Immunometabolic, Vascular, and Epigenetic Determinants of Periapical Healing in Diabetes: A Narrative Review.

The bidirectional relationship between diabetes mellitus and apical periodontitis is a central focus within endodontic medicine. While clinical data consistently show a higher prevalence of apical periodontitis and delayed periapical healing in diabetic patients, the mechanisms driving this association remain to be fully clarified. This review aims to synthesize the current evidence to elucidate the specific cellular and molecular pathways through which uncontrolled hyperglycaemia may compromise periapical healing. A narrative review of current literature was conducted, integrating evidence from endodontic microbiology, immunometabolism, vascular pathophysiology, bone biology, and epigenetics. Evidence was drawn from human clinical studies, animal models, and in vitro investigations of diabetic apical periodontitis, alongside cross-tissue extrapolations from other diabetic complications, including periodontitis, diabetic nephropathy, and diabetic retinopathy. Diabetes-associated impairment of periapical healing is proposed to involve several interconnected mechanisms: (1) microbial dysbiosis with endotoxin accumulation; (2) microvascular dysfunction, encompassing impaired angiogenesis and endothelial insulin resistance; (3) innate and adaptive immune dysregulation, characterized by aberrant NETosis and pathological Th17/Treg imbalance; (4) uncoupled bone remodelling with a dysregulated RANKL/OPG ratio; and (5) hyperglycaemia-driven epigenetic reprogramming of stem cells, proposed to establish a barrier to tissue regeneration that may endure beyond glycaemic correction. We therefore hypothesize that diabetes mellitus does not act merely by amplifying periapical inflammation, but instead disrupts several processes required for periapical healing. Importantly, while some mechanisms inferred from other diabetic tissues offer plausible explanations, they remain to be directly validated within the periapical microenvironment. This mechanistic framework highlights candidate targets for host-modulation approaches, given that conventional chemomechanical disinfection may be insufficient to resolve the dysregulated host microenvironment in diabetic apical periodontitis. Adjunctive strategies directed at inflammation, immunometabolic dysregulation, uncoupled bone remodelling, and epigenetic memory warrant investigation as potential means to improve periapical healing outcomes in the diabetic population.