## 4 Discussion  
In recent decades, many authors have sought to identify factors that minimize damage during implant site preparation [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. An appropriate procedure should procure a thin layer of necrotic bone subsequently replaced by vital bone tissue [25; 26; 27; 28]. All of the surgical factors that increase the thickness of the bone necrotic layer can negatively compromise implant osseointegration. Extension of the necrotic zone around the preparation site is considered proportional to the amount of heat generated during osteotomy, which can be related to different factors: (i) the operator (pressure, status, movement, speed, and duration of drilling); (ii) the manufacturer (design and sharpness of the drill and the irrigation system); (iii) the implant site (cortical thickness, bone density, and depth drilled); (iv) the patient's age; (v) the surgical method (drilling, ultrasonic, and condensation [1; 2; 3; 7; 8; 9]). The bone damage is related to the magnitude of the temperature elevation and the time the tissue is subjected to a damaging temperature, identified as 47 \({}^{\circ}\)C for 1 min [15; 16; 17; 18; 19; 20; 21; 22]. Heat generation, as evidenced by [PERSON] and [PERSON] [20], can also be influenced by the manufacturer's precision (sharpness of the cutting tool) [15] and by the surface deformation and roughness shown by the worn burs that cause a more significant and continuous temperature rise than new burs [16; 17]. Drill wear is another important factor in heat generation during bone drilling [1; 9]. It is an unavoidable and irreversible process, which increases friction in the cutting zone [12]. As well as a negative thermal impact, wear causes higher cutting forces and drill vibrations, which can result in cutting edge breakage or complete drill breakage in the flute or shank zone [12]. The literature data reports that, for thermal impact, ultrasonic tips are safe when properly used [37]. Ultrasonic vibrations provide a \"gentler action\" involving less local delivery of mechanical energy than rotating techniques [8; 37]. This study showed the capacity of UISP to better preserve the cortical and cancellous bone structure and vascularization in comparison with the conventional surgical drill technique. The SEM evaluation of this research evidenced that the use of surgical bone drills can be destructive, breaking off large fragments of trabeculae and weakening bone in the vicinity of the implant site, leaving bone fragments likely to occlude medullary spaces and the three-dimensional cortical bone vascular canal system. Bone vascular canal lesions may interfere with peri-implant bone nutrition and cortical bone damage may stimulate early osteoclastic activation [16]. In cancellous bone, the broken trabeculae  
Figure 6: SEM analysis of ultrasonic implant site preparation: (**a**) The spongious structure of the implant site reveals intact trabeculae and a reduction of fractures. (**b**) SEM micrograph magnification shows how the exposed spongious bone presented cleaned surfaces. can be removed by the drill and the cooling fluid, or will form the peri-implant bone structure [38]. Detached trabeculae stuffed in the surgical implant drill-bone interface may produce an intraoperative increase in the insertion torque levels, causing thermal bone damage; the presence of necrotic bone tissue in the bone-fixture interface may also cause macrophage osteoclastic activity, reducing the primary stability of the implant and delaying the osseointegration process. Cortical bone preparation with Piezosurgery(r) allows the preservation of the bone surface, considerably decreasing the presence of micro-fractures and a smear layer. The characteristic cleaned bone surface also avoids closure of bone vascular canals by the compression of bone debris between bone surfaces and the cutting device. In cancellous bone, Piezosurgery(r) assures a precise cutting of the trabeculae and a reduction of cracks weakening the bone structure and fragments compressed into the trabecular architecture.