Mechanical and Viscoelastic Properties of a Temperature-Responsive Photocurable Resin for 3D Printed Orthodontic Clear Aligners

Mechanical and Viscoelastic Properties of a Temperature-Responsive Photocurable Resin for 3D Printed Orthodontic Clear Aligners | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Mechanical and Viscoelastic Properties of a Temperature-Responsive Photocurable Resin for 3D Printed Orthodontic Clear Aligners Jin-Young Choi, Hoon Kim, Seong-Hun Kim, Su-Jung Kim, Jung-Yul Cha, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4106282/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract This study presents a novel technique for the direct 3D printing of TC-85, a biocompatible material specifically designed for orthodontic uses. This method aims to overcome the biomechanical constraints associated with the conventional thermoforming process used in aligner fabrication. The investigation emphasizes analyzing TC-85's mechanical and viscoelastic properties, focusing on how temperature changes impact these characteristics and their relevance to clinical outcomes. Using a Digital Light Processing (DLP) 3D printer, the photoreactive resin TC-85 is printed, and extensive thermo-mechanical testing is conducted, which includes evaluations of tensile modulus, stress relaxation, and creep behavior. Dynamic Mechanical Analysis (DMA) is conducted at temperatures varying from 30 to 45°C to assess the material's adaptive response to thermal fluctuations. TC-85 is distinguished by its unique mechanical properties, which include a temperature-sensitive stiffness, stress relaxation capability, and shape memory feature. The results demonstrate that TC-85 maintains an enhanced level of residual force and a faster recovery of strain through numerous cycles of loading and unloading. At 40°C, TC-85 displays a substantial reduction in its storage modulus, while maintaining consistent strain recovery and volumetric constancy. The study highlights TC-85's potential in orthodontic treatments, providing adaptable mechanical and viscoelastic properties that enable the exertion of consistent, regulated forces on teeth. Its resistance to force decay, stable volume at raised temperatures, and built-in shape memory enhance hygienic upkeep and patient comfort, positioning TC-85 as a pioneering material for the next generation of clear aligners. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Clear aligners have become increasingly prevalent in adult orthodontics, capturing 15–20% of the global orthodontic market 1 . Their appeal to patients lies in their aesthetic discretion and comfort, while orthodontists benefit from reduced chair time and simplified oral hygiene management 2 . Even with increased applications of clear aligners, clear aligners are considered less effective for achieving certain tooth movements, such as buccolingual tilting, extraction space closure and palatal expansion, compared to conventional fixed appliances 3 , 4 . Additionally, clear aligners are often found to be less successful in correcting major anteroposterior discrepancies 5 . Since the invention of clear aligner orthodontic treatment until now, the conventional materials of choice for clear aligners have been PETG and TPU. Although PETG is very effective in exerting a strong force on teeth, it does not provide the moderate and sustained force preferred for orthodontic treatments. Additionally, the fitting accuracy of aligners produced from these materials are often not ideal due to the constraints of the heat fusion process. Despite attempts to enhance precision through multi-layered urethane/PETG structures, the intrinsic properties of the thermoplastic materials after heat treatment process pose challenges in achieving the optimal accuracy. The direct 3D printing of clear aligners with urethane-acrylic photocurable resins represents a breakthrough, offering improvements in the rheological properties (viscosity and elasticity suitable for orthodontic treatment) and superior fit accuracy compared to the conventional vacuum formed clear aligners 6 , 7 , 8 , 9 , 10 ,1112, 13 .As a spotlighted technology for dental products, 3D printing, especially VAT photopolymerization based 3D printing, such as SLA (Stereolithography), DLP (digital light processing), and LCD, making its way into direct printing of clear aligners is not surprising after all, as the technology has promised and proven itself with its high-quality resolution as well as functional and smart material applications 14 , 15 , 16 , 17 , 18 . For polymers as such, in-depth analysis on their rheological properties is required for thorough understanding of the material. Various static mechanical properties of existing thermoplastics, including water absorption, solubility, surface hardness, transparency, fatigue, creep, and stress relaxation, have been extensively evaluated in numerous studies. These investigations have subsequently paved the way for numerous clinical case studies aimed at optimizing the application of clear aligners in clinical practice. Among a multitude of physical attributes, enhancing device performance and predicting treatment outcomes necessitate a comprehensive understanding of not only static mechanical properties but also force decay due to creep and stress relaxation. This importance stems from the prolonged wear and the repetitive attachment and detachment of clear aligners during orthodontic treatment. In contrast to elastic materials like Ni-Ti wire, the plastics used in clear aligners exhibit viscoelastic properties, existing in an intermediate state between viscous and elastic materials 19 . This viscoelastic nature allows clear aligners to withstand prolonged loading, displaying distinct behaviors depending on the applied load 20 . Creep behavior is characterized by gradual deformation under a repeated and constant load, leading to a decrease in restoring force as the deformation continues. Previous research has indicated that stress relaxation, ranging from 17.9–62%, occurs over a 24-hour period under conditions simulating the oral cavity (37°C and 100% humidity). The degree of relaxation varies with the type of thermoplastic material and the number of layers used, according to empirical evidence 21 . Although the mechanical characteristics of directly printed clear aligners may seem inferior to those manufactured from TPU and PETG with ultra-high molecular weights, directly printed clear aligners offer distinct advantages in orthodontics by minimizing the risk of orthodontic trauma and pain (e.g., side effects observed with Smile Direct Club, incidents of tooth loss, and breakage). When a gentler correction force is needed for tooth alignment, the mechanical properties of the material can be customized by adjusting the temperature or by altering the thickness of the direct printed aligners at the 3D design stage. The 3D direct printed aligners are thermo-responsive, thus react to temperature change immediately which could be used to ease pain or discomfort the patient may experience during the treatment. In the prior study, the thermo-mechanical and viscoelastic properties were analyzed at 37°C and 80°C 22 . However, the oral temperature in clinical situation is seldom sustained at 37°C (body temperature) and rarely reaches the exceptionally high level of 80°C. Instead, the temperature within the oral cavity varies within a smaller range with consumption of food, drinks, and other factors. Therefore, it is important to analyze the properties of the aligners in response to the range of temperatures that aligns more with the actual oral temperatures that the users encounter throughout the day. This study aimed to investigate the changes in mechanical properties relative to temperature. Tensile strength, rheological properties, and creep recovery were measured at more precise temperatures (25°C, 30°C, 35°C, and 40°C) by immersing specimens in a temperature-controlled water bath. An analysis of the clinical implications was then carried out based on these comprehensive results. 2. Material & Method 2 − 1 Specimens preparation The material chosen for the direct-printed aligners was TC-85, obtained from Graphy Inc. in Seoul, Korea. Formulated from the oligomers GR30860 and GR3060, this resin undergoes polymerization with the addition of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as a photoinitiator, known commercially as Irgacure 819 (BASF SE, Ludwigshafen, Germany). A stick-shaped specimen was printed to evaluate the material's mechanical properties, with dimensions set to LW 60 x 14 mm. Considering the commonly used aligner thicknesses of 0.5mm, 0.65mm, and 0.8mm, the specimens were printed with three thicknesses by using computer-aided design. Specimens were printed by the DLP 3D printer, Uniz 4K (Uniz, San Diego, USA). After printing, residual liquid resin on the specimen’s surface was gently removed with a soft scraper, and the specimen was then cured using a post curing machine (Tera Harz Cure, Graphy Inc., Korea) 20 minutes, using UV light within the wavelength range of 385–405 nm under Nitrogen condition 2324, 25 . For Dynamic Mechanical Analysis (DMA) and Viscoelastic Testing, the specimen dimensions were customized to fit the capacity of the DMA equipment (Q800, TA Instrument, USA), which has a maximum load capability of 18 N. Rectangular strips with dimensions of 3 x 40 mm were prepared for the PETG specimens, and 5 x 40 mm for the TC-85 specimens. To ensure uniformity, the average thickness of the specimens was calculated by measuring the thicknesses at three points (two ends and the middle) along the length of each specimen. 2–2 Static Mechanical Property Test (Tensile Test) Tensile test was carried out on seven specimens from each group, immersed in a water bath of constant temperatures of 30°C, 35°C, 40°C, and 45°C, as illustrated in Fig. 1. The tensile test was conducted using a Universal Testing Machine (AllroundLine Z010, 2 kN load cell, Zwick, Germany). Tension was applied to each specimen continuously until fracture with a crosshead speed of 5 mm/min. The static mechanical properties were evaluated by measuring the yield strength and elastic modulus. 2–3 Dynamic Mechanical Property 2-3-1 Dynamic Mechanical Analysis (DMA) Test (Frequency Sweep) To evaluate the rheological properties of the material, dynamic mechanical analysis (DMA) was conducted using a frequency sweep approach. Tests were performed at temperatures of 30°C, 35°C, 40°C, and 45°C, at a strain rate of 0.1%, and frequency range from 0.1 to 100 Hz. The heating rate was maintained at 5°C/min (K/min), utilizing a DMA equipment (Q800, TA instrument, USA). Storage modulus, loss modulus, and loss tangent were measured in relation to temperature. The tests were then repeated three times for each temperature group to ensure reliability of the experiments with an error margin below 10%. 