Antibacterial Orthodontic Adhesive Incorporating Polyethyleneimine Nanoparticles

Objectives: Bonding of orthodontic brackets to teeth is important to enable effective and efficient treatment with fixed appliances. Unfortunately, prolonged treatment is likely to increase the risk for irreversible enamel decalcification caused by cariogenic bacteria. In the present study we evaluated the antibacterial effect of quaternary ammonium polyethyleneimine (QPEI) nanoparticles incorporated in an orthodontic adhesive. Additionally, polymerization and mechanical properties were tested. Methods: QPEI nanoparticles were added into an orthodontic adhesive at 0, 1 or 1.5% wt./wt. concentration (samples a, b and c respectively). Antibacterial activity was tested using the direct contact test (DCT). Degree of monomer conversion (DC) was measured using Fourier transform infra-red (FTIR) spectroscopy. Measurements were taken before light polymerization, after 20 sec and then each 60 sec. for an additional 10 min. Shear Bond Strength (SBS) was tested on bovine teeth etched enamel. Results: DCT results showed a strong antibacterial effect in the 1 and 1.5% wt./wt. test groups (samples b and c). DC of samples a, b and c measured immediately and after 10 min. was: 62.1 – 64.3%, 62.4 – 63.5% and 62.0 – 64.8% respectively. SBS results for samples a, b and c were: 19.88 MPa, 19.61 MPa and 20.57 MPa, respectively. Conclusions: Incorporation of QPEI nanoparticles into Neobond orthodontic cement is desirable for providing antibacterial activity without reducing the adhesion strength or the degree of double bond conversion during the polymerization process.