Periodontal disease and respiratory disease: A systematic review of the evidence," Agado & Bowen (2012) perform a systematic review or meta-analysis style of research to determine whether there is a correlation between periodontal disease and pneumonia, or between periodontal disease and chronic obstructive pulmonary disease (COPD), a "common" condition that includes chronic bronchitis and emphysema. Smoking is a major risk factor for COPD; but pneumonia can be caused by a number of different variables, some of which are environmental. It has long been suspected that there is a link between periodontal disease and either pneumonia or COPD, if not both. However, prior research has been inconclusive if these relationships are causal or correlational. A causal relationship has been hypothesized in some research, as the authors cite the fact that "aspiration of oral bacteria has been implicated in the occurrence of healthcare associated pneumonia and exacerbation of COPD," (p. 3). Therefore, dental practices must be aware of risk factors involved for periodontal disease and different types of respiratory disease. The researchers gathered evidence by searching scholarly databases including Medline, PubMed, and the Cochrane Database of Systematic Reviews. The searches were conducted both electronically and manually. Search terms included "lung disease," "obstructive pneumonia," "periodontal disease," and combinations thereof. However, the authors did not include research on periodontal disease, pneumonia, or COPD that were irrelevant to the current research; the research had to be designed specifically related to the search terms. No practice guidelines, authority opinions, or case studies were included in the meta-analysis of the data. The researchers limited the search to include only journal articles published in English between 1997 and 2011. Moreover, the authors further delimited the data set to include only...

However, the authors included in their search a multitude of types of research designs including randomized controlled/clinical trials, systematic reviews/meta-analyses, longitudinal, cohort, and case control studies, multicenter studies, and also epidemiological studies.
Altogether, only 17 articles culled from databases and 4 culled from hand searching were included in the research. The researchers evaluated each of the studies in terms of strength, using parameters such as length of the design, sample size, use of controls, and regression models. Also, strength of evidence was evaluated in terms of a grading system. This grading system, which rates strength of evidence on various criteria, was developed by the Canadian Task Force on Preventive Health Care. Each of two reviewers read the articles to extract evidence related to the research questions and hypotheses.

The results showed that there is no significant correlation between the independent variable (periodontal disease) and the dependent variables (pneumonia or chronic obstructive pulmonary disease). Some of the articles reviewed, including three other systematic reviews/meta-analyses and seven experimental research designs, provided some inconclusive evidence that there may be a connection between periodontal disease and pneumonia. Likewise, five studies that were robust, longitudinal, or matched case control design showed some evidence of a correlation. Likewise, retrospective analyses reveal a conjectural association between the dependent and independent variables. In spite of these connections, it does not appear that there is either a causal or a strong correlational effect. However, meta-analyses / systematic reviews on the subject do indicate there is "fair evidence" supporting a connection between both pneumonia and COPD and periodontal disease. The authors point out that even a…