Tuesday, November 24, 2009

Malocclusion: Disease of Civilization, Part VII

Jaw Development During Adolescence

Beginning at about age 11, the skull undergoes a growth spurt. This corresponds roughly with the growth spurt in the rest of the body, with the precise timing depending on gender and other factors. Growth continues until about age 17, when the last skull sutures cease growing and slowly fuse. One of these sutures runs along the center of the maxillary arch (the arch in the upper jaw), and contributes to the widening of the upper arch*:

This growth process involves MGP and osteocalcin, both vitamin K-dependent proteins. At the end of adolescence, the jaws have reached their final size and shape, and should be large enough to accommodate all teeth without crowding. This includes the third molars, or wisdom teeth, which will erupt shortly after this period.

Reduced Food Toughness Correlates with Malocclusion in Humans

When Dr. Robert Corruccini published his seminal paper in 1984 documenting rapid changes in occlusion in cultures around the world adopting modern foodways and lifestyles (see this post), he presented the theory that occlusion is influenced by chewing stress. In other words, the jaws require good exercise on a regular basis during growth to develop normal-sized bones and muscles. Although Dr. Corruccini wasn't the first to come up with the idea, he has probably done more than anyone else to advance it over the years.

Dr. Corruccini's paper is based on years of research in transitioning cultures, much of which he conducted personally. In 1981, he published a study of a rural Kentucky community in the process of adopting the modern diet and lifestyle. Their traditional diet was predominantly dried pork, cornbread fried in lard, game meat and home-grown fruit, vegetables and nuts. The older generation, raised on traditional foods, had much better occlusion than the younger generation, which had transitioned to softer and less nutritious modern foods. Dr. Corruccini found that food toughness correlated with proper occlusion in this population.

In another study published in 1985, Dr. Corruccini studied rural and urban Bengali youths. After collecting a variety of diet and socioeconomic information, he found that food toughness was the single best predictor of occlusion. Individuals who ate the toughest food had the best teeth. The second strongest association was a history of thumb sucking, which was associated with a higher prevalence of malocclusion**. Interestingly, twice as many urban youths had a history of thumb sucking as rural youths.

Not only do hunter-gatherers eat tough foods on a regular basis, they also often use their jaws as tools. For example, the anthropologist and arctic explorer Vilhjalmur Stefansson described how the Inuit chewed their leather boots and jackets nearly every day to soften them or prepare them for sewing. This is reflected in the extreme tooth wear of traditional Inuit and other hunter-gatherers.

Soft Food Causes Malocclusion in Animals

Now we have a bunch of associations that may or may not represent a cause-effect relationship. However, Dr. Corruccini and others have shown in a variety of animal models that soft food can produce malocclusion, independent of nutrition.

The first study was conducted in 1951. Investigators fed rats typical dry chow pellets, or the same pellets that had been crushed and softened in water. Rats fed the softened food during growth developed narrow arches and small mandibles (lower jaws) relative to rats fed dry pellets.

Other research groups have since repeated the findings in rodents, pigs and several species of primates (squirrel monkeys, baboons, and macaques). Animals typically developed narrow arches, a central aspect of malocclusion in modern humans. Some of the primates fed soft foods showed other malocclusions highly reminiscent of modern humans as well, such as crowded incisors and impacted third molars. These traits are exceptionally rare in wild primates.

One criticism of these studies is that they used extremely soft foods that are softer than the typical modern diet. This is how science works: you go for the extreme effects first. Then, if you see something, you refine your experiments. One of the most refined experiments I've seen so far was published by Dr. Daniel E. Leiberman of Harvard's anthropology department. They used the rock hyrax, an animal with a skull that bears some similarities to the human skull***.

Instead of feeding the animals hard food vs. mush, they fed them raw and dried food vs. cooked. This is closer to the situation in humans, where food is soft but still has some consistency. Hyrax fed cooked food showed a mild jaw underdevelopment reminiscent of modern humans. The underdeveloped areas were precisely those that received less strain during chewing.

Implications and Practical Considerations

Besides the direct implications for the developing jaws and face, I think this also suggests that physical stress may influence the development of other parts of the skeleton. Hunter-gatherers generally have thicker bones, larger joints, and more consistently well-developed shoulders and hips than modern humans. Physical stress is part of the human evolutionary template, and is probably critical for the normal development of the skeleton.

I think it's likely that food consistency influences occlusion in humans. In my opinion, it's a good idea to regularly include tough foods in a child's diet as soon as she is able to chew them properly and safely. This probably means waiting at least until the deciduous (baby) molars have erupted fully. Jerky, raw vegetables and fruit, tough cuts of meat, nuts, dry sausages, dried fruit, chicken bones and roasted corn are a few things that should stress the muscles and bones of the jaws and face enough to encourage normal development.


