| Objective:The cleanness of curved root canal is troublesome for dentists. Interiorly, passive ultrasonic irrigation is dominant at present.Ultrasonic file can create root canal transportation, and is constrainted by canal-wall stress in curved canals. Mandibular first molars with curved mesial root canal were selected. Straight ultrasonic file was located within0.5mm coronally from start of the curvature. Combine PUI and K File(the same size as dimension of apical portion preparation) agitation to explore whether it will to be an efficacy and feasible protocol or not for curved canals by examinng smear layer removal and the erosion of root canal.Methods:Forty mandibular first molars with curved mesial root canal,whose curvature differed from20°to40°and for which length of the bend varied from4mm to6mm, were selected.They were sectioned longitudinally under water cooling, with only mesiobuccal root remaining.Finally,the crowns were removed at2mm coronal to the cementoenamel junction. All mesiobuccal root canals were instru-mented to F3using handed Protaper system,and randomly divided into four groups according to final irrigation protocols. They are group A:syringe irrigation;group B:#30K File agitation, K File was prebent,introduced to the total root length and agitated100push-pull strokes per minute;group C:passive ultrasonic irrigation (PUI), straight ultrasonic file was located within0.5mm coronally from start of the curvature; group D:combination of#30K File agitation and PUI. All root canals were mesio-distally split. Two halves of them were snicked at start of the curvature and2mm apically from start of the curvature and divided into three sections.They are Ⅰ, Ⅱ,Ⅲ from the coronal to the apical. Then all samples were dehydrated with different concentrations of ethyl alcohol(50%,70%,80%,90%,100%) in sequence,desiccated, and coated with gold. Under the thermal field emission scanning electron microscope, all the samples were observed by a double-blind test. Randomly selected3horizons at each section, took pictures and scored the removal of smear layer and the erosion of the dentin.The average values of them became the final value. The data which presented normally and homogeneously distribution were analyzed using one-way analysis of variance, such as length of the end, the length of root canal and the curvture of root canal.The values for smear layer removal and the erosion, uni-directional sequence data, were analyzed with Kruskal-Wallis test and Mann-Whitney U test. The level of significance was0.05.Results:1.smear layer removal:Group D presented small amounts of scattered or thin smear layers and obtained the lowest score at each section of root canal wall.At section Ⅰ and Ⅱ,there was no significant difference in smear layer removal between group D and group C.Values for smear layer removal were significantly lower in group D and group C than those of group A and group B(P<0.05). At section Ⅲ,the values was significantly lower in group D than that of group A, group B and group C,and which was significantly lower in group B and group C than that of group A(P<0.05).2.erosion of root canal wall:At section Ⅰ and Ⅱ was significant difference in smear layer removal between group D and group C(P<0.05).Values for erosion were significantly higher in group D and group C than those of group A and group B(P<0.05). Group A and group B showed no erosion. At section Ⅲ,there was no erosion in four groups and they were not significant with each other(P>0.05).Conclusion:1.When the length of the bend of root canal varied from4mm to6mm, combination of PUI and K File(the same size as dimension of apical portion preparation) agitation, with ultrasonic file located coronal from the start of the curvature, can remove smear layer from curved canals more efficiently than PUI, K File agitation.2. When the length of the bend of root canal varied from4mm to6mm, combination of PUI and K File(the same size as dimension of apical portion preparation) agitation, with ultrasonic file located coronal from the start of the curvature, showed less erosion than PUI significantly. |
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