Initial forces experienced by the anterior and posterior teeth during dental-anchored or skeletal-anchored en masse retraction in vitro

Objective:To investigate initial forces acting on teeth around the arch during en masse retraction using an in vitro Orthodontic SIMulator (OSIM).Materials and Methods:The OSIM was used to represent the full maxillary arch in a case wherein both first premolars had been extracted. Dental and skeletal anchorage to a posted archwire and skeletal anchorage to a 10-mm power arm were all simulated. A 0.019 × 0.025-inch stainless steel archwire was used in all cases, and 15-mm light nickel-titanium springs were activated to approximately 150 g on both sides of the arch. A sample size of n = 40 springs were tested for each of the three groups. Multivariate analysis of variance (α = 0.05) was used to determine differences between treatment groups.Results:In the anterior segment, it was found that skeletal anchorage with power arms generated the largest retraction force (P < .001). The largest vertical forces on the unit were generated using skeletal anchorage, followed by skeletal anchorage with power arms, and finally dental anchorage. Power arms were found to generate larger intrusive forces on the lateral incisors and extrusive forces on the canines than on other groups. For the posterior anchorage unit, dental anchorage generated the largest protraction and palatal forces. Negligible forces were measured for both skeletal anchorage groups. Vertical forces on the posterior unit were minimal in all cases (<0.1 N).Conclusions:All retraction methods produced sufficient forces to retract the anterior teeth during en masse retraction. Skeletal anchorage reduced forces on the posterior teeth but introduced greater vertical forces on the anterior teeth.     

Effectiveness of an anterior mini-screw in achieving incisor intrusion and palatal root torque for anterior retraction with clear aligners:: A finite element study

ObjectivesTo analyze the biomechanical system of anterior retraction with clear aligner therapy (CAT) with and without an anterior mini-screw and elastics.Materials and MethodsModels including a maxillary dentition (without first premolars), maxilla, periodontal ligaments (PDLs), attachments, and aligners were constructed and imported to finite element software. Three model groups were created: (1) control (CAT alone), (2) labial elastics (CAT with elastics between the anterior mini-screw and buttons on central incisors), and (3) linguoincisal elastics (CAT with elastics between the anterior mini-screw and precision cuts on the lingual sides of the aligner). Elastic forces (0–300 g, in 50 g increments) were applied.ResultsCAT alone caused lingual tipping and extrusion of the incisors. Labial elastics caused palatal root torquing and intrusion and mesial tipping of the central incisors, while linguoincisal elastics produced palatal root torquing and intrusion of both central and lateral incisors. Second premolars were intruded in all three groups, with less intrusion in the linguoincisal elastics group. For the control group, stress was concentrated on both labial and lingual root surfaces, alveolar ridge, and cervical and apical PDLs. Stress was more concentrated in the labial elastics group and less concentrated in the linguoincisal elastics group.ConclusionsCAT produced lingual tipping and extrusion of incisors during anterior retraction. Anterior mini-screws and elastics can achieve incisor intrusion and palatal root torquing. Linguoincisal elastics are superior to labial elastics with a lower likelihood of buccal open bite. Root resorption and alveolar defects may occur in CAT, more likely for labial elastics and less likely for linguoincisal elastics.     

国产微螺钉种植体支抗压低牙齿动物实验研究

目的研究国产微螺钉种植体支抗压低磨牙过程中种植体-骨界面结合状况及种植体稳固度。方法4条成年Beagle犬分别于双侧下颌前磨牙根尖下植入国产微螺钉种植体共8枚。植入后即刻以种植体为支抗对下颌前磨牙施以压低力，力值100g，时间3个月。加力结束后进行种植体及其周围组织的组织学检查。结果所有被加载的8枚种植体均保持良好稳固度，无移位。下颌前磨牙垂直高度平均减小3．12mm，同时出现了一定程度的颊侧倾斜，未见明显根尖及根分歧牙骨质吸收。加载种植体平均骨整合率为39．5％。结论微螺钉种植体支抗可以完成牙齿的压低移动并可保持良好稳固度。骨整合主要发生在种植体-皮质骨界面，松质骨中极少发生骨整合。     

