Interproximal caries is best detected by:

Bitewing (interproximal) views are used to record the coronal portions of the maxillary and mandibular teeth in one image. They are useful for detecting interproximal caries and evaluating the height of alveolar bone. Size 2 film is normally used in adults; the smaller size 1 is preferred in children. In small children, size 0 may be used. A relatively long size 3 is also available. Reference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 260, 65