Assessment of Alloxan-Induced Diabetic Rats as a Periodontal Disease Model Using a Selective Cyclooxygenase (COX)-2 Inhibitor

Abstract

Several recent studies have reported that alloxan-treated rats with long-term hyperglycemia can develop naturally occurring periodontal disease (PD). Our previous studies detected dental caries in the same model. Therefore, these two lesions of different etiologies are expected to occur concurrently. In this study, we evaluated the use of diabetic rats as a PD model by employing a selective COX-2 inhibitor reported to be effective against PD. Six-week-old female F344 rats were divided into 3 groups: intact rats (control), alloxan-induced diabetic rats fed a standard diet (AL) and alloxan-induced diabetic rats fed a diet containing 0.01% etodolac (AL+Et). The animals were euthanized at 26 weeks of age, and their oral tissues were examined histopathologically. Gingivitis, marginal periodontitis and alveolar bone resorption were markedly enhanced along with dental caries in the AL group compared with the control group. However, the COX-2 inhibitor had no effect on periodontal inflammation in the AL+Et group. In addition, in the AL group, periodontitis was notably nonexistent around the normal molars, and gingivitis was scarcely worse than that in the control group. In the diabetic rats, the progression of periodontal inflammation was closely correlated with the severity of adjacent dental caries, and marginal periodontitis was frequently continuous with apical periodontitis. In conclusion, an alloxan-induced diabetic rat is not a model of PD but of dental caries. It is probable that in this model, hyperglycemia may enable crown caries to progress to apical periodontitis, while the associated inflammation may rostrally expand to surrounding periodontal tissue.

Keywords: alloxan; cyclooxygenase (COX)-2 inhibitor; dental caries; diabetes; periodontitis.

Fig. 1.

Study design.

Fig. 2.

Soft X-ray images of alveolar bone resorption and dental caries. M1, the first molar; M2, the second molar; and M3, the third molar. A. The mandible of a rat in the control group. Normal alveolar bone and molars. B. The mandible of a rat in the AL group. Dental caries with a radiolucent area (arrowheads) is observed in the dental crown. In the alveolar bone surrounding the carious molars (M2 and M3), a focal radiolucency is detected in the apical portion of the dental root (arrows). C. The mandible of a rat in the AL+Et group. Alveolar bone resorption (arrow) is similarly observed around one (M3) of the carious molars (arrowheads). Scale bar = 2 mm.

Fig. 3.

Mean scores for alveolar bone resorption (ABR) in the mandibular molars of each group. **Significantly different from the control group (p < 0.01). NS: no significant difference between the AL and AL+Et groups.

Fig. 4.

Mean scores for dental caries in the mandibular molars of each group. **Significantly different from the control group (p < 0.01). NS: no significant difference between the AL and AL+Et groups.

Fig. 5.

Histopathologic features of periodontal and carious lesions. The boxes in Fig. 5A correspond to Fig. 5B and 5C. The boxes in Fig. 5D correspond to Fig. 5E and 5F. A–C. Periodontal tissue adjacent to carious molars in an alloxan-induced diabetic rat. A. Severe caries and pulp necrosis; inflammation of dental pulp is continuous with apical inflammation. Scale bar = 500 µm. B. Moderate gingivitis and marginal periodontitis. Marginal periodontitis is combined with adjacent apical periodontitis (5C). Scale bar = 100 µm. C. Apical periodontitis; abscess formation (arrow) and extensive inflammatory granulation tissue (asterisks) with alveolar bone resorption in the apical portion of a carious molar root. Suppurative inflammation connects to the necrotic dental pulp (arrowheads) through the apical foramen. Scale bar = 100 µm. D-F. Periodontal tissue adjacent to a noncarious molar in an alloxan-induced diabetic rat. D. Normal molar and periodontal tissue. Scale bar = 500 µm. E. Mild gingivitis only. Scale bar = 100 µm. F. Normal apical periodontal tissue. Scale bar = 100 µm.

Fig. 6.

Diagrammatic representation of the possible pathogenesis of periodontal lesions. A. Periodontal disease. B. Dental caries and caries-derived apical periodontitis. C. Caries-derived periodontal and gingival inflammation in the alloxan-induced diabetic rats. D, dentin; P, pulp; E, enamel; G, gingiva; AB, alveolar bone; PL, periodontal ligament; AF, apical foramen.