NEUROSENSORY DISTURBANCES FOLLOWING SURGICAL REMOVAL OF MANDIBULAR THIRD

MOLAR

INDIAN DENTAL ACADEMY

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• INTRODUCTION • NERVE DAMAGE• ANATOMICAL RELATIONSHIP • PRE-OPERATIVE ASSESSMENT• INTRA-OPERATIVE FACTORS• CLINICAL TESTING

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INTRODUCTION

• The face, and in particular the oral and peri oral regions, are among the areas with the highest density of peripheral receptors, presumably because of their remarkable importance in daily life.

• It is difficult to tolerate neurological disturbances in oral and maxillofacial areas compared to other parts of the body

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• Mandibular third molars are the most frequently impacted teeth.

• 91.9% of the extractions are carried out without any serious complications.

• Injury to the lingual, inferior alveolar and sensory branch of the mylohyoid nerves is an infrequent but unpleasant complication.

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Incidence

The risk of developing inferior dental nerve (IDN) deficit ranges from 0.26 to 8.4%.

The risk of lingual nerve (LN) deficit ranges from 0.1 to 22%

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NERVE DAMAGE• The definition of neurosensory dysfunction (also known as

dysesthesia) includes– anesthesia (loss of sensation, usually because of damage to a nerve

or receptor; also called numbness) and paresthesia (abnormal touch sensation, such as burning, prickling, or formication, often in the absence of an external stimulus). Dorland I, Newman

• The consequences and subsequent recovery following nerve damage are dependent upon the severity of the injury, and this is the basis for the classifications of nerve injury proposed by Seddon and Sunderland

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Seddon and SunderlandNeuropraxia (Seddon)First degree injury (Sunderland)

Axonotmesis (Seddon)Second degree (Sunderland)

Neurotmesis (Seddon) Third degree

Fourth degree (Sunderland)

Fifth degree:(Sunderland)

Minor compression,nerve trunk manipulation

More severe compression or"crush" injuries

Traction or compression

injection & chemical injury

Laceration, avulsionand chemical injury

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• Compression injuries -elevation of a third molar with roots in close proximity to the mandibular canal.

• Stretch injuries when raising a lingual mucoperiosteal flap.

• Neurotemesis or Complete section of the nerve trunk may occur if the inferior alveolar nerve penetrates the root of a third molar and is severed duringtooth removal.

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ANATOMICAL RELATIONSHIP

• The Lingual nerve courses from a more lateral to medial position as it approaches the mandibular third molar.

• As the Lingual nerve approaches the third molar, its position with respect to the alveolar bone, is variable.

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• Hölzle and Wolff (2001), the LN lies considerably closer to the oral mucosa with a mean distance of 4.41 ± 1.44 mm.

• Pogrel (1995) The mean vertical distance from the alveolar crest to the LN reported a distance of 8.3 ± 4.1 mm.

• Horizontal Distance of LN to Lingual Plate :2.1 ± 1.1 mm reported by Behnia et al. (2000).

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• In 15% it may lie at or above the crest of the lingual plate of the mandible.

• Kiesselbach and Chamberlain -17.6% of human cadaversthe lingual nerve was at or above the alveolar crest and in some cases may lie in the retromolar tissues.

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The inferior alveolar nerve

• In some cases the nerve is very close to the roots of the mandibular third molars and even makes deep impression on the roots or passing through them.

• The nerve is at risk in these cases during lower third molar surgery

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PRE-OPERATIVE ASSESSMENT

• To avoid surgical complications, proper radiographic assessment is essential to determine the exact topographic relationship between the mandibular canal and the lower molars.

• OPG• PERIAPICAL RADIOGRAPH• CT

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• OPG & IOPA are commonly preferred

• Paralleling technique is the preferred method for obtaining periapical radiographs, as it minimizes geometric distortion and presents the teeth and supporting bone in their true anatomic relationships.

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Limitations

• A fundamental one is that, the three dimensional anatomy is collapsed into a two-dimensional surface, which causes image features representing different anatomical structures to be superimposed.

• Features of diagnostic interest may, therefore, be obscured and diagnostic accuracy is decreased.

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Radiologic criteria indicating need for CT scan

1. Radiolucent band (23%)2. Loss of MC border (32%)3. Change MC direction (39%)4. MC narrowing (57%)5. Root narrrow (36%)6. Root deviation (32%)7. Bifid apex (25%)8. Superimposed (5%)9. Contact MC (7%)

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Does computed tomography prevent inferior alveolar nerve injuries caused

by lower third molar removal?

• Positive radiographic signs (darkening of the root and narrowing of the inferior alveolar canal) were associated with more requests for CT scanning.

• CT does not seem to significantly decrease the risk of producing IAN injury.

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Panoramic vs CT

• The panoramic finding of impacted mandibular third molar root darkening was considered to reflect thinning or perforation of the cortical plate rather than grooving of the root. Cortical thinning or perforation was found in 80% of the cases with this panoramic finding.

