Effects Of Icariin On Bone Formation In The Mid-palatal Suture During The Expansion And Retention Period Of Rapid Maxillary Expansion

As an important clinical technology,rapid maxillary expansion(RME)has been widely used by orthodontists for a variety of malocclusions,including crowding,arch stenosis,and posterior cross-bite.During the RME,the mid-palatal suture is expanded and osteogenesis is activited.New bone continues to deposit on the edge of the bone suture and the maxillary then becomes stable at the new position.However,many problems could occur,such as external root resorption,gingival atrophy,unsymmetrical expansion and repalse phenonmenon.Among all these complications,repalse phenonmenon is the most common.Insufficient bone formation is supposed as one of the most inportant reasons for this complication.Therefore,it's an important step to enhance the new bone formation in order to ensure the effect of RME.Researches at home and abroad have explored many methods to achieve this goal,including bisphosphonate,low-power laser irradiation and TGF-B.However,these methods are inconvenient with high costs and cannot be easily accepted by patients.In recent years,the theroy of traditional Chinese medicine hms been accepted gradually by many researchers and these ancient technologies have drawn more and more attention.With the efforts of reaearchers at home and abroad,more and more taditional Chinese medicine was explored and applied in the clinial use.It has been a hot topic to study the traditional Chinese medicine with the modern molecular biology.In this study,we explore the effect of icariin on the bone remodeling during RME in a rat model,hoping to find a new way to improve the effect of RME and shorten the retention time after RME.Purpose:By establishing the RME model with rats,we aim to observe and analyse the histological changes in the mid-suture and explore the effect of icariin on the bone remodeling during expansion and retention period of RME,hoping to find some theoretical basis to promote the effet of RME with traditional Chinese medicine.Method:Thirty-six male 6-week-old Wistar rats were selected.We assigned these rats into 3 different groups randomly:group A,group B and group C.Group A was designed as a control group.Rats in group B and C were anesthetized and the maxillary models were made with gypsum.Expansion appliances that produced 100g force were made according to the models.These expansion appliances then were fixed between the first and the second molar tooth on both sides of the rats in group B and group C with light-cured resin.On day 7,4 rats in group A?B and C were randomly selected and killed,and the rats left in group B and C were anesthetized again.Then the circle part of the expansion appliance was fixed with light-cured resin for the retention period.The rats left were randomly selected and euthanized on day 14 and 21 respectively.During both the expansion and retention period,rats in group C were given 20mg/kg icariin while equal solvent was given to rats in group A and B.All the maxillary samples were collected and decalcified and then HE staining and immonohisto chemical staining were carried out to assess the bone formation and osteogenesis related factors in the mid-suture.Result:1.Histological changes in the mid-suture during the expansion and retention period of RMEFrom the HE sections,the centre of maxillary mid-suture was composed with fiber like tissue which was rich in fiber,fibroblast,and precursor cells of bone and cartilage.The second layer of the structures was composed by cartilage cells.These oval cells showed bigger volume,light drained cytoplasm and more obvious nuclei.The outer layer of the structure is the edge of the hard bone where the marrow cavities can be seen.During the RME,the mid-maxillary sutures of the rats were widen,with the fiber like tissue in the center area torn.The normal order of these cells was disrupted and the directions of the fibers was changed.Inflammatory response and new blood vessel formation were observed.Further,proliferation of the osteoblasts and new bone formation were significant on the edge of the mature bone layer.When moved to the retention period,the fiber tissue tended to restore its order,with the cells and fibers recovering.New bone and blood vessel formation continued,while inflammatory response disappeared.2.Width change of the maxillaryIt can be detected with naked eye that the maxillary of the rats in group B and C was significantly expanded.The results showed that the width of maxillary in group B and C was significantly higher than group A.However,there is no significant difference between group B and C.3.Number of osteoblastsAt all the time points,there were more osteoblasts in group C than that in group A,which was statistical(p<0.05).Compared with group A,the number of osteoblasts in group B was significantly higher in day 7(p<0.05).However,statistical analysis showed no significant difference between these two groups in day 14 and 21(p>0.05).4.Expression of BMP-2On day 7 and 14,the expression of BMP-2 was higher in group B and group C than that in group A(p<0.05).Further,the expression of BMP-2 in group C was significantly greater than that in group B(p<0.05).However,the expression of BMP-2 showed no significant difference among group A?B and C on day 21(p>0.05).5.Expression of BMP-4At each time point,the expression of BMP-4 was significantly higher in group C than that in group A and group B(p<0.05),and group B was higher than group A(p<0.05).Conclusions:1.During the RME,mechanical expansion force can stimulate the expression of BMP-2 and BMP-4.This effect diminished with time.2.Under the mechanical expansion force,icariin could promote the osteogenic differentiation and the expression of BMP-2 and BMP-4 in the mid-palatal suture.3.Icariion can promote the bone remolding and accelarate the formation of new bone,this would be helpful in maintaining the effect of RME,reducing the repalse and shorten the retention time.