What nerve is most likely damaged in the patient who struggles to purse lips after a facial injury?

The correct answer focuses on the buccal branch of the facial nerve, which is responsible for innervating the muscles of facial expression in the area around the mouth, including the ability to purse the lips. Damage to this specific branch can lead to difficulties in performing actions such as whistling, blowing, or forming a tight seal with the lips, as these functions require coordinated contraction of the orbicularis oris muscle, which is primarily innervated by the buccal branch.

In the context of a facial injury, it's common for the buccal branch to be affected due to its superficial location and its pathway across the facial region. Consequently, when a patient presents with an inability to purse their lips, it strongly indicates that the buccal branch has been compromised.

Other nerves mentioned do not primarily control the lip movements. For instance, the mandibular branch of the facial nerve primarily innervates the muscles of mastication and some of the facial muscles but is not directly responsible for lip movement. The infraorbital branch of the maxillary nerve provides sensation to the skin of the upper lip and does not control muscle action. The inferior alveolar branch of the trigeminal nerve is mainly responsible for sensation to the lower teeth