## 2 Challenges and Innovations in Hearing Aid Fitting: From Conventional Molds to Digital Molds
### Digital Mold  
A study conducted by the U.S. Army Aeromedical Research Laboratory (USAARL Report No. 2020-06) presents a comparative analysis of traditional ear mold generation methods versus those employing ear scanning technologies. The emphasis on comfort arises from the understanding that the more comfortable the hearing protection device is, the more likely users will be to wear it consistently and for as long as necessary, especially in environments with noise levels considered hazardous [13]. Recently, new alternative technologies to traditional ear printing have been developed to eliminate the need for physical mold manufacturing. One such innovation is the Otoscan from Otometrics, a portable 3D ear scanner that creates digital 3D impressions of the ear. However, Otoscan still requires the introduction of a probe into the EEC, which can cause discomfort to the patient. Furthermore, to handle Otoscan effectively, significant learning about how the equipment works is necessary, which led its maker, Otometrics, to create a training program with 27 modules, including videos and questionnaires, to train health professionals in the use of the device [34]. Furthermore, the cost associated with Otoscan limits its use in clinics with reduced financial resources [35]. Although the use of lasers for 3D imaging acquisition is an established practice in several industries, the application of this technology to replicate the complexities of EEC has only recently been researched and implemented. Ear scanning devices, such as the Otoscan and Lantos instrumentation, employ 3D laser mapping techniques to create an accurate digital image of the ear canal, similar to the current practice of dentists constructing custom dental implants [36; 37]. The Artec Space Spider from Artec 3D is another commercially available technology. This technology integrates a portable 3D scanner that uses structured blue light to scan small objects, transforming them into 3D models. A case study highlighted the use of the Artec Space Spider to scan the ear's external structure, aiming to create custom ear prostheses for cases of deformity [38]. This device is accompanied by Artec Studio software (Version 19) for processing and rendering scans. Like Otoscan, its cost may limit its use in environments with fewer financial resources [39]. Another innovation is TinyScan360\({}^{\circ}\), a device designed for measuring ear canals. This scanner has already been successfully tested and shown to be extremely useful for fitting modern hearing aids, allowing for easy and individual customization for the user. TinyScan360\({}^{\circ}\)'s ability to accurately measure spaces as small as the ear canal clearly illustrates the flexibility and effectiveness of these technologies in medical applications. The 3D stereoscopic measuring system, with a design diameter of just 3 mm, allows contactless 3 Dmeasurement, visualization, and reconstruction of small objects such as pipes and holes with diameters of less than 10 mm [39]. Despite significant advances and innovations in the field of auricular scanning, currently, available systems still have substantial limitations that restrict their applicability and effectiveness in broader contexts and with fewer financial resources. Despite being technologically advanced and precise, these devices continue to require the insertion of probes or membranes into the ear canal. Furthermore, the high cost of these systems represents a significant obstacle to their adoption, especially in clinics with limited financial resources, thus restricting access to these technologies in regions with lower purchasing power. Another critical aspect is the operational complexity of these devices. Many require specialized training to handle them effectively. Additionally, given that they were designed for specific situations, such as adjusting hearing aids or creating ear prostheses, they may not be suitable for other applications required in audiology or otorhinolaryngology, such as quickly establishing a diagnosis or monitoring pathologies.