Which virus can mimic the pain of irreversible pulpitis in the orofacial region?

VZV (Varicella-Zoster Virus / Herpes Zoster) in the prodromal phase causes severe, lancinating pain along the distribution of the affected nerve BEFORE the rash appears. In the trigeminal distribution, this pain can mimic irreversible pulpitis or odontogenic pain — patients may present to dentists complaining of severe tooth pain with no dental etiology. This is a classic clinical pitfall: performing endodontic treatment on a 'pulpitic' tooth that is actually the prodrome of herpes zoster. The subsequent vesicular rash clarifies the diagnosis.