Physico-mechanical and antimicrobial properties of an orthodontic adhesive containing cationic curcumin doped zinc oxide nanoparticles subjected to photodynamic therapy

Background: Potential complications on the crown level during fixed orthodontic procedures are white spot, enamel demineralization and tooth decay. This study evaluated the antimicrobial properties of an orthodontic adhesive incorporating cationic curcumin doped zinc oxide nanoparticles (cCur/ZnONPs), which can have the highest concentration of cCur/ZnONPs and shear bond strength (SBS) value simultaneously, against cariogenic bacteria including Streptococcus mutans, Streptococcus sobrinus, and Lactobacillus acidophilus. Materials and methods: Following synthesis and confirmation of cCur/ZnONPs, SBS and adhesive remnant index (ARI) of the test adhesives containing cCur/ZnONPs (1.2, 2.5, 5, 7.5, and 10% wt.) were measured using universal testing machine and stereomicroscope, respectively. After continuously rinsed (up to 180 day), the residual antimicrobial ability of modified adhesives which can have the highest concentration of cCur/ZnONPs and SBS value simultaneously were determined by disc agar diffusion (DAD), biofilm formation inhibition, and metabolic activity assays following photo-activation using light-emitting diode (LED) for 5 min against multi-species cariogenic biofilm-producing bacteria. Results: Adhesive with 7.5% wt. cCur/ZnONPs showed the highest concentration of cCur/ZnONPs and SBS value (14.89 +/- 3.26 MPa, P < 0.05) simultaneously. No significant differences in ARI scores were found between the modified adhesive and control (Transbond XT without the cCur/ZnONPs). 7.5% wt. cCur/ZnONPs following photo-activation was not colonized by the test microorganisms and suppressed 100% metabolic activity of the test microorganisms up to 90 day compared to the control group (cCur/ZnONPs free LED irradiation; P < 0.05). In DAD assay, the reduction of photodynamic disinfection of the 7.5% wt. cCur/ZnONPs against test bacteria was positively associated to the time, in such a way that it was decreased significantly after 60 day. From days 120 onwards, microbial biofilm formation and metabolic activity was progressively increased on 7.5% wt. cCur/ZnONPs adhesive discs compared to the control group (cCur/ZnONPs free LED irradiation). Conclusions: Our findings highlight the photo-activated 7.5% wt. cCur/ZnONPs can serve as an orthodontic adhesive additive to control the cariogenic multispecies biofilm, and also to reduce their metabolic activity.