Smear layer and surface state affect dentin fluoride uptake

ObjectivesPolishing generates a smear layer (SL) on in vitro dentin samples that may influence fluoride uptake. We tested two hypotheses: SL increases fluoride uptake in superficial dentin (H1) and decreases fluoride uptake in deeper layers (H2) irrespectively of the amount of fluoride administered.MethodsPolished bovine dentin with SL present and removed by four methods (5% tannic acid, 20 s [TA]; 17% EDTA, 120 s; 38% phosphoric acid, 60 s [PA]; and 10 s air polishing) was fluoridated with 1200 or 12 000 ppm F (NaF) solution (pH 4.0).ResultsScanning electron microscopy (SEM) revealed that aggressiveness of SL removal varied by method from leaving SL patches behind (TA) to collagen exposure (PA). SL increased KOH-soluble and structurally bound fluoride uptake into superficial and deeper layers compared to SL free surfaces (except PA) following 1200 ppm, but not 12 000 ppm fluoridation.ConclusionPresence of SL and surface conditions influence dentin fluoride uptake depending on fluoride concentration administered.