| Objective: With the improvement of living conditions of our residents in recent years,more and more patients have the experience of receiving orthodontic treatments,but the treatments are generally more than two years,some are even longer.During this period,if patients do not pay attention to oral hygiene,gingivitis,periodontitis,dental caries and other diseases may occur.In the process of oral orthodontic treatment,the speed of tooth movement is mostly 1 mm per month,and in order to speed up the movement of teeth,orthodontist scholars have done a lot of researches to explore the methods of accelerating tooth movement.The current methods of accelerating tooth movement are divided into four categories: surgical methods,gene therapy methods,drug treatment methods and physical therapy.Surgical methods have a certain trauma,while gene therapy is not yet mature,and drug treatment methods may cause some side effects.The laser irradiation is a kind of physical therapy which is to achieve the purpose of accelerating tooth movement mainly by accelerating the formation of osteoclasts and osteoblasts.The semiconductor laser covers the application of other types of laser with small size,long life,low cost,safety and other advantages.As a good way of accelerating tooth movement that cause no trauma and is easy to operate,the semiconductor laser method is more easily accepted by patients and doctors.Under the semiconductor laser irradiation,it is still not so clear that how the alveolar bone structure changes.The animal experimental objects of tooth movement are mostly rats,and vernier caliper are usually used to measure the distance of rats' tooth movement,but the results are not accurate enough with big error.In the observation of alveolar bone remodeling and root resorption,histological sections method is commonly used and slices can only be viewed from a two-dimensional perspective.Micro-CT is a medical CT with spatial resolution of 1-10?m.It can observe that the movement distance of orthodontic tooth,the change of alveolar bone structure and the root resorption from a three-dimensional perspective.In this study,Micro-CT was used to observe the changes of orthodontic tooth movement,alveolar microstructure and root resorption under the laser irradiation of semiconductor,and to explore the effect of semiconductor laser on tooth movement,so as to provide theoretical reference for the acceleration of tooth movement.Methods:1 Establishment of rat tooth movement modelWe used 10% chloral hydrate(300-350mg/kg)to anesthetize animals.We used the nickel-titanium tension spring to reinforce maxillary incisors and the first molar.Through the maxillary two teeth as a support,10 g force value made maxillary first molar move,see Fig.1.2 Semiconductor laser irradiationIsoflurane anesthesia,see Fig.2.After 1 to 14 days of tooth force,we used the semiconductor laser to irradiate(wavelength 980 nm,energy density 10 J / cm2)on the right maxillary first molar area,see Fig.3 and Fig.4.3 Micro-CT scanRats were sacrificed and the specimens were scanned with Micro-CT(SkyScan 1076,Belgium)with a scan parameter of 0.7 ° for each rotation,a total rotation of 180 °,73 kV,142 ?A,a layer thickness of 18 ?m,and an image size of 1024×1024 pixels.Each specimen was scanned for approximately 30 minutes.And then we used Micro-CT's program to reconstruct the picture,each sample's reconstruction time is about 40 minutes,obtaining about 1000 pictures,see Fig.5.CTAn software was used to measure tooth movement distance,root length and the parameters of alveolar bone structure,see Fig.6 and Fig.7.4 Making histological slicesThe specimens were placed in EDTA to decalcified and then embedded by paraffin.We made HE slices of maxillary first molar as the center.Histological changes were observed under light microscope.5 Statistical analysisSPSS 21.0 statistical software was used to analyze the data.The data were expressed as mean ± SD(mean ± SD).One-factor ANOVA was used for the data with normal distribution and variance.The independent samples were used for t-test.The mean number was compared with the variance analysis in four groups,and the LSD test was used for comparison between two groups.Non-normal or variance used nonparametric rank sum test and Kruskal-Wallis H test.Taking ? = 0.05 as the test level,(P<0.05),as the difference,was statistically significant.Results: 1 Tooth movement distanceThere was no significant difference in the distance between the laser group and the control group on the 3rd day(P>0.05).There was significant difference on 7th and 14 th days(P<0.05),and the distance of the laser group(7d: 203.27 ± 32.28 M,14d: 320.80 ± 33.82?m)was significantly larger than that of the control group(7d: 166.93 ± 15.46?m,14d: 259.40 ± 30.01?m).The tooth movement distances of the two groups were significantly different from 0,3rd,7th and 14 th days(P<0.05).The movement rates of both groups on the 3-7 days were slower than that the first days,on day 0-3.During the first 7-14 days,the movement rates of the two groups were faster than that of 3-7 days,see Fig.8 and Table 1,10.2 The condition of root resorptionOn the 3rd and 7rd days,there