Changes in maxillary incisor dental pulp blood flow during intrusion by mini-implants

Aim. The aim of this clinical study was to identify changes in pulpal blood flow (PBF) in human central incisors resulting from short- and long-term intrusive orthodontic forces from mini-implants. Materials and methods. A total of 40 sound upper central and lateral incisors in 20 patients scheduled for intrusion for orthodontic reasons were divided into two groups. From each group, 20 teeth were subjected to intrusive force from mini-implants (Group 1 = Light Force: 40 g; Group 2 = Heavy Force: 120 g), whereas the remaining 20 contralateral teeth were not subjected to forces from mini-implants and served as controls. Laser-Doppler flowmetry (LDF) measurements were recorded at baseline and at 3 days and 3 weeks following intrusion. Results. PBF decreased significantly at 3 days (Light Force Group: 7.72 ± 0.50; Heavy Force Group: 7.72 ± 0.52) and then increased towards baseline at 3 weeks (Light Force Group: 10.37 ± 0.58; Heavy Force Group: 10.31 ± 0.45) following intrusion. Conclusions. In other words, despite slight regressive changes in pulpal tissue in the short-term, PBF improved after 3 weeks following intrusion by mini-implants, indicating that the changes observed in PBF is reversible, even following radical incisor intrusion.     

微种植钉周期性加力压低犬磨牙牙周组织中MMP-2的表达

目的使用微种植钉压低犬磨牙,观察周期性加力不同时间牙周组织中MMP-2的表达。方法选取健康成年雄性纯种Beagle犬3只,于左侧上颌第二、第三前磨牙颊、腭侧根分叉区各植入1颗微种植钉,施加150 g的力压低犬牙;每4周加力1次。左侧磨牙作为实验组,随机分为3组,分别加力12、24、36周,右侧磨牙为空白对照组。处死动物后,取上颌第二、第三前磨牙及其周围牙周组织,固定、脱钙及制作组织学标本,切片后行MMP-2免疫组织化学染色并光镜下观察,IPP软件计算MMP-2的平均吸光度值。采用SPSS17.0 软件包对数据进行统计学分析。结果免疫组织化学染色结果显示,对照组犬磨牙牙周组织中MMP-2仅有少量表达;实验组MMP-2的表达量显著升高;压低24周,牙周组织中MMP-2的表达量达最高;压低36周表达量下降,但与对照组仍有显著性差异;压低12、24、36周组间相比,差异均无显著性（P>0.05）。结论MMP-2参与了犬牙压低过程中牙周组织的改建;在周期性加力过程中,牙周组织中MMP-2的表达没有随着压低时间的延长而明显升高。证明使用微种植钉周期性加力压低磨牙,磨牙牙周组织保持一种动态平衡的骨改建过程。     

The effect of orthodontic extrusion on traumatically intruded teeth

The management of traumatically intruded permanent incisors is controversial. Some authors suggest a decreased incidence of ankylosis in cases treated with orthodontic extrusion. The purpose of this study was to examine two common management techniques for traumatic intrusion, orthodontic extrusion, and observation for re-eruption. The four first premolars of three shepherd dogs were traumatically intruded with a mallet while a holding device was used to prevent tooth fracture. Five to 7 days following the injury, orthodontic force was applied unilaterally while the contralateral tooth served as the untreated control. To facilitate serial periapical radiography, x-ray jigs were fabricated for each animal and tantalum implants were placed in the bone distal to the permanent canine and first and second premolars. Observations included radiographic measurement of tooth movement, clinical estimates of tooth mobility, and radiographic and histologic assessment of root resorption, ankylosis, and periapical pathosis. The amount of traumatic intrusion varied from less than 0.5 to 4.1 mm. Following 11 to 13 weeks of force activation, 10 of 12 traumatized teeth showed clinical, radiographic, and histologic evidence of ankylosis irrespective of orthodontic treatment. Whereas the ankylosed teeth did not move with orthodontic forces, the teeth used for force application were orthodontically intruded 1.7 to 6.5 mm. When the injury to the tooth was severe, orthodontic extrusion had little effect on repositioning of the injured tooth but resulted in undesirable movement of the anchorage teeth. When the injury was less severe, orthodontic forces facilitated repositioning of the affected tooth.     

