## 3 Discussion
It has to be noted that this method allows control over numerous factors, including the protection of adjacent anatomical structures (e.g., teeth, mandibular canal, and mental nerve) and the provision of sufficient width for obtaining access to the teeth and pathologies, as well as the minimal bulk and high stability of the guide [29]. With regard to the last concept, the precise fitting of the template to the cortical bone is crucial to guide the movement of the cutting tool as preoperatively planned. The firmness of the guide can be achieved with a dental [44] or bone support, or both [31; 45]. As previously recommended for computer-guided bone harvesting from the posterior mandible using the same workflow as in the present investigation [33], it seems preferable to produce a template with an extra reference point on the closest tooth rather than a complete bone-borne cutting guide. Indeed, CBCT images taken before and immediately after surgery revealed an average root-mean-square discrepancy of 0.52 mm (0.30-0.97), with enhanced values recorded in the presence of an additional reference point on the nearest tooth, independently of whether it was designed considering preoperative CBCT or intraoral scan data [33]. Furthermore, the highest displacement discrepancies were registered in the mesial and distal osteectomies owing to the inaccurate placement of the template in the antero-posterior direction [33]. The importance of maintaining a safe distance from the surrounding anatomical structures and tooth roots was also emphasised by [PERSON] and [PERSON] in their work assessing the accuracy of computer-guided piezocision [42]. The authors concluded that a safety distance of at least 1.5 mm should be considered during the planning phase. In line with the present work, encouraging results of the computer-guided bone lid technique using 3D printed guides and piezosurgery were also reported by [PERSON] et al. [29]. Clinical and radiological findings at 6 months from the extraction of six maxillary supernumerary teeth and four mandibular impacted teeth demonstrated good bone formation in the extraction area, which was found to be completely filled with new bone. The bone profile recovery and alveolar ridge height at the surgical site were essentially similar to the preoperative situation; moreover, the bone window was fully reintegrated, osteotomy lines were not visible, and no soft tissue introflection could be detected. For the extraction of the mesiodens in the premaxilla in eight patients (four per group), [PERSON] et al. utilised piezosurgery to create a bone lid pedicled on the superior mucoperiosteal attachment either with free-hand or computer-guided surgery [31]. All patients recovered uneventfully and all teeth were extracted successfully, without any alteration of anatomic landmark position (anterior nasal spine position and nasolabial angle value). However, similar to what has been reported in implantology [51; 52], the use of static guides was found to be timesaving in comparison to free-hand bone lid preparation [31]. The reduced duration of surgery, when positively correlated to lower scores of patients' pain and discomfort, may represent a positive factor [53]. The higher efficiency of the combined use of piezosurgery and 3D printed surgical guides over standard surgery has also been documented for genioplasty, with mean surgical times of 47 and 53 min, respectively [47]. Although the introduction of the bone lid technique for endodontic surgery dates back to the 1980s [13], only recently has it been ameliorated by the use of surgical guides and piezoelectric surgery [54]. A thorough description of the advantages of computer-generated precision endodontic surgical stents (PRESSs) is presented in two works from the same group [34; 49]. According to the authors, the main indication consists of the treatment of endodontic lesions in the posterior regions, especially in the mandible, in the presence of large buccal bone thickness and proximity to the inferior alveolar nerve.