“The Thylstrup–Fejerskov (TF) index classifies dental fluorosis in terms of its absence (TF 0) through to the presence of opaque lesions (TF 3), which blend to overtake the entire surface of the enamel, thereby producing the appearance of white chalk (TF 4). In more advanced stages, there is a gradual loss of enamel and anatomical dental deformities (TF 5–9).”
SOURCE: Silva de Castilho L, et al. (2009). Perceptions of adolescents and young people regarding endemic dental fluorosis in a rural area of Brazil: Psychosocial suffering. Health and Social Care in the Community Vol. 17, p. 557.