Objective: The objective was to evaluate the efficacy of MI varnish in preventing white spot lesions in patients with fixed orthodontic therapy. Method The study was performed where 100 patients undergoing orthodontics treatment were allocated randomly to 2 subgroups with differing frequencies of MI varnish application. Degree of mineralisation was measured on the vestibular surfaces of 12 teeth (6 varnish & 6 unvarnished controls) Measurement were taken at 4 sites using camera EOS 750D and then subjected to statistical analysis. Results: The statistical analysis showed difference in the degree of demineralization between treated and untreated teeth, and was statistically significant in terms of time point, frequency of application or specific tooth site. Conclusion: Periodic application of MI varnish can offer some protection against white spot lesions and it is not statistically significant degree if patients have excellent oral hygiene. Additional protection is conferred by applying the product every 3 months compared with every 6 months