Eastbourne Tory MP Nigel Waterson has voted against having fluoride added to tap water.
He has been inundated with letters from people expressing fears about the health implications of the move.
However, a bid to block the fluoridation of water was defeated on a free vote in the House of Commons by 284 to 181.
Mr Waterson said: "This is not the end of the matter.
"It is now up to local water authorities to decide whether to go ahead with introducing fluoride.
"I will be resisting any moves to introduce the substance into our local water supplies."
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