Permanent sensory nerve impairment following third molarsurgery: a prospective studyW. Jerjes, BDS, MSc,a B. Swinson, MBBS, BDS, FDS, AFRSC,b

D. R. Moles, PhD, BDS, MSc, MSc(Hons), DDPH RCS(Eng), MIHPE ILTM,c

M. El-Maaytah, BDS, MSc, PhD, FDS RCPS, LDS RCS,d

B. Banu, BDS, DDS, MCPS, MSc, FDS RCS,e T. Upile, FRCS,f

M. Kumar, BDS, MBBS, FDS, FRCS,g M. Al Khawalde, DDS, MSc,h

M. Vourvachis, DMD, MSc,i H. Hadi, BDS,j S. Kumar, BDS,k andC. Hopper, MBBS, BDS, FDSRCS, FRCSl London and East Grinstead, United KingdomEASTMAN DENTAL INSTITUTE FOR ORAL HEALTHCARE SCIENCES, UNIVERSITY COLLEGE LONDONHOSPITALS, AND QUEEN VICTORIA HOSPITAL

Objective. This prospective study reports the proportion of permanent sensory impairment of the inferior alveolar andlingual nerves and the factors influencing such prevalence after the removal of mandibular third molars under localanesthesia.Study design. There were 1,087 patients with 1,087 mandibular third molars removed under local anesthesia from1998 to 2003. Standardized data collection included the patient’s name, age, gender, radiographic position ofextracted tooth, grade of surgeon, proximity of the inferior alveolar nerve, and the prevalence of lingual and/or inferioralveolar nerve paresthesia.Results. Inferior alveolar nerve injury was 4.1% 1 week after surgery and decreased to 0.7% after 2 years of follow-up, and alteration in tongue sensation occurred in 6.5% of patients 1 week after surgery and decreased to 1.0% after 2years of follow-up.Conclusion. The experience of the operator was found to be a significant factor in determining both permanent lingualnerve (P�.022) and permanent inferior alveolar nerve paresthesia (P�.026). (Oral Surg Oral Med Oral Pathol Oral

Radiol Endod 2006;102:e1-e7)

Injuries to the lingual nerve (LN) and inferior alveolarnerve (IAN) are well recognized complications of thirdmolar surgery. In previous studies, the prevalence ofdamage to the IAN during lower third molar surgeryhas been reported as varying from 0.4%1to 8.4%2 andto the LN as varying from 0%3 to 23%.4

The IAN travels within the mandibular bone and istherefore a supported nerve. Following injury, the nervewill remain in position and regenerate in a relatively

aHonorary Lecturer, Department of Oral and Maxillofacial Surgery,Eastman Dental Institute for Oral Healthcare Sciences.bSpecialist Registrar, Department of Oral and Maxillofacial Surgery,University College London Hospitals.cSenior Clinical Lecturer in Health Services Research, Eastman Den-tal Institute for Oral Healthcare Science, University College London.dSpecialist Registrar, Department of Oral and Maxillofacial Surgery,University College London Hospitals.eSpecialist in Surgical Dentistry, Department of Oral & MaxillofacialSurgery, Eastman Dental Institute for Oral Healthcare Sciences.fSpecialist Registrar, Head and Neck Surgery Unit, University Col-lege London Hospitals.gSpecial Registrar, Department of Oral & Maxillofacial Surgery,University College London Hospitals.hSpecialist, Department of Oral and Maxillofacial Surgery, Royal

Medical Services, Jordan.

short time unless either displaced into the socket ordisplaced by fragments of bone from the roof of thecanal. Thus, after injury to the IAN, good recovery isgenerally expected.5 The anatomic relationship be-tween the IAN and the roots of the third molar teeth hasalso been shown to help predict the likelihood of nerveinjury radiographically.6-8

