C10 Identify the three most common types and causes of amalgam restoration failures.
The high recurrent caries number relates most likely to unreliable caries diagnosis. Traditionally, dentists were taught to diagnose caries by checking if an explorer tended to "stick" if it was pressed into a fissure or a restoration margin. However, a "stick" is more related to friction between the explorer and adjacent surfaces than to disease (e.g., press a pencil between a door and a door-post and you will find it sticks without having a carious disease), and defect margins have often been diagnosed as suffering from "caries."
Because of the above aspects regarding traditional diagnosis of caries, it would probably be better to say that recurrent caries & improper marginal failures contribute with 2/3 of all amalgam failures (57% + 9%), followed by isthmus fractures (14%) and tooth fractures (12%).