BACKGROUND: Several recent studies provide evidence that the oral cavity may influence the initiation and/or the progression of lung diseases such as pneumonia and chronic obstructive pulmonary disease (COPD). RATIONALE: Studies have shown that poor oral hygiene and periodontal disease may foster colonization of the oropharyngeal region by respiratory pathogens, particularly in hospital or nursing home patients. If aspirated, these pathogens can cause pneumonia, one of the most common respiratory infections, especially in institutionalized subjects. Other cross-sectional epidemiologic studies point to an association between periodontal disease and COPD. This systematic review examines the literature to determine if interventions that improve oral hygiene reduce the rate of pneumonia in high-risk populations. FOCUSED QUESTION: Do periodontal diseases or other indicators of poor oral health influence the initiation/progression of pneumonia or other lung diseases? SEARCH PROTOCOL: MEDLINE, pre-MEDLINE, MEDLINE Daily Update, and the Cochrane Controlled Trials Register were searched to identify published studies that related variables associated with pneumonia and other lung disease to periodontal disease. Searches were performed for articles published in English from 1966 through March 2002. INCLUSION CRITERIA: Randomized controlled clinical trials (RCTs), longitudinal, cohort, and case-control studies were included. Study populations included patients with any form of pneumonia or chronic obstructive pulmonary disease (COPD) and periodontal disease, as measured by assessments of gingival inflammation, probing depth, clinical attachment level, and/or radiographic bone loss, or oral hygiene indices. EXCLUSION CRITERIA: Limited to studies of humans. DATA COLLECTION AND ANALYSIS: The summary statistics used to analyze the RCTs included weighted mean differences in rates of disease between control and intervention groups. For cohort studies that measured differences in rates of disease between groups with and without oral disease, weighted mean differences, relative risks, or odds ratios were compared. A meta-analysis was performed on the 5 intervention studies to determine the relationship between oral hygiene intervention and rate of pneumonia in institutionalized patients. MAIN RESULTS: Of the initial 1,688 studies identified, 36 satisfied all inclusion criteria and were read. Of these, 21 (11 case-control and cohort studies [study population 1,413] and 9 RCTs [study population 1,759]) were included in the analysis. 1. A variety of oral interventions improving oral hygiene through mechanical and/or topical chemical disinfection or antibiotics reduced the incidence of nosocomial pneumonia by an average of 40%. 2. Several studies demonstrated a potential association between periodontal disease and COPD. REVIEWERS' CONCLUSIONS: 1. Oral colonization by respiratory pathogens, fostered by poor oral hygiene and periodontal diseases, appears to be associated with nosocomial pneumonia. 2. Additional large-scale RCTs are warranted to provide the medical community with further evidence to institute effective oral hygiene procedures in high-risk patients to prevent nosocomial pneumonia. 3. The results associating periodontal disease and COPD are preliminary and large-scale longitudinal and epidemiologic and RCTs are needed.