When preparing a class II cavity, what is indicated by a hard dark brown spot on the adjacent tooth just below the contact point?

A hard dark brown spot on the adjacent tooth just below the contact point is indicative of demineralized enamel. This condition often appears as a result of early carious processes where the enamel has lost minerals without yet cavitating. It is important to recognize this condition during cavity preparation because it signals the potential for caries development and highlights areas that might need intervention to prevent further decay or to reinforce the enamel structure.

In this context, while dental caries is a possibility, a hard dark brown spot specifically suggests that there has been a loss of mineral content but not necessarily a full carious lesion that would penetrate into the dentin. Enamel hypoplasia, on the other hand, refers to a developmental defect that results in pits or grooves in the enamel and typically is not characterized just by a dark brown spot. Likewise, a non-carious cervical lesion pertains to wear or damage around the gum line usually associated with abrasion or erosion and is not represented merely by a dark brown spot in the enamel.