Saturday, October 10, 2009

Malocclusion: Disease of Civilization, Part III

Normal Human Occlusion

In 1967, a team of geneticists and anthropologists published an extensive study of a population of Brazilian hunter-gatherers called the Xavante (1). They made a large number of physical measurements, including of the skull and jaws. Of 146 Xavante examined, 95% had "ideal" occlusion, while the 5% with malocclusion had nothing more than mild cro
wding of the incisors (front teeth). The authors wrote:
Characteristically, the Xavante adults exhibited broad dental arches, almost perfectly aligned teeth, end-to-end bite, and extensive dental attrition [tooth wear].
In the same paper, the author presents occlusion statistics for three other cultures. According to the papers he cites, in Japan, the prevalence of malocclusion was 59%, and in the US (Utah), it was 64%. He also mentions another native group living near the Xavante, part of the Bakairi tribe, living at a government post and presumably eating processed food. The prevalence of malocclusion was 45% in this group.

In 1998, Dr. Brian Palmer (DDS) published a paper describing some of the collections of historical skulls he had examined over the years (2):
...I reviewed an additional twenty prehistoric skulls, some dated at 70,000 years old and stored in the Anthropology Department at the University of Kansas. Those skulls also exhibited positive [good] occlusions, minimal decay, broad hard palates, and "U-shaped" arches.

The final evaluations were of 370 skulls preserved at the Smithsonian Institution in Washington, D.C. The skulls were those of prehistoric North American plains Indians and more contemporary American skulls dating from the 1920s to 1940s. The prehistoric skulls exhibited the same features as mentioned above, whereas a significant destruction and collapse of the oral cavity were evident in the collection of the more recent skulls. Many of these more recent skulls revealed severe periodontal disease, malocclusions, missing teeth, and some dentures. This was not the case in the skulls from the prehistoric periods...
The arch is the part of the upper jaw inside the "U" formed by the teeth. Narrow dental arches are a characteristic feature of malocclusion-prone societies. The importance of arch development is something that I'll be coming back to repeatedly. Dr. Palmer's paper includes the following example of prehistoric (L) and modern (R) arches:


Dr. Palmer used an extreme example of a modern arch to illustrate his point, however, arches of this width are not uncommon today. Milder forms of this narrowing affect the majority of the population in industrial nations.

In 1962, Dr. D.H. Goose published a
study of 403 British skulls from four historical periods: Romano-British, Saxon, medieval and modern (3). He found that the arches of modern skulls were less broad than at any previous time in history. This followed an earlier study showing that modern British skulls had more frequent malocclusion than historical skulls (4). Goose stated that:
Although irregularities of the teeth can occur in earlier populations, for example in the Saxon skulls studied by Smyth (1934), the narrowing of the palate seems to have occurred in too short a period to be an evolutionary change. Hooton (1946) thinks it is a speeding up of an already long standing change under conditions of city life.
Dr. Robert Corruccini published several papers documenting narrowed arches in one generation of dietary change, or in genetically similar populations living rural or urban lifestyles (reviewed in reference #5). One was a st
udy of Caucasians in Kentucky, in which a change from a traditional subsistence diet to modern industrial food habits accompanied a marked narrowing of arches and increase in malocclusion in one generation. Another study examined older and younger generations of Pima Native Americans, which again showed a reduction in arch width in one generation. A third compared rural and urban Indians living in the vicinity of Chandigarh, showing marked differences in arch breadth and the prevalence of malocclusion between the two genetically similar populations. Corruccini states:
In Chandigarh, processed food predominates, while in the country coarse millet and locally grown vegetables are staples. Raw sugar cane is widely chewed for enjoyment rurally [interestingly, the rural group had the lowest incidence of tooth decay], and in the country dental care is lacking, being replaced by chewing on acacia boughs which clean the teeth and are considered medicinal.
Dr. Weston Price came to the same conclusion examining prehistoric skulls from South America, Australia and New Zealand, as well as their living counterparts throughout the world that had adhered to traditional cultures and foodways. From Nutrition and Physical Degeneration:
In a study of several hundred skulls taken from the burial mounds of southern Florida, the incidence of tooth decay was so low as to constitute an immunity of apparently one hundred per cent, since in several hundred skulls not a single tooth was found to have been attacked by tooth decay. Dental arch deformity and the typical change in facial form due to an inadequate nutrition were also completely absent, all dental arches having a form and interdental relationship [occlusion] such as to bring them into the classification of normal.
Price found that the modern descendants of this culture, eating processed food, suffered from malocclusion and narrow arches, while another group from the same culture living traditionally did not. Here's one of Dr. Price's images from Nutrition and Physical Degeneration (p. 212). This skull is from a prehistoric New Zealand Maori hunter-gatherer:


Note the well-formed third molars (wisdom teeth) in both of the prehistoric skulls I've posted. These people had ample room for them in their broad arches. Third molar crowding is a mild form of modern face/jaw deformity, and affects the majority of modern populations. It's the reason people have their wisdom teeth removed. Urban Nigerians in Lagos have 10 times more third molar crowding than rural Nigerians in the same state (10.7% of molars vs. 1.1%, reference #6).

