"[A]n approach to oral health care that requires the judicious integration of systematic assessments of clinically relevant scientific evidence, relating to the patient's oral and medical condition and history, with the dentist's clinical expertise and the patient's treatment needs and preferences." (American Dental Association)
The evidence pyramid shows you how reliable different types of research are. The lower levels contain information that is based on less evidence, such as expert opinion or very early experiments. Higher up the pyramid, the amount of literature decreases, but it is based on more evidence & thus is more reliable.
This section and the sub-pages are based on the the "Searching the Biomedical Literature" section of the Dental Hygiene Research Guide at the University of Michigan Library.