Tuesday, September 29, 2009

Malocclusion: Disease of Civilization

In his epic work Nutrition and Physical Degeneration, Dr. Weston Price documented the abnormal dental development and susceptibility to tooth decay that accompanied the adoption of modern foods in a number of different cultures throughout the world. Although he quantified changes in cavity prevalence (sometimes finding increases as large as 1,000-fold), all we have are Price's anecdotes describing the crooked teeth, narrow arches and "dished" faces these cultures developed as they modernized.

Price published the first edition of his book in 1939. Fortunately,
Nutrition and Physical Degeneration wasn't the last word on the matter. Anthropologists and archaeologists have been extending Price's findings throughout the 20th century. My favorite is Dr. Robert S. Corruccini, currently a professor of anthropology at Southern Illinois University. He published a landmark paper in 1984 titled "An Epidemiologic Transition in Dental Occlusion in World Populations" that will be our starting point for a discussion of how diet and lifestyle factors affect the development of the teeth, skull and jaw (Am J. Orthod. 86(5):419)*.

First, some background. The word
occlusion refers to the manner in which the top and bottom sets of teeth come together, determined in part by the alignment between the upper jaw (maxilla) and lower jaw (mandible). There are three general categories:
  • Class I occlusion: considered "ideal". The bottom incisors (front teeth) fit just behind the top incisors.
  • Class II occlusion: "overbite." The bottom incisors are too far behind the top incisors. The mandible may appear small.
  • Class III occlusion: "underbite." The bottom incisors are beyond the top incisors. The mandible protrudes.
Malocclusion means the teeth do not come together in a way that's considered ideal. The term "class I malocclusion" is sometimes used to describe crowded incisors when the jaws are aligning properly.

Over the course of the next several posts, I'll give an overview of the extensive literature showing that hunter-gatherers past and present have excellent occlusion, subsistence agriculturalists generally have good occlusion, and the adoption of modern foodways directly causes the crooked teeth, narrow arches and/or crowded third molars (wisdom teeth) that affect the majority of people in industrialized nations. I believe this process also affects the development of the rest of the skull, including the face and sinuses.


In his 1984 paper, Dr. Corruccini reviewed data from a number of cultures whose occlusion has been studied in detail. Most of these cultures were observed by Dr. Corruccini personally. He compared two sets of cultures: those that adhere to a traditional style of life and those that have adopted industrial foodways. For several of the cultures he studied, he compared it to another that was genetically similar. For example, the older generation of Pima indians vs. the younger generation, and rural vs. urban Punjabis. He also included data from archaeological sites and nonhuman primates. Wild animals, including nonhuman primates, almost invariably show perfect occlusion.

The last graph in the paper is the most telling. He compiled all the occlusion data into a single number called the "treatment priority index" (TPI). This is a number that represents the overall need for orthodontic treatment. A TPI of 4 or greater indicates malocclusion (the cutoff point is subjective and depends somewhat on aesthetic considerations). Here's the graph: Every single urban/industrial culture has an average TPI of greater than 4, while all the non-industrial or less industrial cultures have an average TPI below 4. This means that in industrial cultures, the average person requires orthodontic treatment to achieve good occlusion, whereas most people in more traditionally-living cultures naturally have good occlusion.

The best occlusion was in the New Britain sample, a precontact Melanesian hunter-gatherer group studied from archaeological remains. The next best occlusion was in the Libben and Dickson groups, who were early Native American agriculturalists. The Pima represent the older generation of Native Americans that was raised on a somewhat traditional agricultural diet, vs. the younger generation raised on processed reservation foods. The Chinese samples are immigrants and their descendants in Liverpool. The Punjabis represent urban vs. rural youths in Northern India. The Kentucky samples represent a traditionally-living Appalachian community, older generation vs. processed food-eating offspring. The "early black" and "black youths" samples represent older and younger generations of African-Americans in the Cleveland and St. Louis area. The "white parents/youths" sample represents different generations of American Caucasians.


