Photodynamic Therapy, Ozonated Water, and Diode Laser Efficacy in Removing Smear Layer in Carious Dentin and Their Effect on Bond Integrity to Composite Resin

<b><i>Aim:</i></b> To investigate the efficacy of diode laser (DL), photodynamic therapy (PDT), and ozone water on the removal of smear layer (SL) and its assessment via scanning electron microscope (SEM) following its effect on shear bond strength (SBS) on carious affected dentin. <b><i>Materials and Methods:</i></b> Sixty-six caries-affected dentin (CAD) samples were obtained from the dental outpatient department. The occlusal enamel and infected dentin of the included samples were meticulously excised using a water-cooled, slow-speed device, resulting in a flat mid-coronal CAD surface. Based on the effectiveness of SL removal techniques, the samples were categorized into groups (<i>n</i> = 11 each). Group 1: no treatment, Group 2: DL, Group 3: PDT-activated methylene blue (MB), Group 4: 16 ppm ozonated water, Group 5: 17% ethylenediamine tetra-acetic acid (EDTA), and Group 6: 37% phosphoric acid (PA). One pair of samples from each group was assessed under SEM following different conditioning regimes. The remaining samples underwent the application of an adhesive 7th-generation single-bottle adhesive and composite placement. All bonded samples were aged, and SBS assessment was performed via a universal testing machine, and unbonded surfaces were assessed under a stereomicroscope. A one-way analysis of variance was employed, followed by Tukey honestly significant difference (HSD) post hoc tests. Statistical significance was established at a <i>p</i> value of less than 0.05. <b><i>Results:</i></b> The highest SL removal efficiency was observed in the PA group. The lowest SL removal efficacy was examined in the no-treatment group. SL removal efficiency via DL and EDTA was found to be comparable (<i>p</i> > 0.05) and significantly lower than samples conditioned with PA (<i>p</i> < 0.05). Samples conditioned with PDT-activated MB and ozonated water had comparable micro (μ)- SBS scores (<i>p</i> > 0.05). Samples conditioned via EDTA, PA, and diode demonstrated cohesive failure predominantly. <b><i>Conclusions:</i></b> PA is considered the benchmark for effectively removing the SL from dentin affected by caries, as it also enhances bonding strength. Nonetheless, EDTA and DLs present viable alternatives to phosphoric acid.