The intraoral scanners (IOS) have gained a majority of popularity due to their advantages, such as simplicity, high efficiency, patient comfort, accessible storage, and convenient communication between dentists, patients, and technicians [1], [2], [3], [4]. A recent systematic review indicated that IOS could provide a clinically acceptable substitute for conventional impressions limited within a 3-unit fixed dental prosthesis [5]. Scanning the arch span of more than 4 implants could lead to significantly more deviations than conventional impressions [6]. The challenge of the IOS application in edentulous arches remains due to the problem of image “stitching” in the edentulous arch [7,8]. Image “stitching” is the critical process for digital scanning, which can be negatively affected by the insufficient landmarks of the scanned surfaces. The existence of stable artificial landmarks can help the image to be correctly “stitched”.

Previous studies proposed various methods to minimize the stitching deviations on the edentulous scanning by providing artificial landmarks on the edentulous ridges [9], [10], [11], [12], [13]. For instance, Modular chain pieces by Pozzi et al. significantly improved overall accuracy, particularly reducing linear and angular deviations at the most critical posterior implant positions [10]. Scanning aid by Kernen et al. showed accuracy enhancement and found that artificial landmarks in the combination of irregular morphologies and beige color resulted in the highest trueness [9]. A novel-designed scan body with a lateral flag by Huang et al. showed favourable results in vivo and in vitro studies [12,13]. Compared with the previously proposed methods, mostly bulky one-piece auxiliary devices that may be difficult to apply in clinical situations due to the oral cavity's limited space, PAD featured with less volume and more flexibility and simplicity are presented in this study.

Though artificial landmark enhancement on the scanning accuracy has been assessed by multiple studies [9], [10], [11], [12], [13], [14], a few studies analyzed how the artificial landmarks in different configurations influenced the accuracy [9,14]. To the authors’ acknowledgement, the impact of artificial landmarks located at different arch positions has never been studied. This study aimed to evaluate the accuracy of complete-arch implant digital scanning with artificial landmarks located at different arch positions. The null hypothesis was that the artificial landmarks located at different arch positions would not influence the accuracy of complete-arch implant digital scanning.