Materials and methods

The substructure of the systematic review is based on the PRISMA statement. The focused question according to the PICO schema is: “Do diabetic patients with dental implants have a higher complication rate in comparison to healthy controls?”

Search strategies

The systematic literature search was performed by an independent scientist (Burkhard Kunzendorf). The following databases were incorporated in the systematic search for relevant literature: PubMed, Embase, AWMF Online, National Guideline Clearinghouse, Guidelines International Network, and Cochrane Library. The following search terms were used: dental implants AND diabetes, transgingival implants AND diabetes, maxillary augmentation AND diabetes, mandibular augmentation AND diabetes, peri-implantitis AND diabetes, Zahnimplantate AND Diabetes, Kieferkammaufbau AND Diabetes, Periimplantitis AND Diabetes. Electronic search was complemented by an iterative hand-search in the reference lists of the already identified articles. The time period of the literature search was between 10 April and 7 May 2015. Endnote X7 was used for the electronic management of the literature.

Study inclusion and exclusion criteria

During the first stage of study selection, the titles and abstracts were screened and evaluated according to the following inclusion criteria: English or German language, retrospective and prospective clinical trials, observational studies, cross-sectional studies, cohort studies, and case series. During this procedure, the pre-selected publications were evaluated according to the following exclusion criteria: in vitro studies, animal studies, case reports with less than 10 patients, and publications older than 15 years.

Quality and risk of bias assessment of selected studies

A quality assessment of all selected full-text articles was performed. It made no sense to use the Cochrane collaboration tool for assessing risk of bias for randomized controlled studies since the majority of the included studies were not randomized or retrospective case series. Instead, a system modified from the US Agency for Healthcare Research and Quality Methods Guide for Comparative Effectiveness Reviews was used, which asked for the sources of possible bias [7]. The criteria were each judged with low, medium, high, or unknown risk of bias: case selection bias and confounding, attrition bias (loss of participants), detection bias (reliable measures), and reporting bias (selective or incomplete reporting), followed by a summary of the risk.