The point is clear: there's something about industrialization that causes malocclusion. It's not genetic; it's a result of changes in diet and/or lifestyle. A "disease of civilization". I use that phrase loosely, because malocclusion isn't really a disease, and some cultures that qualify as civilizations retain traditional foodways and relatively good teeth. Nevertheless, it's a time-honored phrase that encompasses the wide array of health problems that occur when humans stray too far from their ecological niche.
I'm going to let Dr. Corruccini wrap this post up for me:
I assert that these results serve to modify two widespread generalizations: that imperfect occlusion is not necessarily abnormal, and that prevalence of malocclusion is genetically controlled so that preventive therapy in the strict sense is not possible. Cross-cultural data dispel the notion that considerable occlusal variation [malocclusion] is inevitable or normal. Rather, it is an aberrancy of modern urbanized populations. Furthermore, the transition from predominantly good to predominantly bad occlusion repeatedly occurs within one or two generations' time in these (and other) populations, weakening arguments that explain high malocclusion prevalence genetically.

* This paper is worth reading if you get the chance. It should have been a seminal paper in the field of preventive orthodontics, which could have largely replaced conventional orthodontics by now. Dr. Corruccini is the clearest thinker on this subject I've encountered so far.

34 comments:

Helen said...

Hi Stephan,

Thanks again for a great post. I've been thinking about this, since I became a breastfeeding mother of twins shortly before becoming Weston A. Priced.

I did some research a while ago on breastfeeding and facial development and found that it has a huge impact. This in no way negates the nutritional theory (in fact, K2 and A are abundant in breast milk), but adds a necessary angle. Cultures often drop, or shorten the length of, breastfeeding as they modernize.

I'd like to see a breakdown, though it simply may not be available, comparing the dental health of cultures that retained "extended" breastfeeding (a year or more) while adopting a more westernized diet, to those that did not.

Here are a few sources.

http://www.brianpalmerdds.com/bfeed_oralcavity.htm

http://www.highbeam.com/doc/1G1-200921814.html

http://www.ncbi.nlm.nih.gov/pubmed/17645045?ordinalpos=4&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum

I also saw on PubMed an article by one Pottenger, F.M., on this subject, from 1950, which had no abstract.

So far, my daughters, at 19 months, have great occlusion and wide dental arches, in marked contrast to their mother (bottle-fed).

Jim de Wit said...

Stephan,

Great stuff. I've always wondered who if anyone did a serious follow-up on Price's work. Looking forward to your next post.

BTW, ever since reading Price I've been curious if developmental deformations of the skull could explain near/far sightedness. So I finally did a little searching just now and found an article citing research that argues high carb intake during childhood and the resulting high insulin levels cause elongation of the eye ball. So maybe not a skull deformation, but still looking like a disease of civilization.

Here's my favorite part: The mainstream view holds that genetics and basically studying too much are to blame for modern man's high rate of myopia. However, people like the Vanuatu islanders, who eat a traditional (low-carb) diet and have mandatory schooling for 8 hours a day, have a very low incidence.

http://news.bbc.co.uk/2/hi/health/1909075.stm

I'd love to read more on this topic from you if you find the time to dig into it someday. I apologize in advance if you already have - I'm new to your site.

Cheers!

Mike said...

"... ever since reading Price I've been curious if developmental deformations of the skull could explain near/far sightedness."

Goodness, yes. That seems more than likely.

Here is a dentist writing at the WAPF:

"The entire floor of the orbit or eye sockets, where the visual globes or the eyeballs are housed, is made up of the upper jaw or maxilla. When the maxilla is not well developed, and the face is long and skinny, the eye sockets do not develop properly; the eyeballs cannot develop as a sphere, but may take on a football shape. The resultant developmental pattern can create various ophthalmic issues such as astigmatism or myopia. "

http://www.westonaprice.org/healthissues/facial-development.html

It's really quite tragic. How many people in modern industrialized countries have to put up with crowded and crumbling teeth, poor eyesight, and - doubtless - asthma from constricted airways?

Take Wikipedia on the Australian author Patrick White for a not unusual description of the health of a modern person:

"White developed asthma ... White’s health began to deteriorate—his teeth were crumbling, his eyesight was failing, and he had chronic lung problems ..."

And yet, as Price showed, the Aborigines, living in that same land, and without the advantages of modern technology, were able to maintain a state of health that "command[s] our most profound admiration".

