Evaluation of the long-term antibiofilm effect of a surface coating with dual functionality of antibacterial and protein-repellent effects

The provision of antibacterial properties to resinous restorative/reconstructive materials by incorporating polymerizable bactericides such as 12-methacryloyloxydodecylpyridinium bromide (MDPB) has been attempted. Previously, MDPB was combined with 2-methacryloyloxyethyl phosphorylcholine (MPC) to fabricate a copolymer coating to increase antibacterial effectiveness by protein repelling. In this study, we assessed the longevity of the protein-repelling, antibacterial, and antibiofilm effects of the MDPB-MPC copolymer. After 28 days of water immersion, MPC-containing copolymers exhibited lower adsorption of bovine serum albumin and salivary proteins; after 24 h of incubation, MDPB-containing copolymers demonstrated antibacterial effects against Streptococcus mutans. The copolymer containing both MDPB and MPC showed thinner biofilm formation with a higher percentage of membrane-compromised bacteria than control. The results were consistent with those before aging, indicating the long-lasting antibacterial, protein-repellent, and antibiofilm effects of this copolymer. The durable copolymer developed in this study can be applied to dental resins to control bacteria in the oral environment.

Antibacterial effects and physical properties of a glass ionomer cement containing BioUnion filler with acidity-induced ability to release zinc ion

BioUnion filler is a bioactive glass particle that releases Zn²⁺ in an acidic environment. In this study, the ion release, antibacterial, and physical properties of a glass ionomer cement (GIC) incorporating BioUnion filler (CA) were assessed in vitro. The concentration of Zn²⁺ released from CA into acetic acid was higher than that released into water and its minimum inhibitory concentrations against six oral bacterial species. Moreover, the concentration of Zn²⁺-release was maintained during all the seven times it was exposed to acetic acid. Compared to a conventional cement and resin composite, CA significantly inhibited the growth of oral bacteria and hindered their adhesion on the material surface. Thus, our study outcomes show that the release of Zn²⁺ from CA in the acidic environment does not affect its compressive strength.

Immobilizing Bactericides on Dental Resins via Electron Beam Irradiation

Polymerizable bactericides, such as quaternary ammonium compound-based monomers, have been intensively studied as candidates for immobilizing antibacterial components on dental resin. However, they predominantly exhibit a bacteriostatic behavior, rather than bactericidal, as the immobilized components are left with insufficient molecular movement to disrupt the bacterial surface structure through contact-mediated action. In this study, we developed a novel strategy to increase the density of the immobilized bactericide and enhance its antibacterial/antibiofilm properties by combining a surface-grafting technique with electron beam irradiation. A solution of the quaternary ammonium compound-based monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), was coated on polymethyl methacrylate (PMMA) resin specimens at the concentrations of 30, 50, and 80 wt%. The coated resins were subsequently exposed to 10 MeV of electron beam irradiation at 50 and 100 kGy, followed by thermal stabilization at 60 °C. The antibacterial effect was evaluated by inoculating a Streptococcus mutans suspension on the coated PMMA resin samples, which exhibited bactericidal effects even after 28 d of aging (P < 0.05, Tukey's honestly significant difference test). Transmission electron microscopy and bacteriolytic activity evaluation revealed that the S. mutans cells had sustained membrane depolarization. Furthermore, the antibiofilm effects against S. mutans and bacteria collected from human saliva were assessed. The thickness and the percentage of membrane-intact cells of the S. mutans and multispecies biofilms formed on the MDPB-immobilized surfaces were significantly lower than the uncoated PMMA specimens, even after 28-d aging (P < 0.05, Tukey's honestly significant difference test). Thus, the immobilization of antibacterial MDPB via electron beam irradiation induced rapid membrane depolarization, increasing membrane permeability and eventually causing cell death. Our strategy substantially enhances the antibacterial properties of the resinous materials and inhibits biofilm formation, therefore demonstrating significant potential for preventing infectious diseases in the oral environment.

Barrier membranes for tissue regeneration in dentistry

Background: In dentistry, barrier membranes are used for guided tissue regeneration (GTR) and guided bone regeneration (GBR). Various membranes are commercially available and extensive research and development of novel membranes have been conducted. In general, membranes are required to provide barrier function, biosafety, biocompatibility and appropriate mechanical properties. In addition, membranes are expected to be bioactive to promote tissue regeneration.

Objectives: This review aims to organize the fundamental characteristics of the barrier membranes that are available and studied for dentistry, based on their components.

Results: The principal components of barrier membranes are divided into nonbiodegradable and biodegradable materials.

Nonbiodegradable membranes are manufactured from synthetic polymers, metals or composites of these materials. The first reported barrier membrane was made from expanded polytetrafluoroethylene (e-PTFE). Titanium has also been applied for dental regenerative therapy and shows favorable barrier function. Biodegradable membranes are mainly made from natural and synthetic polymers. Collagens are popular materials that are processed for clinical use by cross-linking. Aliphatic polyesters and their copolymers have been relatively recently introduced into GTR and GBR treatments. In addition, to improve the tissue regenerative function and mechanical strength of biodegradable membranes, inorganic materials such as calcium phosphate and bioactive glass have been incorporated at the research stage.

