Ummmm...Okay. Don't know what to make of this 1944 LIFE ad. I realize it LOOKS like a MAD parody but I swear it's not! This has got to be one of those cases where a word has come to specifically mean something in particular in the ensuing years...and it ain't a toothbrush. "Where's my Prophylactic? I wanna brush my teeth!" Indeed.
UPDATE: As if to prove that you really CAN find anything online if you look, here's a link to a very detailed history of the advertising of the Pro-Brush company...which somehow misses the humor therein. http://www.historic-northampton.org/virtual_exhibits/pro_brush_ads.html