| Root canal therapy is the preferred treatment for endodontics and apical periodontitis to preserve the teeth, due to its complete theoretical system and good clinical effect. However, the success of root canal treatment is affected by various factors, including the complexity of root canal system. Varying degrees of root canal curvature is well reflecting the complexity of the root canal system. Studies had shown that most of the root canals presented curved, but the area of the curved root canal, as well as the degree of bending direction was unpredictable, If instruments and methods for root canal therapy were not chosen appropriately, instruments separation, step formation, root canal transportation,perforations, apical enlargement and other complications would always occur in root canal therapy. All the Complications could hinder obturation of root canals, Which would lead to the failure of root canal treatment in curved canals, and even the teeth could not be saved. Therefore, root canal treatment of curved canals is a matter full of knots in clinical. Given the complexity and particularity of root canal treatment in curved canals, this study established three-dimensional model of curved root canals through reconstruction techniques by using Micro-CT data, then evaluated the quality of preparation techniques on curved root canal system quantitatively, at last evaluated the quality of different filling methods and sealers, in order to providing experimental evidence in selection appropriate methods for curved root canal treatment. Objective:1. To establish three-dimensional models of the teeth with curved single-root canal.2. To compare the apical transportation of different preparation instruments in curved root canals by Micro-CT.3. To evaluate the quality of root fillings completed by cold lateral condensation technique or continuous wave of condensation technique by Micro-CT.4. To analyze the formation of voids in root canals obturated with different sealer materials in combination with continuous wave of condensation technique by Micro-CT.Methods:1. Three-dimensional models of the teeth with curved single-root canal configurations:Samples were scanned by Micro-CT,2D cross-sectional images were acquired by virtue of μCT V6.1 software, the images were set to DICOM format to be output, and then the three-dimensional models of the teeth with curved single-root canal were reconstructed by Mimics software.2. According to the randomized block design, forty eight extracted teeth with curved single-root canal were divided into two groups of twelve samples each, the samples of the four group were prepared by using Mtwo Nickel-titanium instrument/standardized system technique, ProTaper/crown-down technique, OneShape/in-out technique or stainless steel K-file/step back technique. The samples were scanned by Micro-CT before and after root canal preparation,while the samples were kept at the same position. Pre-and postoperative images corresponding to distances 2.0,3.0, and 4.0 mm from the anatomic apex were selected for comparison of apical transportation.3. According to the randomized block design, twenty four extracted teeth with curved single-root canal were divided into two groups of twelve samples each, the canals were prepared by Mtwo and filled with either cold lateral condensation (group CLC) or the continuous wave of condensation technique (group System B). AH-Plus was endodontic sealer of both group.The samples were scanned by Micro-CT before and after root canal obturation after a week, while the samples were kept at the same position.Mimics 10.01 software was used for the three-dimensional volumetric visualization analysis to measure the volume of filling materials and the volume of voids and gaps formation in the obturated root canals.The percentage of filling materials was analyzed separately for the coronal third,middle third,and apical third. Data was statistically analyzed using One-way ANOVA and Student-Newman-Keuls tests.4. According to the randomized block design, twenty four extracted teeth with curved single-root canal were divided into four groups of twelve samples each, the canals were prepared by Mtwo, Each group was obturated by using the continuous wave of condensation technique (System B)in combination with AH-Plus or iRoot SP endodontic sealer. The samples were scanned by Micro-CT before and after root canal obturation after a week, while the samples were kept at the same position. Mimics10.01 software was used for the three-dimensional volumetric visualization analysis to measure the volume of filling materials and the volume of voids and gaps formation in the obturated root canals.The percentage of voids and gaps was analyzed separately for the coronal third,middle third,and apical third. Data was statistically analyzed using One-way ANOVA and Student-Newman-Keuls tests.Results:1. This experiment successfully established models of teeth with curved single-root canal, the model could be used to study morphology of the extracted teeth and root canal system from more than 360 angles (Figure 1), the three-dimensional model also could be used for other different purposes.2. Apical transportation in group stainless steel K files was significantly higher than other three groups(P<0.05), Apical transportation in group Mtwo was lowest (P<0.05),but the time used in group OneShape was least (P<0.05).3. There was no significant difference between group CLC and group System B in terms of the mean volume percentage of root canal filling materials in whole length of root canal (P> 0.05),but the mean volume percentage of filling materials in group CLC was lower than it in group System B in the coronal third (P<0.05). The mean volume percentage of filling materials in the middle third was higher than in the coronal third and apical third in each group (P<0.05).4. There was no significant difference between group AH-Plus and group iRoot SP in terms of the mean volume percentage of voids and gaps (P<0.05). The mean volume percentage of voids and gaps was lowest in middle third and highest in apical third in each group(P<0.05). Conclusion:1. This study successfully established three-dimensional models of teeth with curved single-root canal in vitro by using two-dimensional images of the teeth acquired by virtue of Micro-CT, which laid a foundation for studying dental disease and treatment later.2. Nickel-titanium instruments preparing could better maintain the canal center in curved canals and produce lower apical transportation than the stainless steel K files. Apical transportation produced by Mtwo was lowest.3. Neither of the two obturation techniques could prevent voids and gaps forming. The quality of root canal filling in group CLC was similar to it in group System B in terms of the percentage of filling materials in vitro in the short term.4. This study indicated that none of the root canal filled teeth were free of gaps. Root fillings of similar quality were confirmed in curved root canals using either AH-Plus or iRoot SP sealer in combination with System B obturation system in terms of voids and gaps formation in vitro in the short term. |
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