When you say "the first phase", is that installation of the posts?
My procedure was elongated due to a required bone graft (and the healing period), installation of the post into the grafted area (and the observation period to see if everything would set), then the fitting of a temporary, and finally the fitting of a final.
I could not dive during the graft healing or the post setting, due to concerns over getting sea water in my mouth, and had nothing to do with the mouthpiece.
I don't know enough about it, I will ask my husband for the details, thanks.