Sunni Smile is a toothache cream, presumably manufactured and sold in Persia.
While the Simpsons wandered through a run down Springfield Mall they came across a collection of candle kiosks and Persian CD stores, in what used to be a JCPenney's. The owner of one of the CD stores attempted to sell the Simpsons the latest CD by Nabil, a Persian musician. Homer was reluctant at first, but ultimately agreed when the man offered to throw in some Sunni Smile toothache cream for free.
Behind the Laughter
The Sunni Smile is a reference to Sunni Islam.