## 3 Vitamin D and CKD in Pediatric Patients
### Alteration of Enamel Mineralization
Finally, it is worth remembering that another enamel anomaly can be observed in nephropathic patients as the enamel-renal syndrome (MacGibbon syndrome). This syndrome is a rare genetic disorder transmitted through an autosomal recessive mode and it is characterized by hypoplastic amelogenesis imperfeta, affecting both deciduous and permanent teeth, and causes delayed tooth eruption for teeth impaction, gingival fibromatosisis, multiple calcifications in pulp and gingiva, hyperplastic dental follicles and bilateral nephrocalcinosis [85; 86; 87]. Diagnosis and Treatment of DDEs  
It is appropriate to make a differential diagnosis in CKD patients between intrinsic enamel discolorations (such as DDEs) and extrinsic enamel discolorations. In fact, the latter are very frequent in CKD patients with anemia because pharmacological iron supplementation can, in some formulations, deposit brownish-black spots on the enamel surface [88; 89]. In a recent study, intrinsic discoloration (22%) and extrinsic discoloration (40%) were observed in hemodialyzed children with a statistically significant difference compared to the control group (healthy subjects) [84]. From an operational point of view, extrinsic stains can be removed through the utilization of abrasive pastes during professional oral hygiene follow-up, while intrinsic stains cannot be removed except through conservative interventions. Moreover, DDEs can determine an increase in the risk of dental caries [90; 91], dental erosions, tooth sensitivity and altered occlusal functions [92], and can compromise dental esthetics, especially in those clinical cases in which the anterior dental elements are involved [61; 62]. Enamel opacities can cause esthetic dissatisfaction and can impact social judgments [93]. The aim of the DDEs treatment is to resolve the symptoms and to provide esthetic and functional restoration. The DDEs conservative interventions are divided in invasive treatments (traditional restorative treatments, crowns/veneers), that determine excessive tooth cutting and minimal invasive treatments, which include remineralizing agents, microabrasion-remineralization (Mab-Re) and resin infiltration (RI) techniques [94]. The efficacy of these new treatments for hypomineralised and hypoplastic lesions was analyzed in recent clinical studies [95; 96]. The Mab-Re combines microabrasion and remineralizing products. The remineralizing agents release ions that obliterate the microtags generated by the microabrasion. Instead, in the RI technique, the photopolymerizable resin with lower viscosity fills the intracrystalline spaces in hypoplastic enamel lesions [97], forming an enamel hybrid layer [98]. The infiltration of the resin increases the refractive index of the hypomineralized enamel, reaching values similar to the healthy enamel. In this way, the DDEs are effectively masked after treatment with resin infiltration [98], because the infiltrated enamel looks like the healthy adjacent enamel. According to a randomized clinical trial, the RI technique shows improvements (like lightness and color changes) already after a single session, whereas the Mab-Re technique requires multiple sittings to achieve desirable results [97]. Currently, the RI technique is a valid alternative to traditional techniques and can also lead to a significant improvement in dentinal hypersensitivity and in the mechanical characteristics of the treated enamel [98; 99]. The limitation of this technique is the lack of predictability in the esthetic results compared to the deep enamel opacities, which make the defect not completely permeable to the resin. Further studies are needed to perform a preoperative assessment of the DDEs depth, which is crucial for the choice of treatment when planning [99].