Several systematic reviews with meta-analyses on the effectiveness of periodontal treatment to improve glycaemic control have been published. So far no overview of these systematic reviews has been performed. The main objective of this report was to assess critically these systematic reviews to provide the reader with a high-level synthesis of research evidence. MEDLINE (via PubMed) and EMBASE databases were searched independently and in duplicate to identify systematic reviews with meta-analyses of clinical studies that assessed the relationship between diabetes mellitus and periodontitis. The last database search was performed on 10 March 2015. The reference lists of included systematic reviews were also scrutinized for further publications. The methodological quality of the included systematic reviews was assessed independently with two validated checklists (AMSTAR and OQAQ) by two authors. Disagreements in the assessment were resolved by consensus. A total of 226 potential publications were initially retrieved. Eleven systematic reviews with meta-analyses were finally included. Glycosylated haemoglobin A1c (HbA1c) was the most commonly used clinical endpoint. Meta-analytic estimates from systematic reviews generated an average reduction of 0.46% (median 0.40%) of HbA1c in patients with diabetes mellitus who received periodontal treatment. These meta-analyses had, nevertheless, methodological limitations such as inclusion of trials with different types of risk of bias that hinder more robust conclusions. A recent meta-analysis that included recently published large randomized controlled trials did not show significant change in the level of HbA1c at the 6 mo follow-up. The AMSTAR checklist generated results that were more conservative than OQAQ. Findings from this overview do not support the information that periodontal treatment may improve glycaemic control. Methodological issues described in this overview may guide further research on this topic.