Variation of the modulus of elasticity of aligner foil sheet materials due to thermoforming

Abstract

Objective Investigate and compare the mechanical properties of different aligner materials before and after deep drawing and determine differences in the mechanical properties after thermoforming. Materials and methods Four aligner film sheets from three manufacturers (Duran Plus® [Scheu Dental, Iserlohn, Germany]; Zendura® [ClearCorrect, Bay Materials LLC, Fremont, CA, USA]; Essix ACE® and Essix® PLUS™ [Dentsply Sirona Deutschland, Bensheim, Germany]) were tested in 3‑point bending with support distances of 8, 16, and 24 mm. Dimension of the specimens was 10 × 50 mm2. Two groups each were tested: (1) 10 specimens were investigated in the as-received state (before thermoforming), (2) 10 specimens were deep drawn on a master plate with cuboids of the dimension 10 × 10 × 50 mm3. Then, specimens were cut out of the upper side and lateral walls and were measured in 3‑point bending. Forces and reduction in thickness were measured and corrected theoretical forces of drawn sheets after thickness reduction as well as Young’s modulus were calculated. Results At a support distance of 8 mm and a displacement of 0.25 mm Essix® PLUS™, having the highest thickness in untreated state, showed highest forces of 28.2 N, followed by Duran Plus® (27.3 N), Essix ACE® (21.0 N) and Zendura® (19.7 N). Similar results were registered for the other distances (16, 24 mm). Thermoforming drastically reduced thickness and forces in the bending tests. Forces decreased to around 10% or less for specimens cut from the lateral walls. Young’s modulus decreased significantly for deep drawn foil sheets, especially for Essix® PLUS™. Conclusions Three-point bending is an appropriate method to compare different foil sheet materials. Young’s modulus is significantly affected by thermoforming.

Evaluation of Mechanical Properties of Different Thermoplastic Orthodontic Retainer Materials after Thermoforming and Thermocycling

“…Moreover, three-point bending could represent the forces applied to the thermoplastic retainer during placement in and removal from the oral cavity, clenching, and bruxism. A span length of 8 mm was used in the current study based on the recommendation of previous studies [29,32] As properties, the flexural modulus and hardness are frequently confused. Both characteristics capture how a material behaves in response to contact.…”

“…However, in the current study, since we aimed to evaluate the expected lifespan of orthodontic thermoplastic retainer materials, we performed 10,000 thermocycles to simulate one year of intraoral use [ 27 ]. While previous studies have provided valuable insights into the mechanical properties of different aligner and retainer thermoplastic materials, it is difficult to compare their findings, as they used a wide range of experimental designs and methods [ 19 , 22 , 24 , 25 , 26 , 29 , 31 , 32 ]. Moreover, no ISO specifications or national standards have been proposed for the measurement of the mechanical properties of thermoplastic orthodontic materials.…”

“…Moreover, three-point bending could represent the forces applied to the thermoplastic retainer during placement in and removal from the oral cavity, clenching, and bruxism. A span length of 8 mm was used in the current study based on the recommendation of previous studies [ 29 , 32 ]…”

Integrated manufacturing of direct 3D-printed clear aligners

“…A 10% reduction of aligner material thickness could reduce exerted forces by up to 30% theoretically (11). Thermoforming is an important way to alter material properties like transparency, surface hardness, water solubility, water absorption ability, flexural modulus, and elastic modulus of various aligner material brands and thicknesses (12)(13)(14).…”

Effectiveness and Efficacy of Thermoformed and 3D Printed Aligners in Correcting Malocclusion (Spacing) and Its Impact on Periodontal Oral Health and Oral Microbiome: A Double-Blinded Parallel Randomized Controlled Multicenter Clinical Trial

“…However, aligners have drawbacks, such as achieving good occlusal contacts, retention, and tooth torque. The evidence on the effectiveness of 3D aligners in correcting malocclusion in comparison to conventional thermoformed aligners is lacking, and a more recent update on the systematic reviews and meta-analysis in this issue is warranted [ 13 , 14 , 15 , 16 , 17 , 18 ]. Both therapies also have an impact on the oral microbiota and change in oral flora over a period of time.…”