Behind the Science: Treatment of Caries with Silver Nanocomposites

Behind the Science: Treatment of Caries with Silver Nanocomposites

Author: Marisa Spiniello, Carla Meledandri

Dr. Marisa Spiniello, Deputy Editor for ChemPlusChem, talks to Dr. Carla Meledandri, University of Otago, New Zealand, about her article on treating tooth decay with silver nanoparticles that was published in ChemPlusChem.

The paper describes a strategy to prevent and treat caries which utilizes the electrophoretic movement of charged, antibacterial silver nanocomposite structures to infiltrate teeth and target bacteria.

What was the inspiration behind this study?

This work was inspired by previous clinical experience of my co-author, a prosthodontist, providing me with an exciting opportunity to be involved in true targeted, problem-driven research. At present, dental clinicians do not have a perfect solution to treat infections responsible for decayed teeth (dental caries), or prevent recurrence.

Current treatment options primarily involve drilling, a destructive surgical procedure, followed by the placement of a filling, which has a limited lifetime. Eventual failure of the restoration leads to reactivation of quiescent bacteria located within the tooth structure, and possibility of a secondary infection and further decay.

The starting point for our research was to design and develop an antimicrobial product for treating dental caries that would target the bacterial source of the disease, residual bacteria residing within the dentine tubules at depths of up to several hundred micrometers below the surface of the tooth.

Why was your attention focused on these types of materials?

We initially decided to focus on the delivery of silver nanoparticles to the tooth structure due to their well-known antimicrobial properties and low propensity to induce microbial resistance, but the development of suitable silver nanoparticle-containing structures for this particular application was not necessarily straightforward.

For optimal antimicrobial activity, the silver nanoparticles should remain discrete and have a uniform and controlled size. To transport these antimicrobial silver nanoparticles down the dentine tubules, the delivery system should be biocompatible, have a controlled diameter less than that of the tubules, remain stable in aqueous suspension over a broad pH range and possess a surface charge. These requirements, combined with our research group’s interest in colloidal-based approaches for the preparation of functional nanoscale materials, is what ultimately led to our use of anionic SDS surfactant-based micelle assemblies containing silver nanoparticles (SDS = sodium dodecyl sulfate) for this particular application.

How long did this investigation take?

Overall, I have been working together with my co-author for about four years on the development of new silver nanoparticle-based strategies to treat oral infections that lead to caries and other dental diseases. Once we optimised the formulation and synthesis of the nanocomposite structures to be used in the current study, which took about two years, investigation of the electrophoretic movement of the nanocomposite structures – performed on extracted teeth – was completed in about three to four months.

What is the main significance of your results?

Our results demonstrate successful electrophoretic movement of highly antimicrobial nanocomposite structures into human dentine with enhanced penetration depth when compared to unassisted application. We interpret this as a demonstration of the suitability of the nanocomposite structures for delivery to the tooth via iontophoresis. Iontophoresis is an established drug delivery method that enhances ionic drug penetration using direct current, and it has been used to enhance fluoride delivery in dentistry. More specifically, by placing a charge-inducing device on the tooth’s surface and applying optimized voltage and current, penetration and effectiveness of the drug can be increased. Iontophoresis devices are readily available to clinicians.

Our goal was to explore the potential of this technique for enhanced delivery of other highly-charged materials, such as the negatively-charged nanocomposite materials described in this work, in order to selectively accumulate antimicrobial species deep within tooth structure for the treatment of dental caries, and we believe the results presented show that this is a realistic possibility.

How will you follow up on this discovery?

On the research end, we are interested in investigating the effect of fluid flow in the dentine tubules informed by pulpal blood pressure on the penetration depth of the nanocomposite materials under the influence of an electric current. We also plan to study the antimicrobial effect of the nanostructures against biofilms. On the clinical side, we hope to engage with an industrial partner to collaboratively develop this work toward a clinical trial and a successful commercial outcome.

Do you have any plans for future work extending from this study?

We intend to expand our work towards the development of other antibacterial silver nanoparticle-based materials for the potential treatment of other dental diseases, such as periodontal disease and peri-implantitis – an inflammatory process surrounding dental implants. This may include both colloidal and non-colloidal-based formulations.


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