Hans J. Schindler

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 Hills 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.

Long-term training effects on masticatory muscles.

Neuromuscular adaptations during skill acquisition have been extensively investigated for skeletal muscles. Motor rehabilitation is the main target for application of motor training. Such measures are also relevant for the musculature of the jaw, but few data are available for motor adaptation of the masticatory system. The objective of this study was to evaluate and compare long-term training effects of different motor tasks on masseter and temporal muscles. In 20 healthy subjects, the electromyographic response to unilateral and bilateral maximum voluntary tooth clenching, balancing the mandible on a hydrostatic system under force-feedback-controlled conditions, and unilateral chewing was investigated in an initial session and then in two follow-up sessions separated by 2 and 10 weeks from baseline. Motor tasks were repeated three times for chewing, nine times for maximum biting (MB) and 24 times for the coordination tasks (CT). The sequences of the various motor tasks were applied once in the first session and twice in the second and third sessions. No effects of training were observed for MB tasks except for MB in intercuspation, for which significant yet transient avoidance behaviour occurred in the second session. No significant effects were found for chewing tests. For the CT, however, a robust significant long-term training effect was detected which reduced the electric muscle activity in session 2 by approximately 20% and in session 3 by approximately 40% compared with the initial measurements. The study showed that the masticatory muscles are remarkably prone to motor adaptation if demanding CT must be accomplished.

[Recommendations for the standardized evaluation and classification of painful temporomandibular disorders: an update].

ZusammenfassungHintergrundIm Jahre 2000 veröffentlichte der Interdisziplinäre Arbeitskreis für Mund- und Gesichtsschmerzen in der Deutschen Gesellschaft zum Studium des Schmerzes Empfehlungen zur Diagnostik und Klassifikation von Patienten mit Schmerzen im Bereich der Kaumuskulatur und/oder Kiefergelenke. Ziele der vorliegenden Publikation sind eine Bestandsaufnahme und Aktualisierung der damals gemachten Vorschläge.ErgebnisseSichtung und Bewertung der nach Veröffentlichung der Empfehlungen erschienenen Fachliteratur (bis Dezember 2005) zeigen, dass sich das zweiachsige Stufenkonzept zur Erfassung somatischer und psychosozialer Parameter orofazialer Schmerzen bewährt hat. Einzelne Aspekte der Empfehlungen wurden in Form wissenschaftlicher Belege weiter konkretisiert.SchlussfolgerungenDie vorgeschlagenen Empfehlungen spiegeln die aktuellen Entwicklungen in der Schmerzmedizin wider. Insbesondere in der Zahnärzteschaft sollten sie daher eine noch breitere Verankerung finden als bisher.AbstractBackgroundIn 2000, the interdisciplinary Working Group of Orofacial Pain within the German Chapter of the IASP (German Association for the Study of Pain) published recommendations for the standardized evaluation and diagnostic classification of patients with painful masticatory muscles and/or temporomandibular joints. The purpose of the present study was to critically review and update these recommendations.ResultsAppraisal of the relevant literature published after the release of the recommendations (up to December 2005) shows that the two-axis approach for the assessment of the somatic and psychosocial parameters of the orofacial pain experience has found wide support. Single aspects of the recommendations have been substantiated by additional scientific evidence.ConclusionsThe recommendations reflect the current state of pain medicine. Therefore, they should be considered among practitioners who diagnose and manage patients suffering from temporomandibular disorders.

Aktualisierung der Empfehlungen zur standardisierten Diagnostik und Klassifikation von Kaumuskel- und Kiefergelenkschmerzen

