Novel Antimicrobial Copolymers for Class V Restorations

Objectives: Synthesize polymerizable antimicrobial monomers (AM) and evaluate their effect on physicochemical and mechanical properties of an experimental resin formulated for class V restorations.
Methods: Nucleophilic substitution reaction was employed to synthesize polymerizable quaternary ammonium salts: 2-(methacryloyloxy)-N-(2-(methacryloyloxy)ethyl)-N,N-dimethylethan-1-aminium bromide (ionic dimethacrylate; IDMA1) and N,N'-([1,1'-biphenyl]-2,2'-diylbis(methylene))bis(2-(methacryloyloxy)-N,N-dimethylethan-1-aminium) bromide (IDMA2). Their structures were validated by nuclear magnetic resonance (¹H and ¹³C NMR) and mass spectroscopy. IDMA1 or IDMA2 were incorporated at 10 and 20 weight % into a resin comprised of urethane dimethacrylate (UDMA; 50.91%), polyethylene glycol-extended UDMA (PEG-U; 18.18%) and ethyl 2-(hydroxymethyl)acrylate (EHMA; 30.91%), designated UDMA/PEG-U/EHMA resin (no IDMA, control). Camphorquinone (0.2%) and ethyl 4-(dimethylamino) benzoate (0.8%) were used as photo-initiating system. Triad2000 curing light was employed for sample polymerization. Degree of vinyl conversion (DC; NIR FTIR), flexural strength (FS; 3-point bending) and water contact angle (sessile drop technique) were determined for all copolymers.
Results: Incorporation of AM monomers slightly increased DC of the resins: from 88.1% (control) to 92.1%, 89.7% (10, 20% IDMA1) and 93.0%, 92.5% (10, 20% IDMA2). Their hydrophobicity-hydrophilicity (60.8-65.5 ⁰) was not significantly affected by monomer incorporation. FS of copolymers was reduced from 94.8 MPa (control) to 68.9-71.8 MPa (p<0.05) (IDMA counterparts) independent of monomer type and its concentration.
Conclusions: Incorporation of IDMA1 or IDMA2 monomers into UDMA/PEG-U/EHMA matrix improved the DC and did not alter the hydrophobic/hydrophilic balance of the resins. Accompanying reduction in FS does not disqualify these monomers as AM agents in future design of Class V restoratives.