Tooth Structure Changes after Exposure to Hydrogen Peroxide in vitro

Previous studies suggested that tooth sensitivity after whitening procedures is influenced by factors such as demineralization/re-mineralization and pH changes. Tooth enamel is comprised of 1%, and root cementum about 30% organic matrix, respectively; 90% of cementum matrix is collagen. It is unclear whether hydrogen peroxide treatment affects the mineral phase, the organic matrix, or both to cause tooth sensitivity. Objectives: To investigate changes in enamel and cementum mineral structure and/or protein matrix after tooth bleaching with hydrogen peroxide. Materials and Methods: 12 intact extracted anterior incisors were collected from Stony Brook University Dental Clinic and distributed into three groups (n=4). The control group was immersed in water (22oC) and the two experimental groups were treated either with 35% Hydrofluoric acid or 50% hydrogen peroxide for 30 minutes. The treated teeth were analyzed by infrared microscopy performed in reflection mode (penetration about 10 microns). 2-3 spectra were collected on the crown and root of each tooth and the average determined. Additional teeth were studied by scanning and transmission electronic microscopy for surface alterations. Results: As expected, the crown region of the samples showed mostly mineral and little organic material. Root region showed more protein matrix (collagen); the amount was dependent on the treatment-effect. The untreated root surfaces showed the largest amount of organic material, while the treated groups (both acid and hydrogen peroxide) showed significant loss of organic matrix. Electron microscopy showed a similar pattern of enamel surface alteration using either acid etch or hydrogen peroxide. Conclusion: Hydrogen peroxide treatment of tooth root surface significantly depleted the organic matrix, presumably due to the degradation of its primary constituent, the Type I collagen fibers. Further studies are needed to understand the similar, hydrofluoric acid- and H2O2- induced surface alterations in enamel and cementum.