## 3 Results
**(b,c)** T\({}_{0}\) RCM of the opacity marked as “B,C” in **(a)**, revealed a partially preserved prismatic/interprismatic architecture,  
Figure 3: **(a)** Clinical presentation of a patchy white opacity with low severe hypoplasia of the vestibular one/half of the upper left central incisor in an 11-year-old male. **(b,c)** At T\({}_{0}\), RCM revealed disturbances in enamel arrangement shown as hyporefractive dark areas with lack of the normal crystalline enamel architecture (white arrows) alternated with partially preserved prismatic/interprismatic architecture (white square) or hyperrefractive organic matrix accumulation (dotted circle) within the whole imaged layers. **(d–f)** At T\({}_{2}\), the areas previously dark and low refractive, appeared fulfilled by bright refractive material scattered along the entire field of view and within the whole visible layers: 10 \(\upmu\)m **(d)**, 150 \(\upmu\)m **(e)** and 300 \(\upmu\)m **(f)**. Scale bars: 100 \(\upmu\)m.  
brighter than usual due to the higher organic/inorganic compounds ratio (asterisks) alternated with irregular areas in which the prismatic/interprismatic architecture lacks (dotted areas) at 10 \(\upmu\)m (**b**) and 300 \(\upmu\)m (**c**), respectively, from the surface, corresponding to severe lack of enamel. (**d**) When the enamel is constitutionally absent, as in \"D\" marked in (**a**), the T\({}_{0}\) RCM revealed some roundish holes, corresponding to dentinal tubules. (**e**) At T\({}_{2}\), the boundaries of the yellow/brown opacity of the upper right central incisor turned into a white/cream less severe defect, and the opacity of the upper left central incisor was strongly reduced (dotted black circle), and disappeared in some linear areas (black arrow). (**f,g**) T\({}_{2}\) RCM of the \"D\" area showed a persistent lack of prismatic/interprismatic architecture, but also the improvement in bright/dark contrast, due to the organic compounds fulfilling the interprismatic areas instead of the mineral inorganic part, most strongly visible at the periphery (white arrows) (**f**) and still with deficiencies in some areas of the center (**g**). (**h**) T\({}_{2}\) RCM of \"B,C\" revealed a more homogeneous enamel prisms arrangement. Scale bars: 100 \(\upmu\)m.  
With regard to the clinical responsiveness to treatment, ED \"disappearance\" was found in 7 teeth (in 6 linear and 1 patchy opacities); ED \"reduction\" was reported in 18 teeth (in 2 linear, 10 patchy and 5 diffuse opacities and in 1 low-medium grade hypoplasia); ED \"invariability\" was found in 13 teeth (in 5 patchy and 5 diffuse opacities, in 1 low-medium grade hypoplasia and in 2 severe hypoplasia); no ED \"worsening\" was reported. Before the CPP-ACP treatment (T\({}_{0}\)), RCM highlighted microscopic differences among the various degrees of ED severity, similarly to what found in our previous studies on in vivo RCM features of healthy enamel [35], the in vivo RCM differences between deciduous and permanent enamel [36] and the main in vivo RCM findings in EDs, both in permanent and deciduous teeth [37]. On RCM imaging, the 34 opacities without severe structural macroscopic defects (Figures 1 and 2), showed a fairly preserved enamel architecture, identifiable at the boundaries of the lesion and along the whole visible layers, 300 \(\upmu\)m beneath the surface (Figure 1b,c and Figure 2b,c), while, at the center of the defect, the enamel pattern was replaced by scattered deposits of bright organic substance (Figure 1d,e; Figure 2d). The T\({}_{0}\) RCM pictures of the 2 teeth with low-medium degree of hypoplasia revealed disturbances in enamel arrangement (Figure 3), only occasionally resembling the classical enamel architecture and mainly shown as hyporefractive dark areas with lack of the normal crystalline enamel architecture (Figure 3b) or as hyperrefractive organic matrix accumulation within the whole imaged layers (Figure 3c).