Received: 1 July 2018
Accepted: 28 January 2019
First Online: 4 February 2019
Ethics approval and consent to participate
: Ethical approval was granted by the institutional review board at the Dental Hospital of the Tokyo Medical and Dental University (No. D2015–600).
: Appropriate consent obtained.
: The authors declare that they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.