September 1998 JOURNAL OF THE CALIFORNIA DENTAL ASSOCIATION
Feature Story
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Localized Complications from Local Anesthesia

Daniel A. Haas, DDS, PhD

Copyright 1998 Journal of the California Dental Association.

The inherent safety of local anesthetics allows practitioners to use them frequently with the confidence that adverse events are rare. Nevertheless, complications can occur. The aim of this article is to briefly review the localized adverse events that may result from local anesthetic administration. Descriptions of each complication will be followed by suggestions for prevention and management. In spite of a dentist's conscientious practice, many of these complications cannot always be prevented.

The local anesthetics used in dentistry are considered very safe and have a low incidence of adverse reactions associated with their administration. These adverse events may be classified as either systemic or localized. Systemic complications can occur as a result of psychogenic reactions induced by anxiety, toxicity secondary to high levels of the drug in blood, or allergy. Localized complications may manifest in a number of ways, and the focus of this article is to briefly review them. It is important to note that complications are not always preventable, and their occurrence does not necessarily imply poor technique by the dentist. The reality is that with an estimated 300 million injections being administered yearly in the United States alone,1 even those events that may be considered rare will be experienced by many patients. The following is a summary of local complications.

Prolonged Anesthesia or Paresthesia

Complete anesthesia or an altered sensation in the lip or tongue may persist beyond the expected duration of action of a local anesthetic. Commonly referred to as a paresthesia, these neuropathies may manifest as a total loss of sensation (anesthesia), a burning or tingling, pain to non-noxious stimuli (dysesthesia), or increased pain to noxious stimuli (hyperesthesia).2,3 Prolonged anesthesia or paresthesia in the tongue or lip is known to occur following surgical procedures such as extractions,4,5 and it is assumed that the cause is direct trauma to either the lingual or inferior alveolar nerve. However, persistent anesthesia or paresthesia can also occur following nonsurgical dentistry. Most these are transient and resolve within eight weeks, but they may become irreversible. Whereas the former are an annoyance for the patient, the latter are much more distressing.

There are several putative causes of postinjection paresthesia. Hemorrhage into the nerve sheath may lead to an intraneural hematoma, which then causes pressure on nerve fibers, impairing normal conduction. The hematoma and associated edema usually resorb within several weeks, and symptoms subsequently resolve. If scar formation results, there may be permanent loss of sensation. Direct trauma by the needle may also lead to similar damage. In addition, administration of local anesthetic from a cartridge contaminated by alcohol or sterilizing solution may induce paresthesia.6 Finally, neurotoxicity may be a factor, since a review of the literature suggests that local anesthetics have this potential.7-12

How often do paresthesias occur in nonsurgical dentistry? A recent study led to an estimated incidence of 1 irreversible paresthesia out of every 785,000 injections.13 It has been stated in a legal case in Canada that this low frequency would not warrant advising every dental patient of this risk prior to each injection.14 This same study did note that specific drugs were more likely to be associated with paresthesia. Two drugs, articaine (which is available in Canada and parts of Europe under the trade name Ultracaine, among others) and prilocaine (Citanest), were more likely to be associated with paresthesia compared with the other anesthetics, and this was statistically significant when compared to the distribution of use.13 These same two drugs were again found to be significantly more likely to be associated with paresthesia in 1994.15

The reasons for this relationship to the type of anesthetic are speculative only. Differences in metabolism of these drugs would not be relevant since it occurs in organs away from the site of the neuropathy. Their only common feature is that they are the only injectable local anesthetics in dentistry that have a concentration of 4 percent, whereas the others are lower. It may be conjectured that toxicity may manifest simply because of the higher concentration of these drugs, as opposed to any unique characteristic. Needle trauma to the nerve combined with deposition of a large quantity of drug may be more likely to induce residual nerve damage. Supporting a role of drug concentration are reports of neurologic deficits in animal studies using 4 percent lidocaine16 and in human studies of spinal anesthetics with 5 percent lidocaine.10,11,17 This should be contrasted with the rare reports of neuropathy with 2 percent lidocaine (Xylocaine, among others), which is used in dentistry.

Prevention

There is no guaranteed method to prevent paresthesia or prolonged anesthesia. The inferior alveolar nerve block requires the practitioner to advance the needle near the inferior alveolar and lingual nerves. Practitioners attempt to place the needle near these nerves without intentionally striking them, yet this can occur and may be perceived as an "electric shock" sensation by the patient. Interestingly, this sensation does not imply that paresthesia will result.13 Directly contacting these nerves is not an indication of improper technique, it is simply a risk of carrying out intraoral injections.