• Such information will be important for surgeons to avoid the risk of lingual nerve injury at the time of extraction

Dentomaxillofacial Radiology (2009) 38, 11–16’ 2009 The British Institute of Radiologywww.indiandentalacademy.com

Dentomaxillofacial Radiology (2009) 38, 11–16’ 2009 The British Institute of Radiologywww.indiandentalacademy.com

PRE-OP ASSESSMENTINFERIOR ALVEOLAR NERVE

• Incidences of IDN deficit in fully erupted, partially erupted and unerupted lower wisdom teeth were 0.3%, 0.7% and 3.0%, respectively.

• The incidence of IDN deficit was highest in horizontally impacted(1.7%), distal impaction (1.4%), mesial impaction (1.3%) and vertical impaction (1.1%).

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Radiographic sign

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Radiographic sign

• 964 subjects from 2 studies9,93 were included. • The incidence of IDN deficit was highest in

radiographic sign of • diversion of ID canal by its root (30%),• darkening of root (11.6%) and• deflected root by the ID canal (4.6%).• These 3 signs were found to increase the risk of IDN

deficit significantly

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Adult vs Adoloscence• The removal of impacted teeth from adult patients

was found to be more difficult and it came along with sensory loss more often than in the juveniles.

• To minimize the risk of numbness • check for the necessity of third molar surgery during

adolescence.

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PRE-OP ASSESSMENT LINGUAL NERVE

• 3 studies22,24,29 with 5875 subjects• Incidences of LN deficit in fully erupted, partially

erupted and unerupted lower wisdom teeth were 0.3%, 2.0% and 5.8%,

• LN deficit was highest in distally impacted (4.0%), • horizontal impaction (2.8%), • Mesio angular (2.4%) &• vertical impaction (1.9%).

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INTRA-OPERATIVE FACTORS• 5 studies with 2028 subjects

reported,• 16.2% of the surgery with the IAN

exposed developed postoperative IANdeficit,

• only 1.1% of the surgeries without IAN exposure developed IAN deficit;

• The risk ratio of IAN deficit from intraoperative IAN exposure is 14.9 times more likely than if the IAN is not exposed

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Surgical technique and postoperative IAN deficit

• 20 studies reported the surgical technique and postoperative IDN deficit.

• The incidences of IDN deficit following the buccal approach,

lingual split technique and coronectomy were 2.5%, 5.7% and 0%, respectively.

• The risk ratio of IAN deficit is therefore 2.3 times more likely using the lingual split technique than the buccal approach.

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• leaving small tips of the roots unremoved rather than risking injury to the inferior alveolar nerve.

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INTRA-OP FACTORSLINGUAL NERVE

• 16 paperswith 10,893 subjects reported whether the surgery included raising the lingual flap or not.

• 3.1% with lingual flap raised showed LN deficit• whereas only 1.5% of LN deficit occurred in surgery in

which the lingual flap was not raised. • The risk ratio of LN deficit was 1.94 times more likely to

occur if the lingual flap was raised than if it was not.

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• As stated by BLACKBURN ‘The lesson to be learnt is quite simple, never let the bur enter the tissues on the lingual side of the mandible, whether there is a lingual flap retractor/guard in position or not’.

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INTRA-OP FACTORSLINGUAL NERVE

• 26 studiesreported the surgical technique and postoperative LN deficit.

• The incidences of LN deficit using the buccal approach, lingual split technique and coronectomy were 2.3%, 9.3% and 0.7%, respectively.

• With the increasing depth of impaction,LN deficit could be explained by the probable need to use a lingual retractor during surgery, which itself increased the risk of LN deficit.

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Clinical neurosensory testing

Mechanoceptive• Two-point

discrimination, • Static light touch • Brush directional

stroke tests

Nociceptive• Pin-prick • Thermal discrimination ( localization, sharp/

blunt discrimination)• Dental vitality test

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• Neurosensory testing is designed to determine the degree of sensory disturbance, to monitor sensory recovery and to point out whether or not surgical intervention may be indicated

Pin prick

Two point discrimination

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ASSESSMENT

• All patients were reviewed 1 week after surgery, to assess wound healing status and the presence of any neurosensory deficits related to the lower third molar tooth surgery.

• Self-reported subjective sensory changes were recorded and objective assessments done

• They were monitored regularly postoperatively to assess the pattern of recovery after 1 month, 3 months, 6 months, 1 year and 2 years and beyond, according to the standardized assessments

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• In former studies, alterations of sensation persisting longer than 6 months after injury were commonly considered to be permanent.

• But there are also reports of restitution occurring 7–9 months after surgery

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Time of Recovery

Collateral reinnervation from adjacent nerves may account for some instances of early sensory recovery

Altered sensation that recovered within 3 months (57.9%) Sunderland first- and second-degree nerve injuries,

Altered sensation at 6 months (34.2%) Sunderland third-degree nerve injuries.

The persistence of sensory alteration in 28.9% of sites at 1 yr Sunderland fourth-degree injury

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THANK YOU

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