a role in molecular mechanisms involved with pain, including ion channels and inflammation. Substance P (SP) is a neuropeptide produced by capsaicin neuron cell bodies (localized in trigeminal ganglia and dorsal root) and plays a major role in dental pain and inflammation. Other peptides include cGRP, galanin, somatostatin, and neurokinin A-B. The biological effects of SP are expressed by the binding of specific G protein-coupled NK receptors. Interaction with SP receptors induces vasodilation and allows for plasma extravasation and mastocyte degranulation. SP is highly expressed in dental pulp and dentin. When pain, thermal, and/or chemical stimulation is present, SP production and release increases. Current studies focus on whether controlling Substance P expression may control tooth pain. In addition, dental caries is more likely to develop pulpitis due to less time for the dental pulp to react and protect itself by occluding the dentinal tubules. Based on the tooth injury, sensory nerve fibers react to pulpitis by growing terminal branches into the adjacent surviving pulp, which also changes the cytochemical phenotype. This neural growth typically lasts few a few days and function and form is retained. Thus, pain is poorly localized, and the level of pain stemming from pulpitis varies based on severity, quality, duration, onset, trigger. As caries invades dentin, the number of permeable dentinal tubules correlates with the degree of pain. Intrapulp pressure have an effect on the sensory nerves of varying diameters: blocking larger diameter Aδ-fibres and activating smaller C-fibers. Under hypoxic environments and pulp degeneration (symptom of pulpitis), C-fibers may still function. Once reparative dentin forms, odontoblasts associated with the dentin change, and the pulpal fibroblasts lose p75 expression, which is a neurotrophin receptor. Diagnosis Pulp sensibility tests are routinely used in the diagnosis of pulpitis. Pulp testing is combined with information taken from history, examination and other special investigations such as radiographs in order to reach a diagnosis. Pulp sensibility tests assess the pulp's sensory response to a stimulus. There are three general types: Thermal: Agents are applied to increase or decrease the temperature of a tooth and stimulate a pulp sensory response. Cold tests: Most commonly, ethyl chloride is sprayed onto a small ball of cotton wool and is applied to the tooth, which produces intense cold. Alternatively, snow and other refrigerants such as dichlorodifluoromethane (DDM) have been shown to be effective. Heat tests: Gutta percha can be heated and directly applied to the tooth