After injury, the LN ends tend to retract and becometrapped within scar tissue which may require surgicalrepair, although the success rate of this procedure hasso far been modest.5

iSenior House Officer, Department of Oral and Maxillofacial Sur-gery, Eastman Dental Institute for Oral Healthcare Sciences.jResearch Fellow, Department of Oral and Maxillofacial Surgery,Eastman Dental Institute for Oral Healthcare Sciences.kSenior House Officer, Department of Oral and Maxillofacial Sur-gery, The Queen Victoria Hospital NHS Trust.lSenior Lecturer, Consultant Oral and Maxillofacial Surgeon, Head ofAcademic Surgical Unit, Eastman Dental Institute for Oral Health-care Sciences.Received for publication Mar 23, 2005; returned for revision Dec 13,2005; accepted for publication Jan 19, 2006.1079-2104/$ - see front matter© 2006 Mosby, Inc. All rights reserved.

doi:10.1016/j.tripleo.2006.01.016

e1

OOOOEe2 Jerjes et al. October 2006

In the majority of the review cases, paresthesia wasfound to be temporary and tends to subside within thefirst 6 months.7,9 Some studies have reported a lesserproportion of recovery for the LN compared with theIAN,10,11 though other studies fail to prove thiscase.12,13

The aim of this study was to determine the propor-tion of permanent sensory impairment, the related fac-tors following surgical removal of mandibular thirdmolars, and to present some follow-up and treatmentmodalities.

MATERIAL AND METHODSProspectively recorded data of 1,087 cases who un-

derwent removal of mandibular third molars in theoutpatient Department of Oral and Maxillofacial Sur-gery, Eastman Dental Hospital, from 1998 to 2003 wereanalyzed for the prevalence of permanent sensory nerveimpairment.

The demographic data collected from each patientincluded age, gender, degree of impaction (assessedradiographically as fully erupted, partially impacted, orfully impacted), treating surgeon (specialist or trainee),radiograph proximity to IAN (tooth �2 mm is consid-ered to be close), duration of surgery and postoperativecomplications (permanent paresthesia), and require-ment for a follow-up appointment 1 week after surgery.No patient in this study failed to attend the follow-upappointment.

Data concerning alteration of sensation was collectedas originating from the IAN and/or LN. This wasmainly volunteered by the patient, or the clinician in-quired concerning “paresthesia,” “pins and needles,” or“numbness.” Following the establishment of alteredsensation, patients were reviewed at 3 weeks, 6 months,and up to 2 years. Any symptomatic patient beyond thistime was considered to have permanent nerve impair-ment.

All surgical procedures were performed in 3 similarclinics, equipped with similar surgical instruments, ro-tary and irrigation devices, and materials (sutures andhemostatic agents). Before surgery, each patient wasinformed of possible complications, including the pos-sible risk of nerve damage during the procedure, andprovided full informed consent.

Local anesthesia was achieved (2% lidocaine with1:80,000 epinephrine) by local tissue infiltration andIAN block injection, and no more than 5 cartridgeswere given to any single patient.

An envelope mucoperiosteal flap was reflected andbone was removed with a round bur in a straight hand-piece. In several cases (43 patients), the tooth had to besectioned using a fissure bur. The sectioning in all cases

was performed from the root bifurcation area to the

occlusal surface; no other sectioning technique wasimplemented. These patients were very few, so theywere combined with patients who had standard surgicalapproach with no tooth sectioning. Bone removal andsectioning of the tooth was performed under continuousirrigation with sterile saline solution at room tempera-ture. The wound was carefully irrigated and any bonyspicules removed. The flap was then repositioned andsutured with 4-0 Vicryl. No lingual flap was employedin any of the cases. No patient in this study underwentcoronectomy.

Immediately after surgery all patients were given writ-ten instructions about wound care and possible complica-tions in the postoperative period. For all patients, metro-nidazole (400 mg 3 times daily for 5 days) was prescribedas an antimicrobial agent and ibuprofen (400 mg 3 timesdaily for 5 days) as an analgesic. All patients in this studywere reviewed 7 days after surgery.

