Why does Lord Ganesha have only one tusk? Three stories, three different texts

Ganesha’s single tusk is in his prayers before it is in his idols. The Ganapati Atharvashirsha, a short Upanishadic text recited in temples every day, carries the Ganesha Gayatri, which begins “ekadantaya vidmahe”, roughly, “let us know the one-tusked