Effects of Crest Whitestrips bleaching on subsurface microhardness and ultrastructure of tooth enamel and coronal dentin.

PURPOSE: To describe the complementary subsurface analysis of structural and ultrastructural effects of bleaching with Crest Whitestrips on enamel and coronal dentin METHODS: Human tooth enamel specimens were cycled through a daily regimen including salivary immersions and treatments with commercial tooth whitening gels containing hydrogen peroxide or carbamide peroxide. Treatments with hydrogen peroxide in Crest Whitestrips gel base were carried out for up to 70 hours bleaching (some five fold to the clinical exposure required to produce satisfactory whitening in bleaching strip systems as established by double blind placebo controlled clinical studies) [correction]. Following in vitro laboratory cycling, the teeth were cross sectioned and remounted for observation of microhardness and ultrastructural characteristics in subsurface regions. Ultrastructure was assessed by application of confocal laser scanning microscopy (reflection mode). RESULTS: Peroxide whitening compositions had no effects on subsurface microhardness of enamel or dentin, even under conditions of five fold overbleaching. Crest Whitestrips gel containing up to 6.5% hydrogen peroxide applied for periods up to 70 hours (five kit) overbleaching was found to produce no changes (at a lateral resolution of 200-300 nm) in observed subsurface enamel and dentin ultrastructure or architecture.

Effects of Crest Whitestrips bleaching on surface morphology and fracture susceptibility of teeth in vitro.

OBJECTIVE: This study examined the effects of peroxide tooth bleaching, including Crest Whitestrips hydrogen peroxide treatments, on the fracture susceptibility and surface morphology of human tooth enamel in vitro. METHODOLOGY: Extracted human molars were ground and polished to prepare a uniform substrate for bleaching treatments. A cycling treatment methodology was employed which alternated ex vivo human salivary exposures with bleaching treatments under conditions of controlled temperature and durations of treatment. Bleaching treatments included commercial Crest Whitestrips bleaching gels, which utilize hydrogen peroxide as the in situ bleaching source, and several commercial carbamide peroxide bleaching gels. Control treatments included placebo gels and an untreated group. Crest Whitestrips bleaching included treatment exposures simulating recommended clinical exposures (14 hours of bleaching), along with excess bleaching simulating exposure to five times the suggested Crest Whitestrips use. At the conclusion of treatments, surface color measurements were taken to ensure tooth bleaching. Surface microhardness measures and surface morphological assessments with SEM were conducted to assess the effects of bleaching exposure on the surface morphology and mineral integrity of the teeth. These latter measures were then complemented with assessments of fracture susceptibility utilizing detailed analyses of crack propagation resulting from post-treatment microhardness indentations. RESULTS: Surface microhardness and SEM measures revealed no deleterious effects on the enamel surfaces from any of the bleaching products assessed. This included conditions of excess bleaching exposure or "overbleaching." The analysis of fracture susceptibility similarly revealed no significant effects from tooth bleaching, regardless of the peroxide source. CONCLUSIONS: These results confirm that tooth bleaching from the selected commercial hydrogen peroxide or carbamide peroxide bleaching systems do not produce changes in surface morphology, microhardness or fracture susceptibility of human tooth enamel under in vitro cycling conditions of treatment matching clinical bleaching exposures. These results support the clinical safety of the selected commercial bleaching systems to vital dentition, matching results obtained from the long-term use of these ingredients applied in dental offices and available in commercial formulations.

Impact of Crest Night Effects bleaching gel on dental enamel, dentin and key restorative materials. In vitro studies.

PURPOSE: To examine the effects of a paint-on 19% sodium percarbonate 'overnight' bleaching gel on the structure and integrity of enamel, dentin and some common restorative materials, with a laboratory cycling model. METHODS: Enamel, root dentin and restorative materials (glass-ionomer, composite and amalgam) were prepared in methacrylate molds with surface polishing. A treatment regimen was carried out including diurnal incubation in pooled human saliva and including twice daily toothbrushing with standard fluoridated dentifrice. Test samples were treated daily with Crest Night Effects bleaching gel, which included drying of surfaces, painting of percarbonate bleaching gel, and then incubation throughout the day (8 hours) to simulate overnight wear. Treatments were carried out over 14 days, to simulate clinical exposure periods. Control and test specimens were evaluated for surface and subsurface structure and morphological integrity utilizing surface microhardness, surface profilometry, and confocal laser scanning microscopy. RESULTS: Percarbonate bleaching film treatments had no effects on enamel or root dentin surface microhardness, or on subsurface ultrastructural integrity of enamel and coronal dentin. Surface profilometry confirmed retention of small amounts of residual silicone polymers, which contributed to CLSM air objective appearance and surface roughness measures. Restoratives were generally passive to bleaching gel treatments, though composite showed a tendency to attract retained residual silicone film.