Current Concepts in Local Anesthetics

Women dentists utilize nearly 60 million carpules of anesthetic per year, of the more than 300 million carpules used for oral care annually.¹ Utilizing the most safe, effective, and profound anesthetic is important for patient safety and comfort. While topical anesthetics are frequently used, this article summarizes and updates recent and emerging information regarding injectable local anesthetic agents.

The most commonly used form of anesthetic, local anesthesia is produced by the application or injection of a pharmacologic agent to eliminate pain or sensation in a specific area in the mouth. The only naturally occurring anesthetic agent is cocaine from the coca bush, and this agent has not been used in dentistry since the early 1900s. Injectable local anesthetics — such as the most commonly used synthetic anesthetic, lidocaine, available since 1947 — provide anesthesia for oral soft tissue in specific areas for short periods of time. Injectable local anesthetics are commonly used prior to preparations for restorations, for most surgical procedures, and for other procedures based on the professional judgment of the dentist, combined with assessment of patient safety and comfort.

Types of injectable anesthetics

Local anesthetics are classified by linkages to a carbon chain joined to a hydrophilic group. In general, linkages are two basic ones: amide (NHCO) linkage or ester (COO) linkage. These linkages join to a carbon chain, which is joined to a hydrophilic chain of amino, the latter conferring the pKa of the agent. One key exception is benzocaine, which lacks the amino terminus.

While benzocaine is an ester and used mainly in topical formulations, most injectable anesthetics are amides.³ All anesthetics are weak bases, with a pKa of 7.5 to 9.5. Procaine, whose trade name is Novocain, is the prototype for esters, and is no longer available in dental syringe cartridge form.²

Table 1 summarizes some commonly used local anesthetics. Absorption of the pharmacologic agent is dependent on a number of factors, including whether the pH of the tissue has dropped due to localized infection. Other factors include drug solubility, vascularity of the tissue at the injection site, and the impact of the agent on circulation. Duration is, therefore, highly variable and specific for each drug. [See Physician's Desk Reference (PDR) for duration and potential side effects of specific products.]

Onset of anesthetic action and duration are impacted by a number of factors. The most significant among these appears to be the pH, which drops when infection is present. Other factors include the pKa of the anesthetics, the concentration of drug, the amount of vasoconstrictor present, and the injection technique relative to nerve morphology. Since most anesthetics are vasodilators, leading to rapid diffusion away from the site, use of vasoconstrictors, such as epinephrine, increases the duration of anesthetics alone.

Since 2000, a new injectable anesthetic, Septocaine® — also known as Articaine, Ultracaine, and Carticaine — became available. This new local anesthetic has properties that are similar in time of onset, duration of anesthesia, and profoundness of anesthesia to other commercially available local anesthetics, mostly lidocaine.^4,5,6 Other anesthetics are planned or underway. For example, a novel anesthetic for use with periodontal treatment requires no injection. It is a gel that combines prilocaine and lidocaine (2.5 percent and 2.5 percent, trademark Oraqix, available later this year).

Assessment of pain by patients comparing different types of injectable anesthetics has been limited in the literature.^7,8 Newer systems of delivery include intraosseous injection systems of X-tip and Stabident.^8,9 The Wand syringe has been successfully evaluated compared to lidocaine in profundity of anesthesia and pain perception in a randomized controlled clinical trial.^10,11,12,13 Future articles will focus on these novel delivery systems and how they are used in various offices.

Contraindications and allergic reactions

Contraindications to local anesthetics are numerous; consult the product package insert on local anesthetics or the PDR. Except for Prilocaine, which is metabolized in the kidney and plasma, the amide linkage anesthetics are metabolized in the liver.14 Therefore, impairment in hepatic function in patients is a key contraindication.

The medical history you use should query the patient about current and past health conditions, especially liver and kidney functions, medications, and past allergic reactions. These include tricyclic antidepressants, such as amitriptyline (Elavil); beta blockers, such as propanolol (Inderol); and general anesthetics such as halothane (Fluothane).² There are other contraindications when choosing local anesthetics. Levordefrin is not indicated for use with tricyclic antidepressants, and reduced dosages of epinephrine are recommended. For patients with significant cardiovascular disease, you may choose to consult with their physicians. Recreational use of cocaine by patients can increase the risk of blood pressure and cardiac arrhythmias with injectable anesthetics.^{15,16,17,18,19,20} Data indicate that lidocaine and Prilocaine may be safest for use among pregnant and lactating women.² Paresthesia has been reported occasionally after local anesthesia with many of the amide linkages.¹⁷

Allergic reactions can be confirmed by intradermal testing from an allergy specialist. Most allergic reactions are limited to the outer tissue and can be treated with antihistamines, with the more serious ones treated with epinephrine. The most common side effect of injections is syncope. This should always be treated appropriately, and patients with a history of syncope should be considered for treatment with diphenylalanine.³ Allergic reactions to amide linkage anesthetics are relatively rare, and mostly attributed to the preservatives or antioxidants found in the anesthetic. Ester linkage anesthetics had a higher rate of reported allergy, due to the paraaminobenzoic acid (PABA) preservative.

