Modern endodontic microsurgery (EMS), an effective treatment option for persistent apical periodontitis, has obtained a relatively high success rate with the development of endodontic microscopy, cone-beam computed tomography (CBCT), ultrasonic instruments, and biocompatible root-end filling materials [1,2]. Osteotomy and root-end resection are crucial steps in EMS. Currently, a 3–4 mm diameter osteotomy is recommended, which is the minimal space for manipulating an ultrasonic tip within the bony crypt [3]. Root-end resection with the removal of 3 mm of apical dental tissue, perpendicular to the long axis of the root, eliminates 93% of lateral canals and 98% of apical ramifications and exposes few dentinal tubules [1]. Prudent management must be performed to protect the surrounding tissue and vital adjacent structures [4]. However, freehand EMS still poses many challenges and risks. Anatomical obstacles, such as limited access, thick buccal cortical bone, and proximity to the maxillary sinus and neurovascular bundle, present challenges for clinicians, particularly novices. Damage to important anatomical structures can result in serious postoperative complications, including perforation of the maxillary sinus, pain, and neurosensory changes [5]. Moreover, the size of the osteotomy is directly associated with the speed of healing [6].

Recently, novel “dynamic navigation system” (DNS) technology has been introduced into endodontics to address these concerns [7]. The system is based on image transition and motion-tracking technology that allows real-time visualization of the relationship between the drill and surgical field and provides feedback to the operator. More importantly, the guided process can be performed such that the target site can be located accurately without damaging the adjacent anatomical structures. This technology has made it possible to avoid the unnecessary removal of tissue and decrease the risk of complications, thereby improving the prognosis. The applications of DNS in the field of endodontics include the creation of minimally invasive access cavities [8], negotiation of calcified root canals [9], removal of fiber posts [10], endodontic microsurgery [7], and intraosseous anesthesia [11].

The accuracy of DNS has been verified in the field of implant dentistry in a series of in vivo and in vitro studies. A recent meta-analysis of DNS in implant dentistry concluded that the average global platform, apical, and angular deviations were 1.02 mm, 1.33 mm, and 3.59°, respectively [12]. Accurate apex location is a prerequisite for minimal osteotomy and allows for easier root-end resection. However, evidence on the accuracy of DNS-aided EMS remains scarce and is limited to that obtained from in vitro studies and case reports. Therefore, the main aim of this in vivo study was to assess the accuracy of DNS for guided osteotomy and root-end resection during EMS. The data collected for accuracy evaluation were compared between the maxillary and mandibular arches, left and right sides, anterior and posterior teeth, and patients with a surgical depth greater than or less than 5 mm. Additionally, the success rate of DNS-guided EMS was also evaluated after at least a year's follow-up.