ZusammenfassungHintergrundIm Jahre 2000 veröffentlichte der Interdisziplinäre Arbeitskreis für Mund- und Gesichtsschmerzen in der Deutschen Gesellschaft zum Studium des Schmerzes Empfehlungen zur Diagnostik und Klassifikation von Patienten mit Schmerzen im Bereich der Kaumuskulatur und/oder Kiefergelenke. Ziele der vorliegenden Publikation sind eine Bestandsaufnahme und Aktualisierung der damals gemachten Vorschläge.ErgebnisseSichtung und Bewertung der nach Veröffentlichung der Empfehlungen erschienenen Fachliteratur (bis Dezember 2005) zeigen, dass sich das zweiachsige Stufenkonzept zur Erfassung somatischer und psychosozialer Parameter orofazialer Schmerzen bewährt hat. Einzelne Aspekte der Empfehlungen wurden in Form wissenschaftlicher Belege weiter konkretisiert.SchlussfolgerungenDie vorgeschlagenen Empfehlungen spiegeln die aktuellen Entwicklungen in der Schmerzmedizin wider. Insbesondere in der Zahnärzteschaft sollten sie daher eine noch breitere Verankerung finden als bisher.AbstractBackgroundIn 2000, the interdisciplinary Working Group of Orofacial Pain within the German Chapter of the IASP (German Association for the Study of Pain) published recommendations for the standardized evaluation and diagnostic classification of patients with painful masticatory muscles and/or temporomandibular joints. The purpose of the present study was to critically review and update these recommendations.ResultsAppraisal of the relevant literature published after the release of the recommendations (up to December 2005) shows that the two-axis approach for the assessment of the somatic and psychosocial parameters of the orofacial pain experience has found wide support. Single aspects of the recommendations have been substantiated by additional scientific evidence.ConclusionsThe recommendations reflect the current state of pain medicine. Therefore, they should be considered among practitioners who diagnose and manage patients suffering from temporomandibular disorders.

Neuromuscular Interaction of Jaw and Neck Muscles During Jaw Clenching

AIMS To test the hypothesis that jaw muscles and specific neck muscles, ie, levator scapulae, trapezius, sternocleidomastoideus, and splenius capitis, co-contract at the different submaximum bite forces usually generated during jaw clenching and tooth grinding, and for different bite force directions. METHODS Bite-force transducers that measured all three spatial force components were incorporated in 11 healthy subjects. The test persons developed feedback-controlled submaximum bite forces in a variety of bite-force directions. The electromyographic (EMG) activity of the levator scapulae, splenius capitis, and trapezius muscles was recorded, at the level of the fifth cervical vertebra, by use of intramuscular wire electrodes. The activity of the sternocleidomastoideus and masseter muscles was recorded by surface electrodes. For normalization of the EMG data, maximum-effort tasks of the neck muscles were conducted in eight different loading directions by means of a special force-transducer system. Differences between neck-muscle activity during chewing, maximum biting in intercuspation, and the force-controlled motor tasks were compared with the baseline activity of the various muscles by one-way repeated-measures analysis of variance. RESULTS The results confirmed the hypothesis. Co-contractions of the neck muscles in the range of 3% to 10% of maximum voluntary contraction were observed. Significant (P < .05) activity differences were recorded as a result of the different force levels and force directions exerted by the jaw muscles. Long-lasting action potential trains of single motor units triggered by jaw clenching tasks were also detected. CONCLUSION The findings support the assumption of a relationship between jaw clenching and the neck muscle activity investigated. The low level of co-contraction activity, however, requires further study to elucidate possible pathophysiological interactions at the level of single motor units.

The effect of various jaw motor tasks on body sway.

Alterations of body sway caused by isometric contractions of the jaw muscles have been reported previously. The objective of this study was to test if motor tasks of the masticatory system with different control demands affect body posture differently during quiet stance. Position and sway displacements of the center of foot pressure (COP) were measured for 20 healthy subjects who either kept the mandible at rest or performed unilateral and bilateral maximum voluntary teeth clenching, feedback-controlled biting tasks at submaximum bite forces, or unilateral chewing. Two weeks later the measurements were repeated. Compared with quiet stance, the COP results revealed significant changes during the feedback-controlled biting tasks. Robust sway reduction and anterior displacement of the COP were observed under these conditions. Body oscillations were not significantly affected by maximum bites or by unilateral chewing. For most of the variables investigated there were no significant differences between unilateral and bilateral biting. Robust sway reduction during feedback-controlled biting tasks in healthy subjects involved a stiffening phenomenon that was attributed to the common physiological repertoire of posture control, and might optimize the stability of posture under these conditions.

Comparison of particle-size distributions determined by optical scanning and by sieving in the assessment of masticatory performance.

