1 Department of Oral Hygiene, College of Dental Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
2 School of Dentistry, Chung Shan Medical University, Taichung, Taiwan; Department of Dentistry, Chung Shan Medical University Hospital, Taichung, Taiwan.
3 School of Dentistry, Chung Shan Medical University, Taichung, Taiwan; Department of Dentistry, Chung Shan Medical University Hospital, Taichung, Taiwan. Electronic address: cyc@csmu.edu.tw.