What are the long term consequences of thumb-sucking?

Many. Grinding your teeth can result in headaches, earaches, damage to your teeth and enamel causing erosion of the teeth and sensitivity, increased risk of cavities, and loose teeth. If you grind your teeth, see your dentist to get fitted for a mouth guard.
Thumb sucking. Thumb sucking for too long can cause dental problems. These dental issues can lead to speech abnormalities. As long as the habit is broken by the time permanent teeth come in, everything should be fine.