The influence of preparation size on efficacy of EDTA for smear layer removal in the apical part of root canal: an in vitro SEM study
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Background: Success of RCT relies on proper chemomechanical preparation, effective disinfection of root canal system and its three-dimensional obturation. During canal preparation a smear layer cover is produced. Adequate removal of this smear layer using EDTA is essential for the success of infected root canal treatment. Several parameters, including apical size preparation, affects the smear layer removal ability. Aim: To study the role of the size of apical root canal preparation on removal of smear layer after irrigation with EDTA solution on extracted human teeth. Materials and Methods: Forty-two extracted mandibular molars were included in the study. Radiographic examination with two views, mesio-distal and bucco-lingual, were taken for examination of distal canal. Teeth were selected according to specific inclusion criteria. They were divided into three groups; each contains fourteen samples. Working length was set at minor apical foramen, 1mm from major apical foramen visible under dental operating microscope. Protaper universal system was used for distal canal preparation with the Master Apical File as follows: Group A finishing at F2 (#25/0.08), Group B finishing at F4 (#40/0.06) and Group C finishing at F5 (#50/0.06). Full irrigation protocol was followed with 2ml of sodium hypochlorite in a concentration 5.25%, used between each file and 3ml after completion of canal preparation with activation 20 seconds for 3 cycles using Endo activator. 2ml EDTA solution in a concentration 17% was used for 1 minute with activation using Endo Activator. A 30-guage side vented needle was used for irrigation and set 1mm from minor apical foramen. Final irrigation was done with 5ml saline. Specimens were decoronated and distal root was sectioned bucco-lingually into two halves. The half which showed better apical configuration was selected and immersed in alcohol (70%) for 20 minutes for dehydration. The specimens were further sputter-coated with carbon (C) under vacuum and examined in a Scanning Electron Microscope. The SEM analysis was done at the General Department of Forensic Science and Criminology at the Dubai Police Head Quarter. SEM images were taken at three levels of the apical end, at 2mm, 4mm and 6mm. Total of 6 images fro each specimen. Images were randomly arranged for smear layer evaluation. The evaluation was performed by two blinded observers (endodontists) and reevaluation was done at a second session with 30 days interval. Images evaluation was done on the basis of a 4-grade score system as has been proposed by Hulsmann et al. 1997. Results: Clear root canal walls were found throughout the apical half of the roots in only 11.9%, 19 % and 54.7% of the samples in groups A, B and C, respectively. In comparison between groups, Group C showed to have significantly better scores (p=0.000) than other groups with 81% of the samples had less than 50% of the dentinal walls free of smear layer/debris, while it was only 45.2% and 35.7% of the samples in group B and A respectively. In comparison between levels, at level of 2mm, group C had significantly better results in estimating 0-50% presence of smear layer/debris in the scanned dentinal walls areas (p=0.041). At level of 4mm, also group C showed significantly better results in estimating 0-50% presence of smear layer/debris in the analyzed dentinal walls areas (p=0.002) and in estimating 0-15% of the presence of smear layer analysis (p=0.004). At level of 6mm, significantly better scores in estimating 0-15% of the presence of smear layer/debris in the scanned dentinal walls areas was found in group C (p=0.023). Conclusion: Significant differences between the groups of teeth with different size of apical enlargement were found when various measurement criteria were performed. The present iii results clearly indicate that the ability of irrigation to remove smear layer/debris from the instrumented straight root canals at their apical part is enhanced with increasing the size of apical preparation with the Protaper rotary system.