* These data represent many years of measurements collected by Dr. Arne Bjork, who used metallic implants in the maxilla to make precise measurements of arch growth over time in Danish youths. The graph is reproduced from the book A Synopsis of Craniofacial Growth, by Dr. Don M. Ranly. Data come from Dr. Bjork's findings published in the book Postnatal Growth and Development of the Maxillary Complex. You can see some of Dr. Bjork's data in the paper "Sutural Growth of the Upper Face Studied by the Implant Method" (free full text).


** I don't know if this was statistically significant at p less than 0.05. Dr. Corruccini uses a cutoff point of p less than 0.01 throughout the paper. He's a tough guy when it comes to statistics!

*** Retrognathic.

24 comments:

Mike said...

It's strange you should mention Vilhajmur Stefansson, since he specifically said that the notion of tough food being responsible for the hard teeth of the Eskimo was:

"a comfortable excuse of the dentist"

This was in an article for Harper's Monthly Magazine, November 1935, which is available online. (I don't recall that he mentions teeth in _My Life with the Eskimo_.)

Stefansson asserted that from personal experience he knew their food was mostly not particularly hard:

"Nor do Eskimos chew much, as compared with us. So far as their meat is raw it can be chewed like a raw oyster - slips down similarly."

And he goes through a list of similar comments on other foodstuffs in their diet.

As for using the teeth for work tasks, he comments:

"It is used as a second line of defense by the mastication advocates that even if Eskimos perhaps don't chew their food so very much they do chew skins a great deal. Their chewing of leather is far less than you might believe from what has been said by a particular kind of writer and pictured in certain movies. In any case, skin chewing is mainly by the women, and it is not easy to bring under the conditions of modern scientific thought the idea that the wife's chewing preserves her husband's teeth."

It may be not quite the same issue, but it seems pretty clear that Stefansson did not agree that the Eskimo either had food that was mostly hard or chewed it particularly much - or even (unless female) necessarily used their teeth that much for work tasks.

Stefansson may have been wrong on all counts - although it's too late to check now, since that form of life in its purity can no longer be observed by anyone else - but that's what he said.

anonymous said...

I'm not sure how much softer food of the SAD is. People are snacking on "box" foods all the time: chips, crackers, all manner of unhealthy hard things. Also, that animal with the skull similarity to humans doesn't cook it's food, and there are nutritional difference between cooked and uncooked foods so it might be prejudicial to say that malocclusion developed mostly because of different consistencies. Remember Pottenger's cats.

Stephan said...

Hi Mike,

Thanks for posting that, I had no idea that Stefansson had commented on it. I'll keep it in mind.

Hi Anonymous,

Did you sign up for a google account with the name "anonymous"? You must have, because I don't allow comments from people without accounts.

Crackers and chips are hard and brittle, but not tough. They don't provide much resistance to chewing.

Stephan said...

Anonymous,

By the way, investigators produced malocclusion in numerous animal models by using soft/hard food with identical nutrition, so I doubt nutrient loss due to cooking explains the hyrax result.

Matt Stone said...

Good feedback Mike. I agree there are definitely some irreconcilable inconsistencies here between what the studies Stephan highlights showed and what history has shown. I thought more of the case of the Masai tribe, who hardly chew at all on a diet of milk. No malocclusion there.

Again, it can probably be said that a diet can be so nutritionally impeccable that it doesn't matter what you do. The result is good health. Nothing can ruin your occlusion. The relative difficulty or ease of mastication of the nutritionally impoverished matters is applicable only to the nutritionally impoverished.

Thanks again Stephan.

zach said...

Hi Stephan

I'm anonymous. I'm glad to have found your blog.

Stephan said...

Hi Matt,

I agree with your comment on the Masai, although we don't know how they were using their jaws in ways besides eating. For example, some African cultures chewed twigs to clean their teeth, etc. I'll be discussing it later. There's actually some interesting data on occlusion in the Masai.

Hi Zach,

Nice to meet you.

Ned Clack said...

I'm no expert on the history of the Masai people, but as I understand it their diet of milk and blood is relatively recent. Until about a hundred years ago they were hunter/gatherers but got kicked off their traditional lands by the Brits. As herders they couldn't grow animals fast enough to live on but could milk and bleed them. Incidentally I believe that this (new) traditional diet is only followed by the men when they are warriors (a ceremonial position I hope) after which many of them adopt a more starchy diet.

Greg said...

