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.     

Evaluation of a reinforced slot design for CEREC system to restore extensively compromised premolars

OBJECTIVES: The structural stability and adhesive strength of a large-cavity premolar with a CEREC restoration is a frequent problem in long-term use. This study sought to determine whether an additional reinforced slot could increase tooth/ceramic retention using finite element (FE) analysis and fracture testing. METHODS: The cavity was designed in a typical MODL restoration failure shape when the lingual cusp has been lost. Two FE restored-tooth models with different cavity designs were created using image processing, contour stacking, and mesh generation. Interfacial (normal and shear) stresses were then calculated with and without the slot design for restored teeth under lateral and axial forces and different interfacial conditions (bonded and de-bonding). For validation, a fracture experiment was performed with and without reinforced slot designs for large ceramic CEREC restorations. RESULTS: The maximum stresses at the buccal wall increased when a lateral occlusal force acted on the restored tooth with a slot design. Conversely, the interfacial stresses decreased when the restored tooth received a uniform axial occlusal force. After de-bonding on the buccal tooth/ceramic interface, the stresses increased by an average factor of three over those obtained with a bonded interface. The fracture forces were consistent with the tendencies predicted in FE analyses. CONCLUSIONS: An additional reinforced slot for the CEREC restoration of a large cavity could increase retention when a restored tooth receives an axial occlusal load. However, the benefits of a slot seem to be doubtful for a premolar often subjected to a lateral load.     

Response of the maxillary dentition to a statically determinate one-couple system with tip-back mechanics: A prospective clinical trial

Objective:To quantify the effects of tip-back mechanics on the maxillary first molars and incisors.Materials and Methods:Sixteen subjects with Class II end-on malocclusion were treated with an intrusion arch to achieve distalization of the maxillary molar through tip-back mechanics. Lateral cephalograms were taken prior to molar tip-back (T1), after molar tip-back (T2), and after molar root uprighting (T3). Data were analyzed using the Friedman’s and Wilcoxon signed rank tests to evaluate differences in time points (P ≤ .016).Results:The maxillary first molar distalized 1.53 mm (P = .001) with 6.65° (P = .001) of distal tipping and 0.86 mm (P = .001) of extrusion at T2. Minor relapse of the first molar (mesial direction) was seen at T3. The maxillary incisors flared labially 0.4 mm, and the incisor root apex moved palatally 1.19 mm (P = .005) at T2. At T3, the incisor root apex moved palatally 1.5 mm (P = .003) from T1. An angular change from T1 of 3.31° (P = .008) and 3.53° (P = .014) was seen at T2 and T3, respectively, as a result of palatal root movement of the maxillary incisors.Conclusions:A significant amount of distalization of maxillary molars was attained at the crown level with tip-back mechanics. Palatal root angulation change was significant in the incisors with minimal anteroposterior movement of the incisal edge.     

A comparison between friction and frictionless mechanics with a new typodont simulation system.

This study was designed to explore the differences between friction and frictionless mechanics for maxillary canine retraction with the use of a new typodont simulation system, the Calorific machine system. The unit was designed to observe the whole process of tooth movement and is composed of 3 parts: a temperature regulating system, electrothermodynamic teeth, and an artificial alveolar bone component. The efficiency of maxillary canine retraction was compared with the sliding mechanics (along a.016 x.022-in stainless steel labial arch and nickel-titanium closed coil spring) and a canine retraction spring. The patterns of tooth movement obtained with both of these mechanics were measured 5 times each. Friction mechanics were superior to frictionless mechanics in terms of rotational control and dimensional maintenance of the arch (P <.0001); frictionless mechanics were shown to be more effective at reducing tipping and extrusion (P <.0001). However, the observed differences between the 2 methods were relatively small in terms of their clinical significance, and no differences were found in anchorage control (P =.2078). In conclusion, this study indicated that friction and frictionless mechanics perform similarly.     

