Fundamental principles of efficacy and safety
During an outpatient appointment with an oral surgeon, local anesthesia is the primary tool for ensuring patient comfort. However, drug administration is always an intervention in homeostasis. To ensure the procedure goes effectively and without complications, the clinician must consider four basic factors:
- Injection technique. The accuracy of delivering the solution to the nerve fiber determines the depth of the block.
- Rational choice of drug. It is necessary to clearly understand the pharmacokinetics (how the body affects the drug) and pharmacodynamics (how the drug affects the body) of a specific anesthetic.
- Choice of vasoconstrictor. Vasoconstricting additives radically alter the action profile of the solution.
- Component concentration. The balance between pain relief potency and potential toxicity.
Chemical structure: two branches of anesthetic evolution
From a chemical standpoint, all local anesthetic agents share one common property—they are weak bases. It is precisely this chemical characteristic that allows them to penetrate nerve cell membranes and block impulse conduction.
Globally, all anesthetics are divided into two large groups depending on the type of intermediate chain in their molecule:
- Esters.
- Amides.
Esters: historical heritage
This group includes the classic drugs with which the era of local anesthesia began: procaine (novocaine), benzocaine (anesthesin), and tetracaine (amethocaine).
Pharmacokinetic features:
- The molecules have extremely unstable ester bonds.
- They undergo rapid hydrolysis immediately after administration. Tissue esterases and blood plasma esterases (specifically butyrylcholinesterase, also known as pseudocholinesterase) play the main role in this process.
- Due to rapid degradation, these drugs have a very short half-life.
Clinical significance: Due to their short duration of action and high rate of degradation, esters are very rarely used in modern dental practice, having given way to more advanced molecules.
Amides: the gold standard of modern surgery
Today, the vast majority of local anesthetics in the dentist's arsenal are amides. This group includes: articaine, bumecaine (pyromecaine), bupivacaine (marcaine), lidocaine, mesocaine (trimecaine), mepivacaine, and ropivacaine.
Metabolism and pharmacokinetics: Unlike esters, amides are not destroyed in the bloodstream. Their metabolism occurs in the liver under the action of microsomal enzymes. This process takes time, which is why the inactivation of amides proceeds significantly slower.
Key clinical advantages of amides:
- Duration: Provide a longer working time for the surgeon.
- Permeability: Demonstrate better diffusion into the soft and hard tissues of the maxillofacial region.
- Safety: Extremely rarely cause allergic reactions.
- Reliability: Characterized by high molecular stability during long-term storage and thermal sterilization.
Briefly: answers to topical questions
What is the exact mechanism of action of local anesthetics on the nerve fiber membrane?
The mechanism of action consists in blocking voltage-gated sodium channels and reducing the permeability of the cell membrane predominantly to sodium ions. The drugs in their uncharged (non-ionized) form penetrate the membrane via simple diffusion, become ionized inside the axon, and block the channels from the intracellular side, predominantly in the inactivated state. This prevents cell membrane depolarization, stabilizes its charge, and blocks the generation and conduction of the action potential, primarily the pain impulse.
Which specific vasoconstrictors are used in combination with local anesthetics in dentistry?
Adrenomimetics and hormonal agents that constrict blood vessels are used in combination with local anesthetics. The following vasoconstrictors are used in dentistry:
- Epinephrine (Adrenaline) — a hormone of the adrenal medulla, added in concentrations of 1:100,000 and 1:200,000.
- Norepinephrine (Noradrenaline) — a 0.02% solution is used in a ratio of 1:50,000.
- Levonordefrin — an alternative adrenomimetic.
- Vasopressin — a hormone of the posterior pituitary gland.
- Felypressin — a synthetic analog of vasopressin.
Metabolism is easy to remember by the first letters: "Esters — Esterases" (broken down by plasma esterases), "Amides — Actively metabolized in the liver" (by microsomal enzymes).
Class and exam questions
Why are ester-type drugs rarely used in dentistry today?
The ester bonds in their molecules are unstable, causing the drugs to be rapidly hydrolyzed by blood and tissue esterases. This results in an excessively short duration of anesthesia.
Where and how are amide local anesthetics degraded?
Amides are inactivated significantly slower than esters. Their metabolism occurs in the liver with the participation of microsomal enzymes.
What factors determine the success of local anesthesia during an appointment?
Success depends on proper injection technique, the choice of the drug itself and its vasoconstrictor, as well as the concentration of active substances in the solution.
What are the main practical advantages of amides for an oral surgeon?
Amides provide a longer duration of action, diffuse excellently into tissues, rarely cause allergies, and remain stable during storage.
What else to study on this topic
- Detailed pharmacokinetics and pharmacodynamics of individual amides (articaine, lidocaine, mepivacaine).
- The role of vasoconstrictors in local anesthetic solutions.
- The effect of drug concentration on the risk of toxic reactions.
- Specific techniques of local anesthesia in outpatient surgery.
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Other topics in "Chapter 4. Anesthesia in Oral Surgery (S.A. Rabinovich, S.T. Sokhov)"
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