This study aimed to evaluate the effects of magnesium oxide (MgO) nanoparticle (NP) incorporation on shear bond strength (SBS) and antibacterial property of orthodontic composites. A total of 100 mounted premolar teeth were randomly divided into five groups. In group 1 (control), the brackets were bonded to the teeth using the GC Ortho Connect orthodontic composite, while the brackets of groups 2 to 5 were bonded by the GC Ortho Connect orthodontic composite that contained 0.5%, 1%, 2%, and 4% weight percentages (w/w) of MgO NPs, respectively and then the SBS was measured. In the following, we evaluated the antibacterial properties of the MgO NP-containing composite on Streptococcus mutans (S. mutans) bacteria by the direct contact test method. According to results, there were no significant changes in the SBS as the MgO NP concentration was increased up to 1%, while the SBSs of the 2% and 4% MgO NPs were decreased when compared to the other three groups. The outcomes of the direct contact test indicated the case of 1% as being the minimum ratio of MgO NPs, which almost caused the entire annihilation of the S. mutans bacteria. In conclusion, the orthodontic composite containing 1% MgO NPs can display a significant antibacterial effect against S. mutans bacteria without inducing any negative effect on the SBS.
Keywords: Streptococcus mutans; magnesium oxide; nanoparticles; orthodontic composite; shear bond strength.