Introduction: One of the most important reasons of endodontic failure is the persistence of microbial factors in the root canal system. Therefore, three-dimensional cleaning of the root canal space is very important to eliminate or reduce the irritant factors and microorganisms.Objective: To evaluate the effectiveness of MTWO R and ProTaper Retreatment files as compared with MTWO and ProTaper files in retreatment of the gutta-percha filled root canals.Materials and Methods: In this in-vitro study, fifty extracted single root premolars with approximately straight and similar root lengths were selected. Primary preparation of the root canals was performed by ProTaper rotary system and all of the roots were filled by lateral condensation technique. Then, the teeth were randomly divided into five groups, and each group was retreated with one of the ProTaper, ProTaper Retreatment, MTWO, MTWO R systems and hedstrom hand files. Following the longitudinal splitting of the roots with diamond discs and evaluation of amount of the gutta-percha/ sealer on the root canal walls with stereomicroscope. Obtained results were analyzed with kruskal-wallis and Mann- Whitney u tests.Results: Complete removal of gutta-percha/ sealer did not occur with any of the investigated systems .There is significant statistical differences between test groups at the apical and middle thirds of canals(P=0.849, P=0.315 respectively ).In Hedstrom group, significantly less filling material was observed in the coronal third of canals. Regardindg the duration of retreatment, all of the rotary systems were significantly more rapid than hand files. Rotary files that were specifically designed for retreatment, were significantly more rapid than universal ProTaper.Conclusion: Despite this fact that neither of used techniques in this study were able to remove the filling material completely, but regarding to higher speed and probability of less fracture of the files specifically designed for retreatment (MTWO R and ProTaper Retreatment) as compared with universal rotary files (MTWO R and ProTaper), we suggested that these files can be appropriate choice for root canal retreatment.

Introduction: The success of endodontic retreatment is related to the complete removal of the obturation material from the root canal system. The aim of this study was to evaluate the efficacy of MTWO R and ProTaper retreatment files in removing the Resilon/Epiphany system with or without chloroform during retreatment.Materials and Methods: Sixty distal roots of first mandibular molars were prepared and laterally condensed with Resilon/Epiphany, then divided into four groups (15 each for retreatment): 1) MTWO R/solvent; 2) MTWO R; 3) ProTaper D/solvent; and 4) ProTaper D. The cleanliness of the canal walls was evaluated using radiography; a stereomicroscope and SEM. Data were subjected to ANOVA and Student’s t-test.Results: Neither rotary system performed better than the other when considering the whole root canal, with or without solvent. In the apical portion, ProTaper/solvent showed the best result (P<0.05).Conclusion: In Resilon/Epiphany retreatment cases, ProTaper/solvent was better in the apical portion; however when considering the whole canal, MTWO R and the ProTaper D series had the same performance.

INTRODUCTION: The aim of this in vitro study was to compare the efficacy of two retreatment rotary systems in removal of gutta-percha (GP) and sealer from the root canal walls with and without use of solvent.MATERIALS & METHODS: Sixty single-canalled distal roots of mandibular molars were prepared and root filled with gutta-percha and AH26. Each canal was randomly allocated to receive one of the retreatment techniques, MTWO R or ProTaper. The groups were further divided into two subgroups: with or without the use of solvent. The cleanliness of canal walls was determined by stereomicroscope and scanning electron microscopy.RESULTS: The results showed that MTWO R without the use of solvent was more efficient in material removal compared to ProTaper D (P<0.05). Most remnants were found in the apical third of the canals (P<0.05).CONCLUSION: MTWO R seems to be an efficient rotary system for endodontic retreatment of root canal with GP.

Background and Aim: The aim of this study was to compare the effect of MTWO rotary system and step back hand system in reduction of enterococcus faecalis bacteria from the root canals of human extracted teeth.Materials and Methods: In this study, 62 human extracted teeth were divided into two equal experimental groups with 23 teeth each and one control group two extra control groups with 5 teeth each as negative and positive were chosen for confirmation of the canal reinfection too. All of the samples were prepared by K Flie No 20 and Gates Glidden No 2 and 3 before sterilization. Then the teeth were autoclaved and reinfected with enterococcus faecalis. The experimental groups were instrumented either with MTWO system or step back system. Bacteriological samples were taken after instrumentation to determine the amount of remaining bacteria.Results: In the group 1, fourteen samples and in the group 2, twelve samples represented complete reduction of bacteria. There was not statistically significant difference between two techniques (p>0.05)Conclusion: Both MTWO and step back systems are the same on reduction of the bacteria from root canal system, up to the same apical size.

INTRODUCTION: Root canal preparation is an important process in endodontic therapy.Nickel-titanium (NiTi) rotary file system can be used in single length technique (simultaneous technique) without early coronal enlargement, as well as in crown-down method. The purpose of this in vitro study was to compare single length with crown-down methods’ shaping ability using MTWO NiTi files.MATERIALS & METHODS: Fifteen acrylic-resin blocks containing simulated canals were divided into two experimental groups. In group A, single length technique was used and in group B root canals were prepared by crown-down technique. Pre-and post-preparation canals were photographed in a standardized manner and were superimposed. The inner and outer walls of canal curvature were evaluated at three points (apical, middle and coronal) to determine the greatest change. The data was statistically analyzed using the Student t-test by Statistical Analysis System (SAS) software.RESULTS: Statistical analysis revealed that in group B, dentine was equally removed within the canal coronal to the curvature, whereas in group A, the inner wall was predominantly removed (P<0.01). The two groups had no significant difference at the apical and middle points of the canal curvature.CONCLUSION: Our in vitro study revealed no significant difference between the single length method and crown-down technique using MTWO for preparation of apical and middle portion of canal curvature.

