ortodontist

Decays are also known as dental caries, holes or cavities. They occur when teeth are not properly cleaned. So, if you do not want any decays, you have to clean your teeth effectively. 

When teeth are not cleaned, a slimy layer of germs grow on teeth. This layer is called plaque. When you eat candies, cakes, bread etc. they easily can turn into sugar. And sugar sticks on teeth. So does the bacteria. If you let them stay comfortably on your teeth for a while, they start to create plaque. And plaque turns out to be decay. You do not necessarily eat candies for this. Any food remnant can easily turn into sugar. So, after every eating and drinking session, washing and swilling water is essential. But that’s not enough. Brushing teeth twice a day and also flossing is essential too. Brushing should last at least 2 minutes, using circular movements. After that, flossing comes into stage. By flossing, remnants of food between teeth and every hidden place in mouth where brushes can’t reach. 

But that also is not enough. You have to use less, preferably no sugar on your diet and go on for more mineral rich food like milk and dairies.

Do not forget your regular checks to your dentist. Because some dental decay may not be visible to you easily. 
And another info for smokers. Smokers are more likely to develop periodontitis 2-7 times than non-smokers.