Pain is always an issue in dentistry, and fear of pain is one of the major reasons why patients fail to seek help from a dentist until their emergency is so severe that they are literally driven to seek professional help! They may be terrified when they sit in that big chair, but as soon as the dentist makes them numb, they are so relieved, that they sometimes fall asleep. They discover almost immediately that–surprise–the shots are not very painful.
In general, you hurt yourself more eight or ten times every day doing normal activity than the dentist hurts you with the shot. It’s just that there is a tendency for patients to concentrate on the stimulus of the shot, and by doing that they magnify that stimulus into something much more unpleasant than it should be!
Generally, the anesthesia works very well with just one standard shot. This is especially true if you are not already in pain when you come to the office. On the other hand, inflamed tissue (hot, red, swollen and painful) tends to be acidic in nature. The anesthesia is very PH sensitive. Anesthesia in a normal acid/base environment likes to seep into nerve fibers slowly, which is why anesthetics take some time to set under normal conditions. However, in an acid environment, the nerve fibers look to the anesthesia molecules like they are coated with wax and thus diffusion into the fibers is very slow. In order to overcome this difficulty, we use a LOT more anesthesia than we do if you are not already in pain when you present for treatment.
NOTE: If you are a patient who can’t seem to get numb at the dentist’s office you might want to click here to see the major reasons that anesthesia may fail.
The graphic on the right shows the rough anatomy of the Trigeminal nerve on one side of the head. It is called the Trigeminal because it is actually one nerve that splits into three main branches to give sensory innervation to one entire side of the face. All the cell bodies of the nerves that go to your teeth actually lie in two masses called the Gasserian (Semilunar) ganglia. It is this ganglion that splits into the three branches of the Trigeminal nerve. These ganglia are located under the skull, one in front of each ear.
Each nerve cell (neuron) within the ganglion sends out a long, microscopically thin extension called an axon. The axon extends all the way from the ganglion into its target tooth. The image immediately below shows a generalized picture of a neuron. The cell body is the part that contains the nucleus of the cell. It is this part that actually resides in the semilunar ganglion. The axon is the very long extension of the neuron cell that continues into one of the nerve trunks that issue from the ganglion. While each neuron has only a single axon, that axon can branch multiple times making connections with hundreds of other neurons or somatic cells.
If you would like to learn a little bit more about the microscopic anatomy of neurons in the brain, click on the icon below.
The right hand image below shows most of the maxillary (upper Jaw) branch of the trigeminal nerve as it branches out into the superior dental plexus.
Click here to see a larger version, and more on the anatomy of the maxillary division of the trigeminal nerve. The left hand image below shows the inferior dental plexus of the mandibular branch of the trigeminal nerve. This is composed of thousands of axons from cell bodies located in the Gasserian ganglion. Bundles of axons leave the nerve trunk to enter each tooth. Click here to see an enlargement and a great deal more on the anatomy of the mandibular nerve branches. Click here to see more on the maxillary nerve branches (in the right window below.)
The image above is a rough representation of how individual axons combine within several layers of connective tissue sheaths to form larger nerve bundles. These in turn combine to form nerve trunks. Note that even within the nerve trunks, each individual axon retains its separate identity, thus traveling all the way from the tooth to its cell body in the ganglion on that side of the head.
The nerves in your body never exist separate from a support system composed of several types of connective tissue, and blood vessels of various sizes. In fact, wherever you find a nerve, you will find at least one blood vessel accompanying it. Conversely, wherever you find a blood vessel, you will find at least one nerve accompanying it. Any complex of nerves and blood vessels is called a neurovascular bundle. The blood vessels and nerves in a human body are like the roots of two intertwining trees. The source of the blood vessels is the heart, and the source of the nervous system is the brain and accompanying spinal cord. The intertwined “twigs” in the outer areas of the body combine to form larger and larger branches and “trunks” as they progress toward their respective sources.
