Search Results (67)

The orthodontic landscape is currently witnessing a significant technological evolution with the emergence of direct 3D-printed aligners (DPAs), which promise to close the digital workflow loop by eliminating the geometric limitations and solid model waste inherent to traditional thermoformed clear aligners (TCAs). This review provides a comprehensive analysis of the material science governing this transition from inert thermoplastic sheets to reactive photocurable resins. We explore the fundamental chemistry of DPA materials, and the pivotal role of post-processing in ensuring mechanical integrity and biocompatibility. Beyond passive mechanics, this review highlights preclinical research in functional material engineering, detailing how experimental DPAs are being investigated for the integration of antibacterial agents, remineralization fillers, and drug delivery systems. Furthermore, we evaluate the limited but emerging clinical data on DPAs, contrasting their shape-memory properties and force delivery profiles with conventional appliances, while critically addressing emerging safety concerns regarding monomer elution and microplastic generation. We conclude that while DPA technology offers superior dimensional control, comprehensive life cycle assessments and long-term in vivo trials are essential to fully substantiate their clinical efficacy, overall sustainability, and potential as advanced orthodontic appliances. Full article

To reduce mold costs in composite forming, multi-point tooling technology has been integrated into the hot diaphragm forming process. However, this approach still faces several challenges, including time-consuming prepreg layup, high energy consumption, and poor surface quality. This study proposes a heating pad-assisted multi-point thermoforming process: the prepreg is embedded in the thermal functional layers, placed on the lower mold, and formed via the downward movement of the upper mold to accomplish mold closure. Instead of the conventional rectangular array, this study adopted multi-point tooling with a hexagonal pin arrangement. Compared to traditional configurations, this hexagonal layout increases the punch support area by 9.8%, while its dense punch arrangement improves the accuracy of the molded curved surface. Taking a saddle-shaped surface as the target, a prototype part was fabricated. Subsequent analysis of the part’s surface quality identified three defects: dimples, fiber distortion, and ridge protrusions. The surface dimples were eliminated by adjusting the distance between the upper and lower molds. Notably, ridge protrusion is a defect unique to the hexagonal pin arrangement. We conducted a detailed analysis of its causes and solutions, finding that this defect arises from the combined effect of the pin arrangement and the saddle-shaped surface. Through a series of height compensation experiments, the maximum deviation at the ridges was reduced from 0.46 mm to approximately 0.35 mm, which is consistent with the deviation of defect-free areas. This work demonstrates that the multi-point hot-pressing process provides a potential, efficient, and low-cost method for manufacturing double-curvature composite components, whose effectiveness has been verified through the saddle-shaped case study. Full article

Objectives: This systematic review and meta-analysis aimed to evaluate microbial adhesion and biofilm formation on additively manufactured composite-based orthodontic clear aligners compared with thermoformed aligners and other conventional polymeric materials. The influence of material composition, surface roughness, post-processing parameters, and cleaning protocols on microbial colonization was also assessed. Methods: A comprehensive search of PubMed, EMBASE, Scopus, Web of Science, and the Cochrane Library was conducted up to September 2025. Only in vitro studies investigating microbial adhesion, biofilm biomass, or microbiome changes on three-dimensional (3D)-printed aligner composites were included. Primary outcomes consisted of colony-forming units (CFU), optical density (OD) from crystal violet assays, viable microbial counts, and surface roughness. Risk of bias was assessed using the RoBDEMAT tool. Data were narratively synthesized, and a random-effects meta-analysis was performed for comparable datasets. Results: Five studies fulfilled the inclusion criteria, of which two in vitro studies were eligible for meta-analysis. Microbial adhesion and biofilm accumulation were influenced by the manufacturing technique, composite resin formulation, and surface characteristics. Certain additively manufactured aligners exhibited smoother surfaces and reduced bacterial adhesion compared with thermoformed controls, whereas others with increased surface roughness showed higher biofilm accumulation. Incorporating bioactive additives such as chitosan nanoparticles reduced Streptococcus mutans biofilm formation without compromising material properties. The meta-analysis, based on two in vitro studies, demonstrated higher OD values for bacterial biofilm on 3D-printed aligners compared with thermoformed aligners, indicating increased biofilm biomass (p < 0.05), but not necessarily viable bacterial load. Conclusions: Microbial adhesion and biofilm formation on 3D-printed composite clear aligners are governed by resin composition, additive manufacturing parameters, post-curing processes, and surface finishing. Although certain 3D-printed materials display antibacterial potential, the limited number of studies restricts the generalizability of these findings. Clinical Significance: Optimizing composite formulations for 3D printing, alongside careful post-curing and surface finishing, may help reduce microbial colonization. Further research is required before translating these findings into definitive clinical recommendations for clear aligner therapy. Full article

