## 1 Introduction  
Considered the most common form of sleep obstruction, obstructive sleep apnea (OSA) is a life-threatening health anomaly that many people suffer from today. It is characterized by repeated pharyngeal airway collapse during sleep [1], which means that subjects' breathing frequently pauses while asleep, sometimes for minutes. Bruxism is another symptom that negatively affects sleep quality by significantly harming teeth and damaging temporomandibular joints (TM) [2].  
Lack of sleep hinders focus and concentration during the day, causes chest pain upon waking up [3], causes morning headaches [4], and is a factor in many psychological symptoms such as depression, anxiety, or excessive irritability [5], and even death [6].  
Continuous positive airway pressure (CPAP) treatment is the most commonly used method to treat OSA. It has proven to be the most effective way to prevent sleep obstruction because research has shown that subjects with OSA have significantly greater activity reductions in airway muscles than normal people [7, 8]. A facemask is connected to a machine via a tube and positive airway pressure is mechanically pushed directly into the mouth to keep the airways open (Figure 1).  
However, the problem with this universally accepted method is that it is simply too obstructive. In fact, an in-depth study concerning the effect of CPAP on sleep apnea syndrome revealed that patients showed discontent regarding CPAP because the device that was designed to enhance sleep quality paradoxically hindered sleep because it was too \"bothersome\" [9]. This naturally led to insufficient compliance rates; [PERSON] et al. [10] proved that after months of compliance test results, only very severely affected patients adhered to CPAP devices until the end of the study period.  
As a result, many alternative devices have been developed, such as the mandibular advancement device (MAD), which increases the airway diameter with soft tissue displacement achieved by mandibular protrusion [11]. It is a much smaller form of the oral device, compared to CPAP, which resembles the form of a mouthguard commonly used in sports (Figure 2). This oral device is also known to prevent bruxism in the absence of a CPAP device. A critical problem still persists with MAD in that there is still ongoing debate about the device's actual effectiveness in treating OSA. Many uncertainties regarding MAD have prevented comparably comfortable devices from becoming more widespread clinical sleep treatment services.  
Figure 1: CPAP device for treating OSA.  
Figure 2: MAD [12] for treating OSA.  
Therefore, this research proposes s-Guard: a multisensor embedded OSA monitoring intraoral appliance device specifically targeted for MAD prototypes. This research presents the unique design and development of the MAD-based model that enables sensors to be embedded and presents practical implementation results among institutional review board (IRB) approved subjects. Since this study targets OSA patients, relevant health information monitoring sensors such as temperature, gyroscope, accelerometer, and SpO\({}_{2}\) sensors were embedded. This research is expected to greatly motivate other sensors to be embedded in our proposed model for the application of other disease areas.