Dental nerve blocks and infiltration: the anatomy behind them
- Drugs
Upper teeth are numbed by soaking anaesthetic through thin bone; lower back teeth need a block of the inferior alveolar nerve before it enters the jaw.
See it in 3D: Inferior alveolar nerve · Lingual nerve · V3 mandibular · V2 maxillary · Medial pterygoid · Parotid gland · Mental foramen
What it is
In the maxilla the outer bone is thin and porous, so anaesthetic deposited next to the root tip (infiltration) diffuses to the nerves of a single tooth. The mandible's outer bone in the molar region is thick, so lower molars and premolars usually need an inferior alveolar nerve block: anaesthetic deposited in the pterygomandibular space near the mandibular foramen, on the inner side of the ramus, between the medial pterygoid muscle and the bone. The block numbs the lower teeth on that side up to the midline, the lower lip and chin (mental nerve) and, because the lingual nerve lies close by, the anterior two-thirds of the tongue. The cheek gum of the lower molars needs a separate long buccal injection.
What to know
- Upper teeth: infiltration next to the apex; palatal tissues need palatal injections.
- Lower molars: inferior alveolar nerve block in the pterygomandibular space.
- Landmarks: coronoid notch and pterygomandibular raphe.
- Mental nerve block numbs the premolars, canine and incisors on one side and the lower lip.
- Articaine infiltration can work for some lower teeth.
Step by step
- Confirm the medical history, choose the anaesthetic and check the maximum amount.
- Apply topical anaesthetic and stretch the mucosa.
- Insert the needle at the landmarks for the chosen block or next to the apex for infiltration.
- Aspirate; if blood appears, reposition before injecting.
- Inject slowly and wait for numbness before starting.
Risks and precautions
- Too far back: anaesthetic in the parotid gland causes temporary facial palsy; protect the eye until it resolves.
- Other complications: haematoma, trismus from injury to the medial pterygoid, and rarely lasting lingual or inferior alveolar nerve injury.
- The block fails more often in inflamed «hot» teeth with irreversible pulpitis.
- Blocks are avoided or done with special care in patients with severe bleeding disorders because a deep haematoma can threaten the airway.
Next step / Initial management
- Temporary facial palsy after a block: reassure, protect the eye and observe until it recovers.
- Numbness persisting well beyond the expected duration, or altered taste: document and refer back to the dentist or oral surgeon early.
- Patients with haemophilia or similar: plan nerve blocks with haematology and prefer infiltration where possible.
Test yourself
Think of the answer, then tap the question to see it.
Why does infiltration work for upper teeth but rarely for lower molars?
The maxilla's outer bone is thin and porous; the mandible's outer bone in the molar region is thick.
Where is anaesthetic deposited in an inferior alveolar nerve block?
In the pterygomandibular space, near the mandibular foramen on the inner side of the ramus.
Which additional injection is needed for the cheek-side gum of the lower molars?
A long buccal nerve injection.
Connections
See it in 3D7
The structures of Durgical's 3D anatomy where it is found.
Educational content; it does not replace assessment by a dentist or doctor and is not a clinical instruction. For facial or neck swelling with difficulty swallowing or breathing, a knocked-out tooth or bleeding that will not stop, go to an emergency department at once.
Sources: Inferior Alveolar Nerve Block (StatPearls Publishing (NCBI Bookshelf), 2025); Local Anesthesia Techniques in Dentistry and Oral Surgery (StatPearls Publishing (NCBI Bookshelf), 2023); Anatomy, Head and Neck: Alveolar Nerve (StatPearls Publishing (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.