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Chinese Journal of Dental Research
Chin J Dent Res 22 (2019), No. 3     24. Sep. 2019
Chin J Dent Res 22 (2019), No. 3  (24.09.2019)

Page 197-202, doi:10.3290/j.cjdr.a43114, PubMed:31508608

Fracture Resistance of Roots in Mandibular Premolars Following Root Canal Instrumentation of Different Sizes
Tian, Shi Yu / Bai, Wei / Jiang, Wei Ran / Liang, Yu Hong
Objective: To measure the fracture resistance of mandibular premolar roots following root canal instrumentation with different sizes.
Methods: A total of 100 human permanent mandibular premolars with a straight single canal were decoronated and assigned to 10 groups (n = 10) by block randomisation. In the control group, the roots were uninstrumented, whereas roots in the nine experimental groups were instrumented to different master apical files (MAF) and tapers (MAF/taper): 40/0.05, 45/0.05, 50/0.05, 55/0.05, 60/0.05, 40/0.10, 40/0.15, 45/0.10 and 45/0.15. All roots were subjected to vertical loading until fracture.
Results: Fracture load values for instrumented roots were lower than the intact roots of the control group. In 50/0.05, 55/0.05, 60/0.05, 40/0.15 and 45/0.15 groups, the fracture load values were significantly lower than the fracture load value for the control group (P < 0.05) with a 30% decrease. No significant differences in the fracture modes were detected among the 10 groups (P > 0.05).
Conclusion: Mechanical instrumentation adversely affects the fracture resistance of roots. When the roots of mandibular premolars were instrumented to a MAF equal to or larger than 50 with a taper of 0.05 or to a MAF of 40 or 45 with a taper of 0.15, the fracture load values significantly decreased.

Keywords: tooth fractures, root canal preparation, mandibular premolars