Have you ever dreamed of jumping into a time capsule and taking a blast into the past to observe what teeth were like hundreds, or even thousands, of years ago? Have you ever asked yourself whether some of the common dental diseases that we see today, such as malocclusion and dental caries, were even considered “diseases” back then?
In the Journal of the American Orthodontic Society, Dr. Kevin Boyd takes us through time to explore this question and broaden our understanding of the evolutionary origins of oral disease. Dr. Boyd hypothesizes that malocclusion and dental caries relate to a mismatch between the types of foods we eat today and the dietary regimes under which our jaws and teeth evolved. Although both malocclusion and dental caries are highly prevalent today, they are surprisingly rare in our prehistoric past. They are considered as “dental diseases of civilization”.
Some history: Skeletal remains indicate that hunter-gatherers had almost no malocclusion. Class II and III malocclusion did not appear appreciably in humans until the time of the Industrial Revolution. Although the cause of malocclusion is unclear, it is not likely to be due to recent genomic change. Dr. Boyd mentions that the genome coding for the modern human masticatory apparatus has not changed over thousands of generations.
What then is the leading hypothesis for understanding the etiology of malocclusion? It lies in the “mismatch” theory and how we moved from a “hard,” Paleolithic-type diet of wild whole grains, nuts, and seeds, to a “soft,” high-calorific diet of processed foods. This shift resulted in a massive reduction in our masticatory effort. Because the development of the jaws and face is highly plastic and affected by the muscles around them, decreased muscle usage has led human faces to grow downwards and become more narrow, leading to less space for all of our teeth.
In regards to dental caries, Dr. Boyd mentions that cariogenic bacteria have been co-evolving with humans since we began migrating out of Africa tens of thousands of years ago. However, caries are a relatively recent finding in human history that coincides with the first appearance of refined grains and sugars in our diet, about 1,000 years ago with the introduction of cane sugar to Western Europe. Increased sugar consumption led to a dramatic decrease in the diversity of our oral bacteria, allowing domination by caries-causing strains and increased acid production by these bacteria.
The present: How are all of these factors connected and relevant to today? Moving from a human masticatory apparatus that was best adapted to foods requiring prolonged and forceful chewing to a “softer” diet has affected a prominent factor that relates to malocclusion: muscle usage. Use it or lose it, as the saying goes, and as we lose our muscle strength while being exposed to a less-challenging feeding environment, it results in the “modern melting face.” Less room for all of our teeth can not only result in a cosmetic issue of overcrowding, but it may also increase our risk for caries due to uneven and constant wear of the same teeth, and decrease our oral hygiene due to difficulty cleaning teeth and gums effectively.
The mystery of tomorrow: What is an application of the evolutionary oral medicine that Dr. Boyd discusses? Dr. Mike Mew joins a talk with Dr. Boyd that is cited in his paper to discuss a novel approach to orthodontic diagnosis and treatment called orthotropics. The goal of orthotropics is to defy the modern melting face and convert vertical growth into horizontal growth in order to provide space for the teeth to align naturally. Orthotropics focuses on environmental instead of genetic causes to malocclusion, such as weakened jaw muscles, which may be attributed to evolutionary origins discussed earlier. The aim is to make the “face fit the teeth” and not vice versa through oral myology training, or exercises that correct muscle function and swallowing.
So, the take-home message from being a teeth time traveler with Dr. Boyd is that malocclusion and dental caries can be noted as diseases of civilization. Our ancestors had less than 5% malocclusion, while today we have less than 5% normal occlusion. Evolutionary oral medicine provides us with a way to think, to come up with new ways of treatment and prevention. As Dr. Mew concludes, “I want to force a debate within the profession. If we are treating one-half to one-third of the population in the modern world without knowing the cause, we must be open to debate. That is science and we are scientists. If you do not know where you started, you cannot know where you are going.” Just having a glimpse of the past through this paper may help us understand the difference between the past and the present, in order to better grasp what lies ahead in the future.
You can find the original article here: Boyd, Kevin L. “Darwinian Dentistry Part I: An Evolutionary Perspective on the Etiology of Malocclusion.” Journal of the American Orthodontic Society 11.6 (2011): 34-39. Web. 29 Feb. 2016.
~Katherine Ong, Maryland ’20