| In clinical practice,we often see some mild and moderate Class ? malocclusion patients who refuse orthognathic therapy for fear of the risk of operation and the high cost of operation.They hope that the occlusal can be improved to the greatest extent through the treatment of orthodontic compensatory.In order to meet the needs of these patients,orthodontists have invented the methods of extraction compensation,non-extraction "MEAW" arch,rocking chair arch and intermaxillary traction so as to improve the patient's malocclusion as much as possible.Some of the patients got good results,but there are still some patients with periodontal problems,bone fenestration,bone cracking and other problems due to excessive extraction of teeth,and other problems such as long distance intermaxillary traction will result in maxillary molar elongation,labial inclination of the upper teeth or even occlusion plane to clockwise rotation,which are especially unfavorable to high angle cases.In recent years,domestic scholars have implanted miniscrews into the mandibular external oblique region to treat the mild and moderate Class ? malocclusion,which has made the molar relationship from the proximal to central relationship.Since 2010,this method has been used to treat a large number of Class ? malocclusion patients in our department,and a great deal of clinical experience has been absorbed.However,the research of this technique is relatively lack at home and abroad.There are few systematicreports on the implantation angle,biomechanical research and the evaluation of therapeutic effect.To apply the technique well,you have to meet the following two points:1.Miniscrews implanted have greater stability,It can provide greater support resistance for the whole distal movement of the lower dentition.2.The miniscrews should be located on the buccal side of the root as far as possible,Otherwise,the miniscrews will prevent the root from moving farther away.The emergence of CBCT can be said to provide a lot of more accurate diagnostic information to oral doctors,Because of the advantages of low dose,fast imaging and high accuracy,CBCT has gradually become one of the main tools for oral and maxillofacial examination and diagnosis.In order to more safety to apply this technique to clinical practice,this paper collected CBCT data and made the following four parts of experiments:The anatomic morphology of alveolar bone and the size of the miniscrews,the angle of safe implantation,the related biomechanics and the clinical application of the mandibular external oblique region were studied systematically and comprehensively.This study is divided into four parts:Experiment 1: Three-Dimensional Evaluation of the location of Miniscrews Implantation in the External Oblique Area of the MandibleObjective: to measure the alveolar anatomy of mandibular external oblique region by collecting CBCT in order to provide a relatively safe position for the implantation of miniscrews when the mandibular whole dentition Move far away.Materials and methods: the CBCT data of 75 patients were collected,Four regions at the horizontal level of 3 mm,5 mm,7mm,9 mm below the alveolar crest were measured,between the second premolars and the first molars(L5-L6),the proximal distal roots of the first molars(L6),the first molars and the second molars(L6-L7),between the proximal and distal roots of the second molar(L7)at the external oblique of the mandible,respectively,the thickness of the alveolar bone of the buccal side of the root,the narrowest distance between the root and the root and the distance from the horizontalplane to the mandibular canal.Results:(1)Thickness of buccal alveolar bone(horizontal)The thickness of the buccal alveolar bone were measured at 3mm,5mm,7mm,and9 mm below the crest of the alveolar ridge.The thickness of buccal alveolar bone in the same height was significantly different between L5-L6,L6,L6-L7 and L7(P < 0.05).The thickness increases from proximal to distal in turn,that is,L7 > L6-L7 > L6 > L5-L6,However,the buccal alveolar bone of L6-L7 and L7 was significantly thicker than that of L5-L6 and L6 regions;There were significant differences in the thickness of the alveolar bone of the buccal side in the same area but different height(P > 0.05).The thickness of the buccal alveolar bone has a tendency to increase obviously from the direction of occlusion to gingiva,that is,9mm > 7mm > 5mm > 3mm;The thickness of the buccal alveolar bone was the largest at 9mm below the crest of alveolar crest between the proximal and distal roots of L7,with an average value of 7.31 mm.The thickness of the buccal alveolar bone measured between L5-L6 and the alveolar crest was the smallest,with an average value of 1.02 mm.(2)Narrowest distance between buccal roots(sagittal)The narrowest distance between the roots of the buccal side was measured at the level of 3 mm to 5 mm and 7 mm to 9 mm below the alveolar crest respectively.In the same area,the difference of the narrowest distance between roots measured on different measuring planes was statistically significant(P < 0.05).The narrowest distance between the roots increases in turn from the direction of the occlusion to the gingival.The difference of the narrowest distance between the buccal roots on the same height was statistically significant(P < 0.05).The distance between L5-L6 and L6-L7 is larger than that between L6 and L7.According to statistics,the narrowest distance between the buccal roots is located at the level of 3 mm below the top of the alveolar crest between the proximal and distal root of the second molar(0.49 ±0.66 mm);The maximum value is between the distal root of the first molar and the proximal root of the second molar(L6-L7),and is 9 mm from the top of the alveolar ridge(4.97±2.36mm);The mean of the narrowest distance between the first molar and the second molar(L6-L7)was greater than 3.2mm from the measurement level of 5mm below the top of the alveolar crest;In the region of the second premolar and the first molar proximal root(L5-L6),at the level of 7mm below the alveolar ridge,the mean value of the narrowest distance of the buccal root was greater than 3 mm;However,the mean of the narrowest distance between the first molar and the second molar is less than 3mm.(3)Distance from each section of the first molar and the second molar to the mandibular neural tube(vertical)In the coronal section of the first molar and the second molar,the distances from the plane to the mandibular nerve canal were respectively measured at the level of 3 mm,5mm,7mm and 9mm below the top of the alveolar crest.The results showed that the distance between the first molar and the second molar from the mandibular nerve canal were statistically different(P< 0.05).The distance between the measuring plane of 3 mm,5 mm,7 mm,9 mm below the alveolar crest and the mandibular nerve canal decreased in turn,that is,moving toward the gingival side closer to the mandibular canal;But in the same measuring plane,the distance measured between mandibular nerve canals and different positions was statistically significant(P> 0.05).At the first molar,the distance between 9 mm measuring plane below the alveolar crest and the mandibular canal was minimum 13.4 ±1.70 mm.Conclusion: When a clinician uses miniscrews to implant the mandibular external oblique for the overall distal displacement of the lower dentition,We suggest that it is relatively safe and stable to use a 2.0 mm diameter and 10 mm length microimplant nail.The safe place to implant miniscrews: In the sagittal,the distance between the first molar and the second molar(L6-L7)is about 1 mm away from the middle point;In the vertical,5mm-7mm below alveolar crest.Theoretically,the above initial implantation site of the miniscrews can minimize the probability of root damage and improve the stability of the miniscrews.Experiment 2: Using CBCT to Evaluate the Optimal Angle of Miniscrews Implantation When the Mandibular Total Dentition Moves Far AwayObjective: Based on the conclusion of the experiment,in order to guide the clinical practice,CBCT was used to evaluate the optimal implantation angle of the miniscrews at about 1 mm away from the middle point between the first mandibular molar and the second molar.Materials and methods:A virtual miniscrews,diameter is 2.0 mm and the length is 8mm(Usually length of 10 mm miniscrews has a maximum thread length of 8 mm into bone tissue),was set up in Mimics software.CBCT of 75 newly diagnosed patients were selected,First,the sagittal plane of the mandibular posterior tooth was located,and the coronal section of the distal root of the first molar was obtained.The virtual miniscrews were placed in the buccal cortex of the alveolar crest at 5 mm and 7 mm below the top of the alveolar crest,respectively,and the angle of the miniscrews was changed by adjusting the tip of the virtual implants.When the surface of the distal root of the first molar was just 1 mm away from the virtual implants,Measure the angle between the long axis of the virtual miniscrews and the long axis of the tooth,that is,the maximum angle A.And then repositioned on the sagittal plane of the mandibular posterior teeth,The coronal plane was obtained At the middle point of the first molar and the second molar moved 1 mm to the distal distance at 5mm and 7mm below the crest of the alveolar crest,respectively.The virtual miniscrews was also placed in the buccal cortex of 5mm and 7mm below the alveolar crest respectively,and the angle of the miniscrews was adjusted to the angle of the miniscrews.When the miniscrews is about 2.5 mm away from the buccal cortex,the angle between the virtual miniscrews and the long axis of the tooth was measured.That is,the minimum angle B.Results: The results showed that there was no significant difference between left and right sides(P > 0.05).But the difference of maximum angle A between different sections under alveolar crest was statistically significant(P < 0.05),the minimum angle B difference was not statistically significant(P > 0.05).The maximum angle A of the left andright sides of the mandible at 5 mm below the alveolar crest is 41 ±9.3 °,40.61±9.7respectively.Minimum angle B is 15.34 ±5.1 °,15.23 ±5.5 °respectively.The maximum angle A was 52.66 ±12.0 °and the minimum angle B was about 14.7 ±6.7 °and 14.98±6.1 °respectively.Conclusion: For most patients,the application of miniscrews implant mandibular external oblique zone denture overall far shift,should choose the diameter of 2.0mm,length 10 mm between miniscrews implantation of mandibular first molar and the second molar distal 1mm,alveolar crest below 5mm-7mm;It is suggested that the safe implantation angle of the miniscrews should be 15 °-40 °with the long axis of the tooth.It is believed that a more secure and stable anchorage can be obtained by understanding the above operation points.Experiment 3:Three-Dimensional finite element Analysis of Micro-Implant Nail Anchorage against Distal displacement of dentitionObjective:In order to guide the clinical,a three-dimensional finite element model will be established for the distal displacement of miniscrews in dentition,and the initial displacement of each tooth in three dimensional direction will be studied under the action of different loading sites and different height traction hooks from the biomechanical point of view.Methods: After clinical screening,the mandible and lower dentition of a 22-year-old female with proximal relationship were selected as data collection objects.After the mandibular third molar was extracted