1[2]Eriksen HM,Bjertness E.Prevalence of apical periodontitis and result of endodontic treatment in middle-aged adults in Norway.Endod Dent Traumatol,1991,7:1~4
2[3]Siquerira JF.Aetiology of root canal treatment failure:Why well-treated teeth can fail.Int Endon J,2001,34:1~10