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The Chinese Journal of Dental Research

Year 2002
Volume 5 , Issue 1

Pages: 33 - 42

Performance of Three Nickel-Titanium Instruments for Preparing Curved Root Canals to Two Different Apical Dimensions

X. Wei/G. S. P. Cheung

Objectives: This study aimed to compare the shaping ability of three nickel-titanium rotary instruments for preparing curved root canals to two different apical sizes. Hand instrumentation using stainless steel files and the Step-down technique served as the control. Method and Materials: A total of 56 moderately curved and 8 “S”-shaped canals in the mesial root of extracted human mandibular first and second molars were equally distributed into four groups on the basis of canal curvature. The teeth were embedded and their roots sectioned horizontally at three levels. Instrumentation was carried out in two phases—first to an apical size of 30 (Phase I), and then to size 40 (Phase II). The preoperative and postoperative canal shapes of each section were digitized and compared. Longitudinal changes in canal curvature were evaluated on radiographs taken in both buccal-lingual and M-D directions. Results: Hand files produced significantly more straightening than Ni-Ti rotary systems, which maintained the canal curvature fairly well in Phase I but did straighten it during Phase II preparation. At the apical two-thirds, hand instrumentation resulted in the greatest amount of dentin removal and canal transportation in both stages of preparation. Significantly thinner canal wall on the furcal aspect resulted from hand files in the mid-root level compared to the Ni-Ti systems, which were not significantly different from each other. There seemed to be a difference in the pattern of canal center movement particularly in the mid-root portion among the four groups. More dentin was removed at the coronal third of the canal by Ni-Ti instruments with a large body taper. No instrument separation was recorded. Conclusions: Nickel-titanium rotary instruments resulted in less severe canal transportation than hand instrumentation with stainless steel files. Increasing amounts of canal transportation were evident when the canal was further enlarged from an apical size 30 to size 40, especially with “greater taper” instruments. The Ni-Ti systems tested appeared to be safe up to six uses in moderately curved canals.



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