Abstract: Objective: To explore the effects of metformin (MET) on oral mucosal ulcer (OMU). Methods: OMU models were established with trauma at bilateral buccal mucosa in SD rats (n=24). After 24 hours (d₁), 20 μmol/L MET solution was injected into the ulcer base of left side (MET side) one time per day, with normal saline injected into the right side as the control. The rats were sacrificed at d₂, d₄, and d₇, 8 rats for each time point. Ulcer size was recorded every day. Thickness and proportion of new epithelium, inflammatory cell number in connective tissue, and collagen fiber content were analyzed. Results: At d₁, ulcer size showed good consistency within the same sides and between the bilateral sides (P=0.935). From d₂ to d₇, ulcer size was reduced (P<0.05) and collagen fiber content and thickness of new epithelium were increased persistently. Inflammatory cell number was increased from d₂ to d₄ and then decreased from d₄ to d₇ (P<0.05). Ulcer size was 16% to 37% smaller at MET side from d₂ to d₅ than that of control side (P<0.05), which was comparable bilaterally from d₆ to d₇. Inflammatory cell number was down regulated from d₁ to d₇ at MET side relative to that of control side (P<0.05). Collagen fiber content and thickness of new epithelium was upregulated at MET side from d₂ to d₄ compared with those at control side (P<0.05), which showed no difference bilaterally from d₄ to d₇. Conclusion: MET shows significant improving effect on OMU at early stages, which might relate to the inflammatory inhibition and reparative promotion

Key words: metformin, oral ulcer, histology , epithelium healing