Polarized versus nonpolarized digital images for the measurement of demineralization surrounding orthodontic brackets

Objective: To compare the assessment of demineralized white lesions surrounding orthodontic brackets using images produced with and without polarizing filters to reduce incidental flash reflection. Materials and Methods: Thirty teeth with orthodontic brackets and a systematic arrangement of artificially induced demineralization were used. Standardized digital images of the teeth were taken with and without a cross-polarizing filter. These were repeated after 1 week. All the images were randomly numbered and assessed by an investigator, unaware as to the nature of the study. The presence or absence of demineralization was recorded and compared with the actual demineralization pattern. The lesion area and degree of whiteness (LI%) were measured using computerized image analysis. Twenty images from each group were randomly chosen and duplicated for an assessment of measurement error. Results: The positive and negative predictive values were better from the polarized images (0.97 and 0.84, respectively) than from the nonpolarized images (0.90 and 0.74, respectively). The percentage agreements for the repeat assessments of the same slide were better for the polarized images (96%) than for the nonpolarized images (89%). The limits of agreement and intraclass correlation coefficients between measurements of repeated images were lower for lesion area from cross-polarized images, suggesting better reproducibility, but not for LI%. Conclusion: A cross-polarization filter enhances the subjective assessment of demineralized lesions surrounding an orthodontic bracket and improves the reproducibility of measuring the lesion area. The filter did not improve the assessment of changes in enamel gray levels with demineralization.