Comparative Evaluation of Different Irrigation Fluids on Smear Layer Removal, Root Canal Sealant Penetration Effect and Mechanical Properties of Human Dentin

Objective: To compare the removal of smear layer from root canal wall with different irrigation solutions in vitro and evaluate the penetration of root canal sealers into dentinal tubules and their effects on the mechanical properties of dentin. Methods: 69 human single-rooted premolars and 36 human molars were selected and randomly divided into 5 experimental groups and negative control group according to different irrigation regimens. 5.25%NaClO (A),6%MCJ (B),17%EDTA (C),5.25%NaClO + 17%EDTA (D),6%MCJ + 17%EDTA (E) and negative control group (Distilled water) (DW). Each group were selected for scanning electron microscopy, hot gutta-percha vertical compression filling and micro-hardness testing randomly (n=4). Each group were selected for flexural strength, compressive strength, and ultimate tensile strength testing (UTS), randomly (n=6). Results: The removal effect of smear layer in groups D and E was better than that in groups A, B and the control group ( P < 0.05). The maximum depth and penetration rate of root canal sealer penetration were significantly greater in groups D and E than the control group ( P < 0.05). Group B and E significantly reduced the mechanical properties of dentine (micro-hardness, flexural strength, compressive strength and UTS) ( P ＜0.05). Conclusion: The combination of MCJ and EDTA could better remove the smear layer and promote the penetration of root canal sealers. Furthermore, they had less detrimental effect on the mechanical properties of dentin than the combination of NaClO and EDTA.Clinical Significance: Because traditional Chinese medicine root canal irrigation Morinda citrifolia has good biocompatibility, antibacterial properties and less adverse effects on the mechanical properties of dentin than NaClO, it is expected to replace NaClO as an ideal root canal irrigating solution in clinical practice.