You're sitting in the dentist's chair, gripping the armrests tight as a sudden jolt of pain oozes through your mouth.
"The nerve is just irritated", the dentist claims.
But why does the pain seem so much worse than any scrape or bruise you've ever felt before?
Dental pain is uniquely intense. 'Tis but a scratch if you were to have a similar injury elsewhere in the body. This phenomenon is due to a multitude of factors, such as the density of nociceptive nerve endings in the oral cavity, and the interplay of chronic pain conditions and neural pathways. Let us further explore these many factors.
What is pain, and how do we feel it?
Pain can be defined as ‘an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage (International Association for the Study of Pain, 2021).’(1) In simpler words, pain is basically anything that hurts, whether that be physically or mentally. Pain is something you feel when you fracture your hand, when you get a paper cut, and also what you feel after a break-up with someone you love.
Pain in itself is so vast in how intense it feels, it is hard to measure it. For example, some women get period cramps that are so painful that they struggle to move and have to take medication, some women get period cramps but they can go through the day without taking medications, and some don’t get any at all. This makes it very hard to actually give pain a rating, because pain can be so subjective. Everyone feels a varying degree of pain that it is hard to measure pain on a fixed scale. It is influenced by biological, psychological and social factors.
However, for many years, scientists have tried to develop scales and studies to try and address this variability.
For instance, the McGill Pain Questionnaire is a notable tool that categorizes pain through descriptors like "sharp," "cold," or "terrifying," assigning numerical values based on selected terms. This makes it possible to evaluate pain in a semi-quantitative manner, which has proven very helpful in clinical situations. Similarly, the Defense and Veterans Pain Rating Scale (DVPRS) incorporates numerical scores, facial expressions, and color coding to represent pain levels, providing a multidimensional approach to pain evaluation for diverse populations, such as veterans and those with cognitive impairments.
More cutting-edge research has focused on objective measures of pain. A study by researchers at the University of Colorado Boulder identified distinct brain patterns that correlate with pain intensity. By using brain scans and computational techniques, scientists pinpointed neurological signatures linked to physical pain. This groundbreaking work showed that these patterns could predict pain levels with 90 - 100% accuracy during tests involving heat stimuli. The implications are significant: beyond validating subjective reports, this method could differentiate between physical and emotional pain and monitor the efficacy of analgesics. In simpler terms, imagine a future where, instead of debating who had it worse – your friend's paper cut or your stubbed toe – the neuroscientists settle it for you with a brain scan!
So how do we feel pain and who is the main culprit giving us these unpleasant, hurtful, sensations?
The Brain (Ironic, considering how the brain itself doesn’t have any pain receptors so can’t feel any pain).
Specialised nerve cells known as ‘nociceptors’ (aka pain receptors) transmit pain messages to the brain. These are stimulated by 3 types of stimuli: thermal (temperature), mechanical (pressure), or chemicals. Nociceptors are activated when ion channels and receptors detect heat, pressure, chemical agents or tissue damage. The receptors are then distributed at the nociceptor peripheral terminals. When stimulated, the nociceptors release neurotransmitters (chemical messages) in the nervous system to communicate between cells.
To understand this stimulation at an even micro-level and bring in some neuroscience, let’s zoom-in and have a look at neuronal membranes. The membranes of our cells have a potential difference (voltage) and these membranes are impermeable to charged particles in order to manage the voltage of the membrane. At resting potential, neurons aren’t sending signals. Neurons have charged particles such as sodium (Na+), potassium (K+), calcium (Ca2+) and chloride (1-) ions in them. An ion channel in a membrane is an opening in it.
Whenever there is a membrane imbalance (such as ions leaving or entering the membrane), the neurons can transmit signals. K+ channel leaks are said to play a large role in pain signaling and enabling neurons to respond to stimuli (Tsantoulas and McMahon, 2014). Stimuli can cause K+ channel leaks, and because K+ channels help calm down nerve activity by counteracting the start of action potential (reducing the release of chemicals that transmit signals between nerves), when the channels are not working as well, the nerves can become more active and send electrical signals, leading to an increase in pain sensation.
