C

Electric pulp testing and the sharp, brief pain of reversible pulpitis are mediated by the fast-conducting, thinly myelinated A-delta fibers, which have the lowest excitation threshold to electrical stimuli and produce a rapid, stabbing pain; unmyelinated C-fibers instead convey dull, lingering pain [Virtanen, 1984, PMID 6148846; Bender, 2000, PMID 11199715].