黄金比例面具对种植体支抗压低上切牙改善露龈笑的美学评价初探

目的 利用黄金比例面具对露龈笑进行分类,并评价使用种植体支抗压低上切牙后患者露龈笑的改善程度,探讨种植体支抗压低上切牙治疗露龈笑过程中唇-齿-龈关系的变化趋势.方法 选择17例露龈笑患者,女性16例,男性1例,年龄16～40岁,平均26.2岁.于上颌侧切牙和尖牙间唇侧植入微螺钉种植体支抗压低上切牙,在Photoshop软件中将正面微笑黄金比例面具标准化模板与治疗前后的正面微笑像重叠,比较治疗前后正面微笑像唇、齿、龈在黄金比例面具相应区域内所占比例的变化,定性分析并评价露龈笑的改善程度.结果 17例患者的上切牙均被成功压低,露龈笑明显改善,疗程平均9.8个月.通过黄金比例面具分析发现,治疗前露龈笑形成原因不同,治疗后患者正面微笑像唇-齿-龈关系基本符合黄金比例面具的唇-齿-龈关系.结论 通过使用黄金比例面具对露龈笑患者的唇-齿-龈关系进行分析,可以对使用种植体支抗压低前牙改善露龈笑患者的矫治效果进行初步临床评价.     

Comparison of anterior and posterior mini-implant-assisted maxillary incisor intrusion: Root resorption and treatment efficiency

Objective:To compare, through cone-beam computed tomography (CBCT), the root resorption and treatment efficiency of two different mini-implant-assisted modalities in intruding the maxillary incisors.Materials and Methods:Thirty-two adults who had deep bite and elongated maxillary incisors were randomly allocated to two groups: anterior mini-implant group (AMG) and posterior mini-implant group (PMG). In the AMG, approximately 40 g of force was applied per side with elastic chains from mini-implants placed between the lateral incisors and canines and in the PMG, with beta-titanium wires from mini-implants placed between the second premolars and first molars. This study was conducted on CBCT scans taken before intrusion and after 4 months of intrusion. Data were analyzed by means of a paired t-test, independent t-test, and Pearson’s correlation test.Results:One patient was excluded from the AMG due to mini-implant loosening. While the incisors showed a significant reduction in length and volume, this amount was greater in the AMG, especially in the central incisors (P < .05). Together with the mean intrusion rates of 0.62 and 0.39 mm/mo in the AMG and PMG respectively, the center of resistance of the incisors showed distal movement with labial tipping; these changes were greater in the PMG (P < .001). Volumetric root resorption was correlated with the amount of intrusion (P < .05).Conclusions:Intrusion anchoring from posterior mini-implants is preferred in cases of upright incisors, as the use of such mechanics directs the roots into the spongiosa where they undergo less root resorption and more labial tipping.     

