Bioactive Antibacterial Modification of Orthodontic Microimplants Using Chitosan Biopolymer

Abstract

Titanium alloy (Ti6Al4V)-based microimplants are extensively used as anchorage units in orthodontic treatment; however, they have a high failure rate (10 to 30%). This study aimed to enhance the survivability of these small implants by improving their bioactive and antibacterial properties, via modifying their surface with chitosan. For a stable covalent bond, microimplant surfaces were first functionalized with 3-triethoxysilylpropylamine (APTES) and then grafted either with a succinic acid or polyacrylic acid spacer, followed by attachment with chitosan. Validity tests were conducted on titanium alloy disk (TI) specimens treated with the same chemical process (TI specimens were used to avoid the practical difficulties in testing the small and complex-shaped microimplants). The results confirmed successful APTES functionalization and grafting of succinic- or polyacrylic acid. Anchoring of chitosan was confirmed via X-ray photoelectron spectroscopy (XPS) and confocal laser scanning microscopy (CLSM); furthermore, the anchoring ability of succinic acid, as a spacer, for chitosan was superior to that of polyacrylic acid. Chitosan-modified TI specimens (TI-SA-Ch) showed better biocompatibility with pre-osteoblastic MC3T3-E1 cells, as confirmed from their enhanced adhesion, proliferation, and from cell viability analysis. Biofilm formation of Streptococcus mutans and Streptococcus sobrinus was effectively reduced by 53% and 31%, respectively, on the surface of TI-SA-Ch. These results clearly indicated that chitosan modification might be a promising approach to enhance the bioactive- and antibacterial properties of orthodontic microimplants, and thus, increase their stability in the jaw bone in clinical practice.