Well, it can have more reasons.
You either don't brush your teeth regulary (atleast twice a day) or
you use a wrong tooth brush, usually a hard one. Hard tooth brush
hurts the gums and there you have the problems. Use a soft tooth
brush, it's not true that a hard tooth brush cleans the teeth
better then a soft one.
Other reasons - using one tooth brush for a long time. The tooth
brush is the home for the bacteria from your mouth, from the air
and if in the bathroom is also the toilet, the fecal bacteria are
also there because when you flush the toilet, the micro drops from
it are sprayed about 180 cm around the toilet. Buy a new tooth
brush atleast every 3 months and when you are sick, buy a new one
after you recover.
Keep your tooth brush in a dry place, not on the basin.
Brushing the wrong way - left right movements are wrong. Brush with
circular and up and down movements.
Use an antibacterial mouth wash atleast twice a day.
You can develope a parodontotis, I would suggest you visit a
dentist to check if it is already so far.