Ned, I think you may have it backwards. The Masai have been tending cattle for a long time. They are now being gradually forced into agriculture. The Masai warriors (men of a certain age) were on a special diet, but all Masai ate a diet high in milk, blood, and meat.

Greg said...

With respect to Stefansson, I think those comments were focused on tooth/jaw health post-development, although I would tend to think that he would be highly skeptical that it helped development either.

Stephen, you have the most excellent articles (I have read them all), and I have to say this is the first one that I am highly skeptical of.

Part of this comes out of reading Nutritional and Physical Degeneration and trying to understand why native cultures did not understand that it was the sugar and flour that was damaging them. Certainly there was some willful ignorance. But native cultures always processed foods in ways that required less chewing and made them easier to digest (fermentation and cooking). So there would be a natural tendency that less chewing and easier to digest meant better for you, so flour and sugar seemed good.

I am digressing, but I am just as doubtful that chewing can lead to a properly formed jaw as I am that weight training can lead to a properly formed skeleton. If you want to build a stronger skeleton, tendons, joins, and muscles, weight-training can help. It doesn't seem that the jaw should be much of an exception- it should properly develop through diet, and can be made stronger through physical stress.

Carl M. said...

Chewing gum is popular enough in modern culture. Kids get quite a bit of jaw exercise that way.

Anna said...

I'm nearly halfway through primatologist Richard Wrangham's book Catching Fire: How Cooking Made Us Human. The main point of the books is that the shift from raw to cooked food was a key factor in human evolution. I think I'll pick it back up again this weekend.

Early in the book, around pages 38-42 or so, he argues that cooking foods made them easier to chew and therefore accounts for our significantly smaller and weaker oral anatomy (compared to our primate relatives and early ancestors).

Just before this section he also argues that cooked, easier-to-chew (practically predigested, perhaps?) foods increase nutrient availability and absorbability.

Has anyone else read this book?

Anna said...

I'm nearly halfway through primatologist Richard Wrangham's book Catching Fire: How Cooking Made Us Human. The main point of the books is that the shift from raw to cooked food was a key factor in human evolution. I think I'll pick it back up again this weekend.

Early in the book, around pages 38-42 or so, he argues that cooking foods made them easier to chew and therefore accounts for our significantly smaller and weaker oral anatomy (compared to our primate relatives and early ancestors).

Just before this section he also argues that cooked, easier-to-chew (practically predigested, perhaps?) foods increase nutrient availability and absorbability.

Has anyone else read this book?

Stephan said...

Hi Greg,

I think often the native cultures did understand what modern foods were doing to them, but they ate them anyway. Eating European food was a status symbol.

The animal experiments show that chewing stress can influence jaw shape independently of nutrition in a variety of species. I think it's probably a factor in humans, although not necessarily a dominant one.

Dr. B G said...

Anna,

I am reading it too!!! It is WONDERFUL. Isn't it? He's good.

My emphasis was food science for my bachelors in Nutrition so I like that aspect of his observations on protein being cooked. I'm not certain if I buy it all yet. Raw fish, raw oysters (YUMMMM YUM), carpaccio, raw beef in Korea (duk yu? I forgot the name) and other societies are favored and delicacies. They don't require much chewing b/c they are thinly sliced or finely chopped dishes. Perhaps we do save energy (but I need to burn more *haaa* so I don't get fat again).

Taurine -- I go to back to that. Unless one is eating raw meat/seafood or drinking raw goat/cow milk... where do we get it? It is a conditional essential amino acid. I don't know how it relates to malocclusion. There is a parasite risk for pregnant moms... evolution-wise -- maybe parasites were not significant that would preclude raw meat/seafood consumption...

Taurine is important for neurobio... it binds GABA. It lowers glucoses, BP, chronic pain, anxiety, reduces plaque and raises HDL2b. Works synergistically w/vit A and EPA DHA (which of course in nature occur together in grassfed meat and wild seafood like raw seal/whale).



Stephan, thoughts?

-G

Stephan said...

Hi G,

I don't know much about taurine at this point, I haven't looked into it. I do think it's interesting that many cultures have a tradition of eating raw meat in one form or another.

Robert Andrew Brown said...

Dr B.G. said


"Works synergistically w/vit A and EPA DHA (which of course in nature occur together in grassfed meat and wild seafood like raw seal/whale)."

Thanks fascinating - reading required (-:

4 books on taurine available in part on the web

http://books.google.com/books?id=F5T-34V5-D8C&pg=PA26&lpg=PA26&dq=taurine+brain+oxidation&source=bl&ots=srLhERS3ub&sig=Q1W7B3UDyyB7p5PTCsl7wJ0nq0o&hl=en&ei=_8ERS4TuLY334Aaf-aGVBA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAgQ6AEwAA#v=onepage&q=taurine%20brain%20oxidation&f=false

Ryan Koch @ Health Matters to Me said...

