Experimental Studies On Relevance Of Matrixmetalloproteinases (MMPs) In Gingival Crevicular Fluid To Orthodontic Root Resorption

Root resorption is one of the most common complications during orthodontic treatment. Its mechanism is not clear and there are not effective preventive methods now. It initiates after 2-3 weeks of orthodontic force applied, and persists in the whole course of force application. Severe root resorption may result in root shortening, teeth loosing, and even falling off. It is a difficult situation to deal with in clinic practice. At present, we usually detect root resorption by x-ray film. However, it has such a low precision that it is difficult to detect root resorption in time and clearly. In addition, patients will receive radiation. Thus, it is necessary to find a new method to detect the development of root resorption. The matrixmetalloproteinases (MMPs) family can degrade all extracellular matrix of all tissues including bone. Recently, it is indicated that MMPs are the major enzymes during the rebuilding of periodontal tissues, and may be relevant to root resorption. But the relationship between MMP-1 and MMP-9 in gingival crevicular fluid and root resorption has not been reported. Gingival crevicular fluid is secreted from the gingival crevicular areas and consists of many components. Its composition could be variant according with the changes of surrounding tissues. As it is easy, harmless, and quick to be distilled, the gingival crevicular fluid has been used by periodontists to diagnosis, observe the diseases, and acquire the treating effects now. The objective of this study is looking for a new index which might be related to root resorption experimentally, and a clue to detect the development of root resorption in clinic. In this study, five male, 6 months old miniature pigs, whose average weight is 16.5 kilograms, were selected to prepare an animal root resorption model by applying an excess force of 300g. The gingival crevicular fluids were collected every week, and MMP-1 and –9 were assayed by using the biochemistry techniques of SDS-PAGE, Western bolt and Gel Doc quantitative analysis system. The animals were killed at 1, 2, 4 and 7 week respectively, and the experimental teeth were made histological slices to observe the root resorption. We found that root resorption of the primary lower lateral incisors of miniature pigs were evident by histological features such after the force were applied 1 week. The MMP-9 in gingival crevicular fluid before root resorption decreased markedly comparing to those during root resorption. After the force were applied , the MMP-1 and MMP-9 in gingival crevicular fluid increased at first, then decreased during the second week, after that, it reached the climax and reduced little by little. In conclusion, MMP-1 and MMP-9 in gingival crevicular fluid may play roles in orthodontic root resorption. The content of MMP-1 and MMP-9 ingingival crevicular fluid is more in the early period of root resorption. MMP-9 in gingival crevicular fluid may be involved in root resorption, and it may be more sensitive than MMP-1. The experiment may provide a new method of inspecting root resorption in clinic.