A comparative study of the effect of the intrusion arch and straight wire mechanics on incisor root resorption: A randomized,controlled trial

Objective:To analyze and compare external apical root resorption (EARR) of maxillary incisors treated by intrusion arch or continuous archwire mechanics.Materials and Methods:This cone-beam computed tomography (CBCT) study analyzed 28 deep bite patients in the permanent dentition who were randomly divided into two groups: Group 1, 12 patients with initial mean age of 15.1 ± 1.6 years and mean overbite of 4.6 ± 1.2 mm treated with the Connecticut intrusion arch (CIA) in the upper arch (Ortho Organizers, Carlsbad, Calif) for a mean period of 5.8 ± 1.27 months. Group 2, 16 patients with initial mean age of 22.1 ± 5.7 years and mean overbite of 4.1 ± 1.1 mm treated with conventional leveling and alignment using continuous archwire mechanics for 6.1 ± 0.81 months. The degree of EARR was detected in 112 maxillary incisors by using CBCT scans and a three-dimensional program (Dolphin 11.7, Dolphin Imaging & Management Solutions, Chatsworth, Calif). The CBCT scans were obtained before (T1) and 6 months after initiation of treatment (T2). Differences between and within groups were assessed by nonpaired and paired t-tests, respectively, with a 5% significance level.Results:Significant differences were found for both groups between T1 and T2 (P < .05) indicating that EARR occurred in both groups. However, there were no significant differences when EARR was compared between group 1 (−0.76 mm) and group 2 (−0.59 mm).Conclusions:The Connecticut intrusion arch did not lead to greater EARR of maxillary incisors when compared with conventional orthodontic mechanics.     

In vitro testing of a measuring system for in vivo recording of orthodontically applied forces and moments in the multiband technique

Summary The aim of this study was to measure in vivo the forces and moments acting therapeutically on the individual tooth in connection with the multiband technique. Securing and evaluating the planned in vivo measurements involves analysing the measuring accuracy of the system as a whole by means of corresponding in vitro investigations. Errors in determining the therapeutically effective force system may result from the electrical measurement of the mechanical quantities by the sensor system and from the fixing of the archwire in therapeutic position. The precision of this fixing is influenced by displacements induced by elasticities and mechanical tensions in the measuring system. Calibration test series have shown the sensor system to have a margin of error of less than 2%. The displacements influencing precision fixing of the archwire were determined by means of a laser position measuring system. For a maximum orthodontic force of 1.5N, they are 0.06 mm in the least favourable case. The resulting measuring accuracy was determined analytically or graphically, depending on the key parameters. Successful in vivo studies of the therapeutically applied force systems are to be expected on the basis of these results.Part I of this article is published in J Orofac Orthop/Fortschr Kieferorthop 1996; 57:298–305.     

Stable,dynamic, elastic miniplate osteosynthesis in cranio-maxillofacial surgery: evolution of concepts,biomechanical study and applications

An osteosynthesis of the mandible should be called stable when this type of treatment does not need to be supported by intermaxillary fixation, without disturbing the healing process. In that intention, many techniques of osteosynthesis based on different concepts were proposed during the last century. A classification of these concepts was formulated. The adaptive osteosynthesis which is pragmatically i.e. empirical, wherein the goal is immobilizing the fracture by bringing the fragments together and fixing them with rigid screwed plates. The rigid compressive osteosynthesis which is an extrapolation of the ideas of Lane proposed in 1912. The stable dynamic elastic osteosynthesis whose principles, equipment and technique as their applications were developed exclusively through biomeehanical studies. The basic principle was the recovery of mobility by neutralization of detrimental distraction stresses, and reestablishment of favorable compressive stresses providing dynamic physiological stimulations. The biomechanical characteristics of the plates and the screws made possible the use of the fixation of all types of fractures or orthognathic procedures in mandibular surgery. With the application of mini or microplates in other facial bones and the skull, the art of fracture treatment and of reconstructive surgery of the craniomaxillofacial skeleton, including orthognathic and reconstructive surgery with or without bone grafting, has profoundly changed. At the present time, metal plates are sometimes superseded by resorbable plates and screws. Nevertheless, the fundamental biomechanical principles of osteosynthesis and bone healing remain unchanged.     

