The mylohyoid line is area of attachment of mylohyoid muscle. Lingual cortical plate perforation by infection from premolars and first molar causes sublingual space infection, whereas infection from the third molar involves the submandibular space. (Modified from Flint PW, Haughey BH, Lund VJ, et al, eds. Cummings Otolaryngology: Head and Neck Surgery. 5th ed. Philadelphia: Elsevier; 201