2-3-2 Thermo-Mechanical Cycle Test (Stress Relaxation & Creep Test) The evaluation of creep behavior and stress relaxation for each material was performed using DMA (Q800, TA instrument, USA) and its stress relaxation mode. The specimen was firmly positioned at supporting points to maintain a consistent distance of 10 mm between the fixation zig. Thirteen cycles were carried out, each involving 2% tension maintained for 60 minutes at temperatures of 30°C, 35°C, 40°C, and 45°C, each followed by a 60-minute recovery period. Patterns of stress relaxation and strain recovery were methodically observed throughout the experiments. Importantly, three specimens at each temperature were subjected to repeated testing, confirming that the results from each experiment fell within a 10% error margin. 2-3-3 Shape Memory Property test Among several methods of evaluating the shape recovery effect of materials, the bending test was chosen to qualitatively investigate and directly visualize the shape recovery property 26 , 27 . A U-shaped model was used to simulate a scenario in which a tooth deviates from the occlusal line towards the buccal side under the influence of a bending force exerted by aligners. The central shaft of the U-shaped model had a diameter of 4 mm. Specimens were bent into a U-shape at 80°C, which is above the glass transition temperature (T g ) of TC-85 and were held in this position for 5 minutes (note: T g values were ascertained via DMA) 22 . These specimens, once bent at this elevated temperature, were then quickly cooled to and maintained at 24°C for additional 5 minutes. Upon removing the external force, the initial bending angle (θ initial ) of the folded specimen was measured. Then, the specimens were immersed in a water bath at temperatures of 30°C, 35°C, 40°C, and 45°C, where the shape recovery process was recorded using video capture at a frame rate of 30 FPS over an hour. The initial bending angle (θ initial ) and the bending angle at subsequent times (θ t ) were measured at specified time intervals (10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 30 minutes, and 60 minutes) using the mathematics software GeoGebra, developed by Markus Hohenwarter. The shape recovery ratio was determined using the following equation: $$\mathbf{S}\mathbf{h}\mathbf{a}\mathbf{p}\mathbf{e} \mathbf{r}\mathbf{e}\mathbf{c}\mathbf{o}\mathbf{v}\mathbf{e}\mathbf{r}\mathbf{y} \mathbf{r}\mathbf{a}\mathbf{t}\mathbf{i}\mathbf{o}=\frac{{\varvec{\theta }}_{\varvec{i}\varvec{n}\varvec{i}\varvec{t}\varvec{i}\varvec{a}\varvec{l}}-{\varvec{\theta }}_{\varvec{t}}}{{\varvec{\theta }}_{\varvec{i}\varvec{n}\varvec{i}\varvec{t}\varvec{i}\varvec{a}\varvec{l}}}\mathbf{*}100\mathbf{\%}$$ 3. Result As temperature rose from 30°C to 45°C, a gradual decrease in tensile strength, elastic modulus, and maximum force within a 20% strain was noted. The tensile strength and elastic modulus did not show significant change with varied sample thicknesses (Figs. 2a and 2b). However, for max standard force, the thicker specimen showed much higher max standard force in 20% at 30°C. However, with increasing temperature, this difference diminished, and beyond 40°C, the relationship between max standard force and thickness was not significant (Fig. 2c). Figure 2d displays the elongation at break in relation to both temperature and sample thickness, with all elongation values exceeding 100% and showing large standard deviations. The force distribution resulting from an applied tensile load in relation to thickness and temperature is demonstrated in Fig. 3. The results indicate that the force required for deformation significantly decreases as temperature increases from 30°C to 45°C for all thicknesses. The force deviation based on temperature was the most pronounced in the specimen with 0.8 mm thickness, aligning with the observations in Fig. 2c. Figure 4 presents changes in storage modulus and loss modulus from the DMA frequency sweep at varying temperatures. A distinct decrease in storage modulus was noted as the temperature increases from 30°C to 40°C, but at temperatures beyond 40°C, no significant decrease in storage modulus nor increase in loss modulus was observed. The cycle tests, involving a 2% elongation held for 60 minutes, followed by a 60-minute force release period, showed the pattern of stress relaxation based on temperature (Fig. 5). Specimens exposed to temperatures over 40°C seemed to recover fully to their original form, coupled with a reduction in the magnitude of the applied force. The inherent stress and recovery rates after 13 cycles are detailed in Table 1 . At the end of the 1 hour recording, specimens at 30°C and 35°C exhibited a recovery rate below 80%, whereas those above 40°C, especially at 45°C, showed a recovery rate above 90%, suggesting nearly complete recovery and significant stress relaxation. Table 1 Static force and recovery rate at 30°C, 35°C, 40°C and 45°C at the 13th stress relaxation and creep of 13 repetitions of a cycle of 2% elongation for 60 min and recovery for 60 min Temperature (℃) Static force (N) Recovery rate (%) 30 7.02 78.11 35 2.00 77.20 40 0.45 92.76 45 0.18 99.18 The results of the shape memory experiments highlighted the temperature-dependent behaviors of the material. According to the 1 hour observation of shape recovery, the materials showed the fastest recovery was at 45°C reaching 99% recovery, while the slowest was at 30°C, where only 34.4% recovery occurred after 60 minutes (Fig. 6).The calculated values of shape recovery ratio of TC-85 specimens based on the measured initial bending angles (θ initial ) and bending angles at subsequent times (θ t ) are shown in Table 2 . 4. Discussion In contrast to previous studies that used dumbbell-shaped specimens, this research employed stick-shaped specimens to minimize experimental bias due to variations in specimen width. In the previous experiments, the locations of the fracture during the elongation process under the tensile force were determined by the dumbbell shape in some cases. With the stick-shape specimens, such factors affecting the location of fracture could be eliminated. However, fractures still occurred at the junction between the specimen and the fixed region. This phenomenon is attributable to the material’s significant elasticity and yield strength. However, strain at such high values are not relevant to the clinical use of the clear orthodontic devices, thus there is no issue in deriving a clinical interpretation from these experimental results. The initial hypothesis applied to the previous study was that variations in the thickness of clear aligner devices could lead to unwanted forces on the teeth, with the assumption that aligner thickness significantly affects the orthodontic forces applied. However, results from the previous studies focused on the differences in physical properties between PETG and TC-85 rather than addressing the differences in physical properties based on thickness variations. In this study, only one material was used, and the hypothesis was empirically tested by fabricating TC-85 specimens at three thicknesses of 0.5 mm, 0.65 mm, and 0.8 mm. One of the most significant findings from previous research is that the physical properties of materials, especially TC-85, demonstrate very particular viscoelastic behaviors and temperature-dependent shape memory properties 9 , 22 , 28 . Experiments were conducted at 37°C and 80°C to test the properties near body temperature. However, temperature such as 80°C above T g was a condition too extreme to compare the changed properties to draw clinical meaning. The current study sought to rectify this by evaluating material properties at temperatures that are more representative of conditions within the oral cavity on a daily basis: 30°C, 35°C, 40°C, and 45°C. Theoretically, tensile strength and elastic modulus are derived from maximum tensile and cross-sectional area of the material, thus are independent of the thickness. The current study corroborated this, showing no significant variance in these measurements across different thicknesses. However, a clear trend was observed whereby an increase in temperature led to a decrease in both tensile strength and elastic modulus, which in turn made the material more ductile, requiring less force for deformation. Unlike vacuum formed clear aligners made of materials such as PETG, direct printed aligners can be designed to fit dental anatomy precisely regardless of undercuts. This allows close fit along all surface between the device and teeth, providing more effective orthodontic force. However, the perfect fit requires the device to pass through the height of contour and reach the undercut area. For optimal placement, the device must be able to adapt to dental contours and undercuts with minimal force and have adequate flexibility to avoid discomfort or breakage during the application or removal process. Therefore, lower tensile strength and elastic modulus are considered preferable. Additionally, the temperature-dependent flexibility can be used in advantage to ease the fitting and removal process of the device. For example, the device can be heated in hot water before fitting and heated by drinking warm water above body temperature before removing in order to increase flexibility instantly and ease the tight fit to fit and remove with minimal force required. Maximum standard force is measured in order to investigate the physical properties with thickness factor as an added factor. It was discovered that actual tensile strength varies with the thickness of the device, implying that thinner devices requires smaller force for deformation. In clinical settings where the aligner is to be applied to areas with poor periodontal health or sever undercuts, thinner device would be more advantageous for avoiding applying large force. Although a trend of decreasing force required with increasing temperatures was noted across all thicknesses, no substantial differences were observed above 40°C. Also, the force difference between 0.65 mm specimen and 0.8 mm specimen was relatively small at 30°C and 35°C. Therefore, while the thickness of the device does have some effect on the orthodontic corrective force exerted on teeth, its clinical significance seems insignificant. A stress-strain curve was created to visually demonstrate force variations relative to temperature (Fig. 3). As previously explained, force required for same strain decreased with increased temperature for a given thickness. Although the graph shows how the material behaves until its elongation break, only the initial values of the curve is clinically meaningful, because actual tooth movement occurs within a narrow range of elongation, making values beyond the initial changes less critical in clinical relevance. Similar to the results from previous studies, all specimen