Prevention of prolonged anesthesia or paresthesia:

  • If the patient feels "electric shock," move needle away from this site prior to injecting.

  • Do not store cartridges of local anesthetic in disinfecting solutions.

Most paresthesias are transient and resolve within eight weeks. This is fortunate as there is no definitive means of improving the patient's symptoms. The dentist must show concern and reassure the patient that these events can occur and usually resolve over time. The dentist should note the signs and symptoms and maintain contact with the patient. A change in the character of the symptoms can be an encouraging sign that there may be resolution of the neuropathy. It may indicate that there is healing of the nerve, and with time the patient may regain normal sensation. The patient who has had no change in symptoms over a prolonged period, such as several months, is less likely to have a satisfactory outcome. Restoring sensation by microsurgery may be considered by those with training in this area. It has been stated that microsurgery is most likely to be successful if the patient is evaluated within the first month2 or the first three months.5 There is no guaranteed method of treating prolonged anesthesia or paresthesia.

Management of prolonged anesthesia or paresthesia:
  • Reassure the patient that the condition is usually temporary although, rarely, it can remain indefinitely.

  • Note signs and symptoms and follow up within one month.

  • If symptoms persist for more than two months, refer to an oral and maxillofacial surgeon with experience in this field.

Trismus

Limited jaw opening, or trismus, is a relatively common complication following local anesthetic administration. It can be caused by spasm of the muscles of mastication, which in turn may be a result of needle insertion into or through one of them. The most common muscle to be the source of trismus is the medial pterygoid, which can be penetrated during an inferior alveolar nerve block using any of the three main techniques: the conventional approach, the Vazirani-Akinosi (closed-mouth) technique, or the Gow-Gates. Rarely, the temporalis may be penetrated before it attaches onto the coronoid process if the needle is inserted too far laterally. Even more rarely, the lateral pterygoid muscle may be penetrated if a block is administered too far superiorly. Bleeding into the muscle following injection may also cause muscle spasm and trismus. Furthermore, injection of local anesthetic directly into muscle may cause a mild myotoxic response that can lead to necrosis.18 In the rare situation of an infection from the injection, trismus may also develop.

The main symptom of trismus is the limitation of movement of the mandible, which is often associated with pain. Symptoms will arise from one to six days following an injection. The duration of symptoms and their severity are both variable. Following management, as described below, improvement should be noted within two to three days. If there is no improvement within this time, the dentist should consider other possible causes, such as infection, and treat accordingly.

Prevention of trismus:
  • Follow basic principles of atraumatic injection technique.19

Management of trismus:
  • Apply hot, moist towels to the site for approximately 20 minutes every hour.

  • Use analgesics as required.

  • The patient should gradually open and close mouth as a means of physiotherapy.

Hematoma

A hematoma is a localized mass of extravasated blood that may become clinically noticeable following an injection. In this context, it can occur following the inadvertent nicking of a blood vessel during the penetration or withdrawal of the needle. When carrying out intraoral injections, practitioners often pierce blood vessels; but only when there is sufficient blood leaking out can a hematoma be seen. The vessels most commonly associated with hematomas are the pterygoid plexus of veins, the posterior superior alveolar vessels, the inferior alveolar vessels, and the mental vessels. The patient will notice development of swelling and the discoloration of a bruise lasting seven to 14 days. It is important to note that a hematoma will form independently of aspiration results. A negative aspiration does not guarantee an absence of a hematoma, as the needle may nick a blood vessel either on the way in or upon withdrawal. Aspiration results merely report the contents at the needle tip at the time of aspirating. Similarly, a positive aspiration does not imply that a hematoma will result, since the needle may simply have entered a vein at the time of aspiration, and the amount of blood leaking out from this vessel penetration may be clinically unnoticeable.

Prevention of hematoma:
  • Follow basic principles of atraumatic injection technique.19

  • Minimize the number of needle penetrations into tissue.

  • Use a short needle for the posterior superior alveolar nerve block.

Management of hematoma:
  • If visible immediately following the injection, apply direct pressure, if possible.

  • Once bleeding has stopped, discharge the patient with instructions to:

  • Apply ice intermittently to the site for the first six hours.

  • Do not apply heat for at least six hours.

  • Use analgesics as required.

  • Expect discoloration.

  • If difficulty in opening occurs, treat as with trismus, described above.

