We tracked down the study you read about. It was published in the
Journal of the American Board of Family
Medicine (Jan-Feb., 2009). The investigators used a sublingual (under the tongue) form of vitamin B12. They concluded, "Vitamin B(12) treatment, which is simple, inexpensive, and low-risk, seems to be effective for patients suffering from RAS [recurrent aphthous stomatitis, or canker sores], regardless of the serum vitamin B(12) level."
Excerpt from the People's Pharmacy.