Establishment of a Rat Model of Bisphosphonate-Related Osteonecrosis of the Jaw and a preliminary investigation onits impact on peri-implant bone healing

Background　Bisphosphonate-Related Osteonecrosis of the Jaw(BRONJ) caused by bisphosphonates is a serious adverse reaction that cannot be ignored in clinical practice. The previously established BRONJ animal models have not accurately simulated the actual clinical drug administration environment in terms of administration route and dosage.Objective　To establish a BRONJ rat model that simulates the clinical drug administration environment and to explore its impact on osseointegration and bone healing after implant placement.Methods　Forty male SD rats were randomly divided into a control group and a model group. The model group was treated with zoledronic acid sodium combined with dexamethasone via tail vein injection to simulate the equivalent drug dosage used in clinical malignant tumor patients. The control group was given the same volume of normal saline. After 4 weeks of administration, the first maxillary molars on both sides were extracted to induce BRONJ. Four weeks after tooth extraction, samples from the extraction sockets of each group were randomly taken for modeling and evaluation. The remaining rats underwent implant placement at the same time, and samples were collected 4 weeks after implantation for evaluation. Micro-CT was used to detect the osseointegration and bone healing indicators (BMD, BV/TV, Tb.N, Tb.Sp, Tb.Th) of the extraction sockets and peri-implant bone. HE/Masson staining was used to detect the proliferation and distribution of bone cells, inflammatory cells, connective tissue, and collagen fibers in the extraction sockets and peri-implant bone. Immunohistochemical staining was used to detect the expression of peri-implant bone tissue-related proteins (ALP, COL-1, BMP-2, OPN, OCN, Runx2). Results　Gross observation and Micro-CT examination revealed that the extraction sockets and peri-implant bone in the model group showed nonhealing wounds, exposed necrotic bone, and decreased bone healing indicators (BMD, BV/TV, Tb.N, Tb. Th), while the control group showed good bone healing (P＜0.0001). HE/Masson staining showed that the extraction sockets and peri-implant bone in the model group had bone tissue necrosis, inflammatory cell infiltration, and dissolved bone cell nuclei with unclear structure. The control group showed good healing with abundant connective tissue and collagen fiber proliferation. Immunohistochemical staining showed that the expression of osteogenesis-related genes (ALP, COL-1, BMP-2, OPN) in the model group was downregulated (P＜0.05). Conclusion　This study established a BRONJ rat model that simulates the clinical drug administration environment and preliminarily verified the possible inhibitory effect of bisphosphonates on osseointegration and bone healing around implants.