reached its peak force in the beginning stage of deformation. Compared to peaks of PETG, TC-85 showed significantly lower peak force. This result corroborates the potential of TC-85 to facilitate efficient tooth adjustment with fewer steps and biologically more suitable force. Applying this finding to clinical settings, the thicker the device is, the more movement per step one give. However, thickness over 0.65 mm is expected to have no significant effect. Also, since the material’s flexibility is temperature-dependable, it is possible to minimize side effects and discomfort especially when using an aligner designed for large tooth movement by utilizing warm temperature over body temperature and introducing physiological force to the teeth. As shown in Fig. 4, the temperature increases by 5°C from 30°C to 45°C, storage modulus decreases and tan delta increases. This phenomenon is very natural because it is based on the softening of polymers due to temperature change and also aligns with previous works 9 , 22 . However, in case of an orthodontic device, the temperature at which the viscoelastic properties are maximized must be around 35°C near human body temperature. In this study, as the temperature rises from 30°C to 40°C, the decrease of storage modulus and increase of tan delta occur at a constant rate, but the rate is hindered when the temperature rises above 40°C. Such phenomenon generally occurs around the Tg (glass transition temperature) of polymer materials. It can be inferred that the viscoelastic properties of the material are maximized in an environment at 35°C in the oral cavity near its Tg. Stress relaxation and creep of TC-85 were examined at 2% strain rate to mimic the material deformation during the application of the device (Fig. 5). In the previous study, experiments were conducted under a 1% strain rate condition, which was an inevitable condition due to the low elasticity of PETG. However, focus of this study was to investigate the effect of temperature by using only the TC-85 material, which has high flexibility and correspondingly high elastic range, so the experiments could be conducted at a strain rate of 2%. As the cycles progressed, stress relaxation became evident when the temperature was higher, and the static force also tended to decrease immediately. According to the results of the previous experiment, the amplitude of the initial force tended to be larger at lower temperature, and the static force in stress relaxation condition was also relatively higher at lower temperature. In addition, the creep occurred more clearly at lower temperatures and static force continuously increased as the cycle progressed. From a biomechanical perspective, creep could be seen as beneficial since it minimizes force decay and sustains the orthodontic force applied by the aligners. These results show that in a clinical situation where the orthodontic device is worn and placed under continuous strain, the force exerted from the device to the teeth can be changed with temperature. When a patient wears the aligner, appropriate orthodontic force must be applied to the teeth, and it must occur at a temperature close to oral environment approximately at 35°C. Combined with the results from the previous studies, the higher strain rate resulted in greater force. Therefore, by individualizing movement of each tooth in the set-up process and adjusting the expected strain rate, the ideal orthodontic force can be achieved with specifically controlled applied force 29 , 30 . If the patient experiences pain when installing the device, using water at a temperature higher than body temperature can help by immediately lowering the applied force to 0 N. There may be concerns about permanent deformation of the device due to creep phenomenon and repeated use. However, these concerns could be dismissed by the previous research which confirmed the shape memory property of the newly developed material at 37°C and 80°C followed by this study attempted to look at the shape memory pattern under more detailed conditions. Likewise, the material exhibited quicker recovery at an elevated temperature (Table 2 ). This study provides detailed pattern of shape memory and suggests that warming the clear aligner may be used as a guideline for first-timers and patients in transitions between orthodontic stages to lessen the discomfort. With TC-85, it is possible to control the applied force by distance adjustments rather than thickness control. In the case of thermoformed aligners made with PETG materials, 1 kg tension was generated at a strain rate of 1%, but direct printed aligner generated a force of 100g at 1% and 200g at 2%. Such orthodontic-friendly force range allows the operator to freely plan the orthodontic treatment without concerns on excessive amount of force. This method can be expressed as a force driven system. Even if the oral temperature rises by just 5 degrees, the orthodontic corrective force is clearly released and returns in moderate measures that is more biomechanically suitable. In conclusion, the immediate force when applying the device at body temperature may surpass physiological force. This is a common phenomenon among existing clear aligners, and materials such as PETG exert much greater initial force 31 . However, more efficient tooth movement is ensured with the property of TC-85 which allows stress relaxation to occur immediately and exert the most physiological force. Therefore, when using the device for the first time, it is advised to use it at a higher initial temperature to minimize discomfort and prevent excessive forces. Then, gradual adjustment to oral cavity temperature will ensure a smooth transition to physiological force range for optimal orthodontic corrective force applications. Although the study examined material properties across various temperatures, additional experiments considering different clinical conditions, simulation of installation and removal of the device, and the orthodontic force under fluctuating temperature rather than a fixed temperature in order to derive more clinically meaningful results. In addition, further investigation is necessary on various teeth morphologies and health conditions of periodontal tissues to determine how much tooth movement per set is appropriate to achieve the 1% and 2% strain as assumed in this and previous studies. Limitation 1. The outcomes may differ under conditions of 100% humidity, similar to those in the oral cavity, due to the considerable water absorption characteristic of polyurethane. 2. Prolonging the stress relaxation test beyond 24 hours could provide more significant findings that better reflect the typical wear duration of orthodontic aligners, which usually exceeds 24 hours. Conclusions TC-85, sensitive to body temperature, showcases enhanced shape memory with rising temperatures, reducing the corrective force of clear aligners for improved patient comfort. At 45°C, TC-85 reaches peak flexibility, aiding in comfortable orthodontic correction, while below 30°C, it maintains stiffness and resistance to external deformation. At 30°C, TC-85's elasticity, stress relaxation, and strain recovery properties enable it to deliver a steady, gentle corrective force suitable for orthodontic treatment. TC-85 resists force decay under varied thermal conditions, maintaining its corrective effectiveness through multiple device applications and removals. The stable, cross-linked structure of TC-85 remains consistent at 80°C, providing advantages over PETG in durability and user maintenance. Declarations DATA AVAILABILITY The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. ACKNOWLEDGMENT Experiments were carried out through free support of Anton Paar Korea's rheometer test equipment, and we would like to thank to Anton Paar Korea for helping us. Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. References Ojima, K. & Kau, C. H. A perspective in accelerated orthodontics with aligner treatment. Semin Orthod 23 , 76–82 (2017). Mulla Issa, F. K., Mulla Issa, Z. K., Rabah, A. & Hu, L. Periodontal parameters in adult patients with clear aligners orthodontics treatment versus three other types of brackets: A cross-sectional study. J Orthod Sci 9 , 4 (2020). Robertson, L. et al. Effectiveness of clear aligner therapy for orthodontic treatment: A systematic review. Orthod Craniofac Res 23 , 133–142 (2020). Rossini, G., Parrini, S., Castroflorio, T., Deregibus, A. & Debernardi, C. L. Efficacy of clear aligners in controlling orthodontic tooth movement: A systematic review. Angle Orthod 85 , 881–889 (2015). Djeu, G., Shelton, C. & Maganzini, A. Outcome assessment of Invisalign and traditional orthodontic treatment compared with the American Board of Orthodontics objective grading system. American Journal of Orthodontics and Dentofacial Orthopedics 128 , 292–298 (2005). Narongdej, P., Hassanpour, M., Alterman, N., Rawlins-Buchanan, F. & Barjasteh, E. Advancements in Clear Aligner Fabrication: A Comprehensive Review of Direct-3D Printing Technologies. Polymers vol. 16 Preprint at https://doi.org/10.3390/polym16030371 (2024). Jindal, P., Juneja, M., Siena, F. L., Bajaj, D. & Breedon, P. Mechanical and geometric properties of thermoformed and 3D printed clear dental aligners. American Journal of Orthodontics and Dentofacial Orthopedics 156 , 694–701 (2019). Koenig, N. et al. Comparison of dimensional accuracy between direct-printed and thermoformed aligners. Korean J Orthod 52 , 249–257 (2022). Atta, I. et al. Physiochemical and mechanical characterisation of orthodontic 3D printed aligner material made of shape memory polymers (4D aligner material). J Mech Behav Biomed Mater 150 , 106337 (2024). Schupp, W. et al. Shape Memory Aligners: A New Dimension in Aligner Orthodontics . Journal of Aligner Orthodontics vol. 7 (2023). Bichu, Y. M. et al. Advances in orthodontic clear aligner materials. Bioact Mater 22 , 384–403 (2023). Slaymaker, J., Hirani, S. & Woolley, J. Direct 3D printing aligners - past, present and future possibilities. British Dental Journal1 236 , 401–405 (2024). Panayi, N. C., Efstathiou, S., Christopoulou, I., Kotantoula, G. & Tsolakis, I. A. Digital Orthodontics: Present and Future . Andreu, A. et al. 4D printing materials for vat photopolymerization. Addit Manuf 44 , 102024 (2021). Kim, H., Khan, T. A., Ryu, K.-H., Sohn, I.-S. & Kim, H.-J. Nanocomposite materials for 3D printing. in APPLICATIONS AND INDUSTRIALISATION OF NANOTECHNOLOGY (eds. Ahmed, W. & Maciel, M. A. M.) 91–118 (2022). Lee, J. et al. Average-Accumulated Normalized Dose (A-AND) predicts ultimate tensile strength and elastic modulus of photopolymer printed by vat photopolymerization. Addit Manuf 55 , 102799 (2022). Kim, H. et al. 3D Printing of Polyethylene Terephthalate Glycol–Sepiolite Composites with Nanoscale Orientation. ACS Appl Mater Interfaces 12 , 23453–23463 (2020). Kim, H. et al. Embedded Direct Ink Writing 3D Printing of UV Curable Resin/Sepiolite Composites with Nano Orientation. ACS Omega 8 , 23554–23565 (2023). Fang, D., Zhang, N., Chen, H. & Bai, Y. Dynamic stress relaxation of orthodontic thermoplastic materials in a simulated oral environment. Dent Mater J 32 , 946–951 (2013). Kravitz, N. D., Kusnoto, B., BeGole, E., Obrez, A. & Agran, B. