Failed inferior alveolar block in irreversible pulpitis during pregnancy
A 35-year-old woman has spontaneous throbbing pain in the lower left first molar (tooth 36) for three nights, waking her from sleep; pain is poorly localized and aggravated by hot drinks. Tooth 36 has a deep distal carious lesion, no swelling, probing depths ≤3 mm, and is tender to percussion. Two attempts at inferior alveolar nerve block with 2% lidocaine 1:100,000 (2.2 mL each) and buccal infiltration produced lip numbness but the tooth remained painful to access. She is 28 weeks pregnant. She is anxious, has not eaten, and takes no medication apart from iron. Her blood pressure is 118/72 mmHg. The clinic stocks 4% articaine with 1:100,000 adrenaline, 2% lidocaine with 1:80,000 adrenaline, 3% mepivacaine plain, and 0.5% bupivacaine with 1:200,000. Access is required; there is no swelling and no trismus.
1. Why has the inferior alveolar nerve block failed, and what does lip numbness tell you?
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In irreversible pulpitis, the block often fails not because of poor technique but because of neurophysiology. Inflammation lowers tissue pH, reducing the proportion of uncharged local anaesthetic that can cross the nerve membrane. Nociceptors are sensitised, with upregulation of tetrodotoxin-resistant sodium channels, and central sensitisation amplifies the response. Inflamed pulpal tissue also has increased blood flow, which removes the drug. Success rates for inferior alveolar nerve blocks in irreversible pulpitis are often quoted as around 20–40%, far below the success seen in healthy teeth. Lip numbness confirms that the local anaesthetic reached the inferior alveolar nerve and anaesthetised the mental nerve distribution; it does not guarantee pulpal anaesthesia. It also suggests the deposition was in the correct place, so repeating the same block a third time is unlikely to help and increases the risk of toxicity and needle injury. Anatomical factors such as accessory innervation from the mylohyoid nerve, or a bifid canal, may also contribute.
2. What anaesthetic options would you use now, taking her pregnancy into account?
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I would not repeat a third inferior alveolar block. Supplemental techniques are more predictable. A buccal infiltration of 4% articaine with 1:100,000 adrenaline, given slowly, can diffuse through buccal bone in mandibular molars, particularly when combined with a previous block. Alternatively, an intraligamentary injection delivers 0.2 mL per root directly into the periodontal ligament with a pressure syringe; it is effective for a single tooth and uses a small volume. Intraosseous anaesthesia is another option if equipment is available. In pregnancy at 28 weeks, lidocaine with adrenaline is well established; articaine has less data but is widely used and considered acceptable for a single visit. I would avoid plain mepivacaine because it lacks vasoconstriction and is shorter-acting, and bupivacaine is not my first choice. I would limit the total adrenaline dose, aspirate carefully, avoid supine hypotension by using a semi-upright or left lateral position, keep the appointment short, and monitor her. Anxiety and an empty stomach increase the risk of syncope, so I would let her eat and use calm reassurance.
3. What definitive treatment would you provide today, and what would you prescribe?
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The priority is to remove the inflamed pulp and reduce the pressure in the pulp chamber. If time allows, I would start root canal treatment: access, pulp extirpation, determination of working length, and placement of a calcium hydroxide dressing, with a temporary restoration. If time or anaesthesia is limited, a full pulpotomy removing the coronal pulp to the canal orifices is a reasonable alternative and often relieves pain. Antibiotics are not indicated: there is no swelling, fever, or systemic involvement, and antibiotics do not penetrate the necrotic pulp. For analgesia, paracetamol is the safest choice in the third trimester; NSAIDs such as ibuprofen should be avoided because of the risk of premature closure of the ductus arteriosus and oligohydramnios. I would explain that the tooth needs completion of root canal treatment and a permanent restoration, and arrange review in two to four weeks. I would also document the pregnancy, the failed blocks, and the consent discussion.