Biocomposites based on natural fibres represent a promising solution for the circular economy. The aim of this study was to develop and characterise a biodegradable composite based on sheep wool from herds raised in the Kyrgyz Republic and polylactide (PLA 4032D). Composite samples with a wool–PLA ratio of 50:50 were fabricated by thermoforming at a temperature of 168 °C for 30 s (n = 10). Mechanical properties tests were performed (PN-EN ISO 604—compression tests), for impact resistance (Charpy method), differential scanning calorimetry (DSC), and measurements of density and thermal conductivity. Biodegradation samples were subjected to enriched soil conditions for 6 weeks in two variants (with and without irrigation). The results showed that the addition of sheep wool to the PLA matrix significantly increased compressive strength (23.56 ± 5.23 MPa) and impact energy absorption (226.2 ± 23.8 kJ/m²) compared to neat PLA. After biodegradation, a 59% reduction in compressive strength was observed while maintaining an increase in fracture energy, suggesting a change in the failure mechanism. The density (0.27 ± 0.02 g/cm³) and the thermal conductivity (0.127 W/m·K) comparable to polymer foams indicate potential for thermal insulation applications. Microscopy and DSC analysis confirmed complete biodegradation under soil conditions. The developed biocomposite from Kyrgyz sheep wool demonstrates the potential for valorisation of local fibrous waste for biodegradable materials with functional insulation properties. Full article

This work presents the development and experimental validation of a low-cost, piezoelectret-based energy harvesting system integrated into a custom insole, as a promising alternative for future self-powered wearable electronics. The design utilizes eight thermoformed Teflon piezoelectrets, strategically positioned in high-impact regions (heel and forefoot), to convert footstep-induced mechanical motion into electrical energy. The sensors, fabricated using Fluorinated Ethylene Propylene (FEP) and Polytetrafluoroethylene (PTFE) layers via thermal pressing and aluminum sputtering, were connected in parallel to enhance signal consistency and robustness. A solenoid-actuated mechanical test rig was developed to simulate human gait under controlled conditions. The system consistently produced voltage pulses with peaks up to 13 V and durations exceeding ms, even under limited-force loading (10 kgf). Signal analysis confirmed repeatable waveform characteristics, and a Delon voltage multiplier enabled partial conversion into usable DC output. While not yet optimized for maximum efficiency, the proposed setup demonstrates the feasibility of using piezoelectrets for energy harvesting. Its simplicity, scalability, and low cost support its potential for future integration in applications such as fitness tracking, health monitoring, and GPS ultimately contributing to the development of autonomous, self-powered smart footwear systems. It is important to emphasize that the present study is a proof-of-concept validated exclusively under controlled laboratory conditions using a mechanical gait simulator. Future work will address real-time insole application tests with human participants. Full article

Background/Objectives: Clear aligner therapy has become a mainstream alternative to fixed orthodontics due to its versatility. However, the variability in thermoforming and the limited validation of digital workflows remain major barriers to reproducibility and predictability. Methods: This study addresses that gap by presenting a proof-of-concept digital workflow for clear aligner manufacturing by integrating additive manufacturing (AM), thermoforming simulation, and finite element analysis (FEA). Dental models were 3D-printed and thermoformed under clinically relevant pressures (400 kPa positive and −90 kPa negative). Results and Discussion: Geometric accuracy was quantified using CloudCompare v2.13.0, showing that positive-pressure thermoforming reduced maximum deviations from 1.06 mm to 0.4 mm, with all deviations exceeding the expanded measurement uncertainty. Thickness simulations of PETG sheets (0.5 and 0.75 mm) showed good agreement with experimental values across seven validation points, with errors <10% and overlapping 95% confidence intervals. Stress analysis indicated that force transmission was localized at the aligner–attachment interface, consistent with expected orthodontic mechanics. Conclusions: By quantifying accuracy and mechanical behavior through numerical and experimental validation, this framework demonstrates how controlled thermoforming and simulation-guided design can enhance aligner consistency, reduce adjustments, and improve treatment predictability. Full article

