The histopathological comparison on the destruction of the periodontal tissue between normal junctional epithelium and long junctional epithelium

Background and Objective The barrier function of long junctional epithelium is thought to be important after periodontal initial therapy and periodontal surgery. Although the difference between long junctional epithelium and normal junctional epithelium regarding their resistance to destruction of periodontal tissue has been investigated, the mechanism still remains unclear. Using our rat experimental periodontitis model in which loss of attachment and resorption of alveolar bone is induced by the formation of immune complexes, we investigated the resistance of periodontal tissue containing long junctional epithelium and normal junctional epithelium to destruction. Material and Methods Rats were divided into four groups. In the immunized long junctional epithelium (I‐LJE) group, rats were immunized with lipopolysaccharide (LPS), and curettage and root planing procedures were performed on the palatal gingiva of the maxillary first molars to obtain reattachment by long junctional epithelium. In the immunized normal junctional epithelium (I‐JE) group, rats were immunized without curettage and root planing procedures. In the nonimmunized long junctional epithelium (nI‐LJE) group, rats were not immunized but curettage and root‐planing procedures were performed. In the control group, neither immunization nor curettage and root‐planing was performed. In all rats, periodontal inflammation was induced by topical application of LPS into the palatal gingival sulcus of maxillary first molars. The rats were killed at baseline and after the third and fifth applications of LPS. Attachment loss and the number of inflammatory cells and osteoclasts in the four groups were compared histopathologically and histometrically. Results After the third application of LPS in the I‐ LJE group, attachment loss showed a greater increase than in control and nI‐LJE groups, and inflammatory cell infiltration and osteoclasts were increased more than in the other groups. After the fifth application of LPS , attachment loss was greater and there was a higher degree of inflammatory cell infiltration in nI ‐ LJE and I‐ LJE groups than in control and I‐ JE groups. Conclusion Our findings suggest that the destruction of periodontal tissue is increased in tissue containing long junctional epithelium compared with normal junctional epithelium and that the immunized condition accelerates the destruction by forming immune complexes.