I will take the liberty to expand your request to include other philatelic items with a dental theme.
For several years the US Postal Service ran "dental week" or "dental month" slogan cancels in their high-speed facer-cancelers. I have no idea whether dental week or month came first since the uses I have overlap. Nor are they confined very well to a single week or month, but they do tend to center around February. Perhaps more detail than anyone would want but here goes with what I have at hand ...
" slogan cancels. Two different arrangements of the words among the 3 lines.
" slogan cancels with a large "Smile America" in the first line. Again showing two typesettings of the wording.
" slogan cancels showing different typesettings. The first two have lines of test of increasing length, with the second example having a longer box (Also note the different alignment of the letters from one row to the next). The 3rd and 4th examples have the lower two text lines of equal length - ht e one from Louisville having a very thick-lined box. And the last cancel has a much taller box and wider spacing between the text lines.
The various typesetting varieties seem to demonstrate the purchase and distribution of slogan killers over the span of several years from different manufacturers.
And lastly, I think this "Smile America" slogan spray cancel is an attempt at using a portion of the dental week/month theme. Note it's February use.