muscles presented statistically significant differences among the groups. The differences were observed between groups 1 and 2 (P = .02) and 1 and 3 (P = .038) for the right temporal muscle, and between groups 1 and 2 (P = .029) for the right masseter muscle. Generally, group 1 presented the lowest EMG values for the four muscles evaluated during rest. For isotonic evaluation, none of the groups of muscles presented statistically significant differences.

CONCLUSION

Different vertical facial types do not determine distinct patterns of EMG activity for the masseter and anterior portion of temporal muscles during rest and bilateral mastication.

The adaptive response of jaw muscles to varying functional demands

Jaw muscles are versatile entities that are able to adapt their anatomical characteristics, such as size, cross-sectional area, and fibre properties, to altered functional demands. The dynamic nature of muscle fibres allows them to change their phenotype to optimize the required contractile function while minimizing energy use. Changes in these anatomical parameters are associated with changes in neuromuscular activity as the pattern of muscle activation by the central nervous system plays an important role in the modulation of muscle properties. This review summarizes the adaptive response of jaw muscles to various stimuli or perturbations in the orofacial system and addresses general changes in muscles as they adapt, specific adaptive changes in jaw muscles under various physiologic and pathologic conditions, and their adaptive response to non-surgical and surgical therapeutic interventions. Although the jaw muscles are used concertedly in the masticatory system, their adaptive changes are not always uniform and vary with the nature, intensity, and duration of the stimulus. In general, stretch, increases neuromuscular activity, and resistance training result in hypertrophy, elicits increases in mitochondrial content and cross-sectional area of the fibres, and may change the fibre-type composition of the muscle towards a larger percentage of slow-type fibres. In contrast, changes in the opposite direction occur when neuromuscular activity is reduced, the muscle is immobilized in a shortened position, or paralysed. The broad range of stimuli that affect the properties of jaw muscles might help explain the large variability in the anatomical and physiological characteristics found among individuals, muscles, and muscle portions.

Masseter muscle thickness and mechanical advantage in relation to vertical craniofacial morphology in children

OBJECTIVE

To investigate the relationship between vertical craniofacial morphology and masseter muscle thickness and mechanical advantage in children.

MATERIAL AND METHODS

The sample comprised 72 children (36 F, 36 M), 8.5-9.5 years of age, with various malocclusions and no previous orthodontic treatment. The thickness of the masseter was measured bilaterally by means of ultrasonography, and the recordings were performed both in relaxation and under contraction. Mechanical advantage was measured on the lateral cephalograms as the ratio between the masseter moment and the bite force moment arms. Two linear ratios and three angular measurements were used to describe vertical craniofacial morphology.

RESULTS

The mean masseter thickness was greater in the male group (p<0.05) in both relaxed and contracted conditions. There were no significant sex differences for the mechanical advantage or for the measurements of vertical craniofacial morphology. In females, there is a positive association between masseter muscle thickness and its mechanical advantage. Multiple regression analysis showed a positive association between posterior to anterior facial height ratio in both genders and a negative association between masseter thickness and the intermaxillary angle in females.

CONCLUSIONS

There is a significant association between posterior to anterior facial height and the masseter muscle in children. The importance of the masseter muscle is more evident in the vertical facial morphology of females.

Mandibular muscle morphology in children with different vertical facial patterns: A 3-dimensional computed tomography study

INTRODUCTION

This study was undertaken to assess whether 3-dimensional computed tomography (CT) can be used to evaluate the relationships between the mandibular muscles and craniofacial morphology in children with different underlying vertical facial patterns.

METHODS

Twenty children (mean age, 11.9 +/- 1.6 years) underwent cranial CT examination. Three-dimensional CT images were reconstructed for the evaluation of the cross-sectional size, volume, and spatial orientation of the masseter, medial pterygoid, and lateral pterygoid muscles. These muscle factors were also assessed in relation to vertical and transverse craniofacial form.

RESULTS

Positive correlations were found between the muscles' cross-sectional area and volume, and between muscle size and transverse facial width. Despite the limited sample size, differences were also found in the orientation of the masseter and medial pterygoid muscles in growing patients with different underlying vertical facial patterns.

