Trick: Estimating Age from Temporary and Permanent Teeth in Mixed Dentition

 

A boy has 16 permanent teeth and 8 temporary teeth. How old is he?

a) 9 years

b) 10 years

c) 11 years

d) 12 years

Answer: 10 years

Competitive exams often include such MCQs, and memorizing the numbers can be frustrating. Here’s a simple trick to calculate age based on the number of temporary and permanent teeth, specifically during the mixed dentition period.

Key Points:

1. All temporary (deciduous) teeth disappear by age 12, meaning the number of temporary teeth at 12 years is 0.
2. Permanent teeth start erupting at age 6, so the number of permanent teeth at 6 years is 0.
3. A child has a total of 20 temporary teeth, all of which appear by age 6.
4. The mixed dentition period occurs between ages 6 and 11

 

Trick 1

Lets make a table

Age in years	Temporary tooth	Permanent tooth	Comments
12	0	24	The sum always remains 24.
11	4	20
10	8	16
9	12	12
8	16	8
7	20	4
6	20	0

 

 

Trick 2

Applying algebraic equation:

Age = (Permanent teeth / 4) + 6

Lets see an example

A boy has 12 permanent teeth and 12 temporary teeth. His age is .

Age = (12/4) + 6 = 3 + 6 = 9

He is 9  years old.

This is a quick way to estimate age in competitive exams without memorization!