Robert Andrew Brown said...

Another great find Stephan - and I have a feeling Omega 6 has a part to play in this somewhere.

Food alters gene expression and gene expression is heritable.

gunther gatherer said...

Hi Stephen.

If bad diet and dietary changes are responsible for misalignment and improper growth of jaw, facial and bone structure, there's probably a good deal more to be discovered about what it does to the structures, shapes and functions of the organs themselves.

Francis Pottenger,Price's like-minded contemporary, did a series of experiments feeding raw food to cats. In "Pottenger's Cats", he shows their degradation in health after one generation of cooked food feeding. After 4 generations, he claims they couldn't even breed. He also claims it took about 3 generations of feeding them raw organs to bring them back to their natural state of robust health.

Did you happen to read Pottenger too then? I'd be really interested in your take on his findings. Perhaps raw foods also have a part to play in all this.

Jenny said...

You have a much simpler explanation for malocclusion: the decline of infant nursing that comes with a Western Lifestyle. Unless that is factored into the discussion, I find the conclusions hard to take seriously.

All the traditional peoples you cite who had good tooth arches nursed on demand for about three years per child. The mechanics of nursing are very different from those of bottle feeding.

Even where nursing continued in the modern era, it tended to be done with a more rigid non-demand pattern and most importantly, children were weaned early--often at a year. This makes a huge difference in dental outcomes.

epistemocrat said...

"I believe this process also affects the development of the rest of the skull, including the face and sinuses." This is true.

Gunther Gatherer, my ancestor, Dr. Francis M. Pottenger, Jr., did indeed add valuable insights to this conversation.

That is how the Price-Pottenger Nutrition Foundation got started in 1952, communicating the work of both Weston Price and Francis Pottenger as a wonderful hybrid of insights.

PPNF
http://www.ppnf.org

Andy said...

I have class 2 occlusion. I can barely see my lower teeth when I bite my jaws together, they are behind my upper teeth.

I am 15 years old, 188 cm, weigh 75 kg and I live in Eastern Europe. I eat about 4 eggs every day, 400 g of pork similar to bacon and at least 50 g of butter a day, among other things, so I think I should get enough K2. I avoid wheat. I started eating like this a couple of months ago. Is there any hope my occlusion will improve over time?

They don't sell appropriate doses of vitamin D here, only 400 IU tablets, otherwise I would take it.

Mike said...

"Is there any hope my occlusion will improve over time?"

I'll bet not. Price seems to conclude that it's not just the individual's diet as he's growing that's relevant but the diet of the mother during pregnancy and lactation - and even before conception.

He points out in a number of places in _Nutrition and Physical Degeneration_ that many primitive peoples feed girls special mineral-and-vitamin-rich diets for six months before they allow them to marry. Some of the cattle herders were an exception - but their diet was so rich anyway that mothers-to-be didn't need any extra help. Some of these groups also practised wide-spacing of births to allow the mother to recuperate biologically between pregnancies.

http://journeytoforever.org/farm_library/price/pricetoc.html

I don't know what Stephan has to say but a reasonable hypothesis would seem to be that what counts is a good supply of important minerals, like calcium and phosphorus, in the diet. It's those that are used for building teeth and bone. As well as that, it's likely necessary to have a good supply of animal fat in the diet so that fat-soluble vitamins are there in abundance. You can't utilize calcium in the diet if you haven't got vitamin D there in sufficient quantity.

AFAIK, some of the best teeth of all were found among the Eskimo. It's perhaps worth noting that their diet contained a lot of seafood, which tends to be rich in minerals. One wonders whether eating a percentage of the food raw is of importance here, also, as others have suggested in this thread. It's again interesting to note that "Eskimo" is an Algonkian Indian word meaning "The Eaters of Raw Flesh".

Anna said...

I think Jenny brings up a good point about the prolonged on-demand breastfeeding. It could be an important piece of the puzzle in addition to the nutrition.

