Healthline has a good article on dental anesthesia which you might explore for some other aspects of this issue. If you really get interested and want more details and a good collection of references to the literature, check out Wikipedia. It is interesting that while anesthetics have been around for over a century, I remember hearing as a kid that my grandparents had work done without any anesthesia! Wonder why …

Organization of Chapter

You My Skip to Whatever Subject Interests You Now


Blocking Nerves

Lower Teeth

Upper Teeth

Infiltration Techniques for Some Teeth

How to get you Numb, without Pain

Laughing Gas

Bottom Line – Importance of your being Pain-free


Dental Anesthesia: The Needle!

Most people don’t look forward to a visit to the dentist.  For those truly afraid, see the Chapter IV.6 about Dental Phobia.  Some of this is simply wanting to avoid bad news.  Statements like “You have 16 cavities” are not what anyone wants to hear.  On the other hand, many people who are better informed about the broader aspects of dental care want to go because they know they need to get something repaired that is wrong and has bothered them.  That missing tooth that has been collecting food and causing their bite to shift in strange ways can FINALLY be replaced.

But, whatever the motivations for avoiding the dental office, or on the contrary for seeking out one who can offer needed help, no one likes the NEEDLE. Most dental procedures require that the teeth or gums be anesthetized – that is chemically stopping the flow of nerve messages that tell the brain how much pain there is.

Fewer people these days have the notion that the dentist is going to cause a lot of pain no matter what he does.  The vast majority of procedures are totally painless, once the anesthetic has been given.  But many people are experienced with dentists who inflict considerable pain while giving the shot!  And maybe even then the teeth aren’t quite numb enough.

This chapter will describe the reasons for getting the injection, how many are needed, where for different regions of the mouth the injection must be given, and how the dentist can give injections such as to cause little or no pain.  Also, we will look at the methods of anesthetizing teeth that do NOT involve a needle.


Dental Anesthesia: Blocking the Nerves

Each tooth has a nerve or nerves that enter through the tip of the root (EACH root, if multiple roots are present).  Once inside the pulp chamber, the nerve cell has branches that reach out through the thousands of dentin tubules, but do not extend into the covering enamel.  Thus, while the dentin is richly innervated, and generally very sensitive to touch, cold and sweets, the enamel can be cut, carved or drilled with no discomfort.  For most dental procedures more than just the enamel is involved (exceptions are porcelain veneers, and sealants).  So to avoid pain when dentin is cut, the nerve must be blocked.

To block the nerve a solution is placed near the nerve which has a dissolved chemical which penetrates the nerve and interferes, temporarily, with the passage of electronic transmission of nerve impulses.  While the pain sensors in the dentin are still very active, the telegraph wires have been “cut” and we consciously experience no pain, because the brain does not become aware of it.

The dentist must know how the nerves get to each tooth, and to every part of the gum and bone tissue, in order to properly anesthetize the area for the anticipated treatment.

We will look at the techniques the dentist uses to block each nerve, and do it with little or no pain from the needle, as it penetrates the tissue toward the nerve fiber.


Dental Anesthesia for The Lower Teeth

Mandibular Block

We will start with the lower teeth, for most of the teeth and gum area on each side can be anesthetized with a single injection.  But, while the number of injections may be minimal the failure rate with this one is higher than for any other part of the mouth.  The nerve that connects to all of the lower teeth (on one side) enters the jaw bone behind a little bony ledge we’ll call the “notch”, which lies inside the jaw back behind all of the teeth.  There is also a membrane attached to this notch that extends back toward the throat and is part of the muscle structure in this area.  If the dentist does not go through the notch with his needle then the anesthetic will stay on the wrong side of the membrane from the nerve, and no anesthesia will take place.  The dentist must be certain to “feel out” the bony contours in this area with the tip of his needle to find the “notch” and to make sure he goes over it to the side inhabited by the nerve.

