Distribution patterns of the surface "prismless" enamel in human deciduous incisors

Distribution patterns of the "prismless" enamel were investigated in the labial, lingual, and proximal surfaces of human deciduous incisors under transmitted light through a differential interference contrast. The "prismless" enamel was generally either a short-length (0.2-0.3 mm) type, including island-like and isolated step-like shapes, or a long, band-like type, including relatively short (0.5-1 mm) and longer (2-5 mm) shapes. The island-like type was commonly observed at various intervals in the surfaces; the isolated step-like type was relatively rare. The longer band-like type was found in the maxillary labial and maxillary and mandibular proximal surfaces, but, in the other surfaces, this type was not seen. The surface enamel possessing the longer band-like type was also higher in the ratio of the total length of the "prismless" enamel to the whole surface length than the other surfaces. The frequency of the "prismless" enamel tended to be higher in the cervical region and lower towards the incisal edge.