There are very few disadvantages. They can be listed as;
1- Re-growth of the gum is a possibility, as the gum level is ultimately determined by the bone level underneath it. With laser gum contouring, since no changes are made to the bone level, the gum can grow back. However, the laser treatment can be repeated again.
2- If too much gum is removed, then the root of the teeth – which have different colour from the crown of the tooth – might be exposed. In some such cases, the gum grows back and can correct this.