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We investigated the impact of tongue-thrusting on lingual pressure during fluid intake with a straw. In this study, 12 healthy young dentate individuals (two women and 10 men; 19-33 years) were instructed to drink 15 mL of water with a regular drinking straw at 37 °C, when indicated by the investigator. Participants drank after adjusting tongue position to one of the following patterns: (i) Holding the tip of the straw between the lips (Normal Position: NP), (ii) Sticking out the tongue to the vermilion zone of the lower lip and inserting the straw 1 cm past the front teeth (Tongue-thrusting Position: TP). Five recordings were conducted for each participant in a randomised order. To measure tongue pressure during swallowing, a specially designed 0·1-mm thick sensor sheet (Nitta, Osaka, Japan) with a tactile system for measurement of pressure distribution (I-SCAN; Nitta) was used. Duration, maximal magnitude and integrated value of tongue pressure were analysed based on the wave of tongue pressure recorded while water was swallowed. Magnitude, duration and integrated value of tongue pressure were significantly lower in TP than in NP at the median line (Ch1-3). Magnitude and integrated value of tongue pressure at the lateral part of the tongue (Ch5) were significantly lower in TP than in NP. When duration, maximal magnitude and integrated values were compared by channel, no significant differences were observed in NP, but a significant difference was found between Ch3 and the lateral areas Ch4/Ch 5 in TP. When the tongue was thrust forward, movement dynamics of the entire tongue changed and influenced contact between the tongue and palate during liquid intake with a straw. The impact was noticeably weaker on the median line than in lateral areas. [ABSTRACT FROM AUTHOR]

Parafunctional habits, such as prolonged clenching and bruxism, have been associated with dysfunctional overloading in the temporomandibular joint ( TMJ). In this study, stress distributions in the TMJ were analysed during prolonged clenching, using three-dimensional finite element ( FE) models of the TMJ with and without disc displacement. The aim of this study was to investigate stress distribution of the cartilaginous tissues in the TMJ with and without disc displacement. Finite element models were developed on the basis of magnetic resonance images from two subjects with and without anterior disc displacement. Condylar movements recorded during a 5-min clenching were used as the loading condition for stress analysis. In the asymptomatic model, the highest von Mises stresses were located in the lateral area (4·91 MPa) of the disc surfaces, and after 5-min clenching, the higher stresses were still located at the lateral area (3·65 MPa). In all the cartilaginous tissues, 30-50% of stress reduction occurred during 5-min clenching. In contrast, the von Mises stress in the cartilaginous tissues of the symptomatic model with disc displacement was markedly lower, compared with the asymptomatic model. However, in the condylar cartilage, stress relaxation during clenching was not recognised. Furthermore, relatively high stresses were observed in the retrodiscal tissues throughout clenching. The present results indicate that disc position could be involved in the stress distribution of the TMJ components during prolonged clenching. [ABSTRACT FROM AUTHOR]

Summary Clinicians and investigators need a simple and reliable recording device to diagnose or monitor sleep bruxism (SB). The aim of this study was to compare recordings made with an ambulatory electromyographic telemetry recorder (TEL-EMG) with those made with standard sleep laboratory polysomnography with synchronised audio-visual recording (PSG-AV). Eight volunteer subjects without current history of tooth grinding spent one night in a sleep laboratory. Simultaneous bilateral masseter EMG recordings were made with a TEL-EMG and standard PSG. All types of oromotor activity and rhythmic masseter muscle activity (RMMA), typical of SB, were independently scored by two individuals. Correlation and intra-class coefficient (ICC) were estimated for scores on each system. The TEL-EMG was highly sensitive to detect RMMA (0·988), but with low positive predictive value (0·231) because of a high rate of oromotor activity detection (e.g. swallowing and scratching). Almost 72% of false-positive oromotor activity scored with the TEL-EMG occurred during the transient wake period of sleep. A non-significant correlation between recording systems was found ( r = 0·49). Because of the high frequency of wake periods during sleep, ICC was low (0·47), and the removal of the influence of wake periods improved the detection reliability of the TEL-EMG (ICC = 0·88). The TEL-EMG is sensitive to detect RMMA in normal subjects. However, it obtained a high rate of false-positive detections because of the presence of frequent oromotor activities and transient wake periods of sleep. New algorithms are needed to improve the validity of TEL-EMG recordings. [ABSTRACT FROM AUTHOR]

Awake bruxism is defined as the awareness of jaw clenching. Its prevalence is reported to be 20% among the adult population. Awake bruxism is mainly associated with nervous tic and reactions to stress. The physiology and pathology of awake bruxism is unknown, although stress and anxiety are considered to be risk factors. During sleep, awareness of tooth grinding (as noted by sleep partner or family members) is reported by 8% of the population. Sleep bruxism is a behaviour that was recently classified as a ‘sleep-related movement disorder’. There is limited evidence to support the role of occlusal factors in the aetiology of sleep bruxism. Recent publications suggest that sleep bruxism is secondary to sleep-related micro-arousals (defined by a rise in autonomic cardiac and respiratory activity that tends to be repeated 8–14 times per hour of sleep). The putative roles of hereditary (genetic) factors and of upper airway resistance in the genesis of rhythmic masticatory muscle activity and of sleep bruxism are under investigation. Moreover, rhythmic masticatory muscle activity in sleep bruxism peaks in the minutes before rapid eye movement sleep, which suggests that some mechanism related to sleep stage transitions exerts an influence on the motor neurons that facilitate the onset of sleep bruxism. Finally, it remains to be clarified when bruxism, as a behaviour found in an otherwise healthy population, becomes a disorder, i.e. associated with consequences (e.g. tooth damage, pain and social/marital conflict) requires intervention by a clinician. [ABSTRACT FROM AUTHOR]