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign. American Journal of Orthodontics and Dentofacial Orthopedics 135 , 27–35 (2009). Lombardo, L. et al. Stress relaxation properties of four orthodontic aligner materials: A 24-hour in vitro study. Angle Orthod 87 , 11–18 (2016). Lee, S. Y. et al. Thermo-mechanical properties of 3D printed photocurable shape memory resin for clear aligners. Sci Rep 12 , (2022). Alessandra, C. et al. Comparison of the cytotoxicity of 3D-printed aligners using different post-curing procedures: an in vitro study. Australasian Orthodontic Journal 39 , 49–56 (2023). Lim, B. et al. Influence of Post-Curing in Nitrogen-Saturated Condition on the Degree of Conversion and Color Stability of 3D-Printed Resin Crowns. Dent J (Basel) 12 , 68 (2024). Šimunović, L. et al. Influence of Post-Processing on the Degree of Conversion and Mechanical Properties of 3D-Printed Polyurethane Aligners. Polymers (Basel) 16 , (2024). Wang, Z., Liu, J., Guo, J., Sun, X. & Xu, L. The Study of Thermal, Mechanical and Shape Memory Properties of Chopped Carbon Fiber-Reinforced TPI Shape Memory Polymer Composites. Polymers (Basel) 9 , 594 (2017). Liu, Y. et al. Thermo-Mechanical Properties of Glass Fiber Reinforced Shape Memory Polyurethane for Orthodontic Application. J Mater Sci Mater Med 29 , 148 (2018). Schupp, W. et al. Shape Memory Aligners: A New Dimension in Aligner Orthodontics . Journal of Aligner Orthodontics vol. 7 (2023). Grant, J. et al. Forces and moments generated by 3D direct printed clear aligners of varying labial and lingual thicknesses during lingual movement of maxillary central incisor: an in vitro study. Prog Orthod 24 , (2023). McKay, A. et al. Forces and moments generated during extrusion of a maxillary central incisor with clear aligners: an in vitro study. BMC Oral Health 23 , (2023). Author, C. et al. Force Assessment of Thermoformed and Direct-printed Aligners in a Lingual Bodily Movement of a Central Incisor Over Time: A 14-day In Vitro Study. J Korean Dent Sci 16 , 23–34 (2023). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 02 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 17 Jul, 2024 Reviews received at journal 23 May, 2024 Reviews received at journal 19 May, 2024 Reviewers agreed at journal 17 May, 2024 Reviewers agreed at journal 10 May, 2024 Reviewers invited by journal 08 May, 2024 Editor assigned by journal 08 May, 2024 Editor invited by journal 02 May, 2024 Submission checks completed at journal 30 Apr, 2024 First submitted to journal 15 Mar, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4106282","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":298939113,"identity":"37e4e123-adb7-45c5-ac9f-0d48d7905b0b","order_by":0,"name":"Jin-Young Choi","email":"","orcid":"","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Jin-Young","middleName":"","lastName":"Choi","suffix":""},{"id":298939115,"identity":"873a860b-2c73-4d98-be6d-f516f9c23736","order_by":1,"name":"Hoon Kim","email":"","orcid":"","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Hoon","middleName":"","lastName":"Kim","suffix":""},{"id":298939117,"identity":"15a07c40-0f55-44be-9cd9-03fb4d4899c8","order_by":2,"name":"Seong-Hun Kim","email":"","orcid":"","institution":"Kyung Hee University","correspondingAuthor":false,"prefix":"","firstName":"Seong-Hun","middleName":"","lastName":"Kim","suffix":""},{"id":298939119,"identity":"509a38f5-f0d4-4d38-99cd-fa205d505107","order_by":3,"name":"Su-Jung Kim","email":"","orcid":"","institution":"Kyung Hee University","correspondingAuthor":false,"prefix":"","firstName":"Su-Jung","middleName":"","lastName":"Kim","suffix":""},{"id":298939121,"identity":"1cc0ae3b-8c08-46e4-9482-3f40c63399bc","order_by":4,"name":"Jung-Yul Cha","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Jung-Yul","middleName":"","lastName":"Cha","suffix":""},{"id":298939123,"identity":"3d4238c5-5010-4a7e-9ee5-a7ce3fc070d7","order_by":5,"name":"Ki Beom Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABC0lEQVRIie3Ov0rDQBzA8V84OJdLusnvOOozXAikCsF3kUCmuDuIFAQ72blBwVfodK4JgboovkJcOjm0SxEs6l1UcPDSjh3uO9wfuA/3A3C5djAkrN0lBTLT+yFIAK/UJ2+4mdDM3FET6CbwQwBYvB3hI79qljlEwf7jqlmc48UA9pqaQdKflv8TQYI0LBTEVJzeh5MZ4tGQSU2yyEYOCIuFryDRRAlG9WAlA03qkw4yeP8m+VysPwxpB/u0EqF/IX47WE6Fd2UImMFKK+GXQcoLhREVWcyvx8inNZPVrUyjwkLw+alaLFUS3t2kc3xbJT35MHppXs+O+2ML+ZV/zsQssvO5y+VyuTb0BQ0TUh/dASL1AAAAAElFTkSuQmCC","orcid":"","institution":"Saint Louis University","correspondingAuthor":true,"prefix":"","firstName":"Ki","middleName":"Beom","lastName":"Kim","suffix":""},{"id":298939126,"identity":"0c2c27d1-6ac0-44a2-ba2f-2adac2f3e606","order_by":6,"name":"Hyun-Joong Kim","email":"","orcid":"","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Hyun-Joong","middleName":"","lastName":"Kim","suffix":""},{"id":298939128,"identity":"2ef8f77b-988f-43fa-9f58-22395f42c1cf","order_by":7,"name":"Se Yeon Lee","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Se","middleName":"Yeon","lastName":"Lee","suffix":""},{"id":298939130,"identity":"cc15acbf-60d3-44fb-acd2-c8d56a056d24","order_by":8,"name":"Sunho Jang","email":"","orcid":"","institution":"Graphy, Inc.","correspondingAuthor":false,"prefix":"","firstName":"Sunho","middleName":"","lastName":"Jang","suffix":""},{"id":298939132,"identity":"b070b93a-2f65-455d-b777-08dd61da40a2","order_by":9,"name":"Tanveer Ahmed Khan","email":"","orcid":"","institution":"Graphy, Inc.","correspondingAuthor":false,"prefix":"","firstName":"Tanveer","middleName":"Ahmed","lastName":"Khan","suffix":""},{"id":298939134,"identity":"85d5d2e5-7233-444f-bc29-6dc32ddb491b","order_by":10,"name":"Jinhong Min","email":"","orcid":"","institution":"Graphy, Inc.","correspondingAuthor":false,"prefix":"","firstName":"Jinhong","middleName":"","lastName":"Min","suffix":""},{"id":298939135,"identity":"340efba7-707b-49b2-b729-0a807c706a83","order_by":11,"name":"Jiho Lee","email":"","orcid":"","institution":"Graphy, Inc.","correspondingAuthor":false,"prefix":"","firstName":"Jiho","middleName":"","lastName":"Lee","suffix":""}],"badges":[],"createdAt":"2024-03-15 08:44:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4106282/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4106282/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-93026-0","type":"published","date":"2025-07-02T15:58:45+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":56040617,"identity":"5a5b346b-60ab-46df-9b01-12011d20f14d","added_by":"auto","created_at":"2024-05-07 19:17:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":731344,"visible":true,"origin":"","legend":"\u003cp\u003eThermostatic water bath for universal testing machine for measuring tensile strength according to temperature change; (a) Configuration of constant temperature water bath, (b) Tensile test fixture.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/90375ec6c8ffd6691f9c220c.png"},{"id":56040618,"identity":"c60208eb-1de1-4b0a-8b15-929279ccd9d4","added_by":"auto","created_at":"2024-05-07 19:17:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":105755,"visible":true,"origin":"","legend":"\u003cp\u003eTest result of tensile strength according to thickness and temperature change of tensile specimen in constant temperature water bath of universal testing machine; (a) tensile strength, (b) tensile modulus, (c) maximum tensile force within 20% strain, (d) maximum elongation break.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/7e7e59823e3e2c596c82d2f6.png"},{"id":56040616,"identity":"5d2e3abd-0d1e-4370-9324-92afed576a93","added_by":"auto","created_at":"2024-05-07 19:17:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":80844,"visible":true,"origin":"","legend":"\u003cp\u003eStress-strain graph of tensile strength according to thickness and temperature change of tensile specimen in a constant temperature water bath of universal testing machine; (a) 0.5 mm, (b) 0.65 mm, (c) 0.8 mm.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/7cb28966a0a0ae6c658287df.png"},{"id":56040623,"identity":"0a5b7ad6-ab0d-4020-8acd-794489be443d","added_by":"auto","created_at":"2024-05-07 19:17:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":64368,"visible":true,"origin":"","legend":"\u003cp\u003eRheological property change test according to frequency sweep for each temperature using DMA; (a) storage modulus, (b) loss modulus.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/76e1f4448ad6154e4deffbac.png"},{"id":56040619,"identity":"a622428b-ce17-48c5-a3fc-da87eb7a66c8","added_by":"auto","created_at":"2024-05-07 19:17:11","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":226941,"visible":true,"origin":"","legend":"\u003cp\u003eStress relaxation and creep at 30, 35, 40°C and 45 °C; The cycle of 2 % elongation for 60 min and recovery for 60 min was repeated 13 cycles; (a) 30 °C; (b) 35 °C; (c) 40 °C; (d) 45 °C.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/69181b7ad686144f9f85d014.png"},{"id":56040620,"identity":"6dced125-0042-4bc4-a460-d79bc143c577","added_by":"auto","created_at":"2024-05-07 19:17:11","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":578033,"visible":true,"origin":"","legend":"\u003cp\u003eShape memory effect over time of TC-85.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/c84487a79ea7e17f211c3a7f.png"},{"id":56040621,"identity":"9995e113-bde9-4cd1-b917-399e9feeb5ae","added_by":"auto","created_at":"2024-05-07 19:17:11","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":39963,"visible":true,"origin":"","legend":"\u003cp\u003eRecovery ratio (%) of TC-85 with respect to time (s) in log scale at varied temperatures of 30 °C, 35 °C, 40 °C, and 45 °C.