Smear layer removal efficacy of different irrigation techniques in conservatively instrumented root canals

Background/purpose

Establishing effective irrigation methods is warranted to ensure the predictability of minimally invasive root canal instrumentation. This study aimed to compare the smear layer removal efficacy of different irrigation techniques in root canals instrumented with TruNatomy nickel-titanium rotary instruments.

Materials and methods

Experiment 1: Extracted human mandibular incisors were instrumented using TruNatomy Shaping Files up to Small (#20/0.04), Prime (#26/0.04), or Medium (#36/0.03) (n = 17, each) and irrigated with EDTA, NaOCl, and again with EDTA using syringe irrigation (SI). Experiment 2: Extracted mandibular incisors were instrumented using TruNatomy Small and irrigated with EDTA and NaOCl as in Experiment 1, using (1) conventional laser-activated irrigation (LAI) with an erbium-doped yttrium aluminum garnet laser unit at 30 mJ/10 Hz (LAI 30/10) or 70 mJ/20 Hz (LAI 70/20), (2) photon-induced photoacoustic streaming (PIPS) (20 mJ/15 Hz), (3) ultrasonic-activated irrigation, or (4) SI (n = 13 each). Five additional canals served as negative controls (no irrigation). The smear layer on the canal wall was scored under scanning electron microscopy.

Results

In Experiment 1, the TruNatomy Small group exhibited significantly higher smear layer scores compared to the other groups in the apical and middle thirds. In Experiment 2, the LAI 70/20 and PIPS groups demonstrated significantly lower smear layer scores compared to the LAI 30/10 and SI groups in the apical third.

Conclusion

Conservative instrumentation using the TruNatomy Small reduced the cleaning efficacy of irrigation. However, PIPS performed satisfactory for smear layer removal without injury to the root canal wall.