Local anesthetics allow dentistry to be practiced without patient discomfort. Serious complications associated with the use of these drugs are rare. The occurrence of paresthesia following the use of local anesthesia in dentistry, however, represents an important side effect. This article examines the occurrences of paresthesia to the lingual and inferior alveolar nerve resulting from the injection of local anesthetic agents. Paresthesia can be defined as persistent anesthesia (anesthesia well beyond the expected duration),1 or altered sensation (tingling or itching) well beyond the expected duration of anesthesia.1-4 Tingling and itching are included as part of the definition as these sensations are considered partial anesthesia to the dentist and patient. In general, most dentists and patients would define paresthesia as a prolonged numbness. The definition of paresthesia also includes hyperesthesia and dysesthesia1-3 in which the patient experiences both pain and numbness. Dysesthesia is defined as, painful sensation to nonnoxious stimuli and hyperesthesia as, increased sensitivity to noxious stimuli.2 Paresthesia can also be associated with a burning sensation, and patients can experience drooling, speech impediment, loss of taste, and tongue biting.4 Local anesthetic-induced lingual nerve and/or inferior alveolar nerve paresthesia is generally considered a rare occurrence.5,6 The occurrence of paresthesia in the United States has been studied, and it was found that 51% of paresthesias were related to lidocaine, 51% to prilocaine, and 8% to mepivacaine (these data were obtained prior to the introduction of articaine in the US). The total number is above 100% because twelve of the eighty-three patients studied received more than one local anesthetic agent. Estimates of the use of these local anesthetic agents in the US were 62% lidocaine, 23% mepivacaine, and 13% prilocaine. Symptoms are most commonly associated with mechanical trauma during surgical procedures.5-7 During the administration of local anesthesia prior to treatment of mandibular teeth or their associated structures, the lingual or inferior alveolar neurovascular bundle can be traumatized by the sharp needle-tip, the movement of the needle, extraneural or intraneural hemorrhage from trauma to the blood vessels, or from neurotoxic effects of the local anesthetic.4,6-8 The primary factor in neurotoxicity of local anesthetics appears to be the concentration of the solution.4,9 Paresthesia may occur if, during injection, the patient complains of a sensation described as electric shock along the path of the nerve that is contacted by the needle.1-4,6-8 This article is a review of published data about the incidence of paresthesia induced by the administration of local anesthetic, which is not related to surgical trauma.
Figure 1. The pattern of the numbers of reported cases of paresthesia in Ontario, Canada. * *Reproduced with permission of the publisher from Figure 1: The pattern of the numbers of reported cases of paresthesia in Ontario, Canada, by Haas and Lennon. 4
LITERATURE REVIEW AND ANALYSIS
Because of voluntary medical-legal reporting of the occurrence of paresthesia in Ontario, Canada, and the publication of these data by Haas, Miller, and Lennon, information has been collected regarding the occurrence of paresthesia following administration of mandibular local anesthesia, which is not related to surgical trauma.4,10,11 Data from three reports indicate that articaine and prilocaine show a very high rate of mandibular paresthesia (usually of the lingual nerve), while lidocaine and mepivacaine were rarely associated with this untoward side effect.4,10,11
Because all reported paresthesias were of the lingual nerve, inferior alveolar nerve, or both, maxillary injections are not considered in this analysis. The assumption is that half of all injections are for the maxillary arch,6 and the total number of cartridges was divided in half.
Analysis of the data indicates that articaine has a 4% higher occurrence of paresthesia than prilocaine, though they are both 4% solutions. Although they may not be causative factors, articaine is the only local anesthetic with sulfur or a thiophene ring and an ester bond.1 It is also the only local anesthetic having both an ester and amide bond. The relationship of chemical structure to the occurence of paresthesia should be investigated. A number of recent publications suggest that articaine is associated with a higher rate of paresthesia for mandibular block injections than was calculated in this paper. While the Canadian data were for voluntary reporting of paresthesia, recent data reported all occurrences. Two cases of paresthesia were reported following treatment of 13,000 patients with articaine.12 If half of these were for mandibular procedures, the rate would be two cases for 6,500 mandibular injections, or 1:3,250. Considering that infiltration anesthesia could also have been employed for the mandible, the paresthesia rate may have even been higher. The product insert for articaine, and the publications associated with the study of articaine reported to the Food and Drug Administration (FDA), indicate a paresthesia rate much higher than one in 3,250 usages.13-16 The FDA study reported twenty-one cases of paresthesia in 882 patient treatments, or one in every fourty-two patient treatments. The product insert14 and one publication16 indicate a 1% paresthesia rate. Another publication15 lists paresthesia as one of the minor adverse events found in the study.
Because paresthesia associated with the use of local anesthetics as part of dental care in the United States has been an infrequent event, many dentists and patients are not aware of the potential problem. Besides the range of altered sensations considered as paresthesia (perceived numbness, swelling, tingling, itching), there can be oral dysfunction4 and pain.4,7,17 The dysfunctions include tongue biting, drooling, loss of taste, and speech impediment.4 Pain (dysesthesia or hyperesthesia) is usually not considered when discussing local anesthesia-induced paresthesia. The pain of dysesthesia can severely impact the quality of life,7,17 causing some patients to seek treatment at pain management clinics.6,7,17 The life changes patients experience from these alterations are significant.6,7,17 Minimizing the chance of paresthesia is the best approach. The analysis of data from the study in Canada presented here indicates that 4% articaine has a twenty-fold higher rate of paresthesia compared to 2% lidocaine. Data from more recent studies suggest an even greater disparity in this untoward side effect when comparing articaine and lidocaine.12-16 These data suggest a rate of paresthesia (using articaine for lingual or mandibular block injections) as high as 2% to 4%. As evidenced by the Canadian data from 1993, there were no reported cases of paresthesia with the use of more than 3 million cartridges of lidocaine. Furthermore, there were only five confirmed cases of paresthesia with lidocaine in 21 years. One study of permanent nerve injuries associated with inferior alveolar nerve blocks found the same number of injuries associated with lidocaine (41) as with prilocaine (41). However, national sales figures indicate that lidocaine was used 4.7 times more than prilocaine.7 It should be noted that this study7 was conducted prior to the FDA approval of articaine in the United States.
