Campaigners handed a petition with 14,000 names to Downing Street
A High Court judge is set to review a decision to add fluoride to tap water in Southampton.
Resident Geraldine Milner began a legal challenge against the decision by the South Central Strategic Health Authority.
The SCSHA gave the go-ahead for fluoride despite a public consultation showing major opposition to the move.
The review will be based on government policy, which states most residents need to be in favour of the move.
The SCSHA board's decision was made in February even though 72% of 10,000 respondents in a public consultation opposed the move.
Earlier, the strategic health authority said it was satisfied mass fluoridation was a "safe way" of tackling tooth decay.
A spokesman for the SCSHA said: "The SHA remains confident that the decision made by the SHA Board was carried out in accordance with the relevant legislation laid down by parliament and is in the best interests of the health of local people."
It is the first time a strategic health authority in England, rather than water companies, has been allowed to introduce fluoridation under new laws.
The SCSHA instructed Southern Water to increase levels of fluoride from a natural 0.08 part per million to one part per million.
As a result of the authority's move, activists from Hampshire Against Fluoridation and other supporters delivered a petition with 14,000 signatures to Downing Street on 9 June.
The review is expected to take place in January.