Radiology in orthodontics dr.kavitha /certified fixed orthodontic courses by Indian dental academy

RADIOLOGY IN ORTHODONTICS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com




Introduction



Radiation physics



Radiation biology



Radiographic techniques



Specialized radiographic techniques



Diagnostic imaging of TMJ



Maxillary canine projections



Conclusion


INTRODUCTION
The use of X Rays in an integral part of clinical
dentistry with some form of radiographic examination
necessary on the majority of patients. As a result,
radiographs are often referred to as the clinician’s main
DIAGNOSTIC AID.


RADIATION PHYSICS


XRAY




Discovery by Roentgen in 1895.
X Rays are form of high energy electromagnetic radiation
& part of electromagnetic spectrum, which also includes low
energy radio waves, television & visible light.

PRODUCTION OF X RAYS
X Rays are produced when energetic (high speed) electrons
bombard a target material & are brought suddenly in to rest. This
happens inside a small evacuated glass envelope called X Ray
tube.

X RAY MACHINE



l. X Ray tube
2. Power supply

I.X Ray tube







1) Cathode 2) Anode
When electrons from the cathode
strike the target in the anode,
they produce X Rays.
Cathode -- Consists of Filament (
electron production)
Focusing Cup. (Mb)
Anode -- Consists of tungsten
target embedded in copper stem.
(electron’s kinetic energy is
converted in to X Ray Photon)


II. Power Supply
Functions
1. Provide low – voltage current to heat the X Ray tube
Filament by use of step down transformer.
2. Generate a high potential difference between the anode
and cathode by use of high voltage transformer.


PRODUCTION OF X RAYS
I. BREMSSTRAHLUNG RADIATION.




If High speed electrons hits the nuclei
of a target atom, all its kinetic energy is
transformed in to single X Ray Photon.
The energy of the resultant photon is
numerically equal to the energy of the
electron.

II. CHARACTERISTIC RADIATON.


It occurs when an electron from a
filament displaces an electron from a
shell of a tungsten target atom. When
the displaced electron is replaced by
the outer-shell electron, a PHOTON is
emitted with an energy equivalent to
the difference in the two orbital binding
energies.

PROPERTIES OF X RAYS







They are wave packets of energy of
electromagnetic radiation that originate at the
atomic level.
Each wave packet is equivalent to a quantum of
energy and is called as PHOTON.
Velocity is 3 x 10 8m/s.
Shorter wavelength X - Ray posses Increase
energy and penetrate greater distance.


FACTORS CONTROLLING X RAY BEAM.






i) Exposure time
ET =
No of photons generated
(energy is unchanged) only quantity control.
ii) Tube current
TC = No of photon.
iii) Tube voltage
TV = NO of photons.
Mean energy
Maximal energy.
Bramsstrahlung photons.
Quality control.

FILTRATION
To reduce the patient dose, the less penetrating photons
should be removed. This can be accomplished by placing a
Aluminium filter in the path of the beam.

COLLIMATION
It is a Metallic barrier with an aperture in the middle.
Used to reduce the size of the X Ray beam, and therefore
the volume of irradiated tissue with in the patient.
Types

1. Round
2.rectanqular
3.circle


DOSIMETRY


Determining the quantity of radiation exposure (or) dose.
UNITS OF MEASUREMENT:Quantity

SI Unit

Traditional Unit

(a) Exposure
(b) Absorbed Dose
(c) Equivalent (or)
effective dose
(d) Radioactivity

C/Kg
Gray

Roentgen
Rad

Sievert
Becquerel (Bg)

Rem
Curie


IMAGE RECEPTORS (FILM)
Composition:(i) Emulsion
(ii) Base
Emulsion - It is sensitive to
X Rays & visible light,
records the radiographic
Image.
Base
it is a plastic supporting
material on to which the
emulsion is coated.
Types

direct actions or non
screen film ex- IOPA

indirect actions or screen
film ex- extra oral film (
it is used in combination
with intensifying screen)

INTENSIFYING SCREEN
It transfers X-Ray energy into visible light and this in turn
exposes the screen films. So less radiation exposure and
less radiation time is required.
Base
These are made up of polyester plastic measures .
25mmthickness.
It provides mechanical support for the screen.
Reflecting layer
It is a white layer of titanium
dioxide coated on the base lies beneath
the phosphor layer. It reflects any light
emitted from the phosphor layer back to
the X-Ray film.
Phosphor layer
It consists of light sensitive
phosphor crystals suspended in a
plastic material. When phosphors are
struck by photons, they fluorescence i.e
they emit visible light photons that
exposes X-ray film.


Most common phosphor used are





Calcium tungstate that fluorescence in blue portion of
spectrum phosphor used by rare earth intensifying screen.
Terbium activated gadolinium oxysulfide.
Thulium activated lanthanum oxybromide that fluorescence
in green position of spectrum.
Advantage



They respond to a shorter exposure to X Rays, enