Damage to the inferior alveolar nerve as the result of root canal therapy
M. Anthony Pogrel, DDS, MD, FRCS, FACS
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ABSTRACT
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Background. Endodontic treatment of mandibular molar teeth has the potential to damage the inferior alveolar nerve via direct trauma, pressure or neurotoxicity.
Methods. The author reviewed all cases of involvement of the inferior alveolar nerve resulting from root canal therapy in patients seen in a tertiary referral center during an eight-year period (1998 through 2005). The author had encouraged practitioners to refer patients immediately to a university clinic.
Results. The author saw 61 patients during the eight-year period. Eight patients were asymptomatic and received no treatment. Forty-two patients exhibited only mild symptoms or were seen more than three months after undergoing root canal therapy, and they received no surgical treatment. Only 10 percent of these patients experienced any resolution of symptoms. Eleven patients underwent surgical exploration. Five of these patients underwent exploration and received treatment within 48 hours, and all recovered completely. The remaining six patients underwent surgical exploration and received treatment between 10 days and three months after receiving endodontic therapy. Of these patients, four experienced partial recovery and two experienced no recovery at all.
Conclusions. Early surgical exploration and débridement may reverse the side effects of endodontic treatment on the inferior alveolar nerve.
Clinical Implications. If the radiograph obtained after endodontic therapy shows sealant in the inferior alveolar canal, then immediate referral to an oral and maxillofacial surgeon is indicated if the patient has continued symptoms of paresthesia or pain once the local anesthetic should have worn off. Immediate surgical exploration and débridement may provide satisfactory results.
Key Words: Root canal therapy; mandibular molar teeth; inferior alveolar nerve damage
When root canal therapy is performed on mandibular teeth posterior to the mental foramen, damage to the inferior alveolar nerve is possible.1 Most cases have been reported in connection with the lower second molars, but cases related to the first molars and the premolars also have been reported.2 Three possible mechanisms can be envisaged1,3:
- – mechanical trauma from overinstrumentation into the inferior alveolar canal;
- – a pressure phenomenon from the presence of the endodontic point or sealant within the inferior alveolar canal2,4;
- – a neurotoxic effect from the medicaments used to clean the canal or that are in the sealant.
Treatment remains controversial, varying from a wait-and-see approach5,6 to early,7–11 if not immediate,12,13 surgical débridement of the inferior alveolar nerve via a number of possible approaches. These include extraction of the tooth and approaching the nerve through the socket,11 decortication of the mandible achieved laterally13 from an intraoral4,14,15 and extraoral16 approach, and sagittal splitting of the mandible to expose the nerve within the split.9,17 Most reports are single case reports or small case series.18
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MATERIALS AND METHODS
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Each year, I treat between 150 and 180 patients with damage to the inferior alveolar and lingual nerves from all causes in the Department of Oral and Maxillofacial Surgery, University of California, San Francisco.19,20 An analysis of patients seen from 1991 through 2005 shows that the number of cases of inferior alveolar nerve involvement resulting from root canal therapy reached a low of six cases in one year and a high of 15 cases in another year, with a mean of eight cases per year. Figure 1
shows radiographs of typical cases.
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Figure 1. Typical radiographs of a molar (A) and a premolar (B) showing radiopaque root canal sealant within the inferior alveolar canal.
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I encourage general dentists and endodontists to refer these patients early, if not immediately. Since 1998, my advice has been that if sealant is noted in the inferior alveolar canal on the radiograph obtained immediately after the root is filled, the clinician should monitor the patient carefully and refer him or her without delay if he or she still is experiencing numbness or other symptoms once the local anesthetic should have worn off.
When subsequent imaging the same day confirms the presence of sealant in the canal, I recommend immediate decompression and débridement of the nerve via lateral decortication of the mandible.12 The oral and maxillofacial surgeon performs the surgery in the operating room of a hospital with the patient under general anesthesia.