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/d7d3e78672981568adcbda27.png"},{"id":86179658,"identity":"239c60bc-ec11-4e1d-920e-528a1e9bec98","added_by":"auto","created_at":"2025-07-07 16:18:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2818977,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4106282/v1/5adb97f6-da6b-4eda-9c93-67ab885ccca9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Mechanical and Viscoelastic Properties of a Temperature-Responsive Photocurable Resin for 3D Printed Orthodontic Clear Aligners","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eClear aligners have become increasingly prevalent in adult orthodontics, capturing 15\u0026ndash;20% of the global orthodontic market \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Their appeal to patients lies in their aesthetic discretion and comfort, while orthodontists benefit from reduced chair time and simplified oral hygiene management \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Even with increased applications of clear aligners, clear aligners are considered less effective for achieving certain tooth movements, such as buccolingual tilting, extraction space closure and palatal expansion, compared to conventional fixed appliances \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Additionally, clear aligners are often found to be less successful in correcting major anteroposterior discrepancies \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eSince the invention of clear aligner orthodontic treatment until now, the conventional materials of choice for clear aligners have been PETG and TPU. Although PETG is very effective in exerting a strong force on teeth, it does not provide the moderate and sustained force preferred for orthodontic treatments. Additionally, the fitting accuracy of aligners produced from these materials are often not ideal due to the constraints of the heat fusion process. Despite attempts to enhance precision through multi-layered urethane/PETG structures, the intrinsic properties of the thermoplastic materials after heat treatment process pose challenges in achieving the optimal accuracy. The direct 3D printing of clear aligners with urethane-acrylic photocurable resins represents a breakthrough, offering improvements in the rheological properties (viscosity and elasticity suitable for orthodontic treatment) and superior fit accuracy compared to the conventional vacuum formed clear aligners \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,1112,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e.As a spotlighted technology for dental products, 3D printing, especially VAT photopolymerization based 3D printing, such as SLA (Stereolithography), DLP (digital light processing), and LCD, making its way into direct printing of clear aligners is not surprising after all, as the technology has promised and proven itself with its high-quality resolution as well as functional and smart material applications \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. For polymers as such, in-depth analysis on their rheological properties is required for thorough understanding of the material.\u003c/p\u003e \u003cp\u003eVarious static mechanical properties of existing thermoplastics, including water absorption, solubility, surface hardness, transparency, fatigue, creep, and stress relaxation, have been extensively evaluated in numerous studies. These investigations have subsequently paved the way for numerous clinical case studies aimed at optimizing the application of clear aligners in clinical practice. Among a multitude of physical attributes, enhancing device performance and predicting treatment outcomes necessitate a comprehensive understanding of not only static mechanical properties but also force decay due to creep and stress relaxation. This importance stems from the prolonged wear and the repetitive attachment and detachment of clear aligners during orthodontic treatment. In contrast to elastic materials like Ni-Ti wire, the plastics used in clear aligners exhibit viscoelastic properties, existing in an intermediate state between viscous and elastic materials\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. This viscoelastic nature allows clear aligners to withstand prolonged loading, displaying distinct behaviors depending on the applied load \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Creep behavior is characterized by gradual deformation under a repeated and constant load, leading to a decrease in restoring force as the deformation continues. Previous research has indicated that stress relaxation, ranging from 17.9\u0026ndash;62%, occurs over a 24-hour period under conditions simulating the oral cavity (37\u0026deg;C and 100% humidity). The degree of relaxation varies with the type of thermoplastic material and the number of layers used, according to empirical evidence \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAlthough the mechanical characteristics of directly printed clear aligners may seem inferior to those manufactured from TPU and PETG with ultra-high molecular weights, directly printed clear aligners offer distinct advantages in orthodontics by minimizing the risk of orthodontic trauma and pain (e.g., side effects observed with Smile Direct Club, incidents of tooth loss, and breakage). When a gentler correction force is needed for tooth alignment, the mechanical properties of the material can be customized by adjusting the temperature or by altering the thickness of the direct printed aligners at the 3D design stage. The 3D direct printed aligners are thermo-responsive, thus react to temperature change immediately which could be used to ease pain or discomfort the patient may experience during the treatment.\u003c/p\u003e \u003cp\u003eIn the prior study, the thermo-mechanical and viscoelastic properties were analyzed at 37\u0026deg;C and 80\u0026deg;C \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. However, the oral temperature in clinical situation is seldom sustained at 37\u0026deg;C (body temperature) and rarely reaches the exceptionally high level of 80\u0026deg;C. Instead, the temperature within the oral cavity varies within a smaller range with consumption of food, drinks, and other factors. Therefore, it is important to analyze the properties of the aligners in response to the range of temperatures that aligns more with the actual oral temperatures that the users encounter throughout the day.\u003c/p\u003e \u003cp\u003eThis study aimed to investigate the changes in mechanical properties relative to temperature. Tensile strength, rheological properties, and creep recovery were measured at more precise temperatures (25\u0026deg;C, 30\u0026deg;C, 35\u0026deg;C, and 40\u0026deg;C) by immersing specimens in a temperature-controlled water bath. An analysis of the clinical implications was then carried out based on these comprehensive results.\u003c/p\u003e"},{"header":"2. Material \u0026 Method","content":"\n\u003ch3\u003e2 − 1 Specimens preparation\u003c/h3\u003e\n\u003cp\u003eThe material chosen for the direct-printed aligners was TC-85, obtained from Graphy Inc. in Seoul, Korea. Formulated from the oligomers GR30860 and GR3060, this resin undergoes polymerization with the addition of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as a photoinitiator, known commercially as Irgacure 819 (BASF SE, Ludwigshafen, Germany). A stick-shaped specimen was printed to evaluate the material's mechanical properties, with dimensions set to LW 60 x 14 mm. Considering the commonly used aligner thicknesses of 0.5mm, 0.65mm, and 0.8mm, the specimens were printed with three thicknesses by using computer-aided design. Specimens were printed by the DLP 3D printer, Uniz 4K (Uniz, San Diego, USA). After printing, residual liquid resin on the specimen\u0026rsquo;s surface was gently removed with a soft scraper, and the specimen was then cured using a post curing machine (Tera Harz Cure, Graphy Inc., Korea) 20 minutes, using UV light within the wavelength range of 385\u0026ndash;405 nm under Nitrogen condition \u003csup\u003e2324,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e .\u003c/p\u003e \u003cp\u003eFor Dynamic Mechanical Analysis (DMA) and Viscoelastic Testing, the specimen dimensions were customized to fit the capacity of the DMA equipment (Q800, TA Instrument, USA), which has a maximum load capability of 18 N. Rectangular strips with dimensions of 3 x 40 mm were prepared for the PETG specimens, and 5 x 40 mm for the TC-85 specimens. To ensure uniformity, the average thickness of the specimens was calculated by measuring the thicknesses at three points (two ends and the middle) along the length of each specimen.\u003c/p\u003e\n\u003ch3\u003e2–2 Static Mechanical Property Test (Tensile Test)\u003c/h3\u003e\n\u003cp\u003eTensile test was carried out on seven specimens from each group, immersed in a water bath of constant temperatures of 30\u0026deg;C, 35\u0026deg;C, 40\u0026deg;C, and 45\u0026deg;C, as illustrated in Fig.\u0026nbsp;1. The tensile test was conducted using a Universal Testing Machine (AllroundLine Z010, 2 kN load cell, Zwick, Germany). Tension was applied to each specimen continuously until fracture with a crosshead speed of 5 mm/min. The static mechanical properties were evaluated by measuring the yield strength and elastic modulus.\u003c/p\u003e\n\u003ch3\u003e2–3 Dynamic Mechanical Property\u003c/h3\u003e\n\n\u003ch3\u003e2-3-1 Dynamic Mechanical Analysis (DMA) Test (Frequency Sweep)\u003c/h3\u003e\n\u003cp\u003eTo evaluate the rheological properties of the material, dynamic mechanical analysis (DMA) was conducted using a frequency sweep approach. Tests were performed at temperatures of 30\u0026deg;C, 35\u0026deg;C, 40\u0026deg;C, and 45\u0026deg;C, at a strain rate of 0.1%, and frequency range from 0.1 to 100 Hz. The heating rate was maintained at 5\u0026deg;C/min (K/min), utilizing a DMA equipment (Q800, TA instrument, USA). Storage modulus, loss modulus, and loss tangent were measured in relation to temperature. The tests were then repeated three times for each temperature group to ensure reliability of the experiments with an error margin below 10%.\u003c/p\u003e\n\u003ch3\u003e2-3-2 Thermo-Mechanical Cycle Test (Stress Relaxation \u0026 Creep Test)\u003c/h3\u003e\n\u003cp\u003eThe evaluation of creep behavior and stress relaxation for each material was performed using DMA (Q800, TA instrument, USA) and its stress relaxation mode. The specimen was firmly positioned at supporting points to maintain a consistent distance of 10 mm between the fixation zig. Thirteen cycles were carried out, each involving 2% tension maintained for 60 minutes at temperatures of 30\u0026deg;C, 35\u0026deg;C, 40\u0026deg;C, and 45\u0026deg;C, each followed by a 60-minute recovery period. Patterns of stress relaxation and strain recovery were methodically observed throughout the experiments. Importantly, three specimens at each temperature were subjected to repeated testing, confirming that the results from each experiment fell within a 10% error margin.