In the 20th century, tooth decay was finally tamed through advancements in microbiology, which established connections between cavities and diets heavy in sugar and processed flour. Especially in the U.S., as orthodontics advanced and tooth extraction became less common, a proud open-mouthed smile became the cultural norm. From cigarettes to dish soap, television commercials and magazine ads were punctuated with glinting smiles. Sharing a smile with someone wasn’t just good manners, but a sign that the smiler was a willing recipient of the wonders of modern medicine.

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By the early 20th century, Edward Angle, an American pioneer in tooth “regulation,” had been awarded 37 patents for a variety of tools that he used to treat malocclusion, including a metallic arch expander (called the E-Arch) and the “edgewise appliance,” a metal bracket that many consider the basis for today’s braces. Angle sold all of these standardized parts, in various configurations, as the “Angle system.” Other orthodontists could purchase and use Angle’s inventions in their own practices, thus eliminating the need to design and produce appliances for each new patient.

Today’s orthodontic practices rely on equal parts individual diagnosis and mass-produced tool, often in pursuit of an appearance that’s medically unnecessary. Basic advances in brushing, flossing, and microbiology have largely defeated the problem of widespread tooth decay—yet the perceived problem of oral asymmetry has remained and, in many ways, intensified. The choice to leave one’s mouth in aesthetic disarray remains an implicit affront to medical consumerism.

“The smile has always been associated with restraint,” Trumble writes, “with the limitations upon behavior that are imposed upon men and women by the rational forces of civilization, as much as it has been taken as a sign of spontaneity, or a mirror in which one may see reflected the personal happiness, delight, or good humor of the wearer.” And so orthodontics persists to address a genuine medical necessity, but also (and more often) to enable unnecessary self-corrections.

With an often-unnecessary product—the perfect smile—as the basis of its livelihood, the orthodontics industry has embraced the placebo effect. “A great smile helps you feel better and more confident,” argues the website for the American Association of Orthodontists. “It can literally change how people see you—at work and in your personal life.”

In recent years, however, this promise has collided with the high cost of orthodontics to foster a dangerous new subculture of home remedies for teeth straightening. Guided by YouTube videos and homeopathy websites, some people are attempting to align their own teeth with elastic string or plastic mold kits, an amateur approximation of what an orthodontist might do. This practice has become so widespread that The American Journal of Orthodontics and Dentofacial Orthopedics issued a consumer alert, warning that such unsupervised procedures could lead to lesions around the root of a tooth and in some cases cause it to fall out completely. Excessive pressure can wreak havoc on a mouth and interfere with the root resorption necessary to anchor a tooth in its new position. Yet the popularity of the practice is, in some ways, a product of the orthodontics industry’s own marketing history, which has compensated for empirical uncertainty about its medical necessity by appealing to aesthetic concerns.