UNASSIGNED: Overtreatment design of clear aligner treatment (CAT) in extraction cases is currently primarily based on the clinical experience of orthodontists and is not supported by robust evidence on the underlying biomechanics. This study aimed to investigate the biomechanical effects of overtreatment strategies involving different maxillary anterior teeth intrusion patterns during anterior teeth retraction by CAT in extraction cases.
UNASSIGNED: A finite element model of the maxillary dentition with the first premolar extracted was constructed. A loading method of clear aligners (CAs) based on the initial state field was proposed. The iterative method was used to simulate the long-term orthodontic tooth movement under the mechanical load exerted by the CAs. Three groups of CAs were utilized for anterior teeth retraction (G0: control group; G1: incisors intrusion group; G2: anterior teeth intrusion group). Tooth displacement and occlusal plane rotation tendency were analyzed.
UNASSIGNED: In G0, CAT caused lingual tipping and extrusion of the incisors, distal tipping and extrusion of the canines, mesial tipping, and intrusion of the posterior teeth. In G1, the incisors showed minimal extrusion, whereas the canines showed increased extrusion and distal tipping tendency. G2 showed the smallest degree of posterior occlusal plane angle rotation, while the inclination tendency of the canines and second premolars decreased.
UNASSIGNED: 1. In CAT, tooth displacement tendency may change with increased wear time. 2. During anterior teeth retraction, the incisor intrusion pattern can provide effective vertical control for the lateral incisors but has little effect on the central incisors. Anterior teeth intrusion patterns can alleviate the inclination of canines and second premolars, resulting in partial relief of the roller-coaster effect.

Orthodontic space closure of extraction sites can be initiated early, within 1-week post-extraction, or it can be delayed for a month or more.
This systematic review aimed to evaluate the effect of early versus delayed initiation of space closure after tooth extraction on the rate of orthodontic tooth movement.
Unrestricted search of 10 electronic databases was conducted until September 2022.
Randomized controlled trials (RCTs) investigating the initiation time of space closure of extraction sites in patients undergoing orthodontic treatment were included.
Data items were extracted using a pre-piloted extraction form. The Cochrane\'s risk of bias tool (ROB 2.0) and the Grading of Recommendations, Assessment, Development, and Evaluation approach were used for quality assessment. Meta-analysis was undertaken if there are at least two trials reporting the same outcome.
Eleven RCTs met the inclusion criteria. Meta-analysis revealed that early canine retraction resulted in a statistically significant higher rate of maxillary canine retraction when compared to delayed canine retraction [mean difference (MD); 0.17 mm/month, 95% CI: 0.06 to 0.28, P = 0.003, 4 RCTs, moderate quality]. Duration of space closure was shorter in the early space closure group, but not statistically significant (MD; 1.11 months, 95% CI: -0.27 to 2.49, P = 0.11, 2 RCTs, low quality). The incidence of gingival invaginations was not statistically different between early and delayed space closure groups (Odds ratio; 0.79, 95% CI: 0.27 to 2.29, 2 RCTs, P = 0.66, very low quality). Qualitative synthesis found no statistically significant differences between the two groups regarding anchorage loss, root resorption, tooth tipping, and alveolar bone height.
Based on the available evidence, early traction within the first week after tooth extraction has a minimal clinically significant effect on the rate of tooth movement compared to delayed traction. Further high-quality RCTs with standardized time points and measurement methods are still needed.
PROSPERO (CRD42022346026).

Long-term missing teeth can lead to alveolar bone loss in the edentulous area. Guided bone regeneration (GBR) is a bone augmentation method. It is widely used in clinical practice and broadens the indications of orthodontic treatment to a certain extent. This article reports a case of an adult patient with edentulous space in the maxillary central incisor, which was successfully closed through orthodontic treatment combined with GBR. This study will provide a re-ference for future clinical work.
个别牙长期缺失会导致缺牙区牙槽骨丧失，引导骨再生术（GBR）是骨增量的一种方法，临床应用广泛，一定程度上拓宽了正畸治疗的适应证。本文报告1例正畸治疗结合GBR关闭上颌中切牙缺失间隙的成年患者病例，为今后临床工作提供参考。.

