A Thermosensitive Gel Containing Biodegradable Nanoparticles Carrying Calcium Hydroxide as Antibacterial Intracanal Therapy

Abstract

Aim: To characterise and evaluate mucoadhesive strength and antibacterial properties of a nanotechnological formulation for endodontic disinfection based on biodegradable nanoparticles dispersed in a thermosensitive gel containing calcium hydroxide (Ca(OH)2-NPs-gel). Methodology: Morphology of Ca(OH)2-NPs-gel was studied using transmission electron microscopy. Moreover, Ca(OH)2-NPs-gel was sterilised using gamma irradiation (25 kGy), and the stability after the sterilisation process was studied by measuring Ca(OH)2-NPs-gel average size, polydispersity index, zeta potential and encapsulation efficiency. To assess the ex vivo mucoadhesive strength, extracted single-rooted human teeth were used to measure the force necessary to separate the formulation from the teeth. In addition, the short-time stability of Ca(OH)2-NPs-gel was evaluated monthly, analysing entrapment efficacy, backscattering and transmittance of Ca(OH)2-NPs-gel stored at different temperatures (4°C, 25°C and 37°C). Furthermore, the antibacterial analysis of Ca(OH)2-NPs-gel was performed against Enterococcus faecalis inoculated in extracted human single-root teeth and evaluated by confocal and scanning electron microscopy. Finally, the metabolic activity of bacteria was studied through a resazurin assay to evaluate bacterial survival after treatment. Results: Ca(OH)2-NPs-gel owned a round shape and a smooth surface without particle aggregation. Sterilisation did not induce an alteration in Ca(OH)2-NPs-gel physicochemical properties and Ca(OH)2-NPs-gel presented a high adhesion strength. In addition, 4°C was the best temperature to store Ca(OH)2-NPs-gel. Regarding the antibacterial therapeutic efficacy, Ca(OH)2-NPs-gel possesses suitable antibacterial properties, indicating that it efficiently reduces bacterial biofilms. Conclusion: Calcium hydroxide-loaded PLGA nanoparticles dispersed in a thermosensitive gel have been developed, optimised and characterised, obtaining excellent antibacterial properties and achieving bacterial disinfection levels similar to those of commercial formulations.