A disadvantage of the lingual split technique in oral surgery is:

The lingual split technique involves creating a surgical access on the lingual side of the mandible. This approach can unintentionally lead to the disruption of the thin lingual cortical plate and the underlying soft tissues, which may cause opening up of the facial spaces on the lingual side and the floor of the mouth. This can result in potential complications such as spread of infection and difficulty in wound closure. Therefore, the main disadvantage is the increased risk of exposing and opening these anatomical spaces, which must be carefully managed during surgery to prevent postoperative morbidity.

Reference: Oral and Maxillofacial Surgery, Raymond J. Fonseca, 3rd Edition.