"il s’agit d’un accessoire non blessant permettant de protéger l’ensemble de la bouche et lié au tuba. Vue de face, l’accessoire doit recouvrir entièrement les lèvres."

Translation :
"it is a not wounding accessory linked to the snorkel that is able protect the whole mouth. In front view, the accessory must entirely cover the lips."

We use Carol's mouthguards...
Cheers.