Mandibular advancement devices prevent open mouth snoring. They do so by preventing the palatal tissue in the mouth prevent from vibrating, which, in turn, prevents snoring. Open mouth snoring occurs frequently (according to our experience it accounts for up to about 40% of all snoring cases). Important: In order to use a mandibular advancement device, the nasal passages must be free. Nasal dilators or a nasal douche can clear the nasal passages.