Assessment of antimicrobial properties of silver-doped hydroxyapatite nanoparticle-modified orthodontic composite: an in vitro study

Introduction
Technological progress in nanotechnology is leading to the development of biologically active nanoparticles to address typical issues in orthodontic treatment, such as white spot lesions (WSLs). In order to augment its antibacterial characteristics, orthodontic adhesive has been modified by integrating silver-doped hydroxyapatite nanoparticles.

Objectives
The primary objective was to evaluate the antimicrobial properties and minimum inhibitory concentration (MIC) of silver-doped hydroxyapatite nanoparticles-modified orthodontic composite (AgHA-C). The secondary objective was to assess the ability of AgHA-C to inhibit bacterial biofilm formation below the minimum inhibitory concentration.

Material and methods
MIC of AgHA-C was assessed using broth dilution technique against Streptococcus mutans (S. mutans), Lactobacillus acidophilus (L. acidophilus), and Enterococcus faecalis (E. faecalis). Crystal violet biofilm assay was applied to assess the biofilm effects of AgHA-C on biofilms of S. mutans, L. acidophilus and E. faecalis.

Results
AgHA-C remarkably inhibited the growth of S. mutans, L. acidophilus, and E. faecalis, and MIC was estimated to be 5 μg/ml for all the microbes tested. Below the MIC level of 2.5 μg/ml, AgHA-C potentially inhi­bited the biofilm formation of L. acidophilus (74.71%). However, AgHA-C did not have any effect on the biofilm formation of E. faecalis and S. mutans below the MIC level.

Conclusions
AgHA-C can successfully inhibit S. mutans, L. acidophilus, and E. faecalis within the concentration of 5 μg/ml. It shows selected effect on the biofilms of L. acidophilus at sub-MIC, making it a potential agent for prevention of WSLs.