Portland residents vote today on water fluoridation. (Image credit: Getty Images)

Residents of Portland, Ore., will vote today on whether to add fluoride to their drinking water - a move hailed by some as one of the greatest public health achievements of the 20th century. But critics say a "yes" vote would expose residents to a "risky" chemical in the name of stronger teeth.

Minute amounts of fluoride have been added to American drinking water since 1945 to help curb cavities in kids and delay decay in adults. In 2008, 72.4 percent of the U.S. population had access to fluoridated water, according to the U.S. Centers for Disease Control and Prevention. But in Oregon, the percentage drops to 22, which has created a statewide "dental crisis," according to state epidemiologist Dr. Katrina Hedberg.

"Tooth decay is a serious problem and fluoridation is an effective, affordable and, most importantly, safe way to improve the public's health," Hedberg said in a statement, noting that one in three of the state's first- through third-grade children has cavities, and one in five, has rampant tooth decay. "It is also consistent with the state's effort to focus health care on prevention rather than after-the-fact acute care."

Like cereal fortified with folic acid, milk fortified with vitamin D and salt containing iodine, tap water containing fluoride delivers a healthful supplement that busy bodies don't even have to think about, according to the CDC. Water fluoridation has been shown to reduce a person's risk of tooth decay by 25 percent, and a lifetime supply costs less than a single filling.

But skeptics question the safety of fluoride, citing a 2006 report by the National Academy of Sciences that suggested fluoridation could have serious consequences for certain subgroups of people, such as the very young, the elderly, and the sick.

"Our campaign is not saying there's complete consensus in the science on either side," said Kellie Barnes, a volunteer with the anti-fluoridation group Clean Water Portland. "We're saying the emerging science shows a reasonable amount of concern."

Barnes, a physiotherapist and mother of two, said she hadn't thought about fluoridation until her dentist voiced his skepticism.

"I grew up on the East Coast not thinking about it," she said, referring to her hometown of Baltimore, where water is fluoridated. "But he raised questions about the effectiveness of the policy, and that was concerning to me."

Clean Water Portland has taken safety concerns to heart, publishing a list of 12 reasons to vote "no" on their website. The list also highlights the cost of water fluoridation, and suggests a possible alternative.

"Instead of spending up to $7 million on a fluoridation plant and $500,000 or more a year on fluoridation chemicals, a comparable investment in increased access to care would better help at-risk kids while protecting the entire community from the health risks of fluoridation," the group's website reads. "While fluoridation activists like to focus on Oregon's 'untreated decay' rate, this rate highlights the real issue: a lack of good access to dental care."

Ballots must be delivered to a ballot drop-off location by 8 p.m. PT.