Introduction

obstructions of the upper airway, arousals, OSA
OBSTRUCTIVE SLEEP APNEA
Obstructive sleep apnea (OSA) is characterized by recurrent obstructions of the upper airway, often resulting in oxygen desaturations and arousals from sleep [Continuous positive airway pressure (CPAP) is the most efficacious therapy for OSA [There is a large variety of commercially available customized MADs. Over the years, the customized MAD has evolved from the “mono-bloc” type of appliance, which consists of a single piece giving the mandible a fixed position, towards the current “bi-block titratable” type, which consists of two separate pieces that are dynamically interconnected allowing different degree of lateral and/or vertical movements. Understanding the treatment efficacy and working mechanism of MADs with different design features has an ongoing interest in the clinic [Bi-block titratable MADs may differ in the freedom of mandibular vertical opening. There are two types of bi-block titratable MADs that are commonly used in the treatment of OSA: the Herbst appliance (MAD-H) and the SomnoDent appliance (MAD-S). They predominantly differ in the freedom of vertical opening: the MAD-H only allows limited vertical opening, while the MAD-S allows free vertical opening of the mandible during sleep. A retrospective study suggested no significant difference between MAD-H and MAD-S in changing the AHI [The working mechanism of MAD is related to the improvement of the upper airway dimensions through mandibular protrusion [We hypothesized that MAD-H (allowing limited vertical opening) would lead to better improvement in respiratory parameters and upper airway dimensions compared to MAD-S (allowing free vertical opening), especially in supine position. This hypothesis was based primarily on the notion that gravity may promote more mandibular opening in the MAD-S group in the supine position, which subsequently results in less improvement of the upper airway CSAmin [