# Dual-Mode Antibacterial Orthodontic Composite: Contact-Killing QACs and Sustained CHX Release via Large-Pore Mesoporous Silica Nanoparticles

## TL;DR

A new orthodontic composite was developed that kills bacteria on contact and releases antibacterial agents over time, offering a promising solution for preventing bacterial infections in dental treatments.

## Contribution

The novelty lies in combining contact-killing QACs with sustained CHX release via large-pore mesoporous silica nanoparticles in an orthodontic composite.

## Key findings

- QLMSN@CHX achieved near-complete biofilm eradication within 24 hours.
- The composite maintained high shear bond strength comparable to commercial adhesives after 30 days of aging.
- The material showed good biocompatibility with human dental pulp mesenchymal stem cells.

## Abstract

This study develops a dual-mode antibacterial orthodontic adhesive by integrating quaternary ammonium salt-modified large-pore mesoporous silica nanoparticles (QLMSN@CHX). The material integrates two antibacterial mechanisms: (1) contact killing via covalently anchored quaternary ammonium salts (QACs) and (2) sustained release of chlorhexidine (CHX) from radially aligned macropores. The experimental results demonstrated that QLMSN@CHX (5 wt%) achieved rapid biofilm eradication (near-complete biofilm eradication at 24 h) and prolonged antibacterial activity, while maintaining shear bond strength comparable to commercial adhesives (6.62 ± 0.09 MPa after 30-day aging). The large-pore structure enabled controlled CHX release without burst effects, and covalent grafting ensured negligible QAC leaching over 30 days. The composite demonstrated good biocompatibility with human dental pulp mesenchymal stem cells at clinically relevant concentrations. This dual-mode design provides a clinically viable strategy to combat bacterial contamination in orthodontic treatments, with potential applications in other oral infections. Future studies will focus on validating efficacy in complex in vivo biofilm models.