Pain on Injection

Occasionally, injection of local anesthetic can be accompanied by pain or a burning sensation. Passing the needle through a sensitive structure such as muscle or tendon may cause pain. It may occur during injection if the solution is administered too quickly and therefore distends the tissue rapidly. Local anesthetic solutions that are too cold or too warm may also cause discomfort. Solutions that are more acidic, namely those with vasoconstrictor, may cause a short-lasting burning sensation. Cartridges stored in a disinfecting solution such as alcohol may have residual amounts of solution on the end of the cartridge that can then be administered inadvertently during injection.

Prevention of pain:

  • Inject slowly: Take at least one minute to administer one cartridge.

  • Store cartridges at room temperature.

  • Do not store cartridges of local anesthetic in disinfecting solutions.

Management of pain:
  • Pain or burning on injection is usually self-limiting because it is treated by the onset of anesthesia.

Needle Breakage

This event is very rare. Sudden, unexpected movement of the patient is the primary cause.20,21 It is believed that smaller-diameter needles, i.e., 30 gauge, are more likely to break than larger-diameter, i.e., 25 gauge. Needle breakage usually occurs at the hub, which is the reason for never inserting a needle completely into tissue. Although bending a needle may be considered for injection techniques such as the Vazirani-Akinosi or the maxillary nerve block,22-24 some advise against this practice.25 If it is done, it is important to do so only once because repeated bending will weaken the connection at the hub and predispose the needle to breakage.

Prevention of needle breakage:

  • Do not insert a needle into tissues up to its hub; always leave a portion exposed.

  • Use long needles if a depth of more than 18 mm is required.

  • Use larger-diameter needles (25 gauge is ideal) for the deeper blocks, such as the three mandibular block techniques (conventional, Gow-Gates, and Vazirani-Akinosi) and the maxillary nerve block.

  • Do not apply excessive force on the needle once it is inserted in tissue.

  • If redirecting a needle is required, withdraw it almost completely before doing so.

  • Do not bend a needle more than once.

Management of needle breakage:
  • Remain calm.

  • Ask the patient to remain still; keep their mouth open by not removing your hand.

  • If a portion of the needle is visible, remove it with a hemostat or similar instrument.

  • If the needle is not visible:

  • Inform the patient.

  • Record the events in the chart.

  • Refer the patient to an oral and maxillofacial surgeon.

  • Surgical removal should only be attempted by someone experienced with surgery of the involved region and after radiographs have been taken to help localize the needle.26

Soft Tissue Injury

With the loss of sensation that accompanies a successful block, a patient can easily bite into his or her lip or tongue. Swelling and pain will result following the offset of anesthesia. This event is most common in children or patients who are mentally challenged or demented, such as those with Alzheimer's disease. The child's parent or guardian, or the caregiver with the mentally challenged patient or those with dementia, should be advised to carefully observe the patient for the expected duration of anesthesia. Nevertheless, soft tissue injury may also be a concern for mentally normal patients who are at risk of an exaggerated response to trauma.
Figure 2. Photograph of a lip bitten by a patient with lymphoma. Picture is courtesy of Professor J.H.P. Main, head of oral pathology, University of Toronto.
Figure 2 shows the consequence of a patient with lymphoma who had bitten his lip. Therefore, patients with bleeding abnormalities should also be warned of the risks of lip and tongue biting.

Prevention of soft tissue injury:

    For pediatric, mentally challenged, or demented patients, use a local anesthetic of appropriate duration.

  • Warn the parent, guardian, or caregiver to watch the patient carefully for the duration of soft-tissue anesthesia to prevent biting of tissue.

  • In children, consider placing a cotton roll between the mucobuccal fold for the duration of anesthesia.

  • Explain the risks of soft tissue injury to patients with bleeding abnormalities.
Management of soft tissue injury:

  • Use analgesics as required.

  • Use rinses or applications with lukewarm dilute solutions of salt or baking soda.

  • Consider applying petroleum jelly over lip lesion.

Facial Nerve Paralysis

Anesthesia of the facial nerve may occur if the needle has penetrated the parotid gland capsule and local anesthetic is then administered within. This nerve, the seventh cranial nerve, is contained within the parotid gland and provides motor function through its five branches -- the temporalis, zygomatic, buccal, mandibular and cervical. Needle placement into the parotid may occur if there is overinsertion during an inferior alveolar nerve block or the Vazirani-Akinosi block. The result of anesthesia of these branches of this nerve includes a transient unilateral paralysis of the muscles of the chin, lower lip, upper lip, cheek, and eye. There will be a loss of tone in the muscles of facial expression. In the past, the term Bell's palsy was commonly used to refer to all paralyses of the facial nerve, but it is now restricted to those induced virally.27

Figure 3. An example of the appearance of a patient with a transient facial nerve paralysis. Picture is courtesy of Dr. M. Pavone, Toronto.
Facial nerve paralysis secondary to local anesthetic injection is temporary and will last the expected duration of anesthesia of soft tissue for the particular anesthetic administered. There are risks if there is a loss of the protective reflex to close the eyelid. An example of the appearance of a patient with a transient facial nerve paralysis is shown in Figure 3.

