The eruption date of a deciduous lower first molar is:

• A. 12 months
• B. 16 months
• C. 20 months
• D. 8 months

Answer: (B)

Tooth eruption follows a general timetable where molars appear later than incisors. The deciduous lower first molar typically emerges after the incisors and in the middle of the second year. The most representative average is about sixteen months, with a normal range roughly from fourteen to eighteen months. This reflects the common pattern in which the lower jaw tends to erupt molars slightly earlier than the upper jaw for this tooth.

Eight months is too early for a molar to erupt; twelve months is earlier than average for this particular tooth; twenty months is later than usual for the first deciduous molar (often associated with second molars). So sixteen months best corresponds to the typical eruption timing for the lower first primary molar.