BERKELEY -- A measure that would have required dentists here to disclose the composition of fillings each time they are recommended went down to defeat just before midnight at Tuesday's City Council meeting.

Instead of the mandate proposed by Councilman Jesse Arreguin, the council voted 6-3, with Arreguin and Councilmen Max Anderson and Kriss Worthington opposing, for a measure authored by council members Linda Maio and Laurie Capitelli to "encourage dentists practicing in Berkeley to consider limiting or transitioning away from the use of dental amalgam."

Dental amalgam is material, consisting of about 50 percent mercury, used to fill dental cavities. Mercury is used in fillings to bring together metals -- silver, zinc, copper -- in the form of a paste to fill a cavity; the mercury makes the filling material pliable and enables quick hardening, according to Dr. Hal Huggins, of Colorado Springs, Colo.

Mercury is a known toxin; the degree to which it is harmful in dental fillings is disputed.

"This is a very mild proposal," Berkeley resident Lynn Riordan said in urging the council to require disclosure of mercury in dental fillings as a precautionary measure. "It gives people information."

The question at the heart of the council debate, however, was not whether dental fillings containing mercury are toxic, but whether California law allows cities to write disclosure requirements.

The state Legislative Counsel Bureau weighed in on the side of state control, writing: "It is our opinion that the resolution proposed by the city of Berkeley, which would require a dentist to obtain written informed consent before performing a dental amalgam filling procedure, would, if adopted, be pre-empted by Business and Professions Code section 460, and the Dental Practices Act."

Arreguin argued, however, that the legislative counsel opinion referred narrowly to a proposal by the city's Health Commission that would have required written consent to the procedure and not his proposal that would have required dentists to present patients with a fact sheet on dental fillings before each filling. Currently the state requires that dentists present the fact sheet one time.

A request to get the opinion of the attorney general was incorporated in the adopted Maio-Capitelli ordinance.

"If you sign up as a patient, and you get all this information, and you come in for fillings down the road, you're not going to remember getting that fact sheet," Arreguin said.

Most of the several dozen public speakers at the late-night discussion called for passage of Arreguin's proposal. "Mercury is a toxin," said dentist James Rota. "It should not be in our mouths. It shouldn't be implanted in our teeth."

There were a number of people, however, who stood behind the Maio-Capitelli ordinance. Dr. Norma Solarz, a dentist practicing in Oakland, said the question of disclosure takes people off target. "The harm is untreated dental disease," she said.

Dr. Ariane Terlet, chief dental officer at La Clinica De La Raza, argued that the higher cost of alternatives to mercury fillings makes delivering dental services to the poor more difficult.

"I have a real concern when any government agency tries to come in and 'help' us by regulation," she said.

Arreguin defended his proposal, which called for a council workshop on the question rather than taking a vote that evening.

"Information is never a barrier to quality care; it's just providing information so patients can make an informed decision in consultation with their dentist," he said. "We have to add more teeth to state law."