CLINICIAN'S CORNER

Use of cone-beam computed tomography in thediagnosis of sensory nerve paresthesia secondaryto orthodontic tooth movement: A clinical report

Randeep S. Chana,a William A. Wiltshire,b Anastasia Cholakis,c and Gary Levined

Winnipeg, Manitoba, Canada

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In this article, we report an incident of transient neuropathy secondary to tooth movement involving the inferioralveolar nerve. This clinical report reflects the need to thoroughly examine potentially high-risk patients forneuropathy using advanced diagnostic tools such as cone-beam computed tomography when diagnosingand planning treatment. (Am J Orthod Dentofacial Orthop 2013;144:299-303)

Transient neuropathy secondary to orthodontictoothmovement has been reported as a rare occur-rence.1-7 Nevertheless, reports of paresthesia

during orthodontic treatment reflect the need tothoroughly assess the possible risk of injury to theinferior alveolar nerve before the start of orthodontictherapy as part of the process of informed consent.

Orthodontic treatment involves complicated toothmovements in 3 dimensions. Accurate assessment ofroot proximity to the inferior alveolar nerve in the buccaland lingual dimensions might not be possible withconventional 2-dimensional panoramic radiographs.This indicates the need for a cone-beam computedtomography (CBCT) scan in potentially high-riskpatients. A CBCT scan is considered an accurate methodto evaluate the position of the mandibular canal.8 Todetermine the course of the inferior alveolar nervebundle suggests the need for CBCT before attemp-ting treatment in this area to minimize the risk ofneuropathy.8

Sensory disturbances of the lower lip are morecommonly reported as a result of orthognathic surgeryto the lower jaw,6,9-11 internal rigid fixation of

the University of Manitoba, Winnipeg, Manitoba, Canada.uate student, Division of Orthodontics.ssor and chair, Division of Orthodontics.tant professor and director, Division of Periodontics.tant professor, Division of Orthodontics.thors have completed and submitted the ICMJE Form for Disclosure oftial Conflicts of Interest, and none were reported.t requests to: Randeep S. Chana, D341-780 Bannatyne Ave, Winnipeg,oba R3E 0W2, Canada; e-mail, umchanar@cc.umanitoba.ca.itted, January 2012; revised and accepted, May 2012.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2012.05.024

mandibular fractures,6,12 removal of third molars,6,13,14

dentoalveolar surgery,6,15 endodontic treatment,6,16 ora tumor near the mandibular canal.6,17 To date, thereare only a few case reports of paresthesia after toothmovement impinging the inferior alveolar nerve.1-7

The reported causes of nerve disturbances are allclassified as neuropraxias18 or first-degree nerveinjuries.19 Neuropraxia results from minor compressionof the nerve trunk, causing a conduction blockade.19

Axonal continuity is maintained; this results in atemporary conduction blockade.19 Patients clinicallyreport sensory disturbances lasting from hours tomonths, usually with complete sensory recovery.19 Wepresent a case report of sensory disturbance of the lowerlip and the chin occurring during inadvertent intrusionof a third molar into the inferior alveolar nerve canalduring orthodontic treatment.

CASE REPORT

A healthy 27-year-old man came for orthodontictreatment to address his chief complaint of “correctinghis crooked teeth.” After analyzing his clinical examina-tion findings and records, we determined that anonsurgical extraction treatment plan with a temporaryskeletal anchorage device was necessary to align hisseverely crowded teeth (Fig 1). The clinical examinationshowed a symptomatic endodontically treated maxillaryright first molar (tooth 16; Federation DentaireInternationale tooth numbers are used throughout thisarticle) with a large amalgam restoration. The decisionwas made to extract the symptomatic molar and themaxillary left first premolar (tooth 24). Because thepatient was already missing the mandibular second

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Fig 1. Pretreatment intraoral photographs show severe crowding in both arches.

Fig 2. Initial panoramic radiograph. Arrows show closeproximity of the inferior alveolar nerve canal to themandibular third molars.

