Southern Cross Health Trust chief executive Terry Moore said appointments for Smile NZ had filled up already, showing the high level of demand for dental care among low-income adults.
Fifty-eight New Zealand Dental Association (NZDA) member dentists from 40 clinics around the country will treat around 800 people free-of-charge this month.
New Zealand Dental Association chief executive David Crum said it was wonderful to see so many dentists donating their time.
"From eliminating pain to making it easier to eat and to speak clearly, dental care makes a big difference to people's lives."
Patients also receive oral health education and a free hygiene pack.