Introduction: Although endodontic treatment has markedly changed due to the improvement of instruments and materials, mechanical cleaning remains insufficient to control intracanal infection. Root canal irrigation and intracanal medication are considered necessary. In the present study, a questionnaire survey regarding root canal irrigation methods used in clinical settings at dental university hospitals in Japan was conducted.

 Method: A questionnaire titled “A survey regarding root canal irrigation methods used in clinical settings” was sent to 34 endodontic departments in Japan.

 Results: The response rate to the questionnaire was 88%, and all departments performed root canal irrigation. The timing of root canal irrigation was as follows: Performed every time (root canal enlargement): 30%, Performed as needed (root canal enlargement): 80%, Performed after, not during, root canal enlargement (before root canal application): 3%.

 Instruments used for root canal irrigation were as follows: Syringe: 93%, Passive ultrasonic irrigation: 87%, Sonically activated irrigation: 13%, Others: 3%. Types of syringe were as follows: Root canal syringe: 32%, Syringe and open-ended flat needle: 64%, Syringe and side-vented needle: 32%. Irrigants used were as follows: Sodium hypochlorite solution: 96%, EDTA solution: 96%, Hydrogen peroxide solution: 32%, Saline: 32%, Sterile water: 4%, Citric acid solution: 4%.

 Conclusion: All endodontic departments in dental university hospitals in Japan that answered the questionnaire regarding root canal irrigation performed root canal irrigation. There was a common awareness that root canal irrigation is necessary. Many departments have introduced not only a syringe but also passive ultrasonic irrigation and sonically activated irrigation. As for root irrigation agents, many departments have introduced sodium hypochlorite and EDTA solutions.

 Purpose: An important clinical challenge in endodontics is the constricted and mineralized root canal, which prevents chemical cleaning and leads to periodontitis with pain. Therefore, clinical access to the constricted root canal may ameliorate periodontitis. We recently developed negatively charged nanobubbles containing pressured air to enhance delivery of medications to dentinal tubules. The aim of this investigation was to examine whether nanobubbles can enhance dentin demineralization by enhanced delivery of ethylenediaminetetraacetic acid (EDTA) into dentin.

 Methods: An experimental model was established using porcine tooth roots. Enhanced delivery of medications by nanobubbles into dentinal tubules was confirmed by tetracycline with autofluorescence. The following experimental groups were compared: nanobubbles only, 8.5% EDTA with 50% nanobubbles, 8.5% EDTA, 17% EDTA, and distilled water (control) for a duration of 5 min, 24 h and 72 h. Vickers hardness was determined at depths of 100, 300 and 500 μm in the root canal. Dentinal erosion was assessed by scanning electron microscopy.

 Results: Nanobubbles enhanced the delivery of tetracycline into dentinal tubules. There was no difference in Vickers hardness between distilled water and nanobubbles only. Treatment with 8.5% and 17% EDTA significantly reduced Vickers hardness at a depth of 100 μm (p<0.05 or p<0.01), but not at 300 and 500 μm. Conversely, addition of 50% nanobubbles to 8.5% EDTA significantly reduced Vickers hardness at 100, 300 and 500 μm compared with nanobubbles only and 8.5% EDTA only and reached equilibrium by 5min (p<0.01). Peritubular dentin was exposed by 8.5% EDTA with 50% nanobubbles for 5min. There was no significant difference in size of dentinal tubules by treatment for 24 h and 72 h compared to 5min.

 Conclusions: This investigation demonstrated the utility of the addition of 50% nanobubbles to 8.5% EDTA to enhance dentin demineralization compared with treatment without nanobubbles.

 Purpose: For successful pulpectomy or infected root canal treatment, it is necessary to completely irrigate the root canal following instrumentation, fill the root canal, and seal the crown. The smear layer, an unstructured accumulation of debris composed of organic and inorganic components, forms on the dentinal wall during instrumentation. Generally, EDTA or citric acid is used to remove the smear layer, which prevents access of intracanal medications. However, these irrigants may cause apical root fracture, subsequently inducing dentinal wall demineralization. We recently developed nanobubbles to enhance the delivery of medications to dentinal tubules. The aim of this investigation was to examine the utility of nanobubbles for removing the smear layer.

 Methods: An experimental model was established using porcine tooth roots in vitro. The following groups were compared: nanobubbles for 5 min, 17% EDTA for 1min, 3% EDTA for 2 min, 20% citric acid for 3 min, 4.25% citric acid for 5 min, and distilled water (control). Root canal cleanliness was assessed by scanning electron microscopy. Vickers hardness was determined at the depth of 100 μm from the dentinal wall.

 Results: There was no difference in root canal cleanliness between nanobubbles for 5 min and 20% citric acid for 3 min. Significant exposure of dentinal tubules was observed in nanobubbles compared with other irrigants (p<0.01, n=3). Vickers hardness after treatment with nanobubbles was almost the same compared with distilled water. Treatment with 17% EDTA, 20% citric acid and 4.25% citric acid, however, significantly reduced Vickers hardness compared with distilled water (p<0.05, n=3).

 Conclusion: This investigation demonstrated the utility of nanobubbles for removing the smear layer in root canal treatment.