The influence of irrigant activation, concentration and contact time on sodium hypochlorite penetration into root dentine: an ex vivo experiment.

Virdee, S S; Farnell, Djj; Silva, M A; Camilleri, J; Cooper, P R; Tomson, P L

AIM To establish if irrigant activation techniques, namely manual-dynamic-activation (MDA), passive-ultrasonic-irrigation (PUI) and sonic-irrigation (SI), improve the tubular penetration of sodium hypochlorite (NaOCl) into root dentine when compared with conventional-needle-irrigation (CNI). Secondly, investigate if increasing NaOCl concentration and/or contact-time improves the performance of these techniques. METHODOLOGY A total of 83 extracted human maxillary permanent canines were decoronated to 15 mm and root canals prepared to a size 40,.10 taper. Root dentine was stained with crystal violet for 72 h and embedded in silicone. Eighty specimens were randomly distributed into 16 groups (n = 5) according to the irrigant activation technique, NaOCl concentration (2%; 5.25%) and irrigant contact-time (10 min; 20 min). All activation techniques were used for 60 s in the last minute of irrigation. Additionally, 3 teeth were not exposed to NaOCl to confirm adequate dentine staining had occurred (i.e. negative control). All specimens were subsequently dissected, observed under a light microscope and NaOCl penetration depth (µm) determined by measuring the average width of bleached dentine using ImageJ software. Statistical comparisons were made with paired and unpaired t-tests, ANOVAs followed by post-hoc Tukey and Dunnett's tests, and a general linear model (α < 0.05). RESULTS Overall, NaOCl penetration ranged from 38.8 µm - 411.0 µm with MDA, PUI and SI consistently resulting in significantly greater tubular infiltration than CNI (P < 0.05). The deepest measurements in the coronal, middle and apical segments were all recorded in the MDA; 5.25%; 20 min group and the least in the CNI; 2%; 10 min group. Increasing either irrigant concentration or contact-time resulted in significantly greater NaOCl penetration depths for all techniques and segments of the canal (P < 0.05). However, when irrigant concentration and contact-time were increased together, a significant interaction effect between these two independent variables was observed on overall NaOCl penetration (P < 0.05). CONCLUSIONS Agitating irrigants with MDA, PUI or SI, as well as using greater irrigant concentrations or contact-times, potentiated NaOCl penetration into root dentine. However, longer durations of NaOCl exposure at lower concentrations resulted in similar depths of tubular penetration as those achieved at higher concentrations.