Formation and characterization of hypermineralized zone beneath dentine lesion body induced by topical fluoride in-vitro.

OBJECTIVE: This in-vitro study aimed to evaluate and characterize the hypermineralized zone (Hyper-zone) formed beneath the remineralized dentine lesion body by transverse microradiography (TMR), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS). DESIGN: Demineralized bovine dentine specimens were treated with fluoride solutions (APF, NaF) and remineralized for 2-4 weeks. Then thin sections were prepared to characterize the Hyper-zone by TMR, EDS. Fractured specimen surfaces were observed by SEM. RESULTS: TMR analysis revealed a higher mineral density at Hyper-zone than that of sound dentine (48vol%) ranging from 50 up to 61vol% and the thickness ranging from 197 to 344mum for 4-week specimens, while specimens without fluoride treatment did not show Hyper-zone. SEM pictures at Hyper-zone showed no evident crystal-like deposits in dentinal tubules and no notable difference when compared to that in sound dentine. EDS analysis demonstrated higher concentrations of Ca and P at Hyper-zone than those in sound dentine, which corresponded to the TMR profile, while the magnesium (Mg) concentration was low at this zone. CONCLUSIONS: Demineralized dentine lesions exposed to fluoride and remineralization treatments exhibited Hyper-zone beneath the lesion body, in which the mineral density was higher than that of sound dentine. Possible mechanism for the formation of Hyper-zone was discussed by assuming removal of mineral regulators such as Mg and other organic substances from sound dentine during de-/remineralization processes.