## 4 Discussion
In relation to the tubular diameter in healthy patients, our results indicate that the largest pulpal diameter is found in the middle dentin, gradually decreasing up to the dental-enamel junction (DEJ), on the one hand, and when approaching the pulpal tissue, on the other hand. Our results contradict previous studies [31, 35, 36, 38], since it is described that the largest tubular diameter is found in the region of dentin closest to the pulp and gradually decreases when moving away from it. The variations related to the density and tubular diameter found with other authors may be due to the non-standardization of the places used for the measurement, the non-coincidence of the sample preparation methodology, or the extrapolation of the results measured at different magnifications with the SEM. The data obtained seem to indicate that in cross sections of teeth from subjects with OI, there is a higher mean count of dental tubules in the outermost dentin, and a lower mean count in the innermost dentin (pulp) than in the teeth of healthy subjects. Analyzing the OI type, a lower mean tubular count was found in the more severe phenotype of the systemic disease (OI-III) than in the milder one (OI-I). These differences are also significant with respect to the controls for the OI-I group in the outermost dentin, and for the OI-III group in the deep dentin. Even though various authors describe a decrease in tubular density in patients with OI [14, 19, 23, 29, 30], none of the studies treat this variable in a numerical analytical way. In this research, no significant differences were found between the diameter of the controls and the teeth of OI subjects in total dentin; however, tubules with a significantly larger diameter are found in the external dentin of teeth of OI patients (1.58 um) compared to healthy teeth (0.59 um). Analyzing the OI types, a significantly higher tubular diameter was found in the external and deep dentin of the OI-I group compared to the control and OI-III group, respectively. Regarding the previous literature regarding tubular diameter, most authors agree that it is decreased in patients with OI [23, 29] even less than 1 um [19]; however, there is no consensus with the presence of other structures. [PERSON] et al. [19] also found elongated tubules with a tortuous and irregular trajectory, and other authorsdescribed the presence of structures like canals with a wide diameter (5-25 \(\upmu\)m) [14], also detected with TEM [28] and with confocal laser scanning microscopy (CLSM) [11]. In the cross-sectional pattern, significant differences were detected in the behavior of both the diameter and the tubular density between the control sample and the OI teeth. In both cases, the difference seems to respond to an irregular pattern, far from normal, in which a model of severity associated with the severity of the systemic disease cannot be established [PERSON] et al. [19] hypothesizes that the reduction in tubular density may be because the dentinal tubules do not completely penetrate the thickness of the dentin, causing an excess of intertubular dentin. Indeed, the heterogeneity observed in the pattern of tubular diameter and density at different levels of dentin depth seems to be associated with abnormalities in intertubular dentin secretion and the direction and penetration of abnormal dental tubules. A semi-quantitative elemental analysis (in the absence of standard standards) was carried out using EDS of the amount of Calcium and Phosphorus in control teeth, measured in counts per second (cps). It was found that there was an average of 4.72 \(\pm\) 3.88 cps of Calcium and 6.11 \(\pm\) 4.65 cps of Phosphorus: the amount of Phosphorus exceeding that of Calcium, contradicting previous studies in both temporary and permanent dentition [39; 40; 41].