B

Enamel is not fully mineralised when a tooth first erupts; “posteruptive maturation” continues for roughly the first couple of years. Hardness and mineral density rise markedly during the 2- to 3-year window after eruption, after which changes are far slower (Cardoso et al., 2009, PMID 20016180; Robinson 2014, PMID 25339913). Therefore, an additional period of about 2 years is generally required for complete enamel calcification.