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Beginning in the nineteenth century, fossilized teeth enabled paleoanthropologists to begin unraveling the mysteries of human evolution. More recently, they've provided information on ancient diets, health, climates, and ecology. The tales told by teeth currently stretch from early humans to ancient civilizations and beyond, through periods of famine, war, disease, and starvation. Today, researchers are exploring how tooth-related techniques used to examine life events in the distant past might also be used to identify early-life stress exposure that can put individuals at risk for mental health problems.

Though extremely durable, teeth are not indestructible, as those who discovered the pleasures of refined sugar would learn beginning in the seventeenth and eighteenth centuries. Effective preventive care was then unknown, as was the concept of sterile conditions, and dental quackery was widespread and dangerous. An entry found in a London bill of mortality for a single week beginning on August 15, 1665, listed 111 people who had succumbed from tooth-related issues.

Thankfully, things have gotten better. That said, many people were shocked in early 2023 by nightmarish photos depicting the aftereffects of a widely used but unregulated dental device called an anterior growth guidance appliance (or AGGA). Attracted by claims that it could correct bite issues or overcrowded teeth and eliminate sleep apnea, all without surgery, thousands of hopeful patients shelled out an average of $7,000 to have one of these wire contraptions installed. Unfortunately, instead of health benefits, many patients received damaged gums and jaws, exposed tooth roots, and flared or lost teeth. Accordingly, the use of AGGAs has fallen off dramatically, since most dentists are no longer promoting them.

Controversial dental appliances aside, given the importance of dental health (now a multibillion-dollar industry), improvements in both preventive and restorative care continue today, with promising new therapies being developed around the world. In one such avenue of research, scientists played the role of rodent dentists. But instead of placing fillings into cavity-ridden rat teeth, they inserted stem cells into the holes they'd drilled. The results were spectacular, namely the production of new dentin by the stem cells. In another study, researchers are investigating the potential to stimulate the growth of a second set of adult teeth. The hope is that this and related advances in dental medicine will soon make typical tooth fillings obsolete and dentures a thing of the past.

Teeth of varying sizes, shapes, and functions have been integral in allowing vertebrates to take full advantage of the wealth of resources found on our planet. Not to be forgotten, though, are the microscopic organisms that live on, around, and below our teeth. Divvying up the resources (a.k.a. resource partitioning) also exists in these microenvironments, as does competition and even cooperation between different microscopic organisms. Today, investigators are looking into a link between the presence of a common bacterium (Porphyromonas gingivalis) found in infected gums and the development of Alzheimer's disease.

Before we get to that, though, and before addressing some seriously interesting questions about the origin of vertebrate teeth, we'll put to rest any notion readers might have that "a tooth is just a tooth"—though hammering that notion into the ground like a tent peg might be a better descriptor.

PART I

TOOTHY ADAPTATIONS IN NATURE: THE SPECIALISTS

 

CHAPTER ONE

VAMPIRE BATS DON'T SUCK

—GONZALO FERNANDO DE OVIEDO, SIXTEENTH-CENTURY SOLDIER OF FORTUNE

ONE OF MY favorite things about social media is connecting with people I haven't seen or heard from in decades. When some of these old acquaintances contact me and we get around to career talk, I tell them that I've been teaching anatomy (though I recently retired), working as a research associate at the American Museum of Natural History, and studying bats for over thirty years. With my long-standing love of animals and the macabre, no one seems surprised that with roughly 1,470 species of bats to choose from, I picked the three species of vampire bats as my research subjects. And with their unique feeding behavior (they're the only vertebrates that feed solely on blood) and just-as-unique dental anatomy, these fascinating and long-misunderstood members of the mammalian order Chiroptera have had a lot to tell us about teeth.