Finite element analysis of type B condylar head fractures and osteosynthesis using two positional screws

ObjectiveThe aim of this study was to explore the cause of type B condylar head fracture after parasymphyseal impact, and evaluate the biomechanics of osteosynthesis using two positional screws for the repair of this type of fractures.MethodsA finite element model of the mandible was created, and a parasymphyseal impact was simulated using Mimics 10.01 and Abaqus 6.10 software. The type B condylar head fracture was simulated in the right condyle using a mimics simulation cut with polyplane module according to the analyzed results together with clinical experience, and the left condyle was used as a control. Two positional screws were used for rigid internal fixation of the fracture. von Mises stress distributions in the condyles and screws were analyzed.ResultsThe von Mises stress generated in parasymphyseal trauma simulation showed a significant concentration in the sagittal direction of the condyle. In two-positional-screw osteosynthesis of the condylar head fractures, stress concentration appeared within the screws in the gap area between the two fractured segments and the area around the screw head. A small amount of stress was distributed in the screw holes and on the posterior surfaces of both segments. The von Mises stress was negligible in the fractured sagittal surfaces.ConclusionIt is reasonable to attribute the cause of type B condylar head fracture to the anatomical features of the condyle. The biomechanics of two-positional-screw osteosynthesis revealed that the stress can transmit through the screws to the medial fragments, and the stresses on both sagittal fractured surfaces are minimal.     

Using orthodontic elastic traction during the active period of distraction osteogenesis to increase the effective vertical extension of hemifacial microsomia patients: A multi-center randomized clinical trial

In this study, the aim was to assess whether using elastic traction during the active period of distraction osteogenesis could effectively increase the vertical extension.Patients with Pruzansky-Kaban Type II mandibular deformity were recruited and randomly assigned into Elastic traction + Distraction Osteogenesis group or Distraction Osteogenesis group, respectively. During the active period, the experimental group received orthodontic elastic traction 3 days after distraction osteogenesis implantation, while the control group received no treatment. All the participants underwent computed tomography (CT) examination before surgery, at the end of the active period, 6 months and 2 years after distraction osteogenesis tractor implantation. The primary outcome was the effective vertical extension rate of the mandible from the baseline to the end of the active period after operations, and there were 7 secondary outcomes used.70 patients were included. The effective vertical extension rates were 85.021% ± 7.432% (mean ± SD) and 68.811% ± 9.510% (mean ± SD) in the experimental and control groups, respectively (P = 0.001). The average distances between the lower middle incisor point to the sagittal plane at the end of the active period were 2.485 ± 1.411 mm and 3.938 ± 2.293 mm in the experimental and control groups, respectively (P = 0.026). At the end of the active period of distraction osteogenesis, the average values of the mandibular occlusal plane canting were −4.887 ± 3.126 mm and −0.177 ± 4.029 mm in the experimental and control groups, respectively (P = 0.026).Elastic traction-assisted distraction osteogenesis could improve traction efficiency and facial symmetry.     

直丝弓排齐阶段两种远移尖牙方法的比较

目的:比较直丝弓矫治器排齐阶段2种远移尖牙的方法即尖牙向后结扎法和弹性链状圈牵引法的优缺点。方法:将50例拔除4个第一前磨牙的正畸病例随机分为2组,均使用同种国产直丝弓矫治器,排齐阶段分别采用上述2种方法进行矫治,排齐前后利用模型测量和X线头影测量进行统计学分析。结果:上颌前磨牙颊尖之间、下颌磨牙的4个牙尖之间的宽度变小、尖牙牙冠远中倾斜角度、尖牙远中移动距离和速度、下颌磨牙牙冠近中倾斜角度以及上、下切牙的舌向倾斜内收的变化,牵引法均大于结扎法;上、下颌磨牙近中移动距离的变化,牵引法小于结扎法;以上变化均有显著性差异。其余变化2种方法之间未见显著性差异。结论:2种方法应用于直丝弓矫治器排齐阶段均取得了远移尖牙的效果,然而,必须采取相应的控制支抗的措施以避免其各自的不利影响。     

