## 3 Discussion  
The extraction of deeply impacted mandibular third molars generally requires major ostectomies that may lead to the weakening of the mandible and to compromised healing of the alveolar bone distal to the second molar. An extensive Cochrane Library review on surgical techniques for the removal of mandibular wisdom teeth stated that firm recommendations were not available [11]. Modern alveolar surgery should be accurate and minimally invasive [29]. In this regard, the exposure of impacted teeth and possibly associated lesions through a bone lid performed with piezoelectric surgery has been justified as a technique capable of giving excellent visibility, minimal bone loss, precise cutting ability, and enabling the protection of the inferior alveolar nerve [18]. The main shortcoming of this technique is the risk of sequestration of the bony lid. However, the frequency of this complication is low. In a recent scoping review including 752 bone lids [17], bone lid resorption, necrosis, and removal were rather uncommon and occurred in only 20 cases. The further evolution of this technique is the application of computer-guided surgery: the osteotomy is designed precisely thanks to cutting guides. The technique may appear more complex than a standard extraction with osteotomy; however, the results in the  
Figure 5: Case 1. Postoperative radiological follow-up at 1 year. (**a**) Detail of the panoramic radiograph; (**b**) details of the CT scan distally to tooth 37. Figure 6: Case 2. Radiological follow-up. (**a**) Immediate postoperative control: the alignment of the osteotomy with the preoperative planning is visible; (**b**) 1-year follow-up. literature depict excellent bone volume recovery, enabling implant rehabilitations without the need for regenerative procedures [24; 25]. Computer-guided osteectomies have also been proposed for bone harvesting from various intraoral and extraoral districts with excellent results in terms of harvesting precision in relation to the planning of the desired volume of the graft and duration of the procedure [33; 35; 36; 37; 38]. Piezoelectric surgery appears advantageous over other instruments used for osteectomies. A broad range of inserts are currently available, including saw-shaped inserts presenting a saw thickness below 0.3 mm. Piezonsurgery has been associated with reduced bone trauma [39], increased visibility of the surgical field due to the cavitation effect, and ease and safety of use in areas otherwise difficult to access [40]. Further advantages derive from its combined use with digital technologies. In recent years, computer-guided surgery using piezoelectric devices has been proposed for a variety of applications, including minor [28; 41; 42; 43; 44] and major orthonathic surgery [45; 46; 47], extractions [29; 31], endodontic surgery [34; 48; 49], and mandibular lesion resection [26; 50], as well as cranial vault resection and reconstruction [35]. With regard to the material of the guides, several materials have been employed so far, including titanium [45], polyethylene perephthalate glycol (aka PETG) [47], polymethyl methacrylate (PMMA) [28], and polyamide [33; 46], as in the current study. By using the approach reported in the present article, case-specific stereolithographic surgical guides can be designed during the preoperative surgical planning on CBCT 3D images using dedicated software, and then manufactured through a CAM process. The position, angulation, direction, and depth of the osteotomy can be controlled during the planning phase, optimising the bone lid design [33]. The digital planning procedure allows the creation and selection of different designs. The footprint of the template, in relation to the anatomical structures to be met, primarily guides the choice of the design. With this technical case report, we have intentionally presented two different surgical guide designs: case 1 includes a guide in the shape of a window, whereas in case 2, the guide consisted of a solid piece.