There is a concept in dental radiology called cervical burnout. It presents at what appears to be decay around “the neck” ( cementoenamel junction of the tooth  ) when in reality it is an artifact.
This  patient  presented to my office for a second opinion . She had been advised that there was extensive decay beneath a filling and that multiple procedures needed to be performed. These included periodontal surgery for crown lengthening ( to re-create a biological width ), placement of a post and core and  fabrication of a  crown. The fee would be $ 2,375.00.
When I examined the patient I saw no decay and the radiograph that I took did not reveal decay. The radiograph taken at the first dentists office is a digital X ray as compared to a traditional film based X ray that I utilized. The misdiagnosis is due to a mistake in being able to correctly diagnosis decay  from the radiograph.
It is also noted that the digital radiograph does show a slight marginal discrepancy between the metal restoration and the cervical tooth structure but this does not appear to be a clinically significant finding.