Introduction:
Successful dental treatment by the dentist or the dental surgeon depends upon effective pain control in the patient during the procedures adopted in the dental clinic or office. Dental pain would arise because of various conditions ranging from the most common cause of acute or chronic pulpal pain to jaw infection and swellings, maxillary or paranasal sinus, ENT infections, or even systemic syndromes that may be linked with the pain of unknown dental origin.
What Is the Pain Pathway?
The pain receptors are nerve fibers endings that can be excited by three types of stimuli that may be mechanical, thermal, and chemical in nature for which the appropriate response is evoked. The sensitized fibers or the nociceptors that are present in the dental pulp tissue, that is, the pulp horns, the predentin or the tubular layer, the extracellular spaces or the odontoblast layer, etc. There are also several other chemical secrets within the body that are capable of inducing a response to these tactile stimuli; for example, the pain receptors in any part of the body can be stimulated by hormone and chemical substances like bradykinin, serotonin hormone, histamine, or even prostaglandin fatty acids. When there is a local inflammatory response, like the pain around the tooth, within the pulpal infected tissue, or the infected or swollen gums can further aggravate the feeling of pain. The aggravated pain evoking a prolonged or increased patient sensitivity to such pain impulses is termed hyperalgesia.
Pain mechanisms are always stimulated by two main types of nerve fibers that reply to the impulses generated as pain from the spinal cord to the nerve tracts that ascend into the brain stem.
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The A-delta fibers are responsive to mechanical stimuli as well as the thermal stimulus that creates a feeling of acute or sharp throbbing localized dental pain.
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The C fibers are the second type of fibers that are unmyelinated and are sensitized to chemical, thermal and mechanical stimulus. These fibers, when evoked, produce the sensation of prolonged sensitivity and dental pain.
What Is the Mechanism of Dental Pain?
The dental pulp is not only richly innervated and vascularized, but the neural components involved with the dental pulp tissue, or the root canal is associated with a collective framework of sensory trigeminal axon nerve bundles. The sensory nerve fibers of the dental pulp mainly reach the end of the tooth root or the root canal through the apical foramen. They are associated with both blood vessels and neurovascular bundles that supply the dentition and jaw. The sensory fibers of the root canal or the pulp tissue are the neural endings from the fifth cranial nerve, i.e., the trigeminal nerve. They are afferent sensory fibers that eventually reach or exit the end of the pulp or the root canals of the tooth through the apical foramen.
The pulp tissue of the human tooth is categorized into a coronal pulp and radicular pulp. In the coronal pulp area, the communication is between the nerve structure innervating the pulp and the dentin layer of the tooth. The fibers in the midst of these regions or the intersection have a communication channel between the coronal pulp and the dentin layer also known as the plexus of raschkow.
There are also several intertubular fibers that innervate the dentin as well as the pulp chambers. Here again, is the mechanism of action of the two fibers discussed earlier i.e., the A-delta and the C fibers. These two kinds of fibers are nociceptive in function and penetrate the tooth and it is responsible for the sensitized responses. Both these fibers can sometimes be mixed within a single tooth and vary according to the diameter, function, and independent conduction velocities. For example, when there is a sensation of drilling in the tooth that the patient experiences in the dental clinic during procedures, the sensitivity generated is through the A-delta fibers. Similarly, any cold or sweet stimuli are capable of provoking a sensation through these fibers. So, if there is a source of dental infection C fibers on the other hand are responsible for producing referred dental pain that is often diffuse in characteristic because they indicate irreversible damage to the pulpal tissues and due to innervation in multiple teeth, causing the patient to most exactly realize the correct source of pain. Also, because these fibers are heat activated, they are responsible for evoking burning mouth sensation in certain syndromes and systemic conditions as well.
What Is the Pathway of Touch?
Pathway of touch belongs to ascending tract present in the posterior column of the spinal cord, which carries sensations like pressure, vibration, movement, the position of the body, tactile localization, tactile discrimination, distension of bladder, and rectum, etc. The sensation carried from the lower half of the body is carried through the fasciculus gracilis. The sensation carried from the upper half of the body is carried through the fasciculus cuneatus. Receptors involved are tactile (Messiner's) corpuscles, Merkel's disks, and free nerve endings around the hair follicles.
Process in the pathway of touch is as follows:
First Order Neuron: The peripheral process begins from the respective receptors relay to the cell body in the dorsal root ganglion. The central process enters the posterior white column of the spinal cord and terminates in the nucleus gracilis and cuneatus of the (Messiner's) corpuscles. There it ascends through the lateral white column of the spinal cord to enter the brainstem. In the brainstem, this tract is called the spinal lemniscus. The tract relay in the ventro-postero-lateral nucleus of the thalamus.
Second Order Neuron: It is present in the ventro-postero-lateral nucleus of the thalamus. Fibers arising from the ventro-postero-lateral nucleus of the thalamus pass through the posterior one-third of the posterior limb of the internal capsule. Then the fibers ascend through the corona radiata to reach the postcentral gyrus of the sensory cerebral cortex.
Conclusion:
Thus to conclude, the centralized pathways of pain and touch are responsible for the complex neurophysiologic mechanisms mediated in perceiving dental pain that may vary as a threshold from individual to individual. An understanding of the rich neurovascular supply and pain pathway of dental origin pain can thus help the dental surgeon effectively control and manage the symptoms of pain.
