For one, I don't see that they are a charity, they look like a professional organization to me. For two, they are US, so even if they are a charity they most likely aren't registered as such in Canada. See http://www.cra-arc.gc.ca/tax/charities/donors/menu-e.html For three, charitable donations are NOT deductible at all, much less at 100%. They provide you with tax CREDITS. See http://www.quicktaxweb.ca/content/etc/tc_charitable.php?b= For four, don't expect correct tax advice from a webmaster forum. Call Revenue Canada directly if you want correct answers.
Why would you donate money to a conference for orthodontists that is only run every five years? Seems kinda silly. Put your money into a charity that's actually giving back to society, like the Red Cross. But to answer your question, yes it's 100% tax deducatable if they are a registered charity under the Income Tax Act. From looking at their website, I have severe doubts that they meet this requirement.
Again, charitable donations are not tax deductions, they give you tax credits, and you don't get 100% of a tax credit back.
I'm not an accountant, but I believe tax deductable is the same thing as tax credits. Either way you lower your taxes with them. I never said you get the tax money back.
To answer the OP original question, for federal tax, donations are not deductible in Canada, they give you a tax credit, and it's not 100%. To give you an idea, if I remember correctly, it's 16% for the first 200$ and 29% for anything over that. But tke71709 gave you the best advice:
Tax deductible and tax credit are not even remotely the same. Further, donations are not tax deductible. They are a tax credit and only a percentage thereof. Unless you are contributing a very large sum of money, because of the way the credit is calculated, it will hardly make any impression on your taxes. So to answer the original question: No, donations are not 100% tax deductible.