Enamel Remineralization Ability of Bioactive Glass Containing Resin Adhesive

Objectives: The enamel surface around bonded brackets etched with phosphoric acid is highly susceptible to demineralization. Therefore, further demineralization of the enamel after bracket bonding should be prevented and ideally remineralization should be enhanced. This in vitro study investigated the effects of bioactive glass containing resin on the recovery of the mechanical properties of etched enamel via remineralization in artificial saliva.

Methods: Human enamel blocks were etched with phosphoric acid, fixed on a specimen stage with 4-META/MMA-TBB-based (4-methacryloxyethyl trimellitic anhydride/methyl methacrylate-tri-n-butyl borane)-based resin disks containing bioactive glass (BG) or Sr-containing bioactive glass (SrBG), and then immersed in artificial saliva for 3 months. Nanoindentation testing (ENT-1100a, ELIONIX) of the enamel surfaces was conducted before and after etching and during the immersion at 28°C using three loading conditions (2, 10, and 100 mN) (n=15). Mean values for hardness and elastic modulus were calculated and compared using ANOVA and the Tukey test, with P < 0.05 for statistical significance. Plain and fluoride-containing resin disks were used as comparison. After immersion, enamel surfaces were observed by scanning electron microscopy (JMS-6610LA, JEOL).

Results: The values of the mechanical properties (hardness and elastic modulus) for all the specimens increased gradually with immersion time. The mechanical properties of the etched enamel specimens immersed with BG-containing and SrBG-containing resin disks recovered significantly compared to those with the plain and fluoride-containing resin disks. Although the enamel specimens immersed with plain resin disks showed very porous surface, the specimens immersed with fluoride, BG or SrBG containing resin disks showed less surface roughness after immersion period. These results suggest that BG- and SrBG-containing resin adhesives can accelerate the remineralization of etched enamel, although the recovery was not complete.

Conclusions: Bioactive glass or Sr-containing bioactive glass addition into resin may improve the remineralization ability of etched enamel.