I have concerns too, and that's why I stopped using the product.
Roxy had her last dental done by a Board Certified Dental Vet who expressed concerns over the grain alcohol. When I asked if I should stop using it, he said "I would".
Here is some info on what he recommends using. Maxi/Guard is one product.
Veterinary Medical Center of Long Island Articles
P.S. I would be curious as to what case studies and scientific testing the company did and has that provides the proof the most of the alcohol evaporates before it is even swallowed ???