Since this blockage takes place behind all of the teeth on that side, all teeth are deadened up to the central incisors, at the midline of the jaw.  Also, one side of the tongue goes numb, but the gum tissue on the facial (toward the cheeks) surface of the ridge is still sensitive.  The nerve which supplies this area goes through the cheek in the back and it can always be deadened without removing the needle from the site penetrated for the injection for the teeth.

When doing a lot of work on the lower teeth this block can be done on both sides, but most people don’t appreciate it when their entire tongue is numb and dentists try to avoid it.  It kind of feels like someone placed a large slippery wet piece of meat (which is exactly what it is) in the back of your mouth and you can’t get it out. 


The Mental Block

Often, however, work can be done on one whole side of the lower, plus the front 5 teeth on the other side.  In order to do this the dentist must be aware that some of the nerve that went into the bone behind the “notch” exits from a little hole outside the ridge near the premolars.  It innervates the gum tissue from the premolars forward and the lower lip on that side, and if the anesthetic can be placed INSIDE the hole, it can anesthetize the nerves inside that provide sensation from the teeth in the area.  This nerve is called the Mental Nerve.  Blocking this nerve may be called a Mental Block, but perhaps should not be because most of us have those even when we don’t go to the dental office!

Label “E” shows the Location of the Mental Block

Anyway – to work on just the front half of one side of the lower arch we must get anesthetic into the hole from which the mental nerve exits.  This is not easy – sometimes the precise location of the hole is obscure, and then to get the solution to diffuse into it is challenging.  But if we can do this, the nerve which is inside the bone can be blocked before it gets into the premolars, canine and incisors.

Again, the mental injection need not be made if the full mandibular block is done, but it is useful for a more limited treatment when you want as little numbness as possible, or for extensive treatment when you want to avoid numbing the entire tongue.  The success of this, more conservative approach, will depend upon the skills of your dentist.


Dental Anesthesia for The Upper Teeth

The upper teeth have one disadvantage and one advantage when it comes to anesthesia.  First, there is not one single nerve that can be blocked that will take care of all the teeth on one side.  But, to make up for this, the bone of the upper ridges is thinner than for the lower arch, and anesthetic will actually diffuse through the bone to the individual tooth nerves inside. This infiltration technique will be discussed below.

Otherwise, on the upper arch, the molars, including the third molar, second molar, and half of the first molar, CAN be anesthetized all at once with a specific block. This is called the posterior superior alveolar block, or PSA. For this the dentist much reach OUTSIDE the arch with the needle, by pulling the cheek out and reaching behind the third molar area. The angulation can be tricky, and the injection must be just at the surface of the bone. The location of the needle is important because there is a plexus ob blood vessels just outside the bone surface, and if this is punctured, the patient may get a bruise on the outside of their cheek.

When the PSA block is done with suitable care, it is very comfortable for the patient, because the area of needle penetration does not have very many nerves. BUT – it is limited to the molars, and a supplemental infiltration will have to be done when working on the first molar.


Infiltration Techniques for Some Teeth

The INFILTRATION injection requires the injection of anesthetic at the surface of the bone adjacent to the side of the apex of the tooth of interest.  There is a thin membrane covering the surface of the bone.  The anesthetic must get underneath the membrane to diffuse into the bone, but the membrane is full of nerves.  So the dentist must first numb the membrane with some anesthetic nearby, then penetrate it for the important part of the injection.

Injections for Upper Gum Tissue

Often, the gum tissue on the inside of the upper teeth must be anesthetized as well.  There are two nerves that take care of this, one for the front, and one for the back.  Both nerves are in the palate (roof) of the mouth.  Injection in neither of these areas is fun, but that depends on the skill and care of the dentist.  You can feel relatively little or feel like a bumble-bee stung your palate – that’s largely up to the patience of the dentist.

That is basically all we need to know as far as injections go – we’ll discuss next how the dentist can do certain things to make injections painless, or even avoid them all together.


How to Anesthetize the Mouth without Pain.

