The purpose of this study was to evaluate in vitro the efficacy of both the electronic apex locator (EAL) and auto apical reverse (AAR) functions of the endodontic motor MM Control (Micro-Mega, Besançon Cedex, France) compared with Root ZX II (J Morita, Tokyo, Japan).
After cervical preflaring, the actual lengths (ALs) of 36 single-rooted teeth were obtained up to the apical foramen. The EAL measurements at the marks "APEX" and "0.5" of both devices were obtained using an alginate model. The teeth were divided randomly into 2 groups (n = 18), and root canal preparation was performed with rotary instruments using the AAR function (0.5 mark) of each motor. The length provided by the AAR was compared with the visual length after preparation (AL2). The differences between the electronic lengths and the respective visual measurements were assigned as negative for lower or positive when higher. The means of the absolute values and the percentages of distribution of the electronic measurements between devices were compared.
There was no difference between the devices in terms of the means of the EAL measurements or AAR length (analysis of variance, P > .05). However, the EAL function of MM Control presented a greater percentage of measurements >1.01 mm longer than AL (chi-square, P < .01). The AAR function provided an acceptable apical limit in 83.3% of the cases for Root ZX and 77.8% of the cases for MM Control.
The AAR function of both MM Control and Root ZX II provided an adequate apical limit of preparation in vitro. However, the use of only the EAL function of MM Control resulted in significantly more cases of overextended readings.
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