Forces and moments delivered by the PET-G aligner to a maxillary central incisor for palatal tipping and intrusion

Objective:To evaluate the effect of material thickness and width of the gingival edge on the forces and moments delivered by aligners prepared from Duran foil (PET-G) to a maxillary incisor during tipping and intrusion.Materials and Methods:Aligners prepared from PET-G of three material thicknesses (0.5, 0.625, and 0.75 mm) and three widths of gingival edges (0–1, 3–4, and 6–7 mm) were investigated during incisor palatal tipping and intrusion of 0.5 mm each. Forces and moments were measured with a six-component measuring device. The influence of aligner thickness and aligner extend on the force and moment development were tested for statistical significance (P < .05).Results:The F_x and F_z forces produced during palatal tipping and intrusion by the 0.75-mm aligner material was significantly higher than those produced by the 0.5-mm-thick material (P = .005 and P = .047, respectively). There was no statistical difference between aligner thickness of 0.5 and 0.625 mm and between 0.625 and 0.75 mm. The same behavior was observed for the palatal moment (M_y). The F_x and F_z forces produced during palatal tipping and intrusion by the aligner with an extension of 0–1 mm edge was significantly lower than that of the aligner with a larger extension (3–4 mm edge: P = .003; 6–7 mm: P = .001). However, there was no statistical difference between aligners with a 3–4-mm and a 6-mm edge. The same behavior was observed for the palatal moment (M_y).Conclusions:The forces and moments exerted by the PET-G aligner on teeth vary, depending on the material thickness, width of the aligner edge, and direction of tooth movement.     

双膜透明矫治器移动兔下颌中切牙的效果评价

目的:应用双膜透明矫治器对兔下颌中切牙进行正畸移动,评价双膜透明矫治器移动牙的效果。方法:选用6只新西兰大白兔,实验组为双膜透明矫治器加力组（3只）,设计戴用3步矫治器,每一步牙移动0.33 mm,先戴用薄膜透明矫治器2 d,再戴用厚膜透明矫治器2 d;对照组为常规厚度膜片透明矫治器加力组（3只）,设计戴用3步矫治器,每一步牙移动0.20 mm,每步矫治器戴4 d。在每组兔分别戴用第1、2和3步矫治器后制取模型,测量牙移动数据。采用SPSS 19.0软件包对数据进行统计学分析。结果:2组牙移动表达的精确度从牙冠切端向龈端逐渐降低,实验组的精确度随矫治时间增加呈下降趋势,而对照组的精确度随矫治时间增加无明显变化。实验组牙冠切端、中端和龈端牙移动速率均显著大于对照组（P<0.001）。结论:兔下颌中切牙在透明矫治器的作用下产生倾斜移动。采用双膜透明矫治器矫治,牙移动速率加快,但牙移动表达的精确度降低。     

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.     

不同双膜透明矫治器戴用时间对正畸牙移动效果影响的实验研究

目的 探讨不同双膜透明矫治器戴用时间对正畸牙移动效果的影响。方法 选取9只新西兰大白兔,随机分为实验1组、实验2组和对照组,每组3只。对两个实验组动物采用薄膜（0.625 mm）和厚膜（0.750 mm）两种厚度膜片透明矫治器进行矫治,均设计为每一步矫治使左右下中切牙各远中移动0.33 mm,总矫治时长为12 d;其中实验1组（缩短薄膜矫治器戴用时间）的每步矫治时长为3 d（薄膜矫治器1 d、厚膜矫治器2 d）,共进行4步矫治;实验2组的每步矫治时长为4 d（薄膜矫治器2 d、厚膜矫治器2 d）,共进行3步矫治。对照组配戴厚膜矫治器,但不进行牙移动。测量矫治前及每步矫治结束后实验动物临床冠切点、中点、龈点的牙移动相关指标。对实验组每一步矫治前后及两个实验组之间的牙移动量、牙移动速率及牙移动表达精确度进行比较分析。结果 （1）戴用双膜透明矫治器可有效完成牙移动,与矫治前比较,牙移动量具有统计学意义（P < 0.05）;（2）同一位点实验1组牙移动速率均高于实验2组（P < 0.05）;（3）实验1组缩短薄膜佩戴时间,与实验2组的单步矫治牙移动量差异无统计学意义（P > 0.05）;（4）在进行同一步骤矫治时,实验1组龈点牙移动表达精确度稍低于实验2组,在切点和中点两组的牙移动表达精确度无差异;（5）实验1组和实验2组的牙移动方式均为倾斜移动,且两组的倾斜程度差异无统计学意义（P > 0.05）。结论 （1）缩短薄膜戴用时间可有效提高牙移动速率,且牙移动量无明显差异,但龈点牙移动量表达精确度可能稍有降低;（2）临床可适当缩短薄膜戴用时间,以提高正畸牙移动速率,并可缩短疗程、优化患者感受,尤其适用于需要倾斜移动的病例。     

