Structural and distribution patterns of surface 'prismless' enamel in human permanent teeth.

Using human permanent teeth, structural and distribution patterns of the surface 'prismless' enamel with the occasional presence of indistinct and/or stunted prism structures were investigated by scanning electron microscopy. The 'prismless' enamel was classified into three shapes: step-like, occurring in mid-coronal enamel; band-like, frequently seen in occlusal and fissure enamel, and island-like, found in occlusal and cuspal-coronal enamel. These three 'prismless' shapes were formed by two structural patterns. One was determined by prisms which gradually changed into 'prismless' structures via indistinct and stunted prisms (prism-dependent; P type), and another, probably a variance of the P type, was characterized by prisms which abruptly changed into 'prismless' structures on the incremental lines of Retzius or the fine laminated striations (Retzius-dependent; R type). The P type pattern clearly forming the band and island-like shapes was found in occlusal and cuspal-coronal enamel, whereas the R type pattern forming some of the band-like shapes as well as the step-like shapes might be observed in almost all surface enamel.