Morphology of the most common form of protostylid on human lower molars.

Scanning electron microscopy of the enamel surface and enamel structure in the protostylid area classified as a surface irregularity was performed on 26 human lower third molars. This protostylid class can be regarded as the onset of a cusp formation, while the protostylid pits should be considered to be fissures between a protoconid and a poorly expressed protostylid.