Comparative Evaluation of Anticariogenic Activity of Aqueous Extracts of Green Tea and Pomegranate Peel on Bacteria-Induced Secondary Caries at the Tooth-Resin Interface Using a Dye Penetration Method

Objective To evaluate and compare the anticariogenic efficacy of aqueous extracts of green tea and pomegranate peel at the resin-dentin interface of human premolars subjected to Streptococcus mutans-induced secondary caries. Methodology Twenty-one human premolars were sectioned into 42 specimens, with Class V preparations (3mm x 3mm x 1mm) etched with 37% phosphoric acid. Specimens were divided into three groups: Group I (Control, n=14): Two coats of bonding agent applied and light-cured; Group II (Green Tea): 50% green tea extract applied, followed by bonding agent; Group III (Pomegranate): 30% pomegranate peel extract applied, followed by bonding agent. All specimens were restored with composite in two vertical increments, light-cured for 40 s, and polished. The surfaces were coated with acid-resistant nail varnish, leaving a 1 mm margin around the restoration. After disinfection in 70% ethanol and rinsing twice with sterile phosphate-buffered saline (PBS), specimens were stored in PBS at 4 °C overnight. They were then inoculated with <i>Streptococcus mutans</i> (MTCC 890) in brain heart infusion (BHI) broth containing 1% sucrose for five days to induce artificial secondary caries. Following the cariogenic challenge, specimens were rinsed, sectioned longitudinally through the restoration, hydrated, and stained overnight with 0.1 mM Rhodamine B. Confocal microscopy images were obtained at 10× and 60× magnification. Rhodamine B-infiltrated dentin indicated lesion progression, while a dye-free zone near the resin-dentin interface in the experimental groups represented the inhibition zone. The depth of this inhibition zone was measured from the resin-dentin interface to the Rhodamine B-stained region in micrometers. Results An independent t-test was used for statistical analysis. In the control group, complete Rhodamine B dye infiltration was observed at the resin-dentin interface, with no inhibition zone detected in any of the 14 samples. In contrast, the experimental groups exhibited a distinct dark zone (inhibition zone) devoid of Rhodamine B dye along the resin-dentin interface. The difference between the green tea group (Group II) and pomegranate group (Group III) was found to be non-significant (p=0.052). Conclusion Proanthocyanidin-rich natural collagen crosslinkers, namely pomegranate peel and green tea extracts, can inhibit secondary caries at the resin-dentin interface. As secondary caries is the principal reason for replacement of resin composite restorations, the biomodification of dentin with these natural collagen crosslinkers and matrix metalloproteinase (MMP) inhibitors can stabilize the collagen and protect the resin dentin interface from degradation, thereby decreasing the chances of secondary caries.