Article History
Received: 11 March 2018
Accepted: 23 October 2018
First Online: 8 November 2018
Compliance with ethical standards
:
: The authors declare that they have no conflicts of interest.
: Ethics approval was gained from the Medical Ethical Committee of School of Stomatology, Shandong University (Protocol Number: GR201603).
: The signed information consent forms were acquired from all individuals who were informed of the research proposal.