CONCLUSIONS

Three-dimensional CT can be used for the assessment of soft- and hard-tissue dentofacial forms. Clinicians should note the potential differences in muscle cross-sectional area, volume, and orientation in subjects with different underlying vertical facial patterns.

Avaliação da profundidade do palato e das dimensões do arco dentário superior em indivíduos com má oclusão e diferentes tipos faciais

OBJETIVO: o deste estudo foi avaliar a profundidade do palato e as dimensões do arco dentário superior de indivíduos com má oclusão e diferentes tipos faciais. METODOLOGIA: a amostra empregada neste estudo foi constituída por telerradiografias em norma lateral e modelos de estudo de 135 pacientes com más oclusões de Classe I (n = 45), Classe II (n = 45) e Classe III (n = 45) de Angle, sendo 67 do gênero feminino e 68 do gênero masculino, com faixa etária entre 12 e 21 anos de idade, divididos igualmente em três grupos conforme o tipo facial apresentado: braquifacial, mesofacial e dolicofacial. RESULTADOS E CONCLUSÕES: os resultados obtidos demonstraram que, quanto ao tipo facial, houve diferença estatisticamente significante apenas para a medida da profundidade do palato, sendo que os indivíduos braquifaciais apresentaram palato com menor profundidade (média = 18,18mm), quando comparados aos indivíduos dolicofaciais (média = 19,52mm). Quanto ao dimorfismo sexual, pudemos verificar que os indivíduos do gênero masculino apresentaram médias da distância intermolares superiores (51,36mm) e da profundidade do palato (19,61mm) aumentadas, de forma significante, em relação às médias obtidas para o gênero feminino (50,15mm e 18,37mm para as medidas da distância intermolares e da profundidade do palato, respectivamente). Avaliando o tipo de má oclusão, pudemos constatar que houve diferença estatisticamente significante apenas para a medida do comprimento do arco, sendo que indivíduos com má oclusão de Classe II apresentaram arcos dentários superiores com maior comprimento ântero-posterior (média = 31,23mm) que indivíduos com má oclusão de Classe III (média = 29,64mm). Entretanto, a média da medida comprimento do arco encontrada para o grupo Classe I (30,52mm) não apresentou diferença estatisticamente significante quando comparada às médias obtidas para os grupos Classe II e Classe III.

The clinical usefulness of surface electromyography in the diagnosis and treatment of temporomandibular disorders

BACKGROUND

This article presents a comprehensive review of the recent literature regarding the scientific support for the use of surface electromyography (SEMG) in diagnosing and treating temporomandibular disorders (TMDs).

TYPES OF STUDIES REVIEWED

The authors conducted a Medline search involving human studies using the key words "surface electromyography or electromyography" and "masticatory muscles or temporomandibular disorders or craniomandibular disorders." They also reviewed relevant articles regarding the clinical usefulness of SEMG based on reliability, validity, sensitivity and specificity, as well as additional references included in some of the articles.

RESULTS

The clinical use of SEMG in the diagnosis and treatment of TMD is of limited value when one considers reliability, validity, sensitivity and specificity as measurement standards. SEMG does not appear to contribute any additional information beyond what can be obtained from the patient history, clinical examination and, if needed, appropriate imaging.

CONCLUSIONS

Clinically, the determination of the presence or absence of TMD does not appear to be enhanced by the use of SEMG. However, the modality may be useful in a meticulously controlled research setting.

CLINICAL IMPLICATIONS

SEMG has limited value in the detection or management of TMD and in some instances may lead to unnecessary dental therapy as a solution for those disorders.

The relationship between vertical craniofacial morphology and the sagittal path of mandibular movements

The aim was to investigate the relationship between the vertical craniofacial morphology and the sagittal path of mandibular movements. The study was carried out in 40 subjects who were free of temporo-mandibular disorders. Mandibular movements and maximal jaw opening (MO) were recorded by means of a jaw tracking device. The opening-closing angle (OCA) was defined as the angle between the horizontal plane and the opening-closing path of movements. Vertical craniofacial morphology was assessed on prophile cephalograms by means of the Frankfort Mandibular Plane Angle (MP). The OCA did not differ between males and females (P>0.05). OCA and MP were negatively correlated (r=-0.62; P<0.001). MO was significantly greater in males that in females (P<0.05). MO was negatively correlated to MP (-0.44<r<-0.49; P<0.05). The findings suggest that the low-angle subjects exhibit a more vertical path of the mandibular movements than that of high-angle subjects. Differences in the sagittal path of jaw movements may be partly ascribed to anatomical factors.

