Dioxin can harm tooth developmentBy J. Raloff
In the early 1980s, a Finnish dentist noticed that an unusually large share of her
young patients had soft, discolored molars. Because the affected teeth had emerged bearing
structural defects, she suspected that during infancy, when the teeth were forming beneath
the gums, the children had been exposed to some toxic compound.
The culprit now appears to be breast milk tainted with dioxins, says Satu Alaluusua of
the University of Helsinki Institute of Dentistry. She explained her team's findings in an
interview this week.
Several groups of
epidemiologists worldwide have reported a similar yellowish-brown discoloration of teeth
in children exposed to extremely high concentrations of dioxinlike compounds. To probe
whether the defects that she was observing might reflect a more moderate exposure to the
same pollutants, Alaluusua began exposing adult rats to TCDD, the most potent dioxin.
"We saw a similar mottling of teeth," as well as malformations in their mineral
structure, she told Science News.
To affect human molars, exposures must begin in early childhood. So, Alaluusua tracked
down children whose mothers' breast milk had been analyzed 6 years earlier in a World
Health Organization study. She correlated the incidence of the defects in children's newly
emerging molars with milk concentrations of dioxins and furans, a class of dioxinlike
compounds. Overall, 17 of the 102 children studied bore soft, mottled teeth, which will
remain permanently vulnerable to cavities.
In the Jan. 16 Lancet, Alaluusua's team reports that children who had
encountered the most dioxin in their mother's milk had the highest rate of these tooth
defects. Breast-milk exposure to polychlorinated biphenyls, another group of dioxinlike
chemicals, played little if any role.
The group has also homed in on dioxin's target. The pollutant affects cellular
receptors for epidermal growth factor (EGF), a hormonelike substance that contributes to
development of many tissues.
The researchers removed embryonic tooth tissue from normal mice and from those lacking
active genes for the EGF receptor. After exposure to high concentrations of TCDD, only the
tissue able to produce EGF receptors matured into structures with the telltale defects,
they reported in the December 1998 Laboratory Investigation.
The Finnish team's new data "are very exciting in a scientific sense—and very
concerning in a public-health sense—because they demonstrate effects from [dioxin]
exposures at background levels," says Linda Birnbaum, a toxicologist with the
Environmental Protection Agency in Research Triangle Park, N.C.
Indeed, she notes, the average 50 parts per trillion (ppt) dioxin concentration—and
the maximum of 258 ppt—that the team measured in the fat of Finnish women's breast
milk are within the range at which dioxin taints fat, including that in breast milk, in
the U.S. population.
Moreover, Birnbaum notes, the EGF-receptor link to tooth defects "is perfectly
plausible" given that a number of studies—including some of her own—have
shown that dioxin can alter the number of EGF receptors in various developing tissues,
including the tooth buds of experimental animals.
