Decay on the proximal surface and incisal edge of an anterior tooth involves areas that are generally smooth and free of pits or fissures. Such caries develop on the flat surfaces of the tooth, excluding occlusal pits or root areas. Pit and fissure caries occur mainly on occlusal or lingual/palatal pits, not on proximal or incisal edges. Root surface caries affect the cementum of exposed roots, which is not involved here. Secondary caries arise adjacent to existing restorations, which is not specified in this context. Therefore, decay on proximal and incisal edges of an anterior tooth is classified as smooth surface caries because it involves the cleaner, less retentive flat enamel surfaces.

Reference: Sturdevant's Art and Science of Operative Dentistry, 7th Edition.