[Edaily Reporter NA EUN-KYUNG ] Research findings show that #Graphy Inc.’s directly 3D-printed shape-memory alloy (SMA) clear aligners adhere more firmly to teeth than conventional heat-formed clear aligners, while maintaining orthodontic forces within the clinically recommended range. The thickness of the aligners also remained relatively more uniform after manufacturing compared to heat-formed aligners.

Graphy Inc. announced on the 8th that the results of an international collaborative study comparing the force transmission characteristics of SMA—directly 3D-printed using the shape-memory material “Terahaz TC-85”—and high-performance thermoformed clear aligners over a 30-day period were published in the “International Dental Journal,” the official academic journal of the FDI World Dental Federation. Kim Hoon, a senior researcher at Graphy Inc., also participated as a co-author.

Researchers from Germany, Saudi Arabia, the United Arab Emirates (UAE), Egypt, and South Korea participated in this study. The research team compared SMA directly 3D-printed using Graphy Inc.’s TC-85 with thermoformed clear aligners made from the triple-layer material “Zendura FLX,” analyzing factors such as tooth contact force, the three-dimensional orthodontic force transmitted to the actual teeth, and thickness after manufacturing.

The results showed that the initial tooth contact force of the SMA was 149.7 ± 25.6 N, which was approximately 2.1 times higher than the 69.8 ± 9.0 N measured for the thermoformed aligner. The research team analyzed that the post-manufacturing thickness of the SMA and factors such as tooth fit—as reported in previous studies—may have influenced this difference.

However, the high contact force did not necessarily mean that excessive force was applied to the actual teeth. The actual three-dimensional orthodontic force measured under conditions designed to move the maxillary incisors 0.2 mm was in the range of approximately 0.1–0.5 N for both devices before aging. The research team assessed this as falling within the clinical recommendation range presented in previous studies. They explained that while the SMA made relatively strong contact with the teeth, it transmitted the force required for actual tooth movement at an appropriate level.

Differences were also observed in thickness after manufacturing. The pre-manufacturing thickness settings were similar, with TC-85 at 0.75 mm and Zendura Flex at 0.76 mm. However, the thermoformed devices measured 0.3–0.5 mm in thickness depending on the area, whereas the SMA devices measured 0.8–1.1 mm. The research team analyzed that, unlike the conventional method of molding by pressing a heated sheet onto a dental model, the direct 3D printing method resulted in relatively smaller variations in thickness across different areas.

The study also identified limitations of SMA. In some areas, the actual printed product was thicker than the designed thickness, indicating that further research is needed to improve printing precision.

In particular, this experiment alone did not confirm the shape-memory effect of SMA. While the device aging process took place in water at 37°C, force measurements were conducted at a dry room temperature of approximately 25°C. The research team cited this as a limitation of the study and stated that further research is needed to reflect the shape-memory characteristics in a temperature and humidity environment similar to that of the actual oral cavity.

Kim Hoon, a senior researcher at Graphy Inc., said, “It is difficult to fully explain the forces exerted by a finished clear aligner on actual teeth based solely on the material’s physical properties.” He added, “This study is significant in that it directly compared finished devices to analyze the contact force with teeth, the actual orthodontic force, and thickness differences resulting from manufacturing methods.”

Shim Un-seop, CEO of Graphy Inc., remarked, “Through this study, we were able to confirm not only the potential of SMA but also the challenges that need to be addressed in the future, such as printing precision and force control based on the direction of tooth movement.” He added, “We will continue our research, incorporating shape memory characteristics in actual oral environments, to accumulate relevant evidence.”