Effects of quaternary ammonium chain length on the antibacterial and remineralizing effects of a calcium phosphate nanocomposite
Authors: Ke Zhang, Lei Cheng, Michael D Weir, Yu-Xing Bai, Hockin HK Xu
Journal: International Journal of Oral Science (2015)

Composites containing nanoparticles of amorphous calcium phosphate (NACP) remineralize tooth lesions and inhibit caries. A recent study synthesized quaternary ammonium methacrylates (QAMs) with chain lengths (CLs) of 3–18 and determined their effects on a bonding agent. This study aimed to incorporate these QAMs into NACP nanocomposites for the first time to simultaneously endow the material with antibacterial and remineralizing capabilities and to investigate the effects of the CL on the mechanical and biofilm properties. Five QAMs were synthesized: DMAPM (CL3), DMAHM (CL6), DMADDM (CL12), DMAHDM (CL16), and DMAODM (CL18). Each QAM was incorporated into a composite containing 20% NACP and 50% glass fillers. A dental plaque microcosm biofilm model was used to evaluate the antibacterial activity. The flexural strength and elastic modulus of nanocomposites with QAMs matched those of a commercial control composite (n = 6; P > 0.1). Increasing the CL from 3 to 16 greatly enhanced the antibacterial activity of the NACP nanocomposite (P < 0.05); further increasing the CL to 18 decreased the antibacterial potency. The NACP nanocomposite with a CL of 16 exhibited biofilm metabolic activity and acid production that were 10-fold lesser than those of the control composite. The NACP nanocomposite with a CL of 16 produced 2-log decreases in the colony-forming units (CFU) of total microorganisms, total streptococci, and mutans streptococci. In conclusion, QAMs with CLs of 3–18 were synthesized and incorporated into an NACP nanocomposite for the first time to simultaneously endow the material with antibacterial and remineralization capabilities. Increasing the CL reduced the metabolic activity and acid production of biofilms and caused a 2-log decrease in CFU without compromising the mechanical properties. Nanocomposites exhibiting strong anti-biofilm activity, remineralization effects, and mechanical properties are promising materials for tooth restorations that inhibit caries. The antibacterial activity of dental composites with ammonium polymer additives depends on the polymers' chain length. Dental composites formed from calcium phosphate in its nanoparticulate form are used as a remineralization agent for tooth lesions and to prevent tooth decay. To further prevent decay, which occurs following bacterial biofilm formation, antibacterial agents can be added to the composites. Hockin HK Xu, University of Maryland, USA, Yu-Xing Bai at Capital Medical University in Beijing, and colleagues synthesized quaternary ammonium methacrylates with chain lengths varying from 3 to 18 carbons, and assessed their anti-biofilm activity in calcium phosphate composites. The antibacterial efficacy increased with chain length until a maximum was reached at 16, the efficacy decreasing thereafter. The maximum efficacy resulted in a 10-fold reduction in biofilm metabolic activity and acid production, without any detrimental mechanical effects.