This zone, which lies at the border of the lesion, between the main body and the translucent zone or normal enamel, shows positive birefringence when the section is placed in quinoline and viewed ...

By transmitted light they appear opaque, while the normal enamel is translucent or transparent; by reflected light they appear white. When cleared and mounted in the routine histological manner ...

However, a number of additional confounding factors such as the presence of extrinsic stain or increased enamel translucency on some subjects without fluorosis or at low levels of fluorosis ...