Tveit, A.B.&Halse. A, the effect of a NaF solution and a fluoride varnish on the acid resistance of root dentin.Acta Odontol. Scand. 1982, 40, 35–43Sectioned root dentin surfaces were treated with either a NaF solution for 10 min or a fluoride varnish for 48 h and then exposed to 1 M acetate buffer pH 5.8 for 20 h. Microradiographs of non-fluoride treated specimens (controls) regularly showed a partially demineral-ized zone extending from the surface. the NaF-treated specimens exhibited a lesion with alternating radiopaque and radiolucent zones, which had a mean total depth equal to that of the controls. the varnish-treated specimens showed a demineralized zone which was significantly less deep than those observed in the two other groups. Elemental analyses performed by an electron microprobe showed a positive correlation between the amount of F incorporated and the acid resistance of the tissue.