AIM: With the increased bacterial resistance and the resulting problems in recent years, it seems necessary to find new biocompatible compounds to confront this problem. This research was conducted to optimise the synthesis of cobalt oxide nanoparticles with the highest antibacterial activity. METHODS: In the present study, 9 experiments were designed using the Taguchi method. The effect of three factors of cobalt nitrate, KOH and the stirring time in the synthesis of cobalt oxide nanoparticles with the highest antibacterial activity was investigated. The bactericidal effect of synthesised nanoparticles was evaluated using the colony-forming unit (CFU) and disk diffusion methods. The characteristics of nanoparticles were studied using the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and the scanning electron microscopy (SEM). RESULTS: The results indicated that all three evaluated factors were effective on the antibacterial properties of the synthesised nanoparticles. The best antibacterial activity of cobalt oxide nanoparticles was observed in experiment 9 (cobalt nitrate 0.6 M, KOH 2M and stirring time 60 min). The study of nanoparticles synthesised by FTIR, XRD, and SEM confirmed the formation of cobalt oxide nanoparticles with size (24 nm) and a proper structure (spinel structure). CONCLUSION: Due to the optimal antibacterial properties of the synthesised cobalt oxide nanoparticles, they can be used in the fabrication of dental and medical equipment with antibacterial properties.

AIM:This study was conducted to investigate the effect of applying Gates-Glidden (GG) drill by pre-clinical dental students on root canal treatment quality.METHOD:A total of 56 first molars consisting of 168 canals were selected in this study. For this purpose, 56 students who had been formerly trained by two methods of root canal preparation were randomly divided into two groups (n = 28). Group 1: the step-down method by GG and Group 2: step-back technique without GG. The prepared teeth were filled with gutta-percha/ZOE sealer using lateral condensation. Periapical radiographs were taken before and the following treatment to survey occurrence of preparation errors and CBCT images to determine residual dentine at furcation region.RESULTS:The findings showed that among 10 error types in specimens prepared by students, the occurrence of underfilling, overfilling, inappropriate, ledge formation, and single cone was more common without GG. There were no significant differences in residual dentine amount at furcation region between preparation with and without using GG (P > 0.05).CONCLUSION:Using GG for root canal preparation by dental students resulted in low errors and not an increased dentine removal risk.

Background and aim: There is a high prevalence of root canal transportation in the teeth with the curve. effect of root canal transportation on the success of root canal therapy of tooth is negative and there is no study about comparing RaCe and Neoniti files in root canal transportation. The aim of this study is assessment and comparing two different RaCe and Neoniti files to determine transportation error in various parts of root using CBCT assessment and comparing them with each other.Method: In this experimental study 50 extracted mandibular molar teeth selected. Teeth were divided randomly into two groups i.e. 25 teeth threated with RaCe file (first group) and 25 teeth threated with Neonitu files (second group). in this study to measurement  thickness of dentine in the scan ,before and after instrumentation at the same time we used axial images that obtain from NNT viewer 6.1.0 software .Findings: in the first group ,The mean tooth transportation  in 5 mm of apex  was 0.15 and  in the second group The mean tooth transportation  in 5 mm of apex  was 0.18 mm that there was no statistically significant difference in canal transportation  between RaCe and Neoniti files in five millimeters distant from apex area (p=0.492) and the mean transportation from 9 mm of apex was 0.14 in the second group that There was no statistically significant difference in canal transportation between two  groups (p=0.911).Conclusion: The results indicated that there was no significant difference of tooth transportation between two file systems in 3, 9, 7, 5 and 11mm from the apex and both files were safe.