Effect of unilateral posterior crossbite on the electromyographic activity of human masticatory muscles

Electromyographic evaluation in children having rapid maxillary expansion

INTRODUCTION

The aim of this study was to analyze the electromyographic activity of the masseter and temporalis muscles of children having rapid maxillary expansion (RME) with a bonded rapid maxillary expansion appliance.

METHODS

The sample consisted of 27 children (mean age, 8.6 years) with posterior crossbite who required RME treatment. Electromyographic activity of the masseter and temporalis muscles was analyzed before treatment and after the appliance was removed. The mean interval between the 2 analyses was 5 months. Muscular activity was electromyographically analyzed in rest position, and with maximum voluntary dental clenching and chewing. Differences in the 2 measurements were evaluated by using paired t tests.

RESULTS AND CONCLUSIONS

Electromyographic analysis showed that activity of the masseter and temporalis muscles increased significantly after the expansion appliance was removed during rest, dental clenching, and habitual chewing.

Electromyographic activity and thickness of masticatory muscles in children with unilateral posterior crossbite

The aim of this study was to assess the electromyographic (EMG) activity and thickness of the masseter and anterior temporalis muscles in children with unilateral posterior crossbite (PCB). Thirty-six children (22 boys, 14 girls, and mean age of 8.8 +/- 1.1 years) were divided into the following groups: The case group with 20 PCB patients (10 on the left side, 10 on the right side); the control group with 16 normal occlusion (NOccl) subjects. EMG activity was recorded with bipolar surface electrodes at rest and during maximal clenching. The muscle thickness was measured with real-time ultrasound. Data were compared between groups and between sides. The correlation between EMG activity and muscle thickness was also evaluated. The data were analyzed using the Shapiro-Wilks test, Pearson's correlation and Spearman as appropriate, paired and unpaired t- test, and Mann-Whitney test. The results revealed that the masseter of the crossbite side was more active than that of the non-crossbite side in PCB group during maximal clenching. The comparisons of EMG activity between PCB and NOccl groups revealed some variability in the results, depending on the crossbite side. The ultrasonographic evaluation did not show statistically significant differences between groups, nor between sides in the PCB and NOccl groups. Significant correlation between EMG activity and thickness was observed only in the left masseter in the NOccl group. In conclusion, these findings showed that asymmetric muscle activity of the masticatory muscles was not related to the thickness of these muscles in children with PCB.

Posterior Crossbite and Functional Changes

Objective: To assess, by systematically reviewing the literature, the functional changes of the masticatory muscles associated with posterior crossbite in the primary and mixed dentition.

Materials and Methods: A literature survey from the Medline database covering the period from January 1965 to February 2008 was performed. Randomized controlled trials, controlled clinical trials, and clinical trials that evaluated bite force, surface electromyography, and signs and symptoms of temporomandibular disorders (TMD) were included. Two reviewers extracted the data independently and assessed the quality of the studies.

Results: The search strategy resulted in 494 articles, of which 8 met the inclusion criteria. Children with posterior crossbite can have reduced bite force and asymmetrical muscle function during chewing or clenching, in which the anterior temporalis is more active and the masseter less active on the crossbite side than the noncrossbite side. Moreover, there is a significant association between posterior crossbite and TMD symptomatology.

Conclusion: The consequences of the functional changes for the growth and development of the stomatognathic system deserves further investigation.

Mastigação e atividade eletromiográfica em crianças com mordida cruzada posterior

OBJETIVO: investigar a preferência mastigatória e o comportamento dos músculos mastigatórios, em crianças de 6 a 9 anos, com mordida cruzada posterior. MÉTODOS: 30 crianças foram selecionadas num serviço de Ortodontia de uma universidade pública. Após a concordância na participação no trabalho, foi realizada entrevista com a criança e seu responsável, para investigação de disfunção temporomandibular; análise da preferência mastigatória, por meio de registros em vídeo e avaliação eletromiográfica (EMG) dos músculos masseter e temporal anterior, durante a mastigação solicitada, direita e esquerda, de uma goma de marcar. RESULTADOS: houve diferença significante na atividade EMG dos músculos masseter e temporal anterior entre os lados de trabalho e balanceio, porém não houve diferença estatística quando foram comparadas as atividades EMG entre os lados de mordida cruzada e não cruzada, tampouco entre os lados de preferência e não preferência mastigatória. CONCLUSÃO: na amostra estudada não se verificou assimetria funcional muscular estabelecida.

