Behind The Dentist’s Drill
APPROXIMATELY A THOUSAND YEARS AGO, ON Chiapa de Corzo, a windswept plain on the west coast of Mexico, a Mayan sits on a rock with his head thrown back. In front of him stands the tribal shaman, who is about to begin the ritual of drilling holes in the man’s front teeth before inlaying them with jeweled ornaments.
The shaman places a thick mixture of powdered quartz and water on the upper incisor; this will serve as an abrasive. He then takes a long, thin tube made of jade or some other hard stone and, twirling it between his palms, begins to excavate a perfectly round hole on the tooth’s surface.
The ornamental jewels have been cut from a larger stone with the same drill that is now grinding the tooth, thus ensuring a precise fit. When all is ready, the shaman puts a dab of cement in the cavity and sets the stone in place—so securely that it is still there a millennium later.
This is one of the earliest-known examples of tooth drilling. Other early peoples filed and notched their teeth for ritual purposes or tribal identification, but the Mayans’ use of a drill for that purpose was a monumental step forward. Unfortunately, the technique of drilling was then forgotten for centuries.
Almost as far back as the dawn of civilization, humans have known how to drill holes in shells, bones, or stone to make amulets and beads. Drilling into a living substance was apparently also known since the late Stone Age. A grave in Denmark dated from 2000 to 3000 B.C. contained a male skull in which a molar tooth had a hole drilled into it, close to what would have been the gumline, with a bow drill and a flint bit.
In the second century A.D. two Greco-Roman physicians, Galen and Archigenes, recommended drilling into a tooth. The drill was probably a thin iron shaft with a starlike point that was twirled between the palms. The Jewish Talmud mentions a case where “the master is a physician and [the slave] implores him to treat his eye … or drill his tooth.”
The need for all this drilling is simple. Of all the substances in the human body, the hardest by far is the enamel that covers a tooth. Yet this extreme hardness provides little protection against dental decay. The process begins with plaque, a product of bacterial action on food residues. Bacteria colonize this plaque and secrete acid, which eventually eats a small hole in the enamel. Other bacteria enter the opening to attack the softer, underlying dentin and destroy it from within, creating a large cavity in the tooth but leaving the overlying enamel almost intact. This condition, known as dental caries, is by far the most widespread disease afflicting the human race.
For several millennia operative dentistry—that is, medical efforts to preserve teeth instead of pulling and replacing them—was limited to relieving excruciating pressure by draining the pus created by these infections. This afforded temporary relief, but the decay continued inexorably. In the late Middle Ages attempts were made to fill these cavities with a variety of substances ranging from cobwebs to resin. Nothing worked, because the art of drilling had been lost. Forced to rely only on whatever cracks and holes occurred naturally, medical practitioners could never remove all the decay or prepare the cavity properly to hold a filling.DENTAL DRILLS THROUGHOUT HISTORY
By the mid-1600s small chisels were allowing dentists to chip away bits of enamel. Nevertheless, a tooth could be restored only if the dentist was able to make a decent-sized hole, scoop out the underlying decay, and insert his filling (which by this time often consisted of strips of gold foil) with some assurance that it would stay put. Few dentists were dexterous enough to accomplish this with the primitive tools of the time.
The revival of drilling began with Pierre Fauchard, who is often called the father of dentistry. In 1728 Fauchard, a Parisian surgeon who limited his practice to dentistry, brought out the most important book on the subject published up to then, gathering all the knowledge of his time and presenting it in systematic fashion. (Before Fauchard dental techniques were generally regarded as trade secrets.) The book included a picture of a bow drill, but Fauchard did not mention using it in treatment; instead he discussed its role in the fabrication of prosthetic appliances, such as bridges and dentures. In the second edition, published in 1746, however, he recommended enlarging root canals with the device so that they could be cleaned and filled more thoroughly.
For most of the eighteenth century France was the world’s center of dentistry, and many important innovations arose there. In 1778 another Parisian surgeon, Anselme Jourdain, published a comprehensive text on dentistry in which he pictured an instrument he called a porte écarissoir — the germ of the idea of a mechanical revolving drill. The operator gripped a handle with one hand while turning a crank at the end of a shaft with the other, thus rotating a gear that spun a notched wheel attached to a small drill point. Clumsy as it was, the device could nevertheless fit in the mouth and be used on back teeth.
