The Effect And Mechanism Of The NF-?B In Adult Rats With An Expansion Spring

Objective:Maxillary transverse dysplasia is a common malocclusion in clinical practice,which is often treated by maxillary arch extension.The purpose of maxillary arch extension is to open the palatal suture,which is the distraction osteogenesis of the suture.Nuclear factor-?B(NF-?B)is a relatively popular transcription factor related to osteogenesis in recent years,and pyrrolidine dithiocarbamate(PDTC)is a specific inhibitor of the NF-?B signaling pathway.1?To study the histological changes of anterior palatal suture in rats after installed an expansion spring.2?To study the effect of inhibitor PDTC injection on rats after installed an expansion spring.Method: 1? The model of arch expansion in adult rats was established by simple arch expansion and inhibition of nuclear factor ?B injected.The investigation used 45 adult and male SD rats,which were randomly divided into 3 groups,normal groups and dilation groups and PDTC groups.An expansion spring is installed between the two incisors in dilation groups and PDTC groups.The PDTC groups were intraperitoneally injected with the nuclear factor ?B inhibitor PDTC 100mg/kg 30 minutes before installed of the expanded springs,the same dose of PDTC was intraperitoneally injected at the same time every day.The other groups received intraperitoneal injection of equal doses of normal saline.Each group was randomly divided into 3 groups,5 in each group,and were killed 1,4 and 7 days later.The maxilla of rats was completely removed and fixed in 10% formalin.2?Micro-CT scanning was used to measure the width of the anterior palatal suture in rats.After the maxillary specimens of rats were fixed in 10% formalin for 24 hours,the anterior palatal sutures of rats were scanned with high-resolution Micro-CT to calculate the distance between the anterior palatal bones.3?HE,Masson and Immunohistochemistry were used to detect the changes of the anterior palatal suture tissue.The maxillary bone specimens were decalcified,embedded,sectioned and stained.HE staining was used to observe the morphological structure of anterior palatal suture.Masson staining was used to observe the collagen fibers and new bone.Immunohistochemistry was used to analyze the expression of p65,BMP-2 and OCN.Result: 1?Results of animal modelingThere were no deaths in experimental animals in the modeling process,at the end of modeling,the gap appeared between maxillary incisors of the rats in dilation groups and PDTC groups,this shows that the modeling was successful.The weight of each group of rats in the modeling was observed as follows: rats in the normal control groups weight increased steadily.Statistical analysis of the weight at the beginning and one day after the expansion showed that: at the beginning,there was no significant difference in weight among the three groups(P>0.05).One day later,the weight of the PDTC groups and the dilation groups were lower than the normal groups(P<0.05),but the dilation groups and the PDTC groups has no difference(P>0.05).At the same time,abnormal excitation and behavior of rats in PDTC groups were found after intraperitoneal injection of PDTC.2?Micro-computed tomographic evaluation.After three-dimensional scanning,no fusion of bilateral palatal bone was observed in the normal groups,and instead of a straight line,the anterior palatal sutures of the rats had small projections.Finger-like new bone formation was observed in the anterior palatal sutures of the rats in the dilation groups and the PDTC groups from day 4,new bone formation increased after maxillary expansion for 7day.The width of the anterior palatal suture had no changes in the normal groups,while the widths of the expending groups and PDTC groups increased with the extension of the arch expending time.The width of anterior palatal suture of PDTC groups and the dilation groups was larger than that of the normal groups 1 day after arch expansion,but there was no difference between the two groups,after 4 days expansion,the width of anterior palatal suture of PDTC groups was larger than that of the dilation groups(P< 0.05).3?HE,Masson and Immunohistochemical staining results.HE staining showed that there was no change in tissue morphology in the normal groups,and the anterior palatal suture was composed of osteogenic layer,fibrous embedding layer,intermediate layer,fibrous embedding layer and osteogenic layer.After 4 or 7 days of expansion,a new bone was formed in the suture area with the base located at the tip of the palatal bone toward the suture.Osteoblasts around the new bone gathered and there was neovascularization.From the Masson staining,it was observed that almost all the fibers in the dilation groups and PDTC groups were blue dyed collagen fibers,and the direction of collagen fibers was consistent with that of the new bone,most of that were horizontal without cross-generation,while a few of the new bone and collagen fibers were oblique.Immunohistochemical staining showed that the mean of IOD value of p65 in the new bone margin of the dilation groups was higher than that of the PDTC groups at each time point(P < 0.05).The mean of IOD values of BMP-2 and OCN in normal groups did not change(P > 0.05).At each time point,the mean of IOD value of BMP-2 in the PDTC groups was greater than that in the dilation groups and greater than that in the normal groups(P < 0.05),and the mean of IOD value of BMP-2 in the dilation groups for 4 days was greater than that for 1 day,but there was no statistical difference(P > 0.05).For 7 days,BMP-2 mean of IOD value was greater than 4 days(P < 0.05).The mean of IOD value of OCN showed no difference between the dilation groups and the normal groups after 1 day(P > 0.05),the PDTC groups was larger than the two groups,and the mean of IOD value of OCN in both the dilation groups and PDTC groups increased with the action time(P < 0.05).Conclusion:1.Proliferation and activation of osteoblasts after mechanical tension,BMP-2 expression was increased and mesenchymal cells were transformed into osteoblasts.Collagen fibers increased,providing a scaffold for bone mineral deposition.The proliferation of new blood vessels further promotes suture distraction osteogenesis.2.The direction of ossification of the maxilla is the same as the direction of the dilation force,and the inclined dilation tension can lead to the formation of inclined bone,which may be made maxillary deviation and asymmetry.3.Intraperitoneal injection of PDTC in rats can inhibit the expression of NF-?B p65 subunit in anterior palate suture osteoblasts,which does not affect the growth and development of rats but has other side effects such as nerve excitability.4.NF-?B was involved in the remodeling of anterior palatal suture in rats after dilatation.Inhibition of NF-?B increased the activity of osteoblasts,the expression of osteogenic factor BMP-2,OCN and promote the expansion of the anterior palatal suture,enhance the distraction osteogenesis.