IANB Failure — ORE Part 1 MCQ
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Correct answer: E — Incorrect placement of the needle tip (too low or too far anterior)
The answer is E. The IANB has a baseline failure rate of 15–20%, predominantly caused by inaccurate needle placement relative to the mandibular foramen, particularly positioning that is too low or too far anterior. This operator-dependent technique error accounts for the majority of failures. While anatomical variations (including accessory innervation from the mylohyoid and mental nerves) do contribute to some failures, these are secondary causes and do not explain the primary failure mechanism. Insufficient anaesthetic volume is not a common cause when standard cartridge protocols are followed. Expired cartridges and infection at the injection site are neither recognised causes of anesthetic failure. Discrimination hinges on distinguishing technique-related needle placement error (most common) from anatomical innervation anomalies (less common but occasionally contributory).
Reference: The Annals of The Royal College of Surgeons of England. Inferior Alveolar Nerve Block. 2008. https://publishing.rcseng.ac.uk/doi/full/10.1308/003588408X261834