Saturday, October 3, 2009

Malocclusion: Disease of Civilization, Part II

The Nature of the Problem

In 1973, the US Centers for Disease Control and Prevention (CDC) published the results of a National Health Survey in which it examined the dental health of American youths nationwide. The following description was published in a special issue of the journal Pediatric Dentistry (1):
The 1973 National Health Survey reported 75% of children, ages 6 to 11 years, and 89% of youths, ages 12 to 17 years, have some degree of occlusal disharmony [malocclusion]; 8.7% of children and 13% of youth had what was considered a severe handicapping malocclusion for which treatment was highly desirable and 5.5% of children and 16% of youth had a severe handicapping malocclusion that required mandatory treatment.
89% of youths had some degree of malocclusion, and 29% had a severe handicapping malocclusion for which treatment was either highly desirable or mandatory. Fortunately, many of these received orthodontics so the malocclusion didn't persist into adulthood.

This is consistent with another survey conducted in 1977, in which 38% of American youths showed definite or severe malocclusion. 46% had occlusion that the authors deemed "ideal or acceptable" (2).

The trend continues. The CDC National Health and Nutrition Examination Survey III (NHANES III) found in 1988-1991 that approximately three fourths of Americans age 12 to 50 years had some degree of malocclusion (3).

The same holds true for Caucasian-Americans, African-Americans and Native Americans in the US, as well as other industrial nations around the world. Typically, only 1/3 to 1/2 of the population shows good (but not necessarily perfect) occlusion (4- 8).

In the next post, I'll review some of the data from non-industrial and transitioning populations.

Malocclusion: Disease of Civilization

1. Pediatr. Dent. 17(6):1-6. 1995-1996
2. USPHS Vital and Health Statistics Ser. 11, no 162. 1977
3. J. Dent. Res. Special issue. 75:706. 1996. Pubmed link.
4. The Evaluation of Canadian Dental Health. 1959. Describes Canadian occlusion.
5. The Effects of Inbreeding on Japanese Children. 1965. Contains data on Japanese occlusion.
6. J. Dent. Res. 35:115. 1956. Contains data on both industrial and non-industrial cultures (Pukapuka, Fiji, New Guinea, U.S.A. and New Zealand).
7. J. Dent. Res. 44:947. 1965 (
free full text). Contains data on Caucasian-Americans and African-Americans living in several U.S. regions, as well as data from two regions of Germany. Only includes data on Angle classifications, not other types of malocclusion such as crossbite and open bite (i.e., the data underestimate the total prevalence of malocclusion).
8. J. Dent. Res. 47:302. 1968 (free full text). Contains data on Chippewa Native Americans in the U.S., whose occlusion was particularly bad, especially when compared to previous generations.


Peter N said...

Cool series. Am I right in thinking that the low-fat craze hadn't started yet in 1973, so these kids were likely eating a fair amount of butter and cheese and meat? Or had vegetable oils overtaken natural fats by this time?

Nick said...

Stephen, do you think that flourine in the drinking water is (1) necessary to prevent tooth decay if one is getting adequate amounts of the fat-soluble vitamins, and (2) safe or harmful for drinking?

Stephan Guyenet said...

Hi Peter,

Yes, you're right, although the quality of animal foods had already diminished and people weren't eating many organs. But there's more to it than K2.

Hi Nick,

I don't think fluoride in drinking water is necessary to prevent cavities. Fluoride does increase resistance to cavities, but there's no need to ingest it. It can be applied to teeth at the dentist's office and in toothpaste, neither of which should be ingested. There would be no need for fluoride at all if our diets/lifestyles were better, as Price's research showed. It's not just about the fat-soluble vitamins though, it's also about the minerals and the amount of simple sugars in the diet.

Fluoride in drinking water can definitely be toxic. The amount that gets put into drinking water in the U.S. actually causes obvious physical symptoms in a fraction of people (dental fluorosis). The dose is calibrated so that the percentage of affected people is small, but it's still really common if you're looking for it. I don't know about other forms of fluoride toxicity, but it does make me suspicious. I personally would not drink fluoridated water if I had a cheap and convenient source of non-fluoridated water. My teeth are already full of it so there's no point anyway.

R K @ Health Matters To Me said...

