The purpose of this study is to review the effect of flap design in terms of periodontal status of the preceding second molar after lower third molar surgery. Impacted lower third molar surgery may result in periodontal complications on the distal surface of the adjacent second molar. Flap design that is used during impacted third molar surgery is important to prevent those complications. Several different flap techniques, mainly envelope, triangular (vertical) flaps, and their modifications have been developed to minimize those complications. Each technique has some advantages as well as disadvantages. It is also reported that the selection of a flap design does not seem to have a lasting effect on the health of periodontal tissue. The effect of the type of flap used for lower third molar surgery on the periodontal status of the second molar, as well as the factors that may influence this outcome, has been uncertain. The decision to use on one or the other of the flaps should be based on surgeon's preference.