What's a Meta For?
This month's article by Drs. Cusimano, McLaughlin, and Zernik challenges one of orthodontics' most cherished metaphors-- that of the occlusal wedge. The wedge was a simple, understandable way to explain how the bite opened when molars or bicuspids were extruded or distalized, or how it closed when the molars moved forward after the extraction of bicuspids. It was such an elegant and useful metaphor that it took on an aura of infallibility. Most clinicians accepted and perpetuated it without further thought.
There are some orthodontists-- Charles Burstone for one-- who never believed that moving the teeth along an upper or lower occlusal plane automatically opened or closed the bite. The exception would be when the upper and lower occlusal planes were not parallel. Even in those patients, however, other overriding factors needed to be considered. Despite the attractiveness of the accepted metaphor, these orthodontists knew the occlusion simply doesn't function as though the maxillary and mandibular planes were vectors controlled by an occlusal wedge of posterior teeth.
Brian Arthur, the ingenious Stanford economist and member of the Santa Fe Institute, has said, "Nonscientists tend to think that science works by deduction. But actually science works mainly by metaphor." Before the 17th century, the physical world was thought to be a rather messy, unpredictable, and complex arrangement governed by mystical and magical forces and interpreted by alchemists, magicians, and sorcerers. The movements of planets were arbitrary, the etiologies of diseases obscure, and therapies often absurd. But by the 1660s, Newton had figured out differential calculus and drafted his laws, and suddenly the mysterious planetary orbits became predictable and understandable, as did other physical phenomena.
The metaphor for such Newtonian reliability-- clockwork-- dominated science and, indeed, the rest of secular life for the next two and a half centuries. We still use this figure of speech in today's digital world, though less often than 50 years ago.
Reductionist scientists believed that although the world was full of complexities and ambiguities, with the application of a few nifty laws the confusion could be converted into a simple, predictable system-- just like clockwork. Unfortunately, chaos and complexity theory have by now destroyed the smug satisfaction of Newtonian mechanics, helping us to understand that even the simplest systems remain highly sensitive to variations in conditions and can give rise to extremely complex and unpredictable consequences.
Metaphors may seem trivial, but they contain the essence of ideas and become our mental shorthand for visualizing problems and solutions. Arthur suggests that as we learn more about a topic, the old metaphors become less useful and more unsuitable. He sees the formation of new metaphors as almost unavoidable in any vital discipline and reassures us that they provide more potential for expanding and extending our knowledge than the solutions we find. He feels that bad policy making (read: treatment planning) almost always involves the use of inappropriate metaphors.
My father, God rest his happy, hardworking soul, was the maharajah of metaphors without even knowing it. After a particularly busy day in his barbershop, he would tell me, "Well, they knocked us out of the box today." For him, work was like a baseball game, and his choice of metaphor reflected his childlike eagerness to participate. How much healthier than to say, "Well, they really chewed us up today"-- a clear reference to a savage, life-or-death struggle in the office. Small wonder some people dread going to work.
The wedge is only one of the unsuitable metaphors that have been promoted by orthodontists. I remember reading an article several years ago about how most TMJ disc noise could be compared to a watermelon seed held tightly between two fingers and suddenly spurting forward. A marvelous word painting, but fatally flawed. The TMJ disc doesn't translate independently of the condyle except under extremely pathological conditions that no amount of orthodontic therapy can remedy.
Setting up anchorage in the buccal segments so the teeth are positioned like tent stakes conjures up a reasonable mechanical picture, until one realizes that a tipped-back tooth can move as readily through bone as an untipped one. Vital osseous tissue isn't analogous to inert dirt.
Reliance on "oral gnomons" in growth prediction is a clear and appealing Euclidean concept, but it is a gross oversimplification of a truly complex mechanism that is everything but extensions of trapezoids. Arthur agrees that predictions are nice if you can consistently and accurately do them, because they may help eliminate some undesirable consequences, but he feels that the essence of science lies in the explanation and comprehension that unmask the fundamentals of nature. Angular extensions neither explain nor add to our comprehension of the remarkable phenomenon of facial growth.
Other orthodontic metaphors, such as "burning anchorage" and "jumping the bite", may also need re-evaluation, considering what we know today about these topics.
Lately I've detected a new interest in metaphors in the most disparate disciplines-- economics, physics, biology, sociology, and military science. Don't be surprised if orthodontists follow suit in emphasizing this old way of expressing our perceptions.
But whatever new metaphors orthodontic savants conjure up as they grapple with the multifaceted problems of our specialty in this age of complexity, we need to do our best to make sure they accurately reflect what we really know.
Karl Popper championed the idea that all progress in knowledge results from efforts to deny, rather than to confirm, our theories. Cusimano, McLaughlin, and Zernik have exercised this scientific responsibility in an admirable study that beckons close professional scrutiny.