He or she decorticates the mandible in one block of lateral cortex from approximately the second premolar region (posterior to the mental foramen) to the third molar region. This is carried out in an intraoral approach by using a combination of reciprocating saw and curved osteotomes. In this way, the surgeon can remove the lateral plate as a single piece of bone that can be replaced at the end of the procedure. The surgeon usually then can identify easily the nerve lying within the substance of the marrow of the mandible. He or she then teases the nerve out of the inferior alveolar canal, thoroughly cleans the canal and irrigates it of any foreign material (Figure 2), examines the root of the tooth and, if necessary, performs an apicoectomy or even an extraction.
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Figure 2. Inferior alveolar canal decorticated and the inferior alveolar nerve (arrow) removed from the canal and ready for débridement. The arrow also shows paste within the epineurium.
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The surgeon then examines the nerve itself in this region, and if sealant is found within the epineurium itself, he or she opens and cleans the epineurium and irrigates and cleans the individual fascicles. He or she then replaces the nerve and hollows out the lateral plate of the mandible using a pineapple bur or an acrylic-type bur so that no pressure is placed on the nerve. The surgeon then replaces the lateral plate of bone using one or more 1.5-millimeter screws, taking care to avoid further injury to the nerve. If possible, this procedure should be performed the same day as that of the injury.
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RESULTS
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From 1998 through 2005, I saw 61 patients with clinical and radiographic evidence of sealant in the inferior alveolar canal.
In eight patients, there was clear radiographic evidence of sealant within the canal, but these patients were asymptomatic and remained so indefinitely. Presumably in these cases, the sealant used was relatively nonneurotoxic, and although it was within the bony confines of the canal, the sealant was not within the epineurium; therefore, the fascicles themselves were not affected. These eight patients did not undergo surgery.
In 42 patients, there was clinical and radiographic evidence of sealant or an endodontic point within the canal, but either the symptoms were fairly mild or the delay from the injury to referral was too long for the results to be successful. Consequently, these patients did not undergo surgery and clinicians observed them. Follow-up, often by the patient’s general dentist or the endodontist involved, revealed that fewer than 10 percent of these patients experienced any resolution of symptoms. Pain or dysesthesia was present in 13 (31 percent) of the 42 patients.
I performed surgery in 11 patients in an attempt to relieve symptoms of dysesthesia and return sensation to normal. In five of these patients, I performed surgery within 48 hours of the injury, while in the other six patients, I performed surgery more than one week (10 days to three months) after their injury. In one of these patients, paresthesia did not develop until two days after the endodontic treatment (that is, there was a "lucid" period).
Of the five patients who underwent surgery within 48 hours of their injury, all experienced total resolution of their symptoms within one week and began to feel improvement the day after surgery.
Of the six patients who underwent surgery more than one week after their injury, four achieved partial improvement in sensation and two experienced no improvement at all.
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DISCUSSION
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A review of the literature reveals that this represents the largest published case series of endodontically related injuries to the inferior alveolar nerve. Studies have shown that all root canal sealants are neurotoxic to some degree. The most neurotoxic appear to be those containing paraformaldehyde6 or one of its analogs, including Sargenti paste (N2) or Endomethasone (Spécialtiés Septodont, Saint-Maurdes Fosses, Cedex, France; available only in Canada and Europe).11,21 Other sealants contain analogs of formaldehyde, particularly before they have set (for example, AH 26 [Dentsply Maillefer, Tulsa, Okla.]).10,22 Even root canal sealants that are believed to be more benign, such as zinc oxide and eugenol and calcium hydroxide (owing to its high pH),1 have been shown to be neurotoxic in vitro23–28 and are almost certainly neurotoxic in vivo.21
One of the possible differences between root canal sealants may be that some demonstrate their neurotoxic properties only when they come into direct contact with the individual fascicles, and as long as they are outside the epineurium, they are safe (Figure 3). This would explain cases in which there is clear evidence of sealant within the canal but the patient is asymptomatic. These agents may gain entry to the fascicle because overinstrumentation of the canal before insertion of the sealant may have resulted in an opening through the perineurium.
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Figure 3. A. Endodontic sealant within the inferior alveolar canal but outside the epineurium. B. Sealant within the epineurium and around the fascicles, perhaps the result of a mechanical break in the epineurium caused by overinstrumentation of the root canal into the inferior alveolar canal.