TOWARD THE END OF THE 1700s, American dentistry started coming to the fore. The most famous dental patient of the century was George Washington. The first President suffered grievously from toothache, and he tried a number of dentists before settling on John Greenwood of New York City.
In 1790 Greenwood converted a spinning wheel into a drill. His son, Isaac John Greenwood, who also became a dentist, wrote about it to a colleague in 1860: “My father was the first to use the foot-drill, and he made it himself from an old spinning wheel of my grandmother’s; and, since his death, I myself used it, the same one, altogether in my practice for twenty years, and I have it yet. I never had seen one before, and I know the hand bow-drill was always used before.”
Apparently both father and son used this device to drill into bone and ivory in making artificial dentures. They saw it as a laboratory tool rather than an instrument to be used on living teeth. But despite its usefulness, for some reason no other dentist picked up on this device for almost three-quarters of a century.
By the 1820s the center of dental innovation had moved to the United States. Some of the early dentists in this country were genuine ingenious Yankee mechanics; they began devising drills to help them in practice.
In 1858 John A. Chevalier of New York City invented a geared drill with a mechanism somewhat like that of an eggbeater. Its advantage was that the drill was offset at an angle that allowed better access to the tooth; its disadvantage was that it took two hands to operate. At about the same time, Charles Merry of St. Louis introduced a drill with a flexible shaft, an innovation that was to prove extremely important. Nevertheless the Chevalier and Merry drills were hard to handle and inefficient. A prominent German dentist, Anton Buzer, wrote in 1867, “All the appliances which have been invented to facilitate the drilling of teeth are superfluous.”
Most dentists continued to use simple steel drills that they twirled between thumb and forefinger. The drill’s simplicity was not a virtue from the patient’s standpoint: A medium-sized cavity required at least half an hour of pressure and twirling, so it’s no surprise that many toothache sufferers chose extraction over filling.
Clearly, any real advance required devices powered by some other source than the dentist’s hands. As early as 1856 George F. Green, a mechanic at the S. S. White Company of Philadelphia, the nation’s largest manufacturer of dental supplies, was working on an electric drill. He built several prototypes and patented one in 1870, but electric power was still in its infancy and depended on unreliable batteries. Moreover, Green’s drill was heavy and clumsy and developed little torque. It did not generate much interest.
But Green also invented a “pneumatic engine” that ran on a footoperated bellows. A rubber tube carried the air to a handpiece, to which was attached a small drill, or bur. This was successfully manufactured in quantity by the S. S. White Company; it became the first industrially produced dental engine.
AT THE SAME TIME, SEVERAL inventors were struggling to perfect a clockwork drill. The one that piqued the profession’s interest was invented by an Englishman, George Fellows Harrington. He demonstrated his drill before a meeting of the Odontological Society of Great Britain in 1865, describing it as suitable “for drilling, cutting, grinding and polishing teeth while in the mouth.” Wound, like a clock, with a large key and bearing the triumphant name Erado (Latin for “I scrape out”), Harrington’s drill ran for two minutes per winding and sold for six guineas, a fair sum at the time.
After watching it demonstrated, the society’s president declared the noise it made very objectionable. Harrington countered that he had used it in his practice for twenty-two months with few complaints. Nevertheless he set to work making it quieter, and five years later he demonstrated to the same society his new, improved noiseless drill. Convinced that his invention was the thing of the future, the Briton set sail in 1871 for America to market it. Just as he was crossing the Atlantic, though, the greatest drilling advance yet was unveiled to the profession, one that would completely change its character: the foottreadle drill.
As a child in Ohio James Beall Morrison had apprenticed as a watchmaker, but he switched early to dentistry and entered practice in St. Louis when he was about twenty. After a few years spent in Paris and London—where he patented one of the earliest truly functional dental chairs—he came home to St. Louis in 1870 and set up practice with his brother. He devoted his spare time and energy to developing his invention, and on February 7, 1871, was granted a patent for a foot-powered dental engine similar to Greenwood’s drill of the 1790s. He sold the first one the next spring at a national dental meeting in Binghamton, New York.
