Results

Study selection

There are no guidelines existing to the topic of dental implants and diabetes mellitus. A total of 327 potentially relevant titles and abstracts were found by the electronic search and additional evaluation of reference lists. During the first screening, 230 publications were excluded based on the title and keywords. Additionally, 24 titles were excluded based on abstract evaluation. Seventy-three full-text articles were thoroughly evaluated. A total of 51 papers had to be excluded at this stage because they did not fulfil the inclusion criteria of the present systematic review. Twenty-two articles went into qualitative assessment (Fig. 1). Because of too few studies, heterogenic study design, and incompletely reported data like type of diabetes therapy, quality of glycemic control, and duration of disease, the quantitative data synthesis could not be performed in the way necessary for meta-analysis. Additionally, we identified 20 reviews and meta-analyses. They are excluded from our results.

Evaluation of study quality and risk of bias

The majority (n = 12) of the 22 studies were prospective and one of these studies was a multicenter study. Eight were retrospective and two were cross-sectional studies. Randomization of patients was not readable in any of the studies (Table 1). Despite a low evidence level in terms of study design, there were no major concerns about risk of bias; 13/22 studies were rated with a low risk of bias, 9/22 had a medium risk. No study had a high risk of bias, and consequently no further study was excluded at this stage because of bias (Table 2).

Diabetes and osseointegration

Osseointegration describes the process of formation of a direct interface between the implant and bone, without intervening soft tissue. This process is prerequisite for implant stability and inflammation-free survival. It includes remodeling of the surrounding bone with migrations and proliferation of osteoblasts and supporting connective tissue.