Fluoride Absorption and Release Using LDH Containing Composite Fissure Sealants

Objectives: The aim of this project was to determine, whether Bis-GMA/UDMA based experimental fissure sealants containing Layered Double Hydroxide (LDH) have the ability to absorb fluoride and then subsequently release fluoride.
Methods: Light-cured samples (n=30) of the Bis-GMA/UDMA based fissure sealant, containing no LDH (controls), 7%, 20%, 33% LDH respectively, and one commercial fissure sealant (Delton®, Dentsply, Weybridge UK) with no LDH, but containing a preloaded fluoride content, were prepared and placed in 50 ml universal tubes with 15 ml 0.1 M NaF solution for 24 h, in order to absorb fluoride. The release of fluoride from each group of six samples was then measured by placing each sample in a 50 ml universal tube with 15 ml deionised H₂O. The fluoride ion released was measured using a fluoride ion selective electrode ELIT (Nico2000 Ltd, London UK), at an interval of 1hr, 3hr, 6hr, 24hr, 48hr and 72hr. The samples were then recharged in 0.1 M NaF solution for 24 hr, and allowed to subsequently release the fluoride content. All 30 samples were subjected to the same procedures by repeating the initial recharging procedure twice.
Results: The results of the present study indicated that the Bis-GMA/UDMA based fissure sealant without LDH (Controls) released a relatively minor concentration of the adsorbed fluoride. The preloaded commercial (Delton®) samples without LDH released the preloaded fluoride. Fissure sealants containing LDH were observed to release fluoride and then absorb fluoride from the aqueous solution, and subsequently re-release the fluoride content.
Conclusions: The absorbed fluoride was released in deionised water, even after recharging. One of the key observations from the present study was that the fluoride released from the Bis-GMA/UDMA based experimental fissure sealants increased as the concentration of LDH in the sealant was increased.