\u003c/p\u003e\n\u003ch3\u003e2-3-3 Shape Memory Property test\u003c/h3\u003e\n\u003cp\u003eAmong several methods of evaluating the shape recovery effect of materials, the bending test was chosen to qualitatively investigate and directly visualize the shape recovery property \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. A U-shaped model was used to simulate a scenario in which a tooth deviates from the occlusal line towards the buccal side under the influence of a bending force exerted by aligners. The central shaft of the U-shaped model had a diameter of 4 mm. Specimens were bent into a U-shape at 80\u0026deg;C, which is above the glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e) of TC-85 and were held in this position for 5 minutes (note: T\u003csub\u003eg\u003c/sub\u003e values were ascertained via DMA) \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. These specimens, once bent at this elevated temperature, were then quickly cooled to and maintained at 24\u0026deg;C for additional 5 minutes. Upon removing the external force, the initial bending angle (θ\u003csub\u003einitial\u003c/sub\u003e) of the folded specimen was measured. Then, the specimens were immersed in a water bath at temperatures of 30\u0026deg;C, 35\u0026deg;C, 40\u0026deg;C, and 45\u0026deg;C, where the shape recovery process was recorded using video capture at a frame rate of 30 FPS over an hour. The initial bending angle (θ\u003csub\u003einitial\u003c/sub\u003e) and the bending angle at subsequent times (θ\u003csub\u003et\u003c/sub\u003e) were measured at specified time intervals (10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 30 minutes, and 60 minutes) using the mathematics software GeoGebra, developed by Markus Hohenwarter. The shape recovery ratio was determined using the following equation:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\mathbf{S}\\mathbf{h}\\mathbf{a}\\mathbf{p}\\mathbf{e} \\mathbf{r}\\mathbf{e}\\mathbf{c}\\mathbf{o}\\mathbf{v}\\mathbf{e}\\mathbf{r}\\mathbf{y} \\mathbf{r}\\mathbf{a}\\mathbf{t}\\mathbf{i}\\mathbf{o}=\\frac{{\\varvec{\\theta }}_{\\varvec{i}\\varvec{n}\\varvec{i}\\varvec{t}\\varvec{i}\\varvec{a}\\varvec{l}}-{\\varvec{\\theta }}_{\\varvec{t}}}{{\\varvec{\\theta }}_{\\varvec{i}\\varvec{n}\\varvec{i}\\varvec{t}\\varvec{i}\\varvec{a}\\varvec{l}}}\\mathbf{*}100\\mathbf{\\%}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"3. Result","content":"\u003cp\u003eAs temperature rose from 30°C to 45°C, a gradual decrease in tensile strength, elastic modulus, and maximum force within a 20% strain was noted. The tensile strength and elastic modulus did not show significant change with varied sample thicknesses (Figs.\u0026nbsp;2a and 2b). However, for max standard force, the thicker specimen showed much higher max standard force in 20% at 30°C. However, with increasing temperature, this difference diminished, and beyond 40°C, the relationship between max standard force and thickness was not significant (Fig.\u0026nbsp;2c). Figure\u0026nbsp;2d displays the elongation at break in relation to both temperature and sample thickness, with all elongation values exceeding 100% and showing large standard deviations.\u003c/p\u003e\n\u003cp\u003eThe force distribution resulting from an applied tensile load in relation to thickness and temperature is demonstrated in Fig.\u0026nbsp;3. The results indicate that the force required for deformation significantly decreases as temperature increases from 30°C to 45°C for all thicknesses. The force deviation based on temperature was the most pronounced in the specimen with 0.8 mm thickness, aligning with the observations in Fig.\u0026nbsp;2c.\u003c/p\u003e\n\u003cp\u003eFigure 4 presents changes in storage modulus and loss modulus from the DMA frequency sweep at varying temperatures. A distinct decrease in storage modulus was noted as the temperature increases from 30°C to 40°C, but at temperatures beyond 40°C, no significant decrease in storage modulus nor increase in loss modulus was observed.\u003c/p\u003e\n\u003cp\u003eThe cycle tests, involving a 2% elongation held for 60 minutes, followed by a 60-minute force release period, showed the pattern of stress relaxation based on temperature (Fig.\u0026nbsp;5). Specimens exposed to temperatures over 40°C seemed to recover fully to their original form, coupled with a reduction in the magnitude of the applied force. The inherent stress and recovery rates after 13 cycles are detailed in Table\u0026nbsp;\u003cspan\u003e1\u003c/span\u003e. At the end of the 1 hour recording, specimens at 30°C and 35°C exhibited a recovery rate below 80%, whereas those above 40°C, especially at 45°C, showed a recovery rate above 90%, suggesting nearly complete recovery and significant stress relaxation.\u003c/p\u003e\n\u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eStatic force and recovery rate at 30°C, 35°C, 40°C and 45°C at the 13th stress relaxation and creep of 13 repetitions of a cycle of 2% elongation for 60 min and recovery for 60 min\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTemperature (℃)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStatic force (N)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRecovery rate (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78.11\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e77.20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e92.76\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e99.18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe results of the shape memory experiments highlighted the temperature-dependent behaviors of the material. According to the 1 hour observation of shape recovery, the materials showed the fastest recovery was at 45°C reaching 99% recovery, while the slowest was at 30°C, where only 34.4% recovery occurred after 60 minutes (Fig.\u0026nbsp;6).The calculated values of shape recovery ratio of TC-85 specimens based on the measured initial bending angles (θ\u003csub\u003einitial\u003c/sub\u003e) and bending angles at subsequent times (θ\u003csub\u003et\u003c/sub\u003e) are shown in Table\u0026nbsp;\u003cspan\u003e2\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cdiv\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eIn contrast to previous studies that used dumbbell-shaped specimens, this research employed stick-shaped specimens to minimize experimental bias due to variations in specimen width. In the previous experiments, the locations of the fracture during the elongation process under the tensile force were determined by the dumbbell shape in some cases. With the stick-shape specimens, such factors affecting the location of fracture could be eliminated. However, fractures still occurred at the junction between the specimen and the fixed region. This phenomenon is attributable to the material’s significant elasticity and yield strength. However, strain at such high values are not relevant to the clinical use of the clear orthodontic devices, thus there is no issue in deriving a clinical interpretation from these experimental results.\u003c/p\u003e \u003cp\u003eThe initial hypothesis applied to the previous study was that variations in the thickness of clear aligner devices could lead to unwanted forces on the teeth, with the assumption that aligner thickness significantly affects the orthodontic forces applied. However, results from the previous studies focused on the differences in physical properties between PETG and TC-85 rather than addressing the differences in physical properties based on thickness variations. In this study, only one material was used, and the hypothesis was empirically tested by fabricating TC-85 specimens at three thicknesses of 0.5 mm, 0.65 mm, and 0.8 mm.\u003c/p\u003e \u003cp\u003eOne of the most significant findings from previous research is that the physical properties of materials, especially TC-85, demonstrate very particular viscoelastic behaviors and temperature-dependent shape memory properties \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Experiments were conducted at 37°C and 80°C to test the properties near body temperature. However, temperature such as 80°C above T\u003csub\u003eg\u003c/sub\u003e was a condition too extreme to compare the changed properties to draw clinical meaning. The current study sought to rectify this by evaluating material properties at temperatures that are more representative of conditions within the oral cavity on a daily basis: 30°C, 35°C, 40°C, and 45°C.\u003c/p\u003e \u003cp\u003eTheoretically, tensile strength and elastic modulus are derived from maximum tensile and cross-sectional area of the material, thus are independent of the thickness. The current study corroborated this, showing no significant variance in these measurements across different thicknesses. However, a clear trend was observed whereby an increase in temperature led to a decrease in both tensile strength and elastic modulus, which in turn made the material more ductile, requiring less force for deformation. Unlike vacuum formed clear aligners made of materials such as PETG, direct printed aligners can be designed to fit dental anatomy precisely regardless of undercuts. This allows close fit along all surface between the device and teeth, providing more effective orthodontic force. However, the perfect fit requires the device to pass through the height of contour and reach the undercut area. For optimal placement, the device must be able to adapt to dental contours and undercuts with minimal force and have adequate flexibility to avoid discomfort or breakage during the application or removal process. Therefore, lower tensile strength and elastic modulus are considered preferable. Additionally, the temperature-dependent flexibility can be used in advantage to ease the fitting and removal process of the device. For example, the device can be heated in hot water before fitting and heated by drinking warm water above body temperature before removing in order to increase flexibility instantly and ease the tight fit to fit and remove with minimal force required.\u003c/p\u003e \u003cp\u003eMaximum standard force is measured in order to investigate the physical properties with thickness factor as an added factor. It was discovered that actual tensile strength varies with the thickness of the device, implying that thinner devices requires smaller force for deformation. In clinical settings where the aligner is to be applied to areas with poor periodontal health or sever undercuts, thinner device would be more advantageous for avoiding applying large force. Although a trend of decreasing force required with increasing temperatures was noted across all thicknesses, no substantial differences were observed above 40°C. Also, the force difference between 0.65 mm specimen and 0.8 mm specimen was relatively small at 30°C and 35°C. Therefore, while the thickness of the device does have some effect on the orthodontic corrective force exerted on teeth, its clinical significance seems insignificant.\u003c/p\u003e \u003cp\u003eA stress-strain curve was created to visually demonstrate force variations relative to temperature (Fig.