Apical Pressure and Extent of Irrigant Flow beyond the Needle Tip during Positive-pressure Irrigation in an In Vitro Root Canal Model

Introduction: This study aimed to measure the pressure generated during positive-pressure irrigation at the periapex of an in vitro tooth model using a novel method of measurement, investigating the effect of flow rate and needle design. Apical pressure was correlated with the extent of dye clearance from the end of a needle tip in a plastic root canal model with similar dimensions. Methods: The mesiobuccal canal of a mandibular molar was instrumented to #35/06 and placed into a chamber coupled to a pressure transducer. Irrigation was performed using a digital peristaltic pump using flow rates from 1-15 mL/min with irrigation needles of different sizes and designs. A plastic root canal model instrumented to the same size filled with dye was used to measure the extent of dye clearance beyond the needle tip using the same irrigation conditions. Results: Positive-pressure irrigation revealed a flow rate dependent increase in apical pressure (P < .05). The apical pressure at high irrigation flow rates was several times higher than at low flow rates. Needle designs with safety features yielded statistically significant lower apical pressures than needles without safety features (P < 05). There was no further increase in dye clearance from the end of the needle tip in a plastic root canal model at flow rates higher than 4 mL/min. Conclusions: If apical clearance of dye beyond the needle tip is a measure of irrigation effectiveness, then maximum effectiveness with safe apical pressures can be gained at specific flow rates using specific needle tip designs. The use of an irrigation flow rate of 4 mL/min was able to achieve maximum effectiveness in this study.