Local anesthesia is widely used in dental practice. Local anesthetics are substances that are able to block nerve conduction. This nerve blockage occurs when these substances are injected in the right concentration and in the right place. As a result, pain stimuli caused by dental treatments, such as cavity preparations and extractions, do not reach the brain.
Local anesthesia has the following benefits over general anesthesia (anesthesia).
- The technique is simple.
- Local anesthesia can almost always be applied without risk.
- In addition to pain relief, anesthesia often has a psychological effect. The patient expects less or no pain and will therefore be easier to treat.
- The patient is fully conscious. He can cooperate during the treatment.
- Moreover, when the treatment is completed he can go home immediately. As long as the anesthetic still works, he must be careful not to damage himself.
Substances used for local anesthesia, local anesthesia, block nerve conduction. The pain stimuli cannot reach the brain. The effect of a local anesthetic must be fully reversible. That is, the tissue exposed to the anesthetic fluid must not be damaged in any way. When the anesthetic has been worked out, the condition before the anesthetic must return exactly the same.
The duration of action of the local anesthetics is different and mainly depends on two factors:
- The blood flow to the area to be anesthetized. When the area to be anesthetized has been thoroughly circulated, the anesthetic fluid can be rapidly broken down.
- The composition of the anesthetic fluid.
Because the mouth is a well-blooded area, agents are often added to local anesthetics to reduce blood flow. The anesthesia fluid is therefore absorbed less quickly by the blood. The anesthetic remains in the anesthetic area longer and therefore retains its effect for longer. A substance that narrows blood vessels is called a vasoconstrictor. The use of a vasoconstrictor has the advantage that less anesthetic fluid is required to achieve anesthesia. Another advantage of adding a vasoconstrictor is a deeper and longer effect.
Use of a vasoconstrictor also has disadvantages:
- general toxicity when injected into a blood vessel by accident. The risk of being stung in a blood vessel can be reduced by the use of an aspiration syringe. With an aspiration syringe, when the plunger is withdrawn slightly and the needle is in a blood vessel, a cloud of blood becomes visible in the carpule. The needle must then be inserted at a different location. The maximum dose for local anesthesia can be calculated based on the patient’s body weight. The guidelines for different anesthetic fluids are shown in the table below.
Maximum dose for different anesthetic fluids.
|Active ingredient||Specialité||Vasoconstrictor||Maximum dose (ml) a||Operating time in minutes|
|Articaine||Ultracain D-S ®||
|Articaine||Ultracain D-S forte ®||
Maximum dose for a body weight of 75 kg, where one carpule = 1.8 ml.
- One of the vasoconstrictors that is used is adrenaline. When adrenaline enters the bloodstream, cardiac activity is stimulated and blood pressure can rise. This cannot do much harm to a healthy patient, but problems can arise in two groups of patients: patients with cardiovascular disorders and patients with severe diabetes mellitus.
In dentistry, so-called carpule syringes are generally used. These are syringes for which a carpule, a glass tube with anesthetic fluid, is used. The needles for the syringes are available in various thicknesses and lengths. They are disposable needles. The use of carpules and disposable needles has the advantage that sterility is not a problem. In this way a cross-infection can be prevented. There are different types of carpule syringes.
- The aspiration syringe is a syringe that can also be withdrawn. When a blood vessel is punctured during the injection, blood appears in the carpule during aspiration. The anesthetic fluid should then not be introduced at that location. When injected into a blood vessel, the anesthetic fluid will be spread through the bloodstream through the body. There is hardly any local effect. However, palpitations may occur with an intravasal injection in the patient, which can have serious consequences in risk patients. If a smaller vessel is injected, the patient may get pale skin locally, blanching. When the vasoconstrictor has been worked out after some time, the skin will return to its normal color (see images below).
- The traditional carpule syringe is a syringe that cannot be sucked. The complications as described under the aspiration syringe cannot be avoided. It is therefore recommended to use an aspiration syringe.
- The intraligamentary carpule syringe. This is a syringe that can be injected into the periodontal ligament under high pressure. Because the pressure on the carpule is great, there is a chance that the glass will break. The intraligamentary syringe has a metal sleeve around the carpule for safety.
Application of local anesthesia
Local anesthesia can be applied in various ways.