I've been researching orthodontics for my 11 yo son for over two years, because he has an overbite. The overbite was more pronouced about two years ago, but has somewhat improved on its own as new permanent teeth have come in (in hindsite, I'm glad we didn't do the first phase to bring in his front teeth to protect them from damage). But I don't think his bite will entirely self-correct at this point, despite only grassfed butter in the house, no gluten, minimal sugar, and low omega 6 intake. Yes, I also now wish I had breast-fed him 10 past months (but he was eating so much solid food by then, the nursing "snacks" seemed unnecessary to both of us); I didn't know about his gluten intolerance until last year; and our dietary transition toward away from so many processed foods and grains to more nutrient dense foods didn't start until he was already 5-6 yo, but that's all water over the dam now, eh?.

I've consulted with several orthodontists already. They all show after pictures of So Cal kids with the same cookie-cutter smiles I see all over San Diego, which look incredibly unnatural to me - too straight, pinched, and sort of rodent-like. Looking at the orthodontic mouths move on the kids I see every day is like watching a bad toupee wiggle - that's not what I want done to him. My focus is less on the cosmetic "straight, uniform teeth" aspect and more on the function and overall health ramifications of his teeth, mouth, and face for the rest of his life, which doesn't seem to be addressed very well by the orthodontists I've consulted.

My husband's overbite clearly has created issues for him with biting, chewing, impaired breathing during sleep, etc. He had orthodontics in his late 30s, but didn't do the recommended jaw break procedure; his didn't get a broken retainer replaced when we moved and his teeth have shifted back. I'd like to make sure our son doesn't have the same problems my husband has experienced.

My bite is mostly ok cosmetically and reasonably functional, but I had terrible TMJ headaches in young adulthood (both my husband and I were breast-fed, but like our son, it wasn't long-term; we all were weaned when we could drink from a cup). I haven't had orthodontics, but I did need to have impacted wisdom teeth extracted, so I'm pretty sure my dento-facial development isn't perfect, either. I do experience sleep apnea, but it mostly shows up when my thyroid hormone dose needs a seasonal adjustment up as the days become shorter.

Yesterday I followed a link in a NYT article comment by for NYC dentist who specializes in correcting airway and breathing problems - http://doctorstevenpark.com. His blog about breathing and sleep was interesting. Then I followed a link from his site which led me to this website: www.facefocused.com/proporpos.html. Lo and behold, there's Price and Corruccini mentioned. I still have a lot to look over on the website, but overall, I like how this orthodontist is not only focussed on straightening teeth but also on facial structure and function for good overall breathing and health. Heck of a drive, though... ;-)

I'd love to know what impressions Stephan and the readers have of this approach to orthodontics. I have very little personal experience with orthodontics, as my siblings and I all had teeth straight enough (& parents poor enough) to escape orthodontics, though we didn't escape a few malocclusion issues. My mother on the other hand, has always been complimented by dentists on her perfect bite, and every time she would see a new dentist they would comment and ask who did the work. Her proud reply was always, "Mother Nature". We didn't escape the cavities, despite regular dental care, but my son seems to be escaping those so far.

Robert McLeod said...

I would guess that once you are past puberty you are pretty much stuck with the face and jaw you have.

shel said...

to me, this is almost staggering. have researchers actually stood back and considered the implications of this, and how many areas of modernism this encompasses?

shouldn't this stuff be on the mainstream's front burner, even as a scientific curiosity?

...or is it just a simple case of ignoring fat soluble vitamin research because it's "old fashioned", uninteresting, or not pc?

Stephan Guyenet said...

Hi Helen,

I'm going to comment on breast feeding. I also think it has an impact. My view has broadened since I wrote my original post on maxillonasal development.

Hi Jim,

Right now, I have a little bit to say about vision. I'll mention it in passing in this series. This is another topic where there's a lot of information out there and I could really dive into it. I may at some point. I'm fortunate to know a couple of people who are at the cutting edge of research into vision problems at the University of Washington.

Hi Gunther,

I absolutely agree with what you said about nutrition/lifestyle changes potentially affecting other organs in ways that are more difficult to detect.

I'm not convinced that a 100% raw food diet is ideal for humans, but it's probably good to eat some raw food. Practically every traditional culture has a tradition of eating some amount of raw/fermented vegetables and/or meat.