The “nerve” inside a tooth is really a neurovascular bundle, since it is composed of connective tissue and blood vessels as well as nerve endings. Inflammation in the nerve of a tooth will often affect the chemistry and physiology of the neurovascular tissues all along the course of the nerve trunk making it difficult for anesthesia to penetrate into nerve bundles even at points relatively far removed from the actual site of the toothache. It is easy to see why producing good anesthesia may be quite tricky if the patient puts off coming in for treatment until the inflammation has gotten out of hand.
The detail above is a representation of the fine anatomy of a nerve bundle as it enters into the apex (the tip) of the root of a lower front tooth. Note the extent to which it branches again and again inside the tooth. As the nerve bundle enters into the root, it is composed of several individual axons with accompanying blood vessels, each axon representing a separate neuron (nerve cell). Remember that these neurons actually live well outside of the tooth itself in the Gasserian ganglion on one side of the head. Each branch contains fewer and fewer axons until the branches become so fine that each one represents a separate axon from an individual neuron.
Upon occasion, it is very difficult to produce numbness in a particular tooth. The best way to avoid the (rare) horror show is to be treated when you first feel the pain. Normal toothaches with moderate pain numb out just as easily as any healthy tissue. If your dentist notes something on an x-ray and recommends that you have a filling or a root canal, don’t put it off until it hurts. If you wait until you have acute pain or an abscess, even touching the tooth is painful and getting you numb may be difficult, especially if you are swollen. (Note that if the pulp is entirely dead in a tooth, and there is no pain, the tooth is simply an empty tube that happens to be filled with dead tissue, and the root canal can be done from beginning to end without any shots at all.)
The image above is a more detailed diagram of a cross section of a tooth. The white covering on the tooth is called enamel. It really is white in color, but somewhat translucent and allows the color of the underlying structures to shine through. It is also very hard and quite resistant to acid attack. The brownish yellow material underlying the enamel is called dentin, and it too is hard, but it is much less hard than enamel. The dentin has a density like that of hard bone. It is much less resistant to acid attack than enamel. Underlying the dentin is the nerve of the tooth. The nerve is actually a complex organ. In a healthy state, it is pink and soft, like the lining of your mouth, and is composed of blood vessels, connective tissue and, of course, nerve fibers. The dentin overlying the nerve is permeated with thousands of tiny tubules which run perpendicularly from the nerve to the enamel/dentin interface, and also to the outer surface of the root in areas which are not covered by enamel. These tubules are filled with fluid. The fluid is actually contained within tiny projections from cells that line the inside of the nerve space. These cells are part of the nerve complex and are called odontoblasts. Touching the living dentin (or even a stream of air blown across exposed dentin) produces movement of the fluid in the tubules which transmits impulses back to the nerve making the dentin sensitive to any type of direct stimulus. Because of the presence of these tubules, the dentin is actually quite permeable to fluids.
The image above is a picture of an actual tooth which has been attacked by decay. It has been stained to better show the structures within the tooth. Originally, the tooth was adjacent to two other teeth which made contact with this one at the positions shown by the yellow arrows. Since teeth can move slightly when pressure is applied to them (such as when a person chews or clenches his teeth) the teeth can rub together at the contact points. The combination of acid attack from sugar soaked plaque, plus the friction of the constant rubbing of the teeth at the contact points produces tiny holes in the enamel. The contact on the left side of the tooth shows how acid plus friction can produce a hole in the enamel. This one has not yet penetrated through to the dentin. The contact on the right shows what happens when the enamel has been breached allowing the plaque organisms to penetrate into the dentin. Note that while the hole in the enamel is relatively small, the decay has rapidly progressed within the dentin to a much larger extent due to the relative softness and permeability of the dentin as compared with the enamel. The decay has a tendency to spread along the dentinal tubules from the enamel surface toward the nerve from which the tubules arise.
Surprisingly, when a tooth is attacked by decay in this way, it only hurts when the decay first penetrates through the enamel into the dentin. After a few days, the pain stops because the odontoblasts inside the affected tubules tend to die off fairly quickly. When this happens, the affected tubules are called “dead tracts“. Once the tracts die off, there is no more pain until the decay actually approaches the nerve itself.