Tasdemir, Er, Celik, Yildirim irrigated with 2 mL NaOCI solution using a syringe and irrigation needle, PUI is applied for 30 seconds or one minute, and the root canal is again irrigated in the same manner. This procedure is repeated several times. A second option is to enable a continuous flow of irrigation during PUI. The results of a previous study showed no significant difference between syringe delivery of the irrigant and a continuous flow of irrigant when PUI was used for three minutes.37 This study’s aim was to determine the volume of apically extruded solution only during PUI procedure. Therefore, in order to eliminate the amount of solution possibly extruded during push pressure with the syringe, the root canal was only filled with irrigation solution in each group, and the amount of solution extruded from the apical foramen for three minutes was measured with a pipette. The same canals were used in both groups to eliminate the variables encountered in root canals in different teeth, such as curvature and canal diameter. Previous study reported that ultrasonic irrigation was more effective in removing artificially placed dentine debris from simulated canal extensions from canals with greater tapers.38 This study obtained canals with greater tapers by using Gates Glidden burs and ProTaper instruments. Maximum attention was paid to avoid the instruments’ contact the canal’s walls during PUI procedure. The NaOCl solution’s to be not extruded through the apical foramen or pushed to the less level during PUI may be explained by the effect of acoustic streaming inside the canal, which can move the solution inside the canal from the apical toward the coronal direction. Moreover, the decoronated teeth do not provide a coronal reservoir for the irrigation solution. When activating the intracanal solution using ultrasonic a considerable amount of solution may be lost coronally, decreasing the hydrostatic pressure towards the apex. The objective of this study was to assess the apical extrusion of 2.5% NaOCl solution during PUI. According to the data obtained in the study, the amount of apically extruded irrigant during PUI is fairly little. It must be emphasized that the results of this study should not be directly extrapolated to the clinical situation. No attempt has been made to July 2008 - Vol.2 simulate the presence of vital pulp or periapical tissues, an in vivo model may give different result, as the periapical tissues may serve as a natural barrier, inhibiting debris extrusion. Results may also differ because of positive or negative pressure at the apex and with normal or pathological tissues. Furthermore, this study was limited to teeth with mature root morphology. The observed results should not be generalized to teeth with immature root development and open apicies. PUI’s cleaning efficacy implies the effective removal of dentine debris, microorganisms (planktonic or in biofilm) and organic tissue from the root canal. Acoustic streaming the irrigant enhances its potential to contact a large surface area of the canal’s wall.39 Besides these positive attributes, the fact that PUI, as the final irrigation, does not push the NaOCl solution to periapical tissues may enable it to become a critical component of modern endodontic therapy. CoNCLuSIoNS When a file is passively activated in a canal by ultrasonics for three minutes after instrumentation, it results low risks of apical extrusion of the irrigating solution. REFERENCES 1. Hülsmann M, Hahn W. Complications during root canal irrigation–literature review and case reports. Int Endod J 2000;33:186-193. 2. Zehnder M. Root canal irrigants. J Endod 2006;32:389-398. 3. Zehnder M, Kosicki D, Luder H, Sener B, Waltimo T. Tissue- dissolving capacity and antibacterial effect of buffered and unbuffered hypochlorite solutions. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:756-762. 4. Naenni N, Thoma K, Zehnder M. Soft tissue dissolution capacity of currently used and potential endodontic irrigants. J Endod 2004;30:785-787. 5. Sirtes G, Waltimo T, Schaetzle M, Zehnder M. The effects of temperature on sodium hypochlorite short-term stability, pulp dissolution capacity, and antimicrobial efficacy. J Endod 2005;31:669-671. 6. Gatot A, Arbelle J, Leiberman A, Yanai-Inbar I. Effects of sodium hypochlorite on soft tissues after its inadvertent injection beyond the root apex. J Endod 1991;17:573-574. 7. Gernhardt CR, Eppendorf K, Kozlowski A, Brandt M. Toxicity of concentrated sodium hypochlorite used as an endodontic irrigant. Int Endod J 2004;37:272-280. 201 European Journal of Dentistry