A periapical infection of a MAXILLARY posterior tooth most commonly drains to which location?

Correct answer: C. Buccally, into the buccal vestibule

• A. The SUBLINGUAL space is also mandibular, entered from teeth whose apices lie ABOVE the mylohyoid line — typically premolars and the first molar.
• B. PALATAL drainage does occur, but characteristically from the maxillary LATERAL INCISOR (whose apex curves palatally) and from the PALATAL ROOT of the first molar — it is the exception rather than the rule.
• C. CORRECT. Most maxillary odontogenic infections perforate the BUCCAL cortical plate and drain into the BUCCAL VESTIBULE, because the buccal plate is thinner than the palatal plate and the root apices generally lie closer to it. Whether the swelling then appears intraorally in the vestibule or extraorally in the buccal space is determined by the apex's position relative to the attachment of the BUCCINATOR muscle — above the attachment gives buccal space involvement, below it gives vestibular swelling.
• D. The SUBMANDIBULAR space is a MANDIBULAR pathway, entered from lower molars whose apices lie BELOW the mylohyoid line.

Note: The genuinely dangerous maxillary pathway is superior spread from anterior teeth into the CANINE space and then, via the angular and ophthalmic veins, to a CAVERNOUS SINUS THROMBOSIS. Those facial veins are valveless. Periorbital swelling, proptosis, ophthalmoplegia or altered consciousness with a dental infection is an emergency requiring immediate hospital referral.