Performance of Mandibular Advancement Devices When Opening the Mouth

The aim of this study is to evaluate the kinematic behavior of mandibular advancement devices (MAD) when opening the mouth, by analyzing the influence of the coupling system between the splits and the patient's morphology.

Seven widely used MADs with different coupling mechanisms have been studied in 21 patients (8 females, 13 males). Using validated mathematical MAD models, one per tested device, the trajectories of the lower incisor and the posterior chin area (apophysis geni) were simulated for each device when opening the mouth.

The results show that all MADs maintain mandibular advancement with the mouth closed. However, significant variations occur when the mouth is opened. Devices with bars maintained mandibular advancement more effectively than those with fins, although performance depended on the bars' length and joints' position. In particular, shorter bars and more forward-positioned joints resulted in greater protrusion. Devices with fins consistently caused mandibular retrusion when opening the mouth.

It is not possible to reach general conclusions about the effectiveness of MADs by analyzing any device. Rather, the results obtained are for a specific MAD and may be different for another MAD model. The study also found that mandibular movement patterns differed according to patients' facial biotypes. The results suggest that both the coupling system and patients' morphology must be considered in the design of MADs to maintain effective mandibular advancement during mouth opening.