872 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 59, NO. 3, MARCH 2012 Toothbrushing Region Detection Using Three-Axis Accelerometer and Magnetic Sensor Young-Jae Lee, Student Member, IEEE, Pil-Jae Lee, Kyeong-Seop Kim, Wonse Park, Kee-Deog Kim, Dosik Hwang, and Jeong-Whan Lee*, Member, IEEE Abstract—Due to the possible occurrence of periodontal disease at an early age, it is important to have proper toothbrushing habits as early as possible. With this aim, the feasibility and concept of a smart toothbrush (ST) capable of tracing toothbrushing motion and orientation information was suggested. In this study, we pro- posed the advanced ST system and brushing region classification algorithm. In order to trace the brushing region and the orientation of a toothbrush in the mouth, we required the absolute coordinate information of ST. By using tilt-compensated azimuth (heading) algorithm, we found the inclination and orientation information of the toothbrush, and the orientation information while brushing inner tooth surfaces showed specific heading features that could be reliably discriminated from other brushing patterns. In order to evaluate the feasibility of clinical usage of the proposed ST, 16 brushing regions were investigated by 15 individual healthy sub- jects. The proposed ST system demonstrated 97.1%(±0.91) of the region detection accuracy and 15 brushing regions could be classi- fied. This study also showed that the proposed ST system may be helpful for dental care personnel in patient education and instruc- tion for oral hygiene regarding brushing habits. Index Terms—Accelerometer, magnetic sensor, oral hygiene, pattern classification, toothbrush, toothbrushing patterns, tooth- brushing regions. I. INTRODUCTION R ECENTLY, ubiquitous or pervasive healthcare [1] has emerged as a solution to handle the crisis in the health- care industry, including skyrocketing costs, a growing incident of medical errors, and the lack of insurance coverage in rural and underserved urban areas. Now, those within the healthcare Manuscript received June 5, 2011; revised September 5, 2011, and Octo- ber 26, 2011; accepted November 27, 2011. Date of publication December 22, 2011; date of current version February 17, 2012. This work was supported by the National Research Foundation of Korea funded by the Korea government (MEST) under Grant 2010-0027674. Asterisk indicates corresponding author. Y. J. Lee, P. J. Lee, and K. S. Kim are with the School of Biomedical Engineering, College of Biomedical & Health Science, Konkuk University, Chung-Ju 143-701, Korea (e-mail: zetzlyj@gmail.com; 4265623@naver.com; kyeong@kku.ac.kr). W. Park and K. D. Kim are with the Department of Advanced General Den- tistry, College of Dentistry, Yonsei University, Seoul 120-752, Korea (e-mail: wonse@yuhs.ac; kdkim@yuhs.ac). D. Hwang is with the School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea (e-mail: dosik.hwang@yonsei.ac.kr). *J. W. Lee is with the School of Biomedical Engineering, College of Biomed- ical & Health Science, Research Institute of Biomedical Engineering, Konkuk University, Chung-Ju 143-701, Korea (e-mail: jwlee95@kku.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TBME.2011.2181369 industry are under increasing pressure to provide better service to more people using limited financial and human resources. Based on these trends, healthcare technologies are now evolv- ing to reduce long-term healthcare costs and improve quality of life [2]. Among various diseases depending on lifestyle, gingivitis and tooth decay are diseases, which require preventive mea- sures and techniques. Nevertheless, even in the adult, inadequate toothbrushing styles can cause dental problems such as chronic gingivitis, gum disease, and so forth. There have been many convenient and automatic electronic toothbrushes available in the market; however, there are some skeptical points regarding efficacy and safety of electronic toothbrushes [3]. Recent studies showed that toothbrushing forces [4]–[9] did not provide effec- tive and qualitative ways of evaluating brushing styles such as motions of the brush head and the minimal duration of brush- ing, where it should be done, and so on. Therefore, it would be beneficial to the community in terms of both healthcare and eco- nomics if we could prevent dental health from deteriorating into worse conditions in the early stages. Improvement in educating society about dental health would reduce healthcare costs and improve quality of life. The concept of a smart toothbrush (ST) system capable of tracing brushing motion with respect to the dental arches was first proposed and described [10], [11]. From these preliminary studies, we found that the orientation of toothbrush provides distinguishable information such as the roll and heading an- gles of the toothbrush. The most important problem was the absolute heading information of the toothbrush with respect to a bust mirror in front of the examinee [11]. Even though we might restrict a rotational movement of the head, the location and the orientation of the human body while brushing one’s teeth are unpredictable. Thus, we need to estimate the abso- lute heading information of toothbrush. This kind of problem was well defined and explored in navigational devices in the telematics. The heading (azimuth) angle is defined as the angle between the North Pole and the direction of movement. Estimation of heading angle could be found in gyrocompassing [12], [13], GPS application [14], and magnetometry using a magnetic com- pass [15], [16]. Also, if we used gyro sensor for calculating the azimuth angle, the initial azimuth value and the gyro bias prob- lem would impose another complexity in our application. There- fore, if a two-axis magnetic sensor is placed on the horizontal plane, which is parallel with the Earth’s surface, the heading angle of the ST could be calculated accurately. Otherwise, a tilt error in the heading angle would be introduced. 0018-9294/$31.00 © 2012 IEEE