The purpose of this study was to examine the effect that phosphoric acid etchant, used to remove the smear layer, may have on dentin demineralization inhibition. Fifteen molars had Class V preparations placed on the mesial and distal surfaces, the gingival seat being placed 1 mm below the cementoenamel junction. Randomly, one preparation of each tooth had etchant placed carefully on only enamel for 30 seconds. Etchant was placed on the gingival seat dentin of the remaining preparations, as well as the enamel for 30 seconds. A HEMA dentin primer containing maleic acid was placed and allowed to dry on the unetched dentin, then a Bis-GMA resin with tetrabutyl ammonium tetrafluoroborate was placed. Only the fluoridated resin was placed over the dentin that had been etched. All teeth were then restored with resin composite and subjected to an artificial caries challenge (pH 4.4) for 7 days. Sections 100 microns were obtained, photographed under polarized light microscopy and demineralized areas were digitized. Results demonstrated the mean area (mm2 +/- S.D.) demineralization 0.5 mm from the gingival margin to be: etched dentin (0.77 +/- 0.36); non-etched dentin (1.52 +/- 0.98). A t-test indicated that there was significantly less demineralization when the fluoridated resin came in direct contact with dentin that had the smear layer removed (P < 0.05).