There are a few different reasons why your wisdom tooth may have a flap. One reason is that the tooth may be impacted, meaning it is growing in at an angle and pushing on other teeth. This can cause crowding and damage to neighboring teeth. Another reason for the flap is if there is decay present on the wisdom tooth. The decay can cause the gum tissue to pull away from the tooth, creating a small pocket where bacteria can grow. If left untreated, this can lead to an infection. Finally, some people simply have extra gum tissue around their wisdom teeth, which can make them more susceptible to plaque buildup and inflammation.