The National Dental Association became the American Dental Association in 1922. These are listed in the Mosbaugh All Fund Catalog, Section 9, Medical #110
.01 1913-17 "National Dental Association"
.02 1918 1918-20 "National Dental Association", but gaps in green ornamental frameline above "NDA". Green lighter, showing leaves individually at bottom.
.03 1921 "National Dental Association" The outside lines on NDA logo meet at the bottom
.04 1922 Name changed to "American Dental Association" The outside lines on NDA logo meet at the bottom