Two Kinds Of Research Methods Assessment On The Effect Of Different Nickel-titanium Instruments On Dentinal Microcracks

Objective:This study aimed to evaluate the frequency of dentinal microcracks observed after root canal preparation with K3,TF and ProTaper Universal files using micro-computed tomographic and stereomicroscope analysis.Methods:1.32 mandibular premolars with single oval canal were randomly divided into three experimental groups(n = 8)and a control group(n = 8).32 mandibular premolars were scanned by micro-computed tomography,and then used K3,TF and ProTaper Universal System to prepare the root canal in experimental groups,while the control group were left unprepared.Last scan was taken after the root canals were prepared with instruments sizes 25#/0.06(K3,TF)and F2(ProTaper Universal),respectively.Then,pre-and postoperative cross-section images of the roots(N = 41,148)were screened to identify the presence of dentinal microcracks.2.Roots were sectioned from 3,6,9 mm to the apex and then stained,its status of dentinal microcracks was evaluated under a stereomicroscope.Results:1.Micro-computed tomographic assessmentAll dentinal microcracks identified in the preoperative cross-sections were also observed in the corresponding postoperative images.2.Stereomicroscope assessmentDentinal microcracks were observed in 0%and 45.83%(n=24)of roots from control group and experimental groups,respectively.A statistically significant difference was found between control group and anyone of experimental groups(P<0.05).However,no significant difference was found mong the 3 experimental groups(P>.05).Dentinal microcracks were observed in 21.67%(n=120)of cross-sections from experimental groups.There were no statistically significant differences in incidence rate of dentinal microcracks of cross-sections between group K3 and group TF.A statistically significant difference was found between group K3 and group ProTaper Universal,group TF and group ProTaper Universal(P<0.05).3.Micro-computed tomographic compared with stereomicroscope Stereomicroscope assessed the incidence rate of dentinal microcracks of roots and cross-sections were significantly higher than micro-computed tomographic.Whatever which assessment methods' results,there were no statistically significant differences in incidence rate of dentinal microcracks of roots between experimental groups(P>0.05).Conclusions:There were no differences in dentinal microcracks of roots between group K3,group TF and group ProTaper Universal.Root canal preparation may decrease the resistance form of the root,which increase incidence rate of dentinal microcracks and risk of vertical root fracture.The indeterminacy of Stereomicroscope assessment related to the destructive sectioned method.The highly accurate of Micro-computed tomographic assessment related to the nondestructive method.