Abstract –Clinical tissue changes were recorded during restorative treatment of proximal carious lesions of young premolars and molars. 60 proximal surfaces with radiolucencies in the inner half of the enamel or the outer half of the dentin were treated. The extent and character of the tissue changes were documented with photographs taken during drilling and evaluated after magnification. The maximum extent for each lesion was correlated to the extent of the radiographically observed lesion. The results showed that 70% of the restored surfaces were associated with a breakdown of the enamel surface. When the radiolucency did not extend deeper than into the inner half of the enamel, cavities were found in 61%; for lesions with a radiolucency extending into the outer half of the dentin the percentage was 78%. In the majority of cases the cavity was limited to the enamel. In all cases discoloration was observed in the enamel. The dentin was soft and discolored in 83%. Severe damage of tooth substance was found in 12% of the teet