Introduction

 

BITES, FACIAL GROWTH, AND TMJ DISORDERS

The following manuscript grew out of a desire to understand bites. As a philosophy major, I always tried to get to the bottom of things, and the bite seemed fundamental to dentistry, but the rationales provided to justify the reverential attitude about preserving every bite contact with great care and the worship of centric relation techniques just didn't make sense. Studies of bites had been mostly concerned with tracking variables that seem unrelated to patient's overall health or even the health of the jaw system.  My dental education had taught me how to be a good tooth mechanic but left me without an understanding of how the teeth work physiologically together with the rest of the body.  I felt like I knew the trees well, but I could not see the forest through them. 

Later, living with the primitive hilltribes of Northern Thailand, I noticed that their teeth looked very different from those of my patients.  The harmony and symmetry were remarkable.  Their dental arches were obviously wider, their chewing was smoother, and they had none of the TMJ pathologies I had seen in my patients - even though many of them had worn their teeth down and therefore should have many functional and TMJ problems according to what I had been taught.  Their relative TMJ health was not just due to lower stress levels, because the same healthy harmonious chewing systems were also present among the few of them who lived under great stress due to real physical dangers.  

To research what I had seen, I went to museums to study the craniofacial structures of our most recent ancestors, many from just a few hundred years ago.  In some, both dentitions and TMJs were extremely worn down; and, in a few, they were worn out; but there was no evidence of the unstable bites, narrow upper jawbones, and backwardly rotating lower jawbones commonly found in modern TMJ disorder patients. Their faces were noticeably more forwardly positioned, broader horizontally, shorter vertically, and more symmetrical than those of my patients.  

I learned that several dentists who traveled around the world in the first half of the twentieth century to study the teeth and jaws of tribal people had all noted the same change in facial shape in parallel with the dramatic rise in cavities, gum disease, and tooth crowding that occurred whenever they gave up their traditional diets and adopted a diet of processed foods.  Weston Price and others showed very clear examples of how, within one generation, the children of parents who had wide symmetrical faces and healthy straight teeth developed cavities, gum disease, crooked teeth, and narrow asymmetrical faces after they moved into settlements and began eating government rations of flour, sugar, and canned meats.  Peter Begg showed in great detail how wear of teeth in Aborigines was designed to develop and maintain stable bites.

Unfortunately, these early dental researchers had no way to know which of the changes in diet had caused each of these changes in the jaw system, and some of their work has been misinterpreted.  For example, the rise in cavities and gum disease was due to the increase in sugar and flour; but the narrowing and asymmetry of facial form was not due to the change in content of the food but to its change in consistency, specifically its loss of toughness, and it would occur from grinding any food into flour before consuming it.  Changes in the same direction can be produced in animals just by softening their food, while changes in the opposite direction can be produced in animals by hardening their food. 

From more recent research, I also learned that TMJ disorders are developmental disorders.  They rarely affect young children. The signs and symptoms in populations start to appear just after puberty, especially in females, when average female facial growth patterns diverge from average male facial growth patterns in a more downward and backward direction. 

To understand how modern facial growth so frequently leads to development of TMJ disorders required an extensive study of how the human jaw system and bite were designed to grow and function, and then how they grow and function differently today.  That study revealed that modern facial growth patterns, which have less horizontal growth and more growth down and backward, can also lead to obstructive sleep apnea and forward asymmetrical head posture.  To understand these relationships requires first understanding how the human jaw system was designed to function and the central role of the bite table in that function.  Chapter 1 describes how our jaw system evolved.  Chapter 2 describes the functional harmony it attained in our ancestors.  Chapter 3 describes how it grew and developed to attain that functional harmony.  Chapter 4 describes how it grows and develops differently now.  Chapter 5 describes some of the effects of those changes.