## 1 Introduction  
Today, acquiring an intraoral scanner (IOS) for the dental office can be a major step forward for both the quality of the treatments and the overall impression for the patient also serving as an ideal marketing tool [1]. However, the latest IOSs can be a big investment for the dental office and not all dentits may be able to afford it. Thus, the following question arises: are the IOSs released in the previous years a good and reliable alternative to the latest scanners emerging on the market? The clinical applications of intraoral scanners (IOSs) have increased significantly providing dentits with relevant information that enhance the entire treatment plan and procedure. Minimally invasive dentistry with inlays, onlays and veneers, as well as short span prosthetic restorations, full arch rehabilitation and implant supported restorations can be successfully obtained with the aid of these systems [2, 3, 4, 5]. One of the main advantages of IOSs is the possibility to completely replace the conventional impression, reducing the discomfort for the patient, the working procedure and the overall costs of the impression materials. The immediate evaluation of the quality of the digital impression is another beneficial aspect that enhances the impression procedure [6, 7, 8, 9]. These systems also have a number of limitations including the difficulty in detection of deep preparation margins, the presence of blood and saliva prevents data acquisition of the scanned surface, and also high purchasing and maintenance costs [10]. A key aspect for any long lasting prosthetic restoration is the accuracy of the impression which generates a working model (digital or conventional) that eventually dictates the marginal adaptation and fit of the final restoration. Two variables, \"trueness\" and \"precision\", describe the accuracy of a measurement method (ISO 5725). \"Trueness\" refers to the closeness of agreement between the arithmetic mean of a large number of test results and the true or accepted reference value. \"Precision\" refers to the closeness of agreement between test results [11; 12; 13]. The analysis of the trueness involves a reference virtual model that is generally obtained with an industrial or a desktop laboratory scanner (with accuracy < 5 \(\upmu\)m). This high-quality virtual model is then overlapped in a 3D inspection software with the virtual model obtained with the intraoral scanner which shows the differences and similitudes between the meshes [14; 15; 16]. Primescan (CEREC v.5, Dentsply-Sirona Dental Systems, Bensheim, Germany, 2019) is the latest intraoral scanner from CEREC and uses high-resolution sensors and shortwave light with optical high-frequency contrast analysis for dynamic deep scan (20 mm) [17]. i700 (Medit Link v2.4.4, Medit, Seoul, Korea, 2021) is the latest intraoral scanner from Medit, improving most of the features presented by Medit!500. Data acquisition is based on the principle of 3D in Motion Video Technology/3D Full Color Streaming Capture [18]. CEREC Omnicam (v4.6 Dentsply-Sirona Dental Systems, Bensheim, Germany, 2012), the predecessor of Primescan, is based on the principle of confocal microscopy and active triangulation with a white LED light source [17]. The Planmeca PlanScan (Romexis v4.6.2, powered by E4D Technologies, LLC, Richardson, TX, USA, 2014) works based on the principle of optical coherence tomography and confocal microscopy. It is incorporated with a blue light real-time laser video streaming technology [17]. Medit T500 (Seoul, Korea) is a desktop dental scanner with an accuracy of <7 \(\upmu\)m, that works based on the principle of phase-shifting optical triangulation, using a blue LED light source [19]. Additional information about the intraoral scanners is provided in Table 1.  
The aim of this study was to evaluate the differences in accuracy between four intraoral scanners in the scenario of a short span fixed partial dent