Design of mandibular advancement devices using an evolutionary algorithm.

Abstract

Sleep apnea is a disorder in which breathing is interrupted during sleep [1]. The most common type is obstructive sleep apnea (OSA), in which there is a partial or complete collapse of the upper airway during sleep. Patients with sleep apnea suffer from excessive daytime sleepiness and are at increased risk of developing cardiovascular diseases such as arrhythmias, heart failure and stroke [2]. The main treatments for OSA are Continuous Positive Airway Pressure (CPAP), surgery and Mandibular Advancement Devices (MAD). CPAP is a machine that, by means of a facial or nasal mask, produces a constant positive air pressure in the upper airway, preventing its collapse. The most commonly used surgery removes excess soft tissue from the throat to enlarge the airway. MADs advance the jaw to open the airway and can be either monoblock or two-piece devices. The latter, which are composed of two splints that are fixed to the mandible and maxilla respectively, are more comfortable, as they allow patients to open the mouth. There are different systems for connecting the two splints of these devices, such as bars, screws, telescopic rods or lateral fins, among others. However, not all of these systems keep the lower jaw in a forward position when opening the mouth, producing a retrusion that can lead to collapse of the upper airway. Furthermore, the kinematic behavior of the mechanism formed by the jaw-device assembly depends on the patient's morphology. This means that, when opening the mouth, there are devices that can protrude the mandible in some patients, while retracting it in others. This work studies the behavior of one of the best-known MADs on the market, in which both splints are connected by means of bars. For this purpose, a kinematic model of the maxilla-device assembly has been developed. Then, an evolutionary algorithm has been used to obtain the dimensions that ensure the correct behavior of the MAD.