I found one of these for sale on the net. Here is the description.
The front of this 30 mm diameter piece features a mother and children; the words, "A clean tooth never decays," runs along the upper rim. The back reads, "Presented by the/ Florence Mfg Co/ Florence Mass. U.S.A./ makers of the/ Pro-Phy-Lac-Tic/ Tooth Brush." The Florence Manufacturing Co. was founded in 1866 and became the first company to package its toothbrushes in sanitary individual boxes. Because of the success of its toothbrushes, it changed its name to the Prophylactic Brush Co. in 1924. This indicates that this piece was distributed before then, as the Florence Mfg. Co. name is used. In 1930, the company was bought by Lambert Pharmaceuticals. This piece was probably distributed as a premium for purchasing their products.