Antimicrobial Photodynamic Therapy Using Chitosan-Encapsulated Indocyanine Green Improves Smear Layer Removal and...

An in vitro study to evaluate the efficacy of indocyanine green (ICG) encapsulated in chitosan (CHNPs) and titanium dioxide nanoparticles (TiO₂NPs) activated by 810-nm diode laser on smear layer (SL) removal and shear bond strength (SBS) to caries-affected dentin (CAD).

Sixty extracted human mandibular molars with CAD were randomly assigned to four groups (n = 15). Group 1: 2% chlorhexidine (CHX), Group 2: free ICG-activated PDT (ICG-PDT), Group 3: ICG-loaded TiO₂NPs-activated PDT (ICG-TiO₂NPs-PDT), and Group 4: ICG-loaded CHNPs-activated PDT (ICG-CHNPs-PDT). CHNPs and TiO₂NPs were characterized by scanning electron microscopy (SEM) energy-dispersive X-ray spectroscopy. SL removal was assessed qualitatively via SEM using the Hülsmann scale. A fifth-generation etch-and-rinse adhesive was applied with active scrubbing, and nanohybrid composite buildups were fabricated. Following thermocycling, SBS was measured using notched-edge shear testing machine. Failure modes were assessed stereoscopically. Data were analyzed using one-way ANOVA and Tukey post hoc tests (α = 0.05).

ICG-CHNPs-PDT yielded the lowest SL score (1.04 ± 0.14) and highest SBS (9.79 ± 0.62 MPa), significantly outperforming all groups (p < 0.05). CHX exhibited intermediate performance (SL: 2.16 ± 0.48; SBS: 7.59 ± 0.46 MPa). ICG-PDT (SL: 2.75 ± 0.29; SBS: 6.12 ± 0.43 MPa) and ICG-TiO₂NPs-PDT (SL: 2.81 ± 0.35; SBS: 5.97 ± 0.35 MPa) showed comparable, inferior results (p > 0.05). ICG-CHNPs-PDT demonstrated predominantly cohesive failures (60%), while ICG-PDT and ICG-TiO₂NPs-PDT showed mainly adhesive failures (50%).

Near-infrared antimicrobial photodynamic therapy using chitosan-encapsulated ICG activated at 810 nm significantly enhanced both SL removal and resin-dentin bond strength compared with conventional CHX. The dual chelating and photosensitizing properties of the chitosan-ICG system offer a promising alternative for CAD surface conditioning before adhesive bonding.