Author Description

During sleep, the sudden and repetitive appearance of jaw muscle contractions is termed "rhythmic masticatory muscle activity" (RMMA). RMMA is found in normal sleepers and in patients who also exhibit tooth-grinding during sleep, i.e. sleep bruxism (SB). The consequences of SB are occasional facial pain or jaw dysfunction, headache and tooth damage. However, the pathophysiology of SB is unknown. Therefore, the objectives of the present thesis were to: (1) investigate further the role of cortical events (e.g., K complexes) in the genesis of SB; (2) determine whether a sequence of events dominates in association with the appearance of RMMA-SB activity (e.g., whether brain, heart and muscles are activated simultaneously or sequentially); (3) test whether experimentally induced sleep arousal could trigger SB and tooth grinding, in order to challenge the view that SB is secondary to sleep arousal; (4) assess whether jaw muscle excitability is increased or depressed during sleep. Methods included sleep laboratory polygraphic recordings of brain, heart and jaw muscle activities in order to quantify ongoing RMMA and SB in relation to wake and sleep states in humans. Sleep-related jaw muscle excitability was studied in monkeys.The main results were: (1) the density of cortical K complexes is 2--3 X lower in SB patients than in control subjects; (2) the presence of RMMA-SB in sleep is secondary to the occurrence of micro-arousal that is characterized, in sequence, by the onset of activity in brain and heart, then contractions of the jaw-closing muscles that are coupled with tooth grinding; (3) the use of a vibrotactile stimulation induces RMMA and tooth grinding in 71% of trials in SB patients only; (4) jaw muscle excitability is depressed during sleep in monkeys. In conclusion, these data support the hypothesis that RMMA and SB are secondary to sleep arousal rather than a rise in trigeminal motoneuronal excitability during sleep. Moreover, these findings provide new insights into the pathophysiology of SB by revealing the importance of the physiological mechanisms underlying sleep and arousal as opposed to external factors which traditionally have been emphasized in its pathophysiology, i.e., stress and dental occlusion.