The Construction And Application Of Bilateral Anterior Elevation Prosthesis In Mice Mandibular Condyle

Background Temporomandibular joint(TMJ)has distinct cartilage layers,including fibrous,proliferative,hypertrophic and calcified cartilage zones from superficial to deep of cartilage.Articular chondrocytes are sensitive to biomechanical stimulation,which plays an important role in the proliferation and differentiation of chondrocytes.Occlusion is an important source of biomechanical stimulation of TMJ cartilage.In our previous study,unilateral anterior crossbite(UAC)model in rodents was established,which presented the obvious pathological process of articular cartilage degeneration.However,at present,there are few studies about the animal models to promote the proliferation of chondrocytes.In this study,a new animal model,named the bilateral anterior elevation(BAE)was established in mice.This model takes advantage of the characteristics of the continuous growth of the incisors of rodents and eliminates the native wear of the incisors with the help of mental tubes which creates an edge-to-edge occlusion relation,resulting in a gradual increase of the occlusion vertical height.The increase of the occlusal height of the incisors lead to the increase of the joint cavity volume which is normally in the state of negative pressure,so that the chondrocytes are in the state of tension.In addition,we separated the condylar chondrocytes into the superficial and deep zones respectively from TMJ of 3-week-age SD rat in vitro.Then the cells were exposd to cyclic tensile strain(CTS)of different time and deformation of tension using of FX-4000?(Flexcell International Corporation,USA)to verify the responses of cells to stretching stimulation.Meanwhile,the Sox9-CreERT2;Rosa26-GFP mice were used to trace the change of chondrocytes under the two different occlusal state including BAE and UAC.Methods 1.42 female C57BL/6J mice aged 6 weeks(with the body weight of 17-19 g)were randomly divided into control group(Con)and bilateral occlusal elevation model group(BAE)and each group was randomly divided into 3 weeks,7 weeks and 11 weeks(n=7)according to the time points.BAE mice of the groups were subjected to occlusal stimulation at the age of 6 weeks.Mice in the Con groups were subject to the same procedure but without the adhesion of metal tubes.After the time of stimulation,the mice were killed under deep anesthesia and the TMJs were reserved to further observation.2.The superficial and deep zones of TMJ condyle cartilage of 3-week-age female rats were separated under the microscope in vitro.And then the cells were exposed to CTS using FX-4000? system(Flexcell International Corporation,USA),with different times(1h,2h and 6h)and tension which induce the different level of cell deformation(3%,6% and 12%),respectively.After CTS,cells were collected for further extraction of RNA and proteins to detect the change of related molecules.3.We crossed Sox9-CreERT2 with ROSA26-GFP to obtain Sox9-CreERT2;Rosa26-GFP.Tamoxifen was injected into female double transgene mice at the age of 6 weeks,and UAC or BAE stimulation was performed accordingly.Changes in chondrocytes labeled by GFP were observed after 7d,14 d,3w and 7w of the TMJ condylar cartilage,respectively.Main results1.Under the stimulation of BAE,the length of incisors in mice increased significantly,as well as the cartilage thickness,chondrocytes number,cartilage matrix area with time.2.Chondrocytes from the superficial and deep zones of TMJ condyle cartilage obtained the different characters and expressed different markers.After the stimulation of CTS in appropriate duration of time and deformation in vitro,chondrocytes showed obvious increase in the proliferation tendency especially in the superficial chondrocytes.3.The lineage trace using Sox9-Cre ERT2;Rosa26-GFP transgene mice showed that after BAE,the number of Sox9+ chondrocytes of TMJ condylar cartilage in the proliferating layer increased,but the number was decreased under UAC stimulation.Conclusion 1.Condylar cartilage has strong plasticity,among which chondrocytes still maintain a strong tendency of proliferation and differentiation.2.Under tension stimulation,chondrocytes showed more proliferation tendency.