Unwanted anesthesia of other nerves may also occur. Ocular complications following temporary paralysis of cranial nerves III, IV, or VI,28,29 as well as the optic nerve,30 have been described. The proposed mechanism for these events is intravenous transport of local anesthetic to the cavernous sinus.31 Careful aspiration to avoid intravenous injection should prevent this complication.

Prevention of facial nerve paralysis:
  • Follow basic principles of atraumatic injection technique.19

  • Avoid overinsertion of the needle.

  • For the conventional inferior alveolar nerve block, do not inject unless bone has been contacted at the appropriate depth.

Management of facial nerve paralysis:
  • Reassure the patient of the transient nature of the event.

  • Advise the patient to use an eye patch until motor function returns.

  • If contact lenses are worn, they should be removed.

  • Record details in the patient's chart.

Infection

With the introduction many years ago of sterile disposable needles, infection is now an extremely rare complication of local anesthetic administration. It may occur if the needle has been contaminated prior to insertion. The normal flora of the oral cavity is not a concern since they do not lead to infection in patients who are not significantly immunocompromised. In fact, bacteria enter the tissues with every needle insertion, yet the body's normal defense prevents a clinical infection. In patients who are severely immunocompromised, a topical antiseptic or an antiseptic rinse such as chlorhexidine could be considered prior to needle insertion.

If an infection does occur, it will likely manifest initially as pain and trismus one day postinjection. If these symptoms persist for three days and continue to worsen, the possibility of infection should be considered. At this stage, this patient should be examined for other signs of infection, such as swelling, lymphadenopathy, and fever.

When there is an active site of infection, such as an abscess, needles should not be inserted. This is not only because the low pH will prevent the onset of local anesthetic action, but also because there is the potential for spreading the infection.

Prevention of infection:
  • Use sterile disposable needles.

  • Do not contaminate the needle by contacting nonsterile surfaces outside the mouth.

  • In severely immunocompromised patients, consider a topical antiseptic prior to injection.

Management of infection:
  • Prescribe antibiotics, such as penicillin, in an appropriate dose and duration.

  • Record details in the patient's chart and follow up to determine progress.

Mucosal Lesions

Occasionally, the intraoral mucosa may show signs of sloughing or ulceration. The epithelial layer may desquamate from prolonged application of topical anesthetic. It is possible, but not common, that necrosis of tissues may result from high concentrations of vasoconstrictor, such as 1:50,000. Sites of ulceration consistent with a diagnosis of aphthous stomatitis may also result following local anesthetic administration. For each of these, the lesions will be present for one to two weeks and resolve irrespective of treatment. Drug therapy is seldom warranted. Simple measures such as saline or sodium bicarbonate rinses may assist healing by keeping the sites relatively clean.

Prevention of mucosal lesions:
  • Do not leave topical anesthetic on mucosa for prolonged periods.

Management of mucosal lesions:
  • Reassure the patient; advise him or her of the expected duration of one to two weeks.

  • Use rinses with lukewarm dilute solutions of salt or baking soda, until symptoms resolve.

Summary

The occurrence of localized complications from local anesthesia administration can be minimized by following basic principles of local anesthetic injection technique and the previously listed suggestions for prevention. Nevertheless, in spite of proper technique, complications may occur. Fortunately, most resolve well without permanent sequelae, and appropriate management will facilitate patient recovery from these events.

Author
Daniel A. Haas, DDS, PhD, is an associate professor and head of anaesthesia, Faculty of Dentistry, and associate professor in the Department of Pharmacology, Faculty of Medicine, at the University of Toronto.