Some dentists figure the best way to deal with fear of the SHOT is to just slam the needle home and push the fluid in fast to get it over with.  This technique probably has more to do with alleviating the dentist’s fear of the shot and his lack of willingness to CARE for the patient.  Most dentists use simple techniques that remove most, if not all, pain during the injection, and the vast majority of patients (over 90%) are quite comfortable for this procedure.

The two major techniques for making injections easier for the patient are:  1.  Use a topical anesthetic in the area where the needle will penetrate to reduce this feeling, and; 2.  To move the needle slowly toward its target, injecting anesthetic AHEAD – this will numb the tissues before the needle gets into each area.  In general the more time the dentist takes with an injection, the more comfortable you will be!

For some years now NEEDLELESS injectors have been available.  Here the anesthetic is blasted through the tissue, much like the vaccinations you get in a long line where it just goes pssst! and you are done.  This technique can infiltrate some bone areas so that needle injections are not necessary.  BUT, more typically, it is very effective anesthesia only to superficial tissues so that needle penetration for specific nerve blocks is without sensation – but still necessary.  For kids, especially, the needless injector can be a great help.  They never notice the needle injection later should one be necessary.  BUT, the patient must be warned that the SOUND of the injection is very loud and sudden – a big SNAP! that can startle many people without warning.  Your dentist should demonstrate outside the mouth first so you get used to it.

Another technique that some dentists are finding to be successful is electroanesthesia.  Here some electrical contacts are stuck to your gums and the electrical flow confuses the nerve fibers about message sending – effectively blocking transmission.  This technique does not work completely with all people and it is felt that occasionally it can be a great bother and then you end up getting an injection anyway.


Dental Anesthesia – Nitrous Oxide: To Gas or not to Gas

They call it LAUGHING GAS, but really it is nitrous oxide.  But, it’s nickname is apt, it can make lots of things seem quite funny indeed.  It won’t make dental work fun, but once the work is over if the gas is left on for a while, you will perceive things in your environment in an unusual, and often humorous way.

The most important three effects of nitrous oxide are:  1.  Reduction in sensation of pain (it still hurts but you don’t care so much);  2.  Reduction in apprehension, and: 3.  For kids they don’t remember the procedure as well afterward.  The pain relieving part of it is not by nerve block, but HEAD block if you will.  Pain messages get to the brain, but the brain doesn’t really seem to mind that much.

Many people get some experience with nitrous oxide by breathing the gas out of whipped-cream cans.  You can even eat the whipped cream first.  If you take a deep breath of nitrous oxide there will be a gradual buildup of a buzzing, tingling sensation which lasts about 1 1/2 minutes.  This is a typical concentration for use in a dental office.

One must be aware with nitrous that the repeated breathing of high concentrations of the gas can cause asphyxiation – you do need to come up for air.  In dental offices there is no danger of this happening because oxygen is mixed in with the nitrous, and the concentrations are adjusted for the patients comfort.  

Normally, even with nitrous the dentist will give an injection.  Nitrous can alleviate the fear of the injection effectively – and nitrous alone does not really reduce the reaction to pain as much as would be preferred.


The Bottom Line – The Importance of Eliminating Pain – for YOU and the DENTIST!

There are three reasons to keep the pain level down for patients:  1.  So they won’t hate the dentist;  2.  So they’ll come back and get their work done;  and 3.  So they won’t jump when it suddenly hurts.  This last one is a big one.  Imagine a dental handpiece with a sharp bur (drill bit) turning at 400,000 rpm, poised 1/2 mm from the pulp chamber of your tooth, just a thin layer of dentin between, and the patient has a sudden pain and bites down or jumps.  Painless dentistry means dentistry under control and with minimal risk.

There are people who REALLY don’t want the injection, or hate to be numb.  Most often if they’ve had dentistry, they also don’t have particularly sensitive dentin and small fillings won’t bother them.  The dentist may elect to VERY carefully see if the patient can tolerate a procedure before anesthesia.  But for the vast majority of people local anesthesia is easy, painless, necessary, and renders any dental procedure totally comfortable.