Expert Witness Journal Dec 24 - Journal - Page 48
The IAC can also sit away from the M3M, in close
vicinity or within the roots of the tooth (Iwanaga).
Where the M3M is impacted distally, the surgeon may
create a larger flap and remove cortical bone behind
the tooth. This runs the risk of damage to the LN in
cases of an abnormal nerve pathway (Tojyo).
The LN and M3M
The incidence of LN injury is up to 2% of M3M
extractions (Tojyo).
M3M extractions and IAN damage
There is a heightened risk of neurosensory damage
when the canal shows radiographic narrowing, direct
contact with the roots, a lingual course with or without
cortical plate perforation and an intraroot course of
the canal (RCS).
Ct scan images of root/IAC relationships
The IAN can become damaged, severed or
compressed whilst the roots are elevated (Iwanaga)
Normal Pathway
Abnormal Pathway
The Lingual nerve can enter the oral cavity behind
the M3M over the bone crest (Tojyo) but commonly it
is further forward and below the alveolar crest. The
LN sits in the lingual mucosa but cannot be seen
radiographically.
The reported incidence rate of injury ranges from
0.35019% when the roots are close to the IAN
(Iwanaga).
Is there a way to minimise risks to the nerves?
If an impacted M3M needs removal, then a surgeon
has 2 options:
• remove the whole tooth and the risk nerve damage
• remove the crown and leave the roots in situ,
coronectomy
M3M extractions and radiographs
When a surgical procedure is planned for the removal
of a M3M, the common radiograph taken is a panoral
or OPG. This is a 2-dimensional image with some
distortion.
It is recommended that when the root apices are in a
close relationship with the IAN that a CT scan is taken
to ascertain the relationship (RCS).
For a surgeon to reduce the risks of nerve damage it
has been suggested that one should avoid (Renton) :
• raising a lingual flap
• removing bone distally to the M3M
• applying pressure on the IAN during elevation
• applying a pulling force on the IAN during
elevation
• trying to remove the roots
M3M extractions and Lingual nerve damage
During a surgical procedure for removal of the M3M,
the surgeon will normally raise a soft tissue flap
buccally and lingually to the M3M.
Coronectomy is such a technique
Coronectomy or partial odontectomy involves :
• buccal mucoperiosteal flap
• buccal bone removal
• crown sectioned horizontally or vertically at the root
level
• crown elevate buccally
The advantages are :
• minimal risk to the nerves
• smaller surgical field
• less trauma to the mandible
• faster surgical procedure (30mins)
• faster healing
• resolution of pericoronitis
• less bone resorption distal to the 7
This is to gain exposure and a better perspective of
the impacted molar.
However on raising a lingual flap the surgeon may
either make an incision to release the flap thereby
being at risk of severing the lingual nerve or may use
a lingual flap retractor and the pressure of the retractor may also cause compression or damage to the
lingual nerve (Renton).
EXPERT WITNESS JOURNAL
46
DECEMBER 2024
