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Fatemeh Ostadhossein1 Santosh Kumar Misra1 Indu Tripathi1 Dipanjan Pan1

1, University of Illinois at Urbana Champaign, Urbana, Illinois, United States

The eradication of tenacious dental plaque is of paramount importance, however, their early diagnosis can be a daunting task in dental clinics due to the limitations of current instrumental methods, especially X-ray-based techniques. We approach this problem by integrating antibacterial properties and X-ray contrast enhancement in a single nanoplatform specific to periodontal bacterial colonies. Herein, the synthesis of inherently therapeutic hafnium oxide nanoparticles (HfOx NPs) was achieved, conjugated with cationic macromolecules. These particles could be utilized as X-ray contrast media for dental X-ray radiography and as a bactericidal agent against cariogenic pathogens. Ex vivo studies using extracted human tooth demonstrated striking X-ray attenuation of NPs vs. tooth and could accurately detect the biofilm. Moreover, HfOx NPs exhibited significant antibacterial properties. Electron microscopy revealed that the antibacterial activity occurred via a ‘latch and kill’ mechanism. Mechanistic studies determined that these NPs fragmented bacterial DNA components to exert their antimicrobial effect. CT imaging of NP-treated bacteria verified the contrast enhancement in bacteria-rich regions. Importantly, HfOx NPs effectively inhibited the growth of a mature biofilm on an ex vivo human tooth model.
Prompted by the in vitro and ex vivo results, we evaluated the efficacy of the NPs in an in vivo rodent model (Sprague Dawley rat) of dental biofilm. Mature biofilm grown for a week was treated topically daily for two weeks with 0.02 mg.ml-1 of HfOX NPs. There was a significant inhibition of biofilm compared with chlorohexidine and water treated group. This result was also confirmed by an S.mutans detection kit. Furthermore, the Hf concentration of the collected tissue revealed minute accumulation (<12 ppm) in the gum, whereas in other organs it was down to ppb range. This concentration is in the safe range as the MTT results on the NIH 3T3 fibroblast cells indicated prior to conducting in vivo experiments.
This report is the first to demonstrate that HfOx NPs can be used for simultaneous diagnosis and antibacterial treatment without requiring an additional drug.

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