Effects of hydrogen peroxide bleaching strips on root surfaces in vitro.

OBJECTIVE: This study examined the effects of hydrogen peroxide tooth whiteners on the physical hardness and morphology of human root dentin cycled through bleaching treatments in vitro.
METHODOLOGY: Human root dentin was ground and polished to prepare a uniform substrate for bleaching treatments. Half the root dentin specimens were acid (EDTA) etched to remove the smear layer, while the other half were treated with an intact smear layer. 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 Crest Whitestrips bleaching gels, which utilize hydrogen peroxide as the in situ bleaching source at 5.3 and 6.5% concentrations of hydrogen peroxide, placebo gels containing no hydrogen peroxide, and an untreated control group. Surface color measurements were taken prior to and following bleaching. Effects of bleach on physical properties of dentin were assessed with microhardness, and surface morphology effects were studied with scanning electron microscopy (SEM).
RESULTS: Color assessments confirmed significant ex vivo tooth bleaching by treatments. Surface microhardness values remained the same or increased slightly with bleaching treatments for both smear layer and etched dentin surfaces. SEM measures of non-etched dentin surfaces cycled with bleach showed preservation of the dentin smear layer. SEM of etched dentin treated with bleach showed maintenance of standard tubule diameters.
CONCLUSION: These results confirm that tooth bleaching with hydrogen peroxide bleaching gels at 5.3 and 6.5% concentrations do not produce solubilization reactions on dentin surfaces in vitro, and that dentin smear layers remain intact following bleaching exposures.