\u0026nbsp;3). As previously explained, force required for same strain decreased with increased temperature for a given thickness. Although the graph shows how the material behaves until its elongation break, only the initial values of the curve is clinically meaningful, because actual tooth movement occurs within a narrow range of elongation, making values beyond the initial changes less critical in clinical relevance. Similar to the results from previous studies, all specimen reached its peak force in the beginning stage of deformation. Compared to peaks of PETG, TC-85 showed significantly lower peak force. This result corroborates the potential of TC-85 to facilitate efficient tooth adjustment with fewer steps and biologically more suitable force. Applying this finding to clinical settings, the thicker the device is, the more movement per step one give. However, thickness over 0.65 mm is expected to have no significant effect. Also, since the material’s flexibility is temperature-dependable, it is possible to minimize side effects and discomfort especially when using an aligner designed for large tooth movement by utilizing warm temperature over body temperature and introducing physiological force to the teeth.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;4, the temperature increases by 5°C from 30°C to 45°C, storage modulus decreases and tan delta increases. This phenomenon is very natural because it is based on the softening of polymers due to temperature change and also aligns with previous works \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. However, in case of an orthodontic device, the temperature at which the viscoelastic properties are maximized must be around 35°C near human body temperature. In this study, as the temperature rises from 30°C to 40°C, the decrease of storage modulus and increase of tan delta occur at a constant rate, but the rate is hindered when the temperature rises above 40°C. Such phenomenon generally occurs around the Tg (glass transition temperature) of polymer materials. It can be inferred that the viscoelastic properties of the material are maximized in an environment at 35°C in the oral cavity near its Tg.\u003c/p\u003e \u003cp\u003eStress relaxation and creep of TC-85 were examined at 2% strain rate to mimic the material deformation during the application of the device (Fig.\u0026nbsp;5). In the previous study, experiments were conducted under a 1% strain rate condition, which was an inevitable condition due to the low elasticity of PETG. However, focus of this study was to investigate the effect of temperature by using only the TC-85 material, which has high flexibility and correspondingly high elastic range, so the experiments could be conducted at a strain rate of 2%. As the cycles progressed, stress relaxation became evident when the temperature was higher, and the static force also tended to decrease immediately. According to the results of the previous experiment, the amplitude of the initial force tended to be larger at lower temperature, and the static force in stress relaxation condition was also relatively higher at lower temperature. In addition, the creep occurred more clearly at lower temperatures and static force continuously increased as the cycle progressed. From a biomechanical perspective, creep could be seen as beneficial since it minimizes force decay and sustains the orthodontic force applied by the aligners.\u003c/p\u003e \u003cp\u003eThese results show that in a clinical situation where the orthodontic device is worn and placed under continuous strain, the force exerted from the device to the teeth can be changed with temperature. When a patient wears the aligner, appropriate orthodontic force must be applied to the teeth, and it must occur at a temperature close to oral environment approximately at 35°C. Combined with the results from the previous studies, the higher strain rate resulted in greater force. Therefore, by individualizing movement of each tooth in the set-up process and adjusting the expected strain rate, the ideal orthodontic force can be achieved with specifically controlled applied force \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. If the patient experiences pain when installing the device, using water at a temperature higher than body temperature can help by immediately lowering the applied force to 0 N.\u003c/p\u003e \u003cp\u003eThere may be concerns about permanent deformation of the device due to creep phenomenon and repeated use. However, these concerns could be dismissed by the previous research which confirmed the shape memory property of the newly developed material at 37°C and 80°C followed by this study attempted to look at the shape memory pattern under more detailed conditions. Likewise, the material exhibited quicker recovery at an elevated temperature (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This study provides detailed pattern of shape memory and suggests that warming the clear aligner may be used as a guideline for first-timers and patients in transitions between orthodontic stages to lessen the discomfort.\u003c/p\u003e \u003cp\u003eWith TC-85, it is possible to control the applied force by distance adjustments rather than thickness control. In the case of thermoformed aligners made with PETG materials, 1 kg tension was generated at a strain rate of 1%, but direct printed aligner generated a force of 100g at 1% and 200g at 2%. Such orthodontic-friendly force range allows the operator to freely plan the orthodontic treatment without concerns on excessive amount of force. This method can be expressed as a force driven system. Even if the oral temperature rises by just 5 degrees, the orthodontic corrective force is clearly released and returns in moderate measures that is more biomechanically suitable.\u003c/p\u003e \u003cp\u003eIn conclusion, the immediate force when applying the device at body temperature may surpass physiological force. This is a common phenomenon among existing clear aligners, and materials such as PETG exert much greater initial force \u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. However, more efficient tooth movement is ensured with the property of TC-85 which allows stress relaxation to occur immediately and exert the most physiological force. Therefore, when using the device for the first time, it is advised to use it at a higher initial temperature to minimize discomfort and prevent excessive forces. Then, gradual adjustment to oral cavity temperature will ensure a smooth transition to physiological force range for optimal orthodontic corrective force applications.\u003c/p\u003e \u003cp\u003eAlthough the study examined material properties across various temperatures, additional experiments considering different clinical conditions, simulation of installation and removal of the device, and the orthodontic force under fluctuating temperature rather than a fixed temperature in order to derive more clinically meaningful results. In addition, further investigation is necessary on various teeth morphologies and health conditions of periodontal tissues to determine how much tooth movement per set is appropriate to achieve the 1% and 2% strain as assumed in this and previous studies.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e\u003c/p\u003e"},{"header":"Limitation","content":"\u003cp\u003e\u003cspan\u003e1. The outcomes may differ under conditions of 100% humidity, similar to those in the oral cavity, due to the considerable water absorption characteristic of polyurethane.\u003cbr\u003e\u003c/span\u003e\u003cspan\u003e2. Prolonging the stress relaxation test beyond 24 hours could provide more significant findings that better reflect the typical wear duration of orthodontic aligners, which usually exceeds 24 hours.\u003cbr\u003e\u003c/span\u003e\u003c/p\u003e"},{"header":"Conclusions","content":"\u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTC-85, sensitive to body temperature, showcases enhanced shape memory with rising temperatures, reducing the corrective force of clear aligners for improved patient comfort.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAt 45°C, TC-85 reaches peak flexibility, aiding in comfortable orthodontic correction, while below 30°C, it maintains stiffness and resistance to external deformation.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAt 30°C, TC-85's elasticity, stress relaxation, and strain recovery properties enable it to deliver a steady, gentle corrective force suitable for orthodontic treatment.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTC-85 resists force decay under varied thermal conditions, maintaining its corrective effectiveness through multiple device applications and removals.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe stable, cross-linked structure of TC-85 remains consistent at 80°C, providing advantages over PETG in durability and user maintenance.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDATA AVAILABILITY\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eACKNOWLEDGMENT\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eExperiments were carried out through free support of Anton Paar Korea\u0026apos;s rheometer test equipment, and we would like to thank to Anton Paar Korea for helping us.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Data Availability\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eOjima, K. \u0026amp; Kau, C. H. A perspective in accelerated orthodontics with aligner treatment. \u003cem\u003eSemin Orthod\u003c/em\u003e \u003cstrong\u003e23\u003c/strong\u003e, 76\u0026ndash;82 (2017).\u003c/li\u003e\n\u003cli\u003eMulla Issa, F. K., Mulla Issa, Z. K., Rabah, A. \u0026amp; Hu, L. Periodontal parameters in adult patients with clear aligners orthodontics treatment versus three other types of brackets: A cross-sectional study. \u003cem\u003eJ Orthod Sci\u003c/em\u003e \u003cstrong\u003e9\u003c/strong\u003e, 4 (2020).\u003c/li\u003e\n\u003cli\u003eRobertson, L. \u003cem\u003eet al.\u003c/em\u003e Effectiveness of clear aligner therapy for orthodontic treatment: A systematic review. \u003cem\u003eOrthod Craniofac Res\u003c/em\u003e \u003cstrong\u003e23\u003c/strong\u003e, 133\u0026ndash;142 (2020).\u003c/li\u003e\n\u003cli\u003eRossini, G., Parrini, S., Castroflorio, T., Deregibus, A. \u0026amp; Debernardi, C. L. Efficacy of clear aligners in controlling orthodontic tooth movement: A systematic review. \u003cem\u003eAngle Orthod\u003c/em\u003e \u003cstrong\u003e85\u003c/strong\u003e, 881\u0026ndash;889 (2015).\u003c/li\u003e\n\u003cli\u003eDjeu, G., Shelton, C. \u0026amp; Maganzini, A. Outcome assessment of Invisalign and traditional orthodontic treatment compared with the American Board of Orthodontics objective grading system. \u003cem\u003eAmerican Journal of Orthodontics and Dentofacial Orthopedics\u003c/em\u003e \u003cstrong\u003e128\u003c/strong\u003e, 292\u0026ndash;298 (2005).\u003c/li\u003e\n\u003cli\u003eNarongdej, P., Hassanpour, M., Alterman, N., Rawlins-Buchanan, F. \u0026amp; Barjasteh, E. Advancements in Clear Aligner Fabrication: A Comprehensive Review of Direct-3D Printing Technologies. \u003cem\u003ePolymers\u003c/em\u003e vol. 16 Preprint at https://doi.org/10.3390/polym16030371 (2024).