Novel approach for characterizing clinical load application of superelastic orthodontic wires.

OBJECTIVE: Current standardized in vitro bending experiments for orthodontic archwires cannot capture friction conditions and load sequencing during multi-bracket treatment. This means that clinically relevant forces exerted by superelastic wires cannot be predicted. To address these limitations, this study explored a novel test protocol that estimates clinical load range. METHODS: The correction of a labially displaced maxillary incisor was simulated using an in vitro model with three lingual brackets. Deflection force levels derived from four different protocols were designed to explore the impact of friction and wire load history. These force levels were compared in nickel-titanium (NiTi) archwires with three commonly used diameters. The unloading path varied between protocols, with single or multiple sequences and different load orders and initial conditions. RESULTS: Deflection forces from the new protocol, employing multiple continuous load/unload cycles (CCincr), consistently exceeded those from the conventional protocol using a single continuous unloading path (CUdecr). Mean differences in plateau force ranged from 0.54 N (Ø 0.014" wire) to 1.19 N (Ø 0.016" wire). The CCinr protocol also provided average force range estimates of 0.47 N (Ø 0.012" wire), 0.89 N (Ø 0.014" wire), and 1.15 N (Ø 0.016" wire). SIGNIFICANCE: Clinical orientation towards CUdecr carries a high risk of excessive therapeutic forces because clinical loading situations caused by friction and load history are underestimated. Physiological tooth mobility using NiTi wires contributes decisively to the therapeutic load situation. Therefore, only short unloading sequences starting from the maximum deflection in the load history, as in CCincr, are clinically meaningful.

Nanoalignment by critical Casimir torques.

The manipulation of microscopic objects requires precise and controllable forces and torques. Recent advances have led to the use of critical Casimir forces as a powerful tool, which can be finely tuned through the temperature of the environment and the chemical properties of the involved objects. For example, these forces have been used to self-organize ensembles of particles and to counteract stiction caused by Casimir-Liftshitz forces. However, until now, the potential of critical Casimir torques has been largely unexplored. Here, we demonstrate that critical Casimir torques can efficiently control the alignment of microscopic objects on nanopatterned substrates. We show experimentally and corroborate with theoretical calculations and Monte Carlo simulations that circular patterns on a substrate can stabilize the position and orientation of microscopic disks. By making the patterns elliptical, such microdisks can be subject to a torque which flips them upright while simultaneously allowing for more accurate control of the microdisk position. More complex patterns can selectively trap 2D-chiral particles and generate particle motion similar to non-equilibrium Brownian ratchets. These findings provide new opportunities for nanotechnological applications requiring precise positioning and orientation of microscopic objects.

Non-steady state thermometry with optical diffraction tomography.

Label-free thermometry is a pivotal tool for many disciplines. However, most current approaches are only suitable for planar heat sources in steady state, thereby restricting the range of systems that can be reliably studied. Here, we introduce pump probe-based optical diffraction tomography (ODT) as a method to map temperature precisely and accurately in three dimensions (3D) at the single-particle level. To do so, we first systematically characterize the thermal landscape in a model system consisting of gold nanorods in a microchamber and then benchmark the results against simulations and quantitative phase imaging thermometry. We then apply ODT thermometry to resolve thermal landscapes inaccessible to other label-free approaches in the form of nonplanar heat sources embedded in complex environments and freely diffusing gold nanorods in a microchamber. Last, we foresee that our approach will find many applications where routine thermal characterization of heterogeneous nanoparticles samples in 3D or in non-steady state is required.

Optically Driven Janus Microengine with Full Orbital Motion Control.

Microengines have shown promise for a variety of applications in nanotechnology, microfluidics, and nanomedicine, including targeted drug delivery, microscale pumping, and environmental remediation. However, achieving precise control over their dynamics remains a significant challenge. In this study, we introduce a microengine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that in the presence of a strongly focused light beam, a gold-silica Janus particle becomes confined at the stationary point where the optical and thermal forces balance. By using circularly polarized light, we can transfer angular momentum to the particle, breaking the symmetry between the two forces and resulting in a tangential force that drives directed orbital motion. We can simultaneously control the velocity and direction of rotation of the particle changing the ellipticity of the incoming light beam while tuning the radius of the orbit with laser power. Our experimental results are validated using a geometrical optics phenomenological model that considers the optical force, the absorption of optical power, and the resulting heating of the particle. The demonstrated enhanced flexibility in the control of microengines opens up new possibilities for their utilization in a wide range of applications, including microscale transport, sensing, and actuation.

