The role of dentistry in the field of sleep medicine…are we respecting the physiology?

Abstract

Dentistry plays an extremely important role in sleep medicine, not only in treatment, but also in first-line recognition of the clinical signs, and screening for, sleep disordered breathing. Along with obesity, the incidence of sleep apnea is on the rise, yet it is both under-diagnosed and under-treated. 1 Much of the healthcare budget and resources are spent managing the comorbidities associated with sleep apnea, yet the underlying problem remains undiagnosed. 2 Thankfully, awareness is increasing among the medical and dental professions and the public alike, and one day the future may not equal the past. There is no higher priority for the body than to breathe. We can survive days without food or water, but only minutes without oxygen. The state of sleep, although an active process, relies entirely on physiological autonomic processes to survive. One of the fundamental drivers underlying the pathophysiology of obstructive sleep apnea is the upregulation of the sympathetic nervous system that occurs in response to the struggle to maintain a patent airway. 3 The physiology cannot be escaped. The autonomic nervous system, that fine balancing act between the sympathetic (stress response) nervous system and the parasympathetic (rest and recovery) nervous system, hums away in the background, working hard to maintain homeostasis, the status quo . There are tight physiologic boundaries 4 within which the body must remain to maintain health, and the autonomic nervous system is constantly monitoring afferent sensory input from a myriad of sources to conserve that balance. A reasonable analogy would be all the micro-adjustments a tight-rope walker needs to be constantly making in order to successfully reach the other side. A failure to maintain balance (homeostasis) has dire consequences. The rules that guide the scoring of events throughout a sleep study can tend to sugarcoat the underlying complexity of what is actually happening during frank apnea events and increased upper airway resistance. Somers has shown that even momentary micro-arousals, ones that would not register on the scoring of a sleep study, result in an autonomic response that causes a transient elevation in blood pressure and an upregulation of sympathetic nerve activity. 5 The stress response is critical to survival. Its role is to respond to a challenge, then switch off. 6 The problem is when the sensory input becomes barraged with challenges, as occurs with sleep disordered breathing, the switch is on more than it is off and the sympathetic nervous system becomes upregulated. 7 In this process, the tight physiological boundaries become re-set to maintain a new homeostasis, albeit a pathological one. The baroreceptors accept higher blood pressure as being the new norm, 8 the chemoreceptors accept elevated carbon dioxide levels, and even the muscles fibers that support the pharyngeal airway undergo plastic change from the slow to fatigue Type I fibers, to fast to respond but also fast to fatigue Type II fibers. 10 Everything changes because of the need for physiological economy and homeostasis. So what does this have to do with dentistry? Everything. Our role is not only to provide jaw support to help maintain a patent airway, but just as importantly, to turn down the sympathetic nervous system, which is fundamental to the pathophysiology underlying the health consequences associated with sleep apnea. It may sound confronting, but it is actually quite a basic principle. The autonomic nervous system, like gravity, is pervasive. We may not think about it, but it’s still there, and there will be a physiological response, good or bad, to whatever treatment we provide. Sir Charles Sherrington, 1932 recipient of the Nobel Prize in physiology and medicine, first described the avoidance reflexes to flex away from an aberrant input, which lead to postural compensatory adjustments throughout the entire musculoskeletal system. 11 Dr. Correspondence to: A-M Cole. Email: ammiec@yahoo.com