The new drill was an immediate success. It cut drilling times in half and was much easier on the patient. The best hand-powered drills could reach possibly 100 revolutions per minute; Morrison’s could attain 2,000 rpm. At first such high speed created problems: No burs available at the time could withstand it, and the heat it generated was too much for the tooth to bear. But new materials for burs were soon developed, along with clever contrivances to drip water on the drill point while it turned.
A contemporary evaluation of Morrison’s engine came from one of Europe’s leading dental educators, Julius Scheff, founder of the dentistry school in Vienna. “Speaking of hand drills and burs, I must not omit to mention one of the greatest and most useful achievements of modern times—the dental foot engine. Of course, only a very busy dentist can afford it, its price being too high, and the cost of its acquisition would outweigh the cost of all the other instruments, including the filling materials. But it has so many advantages that every better dentist should possess one.” The price at that time was about sixty dollars, but as production increased and sales boomed, the cost came down to about twenty dollars, well within the reach of every dentist.
Before the foot engine the most laborious effort had been required to clean and fill even the simplest cavity. Most aspiring dentists learned by apprenticeship, since there were few formal schools. The first dental school in the world was founded in Baltimore in 1840; by 1870 there were still only about ten in the entire country. There were no exams to pass, and no license was required anywhere to hang out a sign and start treating patients.
Consequently, when the foot engine eliminated so much of the hard work, the field was flooded with unskilled, untutored, and unscrupulous operators. It took the profession years to get rid of them.
Meanwhile, research continued on power sources that would not rely on human muscle. Despite the unenthusiastic reception Green’s electric handpiece had received, the S. S. White Company continued the research he had started, and in 1883 it produced the first practical electric dental engine, which had a flexible shaft running from the handpiece to the motor. The next year the company brought out the first motorized drill attached to a dental chair and introduced the first foot control, obviating the necessity of switching the motor on and off by hand. At about the same time, C. Edmund Kells of New Orleans became the first dentist to fully electrify his office when he received permission from the local streetcar company to tap its electric lines. He built a sophisticated control panel for his drill (probably an early S. S. White model) and regulated it with a foot switch he designed. By the early 190Os electric drills were widespread, enabling dentists to prepare a typical cavity in less than ten minutes.
MOTORS WERE SOON HUNG from the ceiling, conveniently near the patient, but the power still had to be delivered by a short flexible shaft until 1902, when a folding arm was introduced, transferring power from engine to handpiece by means of an endless belt traveling over a series of pulleys. Around 1915, with footpowered drills rapidly disappearing, the dental unit made its appearance, incorporating into one freestanding machine the electric engine and its accompanying arm, the fountain cuspidor, the light, and other instruments.
Dentists had known for years that the faster the drill rotated, the less discomfort the patient experienced. The pioneer of high-speed drilling was a Belgian, Emile Huet, who as early as 1911 perfected an electric engine capable of 10,000 rpm. He could not interest dental manufacturers in it, however, because at such speeds the handpieces then in use would seize up.
By the 1940s electric dental engines were pushing 6,000 rpm, but a big handicap still existed: The long metal folding arm forced the dentist to work standing up, crouching over the patient, which led to chronic back and leg ailments. When World War II ended, dental manufacturers began seeking a more wieldy substitute for the familiar rotary drill.
A pair of early postwar innovations turned out to be more clever than useful. In 1949 the S. S. White Company brought out a “sand-blasting” device called the Airbrasive, which used compressed carbon dioxide gas to blow a fine stream of abrasive aluminum oxide powder onto the tooth surface. It promised to be quieter and more comfortable for the patient, with less heat generation and no pressure on the tooth. Though highly touted, the machine could make only cup-shaped depressions in the enamel, leaving most of the work still to be done by the rotary drill. The patient wore a rubber sheet over his or her mouth that left exposed only the tooth being treated. A large tube, attached to a strong vacuum, sucked up the used abrasive and recycled it. Unfortunately, the collection system was not completely effective; much of the abrasive bounced back off the rubber sheet and into the dentist’s face. Goggles could be used to shield the eyes, but they quickly frosted over.
