Theories on possible temporal relationships between sleep bruxism and obstructive sleep apnea events. An expert opinion

Background Sleep bruxism (SB) is a term covering different motor phenomena with various risk and etiological factors and potentially different clinical relevance, especially as far as its possible protective role against obstructive sleep apnea (OSA) is concerned. The present expert opinion discusses the possible temporal relationships between the two phenomena. Methods Four hypothetical scenarios for a temporal relationship may be identified: (1) the two phenomena are unrelated; (2) the onset of the OSA event precedes the onset of the SB event within a limited time span, with SB having a potential OSA-protective role; (3) the onset of the SB event precedes the onset of the OSA event within a limited time span, with SB having an OSA-inducing effect; and (4) the onset of the OSA and SB event occurs at the same moment. Results Literature findings on the SB-OSA temporal relationship are inconclusive. The most plausible hypothesis is that the above scenarios are all actually possible and that the relative predominance of one specific sequence of events varies at the individual level. SB activity may be protective against OSA by protruding the mandible and restoring airway patency in those subjects who benefit from mandibular advancement strategies or may even be related to OSA induction, as a consequence of airways’ mucosae swelling resulting from a SB-induced trigeminal cardiac reflex. Conclusions Clinicians should keep in mind that the SB-OSA relationship is complex and that interindividual differences may explain the possible different SB-OSA relationships, with particular regard to the anatomical site of obstruction

Neurobiology of Sleep-Related Movements

Sleep-related movements comprise a broad spectrum of simple and usually stereotyped movements that are sometimes associated with sleep disturbance (insomnia, sleep fragmentation, and non-restorative sleep). They may represent a physiological variant or a sleep disorder, depending on their intensity, frequency, and associated sleep disruption degree. Sleep-related movements involve usually the lower limbs; they can be idiopathic or associated with other sleep disorders, neurological disease, and medical condition or occur as a consequence of drug use. Several pathophysiological hypotheses have been proposed, but for the majority of these disorders, the neurobiological mechanism is far from being completely understood. Further studies are needed to elucidate the pathophysiology of sleep-related movements in order to better appreciate their clinical significance. This chapter describes the neurobiology of sleep-related movements, namely, periodic limb movements, alternating leg muscle activation, hypnagogic foot tremor, high-frequency myoclonus, excessive fragmentary myoclonus, propriospinal myoclonus at sleep onset, neck myoclonus during sleep, sleep bruxism, sleep-related rhythmic movement disorder, sleep-related leg cramps, and sleep starts. We also present a mechanistic model of the potential role of the spinal central pattern generator for locomotion in generating the leg movements