Are aligners capable of inducing palatal bodily translation or palatal root torque of upper central incisors? A biomechanical in vitro study.

OBJECTIVES: Previous studies have shown that aligners have limited ability to control root movements. The purpose of this study was to investigate which modification geometry and foil thickness are optimal for generating the force-moment (F/M) systems required for palatal root torque of maxillary central incisors. MATERIALS AND METHODS: Tooth 11 was separated from a maxillary acrylic model and connected to a movement unit via a 3D F/M sensor. Different modification geometries (crescent, capsular, double-spherical) with different depths were digitally implemented in the labio-cervical region of tooth 11 to induce an increased contact force. We evaluated the F/M systems exerted by aligners with thicknesses of 0.4-1.0 mm. F/M measurements were taken with tooth 11 in the neutral position and during palatal displacement of tooth 11 (simulating its initial clinical movement). RESULTS: The mechanical requirements of palatal root torque are a palatally directed force (- Fy) and a palatal root torquing moment (- Mx). These requirements were reliably achieved with modification depths > 0.5 mm. The modification depth and foil thickness had a significant influence on - Fy magnitudes (linear mixed-effect models, p < 0.01). With the 0.75-mm aligners combined with 1.5-mm deep modifications, the palatal root torque range (palTR) started after an initial palatal crown displacement of 0.09, 0.12, and 0.12 mm for the capsular, crescent, and double-spherical modification geometries, respectively. CONCLUSIONS: A relatively early start of the palatal torque range (after a 0.1-mm palatal crown displacement) and appropriate - Fy magnitudes were achieved with 0.75-mm-thick aligners containing 1.5-mm deep capsular or crescent pressure regions. Subsequent clinical trials are required to confirm the clinical effects of these modifications. CLINICAL RELEVANCE: In vitro testing indicated that modified aligners are capable of generating the F/M components required for palatal root torque of upper central incisors.

Mechanical loads exerted by different configurations of Burstone's 3-piece segmented mechanics during a simulated intrusion of the mandibular incisors.

INTRODUCTION: Burstone's segmented intrusion arch technique allows variable incisor intrusion with lingual or labial tipping, depending on the position and direction of the force vectors exerted by the intrusion springs. To date, systematic biomechanical studies are lacking. This in vitro study aimed to determine the 3-dimensional force-moment systems applied to the 4 mandibular incisors and the deactivation behavior of the appliance by different configurations of the 3-piece intrusion mechanics. METHODS: The experimental setup consisted of a mandibular model segmented into 2 buccal and 1 anterior segment mounted on a 6-axis Hexapod to simulate different incisor segment malpositions. Active elements were bilateral 0.017 × 0.025-in titanium-molybdenum alloy intrusion springs. Nine geometric appliance configurations at different superpositions of the anterior segment between 4 and 0 mm were evaluated. RESULTS: For 3-mm incisor superposition, mesiodistal variation of the contact of the intrusion spring at the anterior segment wire resulted in labial tipping moments between -0.11 and -1.6 Nmm. Variation of the height of force application at the anterior segment showed no significant influence on the tipping moments. During the simulated intrusion of the anterior segment, a force reduction rate of 21% per mm intrusion was observed. CONCLUSIONS: This study contributes to a more detailed and systematic understanding of the 3-piece intrusion mechanics and confirms the simplicity and predictability of the 3-piece intrusion. According to the measured reduction rate, the intrusion springs should be activated once every 2 months or 1-mm intrusion.

Force decay of polyethylene terephthalate glycol aligner materials during simulation of typical clinical loading/unloading scenarios.

