## 1 Introduction  
In recent decades, aesthetics has become increasingly central to orthodontic treatment, leading patients to favor discreet options such as clear aligners, which improve the smile without interfering with daily life [1, 2, 3]. The evolution of aligners can be traced back to the 1940s when [PERSON] proposed the use of a \"positioner\" to move teeth incrementally [4]. Introduced in the 1990s, clear aligners represented a significant advancement in orthodontics by offering removable and nearly invisible devices that allowed for intermittent application of orthodontic forces, which cease during oral hygiene routines and meals. Despite their advantages, traditional aligners made from PET-G (Polyethylene Terephthalalate Glycol-modified) materials tend to experience stress relaxation, resulting in a progressive reduction in force exerted on the teeth, thereby impacting the predictability of tooth movement [5]. With technological advances, aligner production has shifted from thermoforming to direct 3D printing, which allows greater control over structure, thickness, and material properties, while also reducing manufacturing steps and waste, improving both precision and production time [6,7]. Among the 3D printing technologies employed, Direct Light Processing (DLP) and Selective Laser Sintering (SLS) enable the creation of customized aligners with variable thicknesses and optimized configurations tailored to clinical requirements [8,9]. Recent studies suggest that by varying the design and thickness of the aligners, it is possible to influence the force exerted on the teeth, thereby optimizing treatment biomechanics and reducing the need for visible attachments [10,11]. The introduction of rapid prototyping (RP) technologies in recent years has further transformed aligner manufacturing. Originally developed in the 1980s, RP--also known as additive manufacturing--has advanced significantly, finding applications in various fields, including medicine, dentistry, and orthodontics [6]. In orthodontics, the use of digital impressions and 3D printing to produce aligners has greatly reduced errors associated with traditional impression methods and the fabrication of plaster models, which are susceptible to environmental damage and storage issues [12]. Studies have confirmed that 3D-printed models offer high precision and minimal measurement errors, making them a reliable alternative to plaster models [13]. Traditional aligner fabrication involved the thermoforming of plastic sheets over 3D-printed models of planned tooth movements. However, the direct 3D printing of aligners has emerged as a groundbreaking innovation. This approach simplifies the workflow, reduces production time, and allows for better control over aligner properties such as thickness and material composition [6]. Technologies like DLP and SLS play a pivotal role in this evolution. DLP uses photopolymerization to cure entire layers of liquid resin in a single exposure, while SLS relies on a laser to sinter polymer powder, enabling the creation of highly detailed and complex objects [9]. These methods not only enhance production efficiency but also reduce material waste and support the development of on-demand aligner treatments [6,7]. A notable innovation in this field is the NOXI aligner (Sweden & Martina, Due Carrare, Padova, Italy), which uses advanced polyamide material and CAD-CAM technology for direct printing. While aligners are more aesthetically acceptable than traditional fixed metal appliances, they cannot be considered completely invisible. The NOXI aligner features a design optimized for 12 h daily wear, incorporating differential thickness gradients that may influence force distribution. These thickness variations increase from the incisal to the gingival margin and from anterior to posterior teeth, influencing fit and force distribution across different dental elements, thus presenting a compelling alternative to traditional thermoformed aligners [14,15].