Graded changes in enamel component volumes resulted from a short tooth bleaching procedure

• Proportion of the enamel layer affected by short tooth bleaching is unknown.
• After a short bleaching, enamel components were analyzed from the surface inward.
• At the surface, a gradient of probability of changes followed the order: mineral > organic > water > permeability.
• Probability of changes decreased from the surface inward, but followed the same order seen at the surface.
• Despite negligible proportion of affected enamel layer, tooth shade changed significantly.

AimTo test the hypothesis that changes in enamel component volumes (mineral, organic, and water volumes, and permeability) are graded from outer to inner enamel after a short bleaching procedure.Materials and methodsExtracted unerupted human third molars had half of their crowns bleached (single bleaching session, 3 × 15 min), and tooth shade changes in bleached parts were analyzed with a spectrophotometer. Ground sections were prepared, component volumes and permeability were quantified at histological points located at varying distances from the enamel surface (n = 10 points/location), representing conditions before and after bleaching.ResultsTooth shade changes were significant (p < 0.001; 95% CI = −1/−8; power = 99%), and most of the enamel layer was unaffected after bleaching, except at the outer layers. Multiple analysis of covariances revealed that most of the variance of the change in enamel composition after bleaching was explained by the combination of the set of types of component volume (in decreasing order of relevance: mineral loss, organic gain, water gain, and decrease in permeability) with the set of distances from the enamel surface (graded from the enamel surface inward) (canonical R2 = 0.97; p < 0.0001; power > 99%).ConclusionsChanges in enamel composition after a short bleaching procedure followed a gradient within component volumes (mineral loss > organic gain > water gain > decrease in permeability) and decreased from the enamel surface inward.