Microhardness of dentine in primary teeth after topical fluoride applications

Abstract 

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 25μm toward the pulp. Three sets of measurements were made on parallel tracks approximately 150–200μm apart, and the median KHN at each depth were analyzed.

Results

Five arrested and five soft carious lesions were examined. Within the outer 25–200μm, the median KHN of arrested carious lesions (range, 20–46 or 196–451MPa) were greater than those of soft carious lesions (range, 5–20, or 49–196MPa). The difference between them, however, was not statistically significant. At a distance of 225μm or more from the surface of the lesion, the median KHN of both groups were between 20 and 30 (196–294MPa).

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 225μm or more from the lesion surface, the microhardness of both arrested and soft dentinal caries was similar.

Keywords: Microhardness, Dentine, Fluoride