Neurosensory disturvances following surgucal removal of mandibular third molar

NEUROSENSORY DISTURBANCES FOLLOWING
SURGICAL REMOVAL OF MANDIBULAR THIRD
MOLAR
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

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

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

• 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.
J Maxillofac Surg 2003; 61:1379-89

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%
Int. J. Oral Maxillofac. Surg. 2011; 40: 1–10www.indiandentalacademy.com

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

Seddon and Sunderland
Neuropraxia (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, avulsion
and chemical injury
Int. J. Oral Maxillofac. Surg. 2000; 29:331336
Dent Update 2003; 30: 375–382www.indiandentalacademy.com

• 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. Dent Update 2003; 30: 375–382www.indiandentalacademy.com

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.

• 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).
IJOMS. 30: 333-8 , JOMS 1995 53: 1178.JOMS
2000 58: 649-51

Joms 2000 58:649-651

• In 15% it may lie at or above the crest of the lingual plate
of the mandible.
• Kiesselbach and Chamberlain -17.6% of human cadavers
the lingual nerve was at or above the alveolar crest and
in some cases may lie in the retromolar tissues.
J Oral Maxillofac Surg. 1984; 42: 565-67

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

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
CLINICAL DENTISTRY AND RESEARCH 2012; 36(1): 2-7

• 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.

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.
CLINICAL DENTISTRY AND RESEARCH 2012; 36(1): 2-7

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%)
Australian Dental Journal 2006;51:(1):64-68www.indiandentalacademy.com

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.
J Oral Maxillofac Surg. 2012 Jan;70(1):5-1

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 ASSESSMENT
INFERIOR 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%).

Radiographic sign
British Journal of Oral and Maxillofacial Surgery (2004) 42, 21—27

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

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.
J Am Dent Assoc 1980: 101: 240–245.www.indiandentalacademy.com

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%).

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

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. Int. J. Oral Maxillofac. Surg. 2011; 40: 1–10www.indiandentalacademy.com

• leaving small tips of the roots unremoved
rather than risking injury to the inferior
alveolar nerve.
JADA 1980: 100: 185–192.

INTRA-OP FACTORS
LINGUAL 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.

• 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’.
Br J Oral Maxillofac Surg 1992: 30: 72–77.www.indiandentalacademy.com

INTRA-OP FACTORS
LINGUAL 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.
Br J Oral Maxillofac Surg 1992: 30: 78–82.

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

• 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
Int. J. Oral Maxillofac. Surg. 2000; 29:331336www.indiandentalacademy.com

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
Int. J. Oral Maxillofac. Surg. 2010; 39: 320–326

• 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
Int. J. Oral Maxillofac. Surg. 2001; 30: 306–312

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
J Oral Maxillofac Surg 62:592-600, 2004www.indiandentalacademy.com

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Neurosensory disturvances following surgucal removal of mandibular third molar

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