Influence of conventional and energy-intensive irrigation methods on apical pressure created in minimally instrumented molar canals: an ex vivo study

Positive pressure irrigation methods, such as syringe-needle irrigation (SNI), remain the clinical standard in endodontics. However, alternative approaches—including negative pressure systems and laser-activated irrigation—have recently gained attention, warranting further investigation of their apical pressure dynamics. This study evaluated the apical pressures generated by open-ended and side-vented SNI, two erbium lasers, and a multisonic negative pressure (MNP) irrigation system in extracted maxillary molars. Apical pressure was measured in the distobuccal canals of four maxillary molars with varying canal sizes (uninstrumented, #20/04, and #40/04) using a sealed, water-filled chamber connected to a pressure transducer. The tested devices included an Er: YAG laser (2940 nm), an Er, Cr: YSGG laser (2780 nm), an MNP system, and 30-gauge SNI operated at a flow rate of 5 mL/min. In large canals (#40/04), both needle types generated positive pressures below 13.1 mmHg, whereas in minimally instrumented canals (#20/04), pressures ranged from 1.5 to 32.6 mmHg. Side-vented needles produced significantly lower apical pressures than open-ended needles in #20/04 canals (P < 0.05). Needle placement was not feasible in uninstrumented canals. The lasers produced both positive and negative pressures, while the MNP system consistently generated negative apical pressures. These findings indicate that both the irrigation technique and canal size significantly influence apical pressure. In minimally instrumented molar canals, the use of open-ended needles is not recommended due to the risk of generating excessive apical pressure.