## 5 Which Animal Model Is Suitable for Bone Investigation of Osteotomic Effects?
The aspects to take into consideration are:  
* The type and the aim of the study
* The osteotomy device used. The aim of the study has a central role in the correct choice of animal model: when the purpose is to study the osteointegration of endosseous dental implants, its size has to comply with animal and \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Animal**} & **Bone Microscopic and** & **Bone Composition** & **Animal Management** & **Best Type of Study** \\  & **Macroscopic Features** & **and Remodeling** & **Animal Management** & **Best Type of Study** \\ \hline \multirow{4}{*}{Dog} & Similar cancellous & \multirow{2}{*}{Variability of trabecular bone remodeling depending on site, age and species.} & \multirow{2}{*}{Docile, easy handling.} & \multirow{2}{*}{Dental implants and peri-implantitis.} \\  & & & & \\ \cline{1-1} \cline{3-5}  & & & & \\ \cline{1-1} \cline{3-5}  & & & & \\ \hline Non-human & \multirow{2}{*}{Close to humans.} & Comparable to humans. & Difficult to handle and highly trained staff are needed. & Bone implant. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._ \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Advantages**} & **Disadvantages** \\ \hline \multirow{4}{*}{**Ex vivo**} & Low costs & \multirow{4}{*}{Only hypotheses regarding possible clinical correlations Less realistic setting} \\  & No need for ethical approval & & \\ \cline{1-1} \cline{3-5}  & Amount of information on bone damage & & \\ \cline{1-1} \cline{3-5}  & Reproducible conditions & & \\ \cline{1-1} \cline{3-5}  & Large numbers & & \\ \hline
**In vivo and** & Evaluation of bone damage in an in vivo scenario & \multirow{2}{*}{Impossible to perform bone healing evaluations Intermediate costs} \\
**immediate** & Possibility to obtain baseline results to compare with delayed sacrifice in in vivo results & & \\ \hline \multirow{4}{*}{**In vivo and** **delayed sacrifice**} & Bone healing evaluation, with the possibility to obtain both static and dynamic evaluation of osteotomic gap & \multirow{2}{*}{High costs Small numbers Small animal to respect animal testing hierarchy and ethics on animals} \\  & Wide range of parameters to be analyzed & & \\ \cline{1-1} \cline{3-5}  & Closer to clinical setting in humans & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Advantages and disadvantages according to different times of euthanasia in animal models. bone-specific principles [59]. The same rule must be applied to the choice of osteotomy device: a large device must be used on adequately sized bones. Together with these general principles, the choice of a proper animal model has to be influenced by other animal-specific criteria for bone:  
* The specific bone site and its characteristics (femur, tibia, calvaria, mandible, vertebra)
* Bone macroscopic and microscopic features, including size and biomechanical properties
* Bone composition and density
* Bone turnover rates
* Specific conditions for bone healing, such as the critical size defect
* Costs and aspects regarding the management of the animal (including acquisition costs, housing costs and the need for specifically trained staff). In particular, the economical and managerial aspects of animal experimentation have to be underlined. If a small animal model is possible, a larger animal model is to be considered unjustifiable according to Ethics in Animal Research Guidelines: (i) small animals before larger ones have to be selected to respect the animal testing hierarchy (European Communities Council Directive of 23 September 2010 [2010/63/EU]; (ii) compliance must be ensured with the Italian laws for the protection of animals used for scientific purposes (Decree Law No 61 of 4 March 2014) [70]. A particular animal can be highly suitable for a study because of its bone features, but there might not be a funding, logistic or training basis to proceed to the experimentation.