Effect of temperature and ultrasonic activation on the antibacterial efficacy of sodium hypochlorite alone and combined with etidronic acid in an internal root resorption model.

OBJECTIVES

This study compared the antibacterial efficacy of sodium hypochlorite (NaOCl) and a NaOCl-1-hydroxyethane-1,1-diphosphonic acid (NaOCl/HEDP) mixture at 25°C and 37°C, with or without passive ultrasonic irrigation (PUI), in an internal root resorption (IRR) model infected with Enterococcus faecalis biofilm.

DESIGN

Standardized IRR cavities were prepared in extracted maxillary incisors. After 21-day biofilm maturation, specimens were allocated to eight subgroups (NaOCl or NaOCl/HEDP; 25°C or 37°C; conventional needle irrigation [CNI] or PUI; n = 8 each) and a saline control (n = 8). Antibacterial activity was assessed by colony-forming unit (CFU) reduction, and biofilm morphology was evaluated via scanning electron microscopy (SEM). Data were analyzed using factorial ANOVA (irrigant type×temperature×activation), with partial η² and Cohen's f reported (α=0.05).

RESULTS

All experimental groups showed significant bacterial reduction compared with the control (P < 0.001). Significant main effects were observed for temperature (F=89.7, P < 0.001, η²=0.62), activation (F=50.6, P < 0.001, η²=0.48), and irrigant type (F=19.8, P < 0.001, η²=0.26). Temperature had a stronger enhancing effect in the NaOCl/HEDP groups. The greatest reduction occurred with NaOCl/HEDP at 37°C combined with PUI. SEM images confirmed cleaner dentine surfaces and reduced debris in the 37°C and PUI groups, particularly with NaOCl/HEDP.

CONCLUSIONS

Both temperature elevation and PUI improved antibacterial efficacy, and NaOCl/HEDP demonstrated the strongest temperature-dependent response. Their combined use resulted in the highest bacterial reduction, although complete bacterial removal was not achieved.