Funding for this research was provided by:
The authors acknowledge the grant from the 8020 Promotion Foundation
Received: 7 February 2021
Accepted: 1 April 2021
First Online: 30 April 2021
: This research was approved by the Ethics Committee of Nihon University School of Dentistry (No.2016-18).
: Not applicable
: Yoshiyuki Hagiwara, Tetsuo Ohyama, Hiroyasu Yasuda, Keisuke Seki and Takayuki Ikeda declare that they have no competing interests.