Purpose: This study was designed to evaluate the influence of different apical limits of working lengths, electronic and radiographic methods of working length determination, maual and rotary root canal instrumentation on the apical extent of root canal filling material. Materials and Methods: Forty five roots of maxillary central incisors with mature apices were selected and divided into two groups: Group I ( 30 roots), and Group II (15 roots) according to the method of working length determination (electronic or radiographic respectively). Each main group was divided into three equal groups according to the apical limit of working Each group at main group (I) were subdivided into two equal subgroups: 1 and 2 (5 each) according to instrumentation system; rotary proTaper system or Flex-o-file while all roots at group (II) were cleaned & shaped with Flex-o-file. Each canal was obturated. The roots were longitudinally splitting .Under a surgical microscope, the integrity of apical constriction was observed and photographed. The distance between the apical terminus of the root canal filling and the apical foramen were measured and photographed by stereomicroscope. Results: ANOVA test revealed significant difference on the distance between the apical terminus of the root canal filling and the apical foramen were preserved at the three apical limits when working length and rotary canal preparation were carried by Tri Auto ZX headpiece, and when root canal were prepared by Flex-O-file after radiographic working length determination. Under different variables of this study, the integrity of apical constriction showed no significant difference. Conclusion: Electronic working length determination method is more accurate than radiographic method. Tri Auto ZX apex locating headpiece is a reliable method for electronic working length determination, and rotary root canal preparation.