An accurate determination of the status of the pulp is a critical element in achieving the correct diagnosis and treatment plan. An important part of making that diagnosis is determining whether the pulpal tissue of the tooth in question is vital or necrotic. One of the most well-established tools for the evaluation of pulp vitality is the electric pulp test or EPT.
The EPT measures the vitality of the dental pulp indirectly, by sending a gradually increasing electrical current through the tooth to stimulate a sensory response. Every tooth is innervated by nerve fibers arising from the trigeminal (V) nerve nucleus. These fibers enter the tooth in large bundles through the apical foramina and then disseminate into smaller fibers making up the plexus of Raschkow at the periphery of the pulp.
Two types of sensory nerve fibers exist in the dental pulp: myelinated A fibers and unmyelinated C fibers. Both are nociceptors that respond to potentially damaging stimuli by sending signals to the CNS that are interpreted as pain. C fibers are generally located in the center of the tooth in the body of the pulp and mediate dull, poorly localized pain. A fibers extend to the periphery of the pulp, near or somewhat into the dentinal tubules. A fibers mediate acute, sharp pain and are typically the fibers stimulated by EPT.
The earliest use of electricity to diagnose teeth was reported by Magitot, in his book Treatise on Dental Caries, in France in 1867. For many years dentists tried to correlate not just the vitality of dental pulps but also the degree of pulpal damage with early variants of the EPT. By the late 1960s, many investigators had concluded that EPT result could not be correlated with pulpal histology. A positive EPT simply indicated a vital pulp while a negative result indicated a necrotic pulp.
EPT records a number from 0-80. Any response prior to 80 is indicative of a vital pulp. No response at 80 is confirmatory for pulpal necrosis. Unfortunately, there can be false positives where a patient response occurs even when the pulp is necrotic. A number of researches found EPT false positives to be in the range of 25-28%. This usually is a result of current leakage from an inadequately dried tooth or having the current increase too rapid. For optimal results place the EPT tip on a dry tooth with a conducting medium such as toothpaste. Placing the tip on the incisal 1/3 of the tooth generally gives the most accurate reading.
In actuality, a positive response to the EPT only describes the presence of vital nerve fibers in the tooth and not pulpal blood flow, which is a more accurate depiction of pulpal vitality. EPT is particularly helpful in older patients with secondary dentin formation and calcified pulps that are insulated against thermal challenges. As is always the case, using multiple types of pulp testing, along with a complete patient history, and appropriate radiographs to confirm the pulpal diagnosis is the best course of action.