Effects Of Gradually Induced Occlusion Disorders On Condyle Cartilage Morphology And Expression Of IGFs, VEGF And TGF-β

The functional load of temporomandibular joint (TMJ) is mainly from dental-occlusion. Some epidemiologic surveys showed malocclusion may be the one of the causes of temporomandibular disorders (TMD). The chondrocytes of condyle have the ability of remodeling and repairing, which secret many kinds of growth factors and cytokines to regulate the extracelluar matrix which maintains the environments of chondrocytes. The balance between anabolic metabolism and atabolism of condylar cartilarge may be broken after the changes of functional load induced by disordered occlusion. Our research group has found that gradually disordered occlusion can induce the osteoarthrosis like changes and many growth factors and cytokines participate in the process. The present research was carried out in improved gradually induced disordered occlusion in rats. The histomorphological changes and thickness of mandibular condyle cartilage were observed. Meanwhile, the changes of several growth factors in condylar cartilage after occlusion being disordered were also analysed. Insulin-like growth factors (IGFs), including IGF-Ⅰ, IGF-Ⅱ, IGFR-1 and IGFBP-3, are main factors for proliferation and division of chondrocytes. Insulin-like growth factor receptor 1 (IGFR-1) is the main receptor, and Insulin-Like Growth Factor Binding Protein 3 (IGFBP-3) is the main regulatory factors of IGFs. Transforming growth factor-β(TGF-β) maintains the phenotype of chondrocyte. Vascular endothelial growth factor (VEGF) promotes the cartilage to convert to the bone. So, all these growth factors were observed as the effects of gradually induced disordered occlusion on the chondrocytes in mandibular condyle.Forty-eight 8 week-old rats, male and female, were randomly divided into experimental group and control group and there were 4 time points in each group and 3 male or female animals in each point respectively. Gradually induced disordered occlusion (GIDO) was induced as followed: an elastic band was inserted between the first and second left maxillary molars and between the first and second right mandibular molars. The fist molars were moved medially to form the disordered occlusion. The elastic bands were replaced with self-curing resin to keep the gap between the first and second molars after 1 week. After 4 weeks, the left upper third molar and the right lower third molars were moved distally and then the gap was kept too. In the 2 weeks and 4 weeks groups, the two first molar were moved, and the two first molars and two third molars were moved in the 6 weeks and 8 weeks groups.Results:(1) GIDO induced the remodeling of mandibular condylar cartilage, but the thickness of condylar cartilage wasn't significantly different between the left and right side (p>0.05). In the 4 weeks, 6 weeks and 8 weeks groups, the thickness of the cartilage increased compared with the control rat and the 6 weeks groups changed more obviously. In 2 weeks group the whole thickness of cartilage didn't increase (p>0.05). Additionally, some experimental mandibular condyles showed osteoarthrosis like changes. In the 2 weeks group, the thickness of PL increased and formed"rete pegs"structure; in the 4 weeks group, some local necrosis were observed in the PL; in 6 weeks group, the structure of condylar cartilage became irregular and some large necrosis area were observed; in the 8 weeks group, chondral island like structure were observed in the experimental condyles. Pathological changes were observed in female and male rats, which the area was small in 2 and 4 weeks, and it became obvious in 6 and 8 weeks.(2) IGF-Ⅰ, IGF-Ⅱ, IGFR-1 and IGFBP-3 were mainly located in the hypertrophic layer of condyle cartilage. In chondrocytes, IGFs was located in cytoplasm and plasma membrane and IGFR-1 was located in cytoplasm and nucleus while IGFBP-3 was located in cytoplasm, plasma membrane and nucleus. All of them changed during ageing in the experiment period in control groups. IGFs and IGFBP-3 decreased in four control groups during the experiment(p<0.05), while IGFR-1 changed following the changes of IGFs. Two weeks after gradually induced occlusion disorders, IGFs increased in condyle cartilage in male and female rats(p<0.05) and the expression of IGFR-1 was also stronger than control group(p<0.05) and IGFBP-3 increased in female rats(p<0.05) while in male it didn't change(p>0.05). Four weeks later, IGFs decreased in experiment group in both sex groups and in male the expression of IGFs in experiment group was still stronger than control(p<0.01). In the same period, IGFR-1 decreased and in female it was weaker than control group(p<0.01). IGFBP-3 was stronger than control group in female(p<0.01) but weaker than two-week experiment group(p<0.01). There was no difference between experiment and control groups in male(p > 0.05) in four-week-group. In six-week experiment group, further occlusion disorders was performed in rats. The expression of IGF-Ⅰ, IGF-Ⅱ,IGFR-1 and IGFBP-3 increased in experiment group significantly(p<0.01). In eight-week-experiment group, IGFs, IGFR-1 and IGFBP-3 decreased in experiment groups but were still stronger than their control groups(p<0.05).(3) VEGF mainly located in the HL in normal rats, which expressed in cytoplasm and cell membrane. The expression of VEGF decreased during the experimental time in the normal female and male rats (p<0.05). The expression level of 4 weeks group decreased obviously than that of 2 weeks group in the female rat, while that of 4 week decreased obviously than that of 6 weeks in male. In female experimental rats, the expression of VEGF was higher than that of control (p<0.05). In female experimental group, the expression of 4 weeks group was lower than that of 2 weeks group, and increased in 6 and 8 weeks group (p<0.01). In male experimental group, the expression of VEGF in 2, 4 and 6 weeks groups was higher than that in control rats, while in 8 weeks decreased to the normal control level.(4) TGF-βmainly expressed in the HL, which located in the cytoplasm, cell membrane and nucleus. The changes of TGF-βdecreased with the ageing. There was no significantly difference between the 4 weeks and 2 weeks groups, while the expression of TGF-βdecreased from 2 weeks to 8 weeks. In the female experimental group, the expression of TGF-βincreased and then decreased during the experimental period. Highest expression was observed in 4 weeks group, which was similar with control group (p>0.05). But the male experimental group is much higher than control group (p>0.05). In 2 weeks experimental group, the expression of TGF-βdecreased compared with control group (p<0.01). In the 4 weeks, there was no significantly difference between experimental rats and control rats (p>0.05), while the expression of male rat was higher than that of control rats (p<0.01). TGF-βincreased in both sex groups after futher occlusion disorders (p<0.01) and maintain to the end of the experiment. Conclusions:1. Gradually induced disordered occlusion (GIDO) can induce remodeling of condyle cartilage in rats and the disc can adapt to the changes by changing its thickmess. And long time disordered occlusion can induce decompensation of the mandibular condyle, and even the osteoarhrosis like changes.2. GIDO can increase the expression of IGF-Ⅰ, IGF-Ⅱand upregulate its special receptor- IGFR-1 to promote the function of IGFs in the protection of cartilage, while increased IGFBP-3 prevents the process and then pathological changes occur in condyle cartilage.3. GIDO can promote the expression of VEGF in the mandibular condyle in rats, which promotes the transformation of cartilage to bone. VEGF promots the vessel to intrude into the cartilage from bone to destroye the cartilage.4. GIDO can increase the expression of TGF-βin cartilage and TGF-βmay participate the pathological changes of condylar cartilage, which may also protect the chondrocytes in different stages.