In light of the environmental impact of disposable products made from petroleum-based plastics, this study focused on developing biodegradable foam trays made from a starch (PS) derived from potato waste and beer malt flour (BMBF). The objective of this study was to evaluate the effect of the concentration of BMBF on the physical and mechanical properties of potato starch-based foam trays prepared by the thermoforming process at temperatures of 150 °C (upper plate) and 145 °C (lower plate) for 5 min and 40 s. The results showed that increasing the BMBF concentration from 0 to 40% reduced the moisture content from 4.68% to 3.42%, increased the thickness from 2.63 cm to 4.77 cm, and decreased the density from 0.28 g.cm⁻³ to 0.15 g.cm⁻³. Meanwhile, the water absorption capacity increased from 38.7% to 69.7%. In terms of mechanical properties, increasing the BMBF concentration in the PS foam tray resulted in a decrease in hardness from 5.61 N to 2.87 N, a decrease in tensile strength from 2.92 MPa to 0.85 MPa, and a decrease in elongation from 1.42% to 0.59%. Meanwhile, fracturability increased from 2.04 mm to 3.68 mm. FTIR analysis revealed interactions between BMBF and PS in the composite foam tray. Thermogravimetric analysis (TGA) showed two thermal events: one between 20.96 °C and 172.89 °C, and another between 189.14 °C and 517.69 °C, with weight losses of 5.53% and 74.23%, leaving an ash residue of 20.24%. Differential calorimetry analysis (DSC) showed a glass transition at 152.88 °C and a melting at 185.94 °C, with an enthalpy of fusion of 74.11 J.g⁻¹. Higher concentrations of BMBF (>10%) decreased the water resistance, mechanical strength, and flexibility of the PS foam trays. Therefore, a formulation of 90% PS and 10% BMBF was better for producing a foam tray with improved mechanical properties and water resistance, which could be used as a sustainable alternative to conventional single-use plastic. Full article

This study explores the vibrational behavior of Thermoformed Magneto-Piezoelectrets (TMPs), multifunctional materials consisting of thermoformed piezoelectrets with open tubular channels integrated with an additional magnetic layer. The inverse piezoelectric effect was characterized using laser vibrometry analysis, measuring the mechanical response of TMPs subjected to electrical excitation over a frequency range of 0–20 kHz. Vibrational analysis was conducted at 144 spatial points, enabling the construction of detailed three-dimensional (3D) maps of the vibration operational modes and the spatial distribution of the piezoelectric coefficient ($d_{33}$). The results demonstrated significant frequency-dependent behavior, with open channels exhibiting pronounced resonance peaks, whereas valleys displayed smoother and more uniform responses due to enhanced damping effects. The observed heterogeneity in vibrational behavior is attributed to structural variations, material composition, and anisotropic coupling between the piezoelectric and magnetic properties. The findings presented in this research provide a comprehensive understanding of the development and utilization of TMPs, offering parameters for enhancing their application and supporting new discoveries in studies related to the fabrication of novel thermoformed piezoelectric sensors. Full article

In this study, laminates based on polyetherimide (PEI) with contents of carbon fibers (CFs) from 55 to 70 wt.% were fabricated by thermoforming (TF) and ultrasonic additive manufacturing (UAM) methods. The UAM laminates with CF contents above 55 wt.% possessed shear strengths lower by 40% in comparison with those of the TF ones, due to insufficient amounts of the binder in the prepregs to form reliable interlaminar joints. For enhancing the shear strength of the laminates with a CF content of 70 wt.%. up to the levels of the TF ones, extra resin layers with thicknesses of 50, 100, and 150 μm were deposited. By ranking the UAM parameters using the Taguchi method, it was possible to increase the shear strengths by 30% as compared to those of the trial laminates. Further improvements were achieved by artificial neural network (ANN) modeling. As a result, the use of the 50 µm thick extra resin layer made it possible to increase the shear strengths up to 50% relative to those of the trial laminates at a CF content of 70 wt.%. This improvement was achieved via minimizing the number of defects at the interlaminar interfaces. The dependences of both mechanical and structural characteristics of the laminates on the UAM parameters were essentially nonlinear. For their analysis and optimization of the UAM parameters, the direct propagation neural networks with the minimal architecture were utilized. Under the ultra-small sample conditions, the use of a priori knowledge enabled us to predict the results rather accurately. Full article

