The Synthesis, Characterization, and Assessment of Antibacterial Properties of an Orthodontic Adhesive Containing Cerium-Substituted Hydroxyapatite Nanoparticles: An In Vitro Study

Abstract

Introduction White spot lesions (WSLs) are early enamel caries lesions often seen in individuals receiving fixed orthodontic treatment. These lesions occur due to the buildup of plaque and the colonization of bacteria. WSL formation can be prevented by adequate oral hygiene measures and by the incorporation of antimicrobial nanoparticles (NPs) in orthodontic appliances and bonding systems. The aim of this research was to synthesize cerium-substituted hydroxyapatite nanoparticles (Ce-HAp NPs), characterize them, and assess their antimicrobial activity. Materials and methods This in vitro investigation involved the preparation of Ce-HAp NPs using the co-precipitation method, followed by their characterization using scanning electron microscope (SEM), energy-dispersive X-ray (EDAX), and Fourier transform infrared (FTIR). The NPs were prepared and subsequently added to an orthodontic adhesive. Antibacterial testing was conducted using the disc diffusion method against common oral pathogens (Staphylococcus aureus, Lactobacillus acidophilus, and Streptococcus mutans). The zones of inhibition were measured for two different concentrations of the adhesive. Results The Ce-HAp NPs were successfully prepared and had an irregular agglomerated shape, measuring 63 nm in size. The major characteristic chemical groups of Ce-HAp were PO₄^3-, OH-, and CO₃^2-, and it was confirmed by the FTIR spectrum. The EDAX results of the synthesized NPs showed theoretical weight percentages (Wt%) of O, 52.6%; Ca, 20.9%; P, 11.8%; C, 10.3%; and Ce, 4.3%. A higher concentration of 40 µg/mL (30 mm for S. aureus and L. acidophilus and 25 mm for S. mutans) showed good antibacterial activity against the tested bacterial strains, compared to control antibiotics. Conclusion Cerium oxide (CeO₂)-HAp NPs were prepared and incorporated into an orthodontic adhesive. The prepared adhesive exhibited effective antibacterial activity against prevalent oral pathogens.

Keywords: antibacterial activity; cerium; dental; hydroxyapatite; nanoparticles; orthodontic adhesives.

Figure 1. Flow diagram of the methodology

SEM, scanning electron microscope; EDAX, energy-dispersive X-ray; FTIR, Fourier transform infrared

Figure 2. The obtained nanoparticle

Figure 3. FTIR of Ce-containing HAp NPs

FTIR, Fourier transform infrared; Ce, cerium; HAp NPs, hydroxyapatite nanoparticles

Figure 4. SEM image of prepared Ce-HAp NPs

SEM, scanning electron microscope; Ce-HAp NPs, cerium-substituted hydroxyapatite nanoparticles

Figure 5. SEM image of Ce-substituted HAp NP admixed adhesive

SEM, scanning electron microscope; Ce, cerium; HAp NP, hydroxyapatite nanoparticle

Figure 6. Zones of inhibition against antibiotics at different concentrations

a) Staphylococcus aureus, b) S. mutans, and c) L. acidophilus