Background. Endodontic treatment of mandibular molar teeth hasthe potential to damage the inferior alveolar nerve via direct trauma,pressure or neurotoxicity. Methods. The author reviewed all cases of involvement of the inferioralveolar nerve resulting from root canal therapy in patients seen in a ter-tiary referral center during an eight-year period (1998 through 2005).The author had encouraged practitioners to refer patients immediately toa university clinic.Results. The author saw 61 patients during the eight-year period.Eight patients were asymptomatic and received no treatment. Forty-twopatients exhibited only mild symptoms or were seen more than threemonths after undergoing root canal therapy, and they received no sur-gical treatment. Only 10 percent of these patients experienced any reso-lution of symptoms. Eleven patients underwent surgical exploration. Fiveof these patients underwent exploration and received treatment within48 hours, and all recovered completely. The remaining six patientsunderwent surgical exploration and received treatment between 10 daysand 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 reversethe side effects of endodontic treatment on the inferior alveolar nerve. Clinical Implications. If the radiograph obtained after endodontictherapy shows sealant in the inferior alveolar canal, then immediatereferral to an oral and maxillofacial surgeon is indicated if the patienthas continued symptoms of paresthesia or pain once the local anestheticshould have worn off. Immediate surgical exploration and débridementmay provide satisfactory results. Key Words. Root canal therapy; mandibular molar teeth; inferioralveolar nerve damage. JADA 2007;138(1):65-9.

When root canaltherapy is per-formed onmandibular teethposterior to the

mental foramen, damage to the infe-rior alveolar nerve is possible.1 Mostcases have been reported in connec-tion with the lower second molars,but cases related to the first molarsand the premolars also have beenreported.2 Three possible mecha-nisms can be envisaged1,3:dmechanical trauma from overin-strumentation into the inferior alve-olar canal;da pressure phenomenon from thepresence of the endodontic point orsealant within the inferior alveolarcanal2,4;da neurotoxic effect from themedicaments used to clean thecanal or that are in the sealant.

Treatment remains controversial,varying from a wait-and-seeapproach5,6 to early,7-11 if not imme-diate,12,13 surgical débridement ofthe inferior alveolar nerve via anumber of possible approaches.These include extraction of thetooth and approaching the nervethrough the socket,11 decorticationof the mandible achieved laterally13

from an intraoral4,14,15 and extra-oral16 approach, and sagittal split-ting of the mandible to expose thenerve within the split.9,17 Most

A B S T R A C T

Dr. Pogrel is a professor and chairman, Department of Oral and Maxillofacial Surgery, University ofCalifornia, San Francisco, P.O. Box 0440, 521 Parnassus Ave., Room C-522, San Francisco, Calif.94141-0440, e-mail “tony.pogrel@ucsf.edu”. Address reprint requests to Dr. Pogrel.

Damage to the inferior alveolar nerveas the result of root canal therapy

M. Anthony Pogrel, DDS, MD, FRCS, FACS

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reports are single case reports or small caseseries.18

MATERIALS AND METHODS

Each year, I treat between 150 and 180 patientswith damage to the inferior alveolar and lingualnerves from all causes in the Department of Oraland Maxillofacial Surgery, University of Cali-fornia, San Francisco.19,20 An analysis of patientsseen from 1991 through 2005 shows that thenumber of cases of inferior alveolar nerve involve-ment resulting from root canal therapy reached alow of six cases in one year and a high of 15 casesin another year, with a mean of eight cases peryear. Figure 1 shows radiographs of typical cases.

I encourage general dentists and endodontiststo refer these patients early, if not immediately.Since 1998, my advice has been that if sealant isnoted in the inferior alveolar canal on the radi-ograph obtained immediately after the root isfilled, the clinician should monitor the patientcarefully and refer him or her without delay if heor she still is experiencing numbness or othersymptoms once the local anesthetic should haveworn off.

When subsequent imaging the same day con-firms the presence of sealant in the canal, I recom-mend immediate decompression and débridementof the nerve via lateral decortication of themandible.12 The oral and maxillofacial surgeonperforms the surgery in the operating room of ahospital with the patient under general anesthesia.

He or she decorticates the mandible in oneblock of lateral cortex from approximately thesecond premolar region (posterior to the mentalforamen) to the third molar region. This is carriedout in an intraoral approach by using a combina-tion of reciprocating saw and curved osteotomes.In this way, the surgeon can remove the lateralplate as a single piece of bone that can bereplaced at the end of the procedure. The surgeonusually then can identify easily the nerve lyingwithin the substance of the marrow of themandible. He or she then teases the nerve out ofthe inferior alveolar canal, thoroughly cleans thecanal and irrigates it of any foreign material(Figure 2), examines the root of the tooth and, ifnecessary, performs an apicoectomy or even anextraction.

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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.

A B

Figure 2. Inferior alveolar canal decorticated and the inferior alve-olar nerve (arrow) removed from the canal and ready for débride-ment. The arrow also shows paste within the epineurium.

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The surgeon then examines the nerve itself inthis region, and if sealant is found within theepineurium itself, he or she opens and cleans theepineurium and irrigates and cleans the indi-vidual fascicles. He or she then replaces the nerveand hollows out the lateral plate of the mandibleusing a pineapple bur or an acrylic-type bur sothat no pressure is placed on the nerve. The sur-geon then replaces the lateral plate of bone usingone or more 1.5-millimeter screws, taking care toavoid further injury to the nerve. If possible, thisprocedure should be performed the same day asthat of the injury.

RESULTS

From 1998 through 2005, I saw 61 patients withclinical and radiographic evidence of sealant inthe inferior alveolar canal.

