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Local Anesthesia From A to Z

This review discusses different types of local anesthetic agents, available equipment, precautions, and possible complications.

This course was published in the March 2023 issue and expires March 2026. The authors have no commercial conflicts of interest to disclose. This 2 credit hour self-study activity is electronically mediated.

AGD Subject Code: 340


After reading this course, the participant should be able to:

  1. Identify the types of local anesthetic agents available.
  2. List the equipment used in local anesthesia administration
  3. Discuss the precautions required and possible complications of local anesthesia administration.


Dental hygienists have successfully administered local anesthesia for more than 50 years without incident.1–5 Since dental hygienists started administering local anesthesia, no disciplinary actions or formal complaints associated with the delivery of local anesthesia have been reported to state dental boards.3

Dental hygienists are responsible for verifying the laws and supervision levels required in the state in which they are practicing. In addition, they must stay informed about the delivery methods of local anesthesia.

Types of Local Anesthetic Agents

Local anesthetics are one of the most conventionally used agents in the practice of dentistry. Both effective and dependable, this method of pain control has been used successfully in dentistry for more than 150 years.6 Local anesthetics are categorized as either amide or ester. Most of those used in dentistry are amides (lidocaine, mepivacaine, bupivacaine, and prilocaine).7

Articaine is unique because it contains both amide and ester properties. It was developed to deliver a profound anesthesia with a relatively rapid detoxification.6 Esters are typically used for topical anesthetics, which can be used alone or prior to the delivery of the local anesthetic injection.7

Amides and esters metabolize in the body differently. When amides enter the blood, they are still active until they enter the liver where they become metabolized. This is a much slower process than the metabolism of esters. Once esters diffuse into blood vessels, they are rapidly metabolized in the plasma.7

Each time the dental hygienist administers local anesthesia, the time needed for the procedure as well as the physical and mental well-being of the patient needs to be considered. The type of anesthetic and injection technique used should be based on the procedure and patient condition, which includes the medical history, dental hygiene care plan, and patient assessment findings.9

When administering local anesthesia, the dental hygienist must always use the smallest effective dose. When choosing the maximum recommended dose of the drug, both the anesthetic and vasoconstrictor must be considered. The maximum recommended dose (MRD) of the anesthetic is based on which of the two drugs reaches the MRD first. That drug (either the anesthetic or vasoconstrictor) is referred to as the limiting drug. The limiting drug is what determines the MRD.9

Vasoconstrictors are critical components in all local anesthetic solutions when duration of anesthesia is essential to control pain. In North America, the most common vasoconstrictors added are epinephrine and levonordefrin. They increase the duration of anesthesia while providing hemostasis as well as reduce the risk of toxicity.6

If a patient has a preexisting condition, such as cardiac irritability or uncontrolled hypertension, vasoconstrictors should be used judiciously as their use can cause cardiac dysrhythmia or an increase in blood pressure.7 Vasoconstrictor use should not be implemented for any patient who has used cocaine or methamphetamines within 24 hours due to an increased risk of cardiac dysrhythmia, which could conceivably lead to cardiac arrest.10

In the United States, the most frequently used local anesthetic in dentistry is lidocaine containing epinephrine 1:100,000 and it is often seen as the gold standard to evaluate other anesthesia drugs in terms of safety and effectiveness.9,12 It will typically provide sufficient anesthesia for healthy patients.

Lidocaine with epinephrine 1:50,000 may be used for hemostasis, but sparingly because of an increased risk of possible adverse cardiovascular reactions, especially in older adults.9 Hemostasis is the act of arresting or stopping bleeding. Hemostasis is advantageous in managing gingival bleeding during scaling and root planing procedures. Both concentrations of lidocaine will provide approximately 60 minutes of pulpal anesthesia and are considered intermediate-acting.9

The administration of 2% mepivacaine 1:20,000 also contains a vasoconstrictor called levonordefrin. It produces pulpal and soft tissue anesthesia comparable to lidocaine with epinephrine.

