The Rice University Neologisms Database

gold/silver teeth caps A grille in your teeth does resemble a car’s front grille (the part that sits above the front bumper, often made of shiny metal). The metaphor makes sense. Grille is a term that is used by all elements of society nowadays, though the word undoubtedly surfaced in the African-American community. Many African-Americans use grille for fillings, or to be flashy about their wealth. I think one reason for this neologism is the finite word stock. We have three choices to describe our evolving existence: create brand new words, use long phrases, or employ semantic shift. The last option is often the easiest, so the metaphor extending grille from cars to mouth makes sense.