Kirsty Williams AM, the Liberal Democrats leader in Wales, is accusing the Welsh government of not standing by its promise in 2006 that everyone who wanted to register with an NHS dentist would be able to do so.
She says a lot of people either can't register or are having to travel long distances.
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The peer will attack Prime Minister Theresa May for failing to represent the 48% who voted in favour of Remain.
Paul Flynn, MP for Newport West, will open the debate in Westminster Hall.
It will represent another boost to the region, after the announcement Deca Sealand was chosen for a repair hub for defence aircraft.