This study aimed at examining whether tactile examination with an explorer may produce traumatic defects in occlusal fissures. The study was carried out in 10 young male adults each of whom was due to have one pair of newly erupted third molars to be extracted. One randomly selected molar in each pair was clinically examined with a dental explorer and the teeth extracted after 1 week. The teeth were serially sectioned and a total of 196 ground sections were examined in a stereomicroscope. Defects were observed in 60% of the sections from experimental teeth in contrast to 7% in the control sections. There was a positive correlation between the size of the defect and the area of enamel opacity which again was associated with the surface morphology. Results indicate that classical use of sharp explorers may produce irreversible traumatic defects in demineralized areas in occlusal fissures favouring conditions for isolated lesion progression.