BACKGROUND: This in vitro study investigated the effect of three distinct daily loading/unloading cycles on force delivery during orthodontic aligner therapy. The cycles were applied for 7 days and were designed to reflect typical clinical aligner application scenarios. MATERIALS AND METHODS: Flat polyethylene terephthalate glycol (PET-G) specimens (Duran®, Scheu Dental, Iserlohn, Germany) with thicknesses ranging between 0.4 and 0.75 mm were tested in a three-point-bending testing machine. Measurements comprised loading/unloading intervals of 12 h/12 h, 18 h/6 h, and 23 h/1 h, and specimens were exposed to bidistilled water during loading to simulate intraoral conditions. RESULTS: A very large decay in force for the PET­G specimens could already be observed after the first loading period, with significantly different residual force values of 24, 20, and 21% recorded for the 12 h/12 h, 18 h/6 h, and 23 h/1 h loading/unloading modes, respectively (Mann-Whitney U test, p < 0.01). In addition, further decays in force from the first to the last loading period at day 7 of 13.5% (12 h/12 h), 9.7% (18 h/6 h), and 8.4% (23 h/1 h) differed significantly among the three distinct loading modes (Mann-Whitney U test, p < 0.01). CONCLUSION: Although the initial material stiffness of PET­G is relatively high, the transmission of excessive forces is attenuated by the high material-related force decay already within a few hours after intraoral insertion.

Biomechanical model registration for monitoring and simulating large orthodontic tooth movements in the maxilla and mandible.

PURPOSE: Superimposition of digital dental-arch models allows quantification of orthodontic tooth movements (OTM). Currently, this procedure requires stable reference surfaces usually only present in the maxilla. This study aimed to investigate the accuracy of a novel superimposition approach based on biomechanical principles of OTM and the equilibrium of forces and moments (EFM)-applicable in both jaws-for monitoring and simulating large OTM. METHODS: The study included 7 patients who had undergone extraction of the first (PM1-Ex) or second (PM2-Ex) premolar in each quadrant. Digital models taken at start and end of the T­Loop treatment phase were superimposed by applying 3 EFM variants differing in the number of teeth used for registration. Maxillary OTM results for EFM were validated against those for a conventional surface registration method (SRM). In an additional case study, OTM were simulated for PM1-Ex, PM2-Ex and non-extraction treatment strategies. RESULTS: The EFM variant that included all teeth of the dental arch achieved the highest accuracy, with median translational and rotational OTM deviations from SRM of only 0.37 mm and 0.56°, respectively. On average, retracted canines and first premolars were distalized by 3.0 mm, accompanied by 6.2° distal crown tipping and 12.2° distorotation. The share of space closure by molar mesialization was 19.4% for PM1-Ex quadrants and 34.5% for PM2-Ex quadrants. CONCLUSION: EFM allows accurate OTM quantification relative to the maxillary and mandibular bases even in challenging situations involving large OTM. Superimposition of malocclusion and setup models enables realistic simulation of final tooth positions. This may greatly enhance the value of digital setups for decision-making in orthodontic treatment planning.

Trueness of full-arch IO scans estimated based on 3D translational and rotational deviations of single teeth-an in vitro study.

OBJECTIVES: To three-dimensionally evaluate deviations of full-arch intraoral (IO) scans from reference desktop scans in terms of translations and rotations of individual teeth and different types of (mal)occlusion. MATERIALS AND METHODS: Three resin model pairs reflecting different tooth (mal)positions were mounted in the phantom head of a dental simulation unit and scanned by three dentists and three non-graduate investigators using a confocal laser IO scanner (Trios 3®). The tooth-crown surfaces of the IO scans and reference scans were superimposed by means of best-fit alignment. A novel method comprising the measurement of individual tooth positions was used to determine the deviations of each tooth in the six degrees of freedom, i.e., in terms of 3D translation and rotation. Deviations between IO and reference scans, among tooth-(mal)position models, and between dentists and non-graduate investigators were analyzed using linear mixed-effects models. RESULTS: The overall translational deviations of individual teeth on the IO scans were 76, 32, and 58 µm in the lingual, mesial, and intrusive directions, respectively, resulting in a total displacement of 114 µm. Corresponding rotational deviations were 0.58° buccal tipping, 0.04° mesial tipping, and 0.14° distorotation leading to a combined rotation of 0.78°. These deviations were the smallest for the dental arches with anterior crowding, followed by those with spacing and those with good alignment (p < 0.05). Results were independent of the operator's level of education. CONCLUSIONS: Compared to reference desktop scans, individual teeth on full-arch IO scans showed high trueness with total translational and rotational deviations < 115 µm and < 0.80°, respectively. CLINICAL RELEVANCE: Available confocal laser IO scanners appear sufficiently accurate for diagnostic and therapeutic orthodontic applications. Results indicate that full-arch IO scanning can be delegated to non-graduate dental staff members.

