Introduction This study examined the effect of vapor lock on canal debridement efficacy by testing the null hypothesis that there is no difference between a “Closed” and an “Open” system design in smear layer and debris removal using a side-vented needle for irrigant delivery. Methods Roots in the “Closed System” were sealed with hot glue and embedded in polyvinylsiloxane to restrict fluid flow through the apical foramen during cleaning and shaping. For the “Open System”, the apical foramen was enlarged and connected to the external environment via a channel within the polyvinylsiloxane to permit unrestricted fluid flow. Smear and debris scores were evaluated using SEM and analyzed using Cochran-Mantel-Haenszel statistic. Results No difference in smear scores was detected between the two systems at all canal levels. Significant differences in debris scores between the two systems were found at each canal level: coronal (p<0.001), middle (p<0 .001) and apical (p<0.001). Conclusion The null hypothesis was rejected; presence of an apical vapor lock effect adversely affects debridement efficacy. Thus, studies with unspecified or questionable mechanisms to restrict fluid flow through the apical foramen have to be interpreted with caution.

Objectives Root canal treatment forms an essential part of general dental practice. Sodium hypochlorite (NaOCl) is the most commonly used irrigant in endodontics due to its ability to dissolve organic soft tissues in the root canal system and its action as a potent antimicrobial agent. Although NaOCl accidents created by extrusion of the irrigant through root apices are relatively rare and are seldom life-threatening, they do create substantial morbidity when they occur. Methods To date, NaOCl accidents have only been published as isolated case reports. Although previous studies have attempted to summarise the symptoms involved in these case reports, there was no endeavor to analyse the distribution of soft tissue distribution in those reports. In this review, the anatomy of a classical NaOCl accident that involves facial swelling and ecchymosis is discussed. Results By summarising the facial manifestations presented in previous case reports, a novel hypothesis that involves intravenous infusion of extruded NaOCl into the facial vein via non-collapsible venous sinusoids within the cancellous bone is presented. Conclusions Understanding the mechanism involved in precipitating a classic NaOCl accident will enable the profession to make the best decision regarding the choice of irrigant delivery techniques in root canal débridement, and for manufacturers to design and improve their irrigation systems to achieve maximum safety and efficient cleanliness of the root canal system.

Sodium hypochlorite is an effective irrigant for chemical debridement of root canals. However, increasing the intracanal pressure during irrigant delivery may result in irrigant extrusion into the bone and soft tissues surrounding the tooth. Because clinicians often encounter teeth with intracanal communications, the objective of the present study was to examine the effects of canal anastomosis on the generation of periapical fluid pressure at different fluid flow rates and insertion depths. Two similar polycarbonate models were used to simulate a single root with double canals, one containing, and the other without communicating channels between the canals. For both models, periapical pressure increased with increasing irrigant flow rates and insertion depths of a 30-gauge side-venting needle. In the presence of communicating channels, the magnitude of pressure build-up decreased by almost 90% irrespective of the fluid flow rate or needle insertion depth. Pressure reduction in anastomosescontaining roots provides an explanation why pressure generation in single roots is considerably higher. Nevertheless, it is still possible in teeth with canal anastomoses for pressure exceeding the intraosseous pressure to be generated when the fluid flow rate is sufficiently high and when the needle tip is close to the apical terminus.Success in root canal treatment is dependent upon the clinicians' ability to eradicate the source of intraradicular infection. Chemical debridement efficacy is related to the ability of the irrigant to infiltrate the entire canal space 1 . Irrigants are often introduced into root canals by positive pressure via a syringe attached to a hypodermic needle 2 . Sodium hypochlorite (NaOCl) is an effective irrigant for chemical debridement of root canals due to its ability to dissolve the organic components of necrotic and vital tissues, lubricate files during instrumentation, clear dentinal debris, and inactivate/dissolve bacterial biofilms 3 . The efficacy of NaOCl delivery is a function of the needle design, depth of irrigation needle insertion, and the flow rate of irrigant expressed from the needle 1, 2, 4 . The most difficult segment of a canal to be thoroughly irrigated is the apical third of the canal space. Even before endodontics became a dental specialty, anatomical studies have demonstrated that the greatest degree of complexity occurs in the apical third of the canal space 5,6 .There is a subtle balance between efficacy and safety for needle-assisted irrigation of the apical canal space. It is important to implement fluid exchange at the canal terminus by bringing the needle tip close to the working

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