## 7 What Kind of Information Can We Obtain from In Vivo and Ex Vivo Studies of Osteotomy?
In a rotatory bur (drilling bur), it was found by histopathology that the heat generation is mainly dependent on rotational speed: at high rotational speed (3000 r/min), there is a severe thermal osteonecrosis [15]. These results contradict previous findings in the 1960s and 1970s, when ultraspeed or high rotational speed were recommended for avoiding thermal osteonecrosis [78; 79; 80]. Modulating the irrigation temperature can be an effective strategy in reducing heat during osteotomy with a drilling bur. Studies on endosseous dental implant site demonstrated that the use of precooled irrigation at 10 \({}^{\circ}\)C entails a significant reduction in peak temperature compared with what was achieved when irrigating at room temperature [103]. Bone removal approximating the inferior alveolar nerve canal was investigated through an ex vivo experimental study conducted by [PERSON] [107]. Compared to a drill, this ex vivo study confirmed that piezoelectric bone removal approximating the inferior alveolar canal resulted in higher temperature-increasing effects on the surface of the inferior alveolar nerve [107]. The author eventually suggested combined bone removal (i.e., tungsten carbide pre-drilling completed with piezoelectric tip) with 7 \({}^{\circ}\)C pre-cooled irrigation to limit the intracranial temperature increase [107]. During endosseous dental implant site preparation, bone overheating using a piezosurgery was measured, resulting in two times more with respect to a conventional drill [110]. Augmented bone overheating with piezosurgical devices compared to a bur drill was an unexpected finding. Other authors questioned some of the methods that led to these results, such as [PERSON] et al. [111], who discussed the previous ex vivo investigation of [PERSON] et al [110]. For example, ultrasonic tip choice in the experiment can lead to abnormal heat generation if the use is improper for the purpose (side-cutting insert instead of dental implant site preparation insert). [PERSON] et al. (2018) also described that applied pressure load on the handpiece was excessive for that device and this could induce a higher temperature rise [111]. Pressure load should be chosen according to the specific characteristics of the tip and device (piezosurgical, rotatory, and oscillating or reciprocating saw). Moreover, as in the paper of [PERSON] et al [126], the laboratory supported arm for the handpiece should reproduce the movement of the hand in the operative theater (sliding movement is not comparable to rotating movement). Non-overlapping conditions between experimental and clinical setting could lead to distorted interpretation of results from studies conducted in laboratory settings [111]. Previous findings of [PERSON] [126] and [PERSON] [107] about bone overheating with piezosurgical devices were questioned by [PERSON] [114] in a further ex vivo model. He found that the cortical bone temperature during piezosurgical osteotomy was lower than during rotational drilling. Moreover, according to this study, the impact of the drilling factors on bone temperature was in the order of drill diameter, rotational speed, feed speed and the frequency and amplitude of the piezosurgical vibration [114]. Erbium-doped yttrium aluminum garnet (Er:YAG) laser was applied as osteetome in maxilla-facial surgery in 2007 [10]. A single study in vivo compared a Er:YAG laser with the piezosurgical technique, without histomorphometric evaluation but with bone volume measurement by laser triangulation profilometry [104]; considering the limit of investigation methods, the Er:YAG laser showed faster bone healing with respect to the piezosurgical sample. [PERSON] et al. (2018) [116] carried out an in vivo study in rats exposed to inhalation of cigarette smoke, comparing a Er,Cr:YSGG laser (erbium, chromium: yttrium, scandium, gallium and garnet) and trephine drilling. The Er,Cr:YSGG-S group revealed higher bone formation with statistical significance compared to the trephine drilling group.