Development of Novel Therapeutic Dental Adhesives to Inhibit Secondary Caries

Abstract

Despite efforts to reduce the effects of caries at the margins of restorations, the prevalence of secondary caries remains stubbornly high. Dimethylamino-hexadecyl methacrylate (DMAHDM) reduced biofilm viability and acid production when added to dental adhesives. 2-methacryloyloxyethyl phosphorylcholine (MPC) greatly reduced protein adsorption and bacterial attachment. Nanoparticles of amorphous calcium phosphate (NACP) suppressed caries and promoted remineralization. This dissertation incorporated DMAHDM, MPC and NACP to develop an adhesive with antibacterial, protein-repellent and remineralizing properties possessing long-term ion-recharge and re-releases for the first time. The effects of MPC and DMAHDM on calcium (Ca) and phosphate (P) ion release and recharge were established. The objectives of this dissertation were to develop an anti-caries adhesive containing bioactive agents NACP, DMAHDM and MPC, and investigate the effects of DMAHDM and MPC on Ca and P ion release and rechargeability. Incorporating the bioactive agents had no influence on mechanical behavior, as the adhesives had shear bond strength matching commercially available control. Using a human saliva microcosm biofilm model, DMAHDM-containing adhesives had substantial antibacterial functions with significant reductions in biofilm metabolic activity, lactic acid production and colony-forming units (CFU). MPC adhesives also had substantial reductions in protein adsorption, biofilm metabolic activity and CFU. The incorporation of NACP provided continuous Ca and P ion release over 70 days. After the ion release was depleted, specimens were recharged with Ca and P ions, then the ion re-release was measured. One recharge treatment enabled the resin to continuously release high levels of Ca and P ions for about three weeks, thus allowing the patient o potentially use a mouth-rinse for one day every three weeks. With increasing the number of recharge and re-release cycles, the Ca and P ion re-release reached similarly higher levels, indicating a long-term and durable recharge function. The combined incorporation of the bioactive agents produced novel therapeutic and anti-caries adhesives that could greatly reduce biofilm formation on restorative margins, repel proteins, remineralize lesions, and ultimately prevent secondary caries, thus increasing the success rate and the longevity of composite restorations.