Aim of this study was to introduce a feasible and valid technique for the assessment of masticatory performance that is comparable to the standard sieving method. Twenty-one chewing samples (Optosil) comminuted by healthy dentate adults were analysed with a sieving and scanning method. Scanning was performed using a conventional flatbed scanner (1200dpi). All scanned images underwent image analysis (ImageJ), which yielded descriptive parameters such as area, best-fitting ellipse for each particle. Of the 2D-image, a volume was estimated for each particle, which was converted into a weight. To receive a discrete distribution of particle sizes comparable to sieving, five chewing samples were used to calculate a size-dependent area-volume-conversion factor. The sieving procedure was carried out with a stack of 10 sieves, and the retained particles per sieve were weighed. The cumulated weights yielded by either method were curve-fitted with the Rosin-Rammler distribution to determine the median particle size x(50) . The Rosin-Rammler distributions for sieving and scanning resemble each other. The distributions show a high correlation (0·919-1·0, n= 21, P<0·01, Pearsons correlation coefficient). The median particle sizes vary between 3·83 and 4·77mm (mean: 4·31) for scanning and 3·53 and 4·55mm (mean: 4·21) for sieving. On average, scanning overestimates the x(50) values by 2·4%. A modified Bland-Altman plot reveals that 95% of the x(50) values fall within 10% of the average x(50) . The scanning method is a valid, simple and feasible method to determine masticatory performance.

Anterior and posterior neck muscle activation during a variety of biting tasks

Bruxism may be involved in the aetiology of myofascial neck pain. The objective of this study was to test the hypothesis that anterior and posterior neck muscles co-contract during jaw clenching. Ten test subjects developed different feedback-controlled submaximum bite forces in a variety of bite-force directions by means of bite-force transducers. The electromyographic activity of the sternocleidomastoid and supra/infrahyoidal muscles, and of the semispinalis capitis, semispinalis cervicis, and multifidi muscles was recorded by use of surface electrodes and intramuscular wire electrodes, respectively. For normalization of electromyography data, maximum voluntary contraction tasks of the neck muscles were conducted in eight different loading directions. The results confirmed co-contraction of the neck muscles in the range of 2-14% of the maximum voluntary contraction at a bite force ranging from 50 to 300 N. Significant activity differences were observed as a result of the different force levels and force directions exerted by the jaw muscles. Long-lasting tonic activation of specific neck muscles triggered by the jaw-clenching tasks was also detected. These findings support the assumption of a relationship between jaw clenching and the activity of the neck muscles investigated. The low level of co-contraction activity, however, requires further study to elucidate possible pathophysiological interactions at the level of single motor units.

[Therapy of masticatory muscle pain: recommendations for clinical management].

ZusammenfassungMyalgien der Kiefermuskulatur sind die häufigsten nichtinfektiösen Beschwerden in der Kiefer-Gesichts-Region. Nach Zusammenfassung des aktuellen Kenntnisstands zur Physiologie, Ätiologie, Pathophysiologie, Diagnostik und Differenzialdiagnostik wird anhand einer Literaturrecherche der aktuelle Stand der therapeutischen Möglichkeiten dargestellt. Die Ergebnisse zeigen, dass bei der Mehrzahl der Patienten mit nichtinvasiven reversiblen Maßnahmen Schmerzlinderung bzw. -freiheit erreicht werden kann. Im Kurz- und Langzeitvergleich ergeben verschiedene Behandlungsverfahren vergleichbar gute Resultate. Bei chronischen Verläufen mit ausgeprägter psychosozialer Beeinträchtigung ist neben der Standardtherapie die Betreuung durch einen Psychotherapeuten conditio sine qua non.AbstractMyalgias of the masticatory muscles are the most frequent noninfectious complaints in the orofacial region. After summarizing the current knowledge on the physiology, etiology, pathophysiology, diagnosis, and differential diagnosis of masticatory muscle pain, we specifically focus on management recommendations. Results of an extensive literature search show that for the majority of patients pain reduction or pain relief can be achieved with noninvasive reversible methods. Longitudinal short- and long-term studies have revealed that different therapeutic measures are similarly effective. In patients with chronic masticatory myalgias associated with psychosocial impairment, however, additional involvement of a psychotherapist is crucial.

Jaw Clenching: Muscle and Joint Forces, Optimization Strategies

Realistic masticatory muscle and temporomandibular joint forces generated during bilateral jaw clenching are largely unknown. To determine which clenching directions load masticatory muscles and temporomandibular joints most heavily, we investigated muscle and joint forces based on feedback-controlled electromyograms of all jaw muscles, lines of action, geometrical data from the skull, and physiological cross-sectional areas acquired from the same individuals. To identify possible motor control strategies, we applied objective functions. The medial pterygoid turned out to be the most heavily loaded muscle for all bite directions. Biting with accentuated horizontal force components provoked the highest loading within the medial and lateral pterygoids. The largest joint forces were also found for these bite directions. Conversely, the lowest joint forces were detected during vertical biting. Additionally, joint forces with a clear posterior orientation were found. Optimization strategies with the elastic energy as objective function revealed the best fit with the calculated results.