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The effect of flow rate, needle design, and needle placement on apical pressure and irrigant exchange in an in vitro tooth model Park, Ellen


Heavy irrigation forces in a root canal can lead to irrigant extrusion accidents, causing negative sequelae for patients. There are no guidelines for a safe and optimal irrigation flow rate and little data on the apical pressures generated during irrigation. This study aimed to measure the pressure generated during positive and negative pressure irrigation at the periapex of an in vitro tooth model using a novel method of measurement, investigating the effect of flow rate, depth of needle placement, and needle design. Apical pressure was correlated with extent of dye clearance from the end of a needle tip in a similar model. A mandibular molar was prepared 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 size and design. A similar plastic root canal model filled with dye was used to measure the extent of dye clearance beyond the needle tip using the same irrigation conditions. Positive pressure irrigation revealed a flow rate dependent and depth of needle placement dependent increase in apical pressure (P<0.05). Needle designs with safety features yielded statistically significant lower apical pressures than needles without safety features (P<0.05). There was no further increase in dye clearance from the end of the needle tip in a root canal model at flow rates higher than 4 ml/min. During negative pressure irrigation, no positive apical pressures were generated even when the needle was placed at 1 mm from working length while certain needle designs demonstrated superior clearance of dye. Apical pressure is dependent upon flow rate, depth of needle placement, needle design, and positive or negative pressure irrigation. The apical pressure at high irrigation flow rates can be several times higher than at low flow rates, yet there is no further clearance of dye above 4 ml/min. If apical clearance of dye beyond the needle tip is a measure of irrigation effectiveness, then maximum effectiveness can be gained at specifically determined flow rates using specific needle tip designs with safe apical pressures.

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