The occlusal fissure of unerupted third molars as an experimental caries model in man.

The aim of the present investigation was to establish an experimental model for the study of fissure caries development under conditions as similar as possible to the in vivo situation. Twenty-one blocks (2 X 2 X 3 mm) constituting part of the occlusal fissure were made from unerupted human third molars, and implanted for 60 or 90 d in mandibular molars of students. One milliliter of a 50% sucrose solution was applied to the fissures twice a day. After removal, sections were examined microradiographically in polarized light and in the electron microscope. As a control, the morphology and enamel structure of fissures from 10 unerupted third molars were studied. After 90 d a subsurface, radiolucent caries-like lesion was observed in two specimens only. When examined in air in polarized light, however, all sections exhibited caries-like lesions symmetrically located around the fissures. The 60-d material showed similar lesions, but not as frequently as the 90-d specimens. In the experimental material processed for electron microscopy revealed that the fissure plaque mainly consisted of cocci and small rods. Most often the bacteria were separated from the enamel surface by a pellicle.