微种植体支抗压低上前牙的Typodont实验研究

目的在Typodont模型上,模拟临床应用微种植体支抗压低上前牙的过程,研究不同部位支抗对上前牙压低效果的影响。方法制作上前牙槽骨垂直发育过度的标准Typodont模型42个,随机分为ABC三组,每组14个。A组在中切牙间植入微种植体,B组在中切牙和侧切牙间植入微种植体,C组在侧切牙和尖牙间植入微种植体,应用镍钛螺簧施0．98N（100g）力压低上前牙。应用三维坐标测量仪测量牙齿标记点的三维位置并获得点云数据,Imageware12软件测量牙齿的压低量及唇（颊）倾斜度,并同时拟合牙弓曲线,研究牙弓及[牙合]平面的变化。结果①三组中上前牙均有不同程度的压低（0．9220mm±0．3037mm～5．2354mm±0．9620mm）,中切牙的压低量〉侧切牙〉尖牙,微种植体的位置越靠前,压低效果越明显。②所有牙齿均向前移动,上前牙有不同程度的唇倾,微种植体的位置越靠后,牙齿向前移动越少,唇倾越少。③微种植体的位置越靠后,牙弓及[牙合]平面的变化越小。结论①应用微种植体支抗可以有效地压低上前牙,上磨牙并未伸长。②微种植体的位置越靠后,上前牙的压低量越小,唇倾越少,牙弓变化及[牙合]平面角减少的趋势越小。反之亦然。     

无托槽隐形矫治拔牙病例的后牙不同轴倾度对牙齿三维力学影响

目的 研究无托槽隐形矫治技术拔除双侧上颌第一前磨牙病例整体内收前牙，后牙不同轴倾度时，各个牙齿的瞬时受力情况。方法 设置4组后牙不同轴倾度的上颌牙列，T1组后牙为正常牙合轴倾度，T2组后牙在T1组基础上后倾5°,T3组后牙在T1组基础上前倾5°,T4组后牙在T1组基础上前倾10°。拔除双侧第一前磨牙，整体内收前牙0.25 mm,在矫治器六轴力传感器测试平台上测量4组牙列中各个牙齿在三维方向的瞬时力。每组牙列设计12副隐形矫治器。结果 与T1组相比，T2组切牙伸长力减小，尖牙远中向力增加，后牙近中向力减小，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。与T1组相比，T3和T4组切牙舌向力和伸长力增大，尖牙远中向力增大，后牙近中向力也增大，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。结论 后牙后倾时利于前牙转矩的表达，有助于保护后牙支抗，但增加了磨牙的颊向力和伸长力。后牙前倾时，前牙更容易出现转矩丢失，覆牙合加深的现象。后牙越前倾，覆牙合越容易加深，后牙支抗容易丢失。     

Stress distribution pattern in a root of maxillary central incisor having various root morphologies: A finite element study

Objective:To investigate stress distribution in the roots of maxillary central incisors bearing various types of root morphologies with regard to application of different types of orthodontic forces using the finite element model (FEM).Materials and Methods:FEMs of maxillary central incisors with different root morphologies (normal, short, blunt, dilacerated, and pipette) were constructed, and orthodontic forces in various directions (intrusion, extrusion, tipping, and rotational) were applied to the tooth axis at the bracket level.Result:On application of various forces, significantly increased stress was seen at the apex of the root with dilacerated morphology and at the cervical one-third region of the tooth with the short root. Increased stress was observed at the middle one-third region in the tooth with the pipette-shaped root during intrusion and extrusion.Conclusions:In the present study, the stress distribution pattern indicates that the maxillary central incisors with deviated root morphology are at higher risk of root resorption.     

Forces and moments delivered by novel,thinner PET-G aligners during labiopalatal bodily movement of a maxillary central incisor: An in vitro study

Objective:To evaluate whether overloading of teeth can be avoided by utilizing aligners with reduced thicknesses of 0.4 mm or 0.3 mm.Materials and Methods:The experimental setup included an acrylic maxillary jaw model with tooth 11 separated and fixed via a 3-D force-moment transducer to a hexapod for experimental movement. Aligners tested were fabricated on duplicate stone models using commercially available polyethylene terephthalate glycol (PET-G) foils with thicknesses between 0.5 and 0.75 mm, and novel 0.4-mm- and 0.3-mm-thick foils. With the test aligner seated, 11 was bodily displaced in a labiopalatal direction in the range of ±0.25 mm while all six force-and-moment components exerted on this tooth were registered.Results:With the thinnest commercially available 0.5-mm aligner, median forces of −7.89 N and 8.37 N were measured for the maximum 0.25-mm movement of 11 in a labial and palatal direction, respectively. In comparison, force values were 35% and 71% lower for the novel aligners with a thickness of 0.4 mm and 0.3 mm, respectively.Conclusions:Novel “leveling” aligners with reduced thickness may reduce overloading of individual teeth during aligner therapy. Due to form instability of 0.3-mm aligners, we suggest a novel sequence of 0.4–0.5–0.75 mm for aligner systems using several foil thicknesses for load graduation within single setup steps. This would combine low stiffness of the initial aligner and relatively constant load increases throughout the treatment.     

