Objective The study was designed to investigate the relationship between the accuracy of Root ZX and the size of apical foramen, when the apical constrictions were intact or not. Methods Lengths were taken when the needle reached the‘0.5’mark and‘APEX’mark on the Root ZX. The electronic apex locator（EAL）- measured canal working length（L2） and EAL- measured canal length（L1） were then compared with the actual canal working length（L′） and actual canal length（L）. Besides, the areas of apical foramens（S） were measured when the apical constriction were intact or not. Then the measurement deviations and the areas of apical foramens were analyzed by linear correlation and linear regression using the software SPSS 12.0. Statistical significance was considered at P0.05）. However, the accuracy of Root ZX and the size of apical foramen had significant negative correlation when the apical constriction was destroyed（P
