Mate, great question...and you are in luck!
1. Dentists who are registered to practise in New Zealand under Trans Tasman mutual recognition
Dentists who are registered to practise in New Zealand are eligible to apply for General Registration under Trans Tasman mutual recognition (this applies irrespective of where training was undertaken).
The great thing here is that if your wife is accredited in NZ, and although she completed her training in the US, under the Trans-Tasman Mutual Recognition she would be eligible to apply for General Registration in Australia with the DBA.
As well, if your end goal is to move to Australia, you may wish to have her apply for Skilled Migration. At the moment Dentists are on the Skilled Occupation List - Schedule 1. This list does change from year to year and each July 1st it is updated. So, if you wish to migrate to Australia, you may just want to apply for Skilled Migration. Yes, it is a process and there are no guarantees, but with dentists being on the list, it really helps.
The Skilled Occupation List can be found: http://www.immi.gov.au/skilled/_pdf/sol-schedule1.pdf
For more information, please visit: http://www.immi.gov.au/skills/skillselect/index/visas/subclass-189/
You may also wish to consult with a certified migration agent or contact the Australian Embassy in Washington, if you live in the US, or the Australian High Commission in Ottawa, if you are in Canada.
Hope this helps and good luck!