| Temporomandibular disorders (TMD) are a kind of common diseases in dentalpractice. Osteoarthritis (OA) is one of the pathological changes of TMD, which ischaracterized by degradation of articular cartilage extracellular matrix, subchondralbone remodeling, osteophyte formation and chronic inflammation. The previousstudies on the effect of gradually induced disordered occlusion showed that it led toabnormal thickening of the articular disc, temporomandibular joint (TMJ) degeneration,or even cartilage abnormal construction. In the present research, Sprague-Dawley (SD)rats were used to establish a new animal model of experimentally created unilateralanterior crossbite prosthesis. The TMJs were stained with HE and toluidine blue toobserve the changes of morphology, thickness of the condylar cartilages andproteoglycan (PG). Real-time PCR was applied to study the changes of mRNA expression of PCNA, COL II, aggrecan, MMP-3, MMP-9, MMP-13and TIMP-1. Theprotein expression of PCNA, COL II, MMP-3, MMP-9and TIMP-1was calculated bythe area of positive cells percentage. The purpose of the present research was toinvestigate the effect of experimentally created unilateral anterior crossbite prosthesison the cartilage cell proliferation and matrix degradation.Fifty-four female SD rats (weigh140-160g),6weeks of age, were provided by theanimal center of the Fourth Military Medical University. Animals were randomlydivided into an experimental group (Exp) or a sham-operated control group (Con).Each group was equally assigned to three (2,4or8weeks) subgroups according totime point (n=9). The rats were anesthetized. In the experimental group, the leftmaxillary and mandibular incisors were bonded with metal tube in order to create acrossbite relationship between the left incisors. Rats in the control group received allof the above procedures, but no metal tube was bonded. All of the rats received thesame standardized diet throughout the experimental procedure. Experimental animals,together with their controls, were sacrificed at the end of2,4and8weeks after theoperation. The left TMJ tissues were prepared for HE staining for histologicalassessment, toluidine blue staining for detecting the expression of PG in cartilage andimmunohistochemistry (IHC) examination. The right TMJ tissues were used forreal-time PCR analysis.The results were shown as following:1. In the control groups, the surface of the condylar cartilage was intact and smooth.Chondrocytes arranged orderly in the cartilage. Four layers were typicallyrecognized as the fibrous, proliferative, hypertrophic and endochondralossification layers. In the experimental groups, the cartilages showed degradationand it was most seriously in8-week. Three out of nine in8-week experimentalgroup showed cell-free areas. The lesions were characterized as pyknotic nuclei,irregularity of cellular arrangement. The degraded areas typically appeared as a homogeneous eosinophilic mass.2. The thickness of fibrous layer at the middle thirds was increased (P <0.05) andthat of proliferative layer at middle and posterior thirds were increased in the4-week experimental subgroup (P <0.05and P <0.01), that of hypertrophic layerat the middle and posterior thirds were decreased significantly in the8-weekexperimental subgroup (P <0.01), the thickness of the whole layer was increasedat the posterior thirds in4-week experimental group (P <0.05) than that of theage-matched control, whereas there was no significant difference between othergroups (P>0.05).3. The mRNA expression level of PCNA was decreased in the2-and4-week (bothP <0.05) experimental groups, although no difference between the experimentaland control group was noticed in8-week group. That of COL II was decreased in4-week (P <0.05), although no difference in2-and8-week was noticed, whileaggrecan was increased in2-week but decreased in4-and8-week (all P <0.05).Protein expression in cartilage showed that in control groups, PCNA-positivechondrocytes were seen predominantly in the proliferative layer, the percentageof PCNA-positive chondrocytes in experimental group was decreased in2-and4-week compared to their age-matched control (both P <0.05), although with nodifference in8-week. COL II-immunopositivity in experimental groups wassmaller in4-and8-week.4. In the control group, PG distributed evenly and mainly located in theproliferative and hypertrophic layers. In the experimental group, PG loss wasobserved obviously in the4-and8-week.5. The mRNA expression level of MMP-3was increased in4-and8-week (both P <0.05), MMP-9was increased in2-week but decreased in4-week (P <0.01and P<0.05, respectively) and identical to its age-matched control in8-week, andMMP-13and TIMP-1were increased in2-week but decreased in4-and8-week(P <0.05, P <0.05and P <0.01, respectively). Protein expression in cartilage showed that in control groups, MMP-3-and MMP-9-positive chondrocytes wereobserved mainly in the hypertrophic layer, and TIMP-1-positve cells in bothproliferative and hypertrophic layers. The percentage of MMP-3-positivechondrocytes showed no significant differences between the experimental andcontrol groups in2-and4-week, but was increased in the experimental group in8-week (P <0.05). The percentage of MMP-9-positive cells was increased in2-and decreased in4-week in the experimental group, compared to theirage-matched control (both P <0.05), and no difference in8-week was observed.That of TIMP-1-positive cells was increased in2-week, but decreased in4-and8-week in the experimental group (P <0.01, P <0.01and P <0.05, respectively).Conclusions:1. Experimentally created unilateral anterior crossbite prosthesis can lead topathological changes in TMJs and these changes increased with time of unilateralanterior crossbite prosthesis. It can also lead to the decreased of cartilagethickness of the posterior third.2. Experimentally created unilateral anterior crossbite prosthesis can increaseMMP-3, MMP-9, MMP-13and TIMP-1at different time and lead to the changesof expression of COL II and aggrecan. |
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