## 7 What Kind of Information Can We Obtain from In Vivo and Ex Vivo Studies of Osteotomy?
[86] applied an in vivo model of dog alveolar ridges, demonstrating an improved bone healing process in the piezosurgically treated group. The index of viability of bone cells after piezosurgery was studied histologically by numerous authors in bone grafting procedures for dental purposes [124; 125]. Histomorphometric and molecular analysis was evaluated together by [PERSON] et al. [87]; the authors established that piezosurgery may accelerate the earlier phases of the dental implant osteointegration when compared with rotational drilling. Bone surfaces were examined by [PERSON] [88] with three microscopic techniques (light microscopy, environmental scanning electron microscope--ESEM, confocal laser scanning microscope--CLSM) after using different procedures of osteotomy (reciprocate micro-saw, Lindemann bur, ultrasonic osteetome). ESEM and CLSM entail an appraisal of unmodified bony specimens, being non-destructive examination techniques. In this histological investigation, ultrasonic osteetome activity was not related to osteonecrosis of the trabecular bone. CLSM permits a quantitative evaluation of bone surface roughness [88]. [PERSON] and co-workers [91] in an ex vivo model studied in depth the thermal damage to bone as a combined result of the temperature and the duration of elevated temperature: the relation of maximum bone temperature and the period of that increased temperature over the critical value was described. Drilling with carbide spiral drills (2.5-4.5 mm) for dental implantology, the bone temperature persisted around 50 \({}^{\circ}\)C for 50 s in 95% of results, not adequate for avoiding thermal osteonecrosis during drilling (\(\leq\)47 \({}^{\circ}\)C for one minute, as demonstrated by [PERSON] et al.) [120]. Comparing different ex vivo inserts for piezosurgical osteetome, it was found that cortical bone thickness had surprisingly no influence on intraosseous temperature generation, which remained, however, below the threshold of 47.8 \({}^{\circ}\)C for 1 min, without irreversible thermal damage in the bone [94]. These data were statistically supported and in contrast to the previous study of [PERSON], which was conducted with traditional rotary osteotomes [81]. Considering the investigation methods, these results are difficult to compare. The author concluded that in vivo measurements need to be carried out to confirm the data. While cortical bone thickness appeared a secondary factor following piezosurgery, the structure of the bone seemed to be an important factor in the cut characteristics: higher cut lengths and widths were present in the spongeous bone compared to the cortical bone [95]. [PERSON] et al. [96] conducted an in vivo study on rat tibia (histological, histomorphometric, immunohistochemical and molecular analysis); comparative appraisal of bone recovery after osteotomic lines performed by rotating drill or piezosurgery did not demonstrate significant differences between the two animal groups. An in vivo histomorphometric study by [PERSON] et al. [97] revealed no statistically significant differences in comparing bone healing after osteotomy performed with piezosurgery versus oscillatory saws; increased bone remodeling activity in early phases was observed for the piezoelectric surgery group. Cortico/cancellous samples (ex vivo) are a simulation of in vivo conditions frequently used by scholars, but they are affected by greater variability of results. In an ex vivo bone model with a piezosurgical device, three main factors were finally identified among the others for having a great influence on the heat production: working load, working movement management and bone features [99]. [PERSON] et al. in 2015 found that ultrasonic osteotomies cause significantly lower heat compared to rotary bur osteotomies [102]. However, both these scholars concluded that (in vivo) animal studies were essential for understanding how bone healing occurred after ultrasonic osteotomies and how blood flow and biological factors fit together with ex vivo findings [99; 102].