To get started,we will study a little about Anatomy.
That's a huge number! It's hard to brush all your teeth.
Once it gets worse, it doesn't heal naturally. It will never grow again.
Surface
The front teeth have a Lip (Cheek) sied surface and a Tongue ( Lingal/Palate) side surface..
Molars have a 
Cheek side surface,
a Tongue ( Lingal/Palate) side surface,
and an Occlusal surface that is very prone to Painful tooth Decay .
Another important thing is that the teeth are densely lined up in the mouth(dental arches).
Adjacent tooth surfaces are called Interproximal contact areas .
These areas are very prone place for tooth Decay and Periodontal disease .
Adult teeth are numbered from 1 to 8.
There are Five teeth (baby, primary, deciduous, milk teeth) in a child and they are called A to E at each sides.
There are Three front teeth and Two deciduous molars. Upper, Lower, Reft and Light, 20 in total.
Children's teeth (baby, primary, milk, deciduous teeth) lose their roots as they grow up, and Adult teeth(permanent teeth) grow from below.
Even if it is replaced, it will have a bad effect if it is not polished properly.
In addition, children's teeth are weak and thin, so they quickly become cavities and Hurt/Painful very much.
From the time a child enters elementary school, adult teeth begin to grow and milk teeth will change to permanent teeth.
Around the age of six,the first permanent teeth, the first molars (so-called 6-year-old molars), grow at the next (position) of the deciduous teeth E.
Most prone to tooth decay !.
And, It is the most important permanent tooth that supports our health throughout our lives.
It takes time for the shape to grow properly.
Careful tooth brushing is required to avoid tooth decay.
Why does your tooth hurt when it becomes Cavities?
The teeth are not just clogged with hard objects.
Moreover, "Hard Teeth" are not egg shells.
It is a triple structure with a double shell!
The outside is the hardest and is called enamel.
There are no nerves here, so you won't feel any pain when you bite something.
Similarly, even if you have mild cavities and only on the outside, you will not feel any pain.
Inside, it is a little soft and tough dentin.
When your evil cavities reach here, they will cause tingle.
Further inside is a normal/common tissue called the pulp.
Blood is flowing and there are big nerves.
When your cavities reach here, the pain doesn't stop anymore.It does not heal naturally.
Your teeth will die if you could not goto a Dental Clinik.
The boundary between the Teeth and Gums( Gingival margin) are also very prone to tooth Decay and Periodontal disease.
Tartar, hardened(calcified) tooth stains (dental Plaque), also sticks here.
If left as it is, it will cause inflammation of the gums.
This child is bleeding from her gums at tooth brushing.
When you fall into periodontal disease, the alveolar bone that supports your teeth melts, teeth becomes unsupported, loosens, and eventually your teeth will say good-bye one by one.
Also,The tissues of the mouth will suffer from Inflammation.
Bacteria enter the body from Gums and give many Negative effects to the Health.
Refresh your mouth by Tooth brushing.
Bye Bye harmful Tobaccos!
Chewing tobacco is a major cause of oral cancer in Bangladesh.
It is even more dangerous if other factors are added. 
Some literatures by WHO(IARC) are presented.
The International Agency for Research on Cancer (IARC) is the specialized cancer agency of the World Health Organization(WHO).