Tooth contact patterns during stimulation of the rabbit brain

Neurobiological mechanisms involved in sleep bruxism

Sleep bruxism (SB) is reported by 8% of the adult population and is mainly associated with rhythmic masticatory muscle activity (RMMA) characterized by repetitive jaw muscle contractions (3 bursts or more at a frequency of 1 Hz). The consequences of SB may include tooth destruction, jaw pain, headaches, or the limitation of mandibular movement, as well as tooth-grinding sounds that disrupt the sleep of bed partners. SB is probably an extreme manifestation of a masticatory muscle activity occurring during the sleep of most normal subjects, since RMMA is observed in 60% of normal sleepers in the absence of grinding sounds. The pathophysiology of SB is becoming clearer, and there is an abundance of evidence outlining the neurophysiology and neurochemistry of rhythmic jaw movements (RJM) in relation to chewing, swallowing, and breathing. The sleep literature provides much evidence describing the mechanisms involved in the reduction of muscle tone, from sleep onset to the atonia that characterizes rapid eye movement (REM) sleep. Several brainstem structures (e.g., reticular pontis oralis, pontis caudalis, parvocellularis) and neurochemicals (e.g., serotonin, dopamine, gamma aminobutyric acid [GABA], noradrenaline) are involved in both the genesis of RJM and the modulation of muscle tone during sleep. It remains unknown why a high percentage of normal subjects present RMMA during sleep and why this activity is three times more frequent and higher in amplitude in SB patients. It is also unclear why RMMA during sleep is characterized by co-activation of both jaw-opening and jaw-closing muscles instead of the alternating jaw-opening and jaw-closing muscle activity pattern typical of chewing. The final section of this review proposes that RMMA during sleep has a role in lubricating the upper alimentary tract and increasing airway patency. The review concludes with an outline of questions for future research.

Electromyographic assessment of non-functional masseter muscle in an awake animal model

Non-functional activities, such as bruxism, have been implicated in the development of temporomandibular disorders (TMD). It would be of value to have an animal model in which to investigate the processes underlying such disorders. The aim of this study was to determine the electromyographic (EMG) characteristics of experimentally induced, non-functional activity in the jaw-closing muscles of awake, behaving rats and how the EMG characteristics differed from those found under normal conditions. In the same animals, chronic EMG recordings were made prior to and following the insertion of an occlusal cap, which induced non-functional activity. A characteristic EMG pattern was found only during non-functional activity. The durations and amplitudes of the EMG bursts during this activity were significantly different statistically from those found in the same animals under normal conditions.

Bruxism: a review of the literature. Part I

A review of the literature on bruxism--a condition which has been clinically recognized since the late nineteenth century--is presented. It will be seen that there is not complete agreement on the definition of this activity, and its aetiology and treatment remain controversial.