牙齿隐形矫治的三维有限元分析

无托槽隐形矫治器是由塑性膜片材料经热压成型装置制作而成,通过其变形后的回弹力产生矫治力,达到矫治牙齿的目的。但是,隐形矫治器产生的矫治力的大小、方向和作用点不明确,不利于临床治疗的开展。利用三维有限元分析法建立牙齿模型,可以研究隐形矫治过程中不同牙齿的受力和移动模式。文章主要介绍三维有限元模型的建立方法和利用三维有限元分析法分析不同牙齿的牙移动模式与受力情况以及附件和矫治器材料对牙齿移动影响等方面的研究进展。     

附件对隐形矫治器内收上前牙影响的三维有限元分析

目的    通过拔除上颌第一前磨牙后前牙内收的隐形矫治三维有限元模型,分析切牙上设置附件对牙齿移动方式的影响。方法    基于1例成年患者颌骨的锥形束CT影像数据,按照切牙上有无附件,构建4组拔除第一前磨牙的上颌隐形矫治模型,分别为切牙无附件组、侧切牙单附件组、中切牙单附件组和双附件组;导入Ansys Workbench三维有限元软件,设置4个上切牙控根压入内收的隐形矫治过程,分析牙列初始位移和附件的应力分布。结果    切牙无附件组及中切牙单附件组均发生4个切牙的舌向倾斜移动,后牙产生不同程度的近中倾斜移动,尖牙近中倾斜伴有伸长;侧切牙单附件组及双附件组切牙呈整体内收压入移动趋势,切牙附件的龈方可观测到压应力集中。结论    隐形矫治内收上前牙时,在侧切牙放置附件有助于切牙整体内收的表达,而中切牙附件对牙移动方式的影响较小。     

Comparison of alveolar bone thickness and height after slow expansion using quad-helix or clear aligners

ObjectiveThe study was conducted to investigate the thickness and height of the alveolar bone of individual teeth after slow maxillary expansion (SME) with quad helix or clear aligner appliances and hypothesized that there is no difference in buccal alveolar bone thickness or heights in patients treated by either quad helix or clear aligners.Material and MethodsThis is a retrospective study; the records of 22 patients treated between December 2019 to April 2020 by dental arch expansion using either clear aligners or quad helix appliances were retrieved and studied. The results obtained through cone beam computed tomography (CBCTs) before and immediately after maxillary expansion (2 + 1 mm per side) were analyzed (11 in the Quad Helix group and 11 in the clear aligner). The data collected was analyzed using linear and angular measurements obtained through On-demand 3D App software. Furthermore, Statistical Package for Social Sciences (SPSS) version 25.0 was used to present the findings by mean and standard deviations, and Scheffe’s test was applied for comparing forces.ResultsThe results showed that the mean age of patients in the clear aligner group and Quad Helix was 16.27 ± 0.56 years and 15.5 ± 1.53 years, respectively. There was no difference in buccal alveolar bone thickness or heights in patients treated by either quad helix or clear aligners. This is due to the findings that suggest that there was a decrease in bone height and bone width when treated with a quad helix as compared to clear alignment.ConclusionIt can be concluded that the quad helix SME treatment affects alveolar bone integrity; therefore, clear aligners might be better for treating patients than the quad helix.     

