Epidemiology
In a study of 3272 6-year-old children in Oviedo, Spain, the prevalence of black stain was found to be 3.1% [PMID:23414217].
The study did not find a significant difference in the prevalence of black stain between non-emigrant (3058 children) and immigrant (214 children) children in Spain [PMID:23414217].
References
1 Garcia Martin JM, Gonzalez Garcia M, Seoane Leston J, Llorente Pendas S, Diaz Martin JJ, Garcia-Pola MJ. Prevalence of black stain and associated risk factors in preschool Spanish children. Pediatrics international : official journal of the Japan Pediatric Society 2013. link
1 papers cited of 10 indexed.