Comparative Study On The Preparing Effect Of Root Canals With Different Nickel-Titanium Rotary Instruments

ObjectiveExperiment one:To compare the shaping ability of ProTaper Mtwo and K3 nickel-titanium rotary systems using the computer assistant analyze image software measuring the root canal transportation and the decrease of curvature,during the preparation of root canal in extracted human teeth.Experiment two:To compare the cleaning effectiveness of ProTaper Mtwo and K3 nickel-titanium rotary systems with observing and scoring the debris and the smear layer using Scanning Electron Microscope(SEM), after the instrumentation of root canal.Materials and MethodsExperiment One1. Samples collection and storageFifty-four mesio-buccal root of maxillary first molars with MB2 excluded and single unobstructed root canal were collected. The samples which were intact and normal with the apical non-absorption and the apical foramina nearly the same (Initial Apical File was 15 size K file) were stored in 0.9% Sodium Chloride.2. GroupingAll the samples were divided into two groups:group A(≥20°) and group B(< 20°),according to the angle of the root canal. Then, each group was randomly divided into three subsets and prepared by ProTaper Mtwo and K3 respectively. ProTaper system was used as contrast.3. Root Canal preparation During the instrumentation, all types of instruments were powered by a torque-limited electric motor (X-smart), according to the manufacturer's instructions. All root canals were irrigated with 5.25%Sodium hypochlorite (NaOCl) and 17%EDTA.4. Taking and analyzing imagesAll root canals were injected the contrast medium and digital images of all canals were recorded before and after instrumentation. The computer assistant analyze image software was used to form the geometrical central line of pre-instrumented root canals. Then the central line was imaged to the post-instrumented root canals. The root canal transportation and the decrease of curvature were measured.5. Statistical analysisAll the data were analyzed with SPSS 10.0 software package. Subsets in group A or group B were performed by analysis One-Way ANOVA and Student Newman Keuls-q test. Significance level:P<.05 was considered statistically significant.Experiment Two1. Samples collection and storageCentralized all the samples which were prepared separately by ProTaper Mtwo and K3,and collected seven samples of each group randomly.Then twenty-one samples were got and were stored in 0.9% Sodium Chloride.2. Treatment of the samples and GroupingAll the canals were splitted longitudinally along the plane of bending, exposed all inner walls and prepared for SEM investigation. Divided the samples into three groups:group P group M and group K.3. Observation with SEMAll samples were examined under the SEM at 2000 magnification.Separate evaluations were recorded for debris and smear layer of different areas on the inner root canal wall.4. Statistical analysisAll the data were analyzed by Kruskal-Wallis test and Post Hoc Tests. Significance level:.P<0.05 was considered statistically significant.Results Experiment One1.The comparation of the decrease of curvature pre-and post-instrumented root canals with different nickel-titanium rotary systemsThere were significant differences between group AM and the other two groups in group A(P< 0.05),but there was no significant difference between group AK and group AP (P>0.05) In group B, there was no significant difference in group BP group BM and group BK (P>0.05)2.The comparation of the transportation post-instrumented root canals with different nickel-titanium rotary systemsGroup A:In the mesial-distal direction, the transportation at the five points were no significant difference in group AP group AM and group AK (P>0.05).But in the buccal-lingual direction, the transportation at the beginning of the curvature of group AP and group AK were significantly more than that of group AM (P< 0.05).In the other points, there was no significant difference (P>0.05)Group B:Both in the mesial-distal direction and the buccal-lingual direction, the transportation at the five points were no significant difference in group BP group BM and group BK (P>0.05).Experiment Two1. Observation of results of the debris on root canal wall with SEMIn the case of SEM magnification 2000,there was no significant difference in scores of debris at the coronal third of root canal in Group P Group M and Group K (P>0.05).At the middle third and apical third sections, results on cleaning debris in Group P and Group M were significantly better than that of Group K (P< 0.05),but there was no significant difference in Group P and Group M.2. Observation of results of the smear layer on root canal wall with SEMIn the case of SEM magnification 2000, there was no significant difference in scores of smear layer at each section in Group P Group M and Group K (P>0.05).Conclusions 1. Protaper Mtwo and K3 systems all show good shaping ability when preparing the mild curved root canal of maxillary molars. The Mtwo system can better preserve original curvature of root canals, when preparing the middle and severe curved root canal of maxillary molars, which could be the better nickel-titanium rotary instruments for curved root canal of molars.2. Using the NaOCl and EDTA as irrigation, Protaper and Mtwo nickel-titanium rotary systems can do better cleaning effects than K3 in the middle and apical sections,during the preparation.