## 4 Discussion
These data indicate that the amount of calcium and phosphorus increases from the UAD to the deep dentin region, followed by a decrease in the dentin closest to the pulp, coinciding with being the last dentin secreted and, therefore, the lower mineralization of the same can be explained, since the mechanisms of secretion and mineralization of circumpulal dentin are continuous and constant throughout the life of the tooth. In this study, the amount of Calcium and Phosphorus was analyzed, and it was determined that there are no differences in the amount of Calcium between teeth with OI and healthy ones. However, it was found that in all regions except pulpal dentin, the amount of Phosphorus was significantly lower than that found in the same locations of healthy teeth; we also found a mean amount of Phosphorus that was significantly lower than the control group. Regarding the type of OI, it has been established that there is a lower amount of Phosphorus in the teeth with OI-IV than in the control teeth in the outer dentin, with no significant differences in the other study points or with the other OI types. The behavior of the amount of Calcium and Phosphorus in the four study points was studied, and it was determined that there was an increase in Calcium and Phosphorus from the external dentin to the deep one, which would later descend again, exhibiting the same behavior as the control group in both cases. Only the research of [PERSON] et al. [11] was found in relation to studying a primary tooth with CLSM; in their work, they stated that the dentin of OI subjects presents less mineralization, in accordance with our results, and they explain this fact by establishing that the increase in type III collagen could be an obstacle to mineralization. On the other hand, a recent study carried out with Raman spectroscopy in deciduous teeth with mild forms of OI without clinical signs of DGI-I showed an increase in the hardness of OI dentin associated with an increase in mineral content compared to healthy patients [42]. This research has important strengths, such as the presentation of a complete microanalysis of the dentin of deciduous teeth from subjects with a rare disease, OI. The results that demonstrate the differences in the pattern and dentinal mineralization of these teeth allow us to improve our knowledge of the dental affectation of the OI, facilitating a better dental therapeutic approach. The arrangement of 25 deciduous teeth of subjects with OI with a control group is exceptional; this was made possible thanks to the collaborative agreement between the Complutense University of Madrid and AHUCE, and the involvement of the families of children with OI. This research also has limitations, such as the small size of the study sample associated with the rare disease condition of OI. In addition, in recent decades, it has been proposed to move away from the clinical classification of systemic disease, emphasizing genetic mutations. Lastly, the children were not classified according to their pharmacological treatment (beginning and dose), which implies a bias, since it has not been possible to control its action on the dentinal tissue, or the pharmacological deposit of the drug. To date, the effect of systemic bisphosphonates on the process of dental eruption and formation is not clear [43], although alterations in the pathophysiology associated with dentin are described as a rapid deposit of secondary dentin that causes pulpal obliteration in patients with long-term treatments with bisphosphonates [44]. Despite the promising results, adequately designed clinical trials are needed to distinguish the adverse effects of drugs from the dental effects of OI. Another important limitation is that due to the S-shaped trajectory that the dentinal tubules follow through the dentin, not all points could be analyzed perpendicular to its axis, which made it difficult to measure the diameter and tubular density.