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| 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.
(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.
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 after 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 lingual nerve
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 IAN and LN.
Incidence of Nerve-Damage relating to Wisdom Tooth Removal:
Inferior Alveolar Nerve. IAN function is disturbed after 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 lingual nerve
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. The 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
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
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. The 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
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
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:
importance to the Patient and the Oral Surgeon with
regards to Wisdom Teeth Removal, include the:
- Inferior Alveolar (or Inferior Dental) (IAN / IDN)
- Lingual (LN)
- Long Buccal (LB)
- Mylohyoid
- Mental (MH)
The Lingual Nerve also supplies taste.
Hence, trauma to these nerves can result in either numbness, tingling, altered
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).
Hence, trauma to these nerves can result in either numbness, tingling, altered
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.
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.
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.
- Pin Prick Sensation
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.
For this test, the pin is applied at steadily increasing pressures and the patient is
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).
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
tooth (in fact, any teeth), the mouth
needs to be assessed
radiographically (i.e. X-rayed).
This 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).
tooth (in fact, any teeth), the mouth
needs to be assessed
radiographically (i.e. X-rayed).
This 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).