Remineralizing Dental Adhesives Copolymerized with Highly-Charged Macromonomers

Objectives: Strategies to improve resin-dentin interface stability have recently turned to biomimetic remineralization of unprotected collagen. Highly charged polymers are widely accepted as mimics of non-collagenous mineralization proteins. However, covalent immobilization of such materials in resins has not been attempted. The objectives of this study are: 1) To synthesize a highly charged macromonomer with a photopolymerizable reactive group; 2) To immobilize the synthesized macromonomer into a commercial dental adhesive; 3) To evaluate cured materials for degree of conversion (DC), hardness, and mineralization capacity. It is hypothesized that a functionalized adhesive will promote mineralization, preserving adequate DC and mechanical properties that might be compromised if this material were only passively added.
Methods: A highly charged polymer with mineralizing properties is functionalized and characterized by ¹H, ¹³C-NMR with COSY and HSQC, and IR. Photopolymerization with a commercially-available adhesive in 20% feed by mass is monitored for DC by IR (n=3). Mineral deposition from a mineralizing solution and material mechanical properties are characterized by optical and atomic force microscopy.
Results: A rapid, visually-monitored one-pot reaction for polymer functionalization was achieved, affording the desired macromonomer in 100% conversion, with isolated yields in excess of 90%. Successful synthesis was confirmed by ¹H,¹³C-NMR and FTIR-ATR spectroscopy. The mechanical properties and DC (75 ± 5%) of the polymerized resins were comparable to the neat control adhesive with considerable mineral deposition relative to the neat resin, which produced no detectable mineral. Passive addition of the mineralizing polymeric material to the adhesive reduced DC by over 10%, confirming our hypothesis.
Conclusions: We have shown that the covalent immobilization of highly-charged polymers in restorative resins 1) promote greater and more uniform mineralization compared to resins with these materials added passively, 2) improves DC, and 3) maintains desired mechanical properties.