Understanding Pain page 2-DoctorSpiller.com

Referred pain

Tooth related pain can be rather hard to understand.  Pain emanating from one tooth may be felt in another tooth far removed from the actual culprit.  This is why it is sometimes difficult for a dentist to make an accurate decision of which tooth to treat, especially if the tooth that the patient believes is the one that needs treatment shows no actual signs of disease.  In my office, it is not unusual for a patient to present with vague pain in an area of the mouth with no way to decide which tooth is actually at fault.  It becomes a real diagnostic problem when multiple teeth have deep restorations or cavities, but only one of them is the actual culprit.  But which one??   When this happens, I generally send the patient home with an analgesic and ask him or her to return when the pain localizes in one area.

CarpulesComplications from injections are covered on my seven “Local anesthesia” pages .   This includes reasons why anesthetic injections may not work for you.  Click on the icon below to view this material.

In other cases, one tooth may be obviously at fault, but the patient is feeling pain in his ear, eye, temple, or in teeth in the opposite arch as well as in the obviously affected tooth.   Finally, you get the really weird cases in which pain actually coming from, say, a top front tooth is felt in a back bottom tooth.  This actually happened to me when a patient appeared with pain in a lone standing lower back tooth (a molar).  The molar had no cavities or fillings, and did not react badly to cold air or tapping.  I sent the patient home, and she returned the next day with an abscess in a top central front tooth!

There are essentially two reasons that pain in one area may refer to another.

TrigeminalDetail1. The diagram above is a schematic of  the Trigeminal nerve.  This nerve is responsible for all the feeling on one side of your face.  (The other side of your face has its own Trigeminal nerve.)  There are three branches, all of which originate in the semilunar (Gasserian) ganglion.  The Ophthalmic branch gives feeling to the face around the eye, bridge of the nose and the forehead.  The Maxillary branch is responsible for the feeling in your upper teeth and gums as well as the facial area below the eye and above and including the top lip.  The Mandibular branch is responsible for conveying feeling from your bottom teeth, gums and tongue as well as the skin below and including the lower lip.

The actual mechanism of pain referral from one area of the head or neck to another is not well understood.  One theory of referred pain involves the way inflammation affects  the functioning of the nerves.  Pain in a tooth understandably causes inflammation in the nerve bundle that leaves the tooth and, if it is intense enough, it may cause inflammation along the entire length of the affected neurovascular bundle all the way up to the nerve cell bodies (a nerve cell is called a neuron) located in the semilunar ganglion.  Each neuron has hundreds “dendrites” which make contact with other neurons and can, in turn, excite them by excreting chemicals called neurotransmitters.  There are several different kinds of neurotransmitters, some causing excitation of the communicating neurons, and some causing inhibition.  Under normal circumstances each neuron is programmed to excrete “normal” amounts of the various types of neurotransmitter molecules.  When a neuron is inflamed, it is “sick” and may excrete not only unusual amounts of neurotransmitter, but perhaps even different ratios of different types of neurotransmitters.  This imbalance in neurotransmitters can have unpredictable effects on communicating neurons, and may be responsible for exciting neurons that lead to the brain in ways that create the perception of pain in far flung areas of the head and neck.  Thus pain in a back lower tooth may be felt in the ear, eye, or in an entirely different tooth.  Note that the pain never refers to any structure on the opposite side of the face.  This is because the “short circuit” effects only one of the two Trigeminal nerves.  Nerves from one side of the face do not anatomically contact any of the nerves on the other.  Thus, contralateral (opposite sided) “short circuits” are impossible.

2. Your brain is a learning machine.  Not only does it learn math and reading in school, it must also learn to localize pain as well.  Whenever someone touches your arm, hand or face, your brain knows immediately where that stimulus came from because it has had lots of experience being touched in those areas.  Stimulation along any of the pathways from any area of your skin is immediately localized in the brain so you know exactly where the stimulus came from.

On the other hand areas inside your body are not so public and do not receive outside stimulation very often.  When the brain receives stimulation from a deep area, it is not always aware of the exact location of the stimulus.  The brain has an idea of the general area of the distribution of a particular deep nerve trunk, but it has no experience of the specific neural pathways along that trunk.  Thus, a heart attack may be felt as indigestion, or pain radiating down the left arm.  Liver pain is frequently felt as a burning sensation on the skin on the right torso.

Mouth pain is similar to deep body pain.  Pain experienced deep inside a tooth, or deeply inflamed tissue  such as that found in pericoronitis (infection around an unerupted tooth) or aphthous ulcers (canker sores–those painful sores with white centers and red borders that occur on the underside of the tongue, or on the mucous membrane inside the cheeks) can feel very painful in wide expanses of the mouth or head.

Neuritis and Neuralgia

Neuritis means inflammation of a nerve (the suffix “itis” tacked onto any biological entity means inflammation).  The four classic signs of inflammation are redness, swelling, pain and heat.  This is easily visualized when you think of what happens if you hit your finger with a hammer.  In the case of nerves, these processes are often hidden inside normal tissues, but if one could actually see the neurovascular bundle where the neuritis is taking place, one would see them in action.  Inflammatory processes are usually acute, which means that they are generally of short duration and resolve over time.  Neuritises generally manifest as pain in the distribution of the affected nerve, however, in the case of inflamed motor neurons (nerves which control muscles), they may manifest as paralysis of the affected muscles as in the case of Bell’s palsy, which is paralysis of the muscles of the face–generally on one side.  The treatment for neuritis is treatment of the underlying condition causing it; antibiotics for infections, pain medication to allow for healing, etc.

