<unk> is the loss of tooth structure by mechanical forces from opposing teeth.<unk> initially affects the enamel and, if unchecked, may proceed to the underlying dentin.  Once past the enamel,<unk> quickly destroys the softer dentin.
The most common cause of<unk> is bruxism. Functional habits are those such as chewing and swallowing, which usually puts very little force on opposing teeth.  Parafunctional habits, such as clenching and clicking the teeth together nervously, place greater amounts of forces on opposing teeth and begin to wear the teeth.  As expected, wear usually begins on the incisal or occlusal surfaces.
Attrition 
Causality
Unblinding
Impalement
Compliance 
Scientific consensus
Positive feedback
Admissible decision rule