Análise da mastigação em indivíduos que apresentam mordida cruzada unilateral na faixa-etária de 07 a 12 anos

OBJETIVO: analisar a função de mastigação relacionada à mordida cruzada posterior unilateral em crianças na faixa etária de sete a doze anos. MÉTODOS: dez indivíduos de ambos os sexos com mordida cruzada unilateral posterior sem intervenção ortodôntica. Na avaliação fonoaudiológica os itens considerados foram: corte do alimento, lado da mastigação, ritmo, postura labial, escape de alimentos, movimento de mandíbula, participação exagerada da musculatura perioral, acúmulo de alimento no vestíbulo da boca, posição e tamanho do bolo alimentar. RESULTADOS: dos dez indivíduos avaliados, 80% apresentaram mastigação unilateral do mesmo lado da mordida cruzada posterior unilateral e 20% mastigação bilateral. Dos oito indivíduos analisados com mastigação unilateral, os resultados encontrados foram: corte anterior, sem escape de alimentos e movimentos rotatórios 100%; ritmo lento 50% e rápido 50%; lábios fechados 75%; participação exagerada da musculatura perioral 62,5%; sem acúmulo de alimentos 87,5%; bolo alimentar centralizado 75%; tamanho do bolo pequeno 62,5%. CONCLUSÃO: dos casos avaliados, observou-se que 80% confirmam a relação entre mastigação unilateral e mordida cruzada posterior unilateral. Na mastigação, não foram evidenciadas quaisquer outras alterações que possam estar relacionadas à mordida cruzada posterior unilateral e mastigação unilateral.

Ultrasonographic Thickness of the Masseter Muscle in Growing Individuals with Unilateral Crossbite

Objective: To study the bilateral differences in the thickness of the masseter muscles in untreated individuals with lateral crossbite, as well as in subjects with successfully treated functional lateral crossbite, at least three years after the end of treatment.

Materials and Methods: Three groups of growing individuals were studied: (1) untreated group: 38 individuals with unilateral crossbite, (2) control group: 224 subjects without transversal malocclusions, and (3) treated group: 18 individuals with functional lateral crossbite, treated with a quad helix, and at least three years out of retention with all permanent teeth erupted. The thickness of the masseter muscle was measured bilaterally with ultrasonography, using a real time scanner with a 7.5 MHz linear array transducer.

Results: In the untreated group, the thickness of the masseter muscle on the crossbite side was statistically significantly thinner than the one on the normal side (P = .025). No statistically significant differences were found in the thickness of the masseter muscle between the left and the right side in the control group. In the treated group, no statistically significant differences were found in the thickness of the masseter muscle between the former crossbite side and the normal one.

Conclusion: The masseter muscle in untreated individuals with unilateral crossbite is thinner in the crossbite side when compared to the non-crossbite side possibly due to asymmetric activity of the masticatory muscles. Such an asymmetry in thickness of the masseter muscle could not be detected some years after the successful correction of the crossbite.

Unilateral posterior crossbite and mastication

OBJECTIVE

This study was designed to characterize masticatory-cycle morphology, and distance of the contact glide in the closing masticatory stroke, in adult subjects with uncorrected unilateral posterior crossbite (UPXB), comparing the results obtained with those obtained in a parallel group of normal subjects.

STUDY DESIGN

Mandibular movements (masticatory movements and laterality movements with dental contact) were registered using a gnathograph (MK-6I Diagnostic System) during unilateral chewing of a piece of gum. Traces were recorded on the crossbite and non-crossbite sides in the crossbite group, and likewise on both sides in the non-crossbite group.

RESULTS

Mean contact glide distance on the crossbite side in the UPXB group was significantly lower than in the control group (p<0.001), and mean contact glide distance on the non-crossbite side in the UPXB group was significantly lower than in the control group (p=0.042). Cycle morphology was abnormal during chewing on the crossbite side, with the frequency distribution of cycle types differing significantly from that for the noncrossbite side and that for the control group (p<0.001).

CONCLUSIONS

Patients with crossbite showed alterations in both contact glide distances and masticatory cycle morphology. These alterations are probably adaptive responses allowing maintenance of adequate masticatory function despite the crossbite.

