Received: 25 September 2020
Accepted: 21 December 2020
First Online: 8 April 2021
Ethics approval and consent to participate
: This cross-sectional study was approved by the Research Ethics Committee of Qingdao Stomatological Hospital and conducted according to the Declaration of Helsinki. Written informed consent was obtained from all participants prior the study begins.
: Not applicable.
: The authors declare that they have no competing interests.