fa Periodontology Periodontology Original article Original article <p style="text-align: justify;"><strong><span dir="LTR">Background and Aim:</span></strong><span dir="LTR"> Root canal preparation with systems with the least chance of dentin cracking can increase the success of endodontic treatment. This study aimed to compare the One-Shape and XP-endo Shaper rotary files in the</span> <span dir="LTR">dentin crack incidence in the mesiobuccal canals of mandibular first molars.</span><br> <strong><span dir="LTR">Materials and Methods:</span></strong><span dir="LTR"> In this experimental study, 60 eligible extracted mandibular first molars were randomly divided into three groups.</span> <span dir="LTR">The roots were prepared to #30 and 4% taper in the XP-endo Shaper group and</span> <span dir="LTR">#25 and 6% taper in the One-Shape group. The control samples were left intact. All groups were sectioned at 2, 4, and 6mm from the apex and examined under a stereomicroscope at 20&times; magnification. The incidence, location, and type of cracks were analyzed using chi-square test.</span><br> <strong><span dir="LTR">Results: </span></strong><span dir="LTR">There were no cracks in the controls. The crack percentage was 23.33% (n=14) and 11.66% (n=7) in the One-Shape and XP-endo Shaper groups, respectively, with a significant difference with crack-fee samples. There was no significant difference between One-Shape and XP-endo Shaper systems in the three sections (P>0.05). In the 2mm section, cracks were observed in six sections (10%) with One-Shape and four sections (20%) with XP-endo Shaper. In the 4mm section, cracks were observed in one section (5%) with One-Shape and five sections (25%) with XP-endo Shaper. In the 6mm section, cracks were observed in seven sections (35%) with One-Shape and one section (5%) with XP-endo Shaper.</span><br> <strong><span dir="LTR">Conclusion:</span></strong><span dir="LTR"> The One-Shape and XP-endo Shaper systems were similar in crack incidence in the mesiobuccal canal of mandibular first molars.</span><br> &nbsp;</p> <h2 dir="RTL"></h2> Tooth Fractures, Root Canal Preparation, Mandible, Molar 31 36 http://jrdms.dentaliau.ac.ir/browse.php?a_code=A-10-708-8&slc_lang=fa&sid=1 A Delvarani 10031947532846008481 10031947532846008481 No Assistant Professor, Department of Endodontics, Member ship of Dental Material Research Center, Faculty of Dentistry, Tehran Medical Sciences,Islamic Azad University, Tehran, Iran AA Moshary 10031947532846008482 10031947532846008482 No Assistant Professor, Department of Endodontics, Faculty of Dentistry, Tehran Medical Sciences,Islamic Azad University, Tehran, Iran M Ghasemian Yadegari 10031947532846008483 10031947532846008483 No Dentist T Bitaraf taherehbitaraf@yahoo.com 10031947532846008484 10031947532846008484 Yes Assistant professor, Dental Implant Research Center, Dental Faculty, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran