Small vertical changes in jaw relation affect motor unit recruitment in the masseter.

Strategies for recruitment of masseter muscle motor units (MUs), provoked by constant bite force, for different vertical jaw relations have not previously been investigated. The objective of this study was to analyse the effect of small changes in vertical jaw relation on MU recruitment behaviour in different regions of the masseter during feedback-controlled submaximum biting tasks. Twenty healthy subjects (mean age: 24·6 ± 2·4 years) were involved in the investigation. Intra-muscular electromyographic (EMG) activity of the right masseter was recorded in different regions of the muscle. MUs were identified by the use of decomposition software, and root-mean-square (RMS) values were calculated for each experimental condition. Six hundred and eleven decomposed MUs with significantly (P < 0·001) different jaw relation-specific recruitment behaviour were organised into localised MU task groups. MUs with different task specificity in seven examined tasks were observed. The RMS EMG values obtained from the different recording sites were also significantly (P < 0·01) different between tasks. Overall MU recruitment was significantly (P < 0·05) greater in the deep masseter than in the superficial muscle. The number of recruited MUs and the RMS EMG values decreased significantly (P < 0·01) with increasing jaw separation. This investigation revealed differential MU recruitment behaviour in discrete subvolumes of the masseter in response to small changes in vertical jaw relations. These fine-motor skills might be responsible for its excellent functional adaptability and might also explain the successful management of temporomandibular disorder patients by somatic intervention, in particular by the use of oral splints.

[Clinical management of masticatory muscle pain: an update of the recommendations]. / Therapie bei Schmerzen der Kaumuskulatur: Aktualisierung der Empfehlungen.

Besides the different forms of odontalgia, myalgias of the masticatory muscles are the most frequent noninfectious complaints in the orofacial region. After summarizing the recommendations set forth by the Interdisciplinary Working Group of Orofacial Pain within the German Chapter of the IASP (German Pain Society), we present the current state of knowledge regarding the etiology, diagnosis, and therapeutic options, based on an extensive literature search. A systematic literature search was carried out in PubMed, the Cochrane Library, and the database of the Deutsche Zahnärztliche Zeitschrift. The results corroborate our previous recommendations that for the majority of patients pain reduction or pain relief can be achieved with noninvasive, reversible methods. Short- and long-term trials have added more evidence to the fact that different therapeutic measures have similar efficacy. In patients with chronic myalgias of the jaw muscles, involvement of a psychotherapist is crucial. Patient education, oral appliances, physiotherapeutic exercises, and acupuncture are recommended therapeutic measures, while physical therapy, pharmacotherapy, and psychological therapy received a limited recommendation.

The dental occlusion as a suspected cause for TMDs: epidemiological and etiological considerations.

The relationship between the dental occlusion and temporomandibular disorders (TMDs) has been one of the most controversial topics in the dental community. In a large epidemiological cross-sectional survey - the Study of Health in Pomerania (Germany) - associations between 15 occlusion-related variables and TMD signs or symptoms were found. In other investigations, additional occlusal variables were identified. However, statistical associations do not prove causality. By using Hill's nine criteria of causation, it becomes apparent that the evidence of a causal relationship is weak. Only bruxism, loss of posterior support and unilateral posterior crossbite show some consistency across studies. On the other hand, several reported occlusal features appear to be the consequence of TMDs, not their cause. Above all, however, biological plausibility for an occlusal aetiology is often difficult to establish, because TMDs are much more common among women than men. Symptom improvement after insertion of an oral splint or after occlusal adjustment does not prove an occlusal aetiology either, because the amelioration may be due to the change of the appliance-induced intermaxillary relationship. In addition, symptoms often abate even in the absence of therapy. Although patients with a TMD history might have a specific risk for developing TMD signs, it appears more rewarding to focus on non-occlusal features that are known to have a potential for the predisposition, initiation or perpetuation of TMDs.

Influence of neck rotation and neck lateroflexion on mandibular equilibrium.

Neuromuscular interaction between neck and jaw muscles has been reported in several studies. However, the influence of experimentally modified posture of the neck on jaw muscle activity during isometric biting was not investigated so far. The aim of the present study was to test by the aid of simultaneous electromyographic and intraoral bite force measurements whether neck rotation and lateroflexion, in contrast to a straightforward neck position, change the isometric cocontraction patterns of masticatory muscles under identical submaximum bite forces of 50-200 N. Electric muscle activity of all masticatory muscles and changes of the reduction point (RP) of the resultant bite force vectors were examined. An anteroposterior displacement of the RPs could be observed for the rotated and lateroflexed neck position in comparison with the straightforward position. On the other hand, the results revealed no significant differences between bilateral muscle activation under the different test conditions. These findings suggest a force transmission between the neck and the masticatory system, but no essential activity changes in the masticatory muscles under short time posture modification of the neck.

Temporomandibular pain and depression in adolescents--a case-control study.

This study compared the depression status of adolescents with temporomandibular (TM) pain to those without, considering the influence of age, sex, and other pain conditions. From a general population sample of 455 adolescents, 29 cases (mean age, 15.3 years) with current TM pain were compared with 44 age-matched controls without such pain. Study participants were examined for general health status, additional pain sites (back, abdomen, and head) in the previous month, and depression, using a 15-item German-language depression questionnaire. Cases had a statistically significant higher average depression score than controls (14.2 +/- 7.1 vs. 9.7 +/- 6.3; t test, p < 0.01), and they reported more often additional pain. The more pain sites were mentioned, the higher was the depression score [no pain, 4.0 +/- 2.8; four pains, 17.3 +/- 8.0; analysis of variance (ANOVA), p < 0.001]. We conclude that TM pain assessment among adolescents should include a whole-body pain drawing as well as a screening questionnaire to identify pain-related depressive symptoms.

Small unilateral jaw gap variations: equilibrium changes, co-contractions and joint forces.

After complex prosthetic reconstructions, small differences in vertical distances between the left and right side of the jaw may occur during jaw closing, nevertheless providing bilateral tooth contacts in intercuspation by small deformations of the mandible. Their effects on the co-contraction of the masticatory muscles, the temporomandibular joint reaction forces, and the point of application of the resultant bite force vector in the maxillary occlusion plane - the so-called reduction point - have not been investigated, thus far simultaneously in one sample. The main goal of this study was to investigate variations of these measures in an experimental intercuspation simulated by one anterior and two posterior force transmission points.

[Suggestion for a classification of odontalgias]. / Vorschlag einer Klassifikation der Odontalgien.

BACKGROUND: Toothache prevalence in the overall population is considerable. However, for clinical purposes, the classification schemes available do not appear to be sufficiently sophisticated. Moreover, not all known forms of dental pain are considered. A refined classification that meets current standards is therefore introduced. To facilitate diagnosis, the characteristic features of the various types of odontalgia are summarized. RESULTS: The new classification differentiates among seven different origins of pain: 1. dentinal pain (originating from the pulpal tissues), 2. pulpal pain (originating from the pulpal tissues), 3. periodontal pain, 4. alveolar-osseous pain, 5. atypical odontalgia, 6. heterotopic dental pain, 7. odontalgia associated with primary psychosocial factors. CONCLUSIONS: In our opinion, the proposed classification differentiates among the different forms of odontalgia more precisely than all previous ones. However, its viability and advantages over other available classification schemes still need to be verified in daily practice.