Background and Aim: Effective cleaning and shaping of the root canal system is an essential part of a successful root canal treatment and is considered as one of the basic features of rotary instruments. The present study aimed to compare the efficacy of two types of nickel-titanium rotary files namely BioRaCe and MTWO, in reduction of Enterococcus faecalis (E. faecalis) count in the root canal system. Materials and Methods: In this in vitro study, 50 extracted human single-rooted teeth were assigned to two groups plus a positive and a negative control group (20 samples in each group). First, the root canals were sterilized and were then inoculated with E. faecalis (ATCC: 11700). Subsequently, all the root canals were instrumented with BioRaCe and MTWO nickel-titanium rotary instruments. Then, samples were collected from inside the root canals and cultured in a special medium to evaluate the remaining colonies. The Chi-square goodness of fit test was used to assess the difference in bacterial colony count after root canal preparation with the two rotary systems (alpha=0.05).  Results: Complete bacterial growth was observed in both the BioRaCe and MTWO groups. There was no statistically significant difference between the two groups regarding bacterial elimination from the root canal system (P>0.05). Conclusion: Under the limitations of the current study, the two rotary systems exhibited no superiority over each other in terms of their ability to eliminate microorganisms from the root canal system.

Introduction: The purpose of this study was to evaluate the efficacy of three methods in removal of Resilon/new Epiphany self-etch (SE) soft resin endodontic obturation system.Materials and Methods: Thirty extracted single rooted human teeth were prepared for endodontic treatment and obturated with Resilon/Epiphany SE. The roots were randomly divided into three groups; group 1 roots were retreated using MTWO R/MTWO files; group 2 were retreated using MTWO R/MTWO accompanied with chloroform; and group 3 were retreated using MTWO R/MTWO accompanied with Endosolv R. The cleanliness of canal walls was determined using scanning electron microscopy. Data were analyzed using ANOVA and LSD tests.Results: Endosolv R combined with rotary files was more efficient in material removal compared to chloroform combined with rotary files and rotary files alone (P<0.05). Also, chloroform combined with rotary file was more efficient than rotary file alone in removing filling material from the root canals. Significant difference was found within group 1 between the coronal third compared to the middle and apical thirds (P<0.05). In group 2, there were more material remnants in the apical third (P<0.05). In group 3, there was no significant difference between the three segments of the root canals (P>0.05).Conclusion: All techniques left filling material remnants and debris on the root canal walls. Endosolv R combined with rotary files most effectively removed filling materials from the root canals, especially in the apical third.

Introduction: The objective of this in vitro study was to evaluate whether cervical preparation with MTWO files in a crown-down technique influences instrumentation time and the cyclic fatigue resistance of these instruments. Methods and Materials: Two instrumentation techniques were evaluated (manufacturer and crown-down). Each group consisted of 10 kits containing four MTWO instruments (10/0. 04, 15/0. 05, 20/0. 06, and 25/0. 06), which were used to prepare three standard simulated curved resin canals. The mean instrumentation time and the corresponding number of cycles for each instrumentation (NCI) were recorded. The instruments were rotated at a constant speed of 300 rpm in a stainless-steel canal (diameter of 1. 5 mm) at a 90° angle of curvature and 5-mm radius. The center of the curvature was 5 mm from the tip of the instrument. The cyclic fatigue resistance of the files was determined by counting the number of cycles to failure (NCF). Data were analyzed by the Mann-Whitney test. Results: The mean instrumentation time and NCI of files 10/0. 04 and 15/0. 05 were significantly lower (P<0. 05) when the crowndown technique was used compared to the manufacturer’ s method for the same tip size/taper file. There was no significant difference in the mean NCF between the two techniques. Conclusion: The crown-down technique did not interfere with resistance to cyclic fatigue. However, the shorter instrumentation time of files 10/0. 04 and 15/0. 05 could reduce the fracture risk in the case of reuse of these instruments.

Introduction: The aim of this study was to compare the formation of dentinal crack and craze lines in the root dentin during root canal preparation with three different NiTi endodontic systems, naming Reciproc (RCP), ProTaper Universal (PTU) and MTWO.Methods and Materials: One hundred extracted mandibular premolars with single canals were selected and decoronated. The teeth were randomly divided into four groups of 25 each (n=25). In groups 1, 2 and 3 the teeth were prepared using MTWO, PTU and RCP, respectively. While in group 4 (control group) the samples were left unprepared. After preparation, all specimens were sectioned perpendicular to the long axis of root at 3, 5 and 9-mm distances from the apex.The sections were then individually observed under 12× magnification using stereomicroscope. The data was analyzed using the chi-square and Fisher’s exact tests. The level of significance was set at 0.05.Results: No cracks were observed in the control group.All engine-driven systems caused dentinal cracks. MTWO and PTU caused cracks significantly more than RCP (P<0.05). There was no significant difference between RCP and control group (P>0.05).Conclusion: All three engine-driven systems created dentinal defects. Reciproc caused less cracks than MTWO and ProTaper Universal.