TU Xiao-li, LIU Hong-wei, LI Cai-liang, REN Xiao-hua Department of Stomatology, Zhujiang Hospital, Southern Medical University, Guangzhou 510282, China; Department .of Stomatology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China; Department of Stomatology, Guangdong Headquarter Hospital of Chinese People’s Armed Police Forces, Guangzhou 510516, China; Department of Stomatology, 458 Hospital of PLA, Guangzhou 510293, China