Which of the following injections is more likely to cause trismus?

The injection most likely to cause trismus is the PSA nerve block. This is because the PSA block targets the posterior superior alveolar nerve, which is located near areas with significant muscle and vascular structures. If the needle inadvertently traumatizes the pterygoid muscles or the mandibular ramus during the injection, it can lead to muscle spasms and subsequent trismus, characterized by restricted mouth opening.

Injections like the MSA and ASA nerve blocks are less likely to cause trismus because they target nerves that are situated further from the deep muscle tissues where more traumatic interactions might occur. Additionally, infiltration techniques involve delivering local anesthesia directly into the tissue near the site of treatment and do not penetrate as deeply or as close to the muscles that, if damaged, could result in trismus. Therefore, the PSA nerve block, due to its anatomical proximity to influential muscle structures, poses a higher risk for this complication.