References
1. Malamed SF, Handbook of Local Anesthesia, 4th ed. Mosby, 1997, p 259.
2. Colin W and Donoff RB, Restoring sensation after trigeminal nerve injury: a review of current management. J Am Dent Assoc 123:80-5, 1992.
3. Jastak JT, Yagiela JA, and Donaldson D, Local Anesthesia of the Oral Cavity. Saunders, 1995, p 301.
4. Kipp DP, Goldstein BH, and Weiss WW, Dysesthesia after mandibular third molar surgery: a retrospective study and analysis of 1,377 surgical procedures. J Am Dent Assoc 100:185-92, 1980.
5. Fielding AF, Rachiele DP, and Frazier G, Lingual nerve paresthesia following third molar surgery. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 84:345-8, 1997.
6. Shannon IL and Wescott WB, Alcohol contamination of local anesthetic cartridges. J Acad Gen Dent 22:20-1, 1974.
7. Steen PA and Michenfelder JD, Neurotoxicity of anesthetics. Anesthesiology 50:437-53, 1979.
8. Myers RR, Kalichman MW, et al, Neurotoxicity of local anesthetics: altered perineurial permeability, edema, and nerve fiber injury. Anesthesiology 64:29-35, 1986.
9. Kalichman MW, Moorhouse DF, et al, Relative neural toxicity of local anesthetics. J Neuropathol Exp Neurol 52:234-40, 1993.
10. Rigler ML, Drasner K, et al, Cauda equina syndrome after continuous spinal anesthesia. Anesth Analg 72:275-81, 1991.
11. Lambert DH and Hurley RJ, Cauda equina syndrome and continuous spinal anesthesia. Anesth Analg 72:817-9, 1991.
12. Barsa J, Batra M, et al, A comparative in vivo study of local neurotoxicity of lidocaine, bupivacaine, 2-chloroprocaine, and a mixture of 2-chloroprocaine and bupivacaine. Anesth Analg 61:961-7, 1982.
13. Haas DA and Lennon D, A 21 year retrospective study of reports of paresthesia following local anesthetic administration. J Can Dent Assoc 61:319-30, 1995.
14. Supreme Court of Ontario, Trial Proceedings #158/89; Vol 3:494-7, 1989.
15. Haas DA and Lennon D, A review of local anesthetic-induced paresthesia in Ontario in 1994. J Dent Res 75(abs):247, 1996.
16. Fink BR and Kish SJ, Reversible inhibition of rapid axonal transport in vivo by lidocaine hydrochloride. Anesthesiol 44:139-146, 1976.
17. Kane RE, Neurologic deficits following epidural or spinal anesthesia. Anesth Analg 60:150-61, 1981.
18. Benoit PW, Yagiela JA, and Fort NF, Pharmacologic correlation between local anesthetic-induced myotoxicity and disturbances of intracellular calcium distribution. Toxicol Appl Pharmacol 52:187-98, 1980.
19. Malamed SF, Basic injection technique. In, Handbook of Local Anesthesia, 4th ed. Mosby, 1997, pp 132-42.
20. Malamed SF, Handbook of Local Anesthesia, 4th ed. Mosby, 1997, p 246.
21. Burke RH, Management of a broken anesthetic injection needle in the maxilla. J Am Dent Assoc 112:209-10, 1986.
22. Small SC and Waters BG, An alternative approach to mandibular block anaesthesia. Oral Health 73(2):21-3, 1983.
23. Mercuri LG, Intraoral second division nerve block. Oral Surg Oral Med Oral Path 47:109-13, 1979.
24. Yagiela JA, Regional anesthesia for dental procedures. Int Anesthesiol Clin 27:68-82, 1989.
25. Malamed SF, Handbook of Local Anesthesia, 4th ed. Mosby, 1997, p 89.
26. Jastak JT, Yagiela JA, and Donaldson D, Local Anesthesia of the Oral Cavity. Saunders, 1995, p 305.
27. Miles PG, Facial palsy in the dental surgery. Case report and review. Aust Dent J 37:262-5, 1992.
28. Fish LR, McIntire DN, and Johnson L, Temporary paralysis of cranial nerves III, IV, and VI after a Gow-Gates injection. J Am Dent Assoc 119:127-30, 1989.
29. Rood JP, Ocular complications of inferior dental nerve block. Br Dent J 132:23-4, 1972.
30. Tomazzoli-Gerosa L, Marchini G, and Monaco A, Amaurosis and atrophy of the optic nerve: an unusual complication of mandibular-nerve anesthesia. Ann Ophthalmol 20:170-1, 1988.
31. Liebgott B, An anatomical explanation for the infrequent occurrence of diplopia (double vision) following dental local anesthesia. Univ Toronto Dent J 1:36-7, 1987.

To request a printed copy of this article, please contact: Daniel A. Haas, DDS, PhD, Faculty of Dentistry, University of Toronto, 124 Edward St., Toronto, Ontario, M5G 1G6, CANADA.


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