Active droploids.

Active matter comprises self-driven units, such as bacteria and synthetic microswimmers, that can spontaneously form complex patterns and assemble into functional microdevices. These processes are possible thanks to the out-of-equilibrium nature of active-matter systems, fueled by a one-way free-energy flow from the environment into the system. Here, we take the next step in the evolution of active matter by realizing a two-way coupling between active particles and their environment, where active particles act back on the environment giving rise to the formation of superstructures. In experiments and simulations we observe that, under light-illumination, colloidal particles and their near-critical environment create mutually-coupled co-evolving structures. These structures unify in the form of active superstructures featuring a droplet shape and a colloidal engine inducing self-propulsion. We call them active droploids-a portmanteau of droplet and colloids. Our results provide a pathway to create active superstructures through environmental feedback.

Evaluation of orthodontic loads and wire-bracket contact configurations in a three-bracket setup: Comparison of in-vitro experiments with numerical simulations.

So far, no practicable procedure exists to quantify the orthodontic loads applied to teeth in vivo. Dentists therefore rely on experience and simplified mechanical in-vitro experiments comprising deflection of orthodontic wires. Predicting the mechanical behaviour of orthodontic wires during clinical therapy requires understanding of the different contact states at multi-bracket-wire interfaces. This study experimentally investigates the effect of different bracket-wire contact configurations in a three-bracket setup and uses two numerical approaches to analyse and complement the experimental data. Commonly used round stainless-steel wires (diameter: 0.012″ and 0.016″) and titanium-molybdenum alloy wires (diameter: 0.016″ and 0.018″) were tested. All six force-moment components were measured separately for each of the three brackets. The results indicate that a specific sequence of distinct bracket-wire contact configurations occurs. Several transitions between configurations caused substantial changes of effective wire stiffness (EWS), which were consistent among experimental and numerical methods. The lowest EWS was observed for the configuration in which the wire touched only one wing of the lateral brackets. Taking this stiffness as 100%, the transition to a configuration in which the wire touched two opposing wings of the lateral brackets resulted in an increase of EWS of 300% ± 10%. This increase was independent of the wire type. Additional contacts resulted in further increases of stiffness beyond 400%. The results of this combined experimental and numerical study are important for providing a fundamental understanding of multi-bracket-wire contact configurations and have important implications for clinical therapy.

Non-equilibrium properties of an active nanoparticle in a harmonic potential.

Active particles break out of thermodynamic equilibrium thanks to their directed motion, which leads to complex and interesting behaviors in the presence of confining potentials. When dealing with active nanoparticles, however, the overwhelming presence of rotational diffusion hinders directed motion, leading to an increase of their effective temperature, but otherwise masking the effects of self-propulsion. Here, we demonstrate an experimental system where an active nanoparticle immersed in a critical solution and held in an optical harmonic potential features far-from-equilibrium behavior beyond an increase of its effective temperature. When increasing the laser power, we observe a cross-over from a Boltzmann distribution to a non-equilibrium state, where the particle performs fast orbital rotations about the beam axis. These findings are rationalized by solving the Fokker-Planck equation for the particle's position and orientation in terms of a moment expansion. The proposed self-propulsion mechanism results from the particle's non-sphericity and the lower critical point of the solution.

Measurement of anomalous diffusion using recurrent neural networks.

