This procedure is also called “chin shortening surgery” or “reduction genioplasty;” the main goal is to correct the lantern long chin (“bailing bucket”-shaped chin) or forward protrusive chin. The facial contours of these patients in the side view often show not only a disproportional overdeveloped chin or combined depressed midfaces (maxillary hypoplasia) but also overdeveloped mandibles, making jawlines very steep and long (mandibular prognathism). Thus, the “upper depressed–lower protruded” condition results in a typical “crescent-shaped” or “curved knife-shaped” face; several patients with these conditions can also have teeth function problems such as malocclusion or misalignment. Accordingly, surgeons will have to clarify the requirements of patients during preoperative evaluation. If patients only want to improve their undesired face shape, chinbone segmental resection with posterior sliding surgery should be proper for correcting their problem by shortening and backward sliding of the chinbone; however, if patients also want to correct their malocclusion at the same time, they will have to consider extensive two-jaw surgery or prognathic surgery to simultaneously obtain the dual results of facial contour reconstruction and malocclusion correction.
The procedure is very similar to that of chinbone anterior sliding osteotomy and necessitates the same incision in the lower gum. However, in patients undergoing correction for the bailing bucket-shaped chins, the chin bones are mostly obviously overdeveloped. Thus, Dr. Chuang will have to transversely cut through the chinbone right under the mental nerve and remove a segment of it (segmental resection). The thickness of the removed bone will vary depending on the individual situation, and the average reducible distance is approximately 0.8–1 cm. After removing the bone, Dr. Chuang will push the distal section upward or backward and fix it on the main body with steel wires, bone screws, or plates; finally, he will finish the entire procedure after confirming that the central part of the chin is in the correct position. This procedure can reduce the length of the chin in the front view and retract and shorten the jawline in the side view. If necessary, Dr. Chuang will flexibly combine this surgery with either mandible reduction or V-line chin reduction to not only reduce the protrusive or elongated chin but also achieve the perfect small and pointed contour for the lower face. For patients with a congenital depressed midface (maxillary hypoplasia), Dr. Chuang will simultaneously perform paranasal or submalar triangle implants to balance the facial ratio between the midface and chin; thus, the facial deficiencies such as “curved knife face” or “horse face” can be effectively improved in these combined procedures.