Fluoride penetration into the hybrid layer from a dentin adhesive

Purpose: To evaluate the in vitro microleakage of a new fluoride-containing dentin adhesive and to provide evidence for fluoride release from the adhesive and penetration into the dentin. Materials and Methods: Class V preparations with margins in enamel and dentin were made in the buccal and lingual surfaces of six extracted human third molars. Six preparations were restored with Scotchbond Multipurpose (SBMP)/Z100 composite and six with a new fluoride containing dentin adhesive (FB)/Litefil composite. After aging for 30 days in water at 37°C, the teeth were stained with silver nitrate, sectioned and graded by two observers for leakage at the enamel and dentin margins. Selected FB specimens were examined in the scanning electron microprobe using WDS for fluoride and EDS for calcium and phosphorous. Fluoride release into water from disks of FB adhesive was evaluated for up to 112 days using a specific ion electrode. Results: Fluoride leached from the adhesive at a decreasing rate with time. The final rate over 112 days was 0.02 ppm/day (0.2 μg/cm²/day). Leakage at the enamel and dentin margins was similar for both adhesives (MannWhitney U-test; P≤0.05). SEM evaluation showed the presence of a discontinuous hybrid layer of 2-3 μm. Fluoride was present within, but limited to, the hybrid layer for the FB adhesive. The penetration of fluoride could only be confirmed in areas where leakage had occurred.