Brush your teeth morning and evening and floss daily. Oh and avoid sugary snacks between meals. Yeah, yeah - sure but why?
You lose your teeth if they decay. How does decay come about? There is a continual process going on in your mouth called the demineralisation and remineralisation of your teeth. After you eat, the bits of food (especially sticky, sugary foods) left in the plaque around your teeth form acids. These acids dissolve the enamel coating of your teeth (demineralization). The saliva in your mouth will neutralize the acids in time and the dissolved chemicals will be deposited back in the enamel coating (remineralisation).
If we upset the balance between these two processes the enamel becomes thinner and eventually a hole appears. Then the softer tissues inside the tooth are attacked and a cavity appears which has to be filled. If left too long the whole tooth dies and has to be removed. This site explains it simply - http://news.bbc.co.uk/1/hi/health/medical_notes/3776459.stm
If we eat too frequently the saliva doesn’t have time to do its work. If we eat a lot of sugary stuff the saliva cannot cope. Brushing and flossing remove the plaque in which all this takes place - particularly at night when there is little saliva in the mouth. Fluoride in water and toothpaste help by changing the chemical makeup of the deposited enamel to a stronger compound.
Even with the best brushing and flossing and self-care you still have to have regular checkups at the dentist since you can’t catch everything.
Nowadays there is no need to lose your teeth ever. Keep smiling.