Fig 3. Temporary skeletal anchorage devices on the leftside to support anchorage and facilitate distal movementof tooth 36.

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molars bilaterally, retraction of the posterior segmentsinto these edentulous spaces using a temporary skeletalanchorage device and the existing third molars foradditional anchorage was planned. The third molarswould eventually be extracted at the completion oftreatment. The initial panoramic radiograph showedthe close proximity of the mandibular third molars(teeth 38 and 48) to the inferior alveolar nerve (Fig 2).

After extraction of teeth 16 and 24, a temporaryskeletal anchorage device (Vector; Ormco, Glendora,Calif) was placed in each posterior quadrant to facilitateanchorage for the retraction. A maxillary transpalatalarch was cemented on teeth 17 and 27 to facilitateintrusion of these molars and reinforce anchorage. Alltemporary skeletal anchorage devices were placedunder local anesthesia (2% lidocaine, 1:100,000epinephrine) with no postoperative complications (Fig3). Blugloo (Ormco) was placed on the occlusal surfacesof teeth 38 and 48 to free the interocclusal contact tofacilitate the distalization (Fig 4).

For the maxillary arch, sectional mechanical princi-ples were used after bonding with an 0.018-in VictoryMBT (3M Unitek, Monrovia, Calif) prescription fixedappliance. Bondable buttons were used to retract teeth36 and 46 individually with elastomeric power chains.Power chains were used on the buccal and lingualsurfaces so as not to cause a rotational moment whileretracting the mandibular first molars (Figs 3 and 4).

To facilitate the retraction of teeth 36 and 46, 2 mmof Blugloo was placed on the disto-occlusal surfaces ofteeth 38 and 48 on April 5, 2011. After this, the patientcame for routine adjustment appointments on April 26and May 2, 2011, with no postoperative complaints or

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complications. He reported tingling and numbing ofhis lower left lip and chin beginning on May 5, 2011,exactly 1 month after the Blugloo placement. Thenumbing sensation continued to increase to a 90%

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Fig 4. Blugloo placed on tooth 38.

Fig 5. Mechanoceptive testing (2-point discrimination)representing the extent of paresthesia 41 days afterplacement of the temporary skeletal anchorage devices.

Fig 6. Periapical radiograph of tooth 38 and temporaryskeletal anchorage device at the emergency examination.

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loss of feeling in this area by May 16, 2011 (Fig 5),41 days after the temporary skeletal anchorage deviceplacement. On May 16, 2011, he came to the clinic toaddress his concerns of paresthesia. He was assessed bythe attending periodontist (A.C.) and orthodontist(W.A.W.) using mechanoceptive testing via 2-pointdiscrimination. The examination showed paresthesia inthe area innervated by the inferior alveolar nerve (Fig5). At this time, the radiographic examination showedno evidence of pathologic entities and ruled out any po-tential issues with the temporary skeletal anchorage de-vice placed mesially to tooth 38 (Fig 6). The mostreasonable explanation of the sensory disturbance wasthat the third molar was invading the space of the infe-rior alveolar nerve as it was being intruded by the Blu-gloo placed on April 5, 2011.

To confirm this finding, small-field CBCT imaging(K9500; Kodak, Rochester, NY) was taken of the areaof tooth 38 (Fig 7). The CBCT image allowed forvisualization of the course of the inferior alveolar nervein relation to the roots of the teeth and the proximity to

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the temporary skeletal anchorage device in a transverseview (Fig 7). The CBCT images showed that the mesio-buccal root of the mandibular left third molar wasinvading the space of the inferior alveolar nerve inboth the coronal (Fig 8) and sagittal (Fig 9) views. Afterthe radiographic evaluation, the Blugloo was removedfrom teeth 38 and 48, and anterior bite turbos wereplaced to facilitate disclusion. A follow-up examinationwas completed on June 9, 2011, when the patientreported a subjective 90% improvement of hisparesthesia. Once again, 2-point discrimination testingwas completed for objective evaluation of the affectedarea. The patient was able to distinguish 2 distinct points(3 mm apart) where he had previously experiencedparesthesia. Removal of the Blugloo let the tooth torelapse away from the inferior alveolar nerve, allowingsensation to return to the patient's lower left lip andchin. At a subsequent follow-up appointment 1 monthlater, full sensory recovery had taken place.

