The trapezoidal flap design includes two vertical releasing incisions in addition to the horizontal sulcular incision, which allows the flap to be reflected more broadly. This provides enhanced surgical access and superior visibility to the underlying bone and roots compared to other flap designs. The vertical incisions reduce tension on the flap during retraction, minimizing tearing and allowing better manipulation. Therefore, it is preferred for procedures requiring extensive exposure, such as access to impacted teeth or alveolar bone surgery.

Reference: Carranza’s Clinical Periodontology, 13th Edition.