Topic: Breathing and respiration: mechanism, exchange and transport of gases, volumes, disorders· Human Physiology

A baby boy aged two years is admitted to play school and passes through a dental check - up. The dentist observed that the boy had twenty teeth. Which teeth were absent ?

1. Canines

2. Pre-molars

3. Molars

4. Incisors

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Answer: 2. Pre-molars

Key idea: A two-year-old has milk (temporary) teeth only, with dental formula \(\frac{2102}{2102}\).

Per half-jaw: 2 incisors, 1 canine, 0 premolars, 2 molars. Total = \(2\times(2+1+0+2)\times 2 = 20\) teeth, which matches the dentist's count.

The adult set (32 teeth) is \(\frac{2123}{2123}\); the extra 12 teeth are 8 premolars and 4 permanent molars. Milk teeth have no pre-molars. Incisors, canines and molars are all present. Answer: (2).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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A baby boy aged two years is admitted to play school and passes through a dental check - up. The dentist observed that the boy had twenty teeth. Which teeth were absent ?

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