1. Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, PR China;
2. Department of Preventive Dentistry, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, Amsterdam, the Netherlands;
3. Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, PR China