A comparative study on component volumes from outer to inner dental enamel in relation to enamel tufts.

Abstract Background and aim Dental enamel presents marked mechanical properties gradients from outer to inner enamel, a region lacking component volumes profiles. Tufts, structures of inner enamel, have been shown to play a role in enamel resilience. We aimed at comparing component volumes from inner to outer enamel in relation to enamel tufts. Materials and methods Transversal ground sections from the cervical half of unerupted human third molars ( n  = 10) were prepared and histological points were selected along transversal lines (extending from innermost to outer enamel) traced across tufts and adjacent control areas without tufts. Component volumes were measured at each histological point. Results Component volumes ranges were: 70.6–98.5% (mineral), 0.02–20.78% (organic), 3.8–9.8% (total water), 3–9% (firmly bound water), and 0.02–3.3% (loosely bound water). Inner enamel presented the lowest mineral volumes and the highest non-mineral volumes. Mineral, water and organic contents differed as a function of the distance from innermost enamel but not between the tuft and control lines. Tufts presented opaqueness in polarizing microscopy (feature of fracture lines). Organic volume gradient correlated with a relatively flat profile of loosely bound water. Inner, but not outer enamel, rehydrated after air-dried enamel was heated to 50 °C and re-exposed to room conditions, as predicted by the organic/water gradient profiles. Conclusions Component volumes vary markedly from outer to inner enamel, but not between areas with or without tufts (that behave like fracture lines under polarizing microscopy).