Further development of a novel fluoride releasing acrylic orthodontic adhesive

Abstract

White spot lesions (WSL) are a common complication with fixed orthodontic treatment. Fluoride incorporation into orthodontic adhesives is an effective way to prevent WSL. New fluoride releasing adhesives are being developed for this purpose. Four experimental groups were prepared by mixing different ratios of powder (polymethylmethacrylate and sodium fluoride; 10:0, 9:1, 8:2 and 7:3 wt) with liquids (60% methylmethacrylate and 40% 2-hydroxyethylmethacrylate). Therefore, this work aimed to further develop the fluoridated acrylic resin materials for possible use as an orthodontic adhesive. Acetone was added at 0%, 10%, 20%, 30% and 40wt% to reduce the materials’ viscosity. Addition of acetone up to 20% did not have detrimental effects on setting characteristics. The materials continued to release fluoride over 160 days. Different photo-initiators were investigated and the 1% camphorquinone and 1% 2-Dimethylamino ethyl methacrylate group was chosen for further development based on achieving the highest degree of conversion (DoC) at 40s of light curing. To improve bonding characteristics 4-methacryloyloxyethyl trimellitate anhydride (4-META) was added as an adhesion promoting monomer at 0% and 5wt%. The experimental materials were compared with a resin-based orthodontic adhesive (TransbondTMXT) and a glass ionomer cement (KetacTM Cem) as commercial comparator. DoC, fluoride release and recharging, water sorption and solubility were measured. Shear bond strength (SBS) was measured for the 9:1 group at two time points after 30 minutes and 30 days of insertion in phosphate buffered saline. All experimental materials had significantly higher DoC than TransbondTMXT. All experimental materials had comparable or higher fluoride release compared to KetacTM Cem. All of the developed materials showed similar recharge behaviour to the KetacTM Cem specimens. The solubility of the materials increased with increasing NaF concentrations. SBS of the experimental materials were significantly decreased at 30 days water storage compared to 30 minutes and were lower than TransbondTMXT. Addition of 4-META and NaF did not influence the SBS of the material. In summary, the developed light-cured fluoridated material showed good fluoride release and high recharge ability, which may prevent WSL. The developed material shows good DoC, in a reasonable timeframe, which would indicate stability. However, as a result of high water sorption and as a consequence of fluoride release, the SBS of the materials decreased after being in water. In conclusion, this material shows potential as a fluoride releasing orthodontic adhesive, which could help to reduce decay during fixed appliance treatment. Further work is required to iii improve the stability and bond strength of the material, which could involve investigation of different monomer combinations or different fluoride sources.