Effectiveness of HERO 642 versus Hedstro ¨ m files for removing gutta-percha fillings in curved root canals: an ex vivo study B. Aydın 1 *, T. Ko ¨ se 2 & M. K. C ¸ alıs ¸ kan 1 1 Department of Restorative Dentistry and Endodontology, Ege University, _ Izmir; and 2 Department of Biostatistics and Medical Informatics, School of Medicine, Ege University, _ Izmir, Tu ¨ rkiye Abstract Aydın B, Ko ¨se T, C ¸ alıs ¸ kan MK. Effectiveness of HERO 642 versus Hedstro ¨ m files for removing gutta-percha fillings in curved root canals: an ex vivo study. International Endodontic Journal, 42, 1050–1056, 2009. Aim To compare the effectiveness of gutta-percha removal and the maintenance of canal anatomy when using the HERO 642 system or Hedstro ¨m files (H-files) in mandibular molar teeth. Methodology The root canals of 40 mandibular molar teeth were instrumented using H-files and filled with gutta-percha and sealer. After 1 year in storage, the roots were sectioned horizontally to provide apical, middle and coronal root thirds. Sections were photographed, and an individual muffle was pro- duced for each tooth. Teeth were randomly divided into four groups (n = 10) and the gutta-percha removed using either the HERO 642 system or H- files, with or without solvent. Digital images of the root canals were then re-taken. Root thirds were inspected for lateral perforations, and the percentage of the residual canal filling was determined on postoperative images. Transportation and centring ratio were calculated using preoperative and postop- erative images of the cross-sections of root thirds. Results H-files groups were associated with less filling material than the HERO 642 system (H-files–HERO 642 P = 0.056, H-files–HERO 642+solvent P = 0.041, H-files + solvent–HERO 642 P = 0.018, H-files + sol- vent–HERO 642 + solvent P = 0.016). The percentage of residual filling material was similar in the apical thirds, and the contribution of solvent to canal debride- ment was not statistically significant (P > 0.05). Perfo- ration occurred mesiobuccally in 48% of specimens in the apical sections of mesial roots. There were no significant differences for centring ratio, transportation and perforation rate between groups. Conclusions H-files left less gutta-percha overall; however, there was no difference in the apical third. The effect of solvent was not remarkable. Both instru- ment systems created a large number of perforations. Keywords: centring ratio, Hedstro ¨m files, HERO 642, mandibular molar teeth, retreatment. Received 7 December 2008; accepted 31 July 2009 Introduction Nonsurgical root canal retreatment requires complete removal of previous filling materials to enable disinfec- tion and the shaping of the canal system (Stabholz & Friedman 1988, Friedman et al. 1990). However, gutta-percha root fillings cannot be removed com- pletely (Bramante & Betti 2000, Masiero & Barletta 2005), especially from the apical third of the root canal (Masiero & Barletta 2005, Gergi & Sabbagh 2007). Correspondence: Berdan Aydın, DDS, PhD, Department of Restorative Dentistry and Endodontology, Dentistry Faculty, Ege University 009035100 Bornova, izmir, Tu ¨ rkiye (Tel.: +90 232 3880328; fax: +90 232 3880325; e-mail: berdan.aydin @mail.ege.edu.tr, berdansevinc@gmail.com). *Present address: Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607, USA (Tel.: +1 312 9968649; fax: +1 312 9960431; e-mail: berdans@uic.edu, berdansevinc@gmail.com). doi:10.1111/j.1365-2591.2009.01624.x International Endodontic Journal, 42, 1050–1056, 2009 ª 2009 International Endodontic Journal 1050