Ellipsometric analysis of enamel bleached with tooth whitening agents

Objectives: Tooth discoloration can be classified on the basis of localization and etiology. One way of treating discolored teeth is tooth whitening procedure using different concentrations of bleaching agents (hydrogen-peroxide, carbamide-peroxide) depending on the bleaching technique. The aim of this study was to examine and evaluate the effects of bleaching agents on human enamel with ellipsometry. Ellipsometry is a non destructive and contact-free optical technique that investigates refractive indexes (n) and extinction coefficients (k) of thin films. Methods: Extracted human teeth were embedded in polystyrene resin with vestibular/oral enamel surface exposed and polished. Ellipsometer analyses the change of polarization of light which is reflected off a sample, and probes the complex refractive index which gives access to physical parameters that are related to a variety of sample properties including morphology. Measurement of n and k were performed between 246-1000 nm at three different points on untreated and treated enamel surfaces and at two different angles (70o and 75o). The treatment consisted of 10% hydrogen-peroxide bleaching for 30 min. Results: Ellipsometric measurements showed an increase in the refractive index of enamel after bleaching treatment by 10% hydrogen-peroxide: at 70o and 633 nm n70 was 1.521 ± 0.0038 before treatment and 1.542 ± 0.0031 after treatment; at 75o n75 was 1.526 ± 0.0019 before treatment and 1.546 ± 0.0039 after treatment. The measurements proved a 0.0026 increase in the absorption coefficient at 70o and 0.0033 at 75o. Conclusion: This change in the values of refractive index and absorption coefficient implicates that the surface morphology of enamel has changed from a porous structure to a more concise structure after application of 10% hydrogen-peroxide as bleaching agent.