Final answer:
Severe intermittent TMJ pain in patients taking conventional antipsychotics is likely due to extrapyramidal side effects, which are known complications of these medications.
Step-by-step explanation:
Patients taking conventional antipsychotics can experience severe intermittent TMJ pain. The pain is most likely a consequence of extrapyramidal side effects. These side effects are associated with the dopaminergic blockade in the nigrostriatal pathway, which is a common action of conventional antipsychotics.
While other options such as hyperalgesia from alpha-adrenergic blockade, anticholinergic side effects or dislocation of the mandible could theoretically cause pain extrapyramidal symptoms (EPS) are a well-known and frequent side effect of conventional antipsychotics that can lead to conditions such as tardive dyskinesia, dystonia and akathisia which could contribute to TMJ pain.