## 1 Introduction  
Endodontic microsurgery (EMS) is one of the treatment options for endodontically treated teeth with unresolved periapical lesions, anatomically complex roots, and cases of iatrogenic accidents. One major challenge during EMS is ensuring adequate visual and instrumental access to the root apex. This is especially important in scenarios in which lesions have not yet perforated the cortical plate. Some studies have reported that tooth position has an influence on the success rate. In particular, the lower molars have been reported to have a lower success rate than other teeth due to their visual and instrumental access difficulties [1, 2]. Other challenges include avoiding the risk of complications and iatrogenic problems such as pain, swelling, bleeding, and nerve injuries. When performing EMS, management of vital anatomic structures and the adjacent root apex is crucial (including the inferior alveolar nerve, sinus, nasal cavity, greater palatine artery, and mental foramen) [3]. Lastly, minimizing the size of the access window to the apex has been correlated with better healing outcomes [4]. To improve the accuracy during EMS, surgical guides have recently been introduced [5]. Surgical guides have traditionally been used in implantology since 2002 [6]. The placement of dental implants is more accurate and predictable when using a surgical guide with computer-aided design and computer-aided manufacturing (CAD-CAM)technologies than freehand surgery [7; 8; 9]. Thanks to advances in technologies including stereolithography, optical scanning, cone beam computed tomography (CBCT), and 3D printing, surgical printed guides are now fully integrated in digital workflows and have become easy to produce [10; 11; 12; 13]. Several case reports indicate that using 3D-printed surgical guides during EMS allows for more accurate surgical access without the risk of damaging vital structures [1; 14; 15]. All of these printed surgical guides are made of autoclavable, biocompatible resin. They cover the teeth and gums over the entire arch or half of the arch for stability [5; 16]. Although transparent, such guides are made to be thick to compensate for fragility, which leads to visual disturbance and a need to insert a sleeve. To overcome these drawbacks and facilitate the sterilization process and irrigation during surgery, surgical metal guides (SMGs) using cobalt-chrome with laser sintering have recently been designed and introduced in dental surgery [17]. The goal is to make guided surgery faster, easier, and more accurate [18; 19; 20]. Current concepts of removable partial dentures (RPDs) are focused on biomechanical aspects such as stability, retention, and mechanical resistance. To achieve these goals, RPDs are usually made with metal, and the current metal of choice is cobalt-chrome [21; 22]. This metal offers several advantages, such as lightweight, solidity, and the possibility of performing guided surgery without a sleeve. This study introduces a new 3D-printed cobalt-chrome SMG with open-frame structure that may be used for EMS. This SMG fits around teeth, and stability is primarily achieved with metal contacts between the teeth and the metal framework of the guide according to current concepts of RPDs. The application of such concepts to surgical guides is new, and to our knowledge, there are no published cases or studies evaluating this type of guide for EMS. Before considering its clinical use, its feasibility and accuracy must be assessed. The purpose of this study was to evaluate the accuracy of 3D-printed SMGs in comparison to virtual planning in an endodontic surgical simulation model ex vivo using a pig jaw. To assess the accuracy of the surgical guides, virtually planned implants were compared to bone drilled with SMGs in terms of apical and angular deviations. The main hypothesis was that there would be no significant statistical differences between virtually planned implants and drill paths after surgery.