## 4 Discussion  
Bone healing after surgery can be strongly influenced by the surface characteristics of the cut bone; in fact, the presence of debris and closed vascular canals can delay the process itself. Therefore, for skeletal tissue regeneration, it is important to verify which surgical device provides the best surface characteristics to optimize bone recovery. Different morphological aspects will be discussed, from the presence of debris, which makes the surface more or less contaminated and fills any cavities capable of allowing vascularization, to the appearance of microfractures that might facilitate rather than hinder regeneration. As mentioned before, the morphological evaluation of the different effects of osteotomy devices is crucial for ex vivo specimens due to their reproducibility in real clinical settings. This study has been designed in order to maximize the advantage of ex vivo evaluations (that have been performed on fresh human samples collected from the surgical table) to nullify the adverse effects for the patient population (bone samples have been collected from discarded fibula segments) and to allow the implementation and the strictness of laboratory experiments (all the osteotomy procedures have been performed by the same operator, in a laboratory setting, as well as the morphological analysis). The observations under ESEM of the cutting surfaces of human fibulae using three different devices showed that both piezoelectric devices (PM and PP) make regular, smooth, and clean surfaces (Figure 4) compared to the RS, whose cutting surfaces appear irregular and dirty (Figures 2a and 3a). In particular, many scratches, depressions, and reliefs, along with many bone debris/chips, characterize the RS cutting surfaces. These findings are in  
Figure 8: ESEM images of two bone samples cut with the PM (**a**) and PP (**b**). (**c,d**) Enlargements of the squared areas in (**a,b**) show abundant and well-identifiable microcracks (arrows). line with the observations of different authors. [PERSON] and coworkers [27] showed that more smooth shear margins were present in rat bones osteotomized with piezoelectric devices than those obtained with high-speed rotary devices. [PERSON] and coworkers [28] showed a significant accumulation of bone chips on the surfaces of osteectomies of bovine ribs performed with the Lindemann bur, compared to those cut with the sonic and ultrasonic instruments, which showed more precise and clean-cutting surfaces, facilitating their alignment. Furthermore, the same authors point out that the Lindemann bur is the most irregular and traumatic of the three instruments tested, most likely due to the high kinetic energy used by the instrument and the need to apply more pressure during cutting. According to many authors, macro vibrations of saws and burs at high speed can cause trauma and damage to bone, producing heat and debris that can interfere with the healing response [29; 30; 31; 32; 33; 34]. Another interesting finding to discuss is the presence of a'smear layer' (i.e., bone debris) that fills the Haversian canals mainly in RS cutting surfaces (Figure 2b), while in both piezoelectrical devices, the vascular canals are often open and free from debris (Figure 7) since these instruments do not produce as much debris as the traditional RS. As reported by [PERSON] and collaborators [28], in bone surfaces cut with the Lindemann bur, most of the vascular canals of the cortical bone are completely or partially filled with a smear layer. In fact, according to the authors, two types of debris can be observed on bone surfaces, i.e., detached debris, which produces a smear layer, and debris still attached to the bone surface. Other authors have also shown that bone debris, resulting from osteotomy and accumulated in the bony vascular spaces, is a common result after conventional osteotomies with drills and saws, and, consequently, blood perfusion may be limited by this mechanical obstacle [28; 35; 36; 37].