Do Dental Resin Composites Accumulate More Oral Biofilms and Plaque than Amalgam and Glass Ionomer Materials?

Abstract

A long-time drawback of dental composites is that they accumulate more biofilms and plaques than amalgam and glass ionomer restorative materials. It would be highly desirable to develop a new composite with reduced biofilm growth, while avoiding the non-esthetics of amalgam and low strength of glass ionomer. The objectives of this study were to: (1) develop a protein-repellent composite with reduced biofilms matching amalgam and glass ionomer for the first time; and (2) investigate their protein adsorption, biofilms, and mechanical properties. Five materials were tested: A new composite containing 3% of protein-repellent 2-methacryloyloxyethyl phosphorylcholine (MPC); the composite with 0% MPC as control; commercial composite control; dental amalgam; resin-modified glass ionomer (RMGI). A dental plaque microcosm biofilm model with human saliva as inoculum was used to investigate metabolic activity, colony-forming units (CFU), and lactic acid production. Composite with 3% MPC had flexural strength similar to those with 0% MPC and commercial composite control (p > 0.1), and much greater than RMGI (p < 0.05). Composite with 3% MPC had protein adsorption that was only 1/10 that of control composites (p < 0.05). Composite with 3% MPC had biofilm CFU and lactic acid much lower than control composites (p < 0.05). Biofilm growth, metabolic activity and lactic acid on the new composite with 3% MPC were reduced to the low level of amalgam and RMGI (p > 0.1). In conclusion, a new protein-repellent dental resin composite reduced oral biofilm growth and acid production to the low levels of non-esthetic amalgam and RMGI for the first time. The long-held conclusion that dental composites accumulate more biofilms than amalgam and glass ionomer is no longer true. The novel composite is promising to finally overcome the major biofilm-accumulation drawback of dental composites in order to reduce biofilm acids and secondary caries.

Keywords: amalgam; caries inhibition; dental composite; glass ionomer; human saliva microcosm biofilm; protein repellant.

Figure 1

Protein adsorption onto disk surfaces (mean ± sd; n = 6). Incorporation of 3% MPC into the composite significantly decreased the amount of protein adsorption compared to that at 0% MPC and the commercial composite control (p < 0.05). Dissimilar letters indicate values that are significantly different from each other (p < 0.05).

Figure 2

Representative live/dead staining images of dental plaque microcosm biofilms grown for two days on disks: (A) Commercial composite control; (B) RMGI; (C) Amalgam; and (D) Composite with 3% MPC. The composite control with 0% MPC had biofilms similar to (A) and was not included in Figure 2. Live bacteria were stained green, and dead bacteria were stained red.

Figure 3

MTT metabolic assay and lactic acid production of biofilms on the surface of tested materials (mean ± sd; n = 6). Composite with 0% MPC and commercial composite control had biofilms with a relatively high metabolic activity and lactic acid production. However, adding 3% MPC decreased the metabolic activity and lactic acid by half. Values with dissimilar letters are significantly different from each other (p < 0.05). (A) MTT metabolic activity; (B) lactic acid production (mean ± sd; n = 6).

Figure 4

Colony-forming unit (CFU) counts of two-day biofilms on disks (mean ± sd; n = 6). (A) Total microorganism CFU; (B) total streptococci CFU; and (C) mutans streptococci CFU. In each plot, values with dissimilar letters are significantly different from each other (p < 0.05).

Figure 5

Flexural strength and elastic modulus of materials (mean ± sd; n = 6). Values with dissimilar letters are significantly different from each other (p < 0.05). (A) Flexural strength; (B) elastic modulus (mean ± sd; n = 6).