Philadelphia has added the enamel-hardening mineral to its public water since 1955, after a glut of research credited fluoride with a dramatic reduction in cavities and tooth decay among those who drank treated water.
But despite government proclamations calling water fluoridation one of the most important public-health achievements of the 20th century, the rest of the region has been slow to follow.
The percentage of Pennsylvanians with access to fluoridated water - about half - has been nearly stagnant the last 20 years, even as fluoridation rates have steadily increased to about 70 percent in the rest of the country, according to the Centers for Disease Control and Prevention.
Efforts to add fluoride to public water in the state have routinely met stiff resistance. And some communities - like Pottstown, which decided this month to stop fluoridating its water after five decades - have given up on the process.
In New Jersey, the statistics are more dramatic. The percentage of the population with fluoridated water plummeted from a quarter in 2006 to just under 14 percent in 2008, the latest year for which CDC statistics are available.
"The attraction to fluoride has waned over time," said Ronald C. Downie, chairman of the Pottstown Borough Authority, which manages the water system. "We're not out in front of this. We're just reflecting the trends."
The exact reasons for the region's resistance to fluoridation remain elusive. Each dentist seems to offer a different explanation.
In this age of fluoride toothpastes and mouthwashes, some argue that the public benefit of injecting it into the water supply has waned. Others point to the efforts of groups like the Fluoride Action Network, which travels the country opposing public fluoride use, pointing to studies that it says link the chemical to brittle bones and perhaps even cancer.
