BACKGROUND Occlusal interventions may be used in adults with periodontitis. At present there is little consensus regarding the indications and effectiveness of occlusal interventions in periodontal patients. OBJECTIVES To identify and analyse the evidence for the effect of occlusal interventions on adults who have periodontitis in relation to tooth loss, probing depths, clinical attachment level, adverse effects and patient-centred outcomes. SEARCH STRATEGY The search was last conducted in April 2008. We searched the Cochrane Oral Health Group's Trials Register (to 30th April 2008); the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2008, Issue 1); MEDLINE (1966 to 30th April 2008); and EMBASE (1980 to 30th April 2008). There were no language restrictions. SELECTION CRITERIA We included randomised controlled trials (RCTs) assessing occlusal interventions in patients with periodontitis with a follow up of at least 3 months. DATA COLLECTION AND ANALYSIS Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted in duplicate and independently by two review authors. Any disagreements between the review authors were resolved by discussion. The main investigator of the included trial was contacted to obtain missing information. The Cochrane Collaboration statistical guidelines were to be followed for data synthesis. MAIN RESULTS Abstracts of 54 papers were identified by the search. One paper was eligible for inclusion. This paper studied the effect of occlusal adjustment against no occlusal adjustment in patients who were treated with non-surgical and surgical periodontal therapy. Methodological quality assessment of the included paper revealed that randomisation of the patients into the treatment groups was adequate. Allocation concealment, masking of patients and clinicians were not reported and no response to author contact was received. Mean change in attachment level and mean pocket depth were reported in the included trial. Mean difference in clinical attachment level between occlusal intervention and control in the non-surgical group amounted to 0.38 mm (95% confidence interval (CI) 0.04 to 0.72) favouring the occlusal intervention group and was statistically significant. In the surgical group the mean difference in clinical attachment level between occlusal intervention and control amounted to 0.40 mm (95% CI 0.05 to 0.75) favouring the occlusal intervention group and was also statistically significant. The difference in mean pocket depth reduction between the occlusal intervention and control in both the surgical and non-surgical groups was less than 0.1 mm and was not statistically significant. Tooth loss, patient-centred affects and adverse effects were not reported. Meta-analysis was not possible due to the inclusion of only one study. AUTHORS' CONCLUSIONS There is only one randomised trial that has addressed this question. The data from this study are inconclusive. We therefore conclude there is no evidence for or against the use of occlusal interventions in clinical practice. This question can only be addressed by adequately powered bias-protected randomised controlled trials.