Narrow-diameter implant outcomes across glycemic status groups: a systematic review and meta-analysis

Purpose To evaluate whether glycemic status is associated with clinical, radiographic, and biological outcomes of narrow-diameter implants (NDIs) compared with non-diabetic controls. Methods Following PRISMA 2020 guidelines, a systematic search was conducted through August 12, 2026. Comparative studies assessing NDIs in non-diabetic controls and patients with dysglycemia were included. NDIs were defined as implant diameter ≤ 3.75 mm. Glycemic status was based on the definitions reported by the original investigators; reported group-level HbA1c information was used, where available, to further classify study groups for exploratory subgroup analyses. Outcomes included marginal bone loss (MBL), probing depth (PD), implant stability quotient (ISQ), peri-implant soft-tissue health, complications, and survival. Longitudinal studies were synthesized using the mean difference (MD) with a 95% confidence interval (CI) where appropriate. Results Fourteen reports from ten independent studies were included. At short-term follow-up, prediabetic patients showed a small but statistically significant increase in MBL compared with controls (MD 0.10 mm, 95% CI 0.04 to 0.16), whereas no appreciable difference was observed in diabetic patients. Most subgroup analyses by HbA1c category or implant-related characteristics were non-significant and based on sparse data. Pooled analyses showed no statistically significant differences in PD at short- to medium-term follow-up; however, one 5-year study reported increased PD specifically in prediabetic and inadequately controlled diabetic patients. No appreciable differences in ISQ were observed between diabetic patients and controls. Qualitative evidence suggested greater peri-implant soft-tissue inflammation in some dysglycemic groups, particularly with longer follow-up, although its clinical consequences remain uncertain. No implant failures were reported at the available follow-up endpoints in the comparative survival data. Conclusions Based on low-certainty evidence, short- to medium-term NDI outcomes appear broadly comparable across glycemic-status groups. No implant failures were observed in the available comparative data, and the only significant pooled MBL difference was a small short-term increase in prediabetes; however, survival evidence remains limited, and the long-term clinical significance of the observed soft-tissue inflammatory differences is uncertain.