Hi Andy,

I doubt it, but it's worth a try. Since you're eating nutrient dense food already, you might try eating tough foods regularly: beef jerky, raw carrots, tough cuts of meat, etc. If your midpalatal suture hasn't totally fused yet, that might have a chance of changing your occlusion somewhat. I'm not totally clear on the developmental timeline at this point.

Hi Anna,

It looks to me like the guy has a good perspective. Good occlusion is definitely worth more than just aesthetics.

Jenny Light said...

I'm glad you are going to post re: breastfeeding, as I believe it definately has alot of bearing on this subject!

My eldest son (now 13), was breastfed until he was 2 1/2 years old (on demand), with cereals introduced at about six months, and table food at about 9 months. He required orthodontic work due to sucking his finger, as it caused some crowding and stunted one of his teeth. His arch development is good, but not like that of his brother....

My youngest boy (now 9) was exclusively breastfed on demand until the age of one, and continued on demand (with table food) until he was 4 1/2. He has fantastic wide arches, and had plenty of space between his baby teeth with absolutely no crowding.

I never once purchased jarred baby food or formula for either of them. Neither boy has ever been fed soda or juice, and as a result they have nice white tooth enamel.

sverlyn said...

Stephan,

OT, but do you think that eating wheat in the sprouted bread form ( Ezekiel, etc ) mitigates the problems with the grain?

Thanks

Anna said...

In case anyone wants to read more about orthotropics and malocclusion:

www.orthotropics.com/references/bibliography_main.html

I see Corruccini has an earlier paper listed in the bilbiography at that link, though it is focussed on India.

Dane Miller said...

Stephan, I believe there is a write up in the newest Wise Traditions about this topic as well.

www.GarageStrength.com

Stephan Guyenet said...

Hi Sverlyn,

I'm sure it's better than regular non-sourdough bread.

Hi Dane,

I wish I got that.

Lacey said...

Stephan,

If you want to get the Wise Traditions periodical, just let me know. I will gift you a membership to WAPF. Just send in the form on their web site and write that the payment is being sent separately. It would be a small token of appreciation for some of the insights I've gotten from your site.

I have found reading Wise Traditions very interesting and educational, but there are a few elements that strike me as odd. One is the editorial view on homeopathy, which is very positive. Seems out of place given the more logical and evidence-based view of most other topics.

In any case, just say so and I will send the form. I don't have your address, so you will need to send in a form as well.

Regards,
Lacey

Stephan Guyenet said...

Hi Lacey,

I appreciate the offer, but I'm not a WAPF member for a reason. I sympathize with and respect their mission, but I don't want to be labeled as a WAPF adherent. It's very important for me to project an image of impartiality, because there's so much bias floating around in the world of health and nutrition that people are very sensitive to it. Rightfully so. At this point, I have no vested interest except in understanding health/nutrition and passing on the knowledge. I want there to be no doubt about that.

Also, I don't know where my career will lead, and I don't want to be associated with some of the less scientific elements of the WAPF (that Weston Price himself would probably have scoffed at).

Lacey said...

Understood. There are definitely a few elements that, as I said above, strike me as odd. For me, I think the good nuggets of information and the value of considering different perspectives have been worth the effort of sifting through all the other stuff. BTW, you can order copies of the periodical without being a member. I think that works out to be a little more expensive, though (IIRC).

Ken said...

Female face shape and sexual selection.
"Europeans have an evolutionary history going back some 35,000 years on their continent. And this was when and where they evolved their current physical appearance: the shape of their face, the color of their skin, hair, and eyes; the length and form of their head hair. To understand why Europeans look the way they do, we should understand how their environment of sexual selection differed from that of tropical humans".

According to 'Shape analysis' - "Attractivness is not coincident with exaggeration of sexual dimorphism, but is associated with a specific pattern of shape variation, particularly in the jaw"

Mammoth "luau-style" 29,000 B.C.
"The meats were cooked luau-style underground. Svoboda said, We found the heating stones still within the pit and around."

The presence of "heating stones" and "boiling pits" clearly indicates that (nice and tender) slow cooked meat was being eaten by 29,000 BC, therefor changes to the shape of jaws and dental crowding ought to have first shown up 14,000 years before they actually did if softer food had anything to do with those changes.

As you know the first evidence for an impacted wisdom tooth is 13,000 to 15,000 years old.

