Sodium Hypochlorite Before Resin Varnish Fails to Impact Microhardness, Surface Roughness or Microleakage, Finds Study

Enamel demineralization occurs when hydroxyapatite (HA) crystals dissolve due to acidic pH, leading to the loss of calcium and phosphate ions. This process, driven by cariogenic bacteria digesting carbohydrates, increases hydrogen ion concentration in plaque, which diffuses through enamel pores and affects HA crystals in subsurface regions.

Against the above background, Bengü Doğu Kaya, Marmara University Faculty of Dentistry, Department of Restorative Dentistry, Istanbul, Türkiye, and colleagues aimed to evaluate the effect of 5.25% NaOCl application before resin infiltration and resin varnish on microhardness, surface roughness, and DIAGNOdent Pen values in the treatment of white spot lesions (WSLs) through an in vitro study.

For this purpose, the researchers created artificial initial caries lesions in 160 human enamel samples. They divided them into five groups: resin infiltration (ICON), NaOCl + ICON, resin varnish (Clinpro XT), NaOCl + Clinpro XT, and a negative control. Thermocycling aging was performed with 5,000 cycles between 5-55°C (N=32, n=16 for aging subgroups).

Surface roughness (Ra), Vicker’s microhardness (VHN), and DIAGNOdent Pen (DDP) values were recorded at baseline, after demineralization, post-treatment, and post-thermal aging. Micro-CT analysis, microleakage assessment, and SEM imaging were conducted after treatment and aging. Statistical analysis involved Robust ANOVA, Pearson’s chi-square, and McNemar tests.

Key Findings

• The main effects of both group and stage were statistically significant for DDP, Ra, VHN, and micro-CT values.
• All treatment procedures effectively improved demineralized enamel compared to the negative control group.
• Applying 5.25% NaOCl before resin infiltration increased microhardness but also led to higher surface roughness.
• Resin-infiltrated groups exhibited lower microleakage than resin-varnish-treated groups.

In conclusion, the researchers found that applying 5.25% NaOCl before resin infiltration or fluoride-containing resin varnish did not significantly affect microhardness, surface roughness, DIAGNOdent Pen values, or microleakage. All treatment procedures showed improved outcomes compared to demineralized enamel samples, but NaOCl pre-treatment did not enhance or compromise the results. Resin infiltration exhibited superior performance over resin varnish in reducing microleakage and achieving better DIAGNOdent Pen scores, regardless of NaOCl application.

"These findings suggest that while white spot lesions should be treated, NaOCl pre-treatment may not be necessary, simplifying clinical protocols without compromising treatment efficacy," the researchers wrote.

Reference:

Özen, A. M., Kaya, B. D., Atalı, P. Y., & Türkmen, C. (2025). Evaluation of NaOCl application prior to resin infiltrant or fluoride-containing resin varnish in the treatment of white spot lesions: An in vitro study. Journal of Dentistry, 105641. https://doi.org/10.1016/j.jdent.2025.105641