Straight teeth and good occlusion are the human evolutionary norm. They're also accompanied by a wide dental arch and ample room for third molars in many traditionally-living cultures. The combination of narrow arches, malocclusion, third molar crowding, small or absent sinuses, and a characteristic underdevelopment of the middle third of the face, are part of a developmental syndrome that predominantly afflicts industrially living cultures.


(1) Am. J. Hum. Genet. 19(4):543. 1967. (free full text)
(2) J. Hum. Lact. 14(2):93. 1998
(3) Arch. Oral Biol. 7:343. 1962
(4) Brash, J.C.: The Aetiology of Irregularity and Malocclusion of the Teeth. Dental Board of the United Kingdom, London, 1929.
(5) Am J. Orthod. 86(5):419
(6) Odonto-Stomatologie Tropicale. 90:25. (free full text)

16 comments:

Inphidel said...

Thank you Stefan. This is great info once again.

Is there any info on the Xavante's diet?

Steve Parker, M.D. said...

Wow. Great article. I'm glad you addressed the genetic argument. Not sure why the people eating sugar cane didn't have caries.

-Steve

Aidyn said...

Thanks for the article!

Anna said...

This doesn't pertain to humans, but I was reading your post while my husband was watching a National Geographic TV show that featured a zoo gorilla, and it was mentioned that she was born in a zoo and bottle fed because her mother wouldn't nurse her. Did you run across any data on malocclusion in bottle-fed non-human primates (or other animals), Stephan?

Marnee said...

A properly aligned jaw and teeth is terribly undervalued. I wish my teeth were still straight. They look fine but I can tell. Chewing is very difficult -- especially the tearing apart of meat (I eat raw sometimes and have to cut it up like I'm 5). Before I went 0 carb I had jaw pain and rotting gums, no more. I'm only 32! But, if carbs cause malocclusion that is reason enough to never eat them.

Stephan Guyenet said...

Hi Inphidel,

Yes, I have some information on their diet. I'm going to post it at some point. It's hunted and gathered, mostly starchy roots but also animal foods and some fruit.

Hi Anna,

Great question. I found this:

http://www3.interscience.wiley.com/journal/109705291/abstract

Hi Marnee,

I doubt carbohydrate causes malocclusion, unless it's eaten to the exclusion of other types of food.

trix said...

Fascinating info. Thanks.

Mike said...

It seems likely it's more fruitful to ask what's *not* there in the diet when things go wrong.

So far as "starchy" foods go, it doesn't seem that, for example, the isolated Swiss mentioned by Price were exactly avoiding these, since rye bread was one of their staples. And they had very good teeth and well-formed faces. They did not, of course, eat bread *instead of* other important foodstuffs.

There's an interesting article here where a dentist says when cutting he can feel how hard people's teeth are. Whenever he's noticed an extreme of hardness or softness, he asks the patient about his upbringing and diet. Those with hard teeth:

"... were more often born and raised on farms, but also in large cities or small towns where they ate fresh-cooked and raw foods that were freshly obtained from the farm or the garden. They generally started out in life breast-fed and not bottle-fed. The milk consumed in childhood was, without exception, raw and not pasteurized."

http://www.westonaprice.org/archive/silverman.html

Helen said...

@ Steve Parker -

From what I understand, the micronutrients in sugar cane (and probably the fiber, too) protect against caries and help the body metabolize glucose. For instance, sugar cane has significant amounts of chromium, if I remember correctly.

jon w said...

interesting about sugar cane. recently I did 2 wks of field work in an area with a lot of sugar cane and tried it. the jaw workout of stripping the outer "bark" and biting off chunks kept me to just a couple segments a day. but interesting thing was after chewing it to release the juice, then spitting out the mouthful of pulp, my teeth had that clean polished feeling you get after a good brushing. but as soon as you get somebody with a handcranked mill selling plastic bags of the stuff to schoolkids you'd lose that scrubbing effect.

Ken said...

Are malocclusions more prevalent and severe now? A comparative study of medieval skulls from Norway.

"This study indicates a significant increase in both the prevalence and the severity of malocclusions during the last 400 to 700 years in Oslo, Norway."

OK I am converted to the idea that a modern diet can produce malocclusion, however the paper goes on to to say

" Furthermore, although no sex differences were found in the modern sample, females had both a higher prevalence of malocclusions and more severe malocclusions than did males in the past".