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In addition, it is not unusual for patients to experience a so-called "lucid" period. This occurs in cases in which the local anesthetic (most commonly an inferior alveolar nerve block) wears off satisfactorily, and the patient has normal feeling for 24 to 36 hours; the paresthesia or dysesthesia then starts to develop. This appears to be the case with agents that are believed to be less neurotoxic than others. In this case series, I noted eight cases in which this phenomenon occurred. Only one of these eight patients underwent surgical intervention.
Neaverth29 suggested that a higher incidence of dysesthesia develops in patients in whom the nerve involvement is caused by a root canal sealant. Dysesthesia rates after traumatic injury to the inferior alveolar nerve (for example, in third-molar removal) appear to be between 8 and 10 percent20,30 of cases, but they may be higher in cases in which root canal sealants are the cause of the condition, possibly denoting a chemical neurotoxic effect. In this case series, the dysesthesia rate was in excess of 30 percent.
Steroids, administered to reduce the edema and inflammatory response to the sealant within the rigid confines of the inferior alveolar nerve, may provide some relief or allow surgeons to wait a day or two before performing surgery. Some authorities21,31 advise immediate steroid administration, though there is no agreement regarding the type, dosage or duration of steroid treatment. I must note that, to my knowledge, there have been no controlled trials of any treatment protocols involving endodontically related injuries to the inferior alveolar nerve, and the above results and discussion represent primarily my findings and opinions.
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CONCLUSION
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All root canal sealants have the potential to be neurotoxic, and if a radiograph shows sealant to be within the confines of the inferior alveolar canal, the clinician should monitor the patient carefully during the postoperative period. Even if the local anesthetic appears to wear off satisfactorily and sensation returns, clinicians still should follow up patients for 72 hours, because delayed nerve damage caused by less neurotoxic agents is possible. If symptoms are present as soon as the local anesthetic would be expected to have worn off, the clinician immediately should perform decompression and débridement, irrigation and cleaning of the nerve, which may achieve the best results. The number of patients in this case series was small and the results are not statistically significant, but the outcomes for these patients may point in that direction.
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FOOTNOTES
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Dr. Pogrel is a professor and chairman, Department of Oral and Maxillofacial Surgery, University of California, San Francisco, P.O. Box 0440, 521 Parnassus Ave., Room C-522, San Francisco, Calif. 94141-0440, e-mail "tony.pogrel{at}ucsf.edu". Address reprint requests to Dr. Pogrel.
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REFERENCES
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- Conrad SM. Neurosensory disturbances as a result of chemical injury to the inferior alveolar nerve. J Oral Maxillofac Surg Clin North Am 2001;13(2):255–63.
- Knowles KI, Jergenson MA, Howard JH. Paresthesia associated with endodontic treatment of mandibular premolars. J Endod 2003;29(11):768–70.[Medline]
- Nitzan DW, Stabholz A, Azaz B. Concepts of accidental overfilling and overinstrumentation in the mandibular canal during root canal treatment. J Endod 1983;9(2):81–5.[Medline]
- Fanibunda K, Whitworth J, Steele J. The management of thermo-mechanically compacted gutta percha extrusion in the inferior dental canal. Br Dent J 1998;184(7):330–2.[Medline]
- Dempf R, Hausamen JE. Lesions of the inferior alveolar nerve arising from endodontic treatment. Aust Endod J 2000;26(2):67–71.[Medline]