\u003c/li\u003e\n\u003cli\u003eJindal, P., Juneja, M., Siena, F. L., Bajaj, D. \u0026amp; Breedon, P. Mechanical and geometric properties of thermoformed and 3D printed clear dental aligners. \u003cem\u003eAmerican Journal of Orthodontics and Dentofacial Orthopedics\u003c/em\u003e \u003cstrong\u003e156\u003c/strong\u003e, 694\u0026ndash;701 (2019).\u003c/li\u003e\n\u003cli\u003eKoenig, N. \u003cem\u003eet al.\u003c/em\u003e Comparison of dimensional accuracy between direct-printed and thermoformed aligners. \u003cem\u003eKorean J Orthod\u003c/em\u003e \u003cstrong\u003e52\u003c/strong\u003e, 249\u0026ndash;257 (2022).\u003c/li\u003e\n\u003cli\u003eAtta, I. \u003cem\u003eet al.\u003c/em\u003e Physiochemical and mechanical characterisation of orthodontic 3D printed aligner material made of shape memory polymers (4D aligner material). \u003cem\u003eJ Mech Behav Biomed Mater\u003c/em\u003e \u003cstrong\u003e150\u003c/strong\u003e, 106337 (2024).\u003c/li\u003e\n\u003cli\u003eSchupp, W. \u003cem\u003eet al.\u003c/em\u003e \u003cem\u003eShape Memory Aligners: A New Dimension in Aligner Orthodontics\u003c/em\u003e. \u003cem\u003eJournal of Aligner Orthodontics\u003c/em\u003e vol. 7 (2023).\u003c/li\u003e\n\u003cli\u003eBichu, Y. M. \u003cem\u003eet al.\u003c/em\u003e Advances in orthodontic clear aligner materials. \u003cem\u003eBioact Mater\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, 384\u0026ndash;403 (2023).\u003c/li\u003e\n\u003cli\u003eSlaymaker, J., Hirani, S. \u0026amp; Woolley, J. Direct 3D printing aligners - past, present and future possibilities. \u003cem\u003eBritish Dental Journal1\u003c/em\u003e \u003cstrong\u003e236\u003c/strong\u003e, 401\u0026ndash;405 (2024).\u003c/li\u003e\n\u003cli\u003ePanayi, N. C., Efstathiou, S., Christopoulou, I., Kotantoula, G. \u0026amp; Tsolakis, I. A. \u003cem\u003eDigital Orthodontics: Present and Future\u003c/em\u003e.\u003c/li\u003e\n\u003cli\u003eAndreu, A. \u003cem\u003eet al.\u003c/em\u003e 4D printing materials for vat photopolymerization. \u003cem\u003eAddit Manuf\u003c/em\u003e \u003cstrong\u003e44\u003c/strong\u003e, 102024 (2021).\u003c/li\u003e\n\u003cli\u003eKim, H., Khan, T. A., Ryu, K.-H., Sohn, I.-S. \u0026amp; Kim, H.-J. Nanocomposite materials for 3D printing. in \u003cem\u003eAPPLICATIONS AND INDUSTRIALISATION OF NANOTECHNOLOGY\u003c/em\u003e (eds. Ahmed, W. \u0026amp; Maciel, M. A. M.) 91\u0026ndash;118 (2022).\u003c/li\u003e\n\u003cli\u003eLee, J. \u003cem\u003eet al.\u003c/em\u003e Average-Accumulated Normalized Dose (A-AND) predicts ultimate tensile strength and elastic modulus of photopolymer printed by vat photopolymerization. \u003cem\u003eAddit Manuf\u003c/em\u003e \u003cstrong\u003e55\u003c/strong\u003e, 102799 (2022).\u003c/li\u003e\n\u003cli\u003eKim, H. \u003cem\u003eet al.\u003c/em\u003e 3D Printing of Polyethylene Terephthalate Glycol\u0026ndash;Sepiolite Composites with Nanoscale Orientation. \u003cem\u003eACS Appl Mater Interfaces\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 23453\u0026ndash;23463 (2020).\u003c/li\u003e\n\u003cli\u003eKim, H. \u003cem\u003eet al.\u003c/em\u003e Embedded Direct Ink Writing 3D Printing of UV Curable Resin/Sepiolite Composites with Nano Orientation. \u003cem\u003eACS Omega\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 23554\u0026ndash;23565 (2023).\u003c/li\u003e\n\u003cli\u003eFang, D., Zhang, N., Chen, H. \u0026amp; Bai, Y. Dynamic stress relaxation of orthodontic thermoplastic materials in a simulated oral environment. \u003cem\u003eDent Mater J\u003c/em\u003e \u003cstrong\u003e32\u003c/strong\u003e, 946\u0026ndash;951 (2013).\u003c/li\u003e\n\u003cli\u003eKravitz, N. D., Kusnoto, B., BeGole, E., Obrez, A. \u0026amp; Agran, B. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign. \u003cem\u003eAmerican Journal of Orthodontics and Dentofacial Orthopedics\u003c/em\u003e \u003cstrong\u003e135\u003c/strong\u003e, 27\u0026ndash;35 (2009).\u003c/li\u003e\n\u003cli\u003eLombardo, L. \u003cem\u003eet al.\u003c/em\u003e Stress relaxation properties of four orthodontic aligner materials: A 24-hour in vitro study. \u003cem\u003eAngle Orthod\u003c/em\u003e \u003cstrong\u003e87\u003c/strong\u003e, 11\u0026ndash;18 (2016).\u003c/li\u003e\n\u003cli\u003eLee, S. Y. \u003cem\u003eet al.\u003c/em\u003e Thermo-mechanical properties of 3D printed photocurable shape memory resin for clear aligners. \u003cem\u003eSci Rep\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, (2022).\u003c/li\u003e\n\u003cli\u003eAlessandra, C. \u003cem\u003eet al.\u003c/em\u003e Comparison of the cytotoxicity of 3D-printed aligners using different post-curing procedures: an in vitro study. \u003cem\u003eAustralasian Orthodontic Journal\u003c/em\u003e \u003cstrong\u003e39\u003c/strong\u003e, 49\u0026ndash;56 (2023).\u003c/li\u003e\n\u003cli\u003eLim, B. \u003cem\u003eet al.\u003c/em\u003e Influence of Post-Curing in Nitrogen-Saturated Condition on the Degree of Conversion and Color Stability of 3D-Printed Resin Crowns. \u003cem\u003eDent J (Basel)\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 68 (2024).\u003c/li\u003e\n\u003cli\u003e\u0026Scaron;imunović, L. \u003cem\u003eet al.\u003c/em\u003e Influence of Post-Processing on the Degree of Conversion and Mechanical Properties of 3D-Printed Polyurethane Aligners. \u003cem\u003ePolymers (Basel)\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, (2024).\u003c/li\u003e\n\u003cli\u003eWang, Z., Liu, J., Guo, J., Sun, X. \u0026amp; Xu, L. The Study of Thermal, Mechanical and Shape Memory Properties of Chopped Carbon Fiber-Reinforced TPI Shape Memory Polymer Composites. \u003cem\u003ePolymers (Basel)\u003c/em\u003e \u003cstrong\u003e9\u003c/strong\u003e, 594 (2017).\u003c/li\u003e\n\u003cli\u003eLiu, Y. \u003cem\u003eet al.\u003c/em\u003e Thermo-Mechanical Properties of Glass Fiber Reinforced Shape Memory Polyurethane for Orthodontic Application. \u003cem\u003eJ Mater Sci Mater Med\u003c/em\u003e \u003cstrong\u003e29\u003c/strong\u003e, 148 (2018).\u003c/li\u003e\n\u003cli\u003eSchupp, W. \u003cem\u003eet al.\u003c/em\u003e \u003cem\u003eShape Memory Aligners: A New Dimension in Aligner Orthodontics\u003c/em\u003e. \u003cem\u003eJournal of Aligner Orthodontics\u003c/em\u003e vol. 7 (2023).\u003c/li\u003e\n\u003cli\u003eGrant, J. \u003cem\u003eet al.\u003c/em\u003e Forces and moments generated by 3D direct printed clear aligners of varying labial and lingual thicknesses during lingual movement of maxillary central incisor: an in vitro study. \u003cem\u003eProg Orthod\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, (2023).\u003c/li\u003e\n\u003cli\u003eMcKay, A. \u003cem\u003eet al.\u003c/em\u003e Forces and moments generated during extrusion of a maxillary central incisor with clear aligners: an in vitro study. \u003cem\u003eBMC Oral Health\u003c/em\u003e \u003cstrong\u003e23\u003c/strong\u003e, (2023).\u003c/li\u003e\n\u003cli\u003eAuthor, C. \u003cem\u003eet al.\u003c/em\u003e Force Assessment of Thermoformed and Direct-printed Aligners in a Lingual Bodily Movement of a Central Incisor Over Time: A 14-day In Vitro Study. \u003cem\u003eJ Korean Dent Sci\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 23\u0026ndash;34 (2023).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4106282/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4106282/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study presents a novel technique for the direct 3D printing of TC-85, a biocompatible material specifically designed for orthodontic uses. This method aims to overcome the biomechanical constraints associated with the conventional thermoforming process used in aligner fabrication. The investigation emphasizes analyzing TC-85's mechanical and viscoelastic properties, focusing on how temperature changes impact these characteristics and their relevance to clinical outcomes. Using a Digital Light Processing (DLP) 3D printer, the photoreactive resin TC-85 is printed, and extensive thermo-mechanical testing is conducted, which includes evaluations of tensile modulus, stress relaxation, and creep behavior. Dynamic Mechanical Analysis (DMA) is conducted at temperatures varying from 30 to 45\u0026deg;C to assess the material's adaptive response to thermal fluctuations. TC-85 is distinguished by its unique mechanical properties, which include a temperature-sensitive stiffness, stress relaxation capability, and shape memory feature. The results demonstrate that TC-85 maintains an enhanced level of residual force and a faster recovery of strain through numerous cycles of loading and unloading. At 40\u0026deg;C, TC-85 displays a substantial reduction in its storage modulus, while maintaining consistent strain recovery and volumetric constancy. The study highlights TC-85's potential in orthodontic treatments, providing adaptable mechanical and viscoelastic properties that enable the exertion of consistent, regulated forces on teeth. Its resistance to force decay, stable volume at raised temperatures, and built-in shape memory enhance hygienic upkeep and patient comfort, positioning TC-85 as a pioneering material for the next generation of clear aligners.\u003c/p\u003e","manuscriptTitle":"Mechanical and Viscoelastic Properties of a Temperature-Responsive Photocurable Resin for 3D Printed Orthodontic Clear Aligners","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-07 19:17:06","doi":"10.21203/rs.3.rs-4106282/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-17T12:55:47+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-23T10:49:09+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-19T11:18:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"26601123321539499458049399078621960391","date":"2024-05-17T08:10:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"207915675117208072085350855628245108258","date":"2024-05-10T13:27:29+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-08T13:02:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-08T12:56:16+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-05-02T17:48:45+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-30T05:01:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-03-15T08:33:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d830df6b-f500-426a-86a7-87e9b29fb052","owner":[],"postedDate":"May 7th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-07T16:08:53+00:00","versionOfRecord":{"articleIdentity":"rs-4106282","link":"https://doi.org/10.1038/s41598-025-93026-0","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-07-02 15:58:45","publishedOnDateReadable":"July 2nd, 2025"},"versionCreatedAt":"2024-05-07 19:17:06","video":"","vorDoi":"10.1038/s41598-025-93026-0","vorDoiUrl":"https://doi.org/10.1038/s41598-025-93026-0","workflowStages":[]},"version":"v1","identity":"rs-4106282","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4106282","identity":"rs-4106282","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}