The clinical success of tooth‐ and implant‐supported zirconia‐based fixed dental prostheses. A systematic review

The aim was to make an inventory of the current literature on the clinical performance of tooth‐ or implant‐supported zirconia‐based FDPs and analyse and discuss any complications. Electronic databases, PubMed.gov, Cochrane Library and Science Direct, were searched for original studies reporting on the clinical performance of tooth‐ or implant‐supported zirconia‐based FDPs. The electronic search was complemented by manual searches of the bibliographies of all retrieved full‐text articles and reviews, as well as a hand search of the following journals: International Journal of Prosthodontics, Journal of Oral Rehabilitation, International Journal of Oral & Maxillofacial Implants and Clinical Oral Implants Research. The search yielded 4253 titles. Sixty‐eight potentially relevant full‐text articles were retrieved. After applying pre‐established criteria, 27 studies were included. Twenty‐three studies reported on tooth‐supported and 4 on implant‐supported FDPs. Five of the studies were randomised, comparing Y‐TZP‐based restorations with metal–ceramic or other all‐ceramic restorations. Most tooth‐supported FDPs were FDPs of 3–5 units, whereas most implant‐supported FDPs were full arch. The majority of the studies reported on 3‐ to 5‐year follow‐up. Life table analysis revealed cumulative 5‐year survival rates of 93·5% for tooth‐supported and 100% for implant‐supported FDPs. For tooth‐supported FDPs, the most common reasons for failure were veneering material fractures, framework fractures and caries. Cumulative 5‐year complication rates were 27·6% and 30·5% for tooth‐ and implant‐supported FDPs, respectively. The most common complications were veneering material fractures for tooth‐ as well as implant‐supported FDPs. Loss of retention occurred more frequently in FDPs luted with zinc phosphate or glass–ionomer cement compared to those luted with resin cements. The results suggest that the 5‐year survival rate is excellent for implant‐supported zirconia‐based FDPs, despite the incidence of complications, and acceptable for tooth‐supported zirconia‐based FDPs. These results are, however, based on a relatively small number of studies, especially for the implant‐supported FDPs. The vast majority of the studies are not controlled clinical trials and have limited follow‐up. Thus, interpretation of the results should be made with caution. Well‐designed studies with large patient groups and long follow‐up times are needed before general recommendations for the use of zirconia‐based restorations can be provided.     

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.     

Clear aligners generations and orthodontic tooth movement

Clear aligner technology has evolved over the last 15 years, with these appliances continually being modified to increase the range of tooth movements that they can achieve. However, there is very little clinical research available to show how these appliances achieve their results. This article describes the different generations of clear aligners that are available and highlights their use. However, until more clinical research becomes available, aligners cannot be routinely prescribed as an effective alternative to fixed labial appliances.     

不同Ⅱ类牵引模式对无托槽隐形矫治磨牙远移作用的比较：三维有限元研究

目的:构建隐形矫治器上颌磨牙远移中两种Ⅱ类牵引的生物力学研究模型,分析矫治体系在不同加力模式、不同牵引力大小作用下的初始位移及应力分布特点,为该技术的临床应用提供参考。方法:建立隐形矫治推上颌磨牙向远中及两种Ⅱ类牵引模式(牙套加力组与牙齿加力组)的三维有限元模型,采用非线性有限元法分析2种不同加力方式及5种不同载荷(100 g、150 g、200 g、250 g、300 g)下的牙齿移动方式、牙套形变、牙周膜应力分布等,比较其增强前牙支抗效果的异同。结果:不同力值不同加力方法下所有组Ⅱ类牵引均可以使前牙内收,抵抗磨牙远中移动过程造成的前牙支抗丧失,但其牙齿应力分布、牙套形变效果不同：牙齿加力组集中在直接受力的尖牙上,分布不均匀;牙套加力组分布更均匀,随距尖牙距离由近到远逐渐减小,但总体大小较牙齿加力组大。牙周膜等效应力除300 g牙套加力组[(2.87×10 -2) MPa]过大外,其余各组均在牙周膜可承受范围内。 结论:100 g的Ⅱ类牵引即可抵抗磨牙远移反作用力造成的前牙支抗丧失,300 g牙套加力作用下的牙周膜受力过大,尽量避免使用。     

