Sleep Medicine Reviews, Vol. 6, No. 3, pp 213–227, 2002 doi:10.1053/smrv.2001.0183, available online at http://www.idealibrary.com on SLEEP MEDICINE reviews CLINICAL REVIEW The significance of saliva during sleep and the relevance of oromotor movements Norman M. R. Thie 1 , Takafumi Kato 1, 3 , Gaby Bader 2 , Jacques Y. Montplaisir 3 and Gilles J. Lavigne 1, 3 1 University of Montreal, Faculte ´ de Me ´decine Dentaire, CP 6128 succursale Centre-ville, Montre ´al, Que ´bec H3C 3J7, Canada; 2 Institute of Clinical Neuroscience, University of Goteborg, 413 45 Goteborg, Sweden; 3 Sleep Study Center, Sacred Heart Hospital, 5400 Boulevard Gouin Ouest, Montre ´al, Que ´bec H4J1C5, Canada. KEYWORDS sleep, saliva, rhythmic masticatory muscle activity, sleep bruxism, xerostomia, gastric reflux Summary Saliva is an essential component of the oroesophageal milieu and allows for normal speech, taste, mastication, food bolus formation and swallowing. Saliva has important functions in protecting the hard and soft tissues of the oral cavity from acids and pathogenic microbes. A large number of people suffer either subjective or objective alterations in quantity and/or quality of their saliva that may be secondary to disease, medications, medical treatments or emotional events. Sleep-related xero- stomia is a sensation of dry mouth associated with a report of either mouth and/or throat discomfort that induces awakenings for water intake. The prevalence of self- reported dry mouth complaint during sleep (associated with awakening and water intake) in a Canadian survey was estimated at 23%. The biological significance of decreased saliva during sleep is unknown and it is unclear how the oral cavity compensates for this period of relative dryness. The amount of saliva produced is greatest during the waking hours of the day and diminishes dramatically during sleep and may represent another process in the human body that displays a circadian rhythmicity. Salivary secretion during wakefulness is, in part, associated with oromotor activity involving the masticatory muscles. Rhythmic masticatory muscle activity and swallowing are non-disruptive events that occur during normal sleep. We hypothesize herein that lubrication from saliva is necessary during sleep to protect tissue integrity and health of oroesophageal structures.  2002 Published by Elsevier Science Ltd appreciate something fully only once it is gone INTRODUCTION or if there have been changes to it. This certainly applies to saliva that may be diminished, eliminated Most healthy adults take for granted the saliva in or modified secondary to disease, medical in- their mouth and probably sense it only as a fluid terventions (e.g. head/neck radiotherapy), med- needing to be swallowed with a certain frequency ications or idiopathic processes. There can be each day. Like many things in life we tend to considerable oral discomfort and disease as- sociated with decreased salivary secretion. During the day, saliva is required to lubricate the oral Correspondence should be addressed to: Gilles J. Lavigne, tissues to aid in swallowing, speech, digestion, University of Montreal, Faculte ´ de Me ´decine Dentaire, taste and mastication in addition to protecting CP 6128 succursale Centre-ville, Montre ´al, Que ´bec H3C 3J7, the oral tissues, upper gastrointestinal tract and Canada. Tel: 514-343-2310; Fax: 514-343-2233; E-mail: gilles.lavigne@umontreal.ca dentition from acids and microbes [1–4]. Thus, 1087–0792/02/$ – see front matter  2002 Published by Elsevier Science Ltd