These messages then travel to the spinal cord and then to the thalamus (a region of the brain) by 2 different types of fibres: A Delta fibres (fibres that give you the ‘ouch’ when you hurt yourself) and the C fibres (which give you the throbbing pain after the ‘ouch’). The thalamus then transmits these signals to other parts of the brain.
Now, the reason why dental pain feels especially severe is because of how the oral anatomy is wired: one of the largest cranial nerves, the trigeminal nerve communicates stimuli such as touch, pain, and temperature to the brain. Its branches – mandibular, maxillary, and ophthalmic – innervate the teeth and gums. Because of the nerve's direct connection to the brain’s pain-processing centres, dental pain is consequently immediate and sharp, unlike in some other parts of the body. It's almost like dental pain has a direct VIP pass to your brain's pain centers.
Not only this, teeth are surrounded by a dense network of nociceptors. When a tooth is injured or infected, inflammatory mediators such as prostaglandins are released, amplifying nociceptor activation and increasing the perception of pain. The lack of collateral blood flow in teeth, unlike muscles or skin, worsens this condition. Then, infections in teeth can create a buildup of pressure within the rigid confines of the pulp chamber, further intensifying the pain.
Pain itself is also divided into 2 categories: Acute and Chronic. Examples of acute pains are burning yourself or stubbing your toe. This leads you to protect the injured area, and the pain goes away after the injury has healed. However, sometimes, your brain still perceives pain even after the injury has healed and this can be due to physiological or psychological factors. This is known as ‘Acute chronic pain’ and is still being researched about.
Speaking of the phenomenon of acute chronic pain, there exists a particularly intriguing subset of this condition in dentistry: phantom dental pain, or atypical odontalgia. This intriguing phenomenon provides a unique window into how the brain can misread signals or even create them.
Imagine having a persistent discomfort in a tooth or extraction site. But when you visit the dentist, no underlying issues are found. This strange phenomenon is phantom dental pain. Often, it happens after doing operations like extractions or root canals. Since the phenomenon is connected to nerve deafferentation and cortical reorganisation, the brain's involvement in this condition is quite interesting. When there is no more sensory input from the affected tooth (eg. after its removal), the somatosensory cortex, which is responsible for processing sensory input, compensates by amplifying signals from neighboring regions. This neurological miscommunication creates the illusion of ongoing dental pain, vivid and debilitating, despite the absence of physical damage.
A study done by the Tokyo Medical and Dental University also noted that women and individuals with preexisting chronic pain conditions were more susceptible to developing phantom dental pain. Treatment often requires a multifaceted approach, including medications like gabapentin to calm errant nerve signals and behavioural therapies to address the psychological burden of chronic pain. Despite these efforts, success is often limited, showcasing the complexity of this condition and the need for continued research.
Pain is a very complex feeling we get and we still don’t know a lot about it, however, research has been enabling us to understand it more and be able to control it to make medical surgeries and our lives much smoother.
Fun fact: Many nociceptors are polymodals, which means they are also triggered by other different stimuli, which is why spicy foods taste hot. The odd thing is that somehow this ‘pain’, among other pains such as the pain you feel in your muscles after some good exercise, is somehow perceived as pleasurable, even if all of these things activate the same nerves.
Controlling Pain: Painkillers and Anaesthesia
Pain is universal and very important for our survival, but it is also something that could kill us if it is so intense. Medicine has advanced so much over the past few years it is mind-blowing, and painkillers and anaesthesia or only to name a few.
When you have a killer headache, jaw pain, backache,or pull a muscle, and you want to relieve yourself of the pain, many people turn to painkillers such as paracetamol, Ibuprofen, Panadol, Aspirin, and lots more. These can take 5-10 minutes and the pain relief is… well, relieving.
