At what age range are the permanent central incisors most susceptible to tetracycline staining?

Tetracycline binds to calcium ions in forming hydroxyapatite crystals during the calcification of developing teeth. The permanent maxillary central incisors begin crown calcification at approximately 3 months after birth and complete enamel formation around 4–5 years of age. However, all permanent teeth are susceptible to tetracycline staining during their calcification period: from approximately 3 months of age through 7–8 years (when all permanent teeth except third molars have completed crown mineralization). The American Academy of Pediatrics (AAP) advises against tetracycline use in children under 8 years of age for this reason. The resulting staining is intrinsic and irreversible.