DISCUSSION

In this patient, the CBCT images showed that the rootof the mandibular left third molar was encroaching onthe inferior alveolar canal. The explanation for theparesthesia was therefore evidently the inadvertentintrusion of the mesiobuccal root of tooth 38 againstthe canal, causing pressure on the inferior alveolar nerve.Once the Blugloo was removed, tooth 38 relapsed occlu-sally, allowing for relief of the pressure on the mandib-ular nerve and subsequent resolution of the patient'ssymptoms of paresthesia.

Management of this patient emphasizes the impor-tance of the use of CBCT in the diagnosis andconfirmation of various conditions, which are at timesnot evident with normal radiography. Several studieshave shown CBCT imaging to be superior in generatingimages to locate root position and proximity to vital

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Fig 7. Transverse view showing the course of the inferior alveolar nerve in relation to the mesiobuccalroot of tooth 38, the temporary skeletal anchorage device, and the roots of teeth 36, 35, and 34.

Fig 8. Coronal view of the proximity of the mesiobuccal root of tooth 38 to the inferior alveolar nerve.

Fig 9. Sagittal view of the proximity of the mesiobuccal root of tooth 38 to the inferior alveolar nerve.

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structures compared with 2-dimensional radiographs.20

For this patient, CBCT imaging was used to rule outsigns of pathology and confirmed the close rootproximity of tooth 38 to the inferior alveolar nerve in3 dimensions.

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The CBCT image helped us to visualize the position ofthe inferior alveolar canal. The anatomy of the position ofthe inferior alveolar nerve is highly variable from patientto patient. Carter and Keen21 described 3 distinctanatomic patterns of the intramandibular course: type

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1, the nerve courses straight toward the mental foramenlying close to the root apices; type 2, the nerve follows alower pathway in the mandible with dental branchespassing obliquely in an anterosuperior direction to theteeth; and type 3, the nerve divides into 2 branches,one passing superiorly to supply the molars and theother inferiorly to innervate the premolars, canines, andincisors.

According to this classification, this patient had atype 1 intramandibular course.

To our knowledge, there are only 7 cases ofparesthesia reported secondary to orthodontic toothmovement. All of them involved either the mandibularsecond premolar or the mandibular second or thirdmolar invading the space of the inferior alveolarnerve.1-7 The paresthesia resolved within 2 days to4 weeks after the forces were removed or the relevanttooth was extruded. In this case study, the patient'ssymptoms of paresthesia resolved shortly afterremoval of the orthodontic forces placed on thetooth compressing the inferior alveolar nerve. Otherthan baseline neurosensory testing on subsequentfollow-up appointments, he did not require furthertreatment regarding this complication. For patientswith neurologic disturbances, persistence of thesymptoms would require referral to a specialist forinvestigation and management to rule out pathology.

CONCLUSIONS

Although inferior alveolar nerve paresthesia second-ary to orthodontic tooth movement is rare, an increasein reported cases reflects the need for careful examinationof root proximity to these vital structures beforeorthodontic treatment. If predictive factors are notedon the radiographic examination that put a patient athigh risk of nerve damage, he or she should beinformed.22 Technologies such as CBCT imaging shouldbe used to better visualize anatomic relationships withtreatment goals inmind to anticipate injury to the inferioralveolar nerve during treatment. In the case of orthodon-tically induced paresthesia, deactivation of the forceusually resolves the patient's symptoms. However, if theparesthesia persists 2 weeks after removal of the forces,the patient should be referred to a specialist (radiologistor pathologist) to rule out other potential causes.

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