Purpose: This paper investigates the biomechanical effect of thermoformed aligners equipped with complementary biomechanical attachments (CBAs) on periodontal ligaments (PDLs) during the expansion process of the maxillary arch. The analysis was conducted using advanced simulations based on the finite element method (FEM). Methods: High-resolution 3D CAD models were created for four tooth types: canine, first premolar, second premolar, and first molar. Additional 3D models were developed for aligners, CBAs, and PDLs. These were integrated into a comprehensive FEM model to simulate clinical rehabilitation scenarios. Validation was achieved through comparative analysis with empirical medical data. Results: The FEM simulations revealed the following: for canine, the displacement was 0.134 mm with a maximum stress of 4.822 KPa in the amelocemental junction. For the first premolar, the displacement was 0.132 mm at a maximum stress of 3.273 KPa in the amelocemental junction. The second premolar had a displacement of 0.129 mm and a stress of 1.358 KPa at 1 mm from the amelocemental junction; and first molar had a displacement of 0.124 mm and a maximum stress of 2.440 KPa. Conclusions: The inclusion of CBAs significantly reduced tooth tipping during maxillary arch expansion. Among the models tested, the vestibular CBA demonstrated superior performance, delivering optimal tooth movement when combined with thermoformed aligners. Significance: FEM techniques provide a robust and cost-effective alternative to in vivo experimentation, offering precise and reliable insights into the biomechanical efficacy of CBAs in thermoformed aligners. This approach minimizes experimental variability and accelerates the evaluation of innovative orthodontic configurations. Full article

(1) Background: Clear aligners are favored for their aesthetics in orthodontics, with newer 3D-printed technologies allowing the design of aligners with differential thicknesses and materials, offering advantages in terms of force distribution on the teeth, thereby optimizing treatment biomechanics. This study aimed to compare the initial and final forces of three types of 3D-printed aligners (with different thickness gradients and gingival margins) and traditional thermoformed aligners (with different gingival margins), evaluating stress relaxation and force consistency to determine which material and configuration may be optimal for better force distribution; (2) Methods: Twenty-seven 3D-printed aligners with three design variations and 18 thermoformed aligners were analyzed. Customized models were used to assess force at specific points on the upper incisor (1.1) and molar (2.6). A 3 h stress-relaxation test was conducted at 37 °C, and force data were recorded every second using a motorized compression stand. Statistical analysis was performed using ANOVA, post hoc tests, and Kruskal–Wallis tests for comparisons; (3) Results and Conclusions: Aligners with vertical and horizontal thickness gradients and a gingival margin trimmed 2 mm above the gingival contour exerted the highest forces, particularly at incisal/occlusal points. No significant differences in stress relaxation were observed. The force applied to the molars was consistently higher than the force applied to the incisors. These 3D-printed aligners with both horizontal and vertical gradients may offer a viable alternative to thermoformed aligners. Full article

Dielectric materials have gained traction for their energy-storage capacitive and electrically insulating properties as sensors and in smart surface technologies such as in In-Mold Electronics (IME). IME is a disruptive technology that involves environmentally protected electronics in plastic thermoformed and molded structures. The use of IME in a human–machine interface (HMI) provides a favorable experience to the users and helps reduce production costs due to a smaller list of parts and lower material costs. A few functional components that are compatible with one another are crucial to the final product’s properties in the IME structure. Of these components, the dielectric layers are an important component in the smart surface industry, providing insulation for the prevention of leakage currents in multilayered printed structures and capacitance sensing on the surface of specially designed shapes in IME. Advanced dielectric materials are non-conductive materials that impend and polarize electron movements within the material, store electrical energy, and reduce the flow of electric current with exceptional thermal stability. The selection of a suitable dielectric ink is an integral stage in the planning of the IME smart touch surface. The ink medium, solvent, and surface tension determine the printability, adhesion, print quality, and the respective reaction with the bottom and top conductive traces. The sequence in which the components are deposited and the heating processes in subsequent thermoforming and injection molding are other critical factors. In this study, various commercially available dielectric layers were each printed in two to four consecutive layers with a mesh thickness of 50–60 µm or 110–120 µm, acting as an insulator between conductive silver traces overlaid onto a polycarbonate substrate. Elemental mapping and optical analysis on the cross-section were conducted to determine the compatibility and the adhesion of the dielectric layers on the conductive traces and polycarbonate substrate. The final selection was based on the functionality, reliability, repeatability, time-stability, thickness, total processing time, appearance, and cross-sectional analysis results. The chosen candidate was then placed through the final product design, circuitry design, and plastic thermoforming process. In summary, this study will provide a general guideline to optimize the selection of dielectric inks for in-mold electronics applications. Full article

