30.5 Odontogenic Infection and Fascial Space Spread

Why This Is High Stakes

Preparing for Practice outcome 1.9.2 requires registrants to "recognise and manage acute dento-alveolar and mucosal infection". Odontogenic infection is one of the few dental conditions that kills, and the mechanism is airway obstruction or intracranial spread rather than the infection itself.

Pathway of Spread

Infection from a necrotic pulp reaches the periapical bone, erodes through the cortical plate at its thinnest point, and then spreads according to two anatomical relationships:

1. Which cortical plate is thinner at the apex — usually buccal, except for the palatal root of the maxillary first molar, the mandibular second and third molars and the maxillary lateral incisor.
2. Whether the apex lies above or below the muscle attachment, principally buccinator in the maxilla and mylohyoid in the mandible.

Ludwig's Angina

Ludwig's angina is bilateral cellulitis of the submandibular, sublingual and submental spaces. It is a surgical emergency and a genuine airway emergency.

Recognition:

• Bilateral, firm, brawny, non-fluctuant swelling of the floor of mouth and submandibular region
• Elevated and protruding tongue, drooling, inability to swallow saliva
• Trismus, dysphonia ("hot potato voice"), dysphagia
• Rapidly progressive; pyrexia and systemic toxicity

Immediate management is airway assessment first, urgent 999 transfer to a maxillofacial unit, intravenous antibiotics and surgical drainage under general anaesthesia, often with a surgical airway. Attempting to drain this in primary care wastes the only time available.

Red Flags Requiring Urgent Referral

Management Principles

1. Remove the cause. Drainage of pus and removal of the source — extraction or pulp extirpation — is the definitive treatment. Antibiotics alone do not resolve an established abscess.
2. Establish drainage. Incise and drain a fluctuant collection through healthy tissue at the most dependent point, under local anaesthesia delivered as a regional block or by field infiltration around rather than into the inflamed tissue.
3. Antimicrobials only where indicated — systemic involvement, spreading infection, immunocompromise, or where drainage cannot be achieved immediately. First line in the UK is amoxicillin or phenoxymethylpenicillin, with metronidazole added or used alone for anaerobic infection, and clarithromycin in penicillin allergy. Courses are short, typically up to five days, with review at 48 to 72 hours.
4. Analgesia and supportive care, with clear written instructions on what to do if symptoms worsen.
5. Safety-netting — the patient must know which signs mean immediate return or attendance at an emergency department.

Cavernous Sinus Thrombosis

Infection from a maxillary anterior tooth or the canine space can track through the valveless angular and ophthalmic veins, or from the pterygoid plexus through emissary veins, into the cavernous sinus. Features include periorbital oedema, proptosis, chemosis, ophthalmoplegia from involvement of cranial nerves III, IV and VI, and altered sensation over V1 and V2, with severe headache and systemic toxicity. This is a neurosurgical and maxillofacial emergency with significant mortality.

Rule. In any spreading odontogenic infection the sequence is airway, then referral decision, then drainage, then antibiotics — in that order. Prescribing an antibiotic and reviewing in a week is the single most dangerous answer available in an examination stem describing trismus and a raised floor of mouth.

Assessing Severity and Deciding on Referral

The examinable assessment of an odontogenic infection uses a small number of objective signs. Airway compromise — stridor, an inability to swallow saliva, a raised tongue, a change in voice — is the most urgent. Trismus indicates involvement of the masticatory spaces and impedes both airway management and local treatment. Eye closure or periorbital swelling from a canine space or infraorbital infection raises the possibility of cavernous sinus spread. Systemic sepsis — fever, tachycardia, tachypnoea, hypotension, confusion — is assessed with a recognised tool such as NEWS2 and mandates emergency admission. Rapid progression over hours, bilateral submandibular and sublingual involvement, and involvement of the lateral pharyngeal or retropharyngeal spaces all require immediate hospital referral.

The principles of treatment are unchanged whatever the severity: remove the cause, establish drainage, and support the host, with antimicrobials as an adjunct rather than a substitute. An SBA that describes a spreading infection and offers "prescribe antibiotics and review in a week" as an option is testing whether the candidate recognises that drainage and source control come first, and that a patient with airway signs needs an ambulance, not a prescription.

The other examinable dimension is timing. Odontogenic infections can progress from a localised swelling to airway compromise within hours, particularly in children, in diabetic patients and in the immunosuppressed, so a patient sent home with antibiotics must be given explicit safety-netting advice: return immediately if the swelling extends towards the eye or under the jaw, if swallowing or breathing becomes difficult, if the mouth will not open, or if fever and malaise worsen. Recording that advice is part of the expected standard, and its absence is a recognised factor in serious adverse outcomes.