In clinical practice, when a crown is fractured or decayed to the subgingival level, it will affect the fabrication of the restoration and often lead to extraction. The force-methods of clinical crown lengthening include surgical and orthodontic methods, the surgical method being crown lengthening. Crown lengthening is a surgical method that lowers the gingival margin position, exposes the healthy tooth structure, and lengthens the clinical crown, thus facilitating the restoration of the tooth or solving aesthetic problems. 1. Normally, the distance from the bottom of the gingival sulcus to the top of the alveolar ridge is constant, and the distance is called the biological width, including the bonding epithelium and the connective tissue attached to the root surface at the top of the alveolar ridge crown, which is generally about 2 mm wide. The basic principle of crown lengthening is to reduce the level of the alveolar ridge apex and gingival margin by using flap surgery in combination with osteotomy, thus lengthening the clinical crown while maintaining the normal biological width. If only gingivectomy is performed without removing part of the alveolar ridge, the gingiva will often grow back to the preoperative level before the restoration is completed, or inflammatory manifestations such as gingival hyperplasia, redness and swelling, and alveolar bone resorption will occur after the restoration is completed, and this phenomenon is mainly due to the fact that the gingiva alone cannot be removed to meet the biological width requirement. 2. Probe the location and extent of the broken end of the tooth, estimate the position of the gingival margin after surgical debridement, and design the incision. If it is an anterior tooth, the position of the postoperative gingival margin should be considered to be in harmony with the adjacent teeth; if it is a crown lengthening procedure for anterior tooth esthetics, the incision position should follow the physiological shape of the gingiva and pay attention to the different gingival heights of the central incisors, lateral incisors and cuspids. 3. Determine the position of the internal oblique incision according to the new position of the postoperative gingival margin. If the attached gingival width is insufficient, a rootward repositioning flap is required. 4, Flap is turned and the removed gingiva is removed to expose the root surface or root section. 5.Bone trimming is performed to remove some of the supporting bone so that the height of the bone ridge can be positioned to meet the postoperative biological width, generally the top of the bone ridge needs to be lowered to at least 3 mm above the root of the tooth fracture margin. During bone trimming, attention should also be paid to make the height of the bone ridge gradually move with other parts of the bone ridge and neighboring teeth, so that there is no obvious disparity in order to obtain a good gingival profile after surgery. A high-speed turbo drill No. 8 round drill or bone chisel is often used for bone resection.