Comparative efficacy of ultrasonic, diode laser, and manual irrigant activation around an apically separated instrument: an in vitro study.

BACKGROUND

The fracture of a nickel-titanium instrument in the apical third of a root canal presents a significant clinical challenge, as it creates a compacted barrier of dentinal debris and smear layer that is shielded by a vapor lock, severely limiting irrigant efficacy. This study aimed to compare the efficacy of Ultrasonic Activation (UAI), Diode Laser-Activated Irrigation (LAI), and Manual Dynamic Agitation (MDA) in overcoming this barrier by evaluating both irrigant penetration and direct debris removal.

METHODS

Ninety human mandibular first molars with standardized, non-bypassable apically fractured instruments were divided into two parts. Part 1 (n = 45) assessed irrigant penetration using Confocal Laser Scanning Microscopy (CLSM) after activation of Rhodamine B dye. Part 2 (n = 45) evaluated debris and smear layer removal using Scanning Electron Microscopy (SEM) and the Hülsmann scoring system. In both parts, teeth were randomly assigned to one of three final irrigation activation protocols (n = 15 each): MDA (as a control group), UAI, or LAI (970 nm diode laser at 2.0 W).

RESULTS

CLSM analysis revealed that UAI achieved a significantly greater penetration area in the apical section compared to LAI (p = 0.04). Crucially, UAI was the only technique that showed no significant difference in penetration area between the obstructed apical section and the unobstructed control section (p = 0.10). SEM evaluation demonstrated that both UAI and LAI were significantly more effective at removing debris and smear layer than MDA (p < 0.05), with no statistically significant difference between UAI and LAI (p ≥ 0.76).

CONCLUSIONS

Within the limitations of this in-vitro model, ultrasonic activation produced greater apical penetration area than diode laser activation, while ultrasonic and diode laser activation produced significantly better debris and smear-layer removal than manual dynamic agitation. No statistical difference was observed between ultrasonic and diode laser activation for SEM-based cleaning scores. Further studies incorporating thermal safety assessment and biofilm models are required before clinical recommendations can be made.