Comparative Evaluation of Modern Disinfection Methods on Smear Layer Removal and Bond Strength to Caries-Affected Dentin: A KTP Laser, Nanocare Gold, Photodynamic Therapy Study

Objective: To assess the efficacy of four contemporary cavity disinfection protocols-potassium titanyl phosphate (KTP) laser, nanosilver-gold nanoparticle solution (Nanocare Gold), methylene blue-mediated photodynamic therapy (MB-PDT), and chlorhexidine gluconate (CHX)-on smear layer (SL) removal and shear bond strength (SBS) of fifth-generation adhesive bonded to caries-affected dentin (CAD). Methodology: This in vitro experimental study was approved by the Institutional Review Board of King Saud University from July 1st, 2025, to 30th December 2025. Sixty extracted human mandibular molars with carious lesions extending into the middle third of dentin were collected. Following caries removal and surface standardization, specimens were randomly allocated into five groups: Group-I (control, no disinfection), Group-II (2% CHX gel), Group-III (KTP laser, 532 nm, 1 W), Group-IV (MB-PDT with diode laser activation at 638 nm), and Group-V (Nanocare Gold). SL removal was assessed using scanning electron microscopy according to Hülsmann's criteria. Following fifth-generation adhesive application and composite restoration, specimens underwent thermocycling. SBS was measured using a universal testing machine, and failure modes were analyzed stereo-microscopically. Statistical analysis employed one-way ANOVA with post hoc Tukey test (α=0.05). Results: KTP laser demonstrated superior SL removal (1.26±0.032) and the highest bond strength (9.10±1.02 MPa), statistically comparable to Nanocare Gold (1.34±0.044; 8.94±0.97 MPa, p>0.05). MB-PDT showed minimal SL elimination (3.54±0.065) and the lowest bond strength (6.89±0.78 MPa), similar to CHX (p>0.05). Conclusion: KTP laser and Nanocare Gold demonstrated optimal performance for cavity disinfection, effectively removing the smear layer while enhancing adhesive bond strength to CAD.