Q. Why do teeth turn yellow with age? Is there any way to prevent it?
A. Besides the cumulative effect of the many external causes of tooth discoloration over a lifetime, there are at least two structural changes that make teeth more likely to appear yellow as someone grows older. These are the gradual thinning of the enamel, the outer coating of the tooth, and the thickening of the layer under that, called the dentin.
As the enamel thins because of wear and tear and things like acidic foods, the natural yellow-to-brown color of the dentin it covers shows through more and more, according to a review of the literature on tooth discoloration published in The British Dental Journal in 2001.
The yellowing may be more or less obvious, depending on the genetically determined natural color of the dentin and the thickness of the enamel. A further complication is that once the dentin is exposed, other coloring agents are more easily absorbed by teeth.
Meanwhile, “the natural laying down of secondary dentin affects the light-transmitting properties of teeth, resulting in a gradual darkening of teeth with age,” the review continues.
That process cannot be stopped, but care can be taken to minimize enamel loss. Many of its causes are avoidable or treatable, like dry mouth; excessive consumption of sugars, acids and alcohol; bulimia; teeth grinding; and acid reflux disease.
There are many other causes of discoloration, among them inherited and metabolic disorders that affect tooth structure even before old age. Discoloration can also result from certain drugs, like tetracycline taken by children when their teeth are developing, or absorbed while they are in the womb. Beverages like tea, coffee and red wine and foods like blackberries are also well known to discolor the teeth, as is tobacco in any form.question@nytimes.com
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