The cases were distributed among the junior (train-ees) and senior (specialists) staff regardless of their age,gender, or level of complexity. All staff in the traineegroup were senior house officers, whereas the seniorstaff were clinicians on the Specialist Register for Sur-gical Dentistry. The level of supervision and training ofthe senior house officers was according to the nationalstandards. Patients were required to undergo removal ofat least 1 mandibular third molar tooth for inclusion inthis study.

No surgical exploration was implemented for any ofthe patients presenting with paresthesia for less than 2years. Patients who continued to have this symptomover 2 years (permanent) were reviewed to assess theircondition and were advised to undergo surgery forexploration of the area that could include undertakingmicroneurosurgical repair for the appropriate cases.

Statistical methodsThe outcomes of paresthesia affecting the LN and

IAN were summarized as frequencies for a series oftime intervals after surgery. The chi-squared statisticwas used to test for differences in the prevalence of lipand tongue paresthesia (separately) at 2 years aftersurgery within subgroups of the factors under study.Where only 2 subgroups were being compared, theFisher’s exact test was used, because the expectednumbers of patients with paresthesia within subgroupswere small.

RESULTSThe 1,087 treated patients had a mean age of 23.3

(SD 4.2) years, and 585/1,087 (53.9%) were women.All underwent mandibular third molar removal (TableI). The majority of teeth (857/1,087; 78.8%) were par-

tially impacted and around three quarters (843/1087;

OOOOEVolume 102, Number 4 Jerjes et al. e3

77.6%) had roots that appeared radiographically to bewithin or less than 2 mm from the IAN canal roof. Themean time to complete surgery was 18 min (SD 7.3;range 4-39 min).

After 1 week, 45 patients (4.1%) exhibited paresthe-sia in the distribution of the IAN and 71 (6.5%) expe-rienced symptoms of LN paresthesia. The majority ofthese resolved within the first month after surgery. By2 years, 8 patients (0.7%) still exhibited IAN paresthe-sia and 11 (1.0%) paresthesia of the LN (Table II).

Our study of the predictors of permanent IAN par-esthesia after 2 years (Table III) revealed that 0.8% ofthe male and 0.7% of the female patients sustainedpermanent nerve impairment. This was more frequentwith teeth recorded as fully impacted (2.4%) than withpartially impacted teeth (0.6%). The only statisticallysignificant predictor of permanent IAN impairment wasthe experience of the operator (P�.026), with the betterlong-term results being achieved by the more seniorsurgeons.

There was borderline statistical evidence to suggestthat LN paresthesia 2 years after surgery (Table IV) hadslightly higher prevalence in men (1.6%) than women(0.5%) (P�.069). The experience of the surgeon wasthe only statistically significant predictor of permanentLN paresthesia, with a lower proportion of permanentparesthesia being achieved by the senior surgeons(0.4% vs. 1.7%; P�.022).

DISCUSSIONThis study is representative of the spectrum of third

molar surgery undertaken in maxillofacial surgery de-partments under local anesthesia.

Table I. Profile of treated casesCategory Description n (%)

Gender Male 501 (46.1)Female 586 (53.9)

Age (yrs) Mean 23.3Median 22.0SD 4.2Range 17–36

Degree of impaction of3rd molar

Fully eruptedPartially eruptedFully impacted

104 (9.6)857 (78.8)126 (11.6)

Proximity to inferioralveolar nerve

�2 mm�2 mm

244 (22.4)843 (77.6)

Duration of surgery (min) Mean 18.1Median 18.0SD 7.3Range 4–39

Seniority of surgeon Trainee 518 (47.7)Specialist 569 (52.3)

The degree of sensory alteration and subsequent re-

covery following nerve damage depends on the severityof injury, and this forms the basis of the classificationof peripheral nerve injuries proposed by Sunderland14

in 1951. This classification emphasizes the mechanismof injury and importance of each structural componentinvolved.

The classification comprises:

● Compression injuries (neuropraxia).● Severe compression or crush Injuries (axonotmesis).● Stretch Injuries (rupture of endoneurium or peri-

neurium).● Complete section of the nerve trunk (neurotmesis).● Other injuries (perineural inflammation).

