Clinical Investigation of the Efficacy of Chemomechanical Preparation with Rotary Nickel-Titanium Files for Removal of Endotoxin from Primarily Infected Root Canals Frederico C. Martinho, DDS, MSc, Wanderson M.M. Chiesa, DDS, MSc, Ariane C.S. Marinho, DDS, Alexandre A. Zaia, DDS, MSc, PhD, Caio C.R. Ferraz, DDS, MSc, PhD, Jose ´ F.A. Almeida, DDS, MSc, PhD, Francisco J. Souza-Filho, DDS, MSc, PhD, and Brenda P.F.A. Gomes, DDS, MSc, PhD Abstract Introduction: This clinical study was conducted to investigate the ability of chemomechanical preparation with 2.5% NaOCl + 17% ethylenediaminetetraacetic acid (EDTA) and rotary nickel-titanium (NiTi) system in removing endotoxin from primary root canal infection with apical periodontitis. Methods: Twenty-one root canals with necrotic pulps were selected. Samples were collected before (s1) and after chemomechanical preparation (s2). The limulus amebocyte lysate (LAL) assay was used to quantify endotoxins. Results: The LAL assay indicated that endotoxins were present in 100% of the root canals investigated (19/19) before (s1) and after chemomechanical preparation (s2). Anal- yses of the quantitative data revealed that the endotoxin content was significantly reduced at s2 (98.06%) compared with that at s1 (P < .05). Conclusions: Our findings indicate that chemomechanical preparation with 2.5% NaOCl + 17% EDTA and rotary NiTi files was effective in reducing endotoxin load in the root canal infection from primarily infected teeth with apical periodontitis. (J Endod 2010;36:1766–1769) Key Words EDTA, endotoxin, Mtwo system, NaOCl, NiTi, root canal, rotary instrumentation E ndotoxin investigations on primary endodontic infection (1–4) showed strong correlation between oral bacteria lipopolysaccharide (LPS) and the presence of apical periodontitis. Because of the highly toxic activity of endotoxin to periapical tissues (5), such as its capacity to invade dentin tubules (6) and egress into periradic- ular tissues (7), special attempt has been made to eliminate/neutralize it within infected root canals during endodontic therapy. The most commonly used auxiliary chemical substances in endodontic therapy, sodium hypochlorite (NaOCl) and chlorhexidine (CHX gel), showed no detoxifying effect against endotoxin (8). Therefore, proper elimination of endotoxin seems to rely on debridement of the root canal system. Apical patency (9, 10), serial enlargement of the body of root canal (10–12), and establishment of master apical file size (MAF) (12–14) are important measures to reach adequate debridement of the root canal system. Historically, MAF determination by using ‘‘three sizes up from the first file to bind’’ rule (15) has been used in modified forms (16). By using this rule combined with the step-back technique, our previous investigation (1) showed its inefficiency in elimi- nating endotoxin from infected root canals. Even increasing the root canal enlargement, more than 50% of endotoxin-infected dentin was left behind, suggesting the need of an extensive enlargement (2). A greater apical enlargement is beneficial in performing further debridement of the apical third (14), known as a ‘‘critical zone’’ (17). However, because of tooth anatomy, this might be better achieved with nickel-titanium (NiTi) rotary instruments instead of the conventional step-back technique with stainless steel files (14, 18). The superior shaping ability of NiTi rotary files (19), with greater flexibility (20), reduces the incidence of procedural errors (21–24) and consequently yields a higher success rate in root canal treatment compared with conventional technique (23). The Mtwo NiTi rotary instruments have a cross-sectional design resembling a 2- blade S-shaped file (22), with its angle almost vertical (21, 24). Its standardized tapers, ranging between 0.04 and 0.07 mm, and great flexibility (20) produce less canal transportation (24) and few changes in canal shape (21), allowing safe enlargement and removing deeper layers of infected dentin as a result. Currently, there is no clinical study evaluating the efficiency of rotary instruments for elimination of endotoxin from root canals with primary infection. Therefore, the aim of this clinical study was to investigate the ability of chemome- chanical preparation with 2.5% NaOCl + 17% ethylenediaminetetraacetic acid (EDTA) and rotary NiTi system in removing endotoxin from primary root canal infection with apical periodontitis. Materials and Methods Patient Selection Twenty-one patients who attended the Piracicaba Dental School, Brazil for endodontic treatment were included in this research. The age of the patients ranged from 13–73 years. Samples were collected from 21 root canals with pulp necrosis, From the Department of Restorative Dentistry, Endodontic Division, Piracicaba Dental School, State University of Campi- nas, Piracicaba, SP, Brasil. Address requests for reprints to Dr Brenda P. F. A. Gomes, Piracicaba Dental School, University of Campinas, Endodontic Division, Av. Limeira 901, Bairro Areiao, Piracicaba, Sa ˜ o Paulo, Brasil, CEP 13414-903. E-mail address: bpgomes@fop. unicamp.br. 0099-2399/$ - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.08.019 Clinical Research 1766 Martinho et al. JOE — Volume 36, Number 11, November 2010