Polarizing microscopy and microradiography of sound enamel.

Plano-parallel longitudinal sections from 19 sound human premolars were imbibed in water and in air. The total birefringence of the occlusal, the midcoronal and the cervical region of the buccal sound enamel cap was then determined. The volume percentage mineral was measured in the same areas using semi-quantitative microradiography. The results show that when the mean values of both water and air imbibed occlusal and midcoronal enamel are considered, there is a positive correlation between the observed total birefringence and the mineral content. The cervical, fissure and cuspal regions showed a poor correlation between mineral content and total birefringence. In longitudinal sections, the influence of the structural organization and the organic matrix is not marked in the occlusal and midcoronal regions although the cervical, fissure and cuspal regions are probably influenced to the greatest extent by these factors.