Post-gel shrinkage,elastic modulus,and stress generated by orthodontic adhesives

Objectives:To measure post-gel shrinkage, elastic modulus, and flexural strength of orthodontic adhesives and to predict shrinkage stress using finite element analysis (FEA).Materials and Methods:The following 6 orthodontic adhesives were tested: Transbond XT (3M Unitek, Monrovia, Calif), Transbond Plus Color Change (3M Unitek), Greengloo (Ormco, Brea, Calif), Ortho Connect (GC America, Alsip, Ill), Trulock (RMO, Denver, Colo), GoTo (Reliance, Itasca, Ill). Post-gel shrinkage was measured using a biaxial strain gauge during light curing. Elastic modulus and flexural strength were measured with a 4-point bending test. Analysis of variance and Student-Newman-Keuls post hoc tests were used to compare the shrinkage, elastic modulus, and flexural strengths among the materials (α = .05). Shrinkage stresses caused by the post-gel shrinkage and elastic modulus values were calculated using a cross-sectional FEA of a metallic bracket bonded to an incisor.Results:Properties were highly different among the adhesives (P ≤ .0001). Transbond XT (0.38 ± 0.09 percent volumetric contraction) and GoTo (0.42 ± 0.05 percent volumetric contraction) had the lowest post-gel shrinkage; Transbond Plus Color Change had the highest (0.84 ± 0.08 percent volumetric contraction). OrthoConnect (6.8 ± 0.6 gigapascals) had the lowest elastic modulus; GoTo (28.3 ± 3.1 gigapascals) had the highest. Trulock (64.1 ± 8.2 megapascals) had the lowest flexural strength; Greengloo (139.1 ± 20.7 megapascals) had the highest. FEA showed that the highest shrinkage stresses were generated with Transbond Plus Color Change and the lowest with OrthoConnect.Conclusions:Post-gel shrinkage of orthodontic adhesives was comparable with restorative composites, which are known to create shrinkage stresses in restored teeth. FEA indicated that this shrinkage creates stresses in the adhesive and in the enamel around the brackets.     

Influence of occlusal hypofunction on the elastic property and bone formation of rat alveolar bone

The purpose of this study was to investigate the influence of occlusal hypofunction on the maintenance of the elastic property and alveolar bone formation using an occlusal hypofunction model. Analyses of the elastic property and bone formation of the alveolar bone were carried out by the compression test and the bone histomorphometry in the two directions (the tooth axis direction and the bucco-lingual direction). The compression test was done with the texturometer to analyse the springiness of bone specimens of the mandibular first molar. Bone histomorphometric analyses were evaluated using double labeled frontal section. Results showed that occlusal hypofunction significantly reduced the springiness and suppressed the alveolar bone formation in the bucco-lingual direction. These results suggested that occlusal function plays an important role in maintenance of the elastic property and bone formation of the alveolar bone.     

摇椅弓滑动法整体内收上颌前牙的三维有限元分析

目的探讨摇椅弓应用于滑动法内收上颌前牙的力学效应。方法 应用ANSYS软件建立上牙列三维有限元模型,分别计算不同深度摇椅弓和不同高度牵引钩内收上前牙时对6个上前牙阻抗中心产生的转矩,并观察二者 联合应用时上前牙初始移动情况。结果 选择不同深度的摇椅弓可产生不同的冠唇向转矩,用以抵消摩擦力及不同高度牵引钩滑动法内收产生的冠舌向转矩,进而实现上前牙的整体移动。在上颌第二前磨牙和第一磨牙之间应用种植体支抗时,2 mm深度的摇椅弓可配合使用7.2 mm高度的牵引钩来实现上前牙的压低及整体内收。结论 摇椅弓可以有效改善内收前牙时出现的直立和舌倾状态,实现压低和转矩的双重控制。