Accidental displacement of the tooth fragment in the anatomical space is one of the unfavourable surgical complications of the mandibular third molar extraction, which has been reported in English literature since Doran (1932) reported the first case (Fig. 10.1). Reported number of the cases are relatively small; however, the actual number should be larger as we empirically know that the patient who’s mandibular third molar is displaced in the floor of the mouth during the extraction is occasionally referred to the hospital. The anatomical spaces around the mandibular third molar include submandibular space, sublingual space, pterygomandibular space, and parapharyngeal space that connect with the retropharyngeal space. Among these, displacement in the submandibular/sublingual space has been the most frequently reported (Fig. 10.2) (Cheung et al. 2010).