The effect of nano-hydroxyapatite toothpaste on enamel surface remineralization. An in vitro study

Purpose: To compare, in vitro, the surface remineralization effect of two fluoride dentifrices. Methods: 90 human enamel specimens, embedded in cylindrical acrylic blocks, washed and polished, served as a study material. The specimens were randomly assigned in equal numbers to the three groups (two test and one control). Initially the microhardness of the enamel surface (SMH) was assessed by Vickers method, while a profilometer was used to evaluate the surface roughness (Ra value). The enamel specimens were subjected to the preliminary demineralization, simulating the initial carious lesion formation. Subsequently, mean SMH and Ra values were re-assessed. Upon demineralization, one half of each specimen was covered with a protective varnish. The exposed fragment underwent the 3-week cycle of pH changes, according to the protocol. The groups were as follows: NHAPF group - toothpaste containing nanohydroxyapatite (nano HAP) and 1,450 ppm F; F group - toothpaste containing 1,450 ppm; and P group (placebo) - distilled water. Upon completion of the treatment period, the enamel microhardness and roughness profile were re-measured. Results: The demineralization procedure resulted in statistically significant reduction of SMH level in all the groups, and the mean post demineralization values were in the range of 49.7 VHN to 51.2 VHN. Remineralization therapies led to statistically significant increase of enamel SMH value (P< 0.0001). None of the groups reached their original baseline level of SMH following the remineralization therapy.