The split-thickness flap involves both the epithelium and the connective tissue (submucosa). In a split-thickness flap, a thin layer of tissue is removed from the surface of the gums, including both the epithelium and a portion of the underlying connective tissue. This type of flap is often used in periodontal surgery to access the underlying bone and tooth roots while minimizing damage to the surrounding tissues. In contrast, a full-thickness flap involves the removal of the entire thickness of the gum tissue, including both the epithelium and the connective tissue.