Poly(amido amine) and rechargeable adhesive containing calcium phosphate nanoparticles for long-term dentin remineralization

Objectives: The objective of the present study was to investigate long-term dentin remineralization via the combination of poly(amido amine) (PAMAM) with a novel rechargeable adhesive containing nanoparticles of amorphous calcium phosphate (NACP). Methods: The NACP adhesive was immersed in lactic acid at pH 4 to exhaust its calcium (Ca) and phosphate (P) ion release, and then recharged with Ca and P ions. Dentin samples were pre-demineralized with 37% phosphoric acid, and then divided into four groups: (1) dentin control, (2) dentin treated with PAMAM, (3) dentin with recharged NACP adhesive, (4) dentin with PAMAM + recharged NACP adhesive. In group (2) and (4), the PAMAM-coated dentin was immersed in phosphate-buffered saline with vigorous shaking for 77 days to accelerate any detachment of the PAMAM macromolecules from the demineralized dentin. Samples were treated with a cyclic remineralization/demineralization regimen for 21 days. Results: After 77 days of fluid flow challenge, the immersed PAMAM still retained its nucleation template function. The recharged NACP adhesive possessed sustained ion re-release and acid-neutralization capability, both of which did not decrease with repeated recharge and re-release cycles. The immersed PAMAM with the recharged NACP adhesive achieved long-term dentin remineralization, and restored dentin hardness to that of healthy dentin. Conclusions: The PAMAM + NACP adhesive completely remineralizes pre-demineralized dentin even after long-term fluid challenges and provides long-term remineralization to protect tooth structures. Clinical significance: The novel PAMAM + NACP adhesive provides long-term bond protection and caries inhibition to increase the longevity of resin-based restorations.