Contrary to popular belief, aspirin is not actually found in the barks of willow trees, but is instead synthesised by using a chemical found in willow trees known as ‘Salicin’. Paracetamol, on the other hand is traditionally made from derivatives of coal tar or petroleum (Researchers Develop Better Way to Make Painkiller From Trees, 2024), however, researchers have recently also been working on ways to make it from a compound found in poplar trees and pine trees (which is also a waste product from the waste industry) using chemical reactions. All of these are known as ‘analgesic drugs’ and are used to relieve pain without causing a loss of consciousness. They all work by preventing the production of ‘prostaglandins’, a pain and inflammation-causing chemical found throughout the body (“Paracetamol Vs. Aspirin: Your Essential Guide to Effective Pain Relief,” 2023).
The big difference between paracetamol and drugs like aspirin and ibuprofen is aspirin and ibuprofen are non-stereoidal while paracetamol is not. Non-stereoidal drugs block the effect of COX enzymes around the body and can reduce inflammations and bring down high temperatures. Paracetamol, on the other hand, blocks the COX enzymes only in the brain, helping reduce pain and fever, but cannot reduce inflammation.
Painkillers used for moderate to severe pains, such as after surgeries, are known as ‘Opioids’, a drug found naturally in the opium poppy plant. It is made up of chemicals that relax the body and relieve pain by attaching to opioid receptors in brain cells and blocking the pain signals between the brain and the body. This causes a lot of dopamine (the ‘pleasure’ neurotransmitter) to be released throughout the body. Opioids are made of chemicals such as codeine, fentanyl, and morphine (yes, morphine!).
Morphine is an amazing painkiller but it can become addictive because it can cause people to feel ‘high’, and thus very dangerous. Opioid misuse can cause slowed breathing, causing ‘hypoxia’, a condition where little oxygen reaches the brain, which can lead to permanent brain damage, a coma, or even death.
Anaesthesia is used for more severe pains such as during surgery. It is the cornerstone of pain management. It numbs a small part of the body, or can cause unconsciousness. They affect the function of the heart, lungs and circulation. They are injected into your veins, or anaesthetic gas is given to you to breath, and they work by blocking signals that pass from your nerves to the brain so you feel no pain.
There are 4 types of anaesthesia: General anaesthesia (stops brain from responding to sensory messages), local anaesthesia (numbs a small part of the body where you are having the operation), regional anaesthesia ( a local anaesthesia is injected into nerves, known as ‘nerve blocks’, that supply a larger area of the body), and, spinal and epidural anaesthesia ( regional anaesthetics used for operations on the lower body such as a caesarean section). You are conscious in all of these except for general anaesthesia, in which you can only gain consciousness after the effect of the drug has worn off. Some people can still choose to be sedated to relax themselves during surgery.
Cool right? If you found this interesting, you should definitely check out the job profiles for anaesthetists. Anaesthetists are one of the most important people during a surgery and to become one takes around 15–18 years of study because of how complex it is! I definitely think it is worth the lives you could save.
Alternatives to Anaesthesia and Painkillers
Currently, there aren’t many alternatives to anaesthesia, especially for major surgeries. However, there are some techniques people use to acute procedural pain relief.
Hypnosis is a ‘method of inducing a trance or dream-like state of deep relaxation or order to treat disorders (Department of Health & Human Services, n.d.)’. It has been practiced for thousands of years by the Egyptians and Celtic, to name a few. It also includes non-pharmacological techniques (relaxation techniques such as guided imagery or virtual reality). Hypnosis is said to have decreased pain to a certain extent and has been effective in minor surgical procedures, but interpretations are limited by a risk of bias.
Another technique used for pain relief and relaxation is Acupuncture. It is a treatment derived from ancient Chinese medicine and involves stimulating sensory nerves under the skin and in the muscles (NHS Website, 2024). This is conducted through inserting fine needles at certain sites in the body and is used in many pain clinics and hospices. This results in the body producing natural substances by stimulating the body’s meridians (energy-carrying channels) such as pain relieving endorphins in the body. A recent experiment found that acupuncture was effective in improving pain associated with endometriosis, however current evidence is still limited therefore acupuncture should be conducted with caution.
I think it’s crazy how these pain relief techniques are thousands of years old yet still so useful today, and combining these techniques with pain killers or conducting them after surgeries in which you had been given anaesthesia could make medical procedures a lot smoother for patients.
References
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