## 1 Introduction  
Computer-assisted design/manufacturing (CAD/CAM) systems have made single tooth indirect restoration easier, faster, and more predictable [1, 2]. Intraoral scanning and milling devices allow simple and fast digital impressions, thus enabling the projection, customization, and finally, milling of the restorations in the same appointment (chairside protocol), with consequent reduction of costs and patient discomfort [3]. The CAD-CAM workflow could also be implemented thanks to the possibility to export the stereolithography (STL) file of the intraoral scan and produce 3D printed casts (3 DCs), which could be useful to clinicians and technicians for material characterization, contact points, and occlusion checks [4, 5]. A single-tooth indirect adhesive restoration can be performed using different processes. The traditional workflow is still frequently used and yet considered by many authors and clinicians the gold standard model for the manufacturing of adhesive restorations [6, 7]. Conventional impressions and casts rely on high-performance materials [8, 9], as polyvinyl siloxane and type IV gypsum show great stability and precision [10] and give the possibility of layering, ultimately enhancing aesthetic outcome with good long-term performances [11; 12]. However, the precision of the master cast is technique-dependent [13] and the operator skill and experience play an important role [14]. Moreover, the use of these materials presents the risk of distortion, expansion, or shrinkage due to numerous steps involved. Additionally, they need large storage spaces and there is a risk of damage during time [15; 16]. The most common application of CAD/CAM in dentistry is the digital acquisition of gypsum casts with the use of extraoral scanners in the dental laboratory. Even though this path may add digitalization errors to the traditional procedure, it is still considered the most trusted method when using a digital workflow is needed in order to employ certain materials [17]. The direct digital workflow with intraoral scans (IOS), on the other hand, presents several advantages; it does not involve chemical reactions, has no storage or recovery issue, and requires less time and fewer steps (no tray selection, wait time, cast setting time, disinfection, or transport). Additionally, it enables real-time evaluation of thickness, undercut, and margin [18]. Recently developed systems obviated the need for powder and reduced the discomfort by the miniaturization of intraoral cameras. However, IOS precision and accuracy is affected by patient movement, saliva, and blood [19], particularly in full-arch scans [20; 21]. Additionally, the utilization of IOS is limited by its steep learning curve and high cost [22]. Both digital and conventional workflows can achieve clinically acceptable results for single crowns and short-fixed prostheses in terms of fit [17; 23; 24]. Fitting of the restorations is closely related to trueness and accuracy of the master cast, and it is considered a key factor for the long-term prognosis of a restoration. As a defect, it can result in decreased mechanical properties, increased plaque accumulation, and, consequently, an increased risk of caries and periodontal disease [25; 26]. In the present paper, according to ISO 5725-1, \"trueness\", one of the evaluations of the general term \"accuracy\", is used to describe the closeness of a measurement to the actual (true) value. The trueness of digital scans has been investigated by surface deviation analysis, with superimposition on a reference model using best fit algorithms [27]. The accuracy of digital scans varies between IOS and conventional impressions, but the deviations have been reported to be minimal for up to 10 teeth in vivo 6. Previous studies also showed that 3D-printed casts (3 DCs) nowadays have good performances in terms of accuracy, reproducibility, and precision [28]. This can be compared to traditional casts for single-tooth crowns [27; 29].