Periodontitis is a multifactorial disease characterized by inflammation and the destruction of periodontal tissues. Several chemical mediators are released during the inflammatory process, such as histamine. There is evidence that this mediator stimulates osteoclastogenesis and, then, bone resorption. Results obtained in our laboratory revealed that cimetidine, an histamine H2 receptor antagonist, reduces alveolar bone loss in the induced periodontal disease. Thus, the purpose of this study is to evaluate whether cimetidine stimulates the repair of periodontal tissues in rat molars with induced periodontitis. A cotton ligature will be placed into the cervix of the second left upper molar to induce periodontal disease (PD). After 7 days, the ligature will be removed and the rats will receive daily intraperitoneal injections of 100mg/kg bw of cimetidine (PCiG) for 7, 15 and 30 days; the rats from sham group (PSG) will receive a saline solution. In the control group (CG), the left upper maxilla (non-ligature molars) will be removed in the experimental periods. The animals will be euthanized; the fragments of hemimaxilla will be fixed in formaldehyde, decalcified in EDTA, and embedded in paraffin. HE-stained sections will be used for morphological analysis and to measure the distance between cementoenamel junction (CEJ) and junctional epithelium insertion level (JE), and the distance between alveolar bone (AB) crest and CEJ. The volume density of inflammatory cells will also be computed. In order to verify whether cimetidine interferes in the bone resorption, sections will be submitted to TRAP method (osteoclast marker) and the number of osteoclasts in the alveolar bone surface will be quantified. The birefringent collagen of the connective tissue subjacent to the gingival epithelium (in distal and mesial regions) will be quantified in picrosirius red-stained sections under polarized light. Statistical analyses will be performed using SIGMA STAT 2.0 (Jandel Scientific, Sausalito, CA, USA); according to the ANOVA will be chosen statistical test and the significance level accepted will be p£0.05.
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