Good question! More than likely if youre a long term denture wearer, resportion in the jaw bone causes you to develop an underbite over time. With All-on-4 treatment, patients in our practice like yourself often can have some of their facial bone loss compensated with the implant-supported teeth. This means that it will likely restore your facial profile to before the bone loss happened, and sometimes that means correcting the underbite!
If youve always had an underbite, it might be more of a skeletal predispositon and might not be corrected with just All-on-4 treatment.
This depends on how severe your underbite is. It would help if you could post a profile photo with your mouth closed and teeth in normal bite, and another photo with your teeth touching (normal bite) and your lips grinning. These would give me an idea as to what correction may be possible. I hope this helps.
In order to give you accurate advice I would need to see profile pictures to see the amount of underbite and X-rays to see the level and the amount of bone. In general there is a possiblity of handling overbite and underbite issues with all on 4 implants.