For documented allergy to both ester and amide groups, diphenylalanine can be used for procedures of short duration. Diphenhydramine has been utilized in selected patients — 17 patients with reported allergy — with efficacy similar to seven patients utilizing Prilocaine. While larger studies are needed, diphenhydramine may be an effective alternative for patients with allergy to local anesthetics.¹⁴

Most reported allergic reactions are due to preservatives, both methylparaben and metabisulfite.¹⁸ Metabisulfite is added as an antioxidant when vasoconstrictors are used in anesthetics. When a patient reports a documented allergy to sulfites, vasoconstrictors in anesthetics should be avoided. For such patients with documented sulfite allergies, utilize plain anesthetics such as Mepivacaine 3 percent or Prilocaine 4 percent available without preservative.²

Latex allergies are commonly reported among patients. However, the latex stopper at the end of most cartridges has not been implicated in adverse reactions among dental patients, based on available case reports.¹⁵ As with many dental issues, no prospective epidemiologic study has evaluated this issue.

Conclusion

Choosing the right anesthetic based on your professional preferences and assessment of patient safety and comfort requires continuous updating in technique, new delivery methods, and new agents. While recent literature addresses each of these, relatively few studies exist that assess patient perceptions of injectable local anesthetics or novel delivery systems. Future studies should set benchmarks for behavioral research on the impact of local anesthetics on patients.

Updating information is essential to keep pace with changes in local anesthetics and novel delivery systems. Even the most experienced woman practitioner should benefit from periodic review of the anatomy associated with local anesthesia and injection protocols to minimize the risk of complications, as well as new and emerging anesthetics.²¹

Click here to download Table 1.

References

1. Malamed SF. Handbook of local anesthesia. 4th ed. St. Louis: Mosby 1997.
2. Haas DA. An update on local anesthetics in dentistry. J Can Dent Assoc 2002; 68(9):546-51.
3. Meechan JG. Effective topical anesthetic agents and techniques. Dent Clin North Am Oct. 2002; 46(4):759-66. Malamed SF, Gagnon S, LeBlanc D. Articaine hydrochloride: a study of the safety of a new local anesthetic. JADA Feb. 2001; 132:177-185.
4. Malamed SF, Gagnon S, LeBlanc D. Efficacy of Articaine. JADA May 2000; 131:635-642.
5. Malamed SF, Gagnon S, LeBlanc D. Efficacy of Articaine. JADA.
6. Donaldson D, James-Perdok L, Craig BJ, Derkson GD, Richardson AS. A comparison of Ultacaine and Citanest Forte in maxillary infiltration and mandibular nerve block. J Can Dent Assoc 1987; 53(1):38-42.
7. Wahl MJ, Overton D, Howell J, Siegel E, Schmitt MM, Muldoon M. Pain on injection of prilocaine plain vs. lidocaine with epinephrine. A prospective double-blind study. J Am Dent Assoc Oct. 2001; 132(10):1396-401.
8. Kleber CH. Intraosseous anesthesia: implications, instrumentation and techniques. J Am Dent Assoc April 2003; 134(4):487-91.
9. Gallatin J, Reader A, Nusstein J, Beck M, Weaver J. A comparison of two intraosseous anesthetic techniques in mandibular posterior teeth. J Am Dent Assoc Nov. 2003; 134(11):1476-84.
10. Ram D, Peretz B. The assessment of pain sensation during local anesthesia using a computerized local anesthesia (Wand) and a conventional syringe. J Dent Child May-Aug. 2003; 70(2):130-3.
11. Gibson RS, Allen K, Hutfless S, Beiraghi S. The Wand vs. traditional injection: a comparison of pain-related behaviors. Pediatr Dent Nov.-Dec. 2000; 22(6):458-62.
12. Johnson J, Primosch RE. Influence of site preparation methods on the pain reported during palatal infiltration using the Wand Local Anesthetic System. Am J Dent June 2003; 16(3):165-9.
13. Blanton PL, Jeske AH. Dental local anesthetics: alternative delivery methods. J Am Dent Assoc Feb. 2003; 134(2):228-34.
14. Uckan S, Guler N, Sumer M, Ungor M. Local anesthetic efficacy for oral surgery: Comparison of diphenhydramine and prilocaine. Oral Surg Oral Med Oral Pathol Oral Radiol Endo July 1998; 86(1):26-30.
15. Shojaei AR, Haas DA. Local anesthetic cartridges and latex allergy: a literature review. J Can Dent Assoc Nov. 2002; 68(10):622-6.
16. Eggleston ST, Lush LW. Understanding allergic reactions to local anesthetics. Ann Pharmacother July-Aug. 1996; 30(7-8):851-7.
17. Haas DA, Lennon D. A 21-year retrospective study of reports of paresthesia following local anesthetic administration. J Can Dent Assoc 1995; 61:319-330.
18. Haas DA. Localized complications from local anesthesia. J Calif Dent 1998; 26:677-682.
19. Finder RL, Moore PA. Adverse drug reactions to local anesthesia. Dent Clin North Am Oct. 2002; 46(4):747-57.
20. Blanton PL, Jeske AH. Dental local anesthetics: alternative delivery methods. J Am Dent Assoc Feb. 2003; 134(2):228-34.
21. Blanton PL, Jeske AH. ADA Council on Scientific Affairs; ADA Division of Science. Avoiding complications in local anesthesia induction: anatomical considerations. J Am Dent Assoc June 2003; 134(6):753-60.

Margaret I. Scarlett, DMD
Dr. Scarlett is the science and women's health editor of Woman Dentist Journal. An accomplished clinician, scientist, and lecturer, she is retired from the Centers for Disease Control and Prevention. You may contact her by email at megscarlett@ mindspring.com.