Definition of Pain
It is one of the most common chief complaint of the patient which makes the person walk into a dental clinic. It is a multifaceted experience involving physical, cognitive, and emotional aspects. International Association for the Study of Pain (IASP) has defines it as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.
- Acute (or transient)- the pain is sharp but soon subsides and it is protective; it warns us of impending tissue damage
- It can last for a few days or a few weeks can follow athletic injuries of the elbow, knee, or elsewhere. We call this as persistent. It can also be protective since it forces us to rest the injured part and avoid further damage
- It can persists long after an injury has apparently healed, possibly for months or years, resulting in chronic pain. This type can be nonprotective.
Receptors
- Nociceptors – found in the skin, muscle, joints, bone and organs (other than the brain) and can fire in response to a number of different stimuli. Three types of nociceptors exist:
- Mechanical nociceptors – detects sharp, pricking type
- Thermal and mechano-thermal nociceptors – detects sensations which elicit pain which is slow and burning, or cold and sharp in nature
- Polymodal nociceptors – detects mechanical, thermal and chemical stimuli
Pathway of transmission of nociceptive information from the orofacial region –
The trigeminal pain system is a complex multilevel system that begins with the detection of tissue damaging stimuli in the periphery, the processing of that input at the level of the medullary spinal cord, and the final perception of what is felt as pain in the cerebral cortex.
Theory
Gate Control Theory – Most accepted theory
- It was given by Ronald Melzack and Charles Patrick (Pat) Wall (Melzack and Wall 1965.
- There are nociceptors and touch fibers and proposed that that these fibres synapse different regions within the dorsal horn of the spinal cord.
- They proposed that signals produced in primary afferents from stimulation of the skin were transmitted to three regions within the spinal cord
– The substantia gelatinosa
– The dorsal column
– A group of cells called transmission cells
It is postulated that a control system or “gate” is present in the dorsal horn of the spinal cord, which passes all the information regarding pain before it reaches the brain. The opening or closing of the gate is controlled by the substantia gelatinosa in the dorsal horn. An “open gate” means that the signals are carried by the transmission cells (i.e., t-cells) to the brain where it is perceived, while a “closed gate” stops the firing of the t-cells and no signal is sent to the brain.
Basic Characteristics of Measure of Pain –
- Allow for a comparison of the magnitude of changes in pain across treatments and pain conditions
- Be relatively free of bias
- Be relatively easy to use
- Be useful for assessing both experimental and clinical pain
- Allow for comparisons with neurobiologic measures in humans and animals to study underlying mechanisms
What is Referred pain ?
Pain that is perceived at a site adjacent to or away from the site of origin. The deep and some visceral pain are referred to other areas. But, the superficial pain is not referred. In the trigeminal system high convergence at the spinal trigeminal nucleus of the trigeminal and cervical primary afferents neurons, originating in the pulp, periodontal, oral mucosa, tegument, muscles and joints, has been implicated in the mechanism.
Article by Dr. Siri P.B.
