Terry C Simpson, Jo C Weldon, Helen V Worthington, Ian Needleman, Sarah H Wild, David R Moles, Brian Stevenson, Susan Furness, Zipporah Iheozor‐Ejiofor

Glycaemic control is a key issue in the care of people with diabetes mellitus (DM). Periodontal disease is the inflammation and destruction of the underlying supporting tissues of the teeth. Some studies have suggested a bidirectional relationship between glycaemic control and periodontal disease. This review updates the previous version published in 2010. The objective is to investigate the effect of periodontal therapy on glycaemic control in people with diabetes mellitus. We searched the following electronic databases: the Cochrane Oral Health Group Trials Register (to 31 December 2014), the Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Library 2014, Issue 11), MEDLINE via OVID (1946 to 31 December 2014), EMBASE via OVID (1980 to 31 December 2014), LILACS via BIREME (1982 to 31 December 2014), and CINAHL via EBSCO (1937 to 31 December 2014). ZETOC (1993 to 31 December 2014) and Web of Knowledge (1990 to 31 December 2014) were searched for conference proceedings. Additionally, two periodontology journals were handsearched for completeness, Annals of Periodontology (1996 to 2003) and Periodontology 2000 (1993 to 2003). We searched the US National Institutes of Health Trials Registry (http://clinicaltrials.gov) and the WHO Clinical Trials Registry Platform for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases. We searched for randomised controlled trials (RCTs) of people with type 1 or type 2 DM (T1DM/T2DM) with a diagnosis of periodontitis. Interventions included periodontal treatments such as mechanical debridement, surgical treatment and antimicrobial therapy. Two broad comparisons were proposed:1. periodontal therapy versus no active intervention/usual care;2. periodontal therapy versus alternative periodontal therapy. For this review update, at least two review authors independently examined the titles and abstracts retrieved by the search, selected the included trials, extracted data from included trials and assessed included trials for risk of bias.Our primary outcome was blood glucose levels measured as glycated (glycosylated) haemoglobin assay (HbA1c).Our secondary outcomes included adverse effects, periodontal indices (bleeding on probing (BOP), clinical attachment level (CAL), gingival index (GI), plaque index (PI) and probing pocket depth (PPD)), cost implications and diabetic complications. We included 35 studies (including seven from the previous version of the review), which included 2565 participants in total. All studies used a parallel RCT design, and 33 studies (94%) only targeted T2DM patients. There was variation between studies with regards to included age groups (ages 18 to 80), duration of follow-up (3 to 12 months), use of antidiabetic therapy, and included participants' baseline HbA1c levels (from 5.5% to 13.1%).We assessed 29 studies (83%) as being at high risk of bias, two studies (6%) as being at low risk of bias, and four studies (11%) as unclear. Thirty-four of the studies provided data suitable for analysis under one or both of the two comparisons.Comparison 1: low quality evidence from 14 studies (1499 participants) comparing periodontal therapy with no active intervention/usual care demonstrated that mean HbA1c was 0.29% lower (95% confidence interval (CI) 0.48% to 0.10% lower) 3 to 4 months post-treatment, and 0.02% lower after 6 months (five studies, 826 participants; 95% CI 0.20% lower to 0.16% higher).Comparison 2: 21 studies (920 participants) compared different periodontal therapies with each other. There was only very low quality evidence for the multiple head-to-head comparisons, the majority of which were unsuitable to be pooled, and provided no clear evidence of a benefit for one periodontal intervention over another. We were able to pool the specific comparison between scaling and root planing (SRP) plus antimicrobial versus SRP and there was no consistent evidence that the addition of antimicrobials to SRP was of any benefit to delivering SRP alone (mean HbA1c 0.00% lower: 12 studies, 450 participants; 95% CI 0.22% lower to 0.22% higher) at 3-4 months post-treatment, or after 6 months (mean HbA1c 0.04% lower: five studies, 206 patients; 95% CI 0.41% lower to 0.32% higher).Less than half of the studies measured adverse effects. The evidence was insufficient to conclude whether any of the treatments were associated with harm. No other patient-reported outcomes (e.g. quality of life) were measured by the included studies, and neither were cost implications or diabetic complications.Studies showed varying degrees of success with regards to achieving periodontal health, with some showing high levels of residual inflammation following treatment. Statistically significant improvements were shown for all periodontal indices (BOP, CAL, GI, PI and PPD) at 3-4 and 6 months in comparison 1; however, this was less clear for individual comparisons within the broad category of comparison 2. There is low quality evidence that the treatment of periodontal disease by SRP does improve glycaemic control in people with diabetes, with a mean percentage reduction in HbA1c of 0.29% at 3-4 months; however, there is insufficient evidence to demonstrate that this is maintained after 4 months.There was no evidence to support that one periodontal therapy was more effective than another in improving glycaemic control in people with diabetes mellitus.In clinical practice, ongoing professional periodontal treatment will be required to maintain clinical improvements beyond 6 months. Further research is required to determine whether adjunctive drug therapies should be used with periodontal treatment. Future RCTs should evaluate this, provide longer follow-up periods, and consider the inclusion of a third 'no treatment' control arm.Larger, well conducted and clearly reported studies are needed in order to understand the potential of periodontal treatment to improve glycaemic control among people with diabetes mellitus. In addition, it will be important in future studies that the intervention is effective in reducing periodontal inflammation and maintaining it at lowered levels throughout the period of observation.