There is a direct correlation
There is a direct correlation between tooth color and age. Over the years, teeth darken as a result of wear and tear and stain accumulation. Teenagers will likely experience immediate, dramatic results from whitening.

In the twenties, as the teeth begin to show a yellow cast, teeth-whitening may require a little more effort. By the forties, the yellow gives way to brown and more maintenance may be called for. By the fifties, the teeth have absorbed a host of stubborn stains which can prove difficult (but not impossible) to remove.

We are all equipped with an inborn tooth color that ranges from yellow-brownish to greenish-grey, and intensifies over time. Yellow-brown is generally more responsive to bleaching than green-grey.

These are also genetic traits that become more pronounced with age. While all teeth show some translucency, those that are opaque and thick have an advantage: they appear lighter in color, show more sparkle and are responsive to bleaching.

Teeth that are thinner and more transparent — most notably the front teeth — have less of the pigment that is necessary for bleaching. According to cosmetic dentists, transparency is the only condition that cannot be corrected by any form of teeth whitening.