Exodontia.Info
Inferior Dental (Alveolar) & Lingual
Nerve
Injuries
The (surgical) removal of lower wisdom teeth
(3rd molars) endangers both the
lingual and
inferior alveolar nerves; as the removal of (lower)
wisdom teeth is carried out frequently, so the
potential number of patients sustaining nerve
damage is likewise high.

The majority of injuries result in transient sensory
disturbance but, in some cases, permanent abnormal
sensation (
paræsthesia), reduced sensation (hypoæsthesia)
or, even worse, some form of unpleasant abnormal
sensation (
dysæsthesia) can occur.

These sensory disturbances can be troublesome, causing
problems with speech and chewing and may adversely
affect the patient’s quality of life.

They also constitute one of the most frequent causes of
complaints and litigation.

As can be seen from the illustrations below, branches of the
Mandibular Nerve (the third and lowermost division of the
Trigeminal Nerve or the 5th Cranial Nerve) can be in close
proximity either to the roots of the wisdom teeth (also the
2nd molars as well) or to either side of the tooth crown.
The spontaneous recovery rate for nerve injuries related to lower wisdom
tooth (3rd molar) removal is quite variable ranging from 50% - 100% for both
the
IAN and LN.

Incidence of Nerve-Damage relating to Wisdom Tooth Removal:

Inferior Alveolar Nerve.  IAN function is disturbed in 4 – 5% of procedures (range
1.3 – 7.8%).  Most patients will regain normal sensation within a few weeks or
months and < 1% (range 0 – 2.2%) have a persistent sensory disturbance.

A higher incidence of
IAN injury has been reported with wisdom teeth that are
horizontally or mesio-angularly impacted and have complete bone cover.

One study has also demonstrated that increasing age is associated with a higher
frequency of
IAN injury (14 – 24 year old patients 1.2%; 35 – 81 year-old patients,
9.7%).

Lingual Nerve.  There is a wide range in the reported frequency of LN injuries
during lower wisdom tooth, with 0.2 – 22% of patients reporting sensory
disturbances in the early post-operative period and 0 – 2%, a permanent
disturbance.

A higher incidence of
IAN injury has been reported with certain types of surgical
technique (using an 'elevator' to 'protect' the
LN) together with deeply impacted
teeth when the surgery is consequently difficult, particularly if distal bone removal is
required.


Most cases of nerve damage during wisdom tooth removal are not identified at the
time of lower wisdom teeth removal but in the post-operative period.

However, careful monitoring of sensory recovery over a three month period should
distinguish between these different types of injury.

Monitoring sensory recovery is undertaken by the application of stimuli to the 'numb'
area.  Responses of the patient will indicate first the arrival of the regenerating
nerve ends and then subsequently the level of recovery.

However, the most sensitive indicator of a sensory abnormality is the patient’s own
subjective report, as minor sensory disturbances may not be detected by testing.


Simple Sensory Testing

A standard protocol for sensory testing does not exist and attempts to standardise
objective evaluation of nerve injuries have been unsuccessful.

Evaluation techniques are subjective or semi-objective at best.


Suggested techniques include:
The likelihood of this occurring depends on both the severity of the injury and the
nerve involved.


Inferior Alveolar / Dental Nerve:

If a sensory disturbance is first noted at review, recovery should be monitored
using the sensory tests described above.

Patients with
paræsthesia in the distribution of the IAN (evoked by touching the lip
or chin) usually require no surgical intervention.

Patients with complete
anæsthesia post-operatively should be evaluated
radiographically (such as an
OPG or a CT scan) to ensure that the roof of
the nerve canal has not been displaced downwards to create an
obstruction to nerve repair and regeneration.  In the extremely rare event that this
has occurred, removal of the bony fragment would seem to be appropriate, without
undue delay.

Referral to an
Oral & Maxillofacial surgeon familiar with this type of procedure or
a
neurosurgeon or a micro-neurosurgeon is important. The patient should know
that full recovery may not be achieved even with surgery though some recovery
may occur even if surgical ‘decompression’ is not performed.

