Comparison of three instruments in the preparation of the curved root canal using the modified double-flared...

Fifty-one extracted intact human first molar teeth with mature root apices were radiographed in a standardized way; their root curvature was determined and they were divided into three groups. One root canal in the mesial root of the mandibular molars, or the major mesiobuccal root in maxillary molars, was prepared with the modified double-flared technique, in one of three ways. The modified double-flared technique involves coronal flaring followed by working length determination and apical preparation. In group 1, unmodified tipped instruments (Flexofile) were manipulated with a balanced force technique. In groups 2 and 3, Flexogates files and Canal Master U files were operated in the manner recommended by the manufacturers. After preparation, the teeth were radiographed. The processed images of the root canals were traced using an image analysis computer software package. Comparisons were made between the preoperative and postoperative shapes of each root canal. A low viscosity polyvinyl siloxane was injected into the prepared root canals and the specimens were demineralized, dehydrated, and cleared. The preparation was evaluated subjectively according to desirable or undesirable criteria. The overall quality of preparation was rated. Statistical analysis showed that there was no significant difference in the overall change of area between the three groups (p = 0.994). There was a significant proportional increase in mesiodistal width in the coronal part of the canals in the Canal Master U group and more of the instruments in this group fractured.(ABSTRACT TRUNCATED AT 250 WORDS)