Abstract
BACKGROUND: Dental caries remains one of the most common chronic conditions worldwide, often requiring treatment that balances effective bacterial control with preservation of healthy tooth structure. In recent years, researchers have explored novel antimicrobial approaches that can be used during minimally invasive caries treatments. Various adjunctive methods have been employed to inhibit the growth of residual bacteria in deep carious lesions. While chemical disinfectants have demonstrated notable antibacterial properties, their effectiveness can be compromised by some side effects, including adverse interactions with restorative materials and potential alterations to dental tissue structure. Consequently, there is a growing need for alternative antibacterial approaches. Among the latest advancements in cavity disinfection are diode lasers and zinc oxide nanoparticles. AIM: Considering the limited number of clinical studies investigating both agents as cavity disinfectants, the primary aim of the present clinical trial was to evaluate the antibacterial effectiveness of a diode laser (976 nm) and zinc oxide nanoparticles in an ethanol-based solution against cariogenic bacteria, specifically Streptococcus mutans, when applied as cavity disinfectants. MATERIALS AND METHODS: Thirty patients with deep cervical carious lesions were randomized into two groups (n = 15). After selective caries removal, baseline carious dentin samples were collected (control). One group received cavity disinfection using a 976 nm diode laser at 1.3 W output, while the other was treated with zinc oxide nanoparticles (50 μg/mL ethanol-based solution). Zinc oxide nanoparticles were prepared and characterized using transmission electron microscopy and X-ray diffraction to confirm morphology and crystallinity. Post-intervention dentin samples were collected via colony-forming units (CFU) for microbiological analysis. RESULTS: Transmission electron microscopy revealed spherical zinc oxide nanoparticles with diameters averaging 18 nm. X-Ray diffraction confirmed high crystallinity. Both the laser diode and zinc oxide nanoparticles groups showed significant reductions in colony forming unit post-disinfection (p < 0.001). The diode laser group had significantly higher colony forming unit (mean: 8.27 ± 0.80 CFU/mL) compared to the zinc oxide nanoparticles group (mean: 3.47 ± 0.74 CFU/mL). Percentage of bacterial reduction was lower in the laser diode group (93.77%) than the ZnO NPs group (97.4%). CONCLUSION: Spherical-shaped zinc oxide nanoparticles with particle sizes around 25 nm and 50 μg/mL concentration in ethanol-based solution demonstrated superior antibacterial efficacy, suggesting they are a promising alternative for cavity disinfection in conservative caries management. CLINICAL SIGNIFICANCE: The results of the trial open new possibilities for improving patient outcomes by integrating more targeted and conservative disinfection options into everyday dental practice. CLINICAL TRIAL REGISTRATION: This study was registered on clinical trial ( www. CLINICALTRIALS: gov ).