Wide gap between front lower center teeth. had tartar buildup removed and dentist said he didn't know why i had such a gap. can i use dental gap band?

Yes: however, you may want to consult an oral surgeon regarding possible gingival or palatal grafting.

May cause tooth loss: Close the space between 2 teeth and smaller spaces open on the sides of the teeth away from the original space. And if a band slips below the gum line (perhaps while you're asleep) it will destroy the tooth-supporting bone and you will loose the teeth. Best idea, see an Orthodontist for an Initial Examination (usually free) and a frank discussion about your treatment options.