Dental crowding in a prehistoric population.
"All of the mandibles presented incisor crowding with a majority of minimal and moderate irregularities, but in seven cases there were extreme irregularities and in two canine impaction was observed. These results are in contrast with the literature where it is reported that malocclusions were rare in prehistoric populations. The findings of this study suggest that crowding may be of a genetic origin and might not be caused by excessive tooth size or changes in environmental factors (masticatory activity)."

Robert Andrew Brown said...

Ken thanks

Your link

http://ejo.oxfordjournals.org/cgi/reprint/26/2/151.pdf

suggest the population were farmers and sheep breeders.

Omega 6 from grains could be a factor. Omega 6 has a part in the control of bone formation.

Was this an inland population. Where did they get their Omega 3 from.

Are there any mineral deficiencies in the region?

Ken said...

Even the proponents of the soft food theory like Robert Corruccini accept the genetic factors are not equally distributed.

Bioarchaeology: interpreting behavior from the human skeleton
"To be sure, some populations appear to have a genetic predisposition for occlusal abnormalities (see Corruccini, 1991)."

Malocclusions are most common in Europeans but that has probably been true for 15,000 years. Patterns of correlation between genetic ancestry and facial features suggest selection on females is driving differentiation So malocclusion likely stems from a time of intensive sexual selection of women for feminine looks (ie delicate features and smaller jaws). Civilisation's soft food can make things worse I'll grant you.

Joanne at Open Mind Required said...

Genetics must also play a strong role in facial formation. I have three older siblings (a sister from father 1, two brothers from father 2, and me, father 3).

My parents and my siblings have RH- blood and I am RH+ (which was how I found out I must have had a different father). My siblings had horribly crooked teeth. My brother, a couple years older than me, had teeth growing out the side of his gums because of the crowding.

I was bottlefed and sucked my thumb for years, and yet I have beautiful teeth. (I was also the only one who escaped severe acne that plagued everyone.)

At 19 years, an Army dentist filled all my molars and pulled my wisdom teeth. I'll never know if it was necessary or if he was just practicing on me.

Ed said...

Regarding cats and cooked food, I think the answer turned out to be really simple. Cooking breaks down taurine, which cats don't synthesize and can't live without.

http://www.vetlord.org/taurine-is-essential-for-cats/

I think the whole Pottinger experiment with cats & cooked food is mildly interesting, at best. I'm unsure about what lesson to draw from it, other than the general concept of sticking to a diet with which an organism has evolved.

Constantine said...

Although Price downplayed it, I still believe that, at least with Europeans, the mixing of groups with differing physical traits is one of the pieces of the puzzle. Maybe not the main piece, but a significant one nonetheless.

The early "hunter" Europeans, for instance, often had very large heads and faces, large teeth, high cheek bones, salient ridges, etc.

Successive waves of later, "farmer" Europeans were (in the initial stages, at least) clearly of people with more gracile features: smaller teeth and jaws, rounded/smaller faces, smaller skulls and bodies.

The skull shapes of earlier vs. invading Europeans were often diametrically opposed, the former often being broad headed while the latter long.

It's not hard to imagine how a cocktail like this would produce some people with disharmonious facial features (and crooked teeth).

Also, I would think that urban areas would amplify this process, since cities tend to attract and concentrate people of disparate ethnicities.

Ed said...

Constantine,

"Successive waves of later, "farmer" Europeans were (in the initial stages, at least) clearly of people with more gracile features: smaller teeth and jaws, rounded/smaller faces, smaller skulls and bodies."

How much of that was genetic, and how much environmental? If they were getting less vitamins A, D, K, and fewer minerals (due to phytates) from their grain diet, I think it is plausible that their bone structures were malformed vs. the potential provided by their genetic blueprint.

Not to mention their whole bodies were probably smaller due to less protein intake.

I suppose that is difficult to know, and your hypothesis might have something to add to the situation, but there is a reason Price downplayed it, and that was that the facial malformation of mixed-blood children varied by diet, not by genetic mix (in his observations anyway).