Anesthetics that do not contain a vasoconstrictor are generally shorter in duration. Mepivacaine 3% plain does not contain a vasoconstrictor and should provide approximately 30 minutes of pulpal anesthesia. It is recommended for patients who have a sensitivity to vasoconstrictors or for short procedures.9

Prilocaine 4% contains a 1:200,000 concentration of epinephrine which gives adequate local anesthesia. It is also metabolized more efficiently by the liver than mepivacaine and lidocaine. Prilocaine 4% plain may elicit a different response based on the location of the injection. It is considered short-acting (only giving 10 minutes to 15 minutes of anesthesia for a supraperiosteal injection). For a nerve block, it will provide a longer duration of 60 minutes to 90 minutes.9 Prilocaine is contraindicated for patients with a history of methemoglobinemia or other medical conditions characterized by reduced oxygen-carrying capacity.11

Bupivacaine 0.5% contains a 1:200,000 concentration of epinephrine and is considered the strongest of all amide anesthetics. It is recommended when local anesthesia is required for longer time periods (90 minutes or longer) and when post-operative pain is expected. It is not recommended for children or patients with special needs. Because of its extended anesthetic effect, it increases the risk of post-operative injury (lip or cheek biting).9

Articaine is in a 4% solution with 1:100,000 or 1:200,000 concentration of epinephrine. Articaine is 1.5 times more potent than lidocaine and, therefore, requires less to produce a comparable state of anesthesia. It avoids metabolism in the liver and is therefore safer for patients with hepatic disease.9 A lower dose of 4% articaine is needed because of its increased effectiveness. Because of its enhanced diffusibility, less injections are typically necessary.8 An overview of local anesthetics appears with the web version of this article.

Nerve Blocks vs Local Infiltrations

Nerve blocks and local infiltrations vary greatly in the depth of insertion and the amount of tissue anesthetized. State practice acts determine the type of injection the dental hygienist is permitted to administer.13 Most states allow dental hygienists to administer both.

Articaine is a good option for dental hygienists who practice in states where blocks are not permitted. With Articaine, buccal infiltrations can defuse to the lingual surfaces, allowing for a more profound anesthesia than an infiltration would provide.8

For field blocks, the needle is inserted near large terminal nerve branches above the apex of the tooth to be anesthetized. Nerve blocks are preferred to other techniques because they are the only type of local anesthesia to produce profound pulpal and soft tissue anesthesia for larger areas. The anesthetic agent is injected in the area of a major nerve trunk to anesthetize the nerve’s area of innervations.9

Local infiltration injections are used when gingival/​soft tissue anesthesia is desired in a specific/​limited area. The injection is inserted close to the superficial, smaller terminal nerve endings. This provides pain relief only in the area of anesthetic diffusion. Local infiltrations also aid in hemostasis in the specific area the dental hygienist is treating.9


Many different types of local anesthetic syringes are available. The dental hygienist should choose the syringe that is most comfortable. Hand size and preference of a thumb ring or half-moon handle should be considered when making a selection. For more information on syringe selection, visit the web version at:

The location and the depth of penetration will determine which size (gauge and length) needle will be used. The dental hygienist’s personal preferences may be considered if there is more than one option for the type of injection given.

In dentistry, stainless steel, pre-sterilized, extra short, short, or long needles are part of the armamentarium. Although lengths may vary from brand to brand, it is typical for extra short needles to be 12 mm in length. Short needles are 20 mm in length and long needles are 32 mm in length. The gauge is the diameter (or width) of the needle. The larger the gauge number, the smaller the diameter of the needle and lumen.

Needles used in dentistry range in gauge sizes of 25, 27, and 30.9 Patients cannot perceive any difference regarding their discomfort level with a smaller gauge needle.14 A larger gauge needle is often preferred because there is less deflection as the needle penetrates through deeper tissues. Aspiration is typically more reliable with a larger gauge needle as the larger lumen aids in the facilitation of aspirations.14


Even when all precautions are taken, a complication or adverse reaction is always possible. The dental hygienist must be aware of how to recognize and care for any possible complication that may arise after administering local anesthetic.

Methods to help with the successful administration of local anesthesia include thoroughly reviewing the patient’s medical history before treatment begins and keeping an emergency kit available in the event of an adverse reaction.

The dental hygienist must be confident and assure the patient throughout the administration of the anesthetic solution. The minimum amount of local anesthesia should be used with the lowest concentration of vasoconstrictor available. To deliver a safe and comfortable injection, aspiration and a slow injection rate are important.15

The dental hygienist must aspirate before injecting any local anesthetic solution. This will reduce the potential outcome of injecting directly into a blood vessel. If the anesthetic is injected into a blood vessel, vital organ function can be altered. If there is a positive aspiration, the needle must be withdrawn, the cartridge replaced, and all steps for injection, including aspiration must be performed.