The paresthesia rates listed for articaine, and to a lesser extent prilocaine, raise questions regarding the use of these local anesthetics:
(1) Does the risk of paresthesia warrant use of articaine and prilocaine for lingual nerve, inferior alveolar nerve, and other mandibular block injections?
(2) Does the risk of paresthesia with articaine and prilocaine for mandibular block or lingual block injections warrant the use of special informed consent? Based on this analysis of data it appears informed consent is merited in performing mandibular block and lingual block injections with articaine or prilocaine. The risk of paresthesia is so remote in all other administrations of local anesthesia that consent seems unnecessary. Previously, the medicolegal environment has not considered the issue in this context. In 1989, the Ontario High Court18 ruled that informed consent was not necessary before administering local anesthesia because the expert witnesses said the risk was infinitesimal, minimal, extremely small, or in order of magnitude of 1:800,000. Based on the Canadian study,4 the rate of paresthesia in Ontario for 1993 was estimated to be 1:785,000. Although this was true, ten of the fourteen cases were associated with the use of articaine in mandibular block injections and the other four were from the use of prilocaine with mandibular block injections.
(3) The Canadian data do not provide information regarding the duration of paresthesia in the cases reported. This would certainly be one important consideration when deciding on the use of these agents for local anesthesia. Analysis of the available data indicates that there are areas for future studies, and more specific data needs to be collected. For example, improved clinical monitoring/recording of extent, degree, and duration of paresthesia; clear definition of terms; the specific type of injections administered, and; differentiating paresthesia from minor adverse events related to administration of anesthesia. These data would improve our understanding of the problem. In summary, the incidence of paresthesia of the lingual nerve and inferior alveolar nerve should be considered when selecting a local anesthetic agent for anesthetizing the mandible and its associated structures.
1. Malamed SF. Handbook of Local Anesthesia. 4the ed. St. Louis, Mo: C.V. Mosby Co; 1997: 248;249;63-64.
2. Jastak JT, Yagiela JA, Donaldson D. Local Anesthesia of the Oral Cavity. Philadelphia, Pa: W.B. Saunders Co; 1995:301.
3. Haas DA. Localized complications from local anesthesia. J Calif Dent. 1998;26:677-682.
4. Haas DA, Lennon D. A 21-year retrospective study of reports of paresthe sia following local anesthetic administration. J Can Dent Assoc. 1995;61:319-330.
5. Pogrel MA, Kaban LB. Injuries to the inferior alveolar and lingual nerves. J Calif Dent. 1993;21:50-4.
6. Pogrel MA, Bryan J, Regezi J. Nerve damage associated with inferior alveolar nerve blocks. J Am Dent Assoc. 1995;126:1150-1155.
7. Pogrel MA, Thamby S. Permanent nerve involvement resulting from inferior alveolar nerve blocks. J Am Dent Assoc. 2000;131:901-907.
8. Harn SD, Durham TM. Incidence of lingual nerve trauma and postinjection complications in conventional mandibular block anesthesia. J Am Dent Assoc. 1990;121:519-523.
9. Kalichman MW, Moorhouse DF, Powell HC, Myers RR. Relative neural toxicity of local anesthetics. J Neuropathol Exp Neurol. 1993;52:234-240.
10. Miller PA, Haas DA. Incidence of local anesthetic-induced neuropathies in Ontario in 1994. J Dent Res. 1996;75SI:247.
11. Miller PA, Haas DA. Incidence of local anesthetic-induced neuropathies in Ontario from 1994-1998. J Dent Res. 2000;79Sl:627.
12. Clinical Research Associates Newsletter. 2001;25(6):1-2.
13. Septodont application to United States Food and Drug Administration for approval of articaine local anesthetic (NDA 20-971). 1998;256-259.
14. Septocaine (articaine hydrochloride 4% (40 mg/ml) with epinephrine 1:100,000 injection) product insert 04/2000.
15. Malamed SF, Gagnon S, Leblanc D. Efficacy of articaine: a new amide local anesthetic. J Am Dent Assoc. 2000;131:635-642.
16. Malamed SF, Gagnon S, Leblanc D. Articaine hydrochloride: a study of the safety of a new amide local anesthetic. J Am Dent Assoc. 2001;132:177-184.
17. Pogrel MA, Thamby S. The etiology of altered sensation in the inferior alveolar, lingual, and mental nerves as a result of dental treatment. J Calif Dent. 1999;27:531-538.
18. Supreme Court of Ontario. Trial proceedings No. 158/89; Vol 3:494-497,1989.
Dr. Dower is an associate professor in the Department of Restorative Dentistry at University of the Pacific's School of Dentistry. He has been director of the Local Anesthesia courses since 1979 and implemented a local anesthesia curriculum at UOP that includes three rotations in local anesthesia during students clinical years. Dr. Dower has presented local anesthesia courses, lectures, and table clinics to regional, state, and national dental meetings. His publications and research articles have appeared in Anesthesia Progress, Journal of the American Dental Association, Quintessence International, Journal of General Dentistry, and Journal of the California Dental Association. Dr. Dower also holds a master's degree in Educational and Counseling Psychology.