Raida iii /certified fixed orthodontic courses by Indian dental academy

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1

What is a MRI scan?
Is a radiological technique that uses
magnetism, radio waves and a
computer to produce images of body
waves.


2

How does a MRI scanner work
• Radio waves 10,000 – 30,000 times

stronger than the magnetic field of earth
are sent through the body.
• Body produces radio waves of its own.
• Scanner picks up these signals and a
computer turns them into an image.


3

Magnetic Resonance
Imaging
A type of emission
imaging
Essentially imaging of
water in the tissue


4

Magnetic Resonance Imaging
Principle


5

When images are displayed; intense
signals show as white and weak ones as
black.
Intermediate as shades of gray.
Cortical bone and teeth with low presence
of hydrogen are poorly imaged and appear
black.

6

MRI can clearly differentiate the soft
tissue components
Preferred imaging technique when
information regarding the articular disc or
the presence of adhesions,or joint effusion
is desired


7

How is an MRI scan performed?
• Out patient procedure
• Patient needs to relax.
• All metallic objects need to be removed

before the scan
• Remove all hearing aids or pace makers.


8

MRI


9

Dental applications
• Relation of orthodontics and TMD

(Temperomandibular disorders).
• Post treatment
• Results of orthognathic surgeries.
• Effects of mandibular advancements in
obstructive sleep apnea.


10

Indications

Assessing diseases of the TMJ
Cleft lip and palate
Tonsillitis and adenoiditis
Cysts and infections
Tumors

11

Contraindications
 Patients with cardiac pacemakers.
 Patients with cerebral metallic aneurysm clips.

Slight movement of the clip could produce
bleeding
 Stainless steel and other metals produce
artifacts ; obliterate image details of the facial
area.

12

Shortcomings

 Inability to identify ligament tears or

perforations
 Dynamics of tissue joint not possible
 Cannot be used in patients suffering from
claustrophobia.

13

3D Imaging
Historical perspective


14

3D Imaging
Necessity
- Our pts. are 3D therefore we
need to record their morphology
in 3D
- Drawbacks of cephalometrics
2 dimensional representation
of a 3 dimensional object


15

3D Imaging

With dimensionally accurate records, not only
can t/t be planned and simulated,but
implemented through methods such as
computerized wire bending & fabrication of
appliances by CAD/CAM
Development of future technologies and
approaches to Orthodontics

16

Basic principles of 3D imaging
Two main geometrical
strategies
1. Orthogonal measurement
2. Measurement by
triangulation
1. Orthogonal – Location of 3rd
dimension(z) by a technique
separate from that used to
measure the other two
dimensions.(x & y)
- Object sliced in layers –
physically or optically

17

Basic principles of 3D imaging
2. Triangulation
Images captured from two positions


18

Methods of 3D Facial Imaging

LASER (Light Amplification by Stimulated
Emission of Radiation)
Structured light
Laser scanner
- Scanner record distortion
of projected laser pattern on
the face to provide a’ surface map’

19

- Simultaneously image is recorded by a digital
-

camera
This image is layered over the surface map


20

Structured Light
- Projection of a structure of lines or grids onto the face
- As the projected pattern is distorted by the contours of
face, this distorted pattern is recorded by a digital
camera


21

Obtaining 3D Dental Models
Destructive scanning
Non destructive scanning
Destructive scanning
- Variant of orthogonal slicing method
- Study cast is invested in a solid matrix of
contrasting colour
-Surface of the block is then sliced parallel to
the occlusal plane
- Laser scan of the 2D surface is made
- An additional 0.003” layer of the block is
ground away and another scan is made

22

Obtaining 3D Dental Models
Non destructive scanning
- Laser stripe is projected on the surface of
plaster cast and distortion pattern is recorded by
a digital camera


23

3D Craniofacial Skeletal Imaging
Anatomic Reconstructions
Computed Tomography Scans
Cone Beam Computed Tomography


24

Anatomic Reconstructions (CRIL Method)
- Integrated 3D model of the craniofacial
structures is formed using lat.&fro. ceph;
photographs & 3D models of dental casts.
- Equipments – i. Calibrated stereo x ray device
ii. Calibrated stereo camera
iii. 3D models of study casts from Align
Technology

25

• Step 1 – generating 3D

dental models of upp &
low teeth and creating Tiepoint bearing aligners
- Tie points are reference
points (like implants of
Bjork) which facilitates
merging of images

26

• Step 2 – placing facial Tie points

• Step 3 – generating a 3D photographic
model of the face


27

• Step 4 – generating a 3D x ray model of
the craniofacial skeleton


28

• Step 5 - Merging the several 3D models
- The CRIL software is used to merge the
data in a single frame of reference
- At least 3 common tie-points are required
in each overlapping


29

• Step 6 – Viewing the integrated 3
Dimensional model

The resulting 3D craniofacial model is viewed
interactively using Align’s TREAT software


30

Computed Tomography Scans
- Post processing software allows for
reconstruction of transverse slices in any plane


31

Cone Beam Computed Tomography
- Like conventional CT but various modifications are
done to optimize them for craniofacial imaging
- Reduced chamber volume just enough for head and
neck
- Real time feed back betn sensor and X ray source
- Cone beam projection of x rays

