| Objective: the maxillofacial effect of the functional appliance has beenone of the fouse for the orthodontic doctor. The Condylar bone remodelingdirectly affect the morphological and function of the jaw. The study found thatthe periodic mechanical stress stimulusing the condylar cartilage can cause thecorresponding organization reconstruction. The body gets external stimuli,which can transfer to the body by pluralities of signal pathways. Themechanical signal convert biological signal, thereby causing the correspondingreconstruction of the condylar cartilage.Extracellular regulated protein kinaseis one of the member of the Mitogen activated protein kinase. It can raise avariety of extracellular signals(Growth factor,Cytokine,The tumor promoteretc.)and transfer to the nucleus gradually aftert phosphorylation and activation.Meanwhile, it can activate nuclear transcription factor,such as C-myc, C-junand so on. Thus, it paticipates in varieties of Physiological process, Cellgrowth, development, division and differentiationetc.. This experimentestablishs animal experimental model of functional mandibular protrusion toobserve the histological changes of the condylar cartilagein rats at differenttime points by histological staining and immunohistochemistry stainingmethod. Meanwhile, it can observe the change of the ERK in this process. Sowe can study adaptive remodeling of the Temporomandibular joint condylarcartilage morphology systematically by affecting the position change of themandible in order to provide experimental basis for clinical bone orthopedictreatment.Methods:Seventy4-week-old male Sprague-Dawley rats were used inthis study, weighed about80g. According to the experimental cycle（1d,3d,7d,14d,21d,28d and35d）, the animals were divided equally and randomly into7experimental groups (n=5rats) and7control groups (n=5rats) after adaptive feeding one week. Functional appliances that were fitted to the upperincisors of animals in the experimental groups were worn24hours a day,which were self-made. In order to increase the stability of appliance, a powerchain that was placed across the head, while the control group wearing nothing.All animals were fed a soft diet and free water.In order to ensure the animal’sweight be the same, we fed the rats in the experimental group freely and fedthe control group regularly.The animals in the experimental groups, togetherwith their matched controls, were killed respectively after1,3,7,14,21,28and35days. The bilateral condylar were placed in4%paraformaldehydewhich fixed for24hours at4℃, decalcified in10%of the EDTA, and thenconventional Paraffin-embedded after two weeks. The sections were cut into5μm in thickness. HE staining for histological features, immunohistochemistryof ERK was applied to observe it’s express distribution and variation.Negative control group with PBS.Results:1Histological observationHistological features of condylar cartilage: condylar cartilage had itsunique boundaries, according to the different of cell morphous which could be divided into:①F iber layer②Proliferative layer③Maturity layer④Hypertrophic layer⑤Calcified cartilage layer. The control group: Microscope showde that a layer of frbious tissue was disc which surrounded thecondylar cartilage surface. The thickness of the condylar cartilage gradually thinner from back to front. With the passage of time, the condylar cartilage had age-related change. The change of cartilage in the middle and posterior is significant. The change of fiber layer and proliferative layer is unconspicuous,while the decrease of hypertrophic layer is obvious. The experimental group: at the same time, condylar cartilage is muchmore thicker in experiment group than control group, the difference is remarkable in posterior.the thickness of anterior changes unobviously. Thenumber of cells in the proliferative layer and maturity laye increase.Thecell volume of hypertrophic layer enlarges and extracellular matrix increase. 2Immunohistochemical resultsThe negative control group(PBS instead of first antibody) had no positivestaining granules. The positive standard of p-ERK: cell shape was integrity,structure was clarity. The nucleus is brown yellow. The color of positive cellswas sianificantly higher than background color. Results showed that p-ERKwas mainly expressed at the germinal and hypertrophic zones.The variation ofp-ERK: as time goes by, it has a steady decline in the control group Withingroup comparisons. But the expression level had no significantdifference(P>0.05). Comparison between groups: At the1st day, theimmunohistochemical score (IHS) of p-ERK in experimental group was2.8±0.84, while the control group was2.6±0.89(P>0.05). At the third day,there was no significant difference between the experimental group and thecontrol group (P<0.05). After7days, IHS of the experimental group hadincreased to8.4±1.34, which was significantly higher than that of the controlgroup (2.6±0.89)(P<0.05).Compared with the former group, the two also hadthe difference of Statistics（P<0.05). On the fourteenth day, the differencebetween he experimental group and the control group had the most significant（P<0.01）. But from then on, the downward trend of p-ERK appeared, andthe IHS of experimental group fell to5.2±1.09. But it exceeded the one of thecontrol group as well. On the28th day, IHS of the control group was also lessthan that of the experimental group (4.0±1.41VS2.6±0.89)(P<0.05).At theend of the experiment (35day), IHS of the control group wasIHS=2.8±2.17,and the experimental group IHS=2.6±1.34(P>0.05). Compared with theformer group, there was also no difference.Conclusions:1.The condylar cartilage of growing rat appeared age-related change by the time, the thickness of condylar cartilage was thin gradually. Its thickness appeared adaptive remodeling after functional mandibular protrusion. And the Mandibular grew.2. p-ERK involved in the bone remodeling process of the rat’s condylar cartilage after functional mandibular protraction. 3.The mechanical force-biochemical signal transduction of the bone remodeling process of the rat’s condylar cartilage is mediated by p-ERK. |
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