But it depends on what causes it.

It is possible that the upper dentition is protruding, or the bimaxillary protrusion (both upper and lower dentition are protruding) causes the teeth to protrude outward, resulting in the mouth not being closed.

It may also be a developmental problem, such as a short upper lip.

Simple dentition protrusion, unless it is more serious, will cause the lips to fail to close. But if you have done orthodontics, you still have this problem. It may be the bony bimaxillary protrusion, that is, the upper and lower jaws, not just the dentition, which is more prominent in the development process. This problem requires not only orthodontics to correct teeth, but also orthognathic surgery to achieve better results.

If the reason is that the upper lip is too short, cosmetic surgery may be needed to solve this problem.

You can go to a bigger stomatological hospital or plastic surgery hospital for consultation.