A union is calling for more answers on the safety of mobile dental units after formaldehyde was found in some clinics.
This led to units being pulled from service and 116 tested for the chemical compound.
Staff complained about itchy eyes, headaches and skin irritation, but the DHB said the health risks were low or negligible.
Organiser for the National Union of Public Employees Janice Gemmel said answers are still needed however.
She said it is not clear if all vans have been tested, including the less permanent level 1 campervan units, and said they should be.
"It is about identifying is there a real genuine risk? What has to be done to ensure safety for both the staff and, of course, the children?"
The clinics provide dental care for tens of thousands of primary school children.
In Canterbury, after dental staff complained of various ailments following the introduction of new mobile clinics, Canterbury District Health Board tested the clinics and found formaldehyde levels three times national health standards.
It then alerted other DHB's around the country which then began their own testing, and several have followed suit by taking mobile clinics out of service.
NUPE has refused to allow its members to work in the clinics until thorough testing is completed.
The Health Ministry said it is a matter for individual DHBs.