Funding for this research was provided by:
Grant-in-Aid from the Japanese Ministry of Education, Science and Culture (24593034)
Received: 21 August 2015
Accepted: 29 January 2018
First Online: 6 February 2018
: KH is assistant professor, TF is academic researcher and UY is professor in Department of Oral and Maxillofacial Surgery, Yamaguchi University Graduate School of Medicine, Ube, Japan.
: Institutional review board (IRB) approval from the ethical committee of the Yamaguchi University Hospital was obtained for this study (Ref H26–179). As this study was retrospective, informed consent was waived by the IRB.
: Not applicable
: The authors declare that they have no competing interests.
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