## 1 Introduction  
Clear aligner therapy has undergone substantial advancements in recent years, offering advantages such as reduced treatment durations and fewer emergency appointments compared to fixed appliances, particularly for mild to moderate malocclusions [1]. Nevertheless, patient compliance remains the primary limitation of clear aligner treatment, as optimal outcomes rely on wearing these aligners for approximately 22 h per day [2]. This requirement is dictated by the mechanical behavior of the materials used; insufficient wear time results in suboptimal force application, thereby compromising the efficiency of tooth movement [3]. Several studies have shown that adherence to the prescribed wear time for removable orthodontic devices is significantly lower than the recommended level [4]. A systematic review by [PERSON] et al. on compliance with removable orthodontic appliances revealed that patient adherence is generally suboptimal, as they wear their appliances for significantly less time than prescribed and often overreport their actual wear duration [5, 6]. Specifically, [PERSON] et al. found that among aligner users, only 36% exhibited full compliance, while 38.3% showed moderate compliance and 25.7% demonstrated poor compliance [7]. In response, recent research has increasingly focused on the development of innovative 3D-printed materials for aligners, aiming to reduce the required daily wear time by exploiting the distinct mechanical properties of these materials [8; 9]. A reduced wear time may also provide aesthetic benefits [10; 11]. Although clear aligners are inherently transparent, [PERSON] et al. demonstrated that the presence of aligners still draws significant visual attention to the mouth, as evidenced by eye-tracking studies comparing gaze patterns across individuals with and without orthodontic appliances [12]. One promising innovation is the development of night-time aligners, designed to be worn for only 10-12 h per day. NOXI (Sweden & Martina, Due Carrare, Padova, Italy) nighttime aligners, developed at the University of Ferrara, are 3D printed using selective laser sintering from a polyamide material. This polymer has been demonstrated to deliver higher and more sustained orthodontic forces due to its reduced stress relaxation properties [13]. Another key feature lies in the ability to create differential thicknesses across various regions of the arch, as well as between the cervical and incisal sections of the aligner. This design flexibility enhances the fit and allows for more effective force delivery, particularly by increasing the force applied to selected teeth where needed [14; 15; 16]. Such mechanical advantages justify the clinical rationale behind the limited daily use of this aligner, offering a more discreet and patient-friendly alternative to full-time aligner wear. Despite these material innovations, patient compliance remains a persistent challenge for all removable orthodontic systems [4; 5; 17; 18]. A systematic review published in 2024 sought to further investigate the complex issue of patient compliance in orthodontics. After screening and analyzing over 3000 articles, the authors concluded that there is currently no clear evidence regarding which factors effectively influence patient compliance, nor how such compliance can be reliably improved [19]. Addressing this gap, the present study proposes a novel, objective method to determine whether a patient has adhered to the prescribed wear protocol. By providing a quantifiable and non-invasive marker of cooperation, this approach also removes the ambiguity that may otherwise exist in the patient-clinician relationship--namely, the clinician's inability to verify the accuracy of self-reported compliance. Colorimetry has long been employed in dentistry to assess the aesthetic and functional stability of dental materials. It provides quantitative data that eliminate subjectivity in visual shade selection and is commonly used in restorative dentistry, prosthodontics, and, increasingly, in orthodontics [20].