- Radiation exposure – 20%of conventional CT
- Precision of 0.28mm which 5-10 times more

32

Softwares for Orthodontics
• Many companies have developed softwares to

help the Orthodontist in diagnosis and treatment
planning
- Dentofacial planner
- Vistadent
- Sure smile
- Dr.Ceph
- Digiceph
- eModels
- OrthoCAD

33

OrthoCAD
Diagnosis
Space analysis
Treatment simulations- tooth movement,extn,occlusal contacts


34

Teleradiology
• Teleradiology is the electronic transmission
of radiological images from one location to
another for the purposes of interpretation
and/or consultation.
• When a teleradiology system is used to
produce the official authenticated written
interpretation,- there should not be a
significant loss of spatial or contrast
resolution from image acquisition through
transmission to final image display.

35

Electromyography


36

• Electromyography is defined as the

recording and study of the intrinsic
skeletal muscle by means of surface or
needle electrodes .

• Electromyography is the instrument used.

• The structural basis of EMG is the motor
unit.


37

Motor Unit Potential
• During each twitch of the muscle fibre, a
minute electrical potential is generated,
which is dissipated into the surrounding
tissues.
• The duration may be there for
2 –3 millisecond or 4 millisecond.


38

• Majority of the motor unit potential have an

•

•

amplitude of around 5mv.
Einthoven first discovered a muscle contraction
gives a idiomuscular current.This is referred to
as an action potential.the current is so small
that it has to be amplified several hundred
times.
Using electromyography one can get a
relatively accurate picture of the muscle activity
under diverse functional conditions.


39

Technique
• Two types of electrodes are mainly used –
• Surface electrodes ( skin)
• Needle electrodes


40

Needle electrode
• Superior to surface electrodes and produce
•
•
•

better Electromyograms.
Lesser technical artifacts
Distance between muscle and electrode is
constant
May cause infection and is painful


41

Surface electrodes
• non invasive and reduced risk of infection
• Possibility of loosening of electrodes while
•

nerve stimulation.
Errors in variation between distance of
muscle an electrodes


42


43

Drawbacks
• Impossible to know how much activity of
the muscle being missed.
• Movement cannot be inferred from
electromyography alone, because
antagonistic muscles may be working
synergistically to produce movement or
provide stabilization.


44

Electromyography in orthodontics
• Muscles of importance ( figure )


45

EMG activity in class II div 1
• Graber points out –
class I -normal muscle activity
(except open bite )
class II div 1 – abnormal muscle activity
class II div 2 – compensatory muscle
activity.


46

Electromyographic activity during
swallowing
• Winders et al (Angle Orthod) buccal and

lingual musculature do not contract during
swallowing unless there is an anterior open
bite and anterior skeletal dysplasia.
• In tongue thrust habit there is increase in
genioglossus activity and hypertrophy of
the tongue muscles (EMG activity
increases during hypertrophy).

47

Cine Radiography
• This is a basically a radiographic motion
picture.

• Cine camera-240frames/sec.

• It is used to visualize the swallowing
pattern.


48

Occlusograms
• It is a tracing of photograph or photocopy
of dental arch.

• Uses.


49


50


51

Holography
• It is a photographic technique for

recording and reconstructing images in
such a way that 3D objects can be
obtained.
• The recorded images are called
Holograms.
• Orthodontic applications of holography
includes:

52

CONCLUSION
Accurate patient’s record and reliable
informations are key to our understanding of
orthodontics. The goal would be to develop
methods with which clinicians can accurately
simulate treatment scenarious and select optimal
biomechanics for the treatment of patients. The
patient’s records ( photographs, radiographs and
study models) has not changed for decades
despite of its limitations.
Newer approaches will allow objectives to
review and investigate the clinical diagnosis and
treatments based on 2D record.

53

References
• T M Graber,Vanarsdall R L : Orthodontics•
•
•
•
•

Current Principles and Techniques.
Jacobson : Radiographic Cephalometry
Goaz,White : Oral Radiology – Principles and
Interpretation.
Harring J I, Jansen L : Dental RadiographyPrinciples and Techniques
Pasler F A : Colour Atlas of Radiology.
Kapila & others : Craniofacial Imaging in
Orthodontics : Historical Perspective,current
status,and future developments. Angle Orthod,
1999; 69:491-506

54

• J J Menig. The DenOptix Digital Radiographic System.

JCO,1999; 33: 407-410.
• Seminars in Orthodontics, December 2001,Vol 7 No 4 :
1. Baumrind, Boyd : Integrated Three Dimensional
Craniofacial Mapping: Background,Principles and
Perspectives
2. Hans et al : Three Dimensional Imaging : The Case
Western Reserve University Method.
3. O C Tuncay: Three Dimensional Imaging and Motion
Animation
4. J Mah, A Bunman: Technology to create Three
Dimensional Pt. Record.
5.Curry,Baumrind : Integrated Three Dimensional
Craniofacial Mapping at the Craniofacial Research
Instrumentation Laboratory/University of the Pacific.
6. W R Redmond : The Digital Orthodontic Office:2001.

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Raida iii /certified fixed orthodontic courses by Indian dental academy

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