## 1 Introduction  
Advances in computer-aided design/computer-aided manufacturing (CAD/CAM) technology have replaced many conventional techniques for dental prostheses fabrication [1; 2]. The intraoral scanner (IOS) system has particularly enhanced the impression procedure. Using IOSs, a digital image of the dental arch can be obtained by acquiring a digital impression directly in the mouth, without a tray or impression material, which are needed in conventional techniques [3; 4]. The IOS is an important system in the digital workflow using CAD/CAM technology and has undergone continuous advancement in recent years. The current IOS system is used for the fabrication of most prosthetic restorations, such as inlays/onlays, copings and frameworks, single crowns, and fixed partial dentures [5]. However, for the fabrication of a long-span prosthesis, the impression obtained by the IOS system is not as accurate as that by the conventional technique [6]. In other words, when scanning a long-span arch using an IOS, errors in stitching images could occur; thus, conventional impression methods are still required [7]. As in the conventional technique, in addition to obtaining an accurate impression, the reproduction of an accurate interoclusal relationship is important for the fabrication of an accurate prostheses through digital workflow using IOSs [8]. Buccal bite registration is used in most IOS systems to obtain the virtual interoclusal record (VIR) of the maxillary and mandibular arches. This method is defined as intraoral digital scans capturing the buccal surface of approximately three teeth of both arches in maximum intercuspation [9]. Using the software matching process of each IOS system, both buccal scan images and intraoral scans of the maxillary and mandibular arch are automatically aligned [10]. Several studies have been conducted to evaluate the accuracy of IOSs in VIRs. When the buccal bite registration method is used to align the full-arch scans, there could be interarch and interoclusal distortion [1]. Alteration of occlusal contact points could occur more in the complete arch scan than in the quadrant arch scan [11]. In addition, the deviations of occlusal contact points are higher in the posterior teeth than in the other regions of the arch [12]. The span and location of the edentulous area in the full arch model could also affect the dimensional accuracy of a VIR [13]. In several studies, a high level of accuracy was found only in the VIR of a single missing posterior tooth group [13,14]. To obtain a more accurate occlusal record in the full-arch scan, a combination of the recording areas, such as the combination of the right and the left lateral sections, is suggested [15]. The majority of previous studies regarding the accuracy of VIR were conducted under the full-arch scan models [5,7,16]. It is relatively hard to assess the influence of edentulous conditions on VIR due to the distortions in full-arch scan data itself. Therefore, clinically, current research recommended that most restorations such as single crown and short-span fixed partial denture (FPD) are fabricated on the digital working model generated from quadrant scan [5]. Moreover, to date, it is not recommended to use full-arch impressions obtained by IOS in fabrications of FPD [5,14]. However, there is rare information about the accuracy of VIR from quadrant scans under various edentulous conditions. Although [PERSON] et al. studied the accuracy of VIRs in quadrant scans by various IOSs [9] and [PERSON] et al. studied the accuracy of VIRs in full-arch scans of different edentulous conditions [13], to the best of our knowledge, no study has evaluated the accuracy of VIRs in quadrant scans under varying partial edentulous conditions. Moreover, it is uncertain how the span and location of the edentulous area in the quadrant scan affect the accuracy of VIRs. The purpose of this in vitro study was to evaluate the accuracy of VIRs of quadrant scans with different spans and locations of edentulous areas using three IOS systems.