They are highly sensitive to cold.
They are vitally important to our life.
They are a living part of our body.
They are a chief source of our pain.
It has to be removed in time by a dentist.
It is a rare oral disease among old people.
It contains many nerves and blood vessels.
It is a sticky and colorless film on the teeth.
It can change into acids causing damage to their outer covering.
It greatly reduces their resistance to the attacks of bacteria.
It makes their nerves and blood vessels more sensitive to acid food.
It combines with food particles to form a film on their surface.
Unhealthy living habits.
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