Thanks for listing your sources, Stephan. Much appreciated and very professional!

Stephan Guyenet said...

Hi peter,

Actually, now that I think about it, vegetable oils had already replaced animal fats to a large degree by the 70s. Butter consumption was way down compared to the turn of the century.

Mike said...

"vegetable oils had already replaced animal fats to a large degree by the 70s."

I don't know the figure, but I'd have thought so. More convenient for the housewife to slop a little oil out of a bottle apart from anything else. Convenience may do for us all in the end.

Still, if the issue *is* getting enough animal fat, there was still fat in meat and fish, butter on bread, and butterfat in cheese and full-cream milk. I'll bet intake in all those forms has fallen since the 70s.

The other issue - though I have no idea how important it might be - would, I suppose, be depletion of nutrients in the soil.

As far as I can tell, really heavy use of artificial fertilizers (as opposed to animal manure) is a post-war phenomenon. It's resulted in high yields of crops, of course; but it's also said that's it's meant trace elements have been pulled from the soil and not replaced.

Robert Andrew Brown said...

A UK paper showed a reduction in mineral content of the UK soil / foods of 20% - 70%.

I have written to the USDA asking how historic US mineral intake is computed.

PGE2 is a downstream Omega 6 product. This paper suggest it can influence teeth movement and jaw formation.

"Furthermore, PGE2 plays an
important role as a mediator of bone remodelling under
mechanical forces"

Vitamin D may also be a factor

PGE1 is also a factor it appears. Fats imbalances can cause reductions in PGE1 formation.

Stephan Guyenet said...

Hi Mike,

In the 1970s, people were still drinking whole milk, although butter consumption was already much lower than at the turn of the century.

Not all fat is created equal when it comes to fat-soluble vitamins. Dairy fat is exceptionally rich in them, while other types of animal fat (lard, the fat on steak) are not particularly good sources. Eggs and organs are good sources.

Then there's the quality of the dairy that also matters. The more vitamin K1 the cows eat (green grass), the more K2 their milkfat contains. The same is probably true of humans, to a lesser extent.

I agree that soil depletion is also a potential problem. The thing that concerns me most is depletion of microminerals. Organic food should be better than conventional in that respect because they have to use whole, natural fertilizers rather than synthetic ones.

Ken said...

The Heritability of Malocclusion: Part 2. The Influence of Genetics.

"while phenotype is inevitably the result of both genetic and environmental factors, there is irrefutable evidence for a significant genetic influence in many dental and occlusal variables. The influence of genetics however varies according to the trait under consideration and in general remains poorly understood"

Stephan Guyenet said...

Hi Ken,

Genetics is involved in every aspect of human development. There are probably genes that confer different degrees of susceptibility to malocclusion. But that doesn't answer the question of what causes the high prevalence of malocclusion in modern societies.

If I understand the theory you're advocating correctly, you're saying that malocclusion has been selected for over time because it comes along with facial features that are perceived as attractive. Here are the reasons I find it implausible:

1) The prevalence of malocclusion increases repeatedly in one generation across races, cultures and locations when they adopt modern foods/lifestyles. This is also true for Caucasians, as shown in Corruccini's study of adults and youths in rural Kentucky (good occlusion to poor occlusion in 1-2 generations). These observations alone are fatal to the genetic change theory in my opinion.

2) What's more attractive, a narrow jaw full of crooked teeth or a broad jaw full of straight teeth? I find it implausible that crooked teeth would have been selected for on the basis of attractiveness.

3) Malocclusion can be life-threatening. It can interfere with normal chewing and breathing. Impacted third molars can become infected. There is strong selective pressure against malocclusion, which is why wild animals almost never have it.

4) A number of things can cause malocclusion in experimental animals independently of genetic changes. These include excessively soft food and things that interfere with vitamin K status. Soft food causes malocclusion in a variety of species including primates.

Stephan Guyenet said...

5) Selection for a small jaw would not explain the prevalence of class III malocclusion (underbite), nor other types of malocclusion like crossbite and open bite.

Robert Andrew Brown said...

It could be some have a genetic disposition, and we are looking for the environmental triggers which would include diet

Robert Andrew Brown said...

Bone modelling potential impact of Omega 6