From bag to bone How does fluoride prevent cavities? And does it come with unnecessary risk?

By CHRISTIAN KNIGHT

News staff writer

April 26

The next time you are staring at an open Google Web page, type "fluoride" on the search bar.

You'll receive 2,200,000 hits in less than a second - depending upon how fast your connection is.

The Google search will show you Web pages like "Fluoride Action Network," which, if you click on the blue link will instantly transfer you to a page with another 120 links to other pages, each of which highlights even more links.

The Fluoride Action Network is a convincing page. It has graphs and photos and diagrams. Most of the people quoted there have "Dr." just before their names or "Ph.D." just after. And their perspective is obvious: No fluoride in water.

But it is still the Internet.

If you are one of those who harbor a general distrust for gleaning information from the Internet, you might try ProQuest. It's a registration-required search engine that allows you to tap into the world's scholarly journals and newspapers without the worry of quoting a high school semester project.

You'll earn 8,976 hits there.

The sources will range from Dublin's newspaper "The Irish Times" to the "Journal of Computational Chemistry," which is so complex, it makes reading Greek seem like Dr. Seuss.

To some degree, all of these journals, newspapers and homepages will answer fragments of the great question about fluoride.

And nearly all of them cite studies, statistics, experts and tragedies to demonstrate that answer.

But they often conflict at the most fundamental levels.

And chances are you'll be no clearer on the subject of fluoride than when you first asked: Is fluoride — sodium fluoride, sodium fluorosilicate — good for me? And: is it good for my neighbor?

That debate is raging in Pagosa Springs, Colo., where a citizen group campaigned to remove the fluoride from its water system. It is raging in Northern Ireland, where, after finding alarming levels of dental fluorosis, the Department of Health introduced legislation this spring to reduce the level of fluoride in the water supply.

And it's raging here, in Hood River.

Advocates on both sides of the local fluoride debate cite credible studies and convincing research to exclaim their points. For a person stuck in the middle, with no idea of which way to choose, this can be confusing.

The article below will not cite a single study. It will merely attempt to explain how fluoride works in your teeth and in your bones.

Straight to the bone —

Hypothetically speaking, the journey of Hood River's sodium fluoride powder to your bones and teeth would begin in a solution at a concrete treatment plant near Dee — six miles from where the city collects the water from three ground water springs near Lost Lake.

A machine would pump the solution into a 76-year-old pressurized, steel pipe, which would carry it down the rolling valley, across the Hood River and into a five-million gallon tank on Riverdale Drive.

Pressurized water would then thrust the sodium fluoride through the city's PVC, cast iron and steel pipe distribution system under the city streets and sidewalks and finally into your own water meter.

From there, all you have to do is turn on your faucet, place your glass underneath, lift it to your lips, tilt your head back and swallow to initiate (or continue) a process that will alter your body's chemical composition forever.

This is where the work and the controversy begin:

Each of your teeth has three layers to it: the pulp, the dentin and the enamel.

The pulp is a soft core, where the blood vessels and living parts of the tooth are, kind of like the core to a cantaloupe.

The enamel is what you see when you smile in the mirror.

The dentin is the layer in the middle. It's harder than the pulp and softer than the enamel.

Both the dentin and the enamel are made up of a meshwork of protein and of pure crystals called hydroxyl apatite, which stack on top of each other to form a microscopic version of columnar basalt. If you look closely enough at your teeth, you will see vertical lines from edge to edge. These are the columns of hydroxyl apatite.

The enamel and dentin are constructed differently enough, however, that the enamel forms as a hard shell and the dentin forms more pliably.

Together, the protein and the hydroxyl apatite form a structure, which gives strength to your teeth.

Each of these hydroxyl apatite crystals is made up of calcium and phosphorous.

"Calcium and phosphate are ionic compounds," says Dr. Michael Meredith, Ph.D., Professor of Integrative Bioscience and a toxicologist in the School of dentistry at Oregon Health and Sciences University. "They will dissolve in water, given enough time. But if you make the water slightly acidic, you will speed up dissolution. It's like vinegar — the acid — dissolving limestone — the calcium."

And when we eat things like breakfast cereal — sugars, starch and dairy — the bacteria in our mouths convert those spoonfuls of bliss into lactic acid, which, is acidic enough to dissolve the calcium phosphate crystals in our teeth.

Fortunately, our bodies — the incredible laboratories they are — have built in a remedy for this process. Within our saliva is a tooth-rebuilding system of ionic calcium and phosphates.

Our saliva washes over our teeth, bathing it in calcium and phosphates, remineralizing damaged hard surfaces.

This is where fluoride becomes part of the equation.

If fluoride were a person, it'd be the most outgoing, gregarious person you'd ever meet. You'd instantly be drawn to him/her. And once you and fluoride met, it'd be hard to split you apart. Chemists have a name for this: reactive.

Molecules that are reactive tend to hook up more with other molecules.

When you introduce fluoride to the calcium and phosphorous within your saliva, the fluoride replaces one of the molecules in the calcium phosphate crystal.

Because the fluoride is more outgoing, more reactive than calcium and phosphorous, it literally replaces the hydroxyl ion at the apex of the hydroxyapatite (calcium phosphate) crystal in your dentin and enamel.

"If you substitute fluoride for that hydroxyl group, you draw the unit cell closer together, shrinking the size of the cell," Dr. Meredith said. "Fluorine is so much more electronegative than oxygen in the hydroxyl ion it actually makes the unit cell of fluoroapatite (calcium phosphate contain fluoride ion) shrink. The consequence of reducing the unit cell, is that it becomes acid resistant."

Fluoroapatite is roughly 10 times more acid resistant than its counterpart hydroxyapatite.

Herein lies a myth:

"Fluoride doesn't strengthen teeth, it makes them more brittle," said Dr. Hardy Limeback, a biochemist and head of preventative dentistry at the University of Toronto. "It's like a porcelain toilet, you drop a wrench in a toilet and it'll crack."

Limeback is one of the world's most prominent critics of water fluoridation. For decades, he followed the mainstream philosophy of teaching fluoride as a dental miracle.

In 1999, however, he earned a grant to study the effects of ingested fluoride on hip fractures. He says he found a direct correlation to the levels of fluoride found in the bone and the incidence of hip fractures — especially in the elderly.

He visited Hood River last weekend to lecture on the topic.

But even Dr. Meredith, a biochemist and toxicologist at OHSU and advocate of water fluoridation, admits that fluoride does not make teeth stronger, that it does, in fact, make them more brittle.

"It's not making them stronger," Meredith said. "You are making them more resistant to acid. But teeth don't as often break from walnuts as they do from caries.

Weakened, brittle enamel is a result of fluorosis, a condition where a large excess of fluoride has been introduced into the tooth structure. Acid, not mechanical damage, is the daily challenge in tooth defense."

If you ingest too much fluoride, you will start producing too many fluoroapatites which will reveal themselves in the form of white splotches on your teeth.

This is called "dental fluorosis." The individual splotches are actually high concentrations of fluoroapatites, which are incredibly resistant to acid, but also very brittle, "like chalk," Meredith said.

"It's the disease of the middle to upper middle-class," Meredith said. "It's the parents trying to use fluoride too much. Fluorosis is seen much more in dentists' children than anyone else."

But remember, whatever is true of the teeth is true of the bone, according to Dr. Meredith.

And the bone is where 95 percent of ingested fluoride ends up, according to Dr. Limeback.

Log in to comment