Laser and Ultrasonic Activated Irrigation on Eradicating a Mixed-species Biofilm

Objectives: Current chemo-mechanical procedures substantially reduce the bacterial load. However, it is not possible to predictably eliminate all bacteria from the entire root canal system. This study investigates the efficacy of laser and ultrasonic activated irrigation on eradicating a biofilm grown in the mesial roots of human mandibular molars.
Methods: A flow cell was used to grow a mixed-species biofilm (Enterococcus faecalis, Streptococcus sanguinis and Fusobacterium nucleatum) over 4 weeks in the mesial root canals of decoronated human mandibular molar teeth. The roots were then subjected to different irrigating protocols. Control roots (n=7) received no further treatment. The remaining tooth roots were chemo-mechanically prepared using: Saline standard irrigation (SI) (n=20); 4%NaOCl and 15% EDTAC with ultrasonic activated irrigation (UAI) (n=20) and laser activated irrigation using power settings of 0.5W (LAI 0.5W) (n=10) and 0.75W (LAI 0.75W) (n=12). Cellular viability was determined using serial plating. One tooth from each group was subjected to qualitative SEM analysis.
Results: Qualitative SEM analysis showed a significant reduction in the bacterial number for each tested irrigation protocol compared to the control group. The bacterial viability of the UAI and LAI groups (0.5W and 0.75W) represented >99.99% reduction in the viability in comparison to the control group. Statistically significant differences were found between Saline SI and UAI; Saline SI and LAI 0.5W treatment groups (One-way ANOVA, P<0.05). However, no statistically significant differences were found between Saline SI and LAI 0.75W or among the UAI, LAI 0.5W or LAI 0.75W treatment groups.
Conclusions: Chemo-mechanical irrigation significantly reduced the bacterial load from the root canal. However, no significant reductions in bacterial number were found between UAI and LAI protocols.