Molar and Incisor Hypomineralization (MIH) is a qualitative developmental defect of the dental enamel with a multifactorial aetiology defined in 2001 as an "hypomineralization of systemic origin affecting one or more permanent molars, usually first permanent molars (FPMs) with or without the involvement of one or more affected permanent incisors". Due to its porous structure with an altered prism organization and an increased content of proteins, the hypomineralized enamel has reduced mechanical properties and a lower refractive index in comparison to the sound enamel. MIH is associated to a large number of objective and subjective problems as an altered aesthetics, an increased risk of plaque accumulation, caries and/or post-eruptive breakdown, reduced retention rates of adhesive materials, hypersensitivity and difficulty in anesthetizing the affected teeth that make its management a challenging condition. MIH is a very widespread pathology with a worldwide prevalence ranging from 2.8 to 44% and a global average prevalence of 13.1% with significant geographical differences. In 2015, the number of global prevalent cases was estimated at 878 million people with a percentage of needing-care cases of 27.4% (in mean 240 million prevalent cases). In Europe, MIH prevalence rates between 3.6 to 25%. Regarding Italy, a limited number of prevalence studies are available. Recently, literature reports that the presence of MIH-like lesions in primary dentition, especially on second primary molars, may be a predictive factor for developing MIH in permanent dentition. However, the absence of this defect called Hypomineralized Second Primary Molars (HSPM) does not rule out MIH development. The early diagnosis of HSPM is very useful to early diagnose MIH and reduce its care burden. The reported HSPM global prevalence rate ranges from 0 to 21.8% with a global average about 7.88%. MIH and HSPM are both very widespread pathologies affecting an increasing number of children worldwide and represent a significant problem in pediatric dentistry. The aim of this study is to estimate the prevalence of MIH in Italian (Trieste), Spanish (Huesca, Zaragoza) and Turkish (Istanbul) children. The hypothesis is that the estimated prevalence of MIH may be in line with that reported in literature and that the presence of HSPM in primary dentition may be associated with MIH development in permanent dentition.

Inclusion Criteria:

• Age: 6-16 years;
• Signature of the informed consent to the study by patients' parents or by their legal guardians

Exclusion Criteria:

• Fluorosis, white spots, amelogenesis imperfecta, hypoplasia or other dental enamel defects in differential diagnosis with MIH and HSPM;
• Patients not sufficiently cooperative;
• Children with orthodontic devices hiding the teeth to consider

Subjects will be selected among patients attending the involved Dental Clinics according to the following criteria