Personally, I have a long face, and as a teenager I had a palate expander installed:

http://www.haasortho.com/site.cfm/Appliances.cfm

One one-quarter crank in the morning, one one-quarter crank in the evening! Sort of a torture device but it didn't really hurt :-)

I had cross-bite, which was basically overbite on one side and underbite on the other. In college I had jaw surgery.

My parents families were full of wide faces and teeth that fit, but my mother became slavishly devoted to margarine, low fat chicken and milk, and whole wheat, so that's what my sister and I ate (my sister also had jaw surgery to correct severe malocclusion.)

Now my children, who receive whole milk, vitamin D and K supplements, etc, are growing up with wide faces that looks gorgeous. Wide spaces between their baby teeth, plenty of room for adult teeth.

Fundamentally it does not seem totally implausible that genetic factors might be at play, but when you see (through personal experience and reading of others experiences) just how rapidly (one generation) and dramatically facial structure can be altered, I get the feeling that the genetic effect is swamped by the environmental effect.

Stephan Guyenet said...

Hi Constantine,

That's basically the "tooth size-jaw size dysharmony" theory.

The problem with the theory is that genes don't dictate the absolute size of body parts. Tissues develop relative to one another, and the whole process is plastic. That's why you never see someone with Shaquille O'Neil-sized feet on a Tom Cruise-sized body.

The other problem with the theory is that genes for body part size don't segregate independently, i.e. you probably can't separate the "big jaw allele" from the "big teeth allele", because neither of them exists as an independent entity.

This makes sense from an evolutionary standpoint, because it's a system that can accommodate genetic mixing. Imagine if you had a brain size-skull size dysharmony where the brain were too big for the skull... that would be bad news. So the way the body works is the skull grows to accommodate the brain, whether it ends up being small or large.

I'm sure there are genetic factors that influence the susceptibility to malocclusion during exposure to abnormal stimuli. But I doubt they would create malocclusion in the proper context.

Constantine said...

Ed and Stephan,

Good stuff...thanks. Yeah, I totally agree that nutrition has a lot to do with it in probably most people and most cases; that's why I've been so interested in Price's work. But I can't escape the feeling that it's not the whole story....

Stephan,

I'm new to genetics (and am catching up) but was writing under an intuitive assumption that genes "scale." I was thinking along even more qualitative lines.

A couple of dentists have said that overbites are associated with dolichocephaly (a long skull). I've never heard of dolichocephaly itself being a result of bad nutrition. It was even more prevalent among ancient peoples pre-agriculture. I've heard dog breeders say the same about their long-headed dogs. And that the really brachycephalic (wide headed) dogs would often have the opposite condition (underbite).

It's just really interesting to me, I guess. Imagine a big brute of a hunter with exaggerated features getting "warped" by dolichocephaly. LOL

Stephan Guyenet said...

Hi Constantine,

I'm definitely willing to believe that the susceptibility to malocclusion is influenced by genetics; it would be very surprising if it weren't. Dolichocephaly may be one of these factors, but it doesn't mean it will doom you to an overbite under good circumstances.

I don't think nutrition is the whole story either. How you use your jaws during development is critical as well.

MangoManDan said...

Like Anna, I've read some of Dr. Price's thoughts. He has stated that the anatomical features that make one more susceptible to sleep apnea have become more common in the last couple hundred years.

Perhaps the same nutritional changes that may have led to smaller jaws in relation to number of teeth have also led to the rise in apnea. (Sleep apnea is not limited to overweight middle-aged men.)

Freybell said...

Dr. Kate Shanahan (M.D.) includes Weston A Price's findings in her book 'Deep nutrition' and explanes well why she thinks modern diets cause malocclusion. A great read!
http://drcate.com/deep-nutrition-the-ancient-science-of-human-engineering/

balor123 said...

No kidding on the overweight men comment. I'm 5'9" and 165lbs and I have an AHI of 50. I have a slight underbite (and open bite) with a 10.5mm airway too! It was fine until late teens, though I probably had sleep apnea already. Seems my upper arch is very high and narrow, despite orthodontics. My parents are immigrants so I ate relatively well as a kid but my mom is a carboholic and I was bottle fed. Apparently they let me suck on the bottle to pacify me. Looking into double jaw surgery now, mostly to save my teeth (sleep apnea is likely beyond fixing at this point).