Graphy said Sept. 8 that the results of an international collaborative study comparing the force-delivery characteristics of its SMA, directly 3D-printed using its shape-memory material Tera Harz TC-85, with those of a high-performance thermoformed clear aligner over 30 days were published in the International Dental Journal, the official journal of the FDI World Dental Federation. Graphy principal researcher Hoon Kim participated as a co-author.
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Researchers from Germany, Saudi Arabia, the United Arab Emirates, Egypt and South Korea took part in the study. They compared Graphy’s SMA, directly 3D-printed with TC-85, with thermoformed clear aligners made from Zendura FLX, a three-layer material. The study examined tooth contact force, three-dimensional orthodontic forces actually delivered to teeth and post-manufacturing thickness.
The SMA showed an initial tooth contact force of 149.7 ± 25.6 newtons, about 2.1 times the 69.8 ± 9.0 newtons recorded for the thermoformed aligner. Researchers said the difference may have been influenced by the SMA’s post-manufacturing thickness and its tooth fit, as reported in previous studies.
However, the higher contact force did not mean that the SMA applied excessive force to the teeth. When researchers measured three-dimensional orthodontic forces under conditions designed to move a maxillary incisor by 0.2 millimeters, both devices generated forces of about 0.1 to 0.5 newtons before aging.
The researchers said the forces were within clinically recommended ranges reported in previous studies. The findings suggest that although the SMA maintained relatively strong contact with the teeth, it delivered an appropriate level of force required for tooth movement.
Differences were also found in post-manufacturing thickness. Before fabrication, the specified thicknesses were similar, at 0.75 millimeters for TC-85 and 0.76 millimeters for Zendura FLX.
After fabrication, however, the thermoformed aligner thinned to between 0.3 and 0.5 millimeters depending on the area, while the SMA measured between 0.8 and 1.1 millimeters. Researchers said direct 3D printing resulted in relatively smaller variations in thickness across different areas compared with conventional thermoforming, in which a heated sheet is pressed over a dental model.
The study also identified limitations of the SMA. In some areas, the printed aligners were thicker than their designed dimensions, indicating that further research is needed to improve printing accuracy.
The experiment also did not directly confirm the SMA’s shape-memory effect. The devices were aged in water at 37 degrees Celsius, but force measurements were conducted in dry conditions at room temperature of about 25 degrees Celsius.
Researchers cited this as a limitation and said further studies are needed under temperature and moisture conditions that more closely resemble the oral environment to assess the aligner’s shape-memory characteristics.
“Material properties alone cannot fully explain the forces that a finished clear aligner actually delivers to teeth,” said Hoon Kim, principal researcher at Graphy. “This study is meaningful because it directly compared finished aligners and analyzed tooth contact force, actual orthodontic force and differences in thickness resulting from the manufacturing method.”
Shim Woon-seop, CEO of Graphy, said the study identified both the potential of the SMA and areas requiring further development, including printing precision and force control based on the direction of tooth movement.
“We will continue research that reflects shape-memory characteristics under conditions that more closely replicate the actual oral environment and build further scientific evidence,” Shim said.
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