This research arises from the need to rethink children’s play spaces found in the city through new manufacturing methods of solid surface materials such as Krion K-Life 1100, which allow the creation of complex ergonomic shapes. The method consisted of an iterative digital fabrication process, in which a series of molds were developed and adjusted to thermoform a solid surface material, adapting the design in each iteration according to the results obtained. Parametric digital modeling techniques and in-depth curvature analysis were carried out to optimize the geometry, in order to meet the technical limitations of the material and the manufacturing process itself. The results showed that, through precise adjustments in the curvature and thickness of the surface, it is possible to thermoform the solid surface without defects, such as folds or wrinkles, revealing it as a viable material for the generation of complex double-curved geometries, opening up a range of possibilities from the creation of new children’s spaces to parametric facades optimized according to their location. Full article

The paper starts by describing the manufacturing process of cups thermoformed from extruded foils of 80% recycled PET (80r-PET), which comprises heating, hot deep drawing and cooling. The 80r-PET foils were heated up to 120 °C, at heating rates of the order of hundreds °C/min, and deep drawn with multiple punchers, having a depth-to-width ratio exceeding 1:1. After puncher-assisted deformation, the cups were air blown away from the punchers, thus being “frozen” in the deformed state. Due to the high cooling rate, most of the polymer’s structure reached a rigid, glassy state, the internal stresses that tended to recover the flat undeformed state were blocked and the polymer remained in a temporary cup form. When heating was applied, glass transition occurred, and the polymer reached a rubbery state and softened. This softening process released the blocked internal stresses and the polymer tended to recover its flat permanent shape. This relative volume contraction quantitatively describes the shape memory effect (SME) which can be obtained either with free recovery (FR-SME) or with work generation (WG-SME) when the cups lifted their bottoms with different loads placed inside them. The paper discusses the results obtained by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), room-temperature tensile failure tests (TENS) and scanning electron microscopy (SEM). The DSC charts emphasized a glass transition, responsible for SME occurrence. The DMA thermograms and the TENS curves revealed that there are slight differences between the storage modulus and the tensile strains of the specimens cut on longitudinal, transversal, or 45° to the film rolling direction. The SEM micrographs enabled to observe structural differences between the specimens cut parallelly and transversally to the film’s rolling direction. The thermoformed cups were heated on a special experimental setup, which enabled the determination of FR-SME and WG-SME after applying different maximum temperatures and loads placed into the cups, respectively. Full article

Increasing environmental awareness has boosted interest in sustainable alternatives for binding natural reinforcing fibers in composites. Utilizing lignin, a biorenewable polymer byproduct from several industries, as a component in polymer matrices can lead to the development of more eco-friendly and high-performance composite materials. This research work aimed to investigate the effect of two types of lignin (lignosulfonate and soda lignin) on the properties of hemp fiber-reinforced polypropylene composites for furniture applications. The composites were produced by thermoforming six overlapping layers of nonwoven material. A 20% addition of soda lignin or lignosulfonate (relative to the nonwoven mass) was incorporated between the nonwoven layers made of 80% hemp and 20% polypropylene (PP). The addition of both types of lignin resulted in an increase in the tensile and bending strength of lignin-based composites, as well as a decrease in the absorbed water percentage. Compared to oriented strand board (OSB), lignin-based composites exhibited better properties. Regarding the two types of lignin used, the addition of lignosulfonate resulted in better composite properties than those containing soda lignin. Thermal analysis revealed that the thermal degradation of soda lignin begins long before the melting temperature of polypropylene. This early degradation explains the inferior properties of the composites containing soda lignin compared to those with lignosulfonate. Full article