The Accuracy in the Control of the Apical Extent of Rotary Canal Instrumentation Using Root ZX II and ProTaper Instruments: An In Vivo Study Sandra Joia Mizrahi Jakobson, DDS,* Vania Portela Dietzel Westphalen, DDS, MS, PhD,* Ulisses Xavier da Silva Neto, DDS, MS, PhD,* Luis Fernando Fariniuk, DDS, MS, PhD,* Fábio Picoli, DDS, MS, PhD, † and Everdan Carneiro, DDS, MS, PhD* Abstract The accuracy of Root ZX II (J. Morita, Kyoto, Japan) to control the apical extent of rotary canal instrumenta- tion in vivo was assessed. Twenty-four premolars with a single canal were selected. The roots were divided in two groups according to the calibration of the auto- matic apical reverse mechanism of Root ZX II, set at levels 1 and 2. After endodontic access, the preparation was performed with ProTaper instruments (Dentsply Maillefer, Ballaigues, Switzerland) connected to the device. Afterwards, the last file used was introduced into the canal and fixed in place with acrylic resin. The teeth were extracted and ground until exposure of the file. The distance from the instrument tip to the apical foramen was obtained. The percentage of acceptable measurements and the difference between means were submitted to statistical analysis. The differences of set- ting the reverse mechanism at 1 and 2 were not sta- tistically significant. Both settings were not accurate for determining and controlling the apical extent of rotary instrumentation. (J Endod 2008;34:1342–1345) Key Words Apex locator, auto-reverse mechanism, root canal length, Root ZX II T he apical constriction, where the pulp tissue is connected to the apical periodontal tissue, is recommended as the physiological apical limit for instrumentation and filling of the root canal (1). A precise working length prevents transportation of the apical foramen, possible overfilling of the root canal system, and also inadequate debridement, which, in turn, could lead to retained pulp tissue and a lack of healing (2). Custer (3) was the first to introduce the electrical method of locating the apical foramen. Suzuki’s (4) discovery that the values for the electrical resistances between the periodontal ligament and oral mucosa were always constant allowed the development of the first apex locator by Sunada (5). Root ZX II (J. Morita, Kyoto, Japan) is designed for rotary root canal preparation with integrated apex locators. The manufacturers claim that faster and easier root canal preparations, including easy working length determination can be achieved with these devices. Its apical automatic reverse function reverses the rotation when the instrument tip reaches the length previously set by the professional. The purpose of this study was to assess the accuracy of Root ZX II as an apex locator and its automatic apical reverse mechanism while in use with ProTaper instru- ments. Materials and Methods Twenty-four premolar roots with no dilacerations and a single canal were selected for the study. The teeth with mature apices that had been scheduled for extraction for periodontal, orthodontic, or prosthetic reasons in 13 patients were selected. Approval by the institutional review and ethical board and written consent from each patient was obtained before the study began. The patients consisted of 8 males and 5 females ranging from 15 to 51 years of age. Patients with heart pacemakers or those who had a contributory medical history were not included. Teeth with metal restorations or por- celain fused to metal crowns, which could not be completely removed, were not in- cluded. Teeth with open apices were also excluded. Endodontic access was performed with a no. 4 carbide bur (KG Sorensen, Rio de Janeiro, Brazil), and the pulp chamber was copiously irrigated with 1% sodium hypochlorite solution. A no. 10 K file (Maillefer-Dentsply, Ballaigues, Switzerland) was used to verify the presence of possible obstructions and ensure direct access to the apical foramen. The roots were then divided into two groups as follows: group 1: 12 roots prepared using the automatic apical reverse mechanism set at level 1 and group 2: 12 roots prepared using the automatic apical reverse mechanism set at level 2. Biomechanical preparation was performed in a crown-down technique with ProTaper instruments (Dentsply- Maillefer), ending with a finishing 3 file in every root. Once the preset distance was reached, the device emitted a sound and activated the reverse function. After prepara- tion, the last finishing 3 file used was carefully introduced into the canal by hand to verify if the preset distance had been reached and fixed in place using acrylic resin (Dencôr; Artigos Odontológicos Clássico, Ltda, São Paulo, Brazil). The roots were carefully extracted and placed in a coded specimen cup filled with a solution of 10% formalin for 48 hours. After fixation, the teeth were stored in 2.5% NaOCl solution for 48 hours, and the root surfaces were cleaned to remove all organic From the *Department of Endodontics, Pontifical Catholic University of Paraná, Brazil; and † Department of Endodontics, University of Franca, Brazil. Address requests for reprints to Dr Everdan Carneiro, Department of Endodontics, Pontifical Catholic University of Paraná, PUCPR, Imaculada Conceição, 1155, Prado Velho 80215-901, Brazil. E-mail address: everdan.carneiro@pucpr.br 0099-2399/$0 - see front matter Copyright © 2008 American Association of Endodontists. doi:10.1016/j.joen.2008.08.009 Clinical Research 1342 Jakobson et al. JOE — Volume 34, Number 11, November 2008