However, a small number of acute neuritises settle down to become chronic situations, and these can present a serious long term problem, presenting as phantom pain or serious sensitivity in the distribution of the affected nerve.  This condition is known as a neuralgia (The suffix “algia” means pain).  Neuralgias can be quite difficult on a patient, because the chronic pain may require long term pain management.  Sometimes non steroidal anti inflammatory drugs are sufficient to control the symptoms, however, some cases require more potent narcotics.  This is a dangerous solution since narcotics are habit forming and doctors are reluctant to write too many class II narcotic prescriptions. No doctor wants to turn his or her patient into an addict, and the DEA (Federal Drug Enforcement Administration) will eventually arrest the doctor.  When this type of pain occurs, it is always advisable to try using one of the anticonvulsant drugs such as Neurontin (gabapentin), Tegretol (carbamazepine) or Lyrica (pregabalin).

Trigeminal Neuralgia

(Tic douloureux) The most painful disease in all of medicine!

Trigeminal neuralgia is a seizure-like condition which causes episodes of intense, stabbing, electric shock-like pain in certain areas of the face.  This pain is usually unilateral (on one side of the face only), but in 5% to 10% of patients it may occur bilaterally (on both sides of the face), although attacks do not generally occur on both sides of the face at the same time.  Patients with multiple sclerosis are more likely than other people to experience trigeminal neuralgia, and when they do have TN, are more likely to experience it bilaterally.

The distribution of the pain varies from patient to patient depending upon which branches are affected.  The pain is debilitating.  The “shocks last seconds, but come in bursts that can last for several hours.  It is sometimes referred to as the “suicide disease” because of its intractability and persistence, and because of the sheer misery it causes the patient and those who must live with him or her.  This disease generally strikes after the age of fifty, but rare cases have been seen in younger patients.  Women are effected more frequently than men.  The pain may be spontaneous, but most of the time it is stimulated by light touching of certain “trigger points” located virtually any place on the head, face or inside the mouth or nose.  Men may avoid shaving particular areas of their faces and women may not apply makeup to their trigger points.  In rare instances, patients have been known to starve to death because the trigger point is located in the mouth.

Trigeminal neuralgia is not treated by dentists, but dentists are often involved in its diagnosis, mostly by way of misdiagnosis of toothaches.  Trigeminal neuralgia is often mistaken for very serious tooth pathology when it first appears, and almost invariably results in the loss of one or more of the patient’s natural teeth.  This result is the tragic consequence of the rarity of the disease and the similarity of the symptoms of trigeminal neuralgia with the symptoms of an acute pulpitis (inflammation of the nerve inside a tooth) which may refer serious pain throughout large parts of the distribution of the trigeminal nerve.  The tip off that this is not a normal toothache comes after the tooth (teeth) have been extracted, but the pain still persists unabated.  A dentist may practice for decades before seeing a case of trigeminal neuralgia.  His job is to relieve pain, and the worse the pain, the more pressing is the need to relieve it!  There are no definitive methods for the differentiation of the pain caused by trigeminal neuralgia from the pain that may be referred by a severe  pulpitis, so a misdiagnosis and the consequent extraction of one or more teeth is quite understandable in light of the severe pain the patient presents in the dental office.  The tooth may be a most likely culprit simply because trigeminal neuralgia may manifest (in part) as a severe toothache.

There is hope.  Trigeminal neuralgia can be treated in one of two ways:

  • Drug therapy–A number of anticonvulsant drugs are available to reduce the frequency, intensity and duration of attacks:
  • Surgery–Several forms of surgical correction of trigeminal neuralgia are available.  They are generally effective, but not always permanent.  Most are done under general (complete) anesthesia and are considered safe for all categories of patient.  These surgeries fall into three general categories.
    • The most frequently performed types are called rhizotomies.   A rhizotomy is done either by the chemical, electrical or mechanical ablation (destruction) of the Semi Lunar ganglion (also called the gasserian ganglion).   Rhizotomies usually result in permanent numbness of at least part of the effected side of the face.  The numbness is considered by most patients to be a small price to pay for relief from this painful condition.
    • The second category of treatment is called microvascular decompression surgery and is done by the placement of Teflon implants between the nerve and the offending blood vessels.   This option rarely produces numbness, but is a complicated and very expensive procedure.
    • The third and newest surgical treatment is not surgery at all.  It is called Gamma Knife Radiosurgery (GKRS), and it involves aiming 201 beams of cobalt-60 radiation focused precisely on a specific region in the brain–in this case the trigeminal nerve root.  This precise concentration of radiation radiates the structure in question without damaging surrounding areas.  The pain of TN usually subsides within several weeks. The Gamma knife is used for numerous brain lesions including virtual cures for some seizure disorders and Parkinson’s disease.

U_of_ManitobaIn my opinion, the very best graphic demonstration explaining the mechanism and various treatments of trigeminal Neuralgia has been posted on the web by the University of Manitoba in Canada and can be seen by clicking on the icon aboveThe tutorial requires the installation of the Macromedia Shockwave Flash plug-in, which can be downloaded for free at the linked site.

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