In vitro assessment of needle and irrigant penetration when using different irrigation needle tips

The aim of this study was to compare the needle and irrigant penetration depth of a newly developed multi-vented polymer needle (30G), with three established needle designs - an open-ended metal needle (30G), a side-vented polymer needle (30G), and a notched metal needle (27G) used as a reference control. The effect of manual dynamic activation (MDA) was also measured. The null hypotheses were that the irrigant penetration would be the same regardless of needle tip, and the addition of MDA would make no difference in terms of irrigant penetration.

A total of 120 mesial roots from mandibular molars were instrumented to a size 25/07, with reciprocating files. The maximum needle penetration depth was measured for each needle tip, using a rubber stop. Syringe irrigation was performed using a sodium diatrizoate solution, first with needle placement halfway down the root canal (working length subtracted from the canal length), and then 1 mm from the working length. MDA was performed. A digital radiograph was taken before the initial irrigation, after the initial irrigation, after the final irrigation, and after MDA. Digital subtraction was performed, and irrigant penetration was measured by a blinded operator. Non-parametric statistical tests were conducted using Mann-Whitney U-test and Wilcoxon signed-rank test.

The multi-vented polymer needle had a significantly deeper needle penetration (mean value: 99%), compared to other test needles. The deepest irrigant penetration was achieved using the multi-vented polymer needle (mean value: 98%) and the open-ended metal needle (mean value: 99%). A significantly deeper irrigant penetration, was achieved by adding MDA, regardless of needle tip.

The multi-vented polymer needle and the open-ended metal needle showed superior performance in terms of irrigant penetration. However, the irrigant penetration only managed to reach the working length when MDA was added.