Remineralization of Dental Caries in Rats Using a Peptide Formulation in vivo

Objectives: To create caries in rat molars and to remineralize in vivo using a gel formulation containing amelogenin derived peptide as a mineralization catalyst, and ionic Ca/PO₄ precursors.
Methods: Specific pathogen-free Sprague-Dawley rats were used for this study. All animal care and experimental protocols were approved by UW Office of Animal Welfare. Starting as weaning pups, caries were induced by oral inoculation with Streptococcus mutans followed by high sucrose diet until caries were confirmed. Prior to treatment, animals were randomly separated into 4 groups: (1) Baseline (sacrificed immediately for caries characterization), (2) No treatment (negative control), (3) Ca/PO₄ gel only treatment, and (4) Peptide/Ca/PO₄ gel treatment. The resulting caries (Group-1) were characterized by optical microscopy, scanning electron microscopy (SEM) and nanoindentation. Gel formulations were administered topically on molars of Group-3 and -4 daily for 2 weeks, whereas Group-2 received no treatment. At the end of treatment, molars were collected from euthanized animals for examination. Statistical analyses were performed using Student’s T-test, p<0.05 was considered significant.
Results: Enamel caries were prominent after 4 weeks post inoculation as confirmed by fluorescence microscopy, SEM and nanoindentation. Resulting caries had average hardness of 1.3±0.4 GPa less than 40% of that of unaffected enamel (3.3±0.4 GPa) as measured by nanoindentation. After 2 weeks of peptide/Ca²⁺/PO₄^3- formulation treatment, carious lesions in the Group-4 were remineralized by establishment of new mineral layers up to 12±3 micrometer thick with average hardness of 2.2±0.4 GPa. Group-3 which received Ca²⁺/PO₄^3- only gel treatment revealed significantly thinner mineral layer with high degree of discontinuity. No remineralization was found in the no-treatment Group-2.
Conclusions: Caries on rats were treated by remineralization in vivo using gel formulations containing amelogenin derived peptide/Ca²⁺/PO₄^3- and resulted in new mineral formation on the carious lesions.