See all those nooks and crannies? They're prime breeding ground for tooth decay.

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It often seems as if people who have fillings have them in their back teeth. Is that really true, or does it just appear that way? In this article, we'll peek into the mouths of everyone from babies to seniors and try to figure out which teeth are most likely to decay and what the causes are. Then we'll take a brief look at what you can do to keep your teeth well into old age.

The teeth most likely to decay and develop cavities change based on whose mouth we're talking about. In infants and very young children, baby-bottle tooth decay reigns as the most likely cause of cavities. This type of decay develops most often in the upper, front teeth when babies doze off with bottles of milk, juice or other sugary drinks. Sugar remains on the teeth throughout the night, creating decay-causing bacteria. A similar problem can occur in toddlers when they are allowed to carry around a sippy cup full of sugar all day [source: Mayo Clinic].

In older children, teenagers and adults, the most likely teeth to decay or develop cavities are the permanent back teeth. These teeth, which come in beginning about age 6, are known as molars, premolars and wisdom teeth. Their job -- chewing and grind food -- dooms them [source: WebMD]

Open wide and we'll take a look at why these particular pearly whites are the ones that cause the most trouble.