The moment 9-year-old Sara Hassa opened her mouth, the Multnomah County dental hygienist peering down at her knew one thing for certain.

“You don’t live in Portland, do you?” Debra Mendoza said.

Sara, a fourth-grader, shook her head. “Beaverton,” she replied.

Neither she nor her sister, seated in another dental chair down the hall in the county clinic just off Southeast Powell Boulevard, has ever had a single cavity, said the girls’ mother, Shukri Elmi.

“Just beautiful teeth,” Mendoza said later, adding, “You don’t get to see that a lot in Portland.”

County health officials attribute much of that contrast to fluoridated water – Beaverton has it, Portland doesn’t.

That gap, they say, is why Multnomah County has emerged as a leading voice in supporting Mayor Sam Adams’ proposal to start adding fluoride to public water supplies.

“The evidence is very clear that fluoride in water is a very positive health action,” county commissioner Chairman Jeff Cogen said. “Not doing so has left us with some of the worst dental-health outcomes in the country.”

Cogen cited soaring public health costs, needlessly suffering through extractions and root canals, and issues of “health equity” in arguing that Portland should reverse its long-standing opposition to fluoridated public water.

“We have a dental crisis in Oregon,” he said. “Moving toward fluoridation represents an important first step in trying to address that.”

A majority of Portland city commissioners has come out in support of fluoridating drinking water from Bull Run reservoirs. A vote is scheduled for Sept. 12.

Others, including Gov. John Kitzhaber, also have endorsed the proposal.

There is opposition, as well, some of it dating back decades.

Portland voters in 1980, for instance, reversed a vote taken two years before to fluoridate water supplies. A city advisory panel in 1994 recommended against using fluoride.

An anti-fluoride group now is launching an initiative effort, asking voters in 2014 to permanently ban fluoride from public water.

A website maintained by the group, Oregon Citizens for Safe Drinking Water, says “numerous studies have shown serious, adverse health consequences from fluoride ingestion.” Those can include osteosclerosis, sinus trouble, perforation of the nasal septum, chest pains, coughs, thyroid disorders, anemia, dizziness, weakness and nausea, according to the site.

However, staff at the county’s five public dental health clinics say they see dozens of clients daily who would benefit from fluoridated water.

Dr. Selynn Edwards, for instance, works at the county’s Southeast Dental Clinic off Powell. She said the difference between Multnomah County patients and those she saw where she used to work in Beaverton could not be more stark.

“It’s just huge,” she said, “especially when you see anywhere from three to five children daily whose dental needs are unbelievably extensive.”

Dr. Alyssa Franzen, dental director for the county’s Health Department, said it’s not uncommon for exams of toddlers ages nine to 36 months to reveal 10 or more teeth needing immediate treatment.

“The whole goal is trying to prevent something like that from happening in the first place,” she said. “And a key part of that prevention strategy is fluoridation.”

The county’s Cogen moved to Oregon from Florida 20 years ago. He said his first experience with a Portland dentist played out much like Sara Hassa’s did, with his dentist taking one look at his teeth and saying, “You didn’t grow up here, did you? You don’t have any cavities.”

By the time his own Portland-born daughter, Johanna, was six years old, Cogen said, she’d had five cavities.

“I know that may sound purely anecdotal,” Cogen said. “But from what I hear from our dental clinic folks, they see it all the time.”