Injuries to the inferior alveolar nerveInjuries to the IAN may be anticipated preoperatively

by radiographic examination. Although standard radio-graphs give only a 2-dimensional view, it is possible topredict risk by assessing the location and morphologiccharacteristics of the canal in relation to the mandibularthird molar.6-8

Alteration of sensation results from either direct orindirect trauma to the nerve during surgical instrumen-tation.6,15 The use of root elevators may result in blunttrauma to IAN. The nerve can either be compressed bythe elevator itself or by the elevated roots. The IANmay be disrupted by rotating instruments16 or followingIAN block injections.17 Other factors include full bonyimpaction, apices extending into or below the level ofthe neurovascular bundle, clinical observation of theneurovascular bundle during surgery, and excessivehemorrhage into the socket during surgery. As a result,neuropraxia or axonotmesis may occur at any timeduring surgical removal of third molars. Neurotmesismay also occur if the IAN passes directly through theroot of the tooth and can be transected on its elevation.

The prevalence of permanent numbness was com-pared with former publications and found to be consis-tent with some1,3,18,19 but inconsistent with oth-

Table II. Prevalence of lip and tongue paresthesia atspecific time intervals after surgeryTime after

surgeryLip paresthesia,

n (%)Tongue,n (%)

1 week 45 (4.1) 71 (6.5)2 weeks 19 (1.7) 30 (2.8)3 weeks 19 (1.7) 23 (2.1)1 month 18 (1.7) 17 (1.6)6 months 17 (1.6) 15 (1.4)2 years 8 (0.7) 11 (1.0)

ers.2,13,16,20

OOOOEe4 Jerjes et al. October 2006

Lingual nerve injuryDespite every effort to avoid trauma to the LN during

lower third molar surgery, LN anesthesia, paresthesia,or dysesthesia may result. It may be difficult to avoidencountering the nerve during surgery owing to itsvariable position. A combined anatomic and clinicalstudy by Kiesselbach and Chamberlain21 showedmarked variability in the position of the LN in the thirdmolar region. They stated that the surgeon cannot relyon the lingual plate to act as a protective barrier to thenerve during third molar surgery, because the LN maylie above the bone in this area. There is also anatomicvariation of the LN as it crosses the retromolar padarea, which increases the possibility of being trauma-tized during incision, retraction, buccal flap elevation,

Table III. Predictors of permanent lip paresthesia at 2

Category Description

Gender MaleFemale

Degree of impaction of 3rd molar Fully eruptedPartially eruptedFully impacted

Proximity to inferior alveolar nerve �2 mm�2 mm

Patient age group 17–20 years21–25 years26–30 years31� years

Seniority of surgeon TraineeSpecialist

P values are from chi-squared tests except where specified by asterishave low expected frequencies (�5) for some cells of the tables.

Table IV. Predictors of permanent tongue paresthesia

Category Description

Gender MaleFemale

Degree of impaction of 3rd molar Fully eruptedPartially eruptedFully impacted

Proximity to inferior alveolar nerve �2 mm�2 mm

Patient age group 17–20 years21–25 years26–30 years31� years

Seniority of surgeon TraineeSpecialist

P values are from chi-squared tests except where specified by asterishave low expected frequencies (�5) for some cells of the tables.

tooth or follicle removal, and suturing.

It has been documented that LN impairment mayoccur when raising the mucoperiosteal flap from thelingual aspect of the mandible22 or from from clumsyinstrumentation, or it may be due to fracture of thelingual plate. Inserting a periosteal elevator under thelingual periosteum protects the LN from disruption ordirect trauma by rotating instruments; however, there isan increased chance of stretching the nerve in the handsof less experienced surgeons.13,15,23,24

