Dentin color changes after caries excavation and photodynamic therapy

Objective: The aim of this pilot study was to investigate the influence of ascorbic acid on tooth discoloration after the use of antimicrobial photodynamic therapy (aPDT) in deep carious lesions. Method: Human extracted carious molars were collected and the ones presenting caries involving at least 2/3 of the dentin depth in X-rays, were included in the study.  The teeth were then randomly divided into 3 groups (n=5) receiving different treatments after stepwise caries excavation: G1, standard aPDT treatment; G2, aPDT treatment followed by ascorbic acid (60% w/v solution) application and a negative control group; G3, no treatment. For aPDT, the photosensitizer (blue, phenotiazine chloride) was applied in the cavity for 1min, washed-out with air-water spray (10s) and then laser activated. Laser irradiation (660nm) was done at 6 different points (60s/point, 100 mW/cm²) covering the whole cavity bottom. Standardized images of the remaining dentin were obtained from all samples, using a stereo microscope, at different time points: t_O = after caries excavation, t₁ = after photosensitizer, t₂ = at treatment end. At each time point changes in dentin color were measured using the software Photoshop. On each image, the brightness value (K-value, grey scale) was measured at 4 different areas. The groups mean K-values were separately analyzed at each time point using ANOVA and Tukey test at 5% of significance. Result: At t_O no significant difference was detected between the groups (p>0.05), at t₁ G3 presented statistically significant lower means than all the other groups (p<0.05), and at t_2, G2 presented brightness means statistically significant lower than G1 (p<0.05) but not significantly different from G3 (p>0.05). Conclusion: Under the conditions of this pilot study, the use of ascorbic acid after PDT in deep dentin caries results in recover of dentin brightness to values similar to non-PDT-treated dentin.