Anomalous diffusion occurs in many physical and biological phenomena, when the growth of the mean squared displacement (MSD) with time has an exponent different from one. We show that recurrent neural networks (RNNs) can efficiently characterize anomalous diffusion by determining the exponent from a single short trajectory, outperforming the standard estimation based on the MSD when the available data points are limited, as is often the case in experiments. Furthermore, the RNNs can handle more complex tasks where there are no standard approaches, such as determining the anomalous diffusion exponent from a trajectory sampled at irregular times, and estimating the switching time and anomalous diffusion exponents of an intermittent system that switches between different kinds of anomalous diffusion. We validate our method on experimental data obtained from subdiffusive colloids trapped in speckle light fields and superdiffusive microswimmers.

Experimental friction and deflection forces of orthodontic leveling archwires in three-bracket model experiments.

OBJECTIVE: In vitro testing of archwires in a multibracket model may provide estimates of force-moment (F/M) systems applied to individual teeth in a realistic geometry. Such investigations have mostly been performed by continuous wire deflection, leading to frictional forces biasing the pure deflection forces. Aim of this study was to quantify this bias and the pure deflection forces for leveling archwires. MATERIALS AND METHODS: Three nickel-titanium (NiTi) and two multistranded wires were tested in a three-bracket model simulating vertical movement of an upper incisor with a typical interbracket distance of 8 mm (intercenter). To determine pure deflection forces, the middle bracket was first leveled incrementally from its vertical malposition to neutral position with repeated wire insertion at each step (so-called "static leveling mode"). For comparison, forces at the middle bracket were also determined during dynamic leveling with or without ligation of the wire at the lateral brackets by either elastic, tight or loose steel ligatures. RESULTS: The dynamic mode resulted in significantly lower mean leveling forces for all the tested wires (ANOVA [analysis of variance], p < 0.01) compared to the static mode. Expressed in numbers, dynamic wire unloading resulted in mean force underestimation of 53 ± 9% (loose steel ligatures), 56 ± 11% (elastic ligatures) or 91 ± 29% (tight steel ligatures). CONCLUSIONS: Orthodontic tooth movement is quasi-static. This concerns the initial hyalinization phase in particular. Thus, especially static testing of archwires provides valid reference data for the peak forces exerted directly after clinical insertion of a leveling wire. In dynamic wire testing, significant underestimation of actual forces exerted on individual teeth may occur due to experimental friction, which might considerably differ from that occurring during clinical therapy. This aspect has to be taken into account in the interpretation of published stiffness values for orthodontic wires, and in the selection of the appropriate archwire for leveling of the present tooth malposition, respectively.

Effect of variable periodontal ligament thickness and its non-linear material properties on the location of a tooth's centre of resistance.

In orthodontics, the 3D translational and rotational movement of a tooth is determined by the force-moment system applied and the location of the tooth's centre of resistance (CR). Because of the practical constraints of in-vivo experiments, the finite element (FE) method is commonly used to determine the CR. The objective of this study was to investigate the geometric model details required for accurate CR determination, and the effect of material non-linearity of the periodontal ligament (PDL). A FE model of a human lower canine derived from a high-resolution µCT scan (voxel size: 50 µm) was investigated by applying four different modelling approaches to the PDL. These comprised linear and non-linear material models, each with uniform and realistic PDL thickness. The CR locations determined for the four model configurations were in the range 37.2-45.3% (alveolar margin: 0%; root apex: 100%). We observed that a non-linear material model introduces load-dependent results that are dominated by the PDL regions under tension. Load variation within the range used in clinical orthodontic practice resulted in CR variations below 0.3%. Furthermore, the individualized realistic PDL geometry shifted the CR towards the alveolar margin by 2.3% and 2.8% on average for the linear and non-linear material models, respectively. We concluded that for conventional clinical therapy and the generation of representative reference data, the least sophisticated modelling approach with linear material behaviour and uniform PDL thickness appears sufficiently accurate. Research applications that require more precise treatment monitoring and planning may, however, benefit from the more accurate results obtained from the non-linear constitutive law and individualized realistic PDL geometry.

