###### Abstract  
Anxiety in dental patients has caused inconvenient experiences during their dental visits due to the noise generated by the dental handpiece. High-frequency sounds generated by the handpiece have been challenging to reduce using the active control method that targets low-frequency sounds, as well as the difficulty in applying the noise control method using sound-absorbing materials, because the size of the handpiece is small. As an alternative, a method that can reduce noise and provide stability by playing music to patients is being studied. However, in most studies, there are inconveniences such as the need to turn the music volume higher to cover dental handpiece noise or having to wear headphones to play music. In this study, in order to reduce this inconvenience and optimize the noise reduction effect of music, we propose a technology that converts music into sound masking and a unit chair equipped with a bone conduction speaker that plays music, and through clinical trials with 35 patients, it was confirmed that the proposed system made the patients emotionally stable. In addition, by analyzing the causes of these emotional changes, it suggests that the preferred genre of music by patients should also be considered. sound masking; handpiece noise; unit chair; noise reduction; notch filter +
Footnote †: journal: Medical  
Applying the passive noise reduction method to dental handpiece noise management is challenging because passive materials need to be thicker and heavier [3]. Active noise control techniques are useful for reducing low-frequency noise [4], but they are challenging to implement for high-speed dental handpieces [5]. The direct noise reduction method therefore requires extensive studies taking into account the complicated characteristics of the handpiece noise. There is research that demonstrates the benefits of playing music to patients in reducing noise and anxiety [6; 7; 8]. Another study used music through speakers or a headset as a way to intervene in dental anxiety in patients [9]. However, various drawbacks were discovered in order for patients to receive indirect noise reduction effects, including the need for louder music than the sound of the dental handpiece, the need for the patients to wear headphones, and the disruption of patient and doctor communication [10]. In this study, we propose a sound masking technology specialized for dental handpiece noise to improve the psychological noise reduction effect through music. In the proposed system, a bone conduction speaker was mounted on the headrest so that the patient could listen to music immediately after lying on the unit chair, and sound masking technology was applied to the music to control the noise of the dental handpiece. The unit chair is a chair on which a patient can lie down to receive dental treatment and is equipped with various parts such as a dental handpiece and a dental operation light, but the possibility of using the headrest as a part of it has not been studied except for when the patient's head is rested [11]. Sound masking is a process in which an initial sound (called maskee) is overlaid with another sound (called masker) that can eliminate its component to make it less recognizable, affecting the auditory nerve stimulation of a person. Sound masking has been investigated and applied from insulating private office rooms [12] to masking industrial noise [13], but none yet for the noise generated by the dental handpiece. Sound masking technology can be divided into simultaneous masking (SM), which is a frequency-domain masking, and temporal masking (TM), which is a time-domain masking [14]. SM is a method in which the maskee sound and the masker sound are presented at the same time to shield the maskee sound, and TM is a method in which the other sound (maskee) in front or behind is shielded through a sudden sound stimulus (masker). Because music can be used as a masker due to the characteristics of continuous sound, the SM method was applied in this study.