These metabolic processes are a physiological phenomenon, and caries is ubiquitous and natural at the crystal level. Mineral loss and subsequent cavity formation are the result of an imbalance in the dynamic equilibrium between tooth mineral and plaque fluid. Without this information, a logical decision about treatment is impossible. It is difficult to judge lesion activity histologically and unwise to attempt diagnosis in a laboratory simulation of a clinical setting. Diagnosis requires a warm human being and a clinical nose.
Secondary caries is the lesion at the margin of an existing restoration.
In that setting, histological examination of artificial and natural lesions around restorations may show lines of demineralized tissue running along the cavity wall. These are called wall lesions, and they are the result of microleakage. It is also important to consider residual caries, which is residual demineralized tissue left in the tooth during cavity preparation. This group removed the enamel lid from large occlusal lesions, leaving extensively demineralized dentine. The cavities were then sealed with acid-etch composite restorations.