Gotta say, Steve-o, that I'm also skeptical of the influence that mastication and tough foods have on occlusion, but that's certainly some convincing evidence that you discovered!

My contention comes from a similar argument posted by Greg above, in that native cultures across the world seemed to enjoy softer, well-cooked foods rather than foods that required lots and lots of chewing. The only tough foods I can think of are dried meat, raw vegetables, and gritty, undercooked whole grains. I really don't consider tough meat a "chewy food," as meat could easily be softened in stews or through pounding -- and, if eaten raw, meat can be digested fully in the stomach when swallowed whole.

A documentary called The Hunters provides great footage of Bushmen of the Kalahari swallowing huge chunks of charred giraffe meat very, very quickly -- a few chomps and down the hatch.

One more thing: I get a little irked when archaeologists and athropologists suggest that cooking meat was an advantage to early humans after fire came along because it made it easier to chew than raw meat. These folks forget to take into account that a human being can gulp down meat like a wolf and digest it with little to no chewing at all. Over-mastication is not necessary or desirable.

Anyway, just some food for thought. Thanks for the post, Stephan!

Monica said...

"I think often the native cultures did understand what modern foods were doing to them, but they ate them anyway."

I think so, too. Price has an interesting part of his book, I think on the Torres Strait Islanders, describing how the natives revolted and attacked whites due to a government-placed food store on their island. There is another instance where a native trible (can't remember which) attacked a white village on the coastline because they felt it was cutting off their access to seafoods.

It does seem that they understood that modern foods were ruining their health. (Too bad this knowledge seems to have faded into obscurity among the general public and medical profession.) Some groups, it seems, took to these foods more readily than others. Many others had no choice.

gallier2 said...

Concerning mastication of hard stuff I can definitly say that bantu do chew very hard stuff. My wife and her son (and a lot others I witnessed from Gabon, Kenya and Comoros), bite chicken bones until they are completly ground. They also eat kaolinite (calaba) which are stones (not extremly hard but nonetheless). And some of the plants they eat are rather coarse. This doesn't change the fact that they enjoy also soft and sweet things.

gallier2 said...

Concerning mastication of hard stuff I can definitly say that bantu do chew very hard stuff. My wife and her son (and a lot others I witnessed from Gabon, Kenya and Comoros), bite chicken bones until they are completly ground. They also eat kaolinite (calaba) which are stones (not extremly hard but nonetheless). And some of the plants they eat are rather coarse. This doesn't change the fact that they enjoy also soft and sweet things.

Stephan said...

Hi Gallier2,

Thanks for that anecdote. Why do they eat kaolinite?

JD said...

Great article and comments.
I especially found this comment 'interesting'!
~~~~~~~~~~~~~~~
Dr. B G said...

My emphasis was food science for my bachelors in Nutrition

Taurine. Unless one is eating raw meat/seafood or drinking raw goat/cow milk... where do we get it? It is a conditional essential amino acid.

-G
~~~~~~~~~~~~~~~
Bravo to the Meat and Dairy Industrial Complex! It seems they have done an excellent job of biasing and misinforming both the public and the professionals - "Dr"'s, Nutritionist, Registered Dietitians... It seems they are still being fed a steady diet of meat and dairy - biases, mythology, propaganda, fallacies...

Can we "get" Taurine from non-meat and non-milk products?
I will guess that when you ask where can humans get Taurine (http://en.wikipedia.org/wiki/Taurine) from you also are considering the precursors/pre-synthesis nutrients the human body needs to create (synthesize) Taurine. e.g. Vitamin A synthesized from Beta-Carotene (http://en.wikipedia.org/wiki/Beta-Carotene).
So if someone asks where do humans "get" Vitamin A (http://en.wikipedia.org/wiki/Vitamin_A), one could correctly answer Beta-Carotene.
Fact: The adult human can produce it's own Taurine (synthesize/manufactured from cysteine when there is sufficient B6 present) when given a wide variety of protein sources (animal parts, secretions of mammary glands and yes vegetable (vegan as well) sources.
I am open to learning... Does anyone have any verifiable, unbiased, peer reviewed research that definitively concludes that humans on a vegan diet can not synthesize Taurine from plant based proteins?

JD Mumma, Ami.

Kirsten said...

Very helpful information as I make decisions for my daughter and her dental crowding. That graph is just what I needed to see. Her dentist recommended we start pulling teeth at age 6 1/2. We didn't listen.