Introduction: This study aimed to compare the incidence of dentinal Crack formation by instrumentation with ProTaper Universal system (rotary, multi-file system), SafeSider (reciprocation movement, multi-file system) and Neolix (rotary, single-file system). Methods and Materials: In this in vitro study, 60 freshly extracted mandibular first molars were randomly divided into three experimental groups (n=15) and a control group containing unprepared teeth (n=15). Instrumentation in different groups was accomplished using either ProTaper, Neolix or SafeSider systems up to 25/0. 08. The teeth were then sectioned at 3, 6 and 9 mm from the apex, and observed under a stereomicroscope for presence of dentinal Cracks. Data were analyzed with Chi square test, Fisher’ s exact test and Bonferroni correction. Results: Micro Cracks were seen in all experimental groups (13. 3% in ProTaper, 26. 7% in SafeSider and 40% in Neolix). There was a significant difference between Neolix and the control groups in microCrack formation (P=0. 042). Micro Cracks mainly occurred in the coronal section (9 mm). No microCrack occurred in the control group. Conclusion: Neolix rotary single-file system caused more dentinal Cracks compared to the unprepared Roots. All the instrumentation systems increased the number of micro Cracks compared to unprepared teeth.

Objective: This study investigated the effect of glide path preparation and different instruments in creating dentinal Cracks during Root canal instrumentation. Methods: Eighty maxillary molars were divided into four groups (n=20). The mesiobuccal Root canals were prepared using two rotary systems (Group 1: Hyflex EDM and Group 2: ProTaper Gold) and two reciprocating systems (Group 3: WaveOne Gold and Group 4: Reciproc Blue R25). In each group, ten specimens were prepared using the designated glide path files. Methylene blue dye was injected into the Root canals to highlight dentinal Cracks. The samples were then sectioned and examined under a microscope to count the number of dentinal Cracks at the apical, middle, and coronal thirds. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests (P<0.05). Results: When glide path files were not used, the number of Cracks was comparable across the groups in coronal, middle and apical sections (P>0.05). Among the samples prepared with glide path files, those instrumented with WaveOne Gold showed a significantly higher number of dentinal Cracks in the coronal section compared to ProTaper Gold (P<0.05), and in the middle section compared to both HyFlex EDM and ProTaper Gold (P<0.05). In the apical section, no significant difference in the number of Cracks was observed among the groups (P=0.627). Conclusions: Glide path preparation with rotary systems (ProTaper Gold and HyFlex EDM) resulted in fewer dentinal Cracks in the mesiobuccal Root canals of maxillary molars compared to a reciprocating system (WaveOne Gold).

Background and Aim: Today several materials have been used for Root- end filling in endodontic surgery. Optimal properties of Pro Root MTA in in-vitro and in-vivo studies have been proven. On the other hand, based on some studies, Root MTA (Iranian Pro Root MTA) and Portland cement are similar to Pro Root MTA in physical and biologic properties. The aim of this study was to evaluate bacterial leakage (amount and mean leakage time) of four Root- end filling materials. Materials and Methods: In this experimental in-vitro study, seventy six extracted single- Rooted human teeth were randomly divided into six groups for Root-end filling with gray Pro Root MTA, white Pro Root MTA, Root MTA (Iranian Pro Root MTA), Portland Cement (type I) and positive and negative control groups. Root canals were instrumented using the step- back technique. Root- end filling materials were placed in 3mm ultra sonic retro preparations. Samples and microleakage model system were sterilized in autoclave. The apical 3-4 mm of the Roots were immersed in phenol red with 3% lactose broth culture medium. The coronal access of each specimen was inoculated every 24h with a suspension of Streptococcus sanguis (ATCC 10556). Culture media were observed every 24h for color change indicating bacterial contamination for 60 days. Statistical analysis was performed using log- rank test with P<0.05 as the limit of significance. Results: At the end of study 50%, 56.25%, 56.25% and 50% of specimens filled with Gray Pro Root MTA, White Pro Root MTA. Root MTA and Portland Cement (type I) had evidence of leakage respectively. The mean leakage time was 37.19±6.29, 36.44±5.81, 37.69±5.97 and 34.81±6.67 days respectively. Statistical analysis of data showed no significant difference among the leakage (amount and mean leakage time) of the four tested Root- end filling materials (P=0.9958). Conclusion: Based on the results of this study, there were no significant differences in leakage among the four tested groups at 60 days. The results suggest that Root MTA and Portland Cement can be used as less expensive Root filling materials.

