Editing Toothache (section)

==Pathophysiology==
{{multiple image
| align     = right
| direction = vertical
| width     = 180

| image1    = Cross sections of teeth labels.png|
| caption1  = 1: crown, 2: root, 3: enamel, 4: dentin and dentin tubules, 5: pulp chamber, 6: blood vessels and nerve within root canal, 7: periodontal ligament, 8: apex and periapical region, 9: alveolar bone.

| image2    = Innervation of the dentition.png
| caption2  = V<sup>2</sup>: [[maxillary nerve|maxillary division]] of trigeminal nerve, V<sup>3</sup>: [[mandibular nerve|mandibular division]] of trigeminal nerve, A: the [[superior alveolar nerves]] and [[superior dental plexus|plexus]], B: the [[inferior alveolar nerve]] and [[inferior dental plexus|plexus]] running in the body of the mandible.

| image3    = Pulpal dentin junction.png
| caption3  = Dentin-pulp complex. 1: tooth/enamel, 2: dentin tubule, 3: dentin, 4: odontoblastic process, 5: predentin, 6: [[odontoblast]], 7: capillaries, 8: [[fibroblast]]s, 9: nerve, 10: artery/vein, 11: cell-rich zone, 12: cell-poor zone, 13: pulp chamber.}}
<!-- basic dental anatomy -->
A tooth is composed of an outer shell of [[calcification|calcified]] hard [[Tissue (biology)|tissue]]s (from hardest to softest: [[Tooth enamel|enamel]], [[dentin]], and [[cementum]]), and an inner [[soft tissue]] core (the pulp system), which contains [[nerve]]s and [[blood vessel]]s. The visible parts of the teeth in the mouth – the crowns (covered by enamel) – are anchored into the bone by the [[Dental anatomy#Crown and root|roots]] (covered by cementum). Underneath the cementum and enamel layers, dentin forms the bulk of the tooth and surrounds the pulp system. The part of the pulp inside the crown is the [[pulp chamber]], and the central soft tissue nutrient canals within each root are [[root canal]]s, exiting through one or more holes at the root end ([[apical foramen]]/foramina). The [[periodontal ligament]] connects the roots to the bony socket. The [[gingiva]] covers the [[alveolar process]]es, the tooth-bearing arches of the jaws.<ref name=Kumar2004>{{cite book|title=Textbook of Dental Anatomy and Tooth Morphology|year=2004|publisher=Jaypee Brothers Publishers|isbn=9788180612299|url=https://books.google.com/books?id=vWgQ28cQtRQC&q=Textbook+of+Dental+Anatomy+and+Tooth+Morphology|author=Kumar PS}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>{{rp|1–5}}

<!-- dentin feels pain, enamel doesn't -->
Enamel is not a vital tissue, as it lacks blood vessels, nerves, and living cells.<ref name=Napenas2013 /> Consequently, pathologic processes involving only enamel, such as shallow cavities or cracks, tend to be painless.<ref name=Napenas2013 /> Dentin contains many microscopic tubes containing fluid and the processes of [[odontoblast]] cells, which communicate with the pulp. Mechanical, [[Osmosis|osmotic]], or other stimuli cause movement of this fluid, triggering nerves in the pulp (the "[[Fluid dynamics|hydrodynamic]] theory" of pulp sensitivity).<ref name=Petersson2013 /> Due to the close relationship between dentin and pulp, they are frequently considered together as the ''dentin-pulp complex''.<ref name=Tencate2008>{{cite book|author=Nanci A|title=Oral histology: development, structure, and function.|year=2008|publisher=Mosby|location=St. Louis, Mo.|isbn=978-0-323-04557-5|url=https://books.google.com/books?id=nLW3Ts_TDpEC&q=dentin+pulp+complex&pg=PA191|edition=7th}}</ref>{{rp|118}}

<!-- physiologic sensitivity vs pain from disease -->
The teeth and gums exhibit normal sensations in health. Such sensations are generally sharp, lasting as long as the stimulus.<ref name=Napenas2013 /> There is a continuous spectrum from physiologic sensation to pain in disease.<ref name=Napenas2013 /> Pain is an unpleasant sensation caused by intense or damaging events. In a toothache, nerves are stimulated by either [[exogenous]] sources (for instance, bacterial toxins, [[Metabolism|metabolic]] byproducts, chemicals, or trauma) or [[endogenous]] factors (such as [[inflammation|inflammatory mediators]]).<ref name=Hargreaves2011 />{{rp|532–534}}

<!-- pain pathway from teeth to brain + pain definitions -->
The pain pathway is mostly transmitted via [[myelin]]ated [[A delta fiber|Aδ]] (sharp or stabbing pain) and unmyelinated [[Group C nerve fiber|C]] [[nerve fiber]]s (slow, dull, aching, or burning pain) of the [[trigeminal nerve]], which supplies sensation to the teeth and gums via many divisions and branches.<ref name=Napenas2013 /> Initially, pain is felt while noxious stimuli are applied (such as cold). Continued exposure decreases firing thresholds of the nerves, allowing normally non-painful stimuli to trigger pain ([[allodynia]]). Should the insult continue, noxious stimuli produce larger discharges in the nerve, perceived as more intense pain. Spontaneous pain may occur if the firing threshold is decreased so it can fire without stimulus ([[hyperalgesia]]). The physical component of pain is processed in the [[brainstem|medullary spinal cord]] and perceived in the [[frontal cortex]]. Because pain perception involves overlapping sensory systems and an emotional component, individual responses to identical stimuli are variable.<ref name=Hargreaves2011 />{{rp|474–475}}