OBJECTIVE: To evaluate the morphometric changes in maxillary and mandibular anterior alveolar bone after orthodontic treatment and retention for 18-24 months by cone-beam computed tomography (CBCT).
METHODS: Thirty-four adolescent patients (12 males and 22 females; mean age: 14.29 ± 1.24 years) diagnosed with bimaxillary dentoalveolar protrusion and with extractions of the 4 first premolars were included.
METHODS: The labial and lingual (palatal) alveolar bone thickness, height and root length of the maxillary and mandibular anterior teeth were assessed using CBCT imaging at the pre-treatment (T1), post-treatment (T2) and retention phases (T3). Voxel-based superimpositions of the T2 and T3 images were performed, and the distances of incisal and apical movement between T2 and T3 were measured to determine whether relapses occurred.
RESULTS: After orthodontic treatment, the labial and lingual (palatal) bone height decreased significantly (P < .05) and the labial thickness at the crestal (L1), midroot (L2), and apical levels (L3) had no significant change, while the lingual (palatal) bone thickness at all three levels decreased significantly (P < .05). After 18-24 months of retention, the lingual (palatal) height and the lingual (palatal) thickness at the crestal (L1) level increased significantly (P < .05). There were no obvious incisal and apical movements of the anterior teeth between T2 and T3 (P > .05), indicating that no relapses occurred.
CONCLUSIONS: Even though lingual (palatal) alveolar loss occurred due to the orthodontic treatment, the cervical alveolar bone seemed to recover over time. Therefore, appropriate camouflage treatment can be used in patients with bimaxillary dentoalveolar protrusion, and this treatment will not irreversibly deteriorate periodontal health and affect the orthodontic treatment stability.

Malocclusion has been seriously endangering human oral function. The most effective and mature therapy is orthodontic treatment. But the relationship between the shape of the T-loop and the orthodontic force is unclear, and the precise mathematical model has not been established. In this article, the dynamic orthodontic force prediction model of the T-loop was established by analyzing the treatment process of the T-loop. The model was based on the dynamic resistance model of waxy dental jaw, the theory of beam deformation, and the deformation characteristics of the T-loop. In the experimental process, 11 kinds of orthodontic archwires were used as experimental samples, including 2 kinds of common archwire materials, 7 kinds of cross-sectional sizes, and 10 kinds of clearance distances. The T-loop was put into the extraction space and immersed in 75°C constant temperature water for 2 min. And the experimental data were measured and collected by the dynamic force measuring device. The experimental results show that the cross-sectional size and the clearance distance are positively correlated with the orthodontic force. The influence of the clearance distance on the orthodontic force is greater than that of the cross-section size. The deviation rates between the experimental values of orthodontic force and the theoretical values are between 1.10% and 9.09%, which verifies the accuracy of the dynamic orthodontic force prediction model. The model can predict the orthodontic force, improve the treatment effect, shorten the treatment cycle, and provide reference and guidance for orthodontists to carry out orthodontic treatment safely and effectively.

