1 Department of Oral Health Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, British Columbia, Canada.
2 Department of Chemical and Materials Engineering, Gina Cody School of Engineering and Computer Science, Concordia University, Montreal, Quebec, Canada.
3 College of Dentistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.

The main objective of this study was to develop a natural curcumin-loaded varnish that responds to blue light in an antimicrobial photodynamic therapy-based approach with photoelimination of targeted cells. Fluoride-free curcumin-loaded varnish (CUR-V) consisting of gum rosin (80 wt%) and ethanol (20 wt%) was loaded with 0, 0.25, and 10.0 wt% curcumin and then analyzed with FTIR. Subsequent investigation included applying ~19 mW/cm² blue light for 15, 30, or 60 min (in order of increasing energy dose) to the varnishes and measuring the change in varnish color and the production of reactive oxygen species (singlet oxygen and superoxide anion), as well as performing CFU count and XTT assays of 24-h mono-species biofilms of Streptococcus mutans and Candida albicans. Lastly, a 72-h dual-species biofilm of both species was assessed with a CFU count assay. As the light energy applied to the 0.25% CUR-V and 0.00% CUR-V samples increased, there was a reduced and quantifiable difference in color between these two varnish groups (p < 0.001). In addition, singlet oxygen production was most dependent on curcumin loading in the varnish, while superoxide anion production appeared more dependent on blue light energy (p < 0.001 for both). In subsequent investigations of mono- and dual-species biofilms, the ability to induce an agonistic antimicrobial response as a function of curcumin loading in the natural varnish and blue light energy was demonstrated. Inherently, as curcumin loading and blue light energy increased, the photoelimination of both species investigated increased. As expected, the impact of aPDT on the 72-h biofilm was less than that observed for the 24-h biofilm; however, the more mature dual-species biofilm still observed a photoelimination effect with greater curcumin concentration. This study provides early evidence toward the development of a new natural curcumin-loaded fluoride-free varnish that, when combined with blue light irradiation, shows significant potential to effectively provide a targeted antimicrobial response against cariogenic species. To date, there is no similar approach that can serve as a natural, fluoride-free over-the-counter alternative to assist in caries prevention and treatment.