Changes in Root Canal Length Determined during Mechanical Preparation Stages and Their Relationship with the Accuracy of Root ZX II

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The aim of this study was to determine the variations in root canal length (RCL) occurring during endodontic treatment stages (initial, preflared, and concluded) and correlate them with the accuracy of Root ZX II (RZX).


After coronal access, 26 mandibular molars had the apical foramen of the 52 mesial canals standardized (250 μm) and their respective initial RCL was recorded (RCL1 = initial) by using a clinical microscope (×16) and manual K-file instruments. By using the alginate model, sequential electronic measurements were taken with the RZX. After the initial measurement (EM1), WaveOne Primary instruments were used to prepare the cervical and middle thirds of the root canals, and then the second RCL and EM measurements (RCL2/EM2 = preflared) were obtained. Finally, mechanical preparation was concluded, and the measurement procedures were repeated to obtain the final RCL and EM measurements (RCL3/EM3 = concluded).


Statistically significant differences were observed in all comparisons in the RCL (P < .05). The RCL1 – RCL3 showed the highest variation (0.6 mm), with the extent of specimens reduced by up to 1.75 mm. No statistically significant differences were found in the accuracy of the RZX (P > .05); 100% precision (± 0.5 mm) was found in all stages.


Under the conditions of this study, the authors concluded that during endodontic treatment, the extent of the RCL was reduced, thereby jeopardizing control of the apical limit during instrumentation and/or obturation. The RZX was extremely accurate in all evaluated stages.

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