Nanoparticles for endodontic disinfection
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Newer disinfection strategies in endodontics are aimed to eliminate biofilm bacteria not only from the main canals but also from the uninstrumented portions and anatomical complexities of the root canal system without inducing untoward effects on periradicular tissue. Nanoparticles derived from bioactive materials have the ability to mediate targeted antibacterial efficacy while sparing the mammalian cells. The aim of this article is to provide a concise review of their use in root canal treatment.
KeywordsNanoparticles Disinfection Medication Antibacterial Chitosan
Endodontic therapy treats a complex tissue system consisting of the tooth–pulp–periradicular complex. Complete elimination of bacteria is difficult as significantly high number of bacteria exist within the uninstrumented areas of root canals such as isthmuses and lateral canals.
Nanoparticles (NPs) are microscopic particles with one or more dimensions in the range of 1–100 nm. NPs have a broad spectrum of antimicrobial activity and lesser propensity to induce microbial resistance when compared to antibiotics. Antibacterial NP-based treatment can improve the antibacterial/antibiofilm efficacy.
Root canal disinfection
Root canal sealing
Classification of nanoparticles
Nanoparticles based on composition
Different NPs are being developed and tested for achieving effective root canal disinfection. Based on the spectrum of action and their biocompatible properties, selective NPs are of interest for future clinical application.
Chitosan (CS) [poly (1, 4), β-d glucopyranosamine] is a derivative of chitin. It can be synthesized in various forms such as powder (micro- and NPs), capsules, films, scaffolds, hydrogels, beads, and bandages.
They have excellent antibacterial, antiviral, and antifungal properties. Gram-positive bacteria are more susceptible than Gram-negative ones.
They are also used to reinforce collagen matrices.
It is nontoxic towards mammalian cells.
Color compatible to tooth structure.
Ease of chemical modification.
Bioactive glass nanoparticles (BAG)
BAG consists of silicon dioxide (SiO2), sodium oxide (Na2O), calcium dioxide (CaO2), and phosphorus pentoxide (P2O5) at different concentrations. It is amorphous in nature.
High pH increase in pH due to release of ions in an aqueous environment.
Osmotic effects increase in osmotic pressure above 1% is inhibitory for many bacteria.
Calcium/phosphorus precipitation induced mineralization on the bacterial surface.
The antibacterial property of silver is due to its interaction with the sulfhydryl groups of proteins and DNA, altering the hydrogen bonding/respiratory chain, unwinding of DNA, and interference with cell wall synthesis/cell division.
Silver NPs destabilize the bacterial membrane and increase permeability leading to leakage of cell constituents.
NP incorporated root canal sealers,
NP functionalization for improved antibacterial efficacy,
NP modification for antimicrobial photodynamic therapy (PDT).
Nanoparticle-incorporated root canal sealers
Addition of antibacterial NPs in root canal sealer improves the direct and diffusible antibacterial effects of the root canal sealers.
CS NPs reduce the adherence of E. faecalis to root canal dentin.
Quaternary ammonium polyethylenimine NPs can also be utilized to improve the antibacterial efficacy of various root canal sealers and temporary restorative materials.
It exerts bactericidal effects by adsorption and penetration through the bacterial cell wall. Then, they interact with the protein and fat layer in the cell membrane blocking the exchange of essential ions.
BAG NPs promote closure of the interfacial gap between the root canal walls and core filling materials.
Tailoring of NPs via functionalization modifies the NPs chemically.
The therapeutic agents can be delivered to the site of infection to selectively interact with (and penetrate) the biofilm and bacteria.
NP functionalization can result in higher drug efficacy as more active bioactive molecules can be loaded onto one NP.
The core particle is often protected by several monolayers of inert material. The same layer might act as a biocompatible material.
However, more often, an additional layer of linker molecules is required to proceed with further functionalization. This linear linker molecule has reactive groups at both ends.
One group is aimed at attaching the linker to the NP surface, and the other is used to bind various moieties like biocompatibles (dextran), antibodies, fluorophores, etc., depending on the function required by the application.
Nanoparticle modification for antimicrobial photodynamic therapy
NP-based photosensitizers increase the antimicrobial efficacy of PDT. NPs envelope the bacterial cells with higher concentration on the bacterial cell walls.
Photosensitizers supplemented with NPs.
Photosensitizers encapsulated within NPs.
Photosensitizers bound or loaded to NPs.
NPs themselves serving as photosensitizers.
Cationic methylene blue-loaded poly(lactic-co-glycolic) acid NPs have the potential to be used as carriers of photosensitizer PDT within root canals. Anionic Rose Bengal conjugated CS NPs (CSRBnp) have been developed that showed significantly better properties as compared to either agent alone. It exhibits significantly higher bacterial phototoxicity in both planktonic and biofilm phases.
Improved antimicrobial efficacy can be attributed to:
High concentration of photosensitizers per mass with resultant production of ROS;
Reduced efflux of photosensitizers from the target cell, thereby decreasing the possibility of drug resistance;
Possibility of targeting the bacteria due to greater interaction associated with the surface charge;
Greater stability of photosensitizers after conjugation;
Reduced physical quenching effect;
Controlled release of ROS following photoactivation is possible.
Pitfalls and complications
Risk of silver toxicity.
More a medicament than an irrigant.
Use of silver NPs can lead to browning/blackening of dentin and toxicity toward mammalian cells.
Photosensitizers that are conjugated with different readily available synthetic polymers and liposomes possess limited biocompatibility when applied in vivo.