Light-controlled assembly of active colloidal molecules.

Thanks to a constant energy input, active matter can self-assemble into phases with complex architectures and functionalities such as living clusters that dynamically form, reshape, and break-up, which are forbidden in equilibrium materials by the entropy maximization (or free energy minimization) principle. The challenge to control this active self-assembly has evoked widespread efforts typically hinging on engineering of the properties of individual motile constituents. Here, we provide a different route, where activity occurs as an emergent phenomenon only when individual building blocks bind together in a way that we control by laser light. Using experiments and simulations of two species of immotile microspheres, we exemplify this route by creating active molecules featuring a complex array of behaviors, becoming migrators, spinners, and rotators. The possibility to control the dynamics of active self-assembly via light-controllable nonreciprocal interactions will inspire new approaches to understand living matter and to design active materials.

Novel Method for Superposing 3D Digital Models for Monitoring Orthodontic Tooth Movement.

Quantitative three-dimensional analysis of orthodontic tooth movement (OTM) is possible by superposition of digital jaw models made at different times during treatment. Conventional methods rely on surface alignment at palatal soft-tissue areas, which is applicable to the maxilla only. We introduce two novel numerical methods applicable to both maxilla and mandible. The OTM from the initial phase of multi-bracket appliance treatment of ten pairs of maxillary models were evaluated and compared with four conventional methods. The median range of deviation of OTM for three users was 13-72% smaller for the novel methods than for the conventional methods, indicating greater inter-observer agreement. Total tooth translation and rotation were significantly different (ANOVA, p < 0.01) for OTM determined by use of the two numerical and four conventional methods. Directional decomposition of OTM from the novel methods showed clinically acceptable agreement with reference results except for vertical translations (deviations of medians greater than 0.6 mm). The difference in vertical translational OTM can be explained by maxillary vertical growth during the observation period, which is additionally recorded by conventional methods. The novel approaches are, thus, particularly suitable for evaluation of pure treatment effects, because growth-related changes are ignored.

Microscopic Engine Powered by Critical Demixing.

We experimentally demonstrate a microscopic engine powered by the local reversible demixing of a critical mixture. We show that, when an absorbing microsphere is optically trapped by a focused laser beam in a subcritical mixture, it is set into rotation around the optical axis of the beam because of the emergence of diffusiophoretic propulsion. This behavior can be controlled by adjusting the optical power, the temperature, and the criticality of the mixture.

Forces and moments applied during derotation of a maxillary central incisor with thinner aligners: An in-vitro study.

INTRODUCTION: Recent studies have shown that therapeutic loads applied to individual teeth by aligners may substantially exceed recommended values. The primary purpose of this study was to quantify force and moment components during derotation of a maxillary central incisor when 0.3-mm-thick or 0.4-mm-thick polyethylene terephthalate glycol aligners were used instead of conventional polyethylene terephthalate glycol aligners with a minimum thickness of 0.5 mm. METHODS: The test setup consisted of an acrylic model of a maxilla with a separated right central incisor mounted on a 3-dimensional force and moment sensor. The force and moment components were recorded for aligners with thicknesses ranging from 0.3 to 0.75 mm during ±10° rotation and derotation of the separated incisor. RESULTS: Moments exerted by the thinnest aligner currently available, 0.5 mm, were 73.57 Nmm for the 10° mesiorotation. In comparison, the corresponding moments with the 0.4-mm and 0.3-mm aligners were 41.08 and 17.84 Nmm, respectively. Moment values for derotation of the maxillary right central incisor into neutral position showed nonlinear return curves indicating viscoelastic material behavior. CONCLUSIONS: A significant load reduction can be achieved with the new thinner aligners. Because of the form instability of the 0.3-mm aligner during handling, we suggest the novel sequence 0.4, 0.5, and 0.75 mm for aligner systems based on sequentially increased material thickness. This sequence combines sufficiently low initial aligner stiffness and steady load increases in single setup steps. The viscoelastic behavior of polyethylene terephthalate glycol aligners observed during incisor derotation should lead to a reduction of the high initial load exerted directly after intraoral aligner insertion.

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.