Avaliação ultra-sonográfica dos músculos mastigatórios e dimensões faciais em crianças com oclusão normale mordida cruzada posterior unilateral

OBJETIVO: avaliar a espessura dos músculos masseter e porção anterior do temporal por meio da ultra-sonografia e as dimensões faciais de crianças com oclusão normal e mordida cruzada posterior unilateral, na dentição decídua e mista inicial. MÉTODOS: foram selecionadas 49 crianças, de ambos os gêneros, divididas em quatro grupos: decídua-oclusão normal, decídua-mordida cruzada, mista-oclusão normal e mista-mordida cruzada. A espessura muscular foi comparada entre os lados direito e esquerdo (oclusão normal); e normal e cruzado (mordida cruzada) (teste "t" Student), e relacionada às dimensões faciais e variáveis corporais (teste de correlação de Pearson e Spearman). As dimensões faciais foram mensuradas sobre fotografias frontais padronizadas: altura facial anterior (AFA), distância bizigomática (DB) e intergoniana (DI) e razões AFA/DB e AFA/DI. RESULTADOS: observou-se que o músculo temporal no repouso apresentou espessura maior no lado cruzado no grupo mista-cruzada (p=0,05). O masseter não apresentou diferença significativa entre os lados em todos os grupos. As variáveis peso e altura não apresentaram correlação com a espessura muscular; já DB e DI apresentaram correlação positiva e as razões AFA/DB e AFA/DI, correlação negativa, com a espessura do masseter em todos os grupos, indicando que crianças com faces mais longas possuem menor espessura deste músculo. CONCLUSÃO: na amostra estudada, os exames da espessura dos músculos mastigatórios e das dimensões faciais demonstraram que a influência das características funcionais sobre as estruturas craniofaciais pôde ser observada já em crianças de pouca idade.

Relationship between orthodontic anomalies and masticatory function in adults

INTRODUCTION

Normal mastication requires the coordinated action of many elements, including teeth, salivary glands, tongue, and masticatory muscles. Dysfunction in any of these areas can result in impaired masticatory function. Few studies dealt with the influence of occlusal conditions on the masticatory function. Our aim in this study was to examine to what extent masticatory function is impaired in subjects with occlusal anomalies.

METHODS

Masticatory function was studied in 102 untreated adults. They were observed while chewing a standard test food for 20, 30, and 40 chewing strokes. Orthodontic condition was assessed with the index of complexity, outcome, and need (ICON). From the masticatory test, 3 variables were obtained: median particle size (MPS), broadness of the particle distribution (BPD), and masticatory frequency (F).

RESULTS

MPS was significantly larger in subjects with ICON scores >43 (definite-need subsample) than in subjects with ICON scores < or =43 (no-need subsample) when the masticatory test was performed with 20, 30, or 40 cycles (P =.05, .03, and .01, respectively). BPD also followed the same trend, but the differences were not significant (P = .33, .16, .14 for 20, 30, and 40 cycles, respectively). Also, the differences in F between the 2 subsamples were not significant (P = .26, .45, .37).

CONCLUSIONS

The results suggest that, in addition to esthetic considerations, improving a patient's chewing function by improving occlusal relationships could be an indication for orthodontic treatment.

Condylar Asymmetry in Bilateral Posterior Crossbite Patients

Objective: To investigate whether patients with bilateral posterior crossbite have asymmetrically developed condyles.

Materials and Methods: The study group consisted of 75 patients with bilateral posterior crossbite, and a control group of 75 subjects with normal occlusion. Condylar, ramal, and condylar plus ramal asymmetry values were computed for all of the subjects on orthopantomograms. Data were analyzed statistically by means of paired t-test and Student's t-test.

Results: The patients with bilateral posterior crossbite had more asymmetrical condyles relative to the controls. However, there were no statistically significant differences in condylar, ramal, or condylar plus ramal heights between left and right sides in both the control and crossbite groups.

Conclusion: Patients with bilateral posterior crossbite can have asymmetrical condyles and might be at risk for the development of future skeletal mandibular asymmetries.

