Up to approximately what age does systemically ingested fluoride continue to benefit the developing permanent dentition (excluding third molars)?

Correct answer: C. Age 8

• A. By 16 all relevant crowns are long since formed; only topical benefit remains.
• B. By age 3 the crowns of most permanent teeth are still forming — benefit continues well beyond this.
• C. Correct. Crown mineralisation of the permanent dentition (second molars aside) is essentially complete by around AGE 8, so systemic fluoride can only be incorporated into developing enamel up to roughly that age. This is also why the risk window for dental FLUOROSIS effectively closes at about 8 — after which excess systemic fluoride can no longer affect the crowns of the anterior teeth that matter cosmetically.
• D. Age 6 corresponds to first permanent molar eruption, but crown formation of other permanent teeth continues.