Calcium and Phosphate Rechargeability of Protein-repellent and Remineralizing Dental Adhesive

Objectives: Nanoparticles of amorphous calcium phosphate (NACP) can suppress caries and promote remineralization. 2-methacryloyloxyethyl phosphorylcholine (MPC) can reduce protein and bacterial attachment. There has been no report on the effect of MPC on calcium (Ca) and phosphate (P) ion release and recharge. The objectives of this study were to develop an adhesive containing NACP and MPC, and investigate the effects of MPC on Ca and P release and rechargeability.
Methods: PMGDM (pyromellitic glycerol dimethacrylate), EBPADMA (ethoxylated bisphenol A dimethacrylate), HEMA (2-hydroxyethyl methacrylate), and BisGMA (bisphenol A glycidyl dimethacrylate) were used to fabricate the adhesive PEHB. Adhesives tested were: (1) Scotchbond Multi-Purpose (SBMP, 3M); (2) PEHB+20% NACP; and (3) PEHB+20% NACP+3% MPC. Dentin shear bond strengths were measured. Calcium and phosphate ion release was monitored over 10 weeks. Exhausted specimens were recharged and ion re-release was monitored for three 14-day cycles. Protein-adsorption was measured by a micro bicinchoninic acid method. A model using human saliva as inoculum was used to analyze live/dead bacteria, metabolic activity and colony-forming units (CFU).
Results: Bond strengths of SBMP, PEHB, PEHB+NACP, and PEHB+NACP+MPC were (23.0±4.5)MPa, (22.60±5.5)MPa, (24.0±4.8)MPa, and (21.9±5.4)MPa, respectively (p>0.05). Cumulative calcium and phosphate ions released over 70 days were (3.25±0.01)mmol/L and (1.42±0.01)mmol/L for control adhesive, and (4.78±0.03)mmol/L and (2.15±0.01)mmol/L for MPC-containing adhesive. Recharged specimens showed calcium re-release of (0.46±0.01) for control and (0.41±0.01)mmol/L for experimental adhesive. Phosphate re-release was (0.19±0.01) for control and (0.18±0.01)mmol/L for MPC-containing adhesive. MPC significantly reduced protein adsorption and biofilm metabolic activity (p<0.05). Adding MPC provided one log reduction in CFU of total microorganisms, total streptococci and mutans streptococci.
Conclusions: MPC+NACP adhesive yielded protein-repellent and antibacterial activities without compromising the release and rechargeability of calcium and phosphate ions as well as dentin bond strength. Novel bioactive MPC+NACP adhesive is promising to repel proteins/bacteria and inhibit secondary caries at the restoration margins.