- Orstavik D, Brodin P, Aas E. Paraesthesia following endodontic treatment: survey of the literature and report of a case. Int Endod J 1983;16(4):167–72.[Medline]
- Forman GH, Rood JP. Successful retrieval of endodontic material from the inferior alveolar nerve. J Dent 1977;5(1):47–50.[Medline]
- Gallas-Torreira MM, Reboiras-Lopez MD, Garcia-Garcia A, Gandara-Rey J. Mandibular nerve paresthesia caused by endodontic treatment. Med Oral 2003;8(4):299–303.[Medline]
- Scolozzi P, Lombardi T, Jaques B. Successful inferior alveolar nerve decompression for dysesthesia following endodontic treatment: report of 4 cases treated by mandibular sagittal osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;97(5):625–31.[Medline]
- Spielman A, Gutman D, Laufer D. Anesthesia following endodontic overfilling with AH26: report of a case. Oral Surg Oral Med Oral Pathol 1981;52(5):554–6.[Medline]
- Yaltirik M, Ozbas H, Erisen R. Surgical management of overfilling of the root canal: a case report. Quintessence Int 2002;33(9): 670–2.[Medline]
- Pogrel MA. Neurotoxicity of available root sealant pastes (letter). Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;98(4):385.[Medline]
- Grotz KA, Al-Nawas B, de Aguiar EG, Schulz A, Wagner W. Treatment of injuries to the inferior alveolar nerve after endodontic procedures. Clin Oral Investig 1998;2(2):73–6.[Medline]
- Kothari P, Hanson N, Cannell H. Bilateral mandibular nerve damage following root canal therapy. Br Dent J 1996;180(5):189–90.[Medline]
- Littler B. Removal of endodontic paste from the inferior alveolar nerve by sagittal splitting of the mandible (letter). Br Dent J 1988; 164(6):172.[Medline]
- LaBanc JP, Epker BN. Serious inferior alveolar nerve dysesthesia after endodontic procedure: report of three cases. JADA 1984;108(4): 605–7.
- Evans AW. Removal of endodontic paste from the inferior alveolar nerve by sagittal splitting of the mandible (letter). Br Dent J 1988; 164(1):18–20.[Medline]
- Montgomery S. Paresthesia following endodontic treatment. J Endod 1976;2(11):345–7.[Medline]
- Pogrel MA. The results of microneurosurgery of the inferior alveolar and lingual nerve. J Oral Maxillofac Surg 2002;60(5):485–9.[Medline]
- 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 Assoc 1999;27(7):531, 534–8.[Medline]
- Morse DR. Endodontic-related inferior alveolar nerve and mental foramen paresthesia. Compend Contin Educ Dent 1997;18(10):963–8, 970–3, 976–8 passim; quiz 998.[Medline]
- Rowe AH. Damage to the inferior dental nerve during or following endodontic treatment. Br Dent J 1983;155(9):306–7.[Medline]
- Asgari S, Janahmadi M, Khalilkhani H. Comparison of neurotoxicity of root canal sealers on spontaneous bioelectrical activity in identified Helix neurones using an intracellular recording technique. Int Endod J 2003;36(12):891–7.[Medline]
- Asrari M, Lobner D. In vitro neurotoxic evaluation of root-end-filling materials. J Endod 2003;29(11):743–6.[Medline]
- Hume WR. An analysis of the release and the diffusion through dentin of eugenol from zinc oxide-eugenol mixtures. J Dent Res 1984;63(6):881–4.[Abstract/Free Full Text]
- Hume WR. Effect of eugenol on respiration and division in human pulp, mouse fibroblasts, and liver cells in vitro. J Dent Res 1984;63(11):1262–5.[Abstract/Free Full Text]
- Hume WR. The pharmacologic and toxicological properties of zinc oxide-eugenol. JADA 1986;113(5):789–91.
- Hume WR. In vitro studies on the local pharmacodynamics, pharmacology and toxicology of eugenol and zinc oxide-eugenol. Int Endod J 1988;21(2):130–4.[Medline]
- Neaverth EJ. Disabling complications following inadvertent overextension of a root canal filling material. J Endod 1989;15(3):135–9.[Medline]
- Haas DA, Lennon D. A 21 year retrospective study of reports of paresthesia following local anesthetic administration. J Can Dent Assoc 1995;61(4):319–20, 323–6, 329–30.
- Gatot A, Tovi F. Prednisone treatment for injury and compression of inferior alveolar nerve: report of a case of anesthesia following endodontic overfilling. Oral Surg Oral Med Oral Pathol 1986;62(6): 704–6.[Medline]
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ABSTRACT
MATERIALS AND METHODS