If, after 3 months after the injury, monitoring reveals little or no sensory recovery,
referral is again indicated.  A further
X-ray to assess the continuity of the IDN canal
is obtained and surgical exploration and ‘decompression’ of the nerve is considered
if the canal is disrupted, if there is very little recovery of sensation or if there is
significant
dysæsthesia.

However, the results of surgery are variable and sometimes disappointing.


Lingual Nerve:

If the
LN is knowingly cut during wisdom tooth removal, it should be immediately
repaired.

This may not be possible in dental practice and immediate referral to an
appropriate experienced
Oral & Maxillofacial surgeon is indicated. In the majority
of patients, the injury is only discovered post-operatively.

At early review, the presence of some sensation in response to stimulation of the
tongue suggests that the nerve is at least partially intact; no treatment is
indicated but sensory monitoring is required.

Complete
anæsthesia could be caused by both a crush or cutting injury and so
surgical intervention is not indicated initially.

However, the absence of progressive sensory recovery by 3 – 4 months post-injury
is an indication for surgical exploration at an appropriate
Oral & Maxillofacial
unit.

If, at the time of surgery, the nerve is found to be intact and of fairly uniform
thickness but merely constricted by scar tissue, it should be freed (
external
neurolysis
) and the wound closed.  This is unusual however and more commonly
the nerve is found to have been cut.

If a
neuroma has developed, this can be seen as a marked expansion at the site of
the injury and must be removed together with the damaged segment of
the nerve. A nerve graft is then used. The results of surgery are very variable;
some patients regain good sensation whilst others show little if any improvement.

One study showed a success rate of 80% and a recent prospective study has
shown that the majority of patients consider the surgery worthwhile.  Surgery
should therefore be offered to all patients with
LN injury who show few signs of
spontaneous recovery.


Useful Websites:

www.lingualnerve.org

www.Emedicine.com


Useful Articles:

Australian Dental Journal 1997 -  IAN damage following removal of mandibular 3rd
molar teeth - A prospective study using panoramic radiography

BDJ 2002.  Lingual nerve injury subsequent to wisdom teeth removal — a 5-year
retrospective audit from a high street dental practice

Braz J Oral Sci 2003 - Evidence Based Means of Avoiding Lingual Nerve Injury

Dental Update 2003 - Nerve Damage and Third Molar Removal

JADA 2003 - Lingual Nerve Damage due to inferior alveolar nerve blocks - A
possible explanation

BJOMS 2004 - Current management of damage to the inferior alveolar and lingual
nerves as a result of removal of third molars

BJOMS 2005 - New method for the objective evaluation of injury to the lingual
nerve after operation on 3rd molars

BJOMS 2005 - Objective evaluation of iatrogenic lingual nerve injuries using jaw-
opening exercises

BJOMS 2005 - A randomised controlled clinical trial to compare the incidence of
injury to the IAN as a result of coronectomy & removal of mandibular 3rd molars

J Canad Dent Assoc 2005 - Iatrogenic Paresthesia in the Third Division of the
Trigeminal Nerve - 12 Years of Clinical Experience

BDJ 2006 - Simplifying the assessment of the recovery from surgical injury to the
lingual nerve

CDAJ 2007 - Permanent Nerve damage from IAN Blocks - An Update to include
Articaine

Cochrane Collaboration 2008 - Interventions for Iatrogenic IAN Injury (Protocol)

Oral Surgery 2008 - IAN decompression and neurolysis

J Oral Maxillofac Surg 2009.  The Anatomic Structure of the Inferior Alveolar
Neurovascular Bundle in the 3rd Molar Region

Dental Update 2010.  Prevention of Iatrogenic Inferior Alveolar Nerve Injuries in
Relation to Dental Procedures.

Oral Surgery 2010.  Correlation of the radiological predictive factors of Inferior
Alveolar Nerve injury with Cone Beam Computed Tomography findings.

J Oral Maxillofac Surg 2010.  Diagnostic Accuracy of Panoramic Radiography in
Determining Relationship Between Inferior Alveolar Nerve & Mandibular 3rd Molar.

