## 2 Related Literature  
In the healthcare industry and business sectors, many innovations for global well-being are being developed as biosensor embedded solutions for enhancing health and wellness. The most commonly applied areas are wristband types, such as smartwatches [13] and ring types [14]. There are many other variations to monitor the health status of users/patients, but intraoral appliance-embedded healthcare solutions have rarely been addressed in previous research.  
For example, [PERSON] et al. demonstrated a sensor-embedded oral appliance to monitor the airway [1]. They fabricated maxillary and mandibular oral appliances from 2 mm thick resin plates using pressure welding. The activity of the left genioglossus (GG) was recorded using two silver ball electrodes attached to the lingual edge of the mandibular oral appliance. Respiratory status and right masseter muscle activity were measured using an airflow sensor and surface electrodes, respectively. Their attempts to apply sensors to oral appliances were impressive, although this solution was only designed for experimental purposes and not for practical purposes.  
[PERSON] et al. [15] developed a flexible surface acoustic wave respiration sensor for monitoring obstructive sleep apnea syndrome. They demonstrated the potential for flexible microsensors for monitoring OSA. [PERSON] et al. [16] also developed a smart system for monitoring apnea episodes in domestic environments with a sound sensor. Their proposed system consisted of a sound sensor, a vibrating element, and a microcontroller to process the collected data to detect OSA during sleep.  
Some wearable-sensor-related researches targeted animal testing also. [PERSON] et al. [17] evaluated live mutton sheep during transportation based on a wearable multisensor system. More up-to-date literature review about the development of sensors are viewable from a review by [PERSON] and [PERSON] [18]. They systematically focused on applications of wearable sensors divided into (a) biophysical tracking, (b) biochemical monitoring, and (c) detection of real-time data.  
[PERSON] et al. [19] developed a measuring system for 3D movement of the denture during function. The system for measuring denture movement consisted of an inertial measurement unit (IMU), a control unit, and a Bluetooth module. The IMU contained a three-axis gyroscope, a three-axis accelerometer, and a three-axis digital compass. The IMU was embedded in a self-curing acrylic resin. An important point of their research was that they successfully embedded several sensors despite the limited space allowed in dentures. They proposed a prototype that may serve as a future diagnostic appliance, such as occlusal examination in a denture, but this was also not developed to a practical level.  
On the other hand, the current research proposes a multisensor embedded OSA monitoring intraoral appliance device, specially targeted for MAD prototypes. Compared to the recent research outlined above, our research was fully designed and tested for practical use. In addition, our proposed solution holds the highest number of embedded sensors known in all oral appliance-related studies thus far, which makes this research more unique considering the fact that MAD devices allow even less space tolerance, compared to normal dentures.