In vitro evaluation of antimicrobial activity of chlorhexidine hexametaphosphate nanoparticle coatings on orthodontic elastomeric chains

This study was conducted to evaluate antimicrobial activity of orthodontic elastomeric chains (OECs) coated with chlorhexidine (CHX) hexametaphosphate (HMP) nanoparticles and its effect on force decay. OECs were coated with CHX-HMP-5 (5 mM CHX and HMP), CHX-HMP-1 (1 mM CHX and HMP) nanoparticle colloidal solutions, CHX-5 (5 mM CHX) and CHX-1 (1 mM CHX) solutions. Release of CHX from coated OECs was evaluated over 28 days. Antimicrobial activity of the eluate collected on day 1 was tested against Streptococcus mutans and Lactobacillus rhamnosus by measuring the zone of inhibition after 4 days. OECs were observed by scanning electron microscope (SEM) to observe surface characteristics comparing: (1) uncoated and coated OECs and (2) before and after release of CHX. Force decay of OECs were measured over 28 days. SEM analysis showed that OECs were coated with nanoparticles. OECs coated with CHX-HMP-5 and CHX-HMP-1 released CHX over 28 days. The eluate from the coated OECs produced zones of inhibition after day 4 towards S. mutans and L. rhamnosus. Both CHX-HMP nanoparticle coated OEC released CHX over a period of 28 days that was capable of inhibiting the growth of S. mutans and L. rhamnosus. For all groups, the largest mean loss of force occurred over the first 24 h, followed by a relative plateau. All groups maintained >50% of the initial mean force over entire experiment of 28 days. This study showed that OECs can be coated with CXH-HMP nanoparticles that continuously elute the antimicrobial for extended periods. The coatings did not alter the force decay of OECs. Use of such coating on OECs can provide antibacterial activity to aid in the reduction of biofilm buildup and prevention of white spot lesions. This approach offers promising clinical applications.