<prompt> Minimal dentinal destruction to get evident on the radiograph:30 microns40 microns20 microns200 microns  <response>: Minimal dentinal destruction of 40 microns is required to be seen on a radiograph.Lesions confined to the enamel may not be evident until approximately 30 to 40 demineralization has occurred. For this reason, the actual depth of penetration of a carious lesion is often deeper than seen in the image. Reference: White and Pharoahs Oral Radiology Principles and Interpretation 7th edition page no 288 