The aim of this study was to explore diabetes mellitus type 2 as a risk factor in the prevalence of chronic apical periodontitis (CAP) in untreated and endodontically treated teeth. The second objective was to describe the correlation between the presence of periapical lesions and blood glucose/glycated hemoglobin levels among diabetic (DM) and non-diabetic patients with endodontically treated or untreated teeth with CAP. This cross-sectional study was conducted on 90 patients (55 with DM, 35 without DM), admitted to the Oral and Maxillofacial Surgery Department of "St. Spiridon" Hospital in Iași, Romania. Endodontic and perapical status was evaluated using the Periapical Index (PAI) based on clinical and radiological evaluations with blood glucose levels and HbA1c analysis. Statistical analysis included data, correlations and regression analysis, and group comparisons using appropriate parametric or non-parametric tests. DM subjects had a higher mean value of untreated teeth with CAP (2.53 vs. 2.00) compared to the control group ( = 0.010) and a lower mean number of endodontically treated teeth without CAP (1.53 vs. 2.74) compared to the control group ( < 0.001). Diabetic patients also had a higher mean number of root-filled teeth with CAP (3.33 vs. 1.94; < 0.001). There was a clear association between diabetes and oral pathology, with diabetic patients having fewer teeth, more untreated teeth, and a higher prevalence of periapical lesions. Elevated blood glucose and HbA1c levels indicated that poor metabolic control negatively impacts periapical healing and overall endodontic health.