External root resorption is one of the rare pathological condition of tooth. It is occurred when periodontal ligament or cementum on the root surface are either damaged or denuded. The causes and classifications have been variously described. Because of the various causes and patterns, and absence of sufficient and consistent evidence for treatment, proper diagnosis and treatment plan based on clinician’s experience and close communication with patient is important. This case report represents the rare case of external root resorption and the treatment. The tooth was retained functionally in oral cavity showing good healing state in 2-year follow-up.

To determine the effect of diabetes on root resorption in periodontitis, we investigated odontoclast formation and root resorption in diabetic rats with periodontitis. Odontoclast formation was observed in three groups of F344 rats: Controls (C) were normal rats without diabetes or periodontitis; the periodontitis (P) group had mandibular first molars to be ligatured; the periodontitis with diabetes (PD) group was intravenously administered streptozotocin (50 mg/kg) to induce diabetes and had mandibular first molars to be ligatured. On days 3, 10, and 20 after ligature, tumor necrosis factor (TNF)-α and receptor activator of nuclear factor-κB ligand (RANKL) expression, odontoclast formation, and root resorption areas were evaluated by immunohistochemistry, tartrate-resistant acid phosphatase staining, and hematoxylin and eosin staining, respectively. The PD group showed frequent urination, weight loss, and hyperglycemia. Numbers of TNF-α- and RANKL-positive cells were higher in the P and PD groups than in the C group. It was more prevalent in PD group on day 3. Odontoclast formation was greater in the P and PD groups than in the C group on days 3 and 10, then decreased to same level as the C group by day 20. Root resorption in the PD and P groups showed increases on days 3 and 10, respectively, compared to the C group. These results suggest that diabetes may transiently increase root resorption on day 3 with high expression of TNF-α and RANKL after periodontitis induction. This study could aid the understanding of root resorption in diabetic patients with periodontitis.