J Oral Maxillofac Surg 2010.  Retrospective Review of Microsurgical Repair of 222
Lingual Nerve Injuries.

BDJ 2010.  Trigeminal Nerve injuries in relation to the local anaesthesia in
mandibular injections
The branches of the Mandibular Nerve that are of
importance to the Patient and the Oral Surgeon with
regards to Wisdom Teeth Removal, include the:

  • Lingual (LN)
  • Long Buccal (LB)
  • Mylohyoid
  • Mental (MH)
Hence, trauma to these nerves can result in either numbness, tingling, altered
sensation or a loss of taste (or a combination or progression of these symptoms).

Trauma, here, covers stretching, crushing or cutting of these nerves.
The degree of trauma will greatly determine the degree of numbness (and loss of
taste) and its duration.  Trauma can be due to use of instruments to remove the
tooth, drills used to remove bone and 'elevators' used to 'protect' the
LN.

Trauma to the
LN & the IAN can also result from the injection of local anæsthetic
(some
local anæsthetics have been found to cause prolonged numbness), fracture
of the
Lingual Plate, jaw fractures, osteotomies for the correction of malocclusion
and the removal of pathology in proximity to the
IAN or the LN (such as peeling a
dentigerous cyst out of its cavity).

As this is a
well recognised complication of lower wisdom tooth removal, patients
need to be warned about the potential for numbness (temporary / permanent) prior
to surgery so that the patient can weigh up the pros & cons and the potential
consequences of the procedure and if needs be, opt for a different surgical
treatment (such as a
coronectomy or operculectomy).
Annotated X-rays
showing the course  
of the
IDN in relation
to the root tips of the
lower wisdom teeth.
  • Mapping out and photographing the area
    involved
Light touch is most commonly tested by gently
applying a wisp of cotton wool to the skin or lining of
the cheek or lips.
However, it is difficult to apply this stimulus in a
reproducible manner and the use of a cotton wool
wisp on moist oral mucosa is difficult.

Greater consistency and reproducibility can be
obtained using
Von Frey hairs.  Stimuli are applied
at random and the area of
anaesthesia can be
mapped by moving outwards in small steps until the
stimulus is felt.
Testing pin prick threshold is often performed using a dental probe or needle but
reproducibility is poor.

Areas of
anæsthesia can be mapped.  If sensation is present within the affected
area on the injured side, then the pin prick sensation threshold is determined.

The probes are drawn a few millimetres across the surface, at a constant
pressure and the patient asked to indicate the point at which the sensation
becomes sharp rather than dull.

The pin prick sensation threshold is noted for a series of randomly chosen
points on both the 'injured' and the 'uninjured' side.

  • Two Point Discrimination

This test can quickly be performed if pairs of
blunt probes with different separations (2 – 20
mm) are mounted around a disc.
The probes are applied at a series of fixed sites
chosen on the lips or tongue, depending on
which has been damaged.

The probes are drawn a few millimetres across
the surface, at a constant pressure and the
patient is asked whether one or two
points are felt.
The minimum separation, that is consistently reported as two points, is termed
the
two point discrimination threshold.

This threshold varies in different regions of the mouth (2 – 4 mm on the tongue
and lip, 8 – 10 mm on the skin over the lower border of the chin).

  • Taste Stimulation

LN injury will result in taste loss.

Cotton wool pledgets soaked in saline solution, sugar solution, vinegar or quinine
solution are drawn 1 – 2 cm across the side of the tongue and the patient asked
to indicate whether they taste salt, sweet, sour, bitter or no taste, before

Stimuli should be applied in random order, to each side of the tongue and rinsing
with tap water between tests.
Treatment
Before the removal of the wisdom
needs to be assessed
radio-graphically (i.e.
X-rayed).


This, amongst other things, will show
whether the
IAN canal is in proximity
to the wisdom tooth and there are
certain appearances on the
OPG
that suggest the
IAN canal is
intimate with the tooth.


Studies have shown that these
aren't always reliable and the
definitive information can be gained
with a
Cone Beam CT scan (often
used for dental implants but rarely
for wisdom teeth).
  • Pin Prick Sensation
Last Updated 24th November 2010