So the malocclusion due to modern diet is obscuring the focus of the genetically caused malocclusion in Europeans.

The sexual selection hypothesis was of selection women for feminine looks (ie small face and jaws) which carried male faces to a more feminine norm as a byproduct. That women had more malocclusion way back when suggests it was they who were the focus of selection for something about their jaws. And of course the
first known impacted wisdom tooth was in a woman.

A modern diet can produce malocclusion, however I am not so sure that modern Europeans' high incidence of it is entirely due to their food. The dental arch is going to be affected by the breadth of the face

Xavante certainly don't suffer from a "characteristic underdevelopment of the middle third of the face". Not to put too fine a point on it they've faces which are particularly broad at the cheekbones. I still think that is genetic.

Ryan Koch said...

Good stuff, Stephan.

The latest Weston Price Foundation journal gets into the subject of malocclusion as well. One facet of this condition I find interesting is the effect of malocclusion on the overall health of human beings.

For example, an article in the WAPF journal is called From Attention Deficit to Sleep Apnea: The Serious Consequences of Dental Deformities. One study referenced in the article suggests that the degree of malocclusion in an individual can accurately predict intelligence levels(1).

Also interesting is the vast difference expansion appliances can make in cases of malocclusion. A British study is referenced about a set of twins in which one twin receives palate expansion while the other does not. The difference is striking! (2)

By the way, Stephan, did you know that the WAPF journal referenced your blog? Check out page 51 of the Summer 2009 journal in a sidebar about linoleic acid and thyroid suppression.

(1) Fonder, A. The Dental Physician. Rock Falls, IL: Medical-Dental Arts, 1985, pp. 339-350.

(2) Eirew, H. An orthodontic challenge. International Journal of Orthodintics, Volume 14, 1976, p. 24.

Stephan Guyenet said...

Hi Jon,

That's a good point. Sugar cane is fibrous and is probably pretty good at removing plaque, even though it's full of sugar.

Hi Ken,

Interesting paper. The medieval teeth had a lot of attrition. I agree with you 100% that genes influence skull shape, including width of the face. Different races clearly have their own characteristic skull shapes. I agree that the Xavante have particularly broad faces and there's likely to be a genetic component to that.

Just a personal observation though: I've noticed that broad faces don't always travel along with broad arches. I'm no longer surprised when I see people with apparently well-developed faces and narrow, crowded arches. I took a look at a friend's arch the other day, expecting it to be broad because he has a broad and well-formed face, but it was narrow. Same with a former co-worker of mine.

When I referred to an underdevelopment of the middle third of the face, I was talking more about the depth than width. Binder's syndrome patients have "dished" faces, but they aren't necessarily narrow overall.

Hi Ryan,

That's cool that they referenced my post!

The more I learn about malocclusion and facial development, the more I agree that it affects many other things. It affects breathing, which affects posture, oxgenation, physical capacity, and influences occlusion itself. It affects chewing and swallowing, breast feeding, and probably susceptibility to sinus infection. I'm going to look up the second reference you posted, thanks.

gabi said...

Ken,

more recent orthodontic studies of Swedish and Norweigian children indicate that non-nutritive sucking habits, such as digit sucking is more prevalent among females than males. It would appear that at about 18 months of age the incidence of digit sucking increases but only (with the exception of one small south-western Swedish community) among girls.

I speculate that this has to do with societal behaviour: I.e. boys also learn to speak later than girls. Boys are generally potty trained and out of diapers later than girls.

Possibly the needs of boys are more readily met by their caregivers than the needs of girls.

For some reason, look at places in the world like India, Pakistan, Afghanistan, China etc. etc. and even in Europe, boys have a higher value than girls. It wouldn't be all that surprising if boy children, even in Europe, get more attention than girls. And thus have less need to comfort themselves through digit sucking than girls.

Matt Stone said...

Stephen,

This series, as always, is so friggin' awesome. I do a lot of hiking in the area in which I live and come across tons of animal skulls. I've yet to see a crooked tooth in many years of paying very close attention. It only stands to reason that we once were part of that club too. The only crooked tooth I've seen on a "wild" animal is at Yellowstone Lake Lodge - a bear's head on display, and the malocclusion is almost imperceptible. But note, it was a Yellowstone bear - a human garbage eater for sure.

Of course sugarcane doesn't cause cavities. Neither does fruit, grain, tubers, or other unrefined carbohydrate foods. Residue on the teeth is inconsequential, as are temporary postprandial rises in blood sugar. I'm supporting that now on my current dietary experiment. I'm not even bothering to brush my teeth as usual.

Stephan Guyenet said...

Thanks Matt, from what I've read it does seem like malocclusion is rare in wild animals-- including "wild humans".