Authors: Trowbridge HO.
Title: Review of dental pain--histology and physiology.
Journal: J Endod
Date: Oct 1986
Citation: 12(10):445-52
Category: Endodontic Biology, Histology and Physiology
Evidence-based Ranking: 5
Purpose/Objective: To describe the histology and physiology of dentinal pain.

Discussion: The pulp is richly innervated and contains both A (myelinated) and C (unmyelinated) nerve fibers. The nerves of the pulp include primary afferent fibers that are involved in pain transmission and sympathetic efferent fibers which modulate the microcirculation of the pulp. The sympathetic efferent fibers reduce the flow of the blood through the pulp by stimulating the smooth muscle cells encircling the arterioles. Myelinated fibers of the pulp have a diameter ranging from 1-4 microns and conduct impulses from 4-30 meters per second (A-delta fibers) or as high as 48 meters per second (A-beta fibers). Unmyelinated fibers on the other hand have individual axons less than 1 micron in diameter with velocity ranges from 0.5-2m/s. Pulpal A fibers are the one that respond to EPT; variability in their numbers in young dentition offers a possible explanation to the unreliability of this test on these type of teeth. Also, 4 types of nerve endings were described: a) marginal fibers b) simple predentinal fibers c) complex predentinal fibers d) dentinal fibers. Both pain and touch sensation have been related to free nerve endings but stimulation of the pulp gives rise only to pain. “Fast pain” is associated with A fibers and “slow pain” with C fibers. Stimulation of A fibers produce a sharp, piercing or stabbing sensation while C fibers produce dull, burning, aching sensation that is usually harder to endure. The hydrodynamic theory of dentin sensitivity (Brannstrom) was also mentioned and it states that stimuli that are capable of eliciting pain when applied to dentin do so because they cause fluid movement to the dentinal tubules. Finally, evidence suggests that inflammatory mediators such as bradykinin, 5-hydroxytryptamine, and some metabolites of arachidonic acid play an important role in initiating hyperalgesia. This results in greater responsiveness to stimuli such as heat, cold, desiccation and mechanical stimulation of exposed dentin.

Reviewer’s comments: A good review of dentinal pain.