Possible Complications

The patient is experiencing paresthesia if numbness remains after the local anesthesia has worn off. It can be caused by injury to the nerve sheath, hematoma, edema or hemorrhage around or into the nerve sheath. Paresthesia is usually temporary, however on rare occasions it can be permanent.16

If the tip of the needle punctures a blood vessel while passing through the tissue, blood will accumulate in the area and a hematoma can occur. Soreness, facial swelling, and trismus can also occur in the area. If a hematoma is suspected, the dental hygienist should immediately apply pressure to the area in order to aid in hemostasis of the punctured blood vessel.7 Ice should be applied to the area immediately and warm packs should be applied the next day. A hematoma typically resolves itself within 7 days to14 days as the blood is resorbed by the body.9

Trismus is most commonly seen after the administration of an inferior alveolar nerve block.16 It is a restriction of the opening of the mouth and caused by injury to muscle fibers that result in a spasm of the muscles of mastication. Due to numbness, the patient typically does not notice it during treatment but is usually symptomatic by the next morning. Typically, within 3 days or 4 days, the trismus dissipates. Recommended treatment includes moist, warm compresses and time.16

Generally, psychogenic reactions occur as a result of a patient’s fears and anxieties about the administration of local anesthesia and the dental procedure about to take place. Syncope and presyncope are among the most frequent emergencies in a dental office.7

Tongue, cheek, and lip biting can be avoided by informing patients of the risk. A reversal injection can also help make the numbness dissipate twice as fast. Although vasodilators are valuable in most situations, using a local anesthetic without epinephrine will reduce the longevity of the local anesthetic.16


Dental hygienists need to consider the type of anesthetic agent, injection site(s) and technique, armamentarium, and precautions that should be taken to reduce the risk of complications before administering anesthesia. 


  1. Teeters A, Gurenlian J, Freudenthal J. Educational and Clinical Experiences in Administering Local Anesthesia: a study of dental and dental hygiene students in CaliforniaJ J Dent Hyg. 2018;92:40–46.
  2. The New York State Senate. Senate Bill S6694B. Available at: nysenate.g/​v/​legislation/​bills/떕/​s6694/​amendment/​b. Accessed February 16, 2023.
  3. Scofield JC, Gutmann ME, DeWald JP, Campbell PR. Disciplinary actions associated with the administration of local anesthetics against dentists and dental hygienists. J Dent Hyg. 2005;79:8.
  4. American Dental Hygienists’ Association. Scope of Practice. Available at:​advocacy/​scope-of-practice/​. Accessed February 16, 2023.
  5. Boynes S, Zovko, J, Bastin M, Grillo M, Shingledecker B. Dental Hygienists’ Evaluation of Local Anesthesia Education and Administration in the United States. J Dent Hyg. 2011; 85:67–74.
  6. Malamed S. Handbook of Local Anesthesia. 7th ed. St. Louis: Elsevier; 2020.
  7. Decloux D, Ouanounoub A. Local anaesthesia in dentistry: a review. Int Dent J. 2021;71:87-95.
  8. DiMarco A, Bassett K. Current perspectives on articaine in dental anesthesia. Decisions in Dentistry. 2022;8(3)25–29.
  9. Logothetis D. Local Anesthesia for the Dental Hygienist. 3rd ed. St. Louis: Elsevier; 2022.
  10. Malamed S. What’s new in local anesthesia. Dimensions of Dental Hygiene. 2013;11(7): 21–22.
  11. Ogle OE, Mahjoubi G. Local anesthesia: agents, techniques and complications. Dent Clin North Am. 2012;56:133–148.
  12. Wang Y, Wang D, Liu J, Pan, J. Local anesthesia in oral and maxillofacial surgery: A review of current opinion. J Dent Sci. 2021;16:1055–1065.
  13. American Dental Hygienists’ Association. Local Anesthesia Administration by Dental Hygienists’ State Chart. Available at:​wp-content/​uploads/떖/葘/​AD_​A_​Local_​Anesthesia_​Chart_떕.pdf. Accessed February 16, 2023.
  14. Flanagan T, Wahl MJ, Schmitt MM, Wahl JA. Size doesn’t matter: needle gauge and injection pain. Gen Dent. 2007;55:216–217.
  15. Brand H, Bekker W, Baart J. Complications of local anesthesia. An observational study. Int J Dent Hyg. 2009;7:270–272.
  16. Malamed S. Complications in local anesthesia. Dimensions of Dental Hygiene. 2006;4(10):28–33.


From Dimensions of Dental Hygiene. March 2023; 21(3)38-41.

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