# 3D-Printed Accessories and Auxiliaries in Orthodontic Treatment
However, according to a recent study by [PERSON] et al., it is recommended to use these models immediately in orthodontic applications to avoid inaccuracies in retainers and  
Figure 1: Dental 3D printing market in the USA (2020–2030) by application, in USD billion. Data from Grand View Research [16]. appliances over time due to the shrinkage of 3D-printed models, which occurs regardless of material type or storage conditions [18]. Three-dimensional printing technologies can be also used to customize the size, shape, and prescription of brackets. The mechanical characteristics of 3D-printed brackets were evaluated by indentation testing and found to be superior to available plastic brackets [19]. The frictional resistance of 3D-printed self-ligating brackets was compared with two ceramic, two metal, and one plastic (commercially available) brackets. Across all combinations of brackets and archwires, 3D-printed polymer brackets demonstrated a sliding resistance comparable to that of existing polymer brackets and lower than that of ceramic and metal brackets [19]. The most studied use of 3D printing in orthodontics is the production of aligners [19]. Directly printed aligners (DPA), introduced in 2021 [20], offer multiple benefits over traditional thermoformed aligners. They offer a better fit to the teeth than traditional methods, thereby possibly reducing the need for attachments [20]. Utilizing 3D printing technology enables the personalization of aligner features, such as material thickness, surface textures, and overall design, providing greater precision in controlling tooth movements [21]. The capacity to adjust the thickness of the aligners is a promising approach to enhance the effectiveness of intended orthodontic movements while reducing unintended tooth movements, thus improving the predictability and accuracy of tooth movements [22]. Furthermore, if we bypass creating printed models and thermoforming, it is possible to reduce the accumulation of errors during the production process. While the design of the aligners and treatment is time-consuming, the manufacturing is faster due to the reduced supply chain: the DPAs can be printed immediately and in the practice [23]. Importantly, directly printed aligners present an eco-friendly option by reducing or even eliminating the need for resin models and plastic sheets traditionally used for thermoforming [21]. Obviating the need to 3D print resin models decreases the costs as well [20]. It has been shown that the traditional aligner fabrication method has a considerable environmental toll [23]. However, some authors are skeptical about DPAs. [PERSON] et al. in their study showed that thermoformed aligners might still have better mechanical properties compared to some directly printed aligners [24]. When it comes to the clinical effectiveness of DPAs, there is still further research needed as of now. DPAs can be effective for mild to moderate malocclusions and the Aliphatic Vinyl Ester Urethane (Tera Harz TC-85, Graphy; Graphy Inc, Seoul, Republic of Korea) [25] also has some beneficial properties when it comes to elasticity and more physiological flexural strength. However, another point worth mentioning is that the manufacturing process of the Tera Harz TC-85-based DPAs is still very technique sensitive and requires specialized equipment for post processing. Despite that, the final product is more susceptible to moisture, impairing the ability to deliver forces in the oral cavity [20]. These technological advancements allowed healthcare professionals to offer more personalized medical devices to each patient. Three-dimensionally printed appliances are crafted specifically for an individual's anatomy, utilizing imaging data and 3D models to design and manufacture medical appliances [10].