Topical anesthesia of intact skin: EMLA cream
The drug is a eutectic solution in which the local anesthetics—lidocaine and prilocaine—are present in a strict one-to-one ratio. A key physicochemical feature of this formulation is its high water content, which ensures that the active components can be absorbed directly through undamaged skin.
The main and absolute prerequisite for the successful use of this cream is the application of an occlusive dressing. If this rule is violated, the following pathogenetic mechanism is triggered:
- Intensive evaporation of the aqueous base of the drug occurs.
- The surface epithelium loses the necessary hydration.
- The absorption of the eutectic mixture into the underlying tissues drops sharply.
The temporal parameters of the drug's action require a long waiting period. The onset of a clinically significant effect occurs no earlier than 60 minutes after application. The maximum pain-relieving effect is achieved on average after 120 minutes. After removing the occlusive dressing, the effect persists for two hours. The depth of anesthetic penetration correlates directly with the exposure time: one hour of application anesthetizes tissues to a depth of about 3 mm, while the maximum possible penetration depth is no more than 5 mm.
Limitations of cream use in dental practice
Despite its high efficacy on the skin, the scope of application of the cream has clear boundaries. Traditionally, it is indicated for preparing patients for vascular needle and catheter insertion prior to the induction of systemic anesthesia, as well as for ensuring pain-free superficial surgical procedures in dermatology, plastic surgery, and cosmetology.
However, in outpatient dental practice, using this drug to anesthetize the mucosa at the intended needle insertion site prior to local injection anesthesia is considered practically unfeasible. The main reason for this limitation is the excessively long latent period (waiting one to two hours is impractical in a standard dental setting).
Anesthesia of mucous membranes: Diplen-LH film
To prepare the oral mucosa for injection, it is optimal to use the domestic self-adhesive film Diplen-LH. It features a combined mechanism of action, simultaneously providing local anesthesia and antibacterial tissue protection.
The multilayer structure and composition of the film include:
- Anesthetic component: lidocaine hydrochloride, providing rapid topical anesthesia.
- Antiseptic component: chlorhexidine, possessing a broad spectrum of activity against the microflora typical of the oral cavity.
- Outer layer: contains brilliant green dye, which gives the film its characteristic bright green color and serves as an excellent visual reference for the dental surgeon during work.
Unlike creams, the self-adhesive film has a very short latent period: the development of a full anesthetic effect on the mucosa takes only 60 to 90 seconds.
Protocol for injection using a self-adhesive film
The technique of working with the film requires following a specific algorithm to ensure maximum safety and comfort. First, a fragment of the required size is cut with scissors. Then, it is fixed with the adhesive side directly onto the mucosa corresponding to the projected intervention.
Key rules for performing the injection:
- The film is strictly not removed before needle insertion. The injection is performed directly through it.
- The film is not removed even after the injection is completed.
The purpose of this protocol is reliable prevention of puncture site infection (thanks to chlorhexidine) and ensuring a prolonged pain-free state of the soft tissues after the injected solution wears off. Biodegradation occurs naturally: the film completely dissolves in the oral cavity within 10–12 hours.
Briefly: answers to topical questions
What are the clinical symptoms of central nervous system systemic toxicity of local anesthetics?
Clinical symptoms of central nervous system systemic toxicity of local anesthetics include various neurological disorders. These include:
- Euphoria;
- Depression;
- Speech disturbance;
- Swallowing disorders;
- Visual disturbances;
- Convulsions;
- Respiratory depression;
- Coma.
Additionally, as the drug concentration in the blood increases, dizziness, paresthesias, and pronounced motor agitation may occur.
Which local anesthetics belong to the amide group, and which belong to the ester group?
Local anesthetics are classified into two main groups depending on the type of bond between the aromatic ring and the amino group.
| Group | Representatives |
|---|---|
| Esters | Procaine (novocaine), benzocaine (anesthesin), tetracaine (amethocaine) |
| Amides | Articaine, bumecaine (pyromecaine), bupivacaine (marcaine), lidocaine, mesocaine (trimecaine), mepivacaine, ropivacaine, prilocaine, etidocaine |
Mnemonic for Diplen-LH composition: CHLAB (Chlorhexidine, Lidocaine, Anesthesia, Brilliant green).
Class and exam questions
Why is an occlusive dressing mandatory when using eutectic cream?
The occlusive dressing prevents intense evaporation of water from the drug. Without it, the surface epithelium is insufficiently hydrated, leading to a sharp decrease in anesthetic absorption into the tissues.
Can lidocaine and prilocaine cream be used before a dental injection?
In dental practice, this is practically unfeasible. The latent period of the drug is at least 60 minutes, making its use before a routine needle insertion impractical.
How to properly perform an injection when using a film with brilliant green?
The needle is inserted directly through the applied film. It does not need to be removed either before or after the injection, as it protects the puncture site from infection and dissolves on its own within 10–12 hours.
What else to study on this topic
- Mechanism of formation of local anesthetic eutectic mixtures
- Spectrum of antibacterial activity of chlorhexidine in the oral cavity
- The process of biodegradation of polymer films on mucous membranes
- Factors affecting drug absorption through intact skin
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