20 May 2024

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An innovative nanotechnological gel as a root canal dressing: first in vitro trials of its effectiveness and depth of penetration into the dentinal tubules

Lara Figini

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The most frequently intracanal antibacterial dressing currently used is calcium hydroxide (Ca(OH)₂), whose antibacterial capacity is due to the alkalinity which produces a release of highly oxidizing free radicals and hydroxyl ions, capable of destroy the bacterial wall, resulting in the death of the microorganisms.

Unfortunately, however, it has been demonstrated that Ca(OH)2 is ineffective in eliminating embedded bacteria in the dentinal tubules due to their anatomical complexity, due to the lack of direct contact with microorganisms, and due to its lack of penetration into the dentinal tubules. Bacteria in the dentinal tubules can represent a significant source of infection during and after endodontic therapy causing infection or reinfection of the root canal.The development of nanotechnology has offered several alternative solutions to resolve the limited disinfection of canal dentinal tubules, obtaining preparations that guarantee a prolonged and constant release of the drug, reducing the required therapeutic dose and possible associated side effects. An additional challenge of Ca(OH)2-NP (calcium hydroxide effectively reduced using nanoparticles NP) is its application in liquid form, which is easily removable, although the liquid form is easier to place inside the tubules. For this reason, a suitable solution would be a formulation that is applied in liquid form and becomes semi-solid within the dentinal tubules. In this area, nanotechnologies offer a wide range of possibilities, one of the most interesting being the dispersion of NPs in stimuli-responsive smart gels. These intelligent gels are able to provide a more prolonged release of the drug in the target area, therefore suitable for the endodontic field.

Specifically, thermosensitive gels are interesting because they exhibit a fluid state until they reach the appropriate temperature, at which point the interaction between their hydrophilic and hydrophobic segments changes, becoming a gel-like structure. A widely used polymer for the production of these gels is Poloxamer 407 (PA 407), a triblock copolymer often used as a surfactant. PA 407 has the ability to vary its fluid or viscoelastic behavior as a function of temperature. This feature would allow the drug to be administered as a fluid allowing the root canal system to be irrigated adequately and, subsequently, the transformation into gel inside the root canal at 37°C allows for greater stability of the drug and a decrease in its solubility.

Materials and methods

In an in vitro study, published soon in the Journal of Endodontics, the authors performed an in vitro and ex vivo analysis to evaluate the irritating power and the ability to penetrate the dentinal tubules of an innovative experimental hydroxide-based gel of calcium with nanoparticles (Ca(OH)₂-NP). The reproducibility of Ca(OH)₂-NP was confirmed by obtaining the average size of the NPs, their polydispersity index, and the entrapment efficiency. Furthermore, the authors performed rheological studies on the Ca(OH)2-NPs-based gel, analyzing its characteristics after oscillatory stress, its average viscosity value, and its properties after temperature changes. Tolerance was assessed using the membrane of a chicken egg embryo. In vitro Ca(OH)2 release was studied using direct dialysis media in aqueous solution to monitor the amount of Ca(OH)2 released. Six extracted human teeth were used to study the penetration depth of fluorescently labeled Ca(OH)2-NP-gel into dentinal tubules and significant differences were detected compared to free Ca(OH)2 calculated using the anova test unidirectional.

Results

The Ca(OH)2-NPs gel was shown to be highly reproducible with an average size of less than 200 nm, a homogeneous population of NPs, negative surface charge, and high trapping efficiency. The analysis of the thermosensitive gel allowed us to determine its rheological characteristics, demonstrating that at 10°C the gel had a fluid-like behavior while at 37°C it had an elastic-like behavior. The Ca(OH)2-NPs gel showed a prolonged release of the drug and an increased penetration depth within the tubular dentin in the most apical areas. Furthermore, it turned out that this drug it did not produce irritation.

Conclusions

From the data of this study, which must be confirmed in other similar in vitro and in vivo studies, it can be concluded that this experimental thermosensitive gel based on calcium hydroxide nanoparticles can constitute a valid alternative as an intracanal antibacterial dressing.

For info: Calcium hydroxide-loaded nanoparticles dispersed in thermosensitive gel as a novel intracanal medicament. Xavier Roig, Lyda Halbaut, Firas Elmsmari Rubén Pareja, Aizea Arrien, Fernando Duran-Sindreu, Luis María Delgado, Marta Espina, María Luisa García, José Antonio González Sánchez, Elena Sánchez-López. Int Endod J. 2024;00:1–15.