Microhardness of dentine in primary teeth after topical fluoride applications

OBJECTIVES: This study measured the microhardness of arrested dentinal caries on primary teeth receiving regular fluoride applications after 30 months. METHODS: Caries on primary upper anterior teeth of preschool children were randomly assigned to receive 38% silver diamine fluoride every 12 months or 5% sodium fluoride varnish every 3 months. Lesions that were hard on probing were considered arrested. At 30 months, very mobile teeth were extracted, sectioned, and polished and they underwent Knoop hardness number (KHN) measurements at sites below the surface at the center of the carious lesion every 25 microm toward the pulp. Three sets of measurements were made on parallel tracks approximately 150-200 microm apart, and the median KHN at each depth were analyzed. RESULTS: Five arrested and five soft carious lesions were examined. Within the outer 25-200 microm, the median KHN of arrested carious lesions (range, 20-46 or 196-451 MPa) were greater than those of soft carious lesions (range, 5-20, or 49-196 MPa). The difference between them, however, was not statistically significant. At a distance of 225 microm or more from the surface of the lesion, the median KHN of both groups were between 20 and 30 (196-294 MPa). CONCLUSIONS: The outermost dentinal surface of carious lesions that had been arrested by topical fluoride application was harder than that of active carious lesions. At a distance of 225 microm or more from the lesion surface, the microhardness of both arrested and soft dentinal caries was similar.