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Cone beam computed tomography is a 3-dimensional high resolution imaging method. The purpose of this study was to compare the effects of 3 different NiTi rotary instruments used to prepare curved root canals on the final shape of the curved canals and total amount of root canal transportation by using cone-beam computed tomography. A total of 81 mesial root canals from 42 extracted human mandibular molars, with a curvature ranging from 15 to 45 degrees, were selected. Canals were randomly divided into 3 groups of 27 each. After preparation with Protaper, Revo-S and Hero Shaper, the amount of transportation and centering ability that occurred were assessed by using cone beam computed tomography. Utilizing pre- and post-instrumentation radiographs, straightening of the canal curvatures was determined with a computer image analysis program. Canals were metrically assessed for changes (surface area, changes in curvature and transportation) during canal preparation by using software SimPlant; instrument failures were also recorded. Mean total widths and outer and inner width measurements were determined on each central canal path and differences were statistically analyzed. The results showed that all instruments maintained the original canal curvature well with no significant differences between the different files (P = 0.226). During preparation there was failure of only one file (the protaper group). In conclusion, under the conditions of this study, all instruments maintained the original canal curvature well and were safe to use. Areas of uninstrumented root canal wall were left in all regions using the various systems.

Introduction Achieving a hermetic apical seal is mandatory to prevent ingress of any microorganisms or periapical fluids into the root canal system. Therefore it is essential to develop new materials having favorable physical, chemical and biological properties.Aim the purpose of this study was to use scanning electron microscopy to compare the marginal adaptation of new formulation of MTA (Harvard MTA), MTA flow and glass ionomer as root end filling materials using ultrasonic root-end preparation.Methodology Thirty-nine extracted single rooted human teeth were prepared using Protaper Next file system (Dentsply/Sirona) and filled with gutta-percha and MTA fillapex sealer (MTA Fillapex; Angelus, Londrina, Brazil) and obturated using cold lateral compaction technique. The apical 3 mm of the roots were sectioned perpendicular to the long axis of the roots. A 3-mm depth root-end cavity was prepared with ultrasonic tips powered by an Enac ultrasonic device. The teeth were randomly allocated into three groups of 13 teeth each according to filling materials tested. Group I the samples were filled with Harvard MTA (Universal, Handmix, Germany, Harvard), Group II filled with MTA Flow (Ultradent Products Inc., South Jordan,UT, USA), group III filled with glass ionomer (Fuji II, GC gold label 2, GC International, Japan). Using SEM the distance between the tested materials and the surrounding dentin was measured at different points. ResultsAccording to the results of Kruskal-Wallis, there was significant difference between the three experimental groups at P value 0.01. The Man Whitney test was used for two-by-two comparison of the groups which revealed no statistical significant difference between MTA flow and MTA Harvard group however; there was statistically significant difference in Glass Ionomer group. Conclusion SEM resultsshowed the presence of gaps in the root-end filling materials in all groups. MTA flow has the best marginal adaptation followed by MTA Harvard while the Glass Ionomer showed the least marginal adaptation.

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