Mechanisms of infiltration anesthesia
Depending on the localization of solution injection and its distribution method, two main types are distinguished:
- Direct infiltration anesthesia. The local anesthetic solution is injected directly into the tissues that will undergo surgical intervention.
- Indirect infiltration anesthesia. The physician creates a specific anesthetic depot in the tissues. From this pool, the drug spontaneously diffuses into deep-seated layers, providing adequate anesthesia of the required area.
Basics of carpule technology
The modern standard for performing injections is carpule technology. It guarantees high sterility and precise dosage of components (including vasoconstrictors) since solutions are manufactured in automated industrial conditions. Legal liability for the drug quality rests with the manufacturer, but the solution itself must have approval from the Pharmacological Committee.
Before performing infiltration anesthesia, the physician must clearly know the composition of the applied solution:
- Percentage concentration of the active substance.
- Trade name and batch number.
- Manufacturer data.
- Presence, type, and concentration of the vasoconstrictor.
- Presence of preservatives and antioxidants.
Cartridge (carpule) design A carpule is a glass or plastic cylinder. At one end, it is closed with a silicone plunger, and at the other, with a rubber stopper crimped with a metal cap. The standard actual volume of the drug in a carpule ranges from 1.7 to 1.8 ml. Important to remember: 2.2 ml carpules produced for Asian and Australian markets are incompatible with syringes standardized for the Russian Federation.
Carpule preparation and signs of defects
Cartridges must be stored in factory blisters or metal containers at room temperature, strictly in a dark place—light destroys light-sensitive vasoconstrictors.
Before injection, the metal cap and rubber stopper are wiped with a gauze pad moistened with 70% ethyl alcohol. It is strictly prohibited to:
- Immerse carpules in disinfectants (chlorhexidine, alcohol). The rubber stopper is semipermeable, so the antiseptic can diffuse inward and contaminate the anesthetic.
- Autoclave cartridges. High temperatures deform the stopper and cause accelerated breakdown of the vasoconstrictor.
Quality control before injection: The drug must not be used if the plunger is pushed past the edge of the cylinder (loss of sterility). Chemical degradation of the solution is also considered a defect: cloudiness, sediment, or color change (yellowing). However, the presence of small gas bubbles is acceptable—this is nitrogen used in the factory to displace oxygen from the cylinder.
Syringes and needles
The injection syringe holds the carpule and creates pressure to expel the liquid through the needle. According to the cartridge fixation mechanism, carpule syringes are divided into:
- Spring-loaded (the carpule is clamped by the return movement of the plunger rod under spring action);
- Breech-loading (the piston part tilts at an angle);
- Bayonet (the connection of the piston part and cylinder occurs via a semi-rotational click-lock).
A carpule needle consists of a metal tube with two beveled ends and an adapter (cannula) for screwing onto the syringe. The rear pointed end of the tube punctures the rubber stopper of the carpule. Needle sizes (length and diameter) are selected strictly according to the type of injection:
- For infiltration anesthesia, needles with a length of 16 or 25 mm and a diameter of 0.3–0.4 mm are optimal.
- For conduction anesthesia, longer and thicker needles are needed—35, 38, or 42 mm (diameter 0.4–0.5 mm).
- For intraligamentary anesthesia—the shortest (10 or 12 mm) and thinnest (0.3 mm) ones.
Use of vasoconstrictors
To reduce toxicity, decrease the required volume of anesthetic, and prolong the anesthetic effect, vasoconstrictor drugs are added to the solution.
The main drug is epinephrine (adrenaline). It is a hormone of the adrenal medulla, available as a 0.1% hydrochloride solution. The working ratio of adrenaline to anesthetic is usually 1:100,000.
Action of epinephrine: Acting on adrenoreceptors, it constricts the vessels of mucous membranes and skin, increases blood pressure and blood glucose levels, and dilates bronchi. Its effect on the heart is complex: due to the pressure increase, the vagus nerve center may be reflexively stimulated, sometimes leading to a slowed rhythm or arrhythmias. Solutions with adrenaline are strictly prohibited to be heated. Alternatively, norepinephrine (1:50,000), levonordefrin, or felypressin (a synthetic vasopressin analogue) can be used.
Preliminary topical anesthesia
Before needle insertion, the mucosal surface is often anesthetized with topical agents. Their main disadvantage is the use of high concentrations of active substances, which increases the risk of toxic effects.
- Diplen-L.H. film — contains lidocaine and the antiseptic chlorhexidine. The edges of the film are marked with brilliant green. The effect occurs in 1–2 minutes, after which the injection needle can be inserted directly through the film.
- Emla cream — used on facial skin and mucous membranes, applied under an occlusive dressing. It is characterized by safety, but has a long latent period (the effect develops in over 1 hour).
- 3% pyromecaine ointment with methyluracil — applied to lesion foci for 10–15 minutes.
- Aerosols (e.g., 10% lidocaine) — sprayed strictly vertically from a distance of about 2 cm. 1–2% solutions of lidocaine and pyromecaine are also used.
Briefly: answers to topical questions
What types of local anesthesia exist in dentistry?
In dentistry, injection and non-injection (topical) types of local anesthesia are used.
The main methods include:
- Infiltration anesthesia — injection of the drug directly into tissues (direct) or creation of a depot for diffusion (indirect). Includes submucosal, subperiosteal, intraseptal, intraligamentary, and intrapulpar techniques.
- Conduction anesthesia — used for anesthesia, in particular, in the mandible.
- Topical anesthesia — superficial non-injection anesthesia using ointments, aerosols, gels, and films.
What is the mechanism of action of local anesthetics on nerve fibers?
The mechanism of action of local anesthetics consists in the blockade of voltage-gated sodium channels, which prevents the depolarization of the cell membrane and the generation of an action potential.
The process includes the following stages:
- Penetration — drugs (weak bases) in unionized form cross the membrane into the axon.
- Ionization — inside the nerve fiber, the molecules become ionized.
- Blockade — the ionized form blocks the channels from the inner side.
Anesthetics bind to channels predominantly in the inactivated state. Efficacy depends on impulse frequency: the more frequently impulses pass, the stronger the suppression of excitation conduction develops.
Y-P-C: Yellowing, Precipitate, Cloudiness — three visual signs of chemical degradation of the carpule. If detected, the drug should be discarded.
Class and exam questions
Can 2.2 ml carpules be used?
In the Russian Federation, the standard volume of dental carpule syringes is designed for 1.7–1.8 ml. 2.2 ml cartridges are manufactured for the Asian and Australian markets and are incompatible with domestic instruments.
Why Is It Forbidden to Soak Anesthetic Cartridges in Alcohol?
The rubber stopper of the carpule has the properties of a semipermeable membrane. The disinfectant solution during soaking penetrates inside the cylinder and compromises the purity of the local anesthetic.
What Is the Difference Between Direct and Indirect Infiltration Anesthesia?
With direct injection, the anesthetic enters immediately into the tissues where the incision will be made. With indirect injection, the solution is deposited nearby, after which it independently infiltrates the required structures via diffusion.
What else to study on this topic
- Features of the application of mandibular conduction anesthesia
- Specifics of intraligamentary anesthesia and selection of instruments
- Pharmacodynamics of Epinephrine and Cardiovascular Effects
- Application Protocols for Emla Cream in Aesthetic Surgery
- Prevention Measures for Complications Caused by High Concentrations of Topical Anesthetics
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