Human masticatory muscle activity and jaw position under experimental stress

Head posture and dental wear evaluation of bruxist children with primary teeth

The aim of the present study was to compare the head position and dental wear of bruxist and non-bruxist children with primary dentition.

METHODS

All the subjects had complete primary dentition, dental and skeletal class I occlusion and were classified as bruxist or non-bruxist according to their anxiety level, bruxism described by their parents and signs of temporomandibular disorders. The dental wear was drawn in dental casts and processed in digital format. Physiotherapeutic evaluation and a cephalometric radiograph with natural head position were also performed for each child to evaluate the cranio-cervical position for the bruxist group (n = 33) and the control group (n = 20). The variables of the two groups were compared, using the Student t-test and Mann-Whitney U-test.

RESULTS

A more anterior and downward head tilt was found in the bruxist group, with statistically significant differences compared with the controls. More significant dental wear was observed in the bruxist children.

CONCLUSIONS

Bruxism seems to be related to altered natural head posture and more intense dental wear. Further studies are necessary to explore bruxism mechanisms.

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.

Surface EMG of jaw elevator muscles: effect of electrode location and inter-electrode distance

This study addresses methodological issues on surface electromyographic (EMG) signal recording from jaw elevator muscles. The aims were (i) to investigate the sensitivity to electrode displacements of amplitude and spectral surface EMG variables, (ii) to analyse if this sensitivity is affected by the inter-electrode distance of the bipolar recording, and (iii) to investigate the effect of inter-electrode distance on the estimated amplitude and spectral EMG variables. The superficial masseter and anterior temporalis muscles of 13 subjects were investigated by means of a linear electrode array. The percentage difference in EMG variable estimates from signals detected at different locations over the muscle was larger than 100% of the estimated value. Increasing the inter-electrode distance resulted in a significant reduction of the estimation variability because of electrode displacement. A criterion for electrode placement selection is suggested, with which the sensitivity of EMG variables to small electrode displacements was of the order of 2% for spectral and 6% for amplitude variables. Finally, spectral and, in particular, amplitude EMG variables were very sensitive to inter-electrode distance, which thus should be fixed when subjects or muscles are compared in the same or different experimental conditions.

The role of parafunctions, emotions and stress in predicting facial pain

BACKGROUND

The authors conducted a study to examine the degree to which parafunctions and emotional states predicted jaw pain in subjects with temporomandibular disorder (TMD) and control subjects.

METHODS

Ninety-six subjects diagnosed with myofascial pain, myofascial pain and arthralgia, disk displacement or no TMD symptoms participated. The authors used experience sampling methodology to collect data on pain, behaviors and emotions. They paged subjects approximately every two hours, but not during sleep. When paged, subjects completed a brief questionnaire containing rating scales of jaw pain, masticatory muscle tension, time and intensity of tooth contact, mood and stress level.

RESULTS

Analyses of variance showed that groups differed significantly (P < .05) in terms of pain; masticatory muscle tension; and a composite variable measuring time and intensity of contact; mood; and stress. The two myofascial pain groups scored higher on these measures than did the group with disk displacement and the control group. The authors used masticatory muscle tension, the composite variable, mood and stress to predict jaw pain using linear regression. The model was significant and accounted for 69 percent of the variance in jaw pain. Because tension was so highly correlated with jaw pain, the authors removed this variable and re-ran the analysis. The second model also was significant and accounted for 46 percent of the variance in jaw pain.

CONCLUSIONS

Parafunctional behaviors, especially those that increase muscle tension, and emotional states are good predictors of jaw pain levels in patients with TMD and healthy control subjects.

CLINICAL IMPLICATIONS

Treatment that helps patients reduce parafunctions, excess masticatory muscle tension, stress and emotional distress should be effective in reducing TMD pain.