Curcumin-photosensitized nanocapsules: biocompatibility and antimicrobial evaluation in primary tooth dentin contaminated with Streptococcus mutans.

Introduction: Dental caries is a multifactorial disease with high prevalence, particularly in vulnerable populations, where Streptococcus mutans contributes to lesion progression via acid production and biofilm formation. Minimally invasive strategies, such as photodynamic therapy (PDT) combined with advanced delivery systems, offer promising alternatives for caries management.

Methods: Zein-based nanocapsules loaded with curcumin (Nano-curcumin) were synthesized via nanoprecipitation and characterized for encapsulation efficiency, particle size, polydispersity, zeta potential, morphology, and curcumin release. Biocompatibility was assessed using rabbit oral mucosal cells via MTT and trypan blue assays. Antimicrobial efficacy was tested in vitro on primary dentin slices contaminated with S. mutans across four groups: Nano-curcumin, Nano-curcumin + PDT, diode laser, and untreated control. Colony-forming units (CFU) were quantified after treatment. Statistical analysis was performed using ANOVA and Tukey's test (p < 0.05).

Results: Nano-curcumin demonstrated high encapsulation efficiency (~100%), spherical morphology, low polydispersity (0.108), and favorable colloidal stability, with sustained curcumin release over 24 hours. Cytotoxicity assays showed >50% cell viability at 100 μg·mL⁻¹ and ~80% at intermediate concentrations (50-75 µg·mL^-¹). Both curcumin nanocapsules and their photosensitized versions significantly reduced S. mutans CFU compared to controls (p < 0.05), with PDT-enhanced nanocapsules showing the greatest reduction, though not statistically different from non-photosensitized nanocapsules.

Discussion: Curcumin-loaded zein nanocapsules are biocompatible and effective against S. mutans, with controlled release properties. Photodynamic activation further enhances antimicrobial activity, supporting their potential as a minimally invasive approach for managing carious lesions, particularly in pediatric dentistry. This strategy integrates a natural photosensitizer with a biodegradable polymeric matrix, providing a safe and innovative alternative for caries control.