Surface anesthesia serves to numb the mucosa. Minor interventions can then be performed. Children often use this method as a pre-anesthetic so that they do not feel an injection needle. This type of anesthetic can be administered in the form of an ointment, a “regular” spray or a spray that causes “freezing.”
Infiltration anesthesia is a form of anesthesia in which the anesthetic fluid is placed on the outside (vestibular and palatal) against the bone. The anesthesia fluid then infiltrates into the spongy bone. When the nerve comes in contact with the fluid, the nerve conduction is blocked. Infiltration anesthesia is applied in the upper jaw and in the front at the lower jaw. Because the upper jaw has many different branches of the n. maxillaris, the nn. alveolares superiores, being innervated, each tooth must be anesthetized separately.
For cavity preparation, it is usually sufficient to place a depot buccally in the cover fold at the root point. For extractions, the mucous membrane must also be palatally anesthetized and palatal anesthesia must therefore be given. A type of conduction anesthesia can also be administered in the palatum, given the course of the nerves at that location.
Infiltration anesthesia can also be used to track the location of pain. It is sometimes difficult for a patient to properly indicate the location of pain. If anesthesia is given, the location can be found on the basis of whether or not the pain disappears (see images below).
The tip of an injection needle has an oblique side. With an injection, the order must always be directed towards the bone. When the needle is inserted this way, the periost is damaged as little as possible. If the periostrum is damaged, the patient may still suffer for some time after the anesthetic has been worked out. This is because the (damaged) periost is very sensitive (see image below).
Conduction anesthesia makes it possible to interrupt the entire nerve conduction of a certain nerve branch. This method is used in the lower jaw in the form of mandibular anesthesia or a mandibular block. The inferior alveolaris nerve lies in the canalis mandibulae, deep in the lower jaw. Anesthesia does not reach the nerve when the cover fold is anesthetized. That is why the anesthetic fluid is injected into the foramen mandibulae. The n. alveolaris inferior enters the mandibula. The branch of the n. mandibularis that goes to the tongue, the lingus nerve, also passes through this area and is therefore usually also stunned. The mental nerve comes from the mental foramen and runs to the lower lip. Because this nerve is a branch of the n again. alveolaris inferior, its sensitive nerve conduction is also blocked.
With the help of guiding anesthesia in the lower jaw, the feeling of part of the face in the region of the mandible is lost. The affected jaw half, half of the tongue and the lip no longer have a feeling. This also means that pain is no longer felt. The muscles of the lips and tongue can still contract, but the movements are not well controlled. A mandibular block works sufficiently for cavity preparation. With extractions anesthesia must also be given buccally in the cover fold to make the gums numb there as well.
Conduction anesthesia in the lower jaw is administered as follows: the patient is asked to open his mouth far. A fold of the ascending branch of the mandible can then be seen in the mouth. The needle is inserted approximately 1 cm above the occlusion surface. The needle is pressed against the ramus mandibulae and brought in so far that the environment of the foramen mandibulae is reached. A depot of approximately one carpule (1.8 ml) of anesthetic fluid is placed in the vicinity of the foramen mandibulae. If the depot is properly laid, a half-sided anesthesia will follow after a few minutes (see images below).
Double-sided mandibular anesthesia should be avoided, as complete anesthetic of the tongue is very unpleasant. This makes swallowing difficult. Blood and saliva can – especially when lying back – end up in the throat and in the trachea.
In the intraperiodontal or intraligamentary form, the anesthesia is administered in the space between the root cement and the bone. Spraying must take place around a number of places around the element. The advantage of this method of anesthesia is that only the relevant element is anesthetized (see image below).
With intrapulpar anesthesia, the anesthetic fluid is injected directly into the pulp. This may be necessary when an element cannot be anesthetized and an endodontic treatment is indicated. The injection needle can be introduced into the pulp chamber as well as into the pulp channels.
Anesthesia in an inflamed area
Sometimes it is difficult to give good anesthesia. Anesthesia in an inflamed area, so with an abscess or phlegmone, is almost impossible: the anesthetic fluid is rendered ineffective by inflammatory fluid. Therefore, an inflamed area is often difficult to anesthetize locally. It is also dangerous to anesthetize in infected area. There is a chance that bacteria can spread through the body.