Mandibular advancement works in two distinct ways: to reduce air turbulence caused by airway obstruction, and to inhibit collapse of the upper airway. By moving the jaw progressively forward, mandibular advancement pulls the tongue and other connected tissues forward. This creates more space between the base of the tongue and the epiglottis. Advancement of the jaw acts on the muscles of the velopharynx and the cross-sectional shape of the upper airway. In a majority of patients, it will increase the calibre (or tone) of the velopharynx musculature, making it less prone to collapse. Various studies have shown that mandibular advancement:
- Tightens the soft tissues of the pharynx’s lateral walls. This reduces air turbulence and the soft tissue vibration that causes snoring.
- Activates the genioglossus muscle and increases airway muscle tone.
- Changes pharyngeal pressures to normalize the physiological properties of the upper airway.
Clinical evidence that oral devices reduce snoring
Hoffstein concluded: Oral devices are beneficial in reducing snoring in the majority of patients. All of the randomized, placebo-appliance-controlled studies except one found significant reduction in snoring, independently of whether it was assessed objectively or subjectively. The Hoffstein review identified 89 publications dealing with oral device therapy involving a total of 3,027 patients between 1982 and 2006. It was found that the success rate, defined as the ability of oral devices to reduce apnoea/hypopnoea index to less than 10, was 54%. Snoring was reduced by 45%.
Ahrens et al: The Ahrens review identified 116 studies dealing with oral device therapy between 1982 and 2009. In concluded that, all types of oral devices investigated were effective in terms of improving AHI or RDI supporting the findings of Hoekema et al. (2004) that adjustable oral devices are generally effective irrespective of their various design features. Non-adjustable devices have poor evidence of effectiveness.
Serra-Torres: The Serra-Torres review focused solely on high level studies and meta-analyses and identified 22 between 2006 and 2016. It concluded that using oral devices helps to prevent snoring and excessive daytime sleepiness, reduce AHI significantly, and bring about beneficial changes in the upper airway. Adjustable and custom-made mandibular advancement devices give better results than fixed and prefabricated appliances. Monobloc devices give rise to more adverse events, although these are generally mild and transient.