Comparing Study On The Effect Of Three Nickel-Tianium Rotary Instruments In Root Canal Preparation

Objective:Pulp and periapical disease is one of the most common diseases in oral clinic, and root canal therapy is the most effective method and commonly used in treatment of these diseases. Root canal therapy included root canal preparation, root canal disinfection and root canal filling. Among them, root canal preparation is the most important ones. Whether root canal therapy succeed largely depends on the quality of root canal preparation. Modern concept of root canal preparation include clean-up and shaping of root canal. The goal for cleaning and shaping of the root canal system is to obtain a continuously tapering funnel from the coronal access (widest diameter) to the apex (narrowest diameter) that flows with the shape of the original canal. Preparation of the canal, especially the apical segment, without weakening the remaining dentin or perforating the root is essential to proper infection control and obturation and to long-term success. The aim of this study is to selected three kinds of nickel-titanium rotary instruments:Protaper, Mtwo and K3, that most commonly used in dental clinical to prepare root canal and compare the time which used in root canal preparation and the images of cross-section pre-and post-instrumentation and the separation of rotary instruments,so as to give a choice to clinician for chose a instrument properly. Methods: Thirty first and second premolars which extracted by various reasons with root fully developed and no absorption, no serious damage to the crown, root canal curvature>25 degrees and not undergo pulp treatment were chosen as samples and random divided into three groups:Protaper (group P), Mtwo (group M), and K3 (group K).All samples were stored in 4% formaldehyde solution in use. Access to pulp chamber of all samples and remove the pulp tissue, then determine the working length by radiogrphs. Lines parallel to ocllusal surface were drew on the root surface 2 and 5mm from the apical foremae and embedded in Bramante model with resin. After the resin hardened, use a low-speed saw to resect all the samples and take images of all the cross section. Then re-embedded block model in Bramante, and prepare all the root canals with proper method given by the manufacturers. Use three kind of nickel-titanium rotary instruments for root canal preparation, and 3% hydrogen peroxide and 5.25% sodium hypochlorite solution were used to irrigate the root canals. Record the time of root canal preparation and root canal-side wear and seperation of the instruments. Results:Among three types of rotary instruments in root canal preparation, group M takes the shortest preparation time, followed by group P and group K. There were significant difference in preparation time. In section 1,there were no significant difference in offset volume of all the root canals among three groups (P>0.05). In section 2, the offset of root canal in group P and group K were significantly greater than that of group M(P<0.05), while the offset of root canals between group P and group K was no significant difference (P> 0.05). Conclusion:All the three kinds of nickel titanium rotary instruments were effective to shape root canals with root canal curvature>25 degrees, Mtwo provides the best ability to maintain the patency of original root canal, and also saves operating time of root canal preparation.