Background and Aim: Mineral Trioxide Aggregate (MTA) is a material used in many endodontic problems.Recently a number of studies have reported that Portland Cement (PC) and MTA have similar physical, chemical and biologic properties. In addition, a material known as Root MTA which is produced in Iran has been claimed to have similar properties to Pro Root MTA. If these claims are true, possible use of PC and Root MTA in clinic instead of Pro Root MTA will be quite cost effective. The aim of this study was to investigate the toxicity of Pro Root MTA, Root MTA and Portland Cement on L929 mouse fibroblasts.Materials and Methods: In this experimental study 0, 4, 24 hours and 7 days' extracts of materials were transferred to cell culture plates containing L929 fibroblasts. After 24 hours incubation, cells were stained by Neutral Red (NR), and optical density (OD) of each cell was read with ELISA reader. Data were analyzed using Tukey HSD and one way analysis of variance. P<0.05 was considered as the level of significance.Results: In all surveyed groups and negative control group, at all time points separated cells from the base of the well were round. Refraction which is a characteristic of cellular death was not observed, whereas the separated cells from the base of well in positive control group showed refractional characteristic.Conclusion: Based on the findings of this study Pro Root MTA, PC and Root MTA have the same biocompatibility. PC seems to have the potential to be used in the same clinical situation as MTA. However in order to replace MTA with these less expensive materials more in vitro and in vivo studies are suggested.

Background and Aim: The goal of endodontics is to seal the Root canal system from the orifice to apical constriction completely and tridimensionally. Hence perforations during Root canal therapy, because of caries or resorptions must be sealed and obturated with ideal materials. The aim of this study was to histologically compare two kinds of mineral trioxide aggregate Root MTA and Pro Root MTA for furcal perforation repair in developed teeth in dog. Materials and Methods: In this experimental study, thirty teeth consisting of second, third and fourth mandibular premolars of five German shepherd dogs were selected. Twenty-four teeth were randomly divided into four experimental groups (6 teeth each). One pair of Root MTA and Pro Root MTA groups studied in one month and the other in three months intervals. Positive and negative control groups was each contained three teeth. In positive control group, perforations were not treated and negative control group contained intact teeth. In experimental groups perforations repaired after one week exposure to oral cavity with Root MTA or Pro Root MTA. After time intervals animals were subjected to vital perfusion and 6 mm histologic sections were prepared. Inflammation and hard tissue formation were ranked by Cox criteria. Data were analysed using Mann-Whitney and Chi-Square statistical tests with P<0.05 as the limit of significance. Results: There was statistically significant lower inflammation and higher hard tissue formation in three months Root MTA and Pro Root MTA groups compared to one month interval (P<0.05). There was no statistically significant difference in inflammation and hard tissue formation between Root MTA and Pro Root MTA in each intervals (P>0.05). Conclusion: Mineral Trioxide Aggregate is an adequate material for furcal perforation repair in dog’s teeth. Root MTA could be a good substitute for Pro Root MTA considering the lower cost and similar characteristics.

To ensure the rail transportations safety, evaluation of fatigue behavior of the rail steel is necessary. High cycle fatigue behavior of a rail steel was the subject of investigation in this research using fracture mechanics. Finite element method (FEM) was used for analyzing the distribution of the stresses on the rail, exerted by the external load. FEM analysis showed that the maximum longitudinal stresses occurred on the railhead. To find out about the relation of Crack growth with its critical size, and to estimate its lifetime, the behavior of transverse Cracks to rail direction was studied using damage tolerance concept. It revealed that transverse Crack growth initially occurred slowly, but it accelerated once the Crack size became larger. Residual service life was calculated for defective segments of the rails. In addition, allowable Crack size for different non-destructive testing intervals was determined; the allowable Crack size decreased as the NDT intervals increased.

Background: Prevention of dentinal Crack formation is of utmost importance in endodontic treatment. This study aimed to evaluate the effect of RaCe, ProTaper, and V-Taper rotary systems on dentinal Crack formation in three Root regions during endodontic treatment. Methods: Seventy human mandibular first molars were selected randomly, and their distal Roots were used. Ten samples were assigned to the control group, and sixty samples were assigned to three groups (n = 20). Each group was prepared with RaCe, ProTaper, or V-Taper rotary files according to the manufacturers’,instructions. A stereomicroscope was used to view Cracks at ×40 magnification. Friedman’, s, chi-squared, and Kruskal-Wallis tests were used for statistical analysis of data (P < 0. 05). Results: A comparison of the three rotary systems did not reveal any significant differences in the number of Cracks between the three Root thirds evaluated (P > 0. 05). A comparison of the number of Cracks in the coronal, middle, and apical thirds in each rotary system showed that the number of Cracks in the middle third was fewer than that in the two other thirds only in the V-Taper group (P < 0. 05), with no significant differences in the ProTaper and RaCe groups between the different Root regions (P > 0. 05). Conclusion: The application of RaCe, ProTaper, and V-Taper rotary files resulted in a similar rate of Crack formation in endodontic treatment. V-Taper files created the minimum number of Cracks in the middle third.

Modeling of Crack propagation by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode Crack growth in linear elastic fracture mechanics. Crack growth process is simulated by an incremental Crack-extension analysis based on the maximum principal stress criterion, which is expressed in terms of the stress intensity factor.In this paper, a procedure to correct the direction of Crack propagation in the analysis of finite element is presented to ensure that a unique final Crack path is achieved for different analysis of a problem by using different increments of Crack. For each increment of Crack extension, finite element method is applied to perform a single region stress analysis of the Cracked structure. Results of this incremental Crack extension analysis are presented for several geometries.