Osteoprotegerin deficiency causes morphological and quantitative damage in epithelial rests of Malassez

Abstract

Epithelial rests of Malassez (ERM), the only odontogenic epithelial structures in periodontal tissue, are proposed to correlate with root resorption, but the detailed mechanism remains unclear. Osteoprotegerin (OPG), the main inhibitor of osteoclastogenesis, plays a pivotal role in inhibiting root resorption, and ERM cells express OPG mRNA in vitro. Thus, in this study, we aimed to clarify OPG expression in ERM in vivo and to explore the role of OPG in ERM to determine whether ERM are associated with root resorption via OPG. We established Opg-knockout (Opg-KO) mice and detected the OPG expression in ERM by immunohistochemical staining in 4-, 6-, 10-, 26- and 52-week-old mice. The ERM of wild-type (WT) mice and Opg-KO mice were evaluated histologically at 4, 10 and 26 weeks of age. Orthodontic root resorption models were established, maxillae were collected after 4 weeks, and ERM were analysed by histomorphometric analysis. In our study, OPG displayed sustained expression in ERM, and OPG deficiency caused the destruction of ERM, characterized by irregular morphology and reduced numbers. Moreover, after orthodontic treatment, the loss of OPG severely damaged ERM, aggravating root resorption. Together, our results demonstrated that ERM expressed the OPG protein in vivo and that OPG deficiency resulted in morphological and quantitative damage to ERM. Furthermore, ERM may be associated with root resorption via OPG, thus helping to explain the mechanism underlying root resorption.

Effects of Photobiomodulation on Root Resorption Induced by Orthodontic Tooth Movement and RANKL/OPG Expression in Rats

“…More recently, it has been argued that protective factors may play an important role around the dental root, including cementum, periodontal ligament and Malassez epithelial remains (ERM). ERM can be related to help maintain root integrity, prevent root resorption and stimulate cement repair [12,38], and according to Wang et al [39] after tooth movement, the loss of OPG severely damaged the epithelial remains of Malassez, aggravating root resorption. This study showed that higher expression of OPG was found at the compression side signaling that LLLT may have stimulated OPG synthesis by fibroblasts, odontoblasts and mesenchymal cells [16] in order to inhibit clastic activity in cementum and dentin.…”