Habitual daily masseter activity of subjects with different vertical craniofacial morphology

Little is known about the habitual daily masticatory activity of subjects with different vertical craniofacial morphology. The purpose of the present study was to compare the daily long-term muscle activity of short-face subjects with that of long-face subjects as assessed in their natural environment. Digital photographs of the facial profile were obtained from a sample of 300 subjects and the ratio between anterior total and anterior lower facial height was assessed (Vertical Facial Index: VFI). Fourteen long-face and 16 short-face subjects were selected from the opposite tails of the frequency distribution of VFI. Long-term masseter activity was monitored for 8 h d(-1) in the natural environment by means of portable one-channel electromyograph recorders over three working days. Assessments included calculation of the number of activity periods (APs) per h (N/h), their mean amplitude (Amean), and their mean duration (Dur). The maximal electromyogram activity did not differ significantly between the short-face and the long-face subjects. There was no significant difference between the two groups investigated in N/h, in Amean and Dur. The findings suggest that habitual activity of masseter muscle in the natural environment was not influenced by the vertical craniofacial morphology as assessed in the present study.

Effect of different masticatory functional and mechanical demands on the structural adaptation of the mandibular alveolar bone in young growing rats

The influence of masticatory functional and mechanical demands on the structural adaptation of the alveolar bone has not been investigated in both animals and humans. The effect of two experimental factors, the insertion of a bite-opening appliance and the alteration of food consistency, was investigated in young growing rats, with a particular emphasis on three-dimensional (3D) bone microstructure. Thirty-six male albino rats were divided into two equal groups, fed with either the standard hard diet or soft diet, at the age of 4 weeks. After 2 weeks, half of the animals in both groups had their upper molars fitted with an upper posterior bite block, an appliance similar to those used in clinical orthodontics. The remaining animals served as a control. After another 4 weeks, the animals were sacrificed, and their left hemimandibles were excised. Bone mineral density (BMD) and bone microstructure parameters of the alveolar process were subsequently measured, using dual-energy X-ray absorptiometry (DXA) and micro-computed tomography (micro-CT). The alveolar process width was also measured. Both experimental factors led to significant shape and structure modification of the mandibular alveolar bone in the growing rat. The bite block applied a continuous light force, which was associated with an inhibition of alveolar process vertical growth and a significant increase of cortical thickness. Soft diet and the consequent reduction of the intermittent forces applied to the alveolar bone during mastication resulted in a reduction of bone mineral density, accompanied by decreased trabecular bone volume and thickness. This rat model could prove to be a useful tool for the in vivo investigation of the role of muscular forces on the shape and structure adaptation of bone.

Relation between vertical facial morphology and jaw muscle activity in healthy young men

The aim of the current investigation was to quantitatively analyze the relation between the activity of masticatory muscles and the inclination of the mandibular plane in a group of 73 healthy white men aged 20-36 years. The three-dimensional coordinates of soft-tissue landmarks gnathion and left and right gonion were digitized using an electromagnetic computerized instrument, the orientation of mandibular plane relative to the true vertical was computed and projected on the anatomical sagittal plane. The electromyographic (EMG) potentials of left and right masseter and temporalis anterior during maximum voluntary teeth clenching were recorded, and the mean EMG amplitude calculated. Two groups of men with opposite facial morphology were then selected: all men with a steep mandibular plane (higher than the mean plus one standard deviation) entered a first group (10 'long face' subjects), while all men with a relatively more horizontal mandibular plane (lower than the mean minus one standard deviation) entered a second group (13 'short face' subjects). Mean EMG potentials computed in the two groups were compared by using Student's t -test for independent samples. All the EMG potentials recorded during maximum voluntary clench in the 'long face' men were lower than that recorded in the 'short face' men, with statistically significant differences for all four analyzed muscles (p < 0.05). In conclusion, a non-invasive three-dimensional method confirmed that facial morphology and muscular function are significantly related, at least in men with a sound stomatognathic apparatus.