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But tooth functions extend far beyond procuring and processing food. These hard, mineral-rich structures, which include variations such as tusks and fangs, often play a crucial role as defensive weapons. According to the World Health Organization, over one hundred thousand people die each year from snakebites—along with three times that number who end up with amputations and other disabling conditions. And one needs only the briefest glimpse of the upper canines of snarling dogs or baboons to know that teeth are an efficient means of expressing strength, dominance, and aggression. Less obvious is their involvement in mating behavior and even parent/offspring relationships, as when young bats use hook-tipped baby teeth to hang on for dear life as their moms navigate the night skies.

Teeth also enable animals to manipulate and change their environments. Tree-trunk-gnawing beavers and water-hole-excavating elephants may come to mind, but researchers examining tooth wear patterns have shown that Neanderthals and early modern humans also used their teeth as tools, to soften tough fibers and animal hides—a practice that continues in some cultures.

Human teeth also project information about the individual. A mouthful of well-formed teeth can portray vitality, power, wealth, and success, while misshapen or absent teeth can lead to the opposite assumption. By the time George Washington was sworn in as president in 1789, he had only a single tooth—a dismal dental condition that could have done serious damage to his standing as the leader of a newly minted nation. Over the last two decades of his life, Washington would go through at least four sets of bulky, ill-fitting dentures. And though much improved from the painful-to-wear appliances of the eighteenth century, dentures remain a source of consternation to this day.

But false teeth, dentures, and the like have been around far longer than the time of the Founding Fathers. Fashioned by ancient Etruscan artisans nearly three thousand years ago in what is now Italy, these pre-Roman Empire dental appliances were composed of filed-down animal and human teeth, and, as we'll discover, they served a surprising purpose.

BACK IN THE animal kingdom, we'll explore why the term "specialized diet" can be a serious understatement—as in one scale-munching fish species with jaws adapted for plucking scales from either the right side or left side of a prey's body, but not both sides. From an evolutionary standpoint, one key benefit for the specialist is the ability to eat things that potential competitors aren't able to eat. Vampire bats stand as a prime example, with each of the three genera using razor-sharp teeth and an assortment of unique adaptations to feed on a widespread but generally untappable resource: blood.

In contrast to those vertebrates with specialized diets are the omnivores—creatures able to consume a wide variety of food sources, though the term generally implies a diet consisting of plants and animals.

But whether a tooth belongs to a specialist or an omnivore, most of its bulk (including the jaw-gripping roots) is made up of dentin, a very bone-like noncellular mixture of hydroxyapatite, tiny tubes of collagen, and water. The tooth's crown (the part that sticks out from the gums) is covered by a thin layer of enamel, the hardest substance found in the vertebrate body. Additionally, all teeth contain a central chamber known as a pulp cavity, which contains blood vessels and nerve endings.

Beyond the importance of teeth to their owners, much of what we know about ancient life on this planet has come from the study of teeth. While other body parts decompose, teeth are far more likely to endure the test of time, in some cases for hundreds of millions of years, as fossils. Once the tooth of a deceased animal is buried (usually under an  accumulation of sediment), it is protected from the effects of general wear and tear, weathering, and erosion. Over time, water, seeping down through the soil, enters the tooth through microscopic pores in the enamel. The water carries with it minerals like silica (think sand, concrete, and glass) and calcite (think limestone and marble). In turn, these substances are transported deeper into the tooth through channels in the dentin. Eventually, the minerals solidify, leaving the tooth even harder than it was in life, and making teeth the most common vertebrate fossils by a wide margin.