Seven communities in York County will vote Nov. 5 on a controversial proposal to fluoridate their water.

The communities are Kennebunk, Kennebunkport, Wells, Arundel, Ogunquit, the coastal section of Biddeford and the Cape Neddick portion of York.

A group of dentists in southern Maine is urging voters to approve fluoridation. The American Dental Association says that fluoridated water has been shown to prevent tooth decay, and that it is safe.

But some people oppose fluoridation, because in large quantities it can be toxic.

“At a public hearing, we received mixed testimony about the pros and cons of fluoride,” said Wells Selectmen Chairman Robert Foley. “I am concerned there are possible side effects of too much fluoride if one is getting it in the water and also from their dentist.”

Foley is among those who have yet to make up their minds on how they will vote on the issue.

Norman Labbe, superintendent of the Kennebunk, Kennebunkport and Wells Water District, said, “The water district is neutral on fluoride. If our customers want it, we’ll do it.”

He said the majority of the total votes from the seven communities will determine the outcome of the proposal.

Stephen Russ of the state Drinking Water Program said children derive the most benefit from fluoridation. He said youngsters who drink fluoridated water have 40 percent fewer cavities.

Fluoride bonds with the structure of the teeth as they form, hardening the outer surfaces against decay-causing acids produced by bacteria.

But too much fluoride is unhealthy. Teeth that have formed in the presence of too much fluoride can display fluorosis. Mild fluorosis shows up as white patches on the teeth. In more serious cases, teeth can be brown and pitted.

In Maine, about 120 communities fluoridate their water, including Portland, Falmouth, Cumberland and Freeport.

Portland didn’t begin fluoridating its water until 1997, after voters in that water district had rejected it four times.

Fluoride is the generic name given to compounds that contain the element fluorine. It has been added into water systems since 1945 in Grand Rapids, Mich. Since then, dramatic reductions in tooth decay have been observed in children raised on fluoridated water.

Norway, in 1952, became the first town in Maine to fluoridate its water.