Oral Surgery · patient case with 2 questions
Anaesthesia and infection spread in the mandible
Patient: Male, 38 years old
Chief Complaint: “The tooth at the back on the bottom is throbbing and my neck is swollen.”
Background: Untreated caries in tooth #19 for months. No systemic disease. Separately, a restoration is planned on tooth #4.
Vital Signs: BP 132/82 mmHg · HR 102 bpm · T 101.8°F · RR 20
Findings: Tender, indurated swelling BELOW the inferior border of the mandible in the region of #19, with the swelling extending medially. Tooth #19 non-vital with a periapical radiolucency. Mouth opening 30 mm. Tongue position normal, voice normal, swallowing intact at present.
Question 1
Which space is involved, and what is the complication to anticipate?
Show answer and explanation
Correct answer: D. The submandibular space, with Ludwig angina if it spreads
- A. The infratemporal space is involved by maxillary third molar infection or a contaminated posterior superior alveolar injection, and produces trismus with retro-maxillary pain.
- B. The buccal space lies lateral to the buccinator and produces cheek swelling. Cavernous sinus thrombosis is a complication of MAXILLARY and midface infection tracking through the valveless facial veins.
- C. The canine space arises from a maxillary canine and produces swelling that obliterates the nasolabial fold.
- D. CORRECT. The apices of the mandibular MOLARS lie BELOW the mylohyoid line, so infection perforating the lingual plate drains into the SUBMANDIBULAR space — producing swelling below the inferior border, exactly as described. The complication to anticipate is LUDWIG ANGINA: bilateral involvement of the submandibular, sublingual and submental spaces, which elevates the tongue and obstructs the airway. It is a rapidly progressive, life-threatening emergency requiring airway protection, intravenous antibiotics and surgical drainage.
Note: The MYLOHYOID LINE decides everything in the mandible. Apices ABOVE it — the premolars and usually the first molar — drain into the SUBLINGUAL space, elevating the floor of the mouth. Apices BELOW it — second and third molars, often the first — drain into the SUBMANDIBULAR space, swelling below the jaw. The warning signs that turn this into an emergency are elevation or protrusion of the TONGUE, a muffled 'hot potato' VOICE, DROOLING or inability to swallow, and any stridor. Assess and document all four at every visit in a spreading infection.
Question 2
Which nerve provides pulpal innervation to tooth #4 when it is present?
Show answer and explanation
Correct answer: D. The middle superior alveolar nerve
- A. The greater palatine nerve is sensory to the PALATAL soft tissue from the canine backwards. It carries no pulpal innervation.
- B. The posterior superior alveolar nerve supplies the maxillary molars except the mesiobuccal root of the first molar, which is the reason a PSA block alone often fails to anaesthetise that tooth completely.
- C. The anterior superior alveolar nerve supplies the central and lateral incisors and the canine — and the premolars too when the middle superior alveolar nerve is absent.
- D. CORRECT. The MIDDLE SUPERIOR ALVEOLAR nerve supplies the maxillary PREMOLARS and the MESIOBUCCAL root of the first molar. It branches from the infraorbital nerve within the infraorbital canal and descends in the lateral wall of the sinus. It is worth knowing that this nerve is ABSENT in roughly 30 to 70 percent of people — when it is, the anterior superior alveolar nerve extends posteriorly to cover the premolars instead. That anatomical variability is why a buccal infiltration over the premolar apex is the reliable technique rather than any named block.
Note: All three superior alveolar nerves are branches of V2 by way of the infraorbital nerve, and they form the superior dental plexus, which is why they overlap so freely. Practical consequence: for a maxillary first molar, supplement the PSA block with a buccal infiltration over the mesiobuccal root.