Clinical And Animal Experimental Study On Tooth Movement In Atrophic Alveolar Bone

In recent years,with the development of social economy and the popularization of oral health awareness,more and more patients,especially adult patients,have begun to pay attention to the aesthetics of the maxillofacial region and dental function,and gradually seek orthodontic treatment.In adult patients,the loss of the mandibular first molar is very common due to the failure to maintain good oral hygiene at an early age.After the tooth is missing,the alveolar bone in the edentulous area is disused atrophy,and its width and height gradually decrease with time.Previous studies have shown that tooth movement to close the molar missing space is a potential solution to the missing first molar in the mandible.Since then,some scholars have succeeded in moving the teeth into the atrophic alveolar bone.The results show that the height and width of the alveolar bone are increased.The alveolar bone height and width measured in the previous studies were mostly carried out on gypsum models or two-dimensional X-ray films,which had many influencing factors and lacked accuracy.In this study,to evaluate the remodeling of the alveolar bone after tooth moving into the atrophy alveolar bone,we used oral cone-beam computed tomography(CBCT)combined with three-dimensional coordinate system to accurately measure the alveolar bone height,width and cortical bone thickness of atrophic alveolar bone before and after orthodontic treatment in patients with mandibular first molar loss.Generally,fixed-orthodontic treatment lasts about two years for adult patients,and the treatment time is longer for complicated cases such as closing the missing tooth space.In the past,some scholars compared local injection of prostaglandins,vitamin D3,pulse electromagnetic field and direct current,and corticotomy to assist tooth movement.Compared with other methods,corticotomy is a safe and effective method to accelerate tooth movement.At present,there is no clinical research report on the use of corticotomy to assist tooth movement in atrophic alveolar bone.Due to the ethical issues,experiments cannot be performed directly in the human mouth.Therefore,this experiment intends to establish an animal model of atrophic alveolar bone,and perform corticotomy in the animal model to assist the movement in the atrophy alveolar bone.Micro-CT was used to explore the effect of corticotomy on the movement of the tooth in the atrophic alveolar bone,in order to provide reference for clinical orthodontists.Part 1: CBCT combined with three-dimensional coordinate system to evaluate alveolar bone remodeling before and after orthodontic closure of atrophic alveolar bone space.Objective: To evaluate the changes of alveolar bone height,width and cortical bone thickness after closing the atrophic alveolar bone space by orthodontic tooth movement with CBCT.Methods: Patients with mandibular first molar loss and atrophic alveolar bone were enrolled.CBCT was taken before and after orthodontic treatment.The height and width of alveolar bone and the cortical bone thickness in the atrophic alveolar bone region(maintenance/closed edentulous space)were measured with Invivo 5.0 software.The changes were analyzed by paired t-test.Results: The width,height of the alveolar bone and cortical bone thickness in the space-maintenance group were reduced significantly.The width of the mesial and distal alveolar bone and the height of the lingual alveolar bone in the space-closure group were significantly increased,while the height of the alveolar bone in the mesial and distal buccal sides was significantly decreased.The thickness of the mesial buccal and lingual and distal buccal cortical bone decreased,only the thickness of the distal lingual cortical bone increased,and the difference in the thickness of the mesial buccal side was statistically significant,the other differences were not significant.Conclusion: CBCT combined with three-dimensional coordinate system can accurately assess the alveolar bone remodeling before and after orthodontic treatment;for those who maintain the space,the alveolar bone is further atrophied and thinner after orthodontic treatment;while,after the tooth movement closed the atrophic alveolar bone space,its width,lingual alveolar bone height and the thickness of the lingual cortical bone increased.Part 2: An animal experimental study of the corticotomy assisting the movement of the tooth in the atrophic alveolar boneObjective: To establish a rat model of atrophic alveolar bone and evaluate the auxiliary effect of corticotomy on the movement of atrophic alveolar bone.Methods: Thirty male Sprague-Dawley rats aged 4-6 weeks were used.All the maxillary first molars were extracted and partial alveolar bones were removed.The alveolar bone atrophy after tooth loss was simulated.After 4 weeks of healing,on the experimental side,the corticootmy was performed in the mesial side of the second molar,and the orthodontic tooth movement was performed simultaneously(CO+TM group),while on the control side only orthodontic tooth movement was performed(TM group).Five rats were sacrificed on days 0,1,3,7,14,and 21 after tooth movement.The bilateral maxillary bones were fixed and Micro-CT scan was performed.Statistical analysis of data was performed using SPSS 20.0 software.Results: 1.The experiment successfully established a rat model of atrophic alveolar bone.2.Measurement of tooth movement showed that the teeth of the two groups were obviously moving on the first day after the force was applied,the movement of the teeth from 3 to 7 days was slow,the movement on the 7-14 days was slightly faster,and the distance of teeth movement from 14 to 21 was small.On the 1st,3rd and 21 st day,the movement of CO+TM group teeth was further than that of TM group,but the difference was not statistically significant.The amount of toot movement of CO+TM group was significantly greater than that of TM group at 7 and 14 days.3.The trabecular bone structure parameters showed that the bone volume fraction of the two groups gradually decreased from the beginning of the movement,and began to increase after 7 days.The bone volume fraction of the CO+TM group was significantly smaller than that of the TM group on the 3rd to 21 st day after the force application;the thickness of trabecular bone began to decrease after the force was applied,and began to increase from 14 to 21 days.The thickness of the trabecular bone in the CO+TM group was smaller than that in the TM group.The difference was significant at 14 days only.The number of trabecular bone began to decrease after the after stressing,and began to increase after 7 days.In the CO+TM group,the number of trabeculae was smaller than that in the TM group;the trabecular separation increased after the force was applied,and the CO+TM group was larger than the TM group,and the difference was significant from 3 to 14 day;the structural model index is the largest at 7day of these two groups,and the CO+TM group is larger than the TM group.Conclusion: Corticotomy can accelerate the movement in the atrophic alveolar bone.The effect of corticotomy accelerating tooth movement in the atrophic alveolar bone may be related to the active absorption of compressed alveolar bone.The trabecular volume fraction,thickness and number decreased,the trabecular separation increases,and the tooth movement resistance decreases,thereby accelerating tooth movement.