不同Ⅱ类牵引模式对无托槽隐形矫治磨牙远移作用的比较：三维有限元研究

目的:构建隐形矫治器上颌磨牙远移中两种Ⅱ类牵引的生物力学研究模型,分析矫治体系在不同加力模式、不同牵引力大小作用下的初始位移及应力分布特点,为该技术的临床应用提供参考。方法:建立隐形矫治推上颌磨牙向远中及两种Ⅱ类牵引模式(牙套加力组与牙齿加力组)的三维有限元模型,采用非线性有限元法分析2种不同加力方式及5种不同载荷(100 g、150 g、200 g、250 g、300 g)下的牙齿移动方式、牙套形变、牙周膜应力分布等,比较其增强前牙支抗效果的异同。结果:不同力值不同加力方法下所有组Ⅱ类牵引均可以使前牙内收,抵抗磨牙远中移动过程造成的前牙支抗丧失,但其牙齿应力分布、牙套形变效果不同：牙齿加力组集中在直接受力的尖牙上,分布不均匀;牙套加力组分布更均匀,随距尖牙距离由近到远逐渐减小,但总体大小较牙齿加力组大。牙周膜等效应力除300 g牙套加力组[(2.87×10 -2) MPa]过大外,其余各组均在牙周膜可承受范围内。 结论:100 g的Ⅱ类牵引即可抵抗磨牙远移反作用力造成的前牙支抗丧失,300 g牙套加力作用下的牙周膜受力过大,尽量避免使用。     

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。     

隐形矫治磨牙远移的三维有限元分析

目的　构建隐形矫治器上颌磨牙远移的生物力学研究模型,分析矫治体系的初始位移及应力分布特点,为该技术的临床应用提供指导。方法 建立隐形矫治上颌磨牙远移的三维有限元模型,在ANSYS软件中采用非线性有限元法通过数值仿真分析求得受力瞬间牙齿在牙周膜及周围牙槽骨等约束下的移动方式、牙套形变、牙周膜应力分布,并探索适宜的Ⅱ类牵引增强前牙支抗的必要性及适宜力值。结果 第二磨牙远移的同时伴有其牙冠远中倾斜、伸长及舌侧倾斜;其余牙表现为唇/颊倾、压低且位移量与距支抗牙距离成反比。牙周膜等效应力越靠近颈缘越大,距离第二磨牙越远越小,均小于牙周组织可承受最大应力。矫治器在第二磨牙处出现应力集中现象,位移峰值小于材料的弹性极限和拉伸极限强度。100 g Ⅱ类牵引可以有效抵抗前牙唇倾,300 g牵引力作用于牙列后超过牙周膜最大承受力值。结论 使用无托槽矫治技术远移磨牙不能实现单纯的整体移动且支抗牙有一定的支抗丧失,需要进行必要的支抗控制。100 g Ⅱ类牵引即可有效抵抗推磨牙带来的前牙支抗丧失,300 g牵引力作用下牙周膜受力过大,尽量避免使用。     

无托槽隐形矫治技术推磨牙向远中的机制与优势

对于轻中度的安氏Ⅱ类错牙合畸形患者,推磨牙向远中是一种常见的治疗方法。随着隐形矫治器的不断发展,应用无托槽隐形矫治技术改善磨牙关系,能达到很高的矫治效率。通过分析患者治疗前后的头颅侧位片及曲面断层片,测量上颌第一、二磨牙的后移量及倾斜角度,发现牙齿的移动方式接近整体移动。文章就无托槽隐形矫治技术推磨牙向远中的机制及优势做一介绍。     