Scanning electron microscopy evaluation of aligner fit on teeth

Objectives:The fitting of aligners on anchorage teeth is a crucial factor in clear aligner orthodontics. The purpose of this experimental study was to evaluate the fitting of two aligner systems, Invisalign and CA-Clear Aligner, using scanning electron microscopy (SEM).Materials and Methods:Passive aligners (Invisalign and CA-Clear Aligner) were adapted on resin casts obtained by stereolithography (STL) files of a patient, and then sectioned buccolingually. Upper and lower central incisors, upper and lower first premolars, and upper and lower first molars were the regions analyzed. Representative microphotographs of sections were taken with a scanning electron microscope (SEM); a total of 160 micrometric measurements were obtained and analyzed with ANOVA tests.Results:Invisalign provided an overall better fit on lower incisors (F = 11.48, P = .0095) and on lower molars (F = 19.93, P = .0012). Considering the different regions, Invisalign provided better fit at the gingival edge of the buccal aspect on lower incisors (F = 11.33, P = 0.0056) and at the gingival edge of the lingual aspect on upper premolars (F =5.34, P = 0.0047). On the upper molars, Invisalign provided better fit at the gingival edge of the buccal aspect, while CA-Clear Aligner provided better fit at the buccal maximum convexity, on the buccal cusp, on the occlusal groove and at the palatal cusp. On lower molars, Invisalign showed a more accurate fit at the buccal aspect points.Conclusions:Invisalign and CA-Clear Aligner exhibited comparable fit on anchorage teeth. Invisalign provided better fit at the gingival edges of aligners, while the CA-Clear Aligner provided better fit on complex occlusal surfaces.     

Maxillary incisor root resorption induced by ectopic canines: A follow-up study, 13 to 28 years posttreatment

Objective: To evaluate the long-term clinical and radiographic effects of maxillary incisor root resorption in cases of ectopic canines treated during the late 1970s and 1980s in Jönköping, Sweden.Subjects and Methods:The material comprised 55 incisors in 38 subjects. The posttreatment follow-up time was 13 to 28 years. All subjects underwent intraoral radiography, 33 were referred for computed tomography or cone beam computed tomography, and 24 also underwent clinical examination. The severity of incisor root resorption was correlated with clinical characteristics. Radiographs of the resorptive lesions were documented in detail and compared with intraoral radiographs taken immediately posttreatment.Results:Four incisors in three subjects had been lost, in part because of root resorption. Of the 36 incisors with root resorption, the lesions were unchanged in 26 teeth, improved in three teeth, and exacerbated in seven. In one case the resorption had progressed to pulpal exposure, necessitating endodontic treatment. For most of the incisors, the periodontal ligament was more clearly defined and the lamina dura showed improved trabeculation. The clinical characteristics of the incisors with resorption were not significantly different from those of sound incisors.Conclusions:In this long-term follow-up, most cases of incisor root resorption induced by ectopic maxillary canines did not progress and teeth with root resorption showed no clinically relevant symptoms. The prognosis for long-term survival of teeth with resorbed roots is good, but in cases where extraction is indicated, lateral incisors with severe root resorption should be extracted in favor of healthy premolars.     

