If you think your natural teeth are too long, then they can oftentimes be shortened by a cosmetic dentist using a procedure called enameloplasty, shaving off some of the superficial enamel of the tooth. Or, if you have front crowns or veneers, they can sometimes be made shorter or redone. .
But the real question is, how short to make them? I suggest you check out the link below, it has a pretty descriptive article I wrote several years that describes how cosmetic dentists decide the best length to make a patient's front teeth.