was no significant difference between the laser group and the control group on the length of the root(P>0.05).On the 14 rd day,the root of the laser group(1.933 ± 0.109mm)was significantly longer than that of the control group(1.840 ± 0.129)(P<0.05).There was no significant difference in the length of the root of the laser group on the 0rd,3rd,7rd and 14 rd days(P>0.05).On the 14 rd day,the root length of the control group was less than that of day 0 and 3rd day(P<0.05),see Fig.9 and Table 2.3 Alveolar bone structure parameters 3.1 Bone Mineral Density(BMD)-PressureOn the 3rd day,there was no significant difference in BMD between the two groups(P>0.05).On the 7rd and 14 rd days,the BMD of the laser group was significantly lower than that of the control group(P<0.05).BMD values showed a downward trend from 0rd day to 14 rd day,see Fig.10 and Table 3,9,10.3.2 Bone Volume Fraction(BV / TV)-PressureOn the 3rd day,there was no significant difference between the two groups in BV / TV value(P>0.05).On the 7rd and 14 rd day,the BV / TV value of the laser group was significantly lower than that of the control group(P<0.05).The values of BV / TV decreased from 0rd day to 14 rd day,see Fig.11 and Table 4,9,10.3.3 Trabecular Separation(Tb.Sp)-PressureOn the 3rd day,there was no significant difference in Tb.Sp between the two groups(P>0.05).On the 7rd and 14 rd days,the Tb.Sp value of laser group was significantly higher than that of control group(P<0.05).The values of BV / TV increased from 0rd day to 14 rd day,see Fig.12 and Table 5,9,10.3.4 BMD-TensionOn the third day,the BMD of the laser group was lower than that of the control group(P<0.05).On the 7rd day and the 14 rd day,the BMD of the laser group was significantly higher than that of the control group(P<0.05).From day 0 to 14 rd day,the BMD values of the two groups decreased firstly and then increased,see Fig.13 and Table 6,9 and 10.3.5 BV / TV-TensionOn the 3rd and the 7rd days,there was no significant difference in BV / TV between the two groups(P>0.05).On the 14 rd day,the BV / TV value of the laser group was significantly higher than that of the control group(P<0.05).From day 0 to 14 th days,the BV / TV values of the two groups decreased firstly and then increased,see Fig.14 and Table 7.3.6 Tb.Sp-TensionOn the 3rd and 7rd days,there was no significant difference in Tb.Sp between the two groups(P>0.05).On the 14 rd day,the Tb.Sp value of the laser group was significantly lower than that of the control group(P<0.05).The values of BV / TV were increased firstly and then decreased from 0rd day to 14 rd day,see Fig.15 and Table 8.4 Histological observation 4.1 Tension sideOn the third day,it can be observed that periodontal ligaments in the two groups were widened,and there were pits-like absorption on alveolar bone,with a few osteoclasts around and periodontal ligament fibers along the traction direction.More vasodilator congestion and a small amount of new alveolar bone in laser group were observed.On the 7rd day,the number of blood vessels increased and the number of fibroblasts rose in the two groups.The number of osteoblasts on the surface of the alveolar bone in the laser group was significantly larger than that in the control group.The osteogenesis was very active and the small margin of the alveolar bone became smooth.On the 14 rd,both groups had significant new bone formation.The new bone formation in the laser group was more than that in the control group,see Fig.16,17,18.4.2 Pressure sideOn the third day,the periodontal ligament of the laser group was more narrowed and the osteoclasts appeared in the absorption layer of the alveolar bone.The numbers of osteoclasts on laser group were more than that of the control group.The transposition of the periodontal membrane and vascular lumen narrowing can be observed in the control group.But here was no vitreous changes and significant changes in blood vessels in laser group.On the 7rd day,the width of the periodontal ligament was restored in the laser group and the control group,and a large number of absorption pockets were observed on the alveolar bone surface.The number of osteoclasts in the alveolar bone of the laser group was significantly increased,which was more active than that of the control group,and absorbed more and deeper.There was occasional root resorption in the laser group,only involving the cementum,and the control group's root absorption was up to dentin.On the 14 rd day,the osteoclasts of the laser group were significantly decreased.The transparent sample in the control group has been basically removed,showing partial root absorption which is deep to dentin,see Fig.19,20,21.Conclusion:1 Semiconductor laser irradiation can speed up the movement of teeth.2 Semiconductor laser irradiation can reduce tooth root absorption during tooth movement.3 Reconstruction of alveolar bone during tooth movement can be accelerated by semiconductor laser irradiation.4 Micro-CT scanning technique can obtain accurate data of alveolar bone microstructure parameters,tooth movement distance and root length from three-dimensional direction. |
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