In Great Britain, IR(ME)R 2017 says a dentist who justifies, takes or clinically evaluates radiographs must be adequately trained: theory and practical experience in the Schedule 3 subjects relevant to that role [1][2][3].
The General Dental Council recommends at least five hours of radiography and radiation protection CPD in each five-year cycle if you undertake radiography. It is highly recommended, and the GDC's recommended topics are not compulsory.
In two studies that checked radiographs against the extracted teeth, the radiograph's sensitivity for calculus was 44% and 50% [1, 2].
Radiology has a name for this problem. A normal variant is an incidental, usually asymptomatic imaging finding that mimics a true pathological condition, and knowing the common ones is what stops a reader ordering imaging or treatment the patient did not need.
A doubled structure on a radiograph has five causes, and they are not versions of one another. One of them is normal anatomy behaving exactly as the machine's geometry says it should. Two are faults at the receptor. The rest sit in between.
Every error in radiographic technique ends at the same decision: expose again, or read what you have. It is a trade-off rather than a rule. A retake costs the patient another exposure, and guidance is explicit that any exposure has to be justified by clinical benefit.