Study Of Orthodontic Root Resorption By Using Micro-computed Tomography In Rat

Objective:As a relatively common side effect, orthodontically induced tooth root resorption(OIRR) has received considerable wide and in-depth research. At present, the root morphology observation in the experimental study relies mainly on electron microscopy(sem) images, root resorption of indirect measurement with laser, the method is more complicated. Micro-CT has shown more advantages in oral medical research, including clearly shows that the three-dimensional structure of teeth and alveolar bone,It provides methods for clinical application in basic research.It is possible to detect tiny resorption lacuna before the root absorption was confirmed by using the high resolution Micro- CT.This research mainly using Micro- CT technique in maxillary first molars of rats mobile force of different values and different stages in vitro specimen scanning and three-dimensional reconstruction, observe and analyze the root anatomical morphology characteristics and the change of alveolar bone. in order to more accurately understand the stress value and the time for orthodontic tooth movement,the movement process of root resorption and alveolar bone resorption and their repair situation, the relationship between provide reference for clinical orthodontic treatment.Materials and Methods:1.Eighty 6-week-old rats were randomly divided into two groups. For the exprement groups, alveolar bone and root resorption was induced by placement of 30g(light group) and 100g(heavy group) force between two incisor and upper left first molar,which is aimed to move the upper left first molar mesially. The contralateral molars served as controls.2.At different time points: day 1, 4, 7, 14, 21, 28,(20 rats were setted same treatment as other groups, but removed force to relapse at day14)animals were executed.3.The maxillary sample were scanned using micro-computed tomography. Using Mimics 10.01 software segment the upper first molar and get three-dimensionalreconstruction.4.Three-dimensional microarchitecture parameters were measured as evidences of the alveolar resorption and root resorption, including the tooth movement distance, root resorption crater volume and depth, BVF, BMD, Tb.Th, TB.N, SMI. Statistical analysis was performed with ANOVA,(significance level P<0.05).5.In vitro samples were dehydrated and embedding, then sections toke HE dyeing.Result :1.Rat orthodontic tooth movement extended gradually over time in light and heavy force group.1 day is the first fast moving stage(displacement immediately), phase 4 ~14 days to move slowly, 14 ~ 28 days for the second fast moving period. In 14, 21, 28 days, light force groups teeth movement under heavy group, difference has statistical significance(P < 0.05).2.The Micro- CT shows that the control group did not see root absorption. Light force group had no significant root absorption in early, root resorption crater volume and depth of 1, 4, and 7 days had no statistical significance difference(P > 0.05), root1/3 and apical 1/3 of mesial side occured small and shallow resorption crater in 14 d,the maximum measured value was in 21 days(P < 0.05). Heavy group found shallow concave shape resorption crater in 4 day on roots’ apical 1/3, compared to 1 day group there was statistically difference(P < 0.05), 21 days appeared resorption crater jagged fusion zone, root morphology were destroyed, the maximum measured value was in 28 days(P < 0.05). At same time point, light force group had a slight degree of root resorption, difference has statistical significance(P < 0.05). Micro-CT imaging findings consistent with histology.3.In the alveolar bone absorption of the Micro-CT measurement indicators, Light and heavy group had the same change trendon on the compression side or tension side.On the compression side, BVF, Tb.Th significantly reduced, Tb.Sp and SMI increased obviously; On the tension side, BVF, Tb. Th increased slowly, Tb. Sp and SMI has a little decrease.Heavy group found Latent excavation of bone resorption after 21 days’ continued strength. Micro-CT imaging findings consistent with histology.4.Both two groups’ root resorption crater have obvious repair phenomenon at repairperiod(P < 0.05), the root resorbtion volume reduced over time.The light group have a high level of root repair, difference has statistical significance(P < 0.05). Micro-CT imaging findings consistent with histology.Conclusions:1.Light force group had no significant root absorption in early, at the middle time(14days) there was low-grade root absorption. Heavy group found low-grade root absorption at early time(4 d), there were shallow concave shape resorption crater on apical 1/3; at the middle time(14 d) there was mid-grade root absorption, resorption crater is “V” shape; at the later period(21 d) there was serious root absorption,appeared resorption crater jagged fusion zone and root morphology were destroyed.2.In the alveolar bone absorption of the Micro-CT measurement indicators, Light and heavy group had the same change trendon on the compression side or tension side.Alveolar bone density decreased on the compression side, and increased on the tension side. Heavy group found Latent excavation of bone resorption after 21 days’ continued strength.3.Both two groups have obvious repair phenomenon at repair period. Light force group basic restore original root shape, heavy group failed to restore to the original root form.4.the use of Micro-CT and mimics the three reconstruction techniques can accurately assess the correlation of root orthodontic root resorption model alveolar performance.After a period of times’(14 d) repair, both two groups’ trabecular bone structure can restore to normal level.