Ct analysis of the position and course of mandibular canal /certified fixed orthodontic courses by Indian dental academy

CT ANALYSIS OF
THE POSITION AND
COURSE OF
MANDIBULAR
CANAL
relevance to sagittal
split DENTAL ACADEMY
INDIAN ramus osteotomy
Leader in continuing dental education
www.indiandentalacademy.com


A IM OF THE STUDY
Is to investigate the position and course of the
mandibular canal through the mandibular ramus
using ct imaging and to relate the findings to
performing sagittal split ramus osteotomies.


INTRODUCTION


The sagittal split ramus osteotomy is now widely used to
correct jaw deformities.



In this tech the mandibular ramus is split on both sides
in the sagittal plane and the distal fragment is moved
forward and backward.



Due to the position and course of mandibular canal, the
IAN is at great risk of injury during ssro.

incidence:- immediate post www.indiandentalacademy.com ranges from 49%-100%
op sensory impairment

PATIENTS AND METHODS




The subjects for this
study included skeletal
class 3 patients with
symetry
A Transaxial ct scan with
a slice thickness of
2mm,scan time
7s,120kv,140ma/s was
done.

35 pts
Age 15-34 yrs
(mean age 23 yrs)

MALES-12


FEMALES-23

CT
LOCATIONS
IN each pt 4 ct scans were made at 4 standardized
locations.
 MF-MANDIBULAR FORAMEN-In a plane at the bottom point of the
foramen.
 MA-MANDIBULAR ANGLE-Point where a line drawn from posterior
point of the second molar intersects the mandibular canal.
 MP-MIDPOINT-At an intermediate between MF and MA.
 MB-MANDIBULAR BODY-At a point close to where a perpendicular
line drawn from the center of the second molar intersects the
inframandibular margin and mandibular canal.

MEASUREMENTS AT EACH POINT
 Total thickeness of the mandible through the

center of mandibular canal.
 Diameter of the inner mandibular canal.
 Narrowest portion of the bone marrow space
between the outer mandibular canal and both
the lateral and medial cortical bone of the
ramus.


RESULTS


Thickness of the mandible increased
from mandibular foramen to the
mandibular body.
14
12
10
8
TCK MN

6
4
2
0

MF

MP

MA


MB

DIAMETER OF THE INNER MANDIBULAR
CANAL (ALMOST SAME)
3

2
DIA MC
1

0

MF

MP

MA

MB


WIDTH OF BONE MARROW-SIGNIFICANT DIFFERENCES NOTED
BETWEEN MP AND MB ON BUCCAL SIDE,AND BETWEEN MF,MA AND MB ON
LINGUAL SIDE.

4
3.5
3
2.5
BUCCAL
LINGUAL

2
1.5
1
0.5
0

MF

MP

MA


MB

Classification of the mandibular canal
position within the bone marrow space.





SEPARETE TYPE-with bone marrow space visible255/280(91.1%).
CONTACT TYPE-with outer surface of the canal and
inner surface of the buccal cortical bone in contact17/280(6.1%).
FUSION TYPE-with outer cortical plate of the canal
not evident-8/280(2.9%).


Course of mandibular canal


Most frequently encountered case was one
in which the bone marrow space between
mandibular canal and the inner surface of
the lateral cortex was present,this type
presents less risk of injury to the nerve
during surgery.



The contact or fusion type anatomy
was detected at various sites from
MF and MA areas.7 rami had
contact at MP.




3 rami contact at MA(4.3%).



3 rami at MF+MP+MA(4.3%).



1 ramus at MF+MP(1.4%).



1 ramus at MP+MA(1.4%).



Only 1 ramus showed no marrow space at MA+MB
areas.

DISCUSSION
The greatest bone marrow space is found at
first and second molar areas.
In 22.9%(16/70)rami had contact or fusion
type of mandibular canal and in many cases
it was observed from mandibular foramen to
the mandibular angle.
Results suggest that a vertical cut of the
buccal side of the mandible performed just
anterior to the mandibular angle may be
advantageous. www.indiandentalacademy.com

Even if a vertical cut is made at the safest site with
careful splitting, the inferior alveolar neurovascular
bundle may be encountered or impaired in
individuals with fusion type mandibular canal.
Various techniques can be used for tretment of
mandibular prognathism mainly intraoral vertical
ramus osteotomy(IVRO), SSRO, and inverted L
osteotomy.
With respect to neurologic damage it seems logical
that IVRO or ILRO would be preferable to SSRO.