and the upper and lower teeth were leveled out,CBCT was photographed and imported it into Mimics17.0 software in Dicom format for3 D generation.Using the inverse function of 3-matic Research 9.0R software,the 3D solid models of mandible,lower dentition,bracket,arch wire and so on were fitted one by one,and the meshes,boundary constraints,etc.Finally,a three-dimensional finite element model of miniscrews for distal mandibular full-dentition was established.Based on the experiment one,two conclusion,The miniscrews position is : Between the first and second molars of the mandible moved about 1 mm distalization,6 mm below alveolar crest,Theminiscrew was implanted at an angle of 30 °to the long axis of the tooth.The clinical treatment was simulated by loading 3 N force / side between the traction hook and the miniscrews.Four conditions are set:?Condition A1: the traction hook with a height of 2mm was fixed between the bilateral lower incisors and the canine brackets.? Condition A2: the traction hook with a height of 7 mm was fixed between the bilateral lower incisors and the canine brackets.?Condition B1: the traction hook with a height of 2mm is fixed between the bilateral canine and the first premolar bracket.Condition B2: the traction hook with a height of 7 mm was fixed between the bilateral canine and the first premolar bracket.The initial displacement of mandibular central incisors,canines,first molars and second molars under different loading conditions was studied.Results:(1)A three-dimensional finite element model of micro-implant Anchorage against distal mandibular full-dentition was established.(2)?Lower middle incisor:When loading A1,B1,B2,a counterclockwise rotation of the root and corona dentis of the lower central incisor occurs in the same tongue direction(the crown movement is obviously larger than the root);but under loading A2,the lower central incisors had clockwise rotation of crown to lip and root to tongue(crown movement was significantly greater than root movement).?Lower canine:When loading A1,A2,the lower canine teeth have counterclockwise rotation of both crown and root to the tongue(the crown movement is obviously greater than the root movement).When the load is B1,the crown and root of the canine are all moving towards distalization,almost without rotation,but the movement trend is small.but under the loading of B2,the canine crown moves to mesialization,and the root moves to distalization(the crown movement is obviously larger than the root movement)clockwise rotation.? The initial movement trend of the first molar and the second molar is similar in the four working conditions.The crown and the root are rotated counterclockwise in the distal direction(the crown movement is obviously larger than the root movement).Conclusion:(1)The 3D finite element model with high geometric similarity and accurate use of micro-implant nail for the distal movement of mandibular whole dentitioncan be established by using the software CBCT,Mimics,3-matic Research 9.0R,Simcenter3 D 12.0.(2)?By changing the height of the traction hook,the rotation of the anterior teeth and even the entire lower dentition can be controlled.?In the treatment of mild to moderate Class ? malocclusion by using miniscrew,it is suggested that the traction hook(oriented to gingival side),which is 2 mm in height,be fixed between the mandibular lateral incisor and the canine.Experiment 4 Evaluation of clinical actual tooth movement before and after treatment with miniscrew removable dentition by using CBCTObjective: In this study,a prospective study was conducted to evaluate the three-dimensional movement of tooth before and after orthodontic treatment with miniscrew removable dentition at the oblique line.Methods: From the orthodontic department,15 patients with mild or moderate III malocclusion were selected.The mandibular total dentition distant movement should be carried out by using the mandibular external oblique miniscrew in the formulation of the correction plan.The CBCTs of the mandible and lower dentition were collected after the implants were implanted and before the distal dentition(T0)and when the distal dentition was completed(T1).All the data were stored in Dicom format and imported into Mimics17.0 for 3D reconstruction of mandible and lower dentition.The relevant mark points were defined on the 3D model and 3D coordinate system was established.The changes of the position of each marker in three-dimensional coordinate system were measured before and after treatment.Results: After 8±2.3 months of correction,the occlusal relationship was significantly improved.? The Lower incisors were retracted 4.1 mm and extruded 2.4 mm at the crown on average,and retracted 2.3mm at the root on average.?The crown of canines showed3.5 mm of distalization,extruded 2.0 mm averagely,and the width between left and right canines were decreased by 1.8 mm averagely.The root were moved distally 2.0mm on average,and the width of two roots were decreased 1.1mm averagely.?The mesial buccal cusp of lower first molar' crowns showed 3.1mm distalization and 1.3mm intrusion andwidth increased by 2.3mm averagely.The mesial root of first molars showed 1.8mm distalization and 0.7mm intrusion on averagely.(4)The mesial buccal cusp of lower first molar' crowns showed 2.9mm and 1.8mm intrusion and width increased by 2.5mm.The mesial root of first molars showed1.7mm distalization and 1.1mm intrusion?There was no statistical difference in the other reference indexes.Conclusion: The implantation of miniscrew at the oblique line can provide sufficient and stable anchorage for distal movement of lower dentition.It is an effective method for the treatment of mild and moderate III malocclusion. |
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