Evaluation of intrusive mechanics of the type "segmented arch" on a macerated human skull using the laser reflection technique and holographic interferometry

Twelve different systems of intrusion, based on the principle of the "segmented arch," were evaluated on a macerated human skull. The number of teeth involved in the anterior unit and the location of the application points of intrusive force were considered to be variables. Initial displacements of the anterior teeth after loading were registered by means of the laser reflection technique and double exposure holographic recordings. An attempt was made to define "this" intrusive system, achieving the most genuine intrusion (for definition, see text) without flaring of the teeth. When two central incisors were incorporated in the sectional wire, strong torque forces appeared, especially when the intrusive forces seized more distally. When four or six anterior teeth were pinned in the sectional wire, tooth movement seemed to be under better control. When the six front teeth were incorporated in the sectional wire, the center of resistance (for definition, see text) was located more to the distal side of the canines. It seemed more difficult, however, to define the center of resistance of the four incisors; it was situated approximately distal to the lateral incisors. In some of the intrusive systems, the teeth underwent independent mesial or distal rotations. This was easily observed with the laser measuring techniques used.     

Force magnitude as a variable in maxillary buccal segment intrusion in adult patients with skeletal open bite:: A double-blind randomized clinical trial

ObjectivesTo compare the effects of two different force magnitudes on maxillary posterior segment intrusion using mini-screws. The null hypothesis was that there would be no difference between the two force magnitudes.Materials and MethodsAdult patients with skeletal open bite and a dental open bite ranging from 3 to 8 mm were recruited for this trial. The comparator group had 200 g of intrusive force applied for posterior segment intrusion, whereas 400 g of force was applied in the intervention group. Primary outcomes were the amount of posterior teeth intrusion and anterior open bite closure.ResultsTwenty-two subjects were randomized to include 11 participants in each group. One participant dropped out in each group, leaving us with 10 subjects to be analyzed per group. There was statistically significant posterior teeth intrusion of 2.42 ± 2.06 and 2.26 ± 1.87 mm for the comparator and intervention groups, respectively, with no difference between them. Statistically significant open bite closure was achieved in both groups, measuring 2.24 ± 1.18 and 3.15 ± 1.06 mm in the comparator and intervention groups, respectively, with no difference between them.ConclusionsBoth the 200 g and 400 g intrusive forces yielded similar outcomes in terms of posterior teeth intrusion and anterior open bite closure.     

Root resorption after orthodontic intrusion and extrusion: an intraindividual study

The aim of this investigation was to compare root resorption in the same individual after application of continuous intrusive and extrusive forces. In nine patients (mean age 15.3 years), the maxillary first premolars were randomly intruded or extruded with a continuous force of 100 cN for eight weeks. Eleven maxillary first premolars from six randomly selected orthodontic patients served as controls. Root resorption was determined using scanning electron microscopy. Quantitative assessment of the percentage of resorbed area of the total root surface was performed on composite micrographs. The severity of root resorption was also assessed by visual scoring of the roots. Root resorption mainly occurred at the apical part of the roots in both experimental groups. A significant difference in root resorption was found between the intruded and the control teeth (P = .006) but not between the extruded and the control teeth. However, the mesial and distal root surfaces showed resorption on 5.78 +/- 3.86% of the root surface of the intruded teeth and 1.28 +/- 1.24% of the root surface of the extruded teeth, and this difference was significant (P = .004). In addition, a large individual variation was found. From this study, it can be concluded that intrusion of teeth causes about four times more root resorption than extrusion. Because the amount of root resorption due to intrusion or extrusion in the same patient is correlated, every clinician should be aware that the extrusion of teeth might also cause root resorption in susceptible patients.     

Change in dental pulp parameters in response to different modes of orthodontic force application

Objectives:(1) To evaluate dental pulp sensitivity by electrical pulp testing and measure aspartate aminotransferase activity in the pulp after 14 days of orthodontic intrusion, and (2) to compare those measurements with measurements obtained in teeth after 7 days of intrusion and 7 days of rest.Materials and Methods:The study sample included 13 subjects (mean age  =  16.5 ± 2.7 years). For every subject, before extraction, two contralateral premolars were included in a spring and loaded by a force. Two study groups were formed: Group A, teeth with 14 days of mechanical load, and Group B, teeth with 7 days of mechanical load plus 7 days of rest. Electrical pulp testing and aspartate aminotransferase activity measurements were performed after 14 days in all tested teeth. After extraction, aspartate aminotransferase activity in the pulp was determined spectrophotometrically at 20°C.Results:Mean aspartate aminotransferase activity values were 0.21 U/mg (SD  =  0.15) in Group A and 0.27 U/mg (SD  =  0.17) in Group B. Mean electrical pulp testing readings were 38.92 µA (SD  =  24.61) in Group A and 36.77 µA (SD  =  26.84) in Group B. Mean values of the intrusive force magnitude did not differ in both groups.Conclusions:Different durations of orthodontic intrusion, defined as 14 days of load and 7 days of load followed by 7 resting days, were not reflected by electrical pulp testing or by aspartate aminotransferase activity levels in the pulp of the affected teeth. However, the response threshold to electrical pulp stimulation was elevated in all tested teeth.     

Root resorptions in upper first premolars after application of continuous intrusive forces

A scanning electron microscopy study of possible root resorptions and their localization after application of continuous forces of different magnitudes was conducted. Twelve upper first premolars, indicated for extraction, were previously intruded with constant forces. The teeth were divided into 3 groups: 1. non-moved control teeth, 2. continuous force application of 50 cN for 4 weeks, 3. continuous force application of 100 cN for 4 weeks. Specially designed NiTi-SE-stainless steel springs were utilized to exert the actual forces. After experimental tooth movement, the extracted teeth were dehydrated, metal-coated and examined by scanning electron microscopy. The intruded teeth showed resorptive areas consisting of lacunae (concavities) in the mineralized root surface. The teeth moved with 50 cN showed in the apical third several, in the medial third few, and in the cervical third no resorptive areas. In the case of the teeth moved with 100 cN, we observed resorptive areas in most of the apical third—including the apex contour—, several in the medial third, and none in the cervical third. In the control group no resorptions were observed. Thus, our results suggest that intrusion of human teeth with continuous forces induces root resorption, depending on the magnitude of force applied.     

无托槽隐形矫治器联合微种植体内收并压低上前牙的三维有限元分析

目的 运用三维有限元技术研究无托槽隐形矫治器联合微种植体内收并且压低上前牙时,使用不同方式的微种植体牵引的治疗效果差异。 方法 获取患者上颌骨及牙体等锥形束CT数据,使用Mimics、Geomagic、Solidworks和Ansys软件建立所需要的三维有限元模型以及无托槽隐形矫治器。根据微种植体的设计不同,分为4个实验组。第1组为空白对照组;第2组在上颌双侧第二前磨牙和第一磨牙之间各植入一颗微种植体,在双侧尖牙牙套上沿内收方向加0.98 N的力;第3组在第2组基础上,在中切牙之间植入一颗微种植体加力0.98 N压低上前牙;第4组在第2组基础上,在双侧中切牙和侧切牙之间各植入一颗微种植体加力0.56 N压低上前牙。对各组进行受力分析,比较不同位点植入微种植体牵引加力时前牙转矩的改变、运动趋势以及应力分布。 结果 4组中所有上颌切牙皆表现出内收和压低的趋势,且伴有不同程度的转矩改变。第3组上颌中切牙及侧切牙在矢状向冠根位移差最小,第4组上颌中切牙及侧切牙压低值最大,第2组最大应力集中值最大。 结论 将微种植体植入上颌中切牙之间进行牵引更利于转矩控制;而植入上颌中切牙与侧切牙之间并联合前牙垂直牵引时更利于单纯压低,在一定程度上避免了“过山车”效应。