THE ANATOMICAL LOCATION OF MANDIBULAR CANAL; ITS
RELATIONSHIP TO SAGITTAL RAMUS OSTEOTOMY BY
RAJCHEL J ELLIS III E
int j adult orthod orthognath surg 1986 vol 1

She reported on the anatomical bucco lingual
location of the mandibular canal using dried
mandibles of adult asians of unknown sex.
They sectioned the dry mandibles at five
locations perpendicular to the sagittal plane of
the body of the mandible.
RESULTS:-she concluded that the greatest
distance between the cortical plate and the canal
was at the level of 1st and 2nd molars while the
smallest distance was at the 3rd molar.

RELATIONSHIP OF THE
MANDIBULAR CANAL TO THE
LATERAL CORTEX OF THE
MANDIBULAR RAMUS AS A FACTOR
IN DEVELOPMENT OF NEURO
SENSORY DISTURBANCE AFTER
BILATERAL SAGITAL SPLIT RAMUS
OSTEOTOMY
BY
YAMAMOTO R,OHNO K,MICHI K
J ORAL MAXILLOFAC SURG 2002; VOL 60

Purpose:- this study evaluated the location of the mandibular
canal canal in the ramus of mandible before the bilateral
sagittal split ramus osteotomy and examined its relationship
with the postoperative sensory disturbance.
Patients and methods:- 20 pts undergoing ssro. The plane
containig the lowest point of the mandibular foramen 22mm
below it was observed on a transaxial cts acquired with a
2mm slice thickness and a slice interval of 2mm. The
relationship between the distance from the mandibular canal
to the external cortical bone and neurosensory disturbance in
the lower lip or mentum more than one year after one year
after surgery was evaluated.

RESULTS:-THE MANDIBULAR CANAL CAME INTO
CONTACT WITH THE EXTERNAL CORTICAL PLATE ON
10 SIDES(25%) AND NEUROSENSORY DISTURBANCE
OCCURRED ON ALL THESE SIDES.
In all these cases the vertical extent of contact ranged
from 2 to 18mm(average 10.6+_4.9 mm)
In 30 sides(75%) showed no contact between canal and
cortical plate of bone.
The neurosensory disturbance usually presented one
year after surgery and occurred in all cases with bone
marrow thickness of 0.8mm or less.
CONCLUSION:-the increased risk of NS disturbance occurred when there
is a contact between canal and external cortical plate should be considered
during SSRO.

TECHNICAL
MODIFICATION OF
SSRO
BY
FUN-CHEE L
Oral surg oral med oral pathal 1992 vol 74

INSTRUMENTATION:- instruments needed are
broad chisel,measuring 2 cm wide 4mm thick with a
curved handle and T shaped bone cleaver.
TECHNIQUE:-adequate removal of cortical bone
along the osteotomy lines until the cancellous layer
is reached is an impotant requisite to achieving a
successful and predictable SSRO.
The only area where cortical bone is not weakend
by cutting instrument is inferior body of the ramus
and posterior part of the body of the mandible.
Attention is needed here.

The rationale of using a curved monobivel instrument is to
direct cleaving edge of the instrument towards the buccal
cortex and to create a plane of cleavage buccal to the inferior
dental canal.
The broad width ensures sufficient separation of the buccal
and lingual cortices for inspection of the inferior dental
neurovascular bundle after the split has been initiated
superiorly.
The use of ‘T’ shaped cleaver at the anterosuperior corner of
the proximal segment with one limb of the “T” in the
osteotomy line and other resting on the buccal cortex of the
distal segment is found to be useful because the force is
distributed and hence the chance of fracture at a particular
preassure point is reduced.

Edging the cleaver along the anterior border of the
proximal segment towards the lower border ensures
a gradual splitting to occur. This process
simultaneously redistributes the force to the different
parts of the bone and guides the plane of split.
The last remaining area of the bone adherence is the
inferior border. Hence the “T” shaped cleaver is used
to edge along the inferior border and prying at the
same time to complete the split.
Because the cleaver is kept below the inferior dental
neurovascular bundle, therefore there is no danger of
injury to structure during this procedure.

The author believe that a deliberate attempt to
effect the split as close to the buccal cotex as
possible and to keep a watchful eye on the
inferior dental canal during instrumentation is an
important factor.
RESULTS:- author succeeded in all the cases
except in four cases where the canal came into
contact with the external cortical bone.

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Ct analysis of the position and course of mandibular canal /certified fixed orthodontic courses by Indian dental academy

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Ct analysis of the position and course of mandibular canal /certified fixed orthodontic courses by Indian dental academy