Conclusions: Currently, there are still insufficient guidelines for barrier membrane choice in GTR and GBR, therefore dentists are required to understand the characteristics of barrier membranes.

Development of endodontic sealers containing antimicrobial-loaded polymer particles with long-term antibacterial effects

OBJECTIVE

The objective of this study is to prepare new dental resins with a long-lasting antimicrobial activity. Specifically, this study evaluates an approach for controlling infection in root canals using sealers containing polyhydroxyethyl methacrylate trimethylolpropane trimethacrylate (polyHEMA/TMPT) particles loaded with cetylpyridinium chloride (CPC). In addition, the physical properties of sealers containing CPC-loaded polyHEMA/TMPT particles (CLP) are determined.

METHODS

PolyHEMA/TMPT particles with 10 (10%-CLP) and 25wt.% CPC (25%-CLP) with different particle sizes were fabricated and incorporated in HEMA-based sealers. CPC-release profiles were evaluated over 14 days of immersion in water, followed by 14 days of storage and 14 days of water immersion. The antibacterial activity of these sealers against Enterococcus faecalis in dentinal tubules was assessed using a root-canal-infection model. Their sealing abilities were evaluated by fluid filtration and physical properties were tested according to the ISO 6876 standard. The long-term antibacterial activity of the cured sealer containing 25%-CLP (∼21μm particle diameter) was re-assessed after 1 year of storage.

RESULTS

After 28 days of immersion, 25%-CLP exhibited a higher and sustained CPC release unlike 10%-CLP. Residual bacteria in root dentinal tubules were eradicated by obturation with 25%-CLP-containing sealers. The incorporation of 25%-CLP (∼21μm) had no adverse effects on the sealing ability and physical properties of the sealer and resulted in long-term antibacterial activity.

SIGNIFICANCE

The incorporation of CPC-loaded particles in HEMA resins yielded endodontic sealers with long-term bactericidal activity against E. faecalis in root canals. These sealers can potentially be used to prevent recurrent apical periodontitis.

Development of novel surface coating composed of MDPB and MPC with dual functionality of antibacterial activity and protein repellency

Resin-based reconstructive/restorative materials with antibacterial effects are potentially useful for preventing dental and oral diseases. To this end, the immobilization of an antibacterial component on the surface of a resin by incorporating polymerizable bactericide such as a quaternary ammonium compound-monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB) is an effective technique. However, the effectiveness of immobilized bactericide is reduced by salivary protein coverage. We address this issue by utilizing 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which exhibits protein repellency, with MDPB to fabricate a novel copolymer, which served as a surface coating on a methacrylate-based resin. This coating provided a more hydrophilic surface than that provided by MDPB coating and reduced the adsorption of bovine serum albumin and salivary protein. To evaluate bacterial growth on the contact surface, Streptococcus mutans suspension was placed on the coated specimen. After 24-h incubation, MDPB/MPC copolymer exhibited killing effects against S. mutans. Moreover, confocal laser scanning microscopy and scanning electron microscopy were used to evaluate biofilm formation after 48-h incubation in S. mutans suspension, which revealed sparse biofilm and dead bacteria in biofilm on the surface coated with MDPB/MPC. Overall, the proposed surface coating on dental resins exhibited protein-repellent ability and inhibitory effects against bacteria and oral biofilms.

Cutting-edge filler technologies to release bio-active components for restorative and preventive dentistry

Advancements in materials used for restorative and preventive treatment is being directed toward "bio-active" functionality. Incorporation of filler particles that release active components is a popular method to create bio-active materials, and many approaches are available to develop fillers with the ability to release components that provide "bio-protective" or "bio-promoting" properties; e.g. metal/calcium phosphate nanoparticles, multiple ion-releasing glass fillers, and non-biodegradable polymer particles. In this review paper, recent developments in cutting-edge filler technologies to release bio-active components are addressed and summarized according to their usefulness and functions, including control of bacterial infection, tooth strengthening, and promotion of tissue regeneration.

Non-biodegradable polymer particles for drug delivery: A new technology for "bio-active" restorative materials

To develop dental restorative materials with "bio-active" functions, addition of the capability to release active agents is an effective approach. However, such functionality needs to be attained without compromising the basic properties of the restorative materials. We have developed novel non-biodegradable polymer particles for drug delivery, aimed for application in dental resins. The particles are made using 2-hydroxyethyl methacrylate (HEMA) and a cross-linking monomer trimethylolpropane trimethacrylate (TMPT), with a hydrophilic nature to adsorb proteins or water-soluble antimicrobials. The polyHEMA/TMPT particles work as a reservoir to release fibroblast growth factor-2 (FGF-2) or cetylpyridinium chloride (CPC) in an effective manner. Application of the polyHEMA/TMPT particles loaded with FGF-2 to adhesives, or those loaded with CPC to resin-based endodontic sealers or denture bases/crowns is a promising approach to increase the success of the treatments by conferring "bio-active" properties to these materials to induce tissue regeneration or to inhibit bacterial infection.