jun-ichiro kinoshita department of esthetic dentistry, school of dentistry, showa university, tokyo, japan hamid jafarzadeh dental research center, department of endodontics, faculty of dentistry, mashhad university of medical sciences, mashhad, ir iran; dental research center, department of endodontics, faculty of dentistry, mashhad university of medical sciences, p.o.box: 91735-984, mashhad, ir iran. tel: +98-5118829501, fax: +98-5118829500 atsufumi manabe department of esthetic dentistry, school of dentistry, showa university, tokyo, japan miki nozawa department of clinical cariology and endodontology, school of dentistry, showa university, tokyo, japan tokiko uchida department of clinical cariology and endodontology, school of dentistry, showa university, tokyo, japan paul vincent abbott school of dentistry, university of western australia, perth, australia