Implant-supported complete dental prostheses are indispensable and reliable options for edentulous jaws [1]. Taking impressions is the first step in the production process of implant-supported prostheses. Inaccurate impressions result in a misfit between the prosthesis and implant abutment, which may lead to mechanical and biological complications that affect the long-term of the implants [2,3]. Thus, accurate impressions are critical to prostheses that are supported by multiple implants.

Conventional open-trayed impression of multiple implants is one of the most widely used strategies. During this procedure, the impression copings are splinted to prevent them from rotation movements. Therefore, this method is recommended over the non-splinting technique [4,5]. However, this workflow is complex, inefficient, and requires substantial clinical experience. It is recommended for experienced dentists only, as inexperienced dentists have been found to have a significantly higher rate of unsuccessful results when using the splinting technique [6]. Moreover, during the conventional workflow, several factors may affect the accuracy of the implant impressions, such as patients’ pharyngeal reflex and the potential deformation of the impression materials.

As computer-aided design/computer-aided manufacturing (CAD/CAM) and digital technologies have flourished, the intraoral scanner (IOS) has become increasingly popular for acquiring implant positions. IOSs are comfortable, efficient, and practical for clinical use. However, IOSs cannot replace all standard practices. Regarding implant-supported fixed dental prostheses, intraoral scanners can be used in single- and three-unit implant scanning [7,8]. In 2020, Revell et al. recommended certain scanners, such as Primescan, for complete-arch implant impressions based on the low deviation values at the implant platform level [9]. However, the accuracy of older models of intraoral scanners is not reliable for scanning edentulous spaces with long inter-implant distances or fully edentulous jaws [7,[10], [11], [12]], especially for inexperienced operators [9,13].

Previous studies have placed auxiliary devices in the edentulous area or custom-designed scan bodies with an extensional structure to obtain reliable digital full-arch implant impressions [14], [15], [16], [17]. These platforms usually require custom-made scan bodies or a second scan to obtain mucosal information. In this study, newly designed prefabricated landmarks were produced. The lack of geometric variation can be overcome by adding landmarks with letter patterns between the scan bodies, providing a solution for the digital implant impression of edentulous jaws. As the prefabricated landmarks do not block the mucosa, only one scan is required. This study aimed to evaluate the accuracy of digital implant impressions in edentulous jaws with or without prefabricated landmarks compared to conventional impressions. Null hypothesis 1: There would be no significant difference in the accuracy between digital impressions with or without prefabricated landmarks tested in two intraoral scanners. Null hypothesis 2: There would be no significant difference in the accuracy between digital impressions without landmarks and conventional impressions.