The influence of occlusion on jaw and neck muscle activity: a surface EMG study in healthy young adults

The electromyographic (EMG) characteristics of masseter, temporalis and sternocleidomastoid (SCM) muscles during maximum voluntary teeth clench were assessed in 27 male and 35 female healthy young adults. Subjects were divided into two groups: (i) 'complete' Angle Class I (bilateral, symmetric canine and molar Class I relationships), and (ii) 'partial' Angle Class I (one to three canine/molar Class I relationships, the remaining relationships were Class II or Class III). On average, standardized muscular symmetry ranged 80.7-87.9%. During maximum voluntary teeth clench, average co-contraction of SCM muscle was 13.7-23.5% of its maximum contraction. On average, all torque coefficients (potential lateral displacing component) were >90%, while all antero-posterior coefficients (relative activities of masseter and temporalis muscles) were >85%. The average integrated areas of the masseter and temporalis EMG potentials over time ranged 87.4-106.8 muV/muV s%. Standardized contractile muscular activities did not differ between 'complete' and 'partial' Angle Class I, and between sexes (two-way analysis of variance). A trend toward a larger intragroup variability in EMG indices was observed in the subjects with 'partial' Angle Class I than in those with 'complete' Angle Class I (significant difference for the temporalis muscle symmetry, P = 0.013, analysis of variance). In conclusion, the presence of a complete or partial Angle occlusal Class I did not seem to influence the standardized contractile activities of masseter, temporalis and SCM muscles during a maximum voluntary clench. Subjects with a 'complete' Angle Class I were somewhat a more homogenous group than subjects with 'partial' Angle Class I.

Quantification of the relative risk of multiple occlusal variables for muscle disorders of the stomatognathic system

STATEMENT OF PROBLEM

There is no consensus on the association between occlusion and temporomandibular disorders (TMD).

PURPOSE

The purpose of this study was to quantify the relative risk of multiple occlusal variables for muscle disorders of the stomatognathic system.

MATERIAL AND METHODS

Eight occlusal features: retruded contact position (RCP) to maximum intercuspation (MI) slide length, vertical overlap, horizontal overlap, unilateral posterior reverse articulation, anterior open occlusal relationship, incisor dental midline discrepancy, mediotrusive interferences, and laterotrusive interferences, were clinically assessed by the same trained operator. The sample consisted of 81 women with a Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) axis I diagnosis of muscle disorder, for example myofascial pain, with or without limited opening, and 48 healthy women (control group). A stepwise multiple logistic regression was used to identify the significant associations between occlusal features and disease.

RESULTS

A slide from the retruded contact position to maximum intercuspation > or =2 mm and mediotrusive interferences were the only 2 occlusal features significantly associated with the presence of myofascial pain according to the RDC/TMD criterion symptoms. The odds ratio for myofascial pain was 2.57 for a slide from RCP to MI > or =2 mm and 2.45 for mediotrusive interferences. The percentage of the total log likelihood for myofascial pain explained by the significant occlusal factors amounted to 10.8% (Nagelkerke's R2=0.108). The multifactorial model, including the 2 significant occlusal factors, showed an acuracy to predict disease of 66.7% (sensitivity 71.6%; specificity 58.3%).

CONCLUSION

Occlusal features showed a low predictive value to detect muscle disorders of the stomatognathic system. Multifactorial complex pathologies, such as TMD, should be studied using multivariate statistical analyses, as univariate models may overestimate some resulting associations.

Kinesiographic study of the mandible in young patients with unilateral posterior crossbite

It is generally assumed that children with posterior crossbites have abnormal mandibular movements; however, this assumption has not been clearly evaluated. The purpose of this investigation was to study the movements and the resting position of the mandible in 2 samples of 30 subjects, one aged 10 to 14 years with right posterior crossbite, the other aged 10 to 15 years with normal occlusion. Subjects in both groups exhibited a Class I skeletal relationship and mesofacial growth pattern. A mandibular kinesiograph was used to record both the mandibular resting position and dynamic movements. Mandibular movements were recorded during (1) maximum excursions (opening-closing, protrusion, right and left excursions), (2) swallowing, and (3) mastication. The results showed no differences between groups in the extension of the movements during closing and protrusion. However, crossbite patients exhibited a significant lateral shift during these movements. Right and left excursions were also similar between groups. The dimension of the freeway space was similar between groups, but the lateral shift found in centric occlusion was also present in the crossbite group when the mandible was at rest. The crossbite group more frequently showed a pattern of abnormal swallowing. No differences were found in any of the parameters studied during the masticatory cycle. There was no relationship between the side of the crossbite and the masticatory preference side. In conclusion, posterior crossbite patients showed a lateral shift in some movements that persisted when the mandible was at rest.