A patient returns a few days after receiving complete maxillary and mandibular dentures complaining of cheek biting. What is the most likely cause?

Cheek biting after new denture delivery is most commonly caused by an increased vertical dimension of occlusion (VDO). When VDO is set too high, the buccal mucosa becomes positioned between the posterior teeth during mastication, leading to inadvertent biting of the cheeks. An increased VDO also prevents normal physiologic rest position, leading to continuous tooth contact and muscle fatigue. Other contributing factors can include excessive buccal flange extension or posterior teeth positioned too far buccally. Habituation issues alone are less likely to cause consistent cheek biting in the early post-insertion period — a structural cause should be ruled out first.