THE 1955 CAVITRON, WHICH used ultrasonic vibrations to power a metal tip that cut into the tooth with the aid of an abrasive slurry, also failed, because the tip wore away as quickly as the tooth. Without the abrasive the machine has remained a useful tool to remove heavy tartar from teeth.
But there were more lasting advances. As new alloys were discovered, handpieces underwent constant improvement. Faster motors and larger pulleys brought rotational speeds up to about 25,000 rpm, while Richard Page, an innovative dentist from Chatham, Massachusetts, devised an ingenious system of oversized belts and pulleys to reach speeds in excess of 150,000 rpm. Still, the century’s biggest advance was yet to come.
Tungsten carbide bits and diamond drills had been perfected in the 1940s, but they didn’t perform well at the conventional slow speeds. It would take ultra-high-speed drills to make these materials fulfill their promise, and when those drills were at last designed, the inspiration came from an unlikely source.
Dr. John Walsh, a dentist serving on the staff of the Royal Australian Air Force in 1945, was responsible for testing the hearing of Aussie airmen with tuning forks. It was well known that bone was a good conductor of sound and vibration—indeed, the fact was widely blamed for the unpleasantness of dental drilling—but Walsh found that above a certain frequency the patient heard nothing. He reasoned that a drill with higher rotational speeds would create less vibration, and he set to work building a high-speed air-turbine handpiece, modeled after larger turbine drills used in industry. The government gave him a small grant to build a prototype, but its bearings seized after two hours of high-speed running. Walsh applied for another grant; the government said no.
Meanwhile Dr. Robert J. Nelsen, a research associate of the American Dental Association at the National Bureau of Standards (NBS) in Washington, D.C., was working on a turbine drill powered by a stream of water under pressure. It ran smoothly at 60,000 rpm with no vibration and almost no sound except the whoosh of the water stream. Introduced in 1953, it was an immediate hit—the first turbine drill to be successfully marketed.
But Nelsen’s discovery was soon overshadowed by the efforts of his NBS coworker Dr. John Borden. Starting in 1946, Borden, working at home with a machinist and toolmaker, produced a functional drill driven by compressed air. It featured a miniature turbine in the head of the handpiece, supported by micro-mini ball bearings lubricated with oil from an atomizer. A fine stream of water directed onto the drill point helped prevent heat buildup in bur and tooth.
BORDEN’S DRILL, THL AIROTOR , created a sensation when he introduced it at the 1957 International Dental Congress. Not only did it attain the unheard-of speed of 250,000 rpm, but its handpiece was light and required no major changes in the way the dentist held or used it. With carbide burs and diamond stones replacing the steel ones that quickly dulled, enamel could be wiped away in a minute or so with a series of gentle strokes. Gaining the proper purchase and torque no longer required bearing down hard, so the patient felt almost nothing.
Since its introduction many manufacturers have made modifications and improvements to the Borden drill: Fiber optics allow a light to shine directly on the bit; advances in ball bearings have brought speeds to above 350,000 rpm; some manufacturers have eliminated the ball bearings, letting the turbine ride on a cushion of compressed air; and finally, in this day of AIDS, the once-delicate handpieces are now manufactured to withstand high-pressure steam sterilization.
The air-turbine drill has revolutionized treatment in many ways. It has made possible better restorations with less sacrifice of tooth structure. It has made the patient more comfortable not only by reducing vibration but also by cutting working time to a fraction of what it was before. And it has allowed dentists to do finer, more complicated work, of a delicacy and sophistication unimaginable just a few decades earlier.
As with all technology, the history of dentistry has had its share of false starts and wrong turns. Unlike virtually every other area, however, progress in dental technology has been indisputably positive in every way. Steam railroads have their enthusiasts, computers have their critics, and nowadays each new medical innovation seems to raise a host of ethical dilemmas; yet absolutely no one wants to go back to the good old days of dentistry. Every advance makes life easier in the dentist’s chair and out of it. A moment’s reflection on dentistry through the years should be enough to temper anyone’s sense of nostalgia.