Scene from the movie: MC Gusto's teeth at 32:20
Real life examples: ASAP Ferg, ASAP Rocky, Kanye, etc.
No, Paul Wall and TV Johnny did not invent the grill. In the 1980s and '90s, New York's Eddie Plein started the trend, drilling gold in the mouths of Big Daddy Kane and Flavor Flav, and later Outkast, Ludacris, and Lil Jon (after moving to Atlanta). A few years passed before Nelly hopped on "Grillz," and that's when things went...awry: the Wikipedia entry for "Grill (Jewelry)" lists such diamond-toothed aficionados as Marilyn Manson, Travis Barker, "members of the metal band Avenged Sevenfold," and Ryan Lochte.
And that's even before A$AP Rocky brought back the simple gold fronts for "Purple Swag," before Kanye strapped on his gold mouthguard, and before Madonna came in and made it uncool.