Custom Oral Appliance..Do I need a new one?

If I got a custom oral appliance (mandibular advancement device) for sleep apnea 6 years ago and haven't been using it at really. If I want to start using it, do I need to have a new one made or can I just use the old one?
I remember someone saying I should need a new one made, but I'm hoping the old one will do, and that my teeth/jaw haven't changed that much...I would imagine that they couldn't have changed much.

Go see the dentist that made it to be sure yout jaw has not changed....We can't determine that.