When a lot of gum is visible when talking or laughing, we call it a "gummy smile." This is not a learned trait, but rather an innate one. The cause of the excessive gum growth can be due to overactivity of the muscle that lifts the upper lip. When this muscle is temporarily suppressed with botulinum toxin, the upper lip hangs down, as it were, during speech and laughter.
The drooping upper lip covers the excessively visible gums. This effect lasts for 3-4 months. This treatment is not easy for everyone, so a consultation is required.