The caries process in anterior approximal (Class III) lesions is functionally the same as those in the posterior. Plaque accumulates in areas of anterior teeth not naturally cleansed by the cheeks, lips, and tongue (e.g. between the gingival crest and the contact area). Bacteria convert dietary carbohydrates into organic acids that dissolve enamel surfaces.
Lesions form in enamel apical to the contact, oval in shape (wider inciso-gingivally than labio-lingually). Lesions in dentin spread symmetrically around the portal for acids through the enamel. Lesions are limited labio-lingually by enamel surfaces. Note that Class V lesions often begin on root surfaces mid-proximal, just apical to the CEJ. These may be difficult to discern radiographically from proper Class III lesions, but may need to handled differently since most margins will be placed in dentin/cementum