Very true.. and that is a good point.
1. Canada and Australia hold a reciprocal accreditation agreement (btw ADC and CDAC)
2. Canada and the USA hold a reciprocal accreditation agreement (btw CODA and CDAC)
However.. the US and Australia still don't recognize each others dental degrees and training.
This may change in the future.. maybe not. Who knows. If someone is really interested in having an Australian, UK, or otherwise postgrad year of training accepted as their state requirement for a license.. they would of course need to contact the US state dental board in which they seek a license and write them a letter detailing what they aim to do and include a syllabus of the proposed training year including contact hours (clincal/research) and subject areas covered. They could always say no.. but it can't hurt to ask if that's what you would like to do.
... Many faculty/heads of departments know each others counterparts in other countries and have connections. If it were possible.. it might also be helpful if you were able to have your local Head of Dept (for example.. if you were trying to convince the NY State Dental Board that doing a year overseas should contribute to your required PGY1-2 year. Then you might try to get the head of AEGD at NYU/Columbia (or someone similar) sign off on the syllabus for a house officer year in London or a GradDipClinDent program in Sydney... stating that he/she felt they were comparable/equivalent) and then submit this to the State Dental Board.