Investigation of the Location of the Apical Constriction in Relation to the Flash Bar of an Apex Locator: A Micro-CT Study.

Abstract

Introduction: This study aimed to locate the anatomical apical constriction (AC) of root canals using micro-computed tomography (micro-CT) and microscopy, and to correlate these findings with the flash bar of the Root ZX electronic apex locator (EAL). The objective was to identify the protocol that positions the file closest to the AC.

Methods: The working lengths of 30 extracted single-rooted teeth were measured using Root ZX EAL with three employment protocols. Group I: Files were advanced in the canals to the "APEX" mark and then withdrawn to the "end of the Blue zone" mark. Group II: Files were advanced to the "APEX" mark and then withdrawn to the "0.5" mark. Group III: Files were advanced only to reach the "APEX" mark. Files were then cemented in place and examined using micro-CT and surgical operating microscope to identify the actual location of the AC. The discrepancies between the locations of the file's tip and the ACs were assessed by 3D slicer software and statistically analyzed.

Results: Significant differences were observed among the three groups based on micro-CT and surgical operating microscope measurements. The end of the blue zone achieved 100% accuracy, the 0.5 mark 85-80%, and the apex mark protocol 0-5% (within a tolerance of ±0.5 mm). An overall positive correlation was found between micro-CT and surgical microscopy measurements (r = 0.91). Working length overestimation beyond the major foramen occurred in 30% of the samples in the 0.5 mark protocol and 60% of the Apex mark group.

Conclusions: The "end of the Blue zone" mark protocol provided the greatest accuracy without file extrusion, followed by the "0.5" mark. The "APEX" mark protocol is not recommended since this protocol placed the file at an average of 1.24mm apical to the AC.