Which muscle is most commonly involved in trismus following an inferior alveolar nerve block injection?

The medial pterygoid muscle is most commonly implicated in trismus following inferior alveolar nerve block (IANB) administration. During this injection, the needle traverses the pterygomandibular space and may inadvertently penetrate or traumatize the medial pterygoid muscle. This causes localized muscle spasm, hematoma formation, or, in rare cases, myotoxicity from the local anesthetic solution. The resulting pain triggers a reflex contraction limiting mandibular opening. The masseter and temporalis are also jaw-closing muscles, but they are not in the direct path of the IANB needle. The lateral pterygoid depresses and protrudes the mandible and is less commonly involved.