Introduction

When clinicians read an interesting research article that is reporting a correlation or association between an oral disease and a particular outcome of interest, they may automatically and incorrectly, jump to the conclusion that the relationship is causal. Prime examples of such misinterpretations frequently occur with the oral-systemic linkages, such as the assumption that periodontitis is one cause of heart disease or of adverse pregnancy outcomes, or that stress causes periodontitis. It is important for clinicians to understand that correlations and associations do not imply causality. In fact, assumptions of causality are a major public health concern. From a public health perspective, any evidence should NOT be considered ‘causal’ unless it has gone through very rigorous scrutiny using standard public health guidelines such as the Bradford Hill Criteria for causality2 or the Hume3 criteria or the Mill4 criteria for causation.

Clinicians often have a poor understanding of causality and in turn, risk delivering incorrect information to their patients and even to the media, which can have far reaching effects. This is a very dangerous practice! One prime example of the result of such misrepresentation of information occurred in 2012 when the American Heart Association (AHA) published a scientific statement in its journal Circulation, stating that a review of the current scientific evidence did not establish a cause and effect relationship between periodontal disease and heart disease.5 Although this AHA review found no direct, causal relationship, they concluded that “heart disease and periodontal disease may occur at the same time in a person because of common risk factors (such as smoking, age and diabetes) and because both conditions produce markers of inflammation.

This statement was absolutely correct as research has definitely shown many correlations and associations between the two, but has never been able to determine a causal relationship. This statement was quickly picked up by the media, and created an uproar within the dental community, leading both the American Dental Association (ADA) and the American Academy of Periodontology (AAP) to make statements in response to the AHA’s statement indicating they were in agreement. The ADA statement indicated “Dentists have long suspected a relationship between heart disease and gum disease,” and added “This new AHA review advises health care professionals to be cautious in making ‘cause and effect’ statements between these conditions.”6

The AAP responded with a more in-depth explanation as they felt the AHA statement had caused significant confusion. The AAP’s response stated: “While the statement itself is scientifically sound, the AHA-issued press release and corresponding media coverage does not accurately reflect the principal conclusions of the statement. The statement is consistent with the Academy's position in that there is an association between periodontal disease and cardiovascular disease, but no causal relationship.”7

This was a prime example of the types of misconceptions and misinterpretations that occur when reading the literature and then disseminating that information incorrectly to patients. Determining causality is a very complex undertaking and requires multiple longitudinal studies, the ability to accurately interpret the current literature, and the application of other very specific criteria for causation. First and foremost, clinicians must understand the difference between research articles in order to determine the strength of the evidence that articles present. For many years now, an evidence pyramid has been in existence to aid clinicians in their clinical decision-making and has gone through numerous iterations over the years. The most current evidence pyramid will be presented further into this course, along with explanations of the various levels of evidence that comprise the pyramid.

With the widespread use of the electronic media, patients are now posing more and more questions to their oral health professionals regarding a wide array of topics concerning their oral health. They look to their clinicians as experts and trust they will provide the best information regarding all topics related to their oral health. Thus, it is imperative that clinicians have a good understanding of how to interpret and apply the latest research findings and be able to accurately differentiate between relationships, associations, correlations and causality in order to best serve their patients.