三种矫治器治疗安氏Ⅱ类2分类对切牙牙根吸收的影响

目的 比较不同矫治器治疗安氏Ⅱ类2分类错牙合畸形患者切牙牙根的吸收状况。方法 选择使用不同矫治器的安氏Ⅱ类2分类成年患者30例,其中传统MBT托槽、自锁托槽以及无托槽隐形矫治器的患者各10例,共计240颗切牙。收集患者治疗前后的锥形束CT(CBCT)影像学资料,并导入Dolphin Imaging软件,Mimics软件以及3-Matics软件测量分析治疗前后切牙牙根吸收情况。结果 传统MBT托槽组和自锁托槽组的上下颌中切牙以及侧切牙的牙齿长度(L)与无托槽隐形矫治器组上下颌中切牙及上颌侧切牙的牙齿长度治疗后较治疗前显著减小,差异具有统计学意义。使用无托槽隐形矫治器的患者下颌侧切牙治疗前后的牙齿长度无显著变化。而三组之间的对比,上下颌中切牙牙齿长度变化无显著统计学差异。无托槽隐形矫治器组上下颌侧切牙的牙齿长度减少量相对更低,差异具有统计学意义(P＜0.05)。此外,无托槽隐形矫治器组平均牙齿长度变化为(-0.37±0.11)mm,显著小于传统MBT托槽组(-1.32±0.47)mm及自锁托槽组(-1.05±0.38)mm。在牙根吸收区域的比较上,各组均表现为腭侧吸收多于唇侧吸收,近中吸收多于远中吸收。结论 无托槽隐形矫治器治疗安氏Ⅱ类2分类错牙合畸形可有效降低切牙牙根吸收严重程度。     

Treatment management between orthodontists and general practitioners performing clear aligner therapy

Objective:To investigate differences in case selection, treatment management, and aligner treatment expertise between orthodontists and general practitioners.Materials and Methods:A parallel pair of original surveys with three sections (case selection, treatment management, and demographics) was sent to orthodontists (N = 1000) and general dentists (N = 1000) who were providers of aligner treatment.Results:Orthodontists had treated significantly more patients with aligners, had treated more patients with aligners in the previous 12 months, and had received more aligner training than general dentists (P < .0001). In general, case confidence increased with increasing experience for both orthodontists and general dentists. After adjusting for experience, there was a significant difference in aligner case confidence between orthodontists and general dentists for several malocclusions. General dentists were more confident than orthodontists in treating deep bite, severe crowding, and Class II malocclusions with aligners (P ≤ .0001). Significant differences were also found for all treatment management techniques except interproximal reduction.Conclusion:There was a significant difference in case selection, treatment management, and aligner expertise between orthodontists and general dentists, although the differences in case selection were small. Overall, it was shown that orthodontists and general dentists elected to treat a variety of moderate to severe malocclusions with aligners but with different utilization of recommended auxiliaries, perhaps demonstrating a difference in treatment goals.     

Effectiveness of casein phosphopeptide‐amorphous calcium phosphate‐containing products in the prevention and treatment of white spot lesions in orthodontic patients: A systematic review

The purpose of the present systematic review was to evaluate the effectiveness of casein phosphopeptide‐amorphous calcium phosphate (CPP‐ACP)‐containing products in the prevention and treatment of active white spot lesions (WSL) in orthodontic patients. Searched the Scopus, PubMed, Web of Science, Cochrane, Virtual Health Language, ClinicalTrials, and Open Gray databases without limitations on the year or language of publication. We included controlled clinical trials with patients with fixed orthodontic appliances under the use of CPP‐ACP‐containing products compared to control, placebo, or other interventions in the prevention and treatment of WSL around orthodontic braces. Case reports, editorials, in vitro studies, annals of congress, and reviews were excluded. To assess the risk of bias, the revised version of the Cochrane tool for randomized trials (RoB 2.0) and Risk Of Bias In Non‐randomized Studies for non‐randomized trials were used. The biases were graded low, moderate, and high according to the tools used. Of the 599 articles found, 11 met the inclusion criteria. Of these, nine were randomized, controlled clinical trials and two were non‐randomized. Two studies were considered to have moderate bias risk, and the most‐used CPP‐ACP presented form was a cream for topical applications. Although CPP‐ACP‐containing products did not differ from other fluoride products, they were able to reduce WSL and neutralize the pH around the orthodontic braces. Products containing CPP‐ACP are effective in preventing and treating WSL around the braces. However, further studies with the same measurement method and periods of use, and other forms of presentation of CPP‐ACP are needed.     

Optimization of arch guided tooth movement by the use of uprighting springs

One of the most important drawbacks of arch guided tooth movement is the friction between bracket and arch wire. In order to reduce frictional forces the application of an uprighting spring is proposed. The influence of uprighting and derotating moments on frictional forces has been measured with a friction testing assembly. Applying appropriate uprighting moments results in a reduction of friction by 73-89 per cent. Derotating moments have only a minor effect on friction. For clinical purposes, the uprighting moment should be 50 per cent of the tipping moment.