“What is the fastest way to fix an underbite?”

In minor cases of underbite, orthodontic treatment such as face mask appliance, braces or clear aligners with the aid of elastic bands may be recommended to move the teeth back into proper alignment. Orthognathic surgery may also be recommended for more severe cases when braces alone won't work.

The fastest to fix is a hard question. To actually fix it might include surgery that actually corrects the discrepancy. Usually, some braces are required after. Long-term best solution. To mask the appearance and not fix it would be crown work on both arches. Drawback is altering your teeth permanently and understanding replacements of the crowns during your lifetime are likely due to oral hygiene, wear and tear...