In eight patients, there was clear radiographicevidence of sealant within the canal, but thesepatients were asymptomatic and remained soindefinitely. Presumably in these cases, thesealant used was relatively nonneurotoxic, andalthough it was within the bony confines of thecanal, the sealant was not within the epineurium;therefore, the fascicles themselves were notaffected. These eight patients did not undergosurgery.

In 42 patients, there was clinical and radi-ographic evidence of sealant or an endodonticpoint within the canal, but either the symptomswere fairly mild or the delay from the injury toreferral was too long for the results to be suc-cessful. Consequently, these patients did notundergo surgery and clinicians observed them.Follow-up, often by the patient’s general dentistor the endodontist involved, revealed that fewerthan 10 percent of these patients experienced anyresolution of symptoms. Pain or dysesthesia waspresent in 13 (31 percent) of the 42 patients.

I performed surgery in 11 patients in anattempt to relieve symptoms of dysesthesia andreturn sensation to normal. In five of thesepatients, I performed surgery within 48 hours ofthe injury, while in the other six patients, I per-formed surgery more than one week (10 days tothree months) after their injury. In one of thesepatients, paresthesia did not develop until twodays after the endodontic treatment (that is,there was a “lucid” period).

Of the five patients who underwent surgerywithin 48 hours of their injury, all experiencedtotal resolution of their symptoms within one

week and began to feel improvement the day aftersurgery.

Of the six patients who underwent surgerymore than one week after their injury, fourachieved partial improvement in sensation andtwo experienced no improvement at all.

DISCUSSION

A review of the literature reveals that this repre-sents the largest published case series ofendodontically related injuries to the inferioralveolar nerve. Studies have shown that all rootcanal sealants are neurotoxic to some degree. Themost neurotoxic appear to be those containingparaformaldehyde6 or one of its analogs, includingSargenti paste (N2) or Endomethasone (Spécialtiés Septodont, Saint-Maur-des Fosses,Cedex, France; available only in Canada andEurope).11,21 Other sealants contain analogs offormaldehyde, particularly before they have set(for example, AH 26 [Dentsply Maillefer, Tulsa,Okla.]).10,22 Even root canal sealants that arebelieved to be more benign, such as zinc oxide andeugenol and calcium hydroxide (owing to its highpH),1 have been shown to be neurotoxic in vitro23-28

and are almost certainly neurotoxic in vivo.21

One of the possible differences between rootcanal sealants may be that some demonstratetheir neurotoxic properties only when they comeinto direct contact with the individual fascicles,and as long as they are outside the epineurium,they are safe (Figure 3). This would explain casesin which there is clear evidence of sealant withinthe canal but the patient is asymptomatic. Theseagents may gain entry to the fascicle becauseoverinstrumentation of the canal before insertionof the sealant may have resulted in an openingthrough the perineurium.

In addition, it is not unusual for patients toexperience a so-called “lucid” period. This occursin cases in which the local anesthetic (most com-monly an inferior alveolar nerve block) wears offsatisfactorily, and the patient has normal feelingfor 24 to 36 hours; the paresthesia or dysesthesiathen starts to develop. This appears to be the casewith agents that are believed to be less neurotoxicthan others. In this case series, I noted eightcases in which this phenomenon occurred. Onlyone of these eight patients underwent surgicalintervention.

Neaverth29 suggested that a higher incidence ofdysesthesia develops in patients in whom thenerve involvement is caused by a root canal

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sealant. Dysesthesia rates after traumatic injuryto the inferior alveolar nerve (for example, inthird-molar removal) appear to be between 8 and10 percent20,30 of cases, but they may be higher incases in which root canal sealants are the cause ofthe condition, possibly denoting a chemical neuro-toxic effect. In this case series, the dysesthesiarate was in excess of 30 percent.

Steroids, administered to reduce the edema andinflammatory response to the sealant within therigid confines of the inferior alveolar nerve, mayprovide some relief or allow surgeons to wait aday or two before performing surgery. Someauthorities21,31 advise immediate steroid adminis-tration, though there is no agreement regardingthe type, dosage or duration of steroid treatment.I must note that, to my knowledge, there havebeen no controlled trials of any treatment proto-cols involving endodontically related injuries tothe inferior alveolar nerve, and the above resultsand discussion represent primarily my findingsand opinions.

CONCLUSION

All root canal sealants have the potential to beneurotoxic, and if a radiograph shows sealant tobe within the confines of the inferior alveolarcanal, the clinician should monitor the patientcarefully during the postoperative period. Even ifthe local anesthetic appears to wear off satisfacto-rily and sensation returns, clinicians still shouldfollow up patients for 72 hours, because delayednerve damage caused by less neurotoxic agents is

possible. If symptoms are present as soon as thelocal anesthetic would be expected to have wornoff, the clinician immediately should performdecompression and débridement, irrigation andcleaning of the nerve, which may achieve the bestresults. The number of patients in this case serieswas small and the results are not statistically sig-nificant, but the outcomes for these patients maypoint in that direction. ■

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Figure 3. A. Endodontic sealant within the inferior alveolar canal but outside the epineurium. B. Sealant within the epineurium andaround the fascicles, perhaps the result of a mechanical break in the epineurium caused by overinstrumentation of the root canal into theinferior alveolar canal.

A B

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13. Grotz KA, Al-Nawas B, de Aguiar EG, Schulz A, Wagner W.Treatment of injuries to the inferior alveolar nerve after endodonticprocedures. Clin Oral Investig 1998;2(2):73-6.

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