Lingual nerve impairment following IAN block in-jections,25 or following the use of lingual retractors12 iswell documented. Hematoma, infection, or even swell-ing6,7 have also been implicated etiologies, and the riskof permanent damage after the use of rotating instru-ments has been reported.16

after surgeryPrevalence,

n (%)Chi-squared

(df) P value

4 (0.8)4 (0.7) 0.050 (1) .549*0 (0)5 (0.6)3 (2.4) 5.711 (2) .0582 (0.8)6 (0.7) 0.30 (1) .567*2 (0.7)2 (0.4)3 (2.0)1 (0.9) 4.179 (3) .2437 (1.4)1 (0.2) 5.130 (1) .026*

h are computed from a Fisher’s exact test. All the chi-squared tests

ears after surgery

Prevalence,n (%)

Chi-squared,

(df) P value

8 (1.6)3 (0.5) 3.173 .069*1 (1.0)

10 (1.2)0 (0) 1.496 (2) .4730 (0)

11 (1.3) 3.216 (1) .060*2 (0.7)5 (0.9)3 (2.0)1 (0.9) 1.768 (3) .6229 (1.7)2 (0.4) 5.200 (1) .022*

h are computed from a Fisher’s exact test. All the chi-squared tests

years

k, whic

at 2 y

k, whic

The technique in which bone removal is imple-

OOOOEVolume 102, Number 4 Jerjes et al. e5

mented was found to have a great effect on the preva-lence of LN injury; Rood16 suggested that permanentdamage to the inferior alveolar and lingual nerves wassignificantly related to the bone removal using a surgi-cal drill and that the application of a Howarth periostealelevator carries no benefit. Absi and Shepherd26 con-firmed these findings.

A study by Rood13 suggested that even if theHowarth periosteal elevator is carefully positioned, itcannot protect the LN along the full length of thesurgical field. He suggested continuous movement ofthe instrument along the surgical field to provide opti-mum protection or using other adequate retractors thatprovide better protection than the Howarth periostealelevator. Greenwood et al.27 suggested using broadretractors to protect the LN and found that they producesignificantly less altered nerve sensation at 1 monththan a Howarth periosteal elevator. Other studies sug-gested that there is no need to apply periosteal elevatorsfor LN protection during third molar surgery.28,29

The prevalence of permanent numbness was com-pared with former publications and, as would be ex-pected, found to be consistent with some1,30,31,32 andinconsistent with others.13,16,20,27

Our data show that the proportion of recovery of theLN is faster than that of the IAN and suggest that mostof the LN injury was due to neuropraxia. This is in linewith other authors’ experience.12,13

Degree of impaction and proximity of the toothto the inferior dental canal

Teeth were considered partially erupted if any part ofthe crown was above the superior border of bone.Permanent nerve dysfunction was slightly higher inteeth classified as fully impacted than in partiallyerupted teeth, whereas teeth classified as fully eruptedshowed no reported cases of nerve injury. This suggeststhat a relationship between prevalence and radiographicposition of teeth is possible. These results are consistentwith some studies.33,34

The relation of the inferior dental canal to the thirdmolar tooth was also one of the factors that increase theproportion of nerve damage. The proximity of the canalto the tooth was recorded at the first assessment, and wefound that in 96% of the temporary paresthesia casesthe surgeons recorded the tooth as being “close” toinferior dental canal. However, statistically, this studyfailed to demonstrate a relationship between IAN par-esthesia and the proximity of extracted tooth to theIAN.

Patient’s age and genderThe present study failed to demonstrate a relation-

ship between the age of the patient and sensory distur-

bances following third molar surgery. This was not thecase in some studies which showed a higher morbidityin patients over 35 years of age.35

The lack of any statistically significant associationsuggests that prophylactic surgery may be unjustifiedand could theoretically cause more complications fol-lowing intervention. These results are consistent withthe guidelines issued by the National Institute for Clin-ical Excellence, which does not support prophylacticwisdom tooth removal. This is still a controversialissue, with some authorities still recommending pro-phylactic third molar surgery.31,35

We found no significant difference between male andfemales patients in relation to lip and tongue paresthe-sias. Some studies demonstrated a female predomi-nance,17 but other studies failed to confirm any associ-ation.23

Surgeon’s experienceThe prevalence of damage of the lingual and inferior

alveolar nerves in our study is in agreement with mostof the documented studies with respect to the surgeon’sexperience.1,20,23,33,36

Trainees showed higher prevalence of LN paresthe-sia in their patients than did their senior colleaguesduring the follow up period. Permanent nerve impair-ment was considered after 2 years of follow-up and was4 times more likely to occur in this group. This could berelated to experience, improper use of force, and instru-ment handling. The same group of surgeons (trainees)treated a slightly higher number of patients with thirdmolars that were close to the IAN. This may be one ofthe reasons for the higher prevalence of permanent IANdamage (7 times more likely to occur).

The prevalence of the permanent damage of the IANand LN is found to be less than the prevalence reportedby Bataineh33 for both the senior and junior staff andquite consistent with the results of Sisk et al.1 for thesenior staff but less for the junior staff.

In our study the number of patients with paresthesiais considered to be relatively small. As such, multipleregression analysis was not implemented to control formultiple factors simultaneously; this might lead to con-founding factors being present which might affect theincidence of paresthesia measured in this study.

Follow-up and treatmentSpontaneous recovery has been reported to occur in

96% of the IAN injuries and 87% of the LN injurieswithin the first 4-8 weeks after surgery.10 Pogrel37

suggested a follow-up regimen as follows: every 2weeks for 2 months, every 6 weeks for 6 months, every

6 months for up to 2 years, and then annually for an

OOOOEe6 Jerjes et al. October 2006

indefinite period. In the absence of active treatment,this frequency seems a little excessive.

Robinson38 reported that recovery after 9 monthsfrom the time of surgery is rare, and it is unlikely thatany recovery will occur after 18 months to 2 years offollow-up. However, some authors have reported re-covery in a small group of patients after 2 years oftreatment.39

Work done by Meyer40 suggests that a recovery ofsensation after 4 weeks indicates neuropraxia and car-ries an excellent prognosis, whereas recovery between1 to 3 months is usually associated with axonotmesis.Any failure to recover after this time usually hints atneurotmesis being the etiology. This carries a poorerprognosis and may require microneurosurgical inter-vention to reapproximate the severed ends.

Table V shows indications and contraindications formicroneurosurgical nerve repair as proposed byMeyer.40

CONCLUSIONThe findings in this study are similar to other pub-

lished series, with permanent sensory loss of the lingualand inferior alveolar nerves noted in 1% and 0.7%,respectively. It is a little disappointing that LN damagewas noted, because no lingual retraction was used inthis series. However, the higher rate of sensory com-plications in the trainee group suggests that at leastsome of the complications may be related to surgicalexperience. This raises a number of important issuesrelated to training. Ideally, third molar removal shouldonly be carried out by experienced practitioners and notby occasional surgeons; however, surgeons are not cre-ated by divine right and need training to gain therequisite level of experience. This will unfortunatelyresult in a higher level of complications even whentrainees are closely supervised. Patients have the right

Table V. Indications for and contraindications to mi-croneurosurgical repairIndicationsComplete anesthesia beyond 3 months.Profound hypoesthesia with no improvement beyond 4 months.Dysesthesia beyond 4 months.Clinically observed nerve severance.ContraindicationsImproving return of sensation.Sensory deficit acceptable to the patient.Central neuropathic pain.Dysesthesia not resolved by a local anaesthesia nerve block.Medical neuropathy.Medically compromised patient.Excessive delay following injury.

to know who will be performing their surgery and may

be unhappy with the increased risk of being treated bya trainee. However, overall the risks of sensory changefollowing third molar removal are still small, with anincreased risk of 1.3% and 1.2% for the lingual andinferior alveolar nerves respectively, when a traineerather than a specialist performs the operation.

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Reprint requests: Waseem JerjesDepartment of Oral & Maxillofacial SurgeryEastman Dental Institute for Oral Healthcare Sciences256 Gray’s Inn RoadLondon WC1X 8LDUnited Kingdom

waseem_wk1@yahoo.co.uk