It comes seven years after Northland DHB accepted a van, making New Zealand the only country other than the United States to have two of the units.
Ronald McDonald House Charities programme manager Grant Hiskens said the scheme saved taxpayer money.
"The current Government loves it. Our PR people are in Wellington all the time. They have spoken recently to people quite high up in the ministry and they are excited about it. The support is there because the Government can see it helps them out."
He said there was a clear separation between the charity andthe fast-food chain.
"If people can't just look at the bigger picture and see we're filling a gap that our Government will not, or cannot, due to the cost, that is a whole other story. Our programmes are supplying something ... the Government will not supply."
Counties Manukau Health chief executive Geraint Martin said the DHB was "delighted to be the recipient of such corporate generosity".
The DHB did not ask for the van without the branding, saying it was aware of the charity's requirements.
Dental Association chief executive Dr David Crum said the Government should be providing basic healthcare.
"We have such a history of providing free basic dental care to children. Now we are heading to allowing fast-food chain corporations to be the funder of that? It's crazy."
Green Party health spokesman Kevin Hague said he convinced his board to halt a similar deal when he ran the West Coast health board.
Labour health spokeswoman Maryan Street said careful judgments had to be made about private-public partnerships in health.
"There will be an inherent contradiction in some of this stuff."