Objective: To investigate the mechanical effects during en-mass retraction of maxillary anterior teeth with clear aligner using three-dimensional finite element method. Methods: Cone-beam CT (CBCT) was used to scan a female orthodontic patient (26 years old, from Department of Orthodontics, Stomatological Hospital of Chongqing Medical University) whose maxillary first premolars were extracted and maxillary dentition had been aligned and leveled. A finite element model including maxillary teeth-periodontal ligament (PDL)-alveolar bone-clear aligner was established by using Mimics 17.0, SolidWorks 2016 and Geomagic Studio 2015 software packages. The process of 0.2 mm en-mass retraction of anterior teeth using clear aligner was simulated by using non-linear contact method of Abaqus 6.14. The trend and displacement of maxillary teeth, the stress distribution of PDL and alveolar fossae, and the deformation trend of clear aligner were obtained and analyzed. Results: Under the experimental condition, lingual crown tipping and distal tipping movement of anterior teeth were observed, and all of them had the tendency of overbite increasing.The maximum displacement of the central incisor, lateral incisor and canine were 25.16, 50.34 and 24.98 μm, respectively. Meanwhile, the second premolar, first molar and second molar had the tendency of mesial tipping movement, and the maximum displacement of them were 33.04, 2.90 and 16.63 μm, respectively. The stress distribution both at the PDL and alveolar fossae were consistent with tooth movement pattern. It was noted that the stress in the PDL of the canine and second premolar were comparatively big, and the corresponding apical areas of alveolar fossae appeared stress concentration. Concurrently, it was found that the clear aligner showed stress concentration at the junction of adjacent teeth with a tendency of crown directional dislocation. Conclusions: During en-mass retraction of anterior teeth with clear aligner, attention should be paid to the overbite and torque in anterior teeth, and the anchorage protection of posterior teeth. At the same time, we should be careful of root resorption of the teeth on both sides of the extraction space.
目的： 通过三维有限元法模拟无托槽隐形矫治整体内收减数正畸患者上前牙的过程，探讨整个矫治系统的力学效应，为正畸临床提供参考。 方法： 选择1例减数上颌双侧第一前磨牙且上颌牙列已排齐整平的女性正畸患者（就诊于重庆医科大学附属口腔医院正畸科，26岁），采用锥形束CT进行扫描，通过Mimics 17.0、SolidWorks 2016、Geomagic Studio 2015等软件建立包含上颌牙齿、牙周膜、牙槽骨和无托槽隐形矫治器的三维有限元模型，导入Abaqus 6.14软件，以非线性接触法模拟配戴无托槽隐形矫治器整体内收前牙0.2 mm的过程，分析上颌牙移动趋势及位移、牙周膜及牙槽窝的应力分布以及矫治器的变形趋势。 结果： 前牙内收过程中牙冠均有舌侧偏远中倾斜移动伴覆■加深的趋势，中切牙、侧切牙和尖牙的最大位移分别为25.16、50.34和24.98 μm；第二前磨牙、第一磨牙、第二磨牙牙冠均有近中倾斜移动的趋势，最大位移分别为33.04、2.90和16.63 μm。牙周膜及牙槽窝应力分布与牙移动趋势相符，拔牙间隙两侧牙周膜应力较大且在牙槽窝根尖处出现应力集中。无托槽隐形矫治器在邻牙连接处应力较大，并有■向脱落的趋势。 结论： 应用无托槽隐形矫治器整体内收前牙时，应注意前牙控根、压低以及后牙支抗的保护，同时应警惕拔牙间隙两侧牙齿出现牙根吸收。.

BACKGROUND: More patients are choosing customized orthodontic appliances because of their excellent esthetics. It is essential that clinicians understand the biomechanics of the tooth movement tendency in customized lingual orthodontics. This study aimed to evaluate the tooth movement tendency during space closure in maxillary anterior teeth with the use of miniscrew anchorage in customized lingual orthodontics with various power arm locations.
METHODS: Three-dimensional finite element models of the maxilla were created with miniscrews and power arms; the positions were varied to change the force directions. A retraction force (1.5 N) was applied from the top of the miniscrews to the selected points on the power arm, and the initial displacements of the reference nodes of the maxillary teeth were analyzed.
RESULTS: After applying force in different directions, power arms located at the distal side of the canines led to larger initial lingual crown tipping and occlusal crown extrusion of the maxillary incisors compared with power arms located at the midpoint between the lateral incisors and canines, and caused a decreasing trend of the intercanine width.
CONCLUSIONS: In customized lingual orthodontic treatment, power arms located at the distal side of the canines are unfavorable for anterior teeth torque control and intercanine width control. Power arms located at the midpoint between the lateral incisors and canines can get better torque control, but still cannot achieve excepted torque without extra torque control methods, no matter whether its force application point is higher than, lower than, or equal to the level of the top of the miniscrews.

OBJECTIVE: To examine the effect of clinical use on both force retention and the deactivation of closed-coil nickel-titanium (NiTi) springs in a 16-week trial.
METHODS: The force-activation curves for NiTi springs were determined before and after clinical use. The rate of tooth movement and maximum force (MF), hysteresis between activation and deactivation, and mean force of the deactivation plateau (MDF) were examined and correlated as a function of 4, 8, 12 and 16 weeks of clinical use. To recover the force properties, the springs were heat treated at 100°C and the results were compared with the preceding data.
RESULTS: A total of 36 springs were analysed. The MF loss after use was 60, 74, 55, and 48 g for the 4-, 8-, 12- and 16-week springs, respectively. Heat treating had little effect on the MF. Clinical use lowered hysteresis by a mean of 180 g*mm compared with the pre-clinical use data, and heat treating increased the hysteresis by a mean of 59 g*mm above the post clinic testing data. The MDF was nominally 100 g less than the MF. Teeth moved approximately 1 mm/month, independent of the force loss.
CONCLUSIONS: The loss of MF and the lowering of the MDF was not time dependent. Heat treating can partially recover the mechanical properties of the used springs.

Gingival invagination is a type of gingival cleft that occurs during orthodontic space closure in some of the orthodontic patients who received tooth extraction. Clinical manifestations may be fine folds in attached gingiva surface, or deep cleft that penetrates the interdental papilla from the buccal to the lingual alveolar process. Gingival invagination can affect the health of local periodontal tissues, the effect and stability of orthodontic treatment. This article reviews the research progress of gingival invagination studies, including the definition, manifestations, causes, influencing factors and effects.
牙龈内陷是需要减数的正畸患者在正畸空间关闭过程中出现的牙龈折痕。临床表现可以为附着龈表面的细微折痕，或贯通颊侧牙乳头至舌侧牙槽突的深折痕。牙龈内陷可影响局部牙周组织健康，并影响正畸效果及稳定性。本文就牙龈内陷的研究进展，包括定义、表现、发生原因、影响因素及产生的影响等进行综述。.

Objective: To investigate the effect of immediate bone grafting at mandibular first molar extraction socket on maintaining alveolar bone height after space closure. Methods: Thirty adult orthodontic patients who need to extract mandibular first molar, totally 38 target teeth, were included. The samples were divided into two groups randomly: graft group and non-graft group. All extraction space was closed orthodontically. Dental models of all patients were taken before extraction (T0), before space closure(T1) and after space closure (T2). The distance, time of the space closure and the velocity of tooth movement were recorded. Probing depth (PD) and clinical attachment level (CAL) at six sites (mesial buccal, buccal, mesial lingual, lingual, distal buccal and distal lingual) on adjacent teeth were measured before extraction (T0) and after space closure (T2). Cone-beam CT (CBCT) was taken at T0 and T2 to compare the changes of alveolar bone height at six sites on adjacent teeth using Invivo Dental 5.0 software. Results: The extraction space in both graft group and non-graft group was closed successfully. However, the space in graft group was closed more slowly than in non-graft group. In graft group, PD and CAL at the six sites on both the second molar and the second premolar did not change significantly after space closure, and CBCT showed that the alveolar bone height of the second premolar had no significant difference after treatment. In non-graft group, alveolar bone height decreased in both adjacent teeth and periodontal attachment loss was found after space closure. On average, alveolar bone height and periodontal attachment of the second premolar decreased (0.75±0.16) mm and (0.64±0.15) mm, respectively. Meanwhile, alveolar bone height and periodontal attachment of the second molar decreased (0.79±0.23) mm and (0.80±0.24) mm, respectively. Conclusions: Bone graft immediately after mandibular first molar extraction could delay alveolar bone resorption and preserve the periodontal attachment of the adjacent teeth during space closure. However, the procedure could slow down tooth movement.
目的： 分析减数下颌第一恒磨牙即刻植骨对间隙关闭后邻牙牙槽骨的保存作用，为临床提供参考。 方法： 选择2010年12月至2013年1月于北京大学口腔医学院·口腔医院正畸科就诊的30例成年正畸患者，共38个下颌第一恒磨牙减数牙位，采用随机数字表法随机分为植骨组与对照组（每组19个牙位）。植骨组减数后即刻植骨，对照组仅减数不植骨，之后所有患者均行常规正畸治疗，关闭拔牙间隙。制取两组患者治疗前（T0期）、排齐整平后（T1期）、间隙完全关闭后（T2期）牙颌模型，记录间隙关闭的距离及时间，并计算牙齿移动速度。测量T0和T2期拔牙间隙两侧邻牙牙周袋深度及附着丧失的变化；分别拍摄T0和T2期锥形束CT，采用Invivo Dental 5.0软件测量两组拔牙间隙两侧邻牙牙槽骨高度的变化。 结果： 植骨组与对照组均成功关闭拔牙间隙，植骨组间隙关闭时间为（17.4±3.0）个月，对照组为（13.3±2.4）个月。与T0期相比，植骨组T2期拔牙间隙两侧邻牙牙周袋深度与附着丧失均无明显改变；T2期植骨组第二前磨牙牙槽骨高度也无显著改变。与T0期相比，对照组T2期拔牙间隙两侧邻牙牙周袋深度均无显著变化，但发生牙槽骨高度显著降低与附着丧失显著增加，第二前磨牙牙槽骨高度降低（0.75±0.16）mm，附着丧失增加（0.64±0.15）mm；第二恒磨牙牙槽骨高度降低（0.79±0.23）mm，附着丧失增加（0.80±0.24）mm。 结论： 减数下颌第一恒磨牙后即刻植骨能延缓牙槽骨吸收，可在间隙关闭过程中较好地维持拔牙间隙两侧邻牙的牙周附着水平，但可导致牙齿移动速度减慢。.