An introduction to antibacterial materials in composite restorations

Abstract

The longevity of direct esthetic restorations is severely compromised because of, among other things, a loss of function that comes from their susceptibility to biofilm-mediated secondary caries, with Streptococcus mutans being the most prevalent associated pathogen. Strategies to combat biofilms range from dental compounds that can disrupt multispecies biofilms in the oral cavity to approaches that specifically target caries-causing bacteria such as S mutans. One strategy is to include those antibacterial compounds directly in the material so they can be available long-term in the oral cavity and localized at the margin of the restorations, in which many of the failures initiate. Many antibacterial compounds have already been proposed for use in dental materials, including but not limited to phenolic compounds, antimicrobial peptides, quaternary ammonium compounds, and nanoparticles. In general, the goal of incorporating them directly into the material is to increase their availability in the oral cavity past the fleeting effect they would otherwise have in mouth rinses. This review focuses specifically on natural compounds, of which polyphenols are the most abundant category. The authors examined attempts at using these either as pretreatment or incorporated directly into restorative material as a step toward fulfilling a long-recognized need for restorations that can combat or prevent secondary caries formation. Repeatedly restoring failed restorations comes with the loss of more tooth structure along with increasingly complex and costly dental procedures, which is detrimental to not only oral health but also systemic health.

Keywords: Caries; antimicrobial compounds; dental materials; restorative dentistry.

Figure 1

Main classes of antimicrobial strategies proposed for use in dental materials. A. Phenolic compounds (more details in Figure 3). B. Quaternary ammonium compounds and broad-spectrum antibiotics; these can be added directly or copolymerized with the material to prevent leaching. C. Small molecule inhibitors with targeted activity against virulent species. G43 and SB5 are specific against glucan-producing glucosyltransferases from Streptococcus mutans.^, D. Antimicrobial peptides (more details in Figure 4). C: Carbon. Cl: Chlorine. H: Hydrogen. N: Nitrogen. O: Oxygen. S: Sulfur.

Figure 2

Sequence of biofilm formation on the surface of enamel and antimicrobial materials. On healthy enamel, after the acquired pellicle is formed and the early colonizers get established, exopolysaccharide production leads to biofilm maturation and ecology modification. The result is a homogeneous coverage of the surface. On the surface of antimicrobial materials, the acquired pellicle may reduce the antibiofilm efficacy, but the early colonization still gets disrupted to different degrees depending on the class of antimicrobial. However, oral bacteria have redundant virulence mechanisms that allow them to attach to dead bacteria on the surface. If the material leaches antimicrobial compounds, there is a chance of distance killing of the bacteria. Either way, the result is either no biofilm or a biofilm with altered morphology and weaker attachment.

Figure 3

Phenolic compounds are classified based on the number of phenol rings in the molecule and the structural elements that bind these rings to one another. One classification includes phenolic acids, stilbenes, flavonoids (with core structure containing rings A, B, and C), and lignans. H: Hydrogen. O: Oxygen.

Figure 4

Antimicrobial peptides are classified based on source (eg, mammalian, insect-derived, or plant-derived), activity (eg, antibacterial and antifungal peptides), amino acid–rich species (eg, proline-rich peptides, histidine-rich peptides, tryptophan, and arginine-rich antimicrobial peptides) and structural characteristics (eg, linear α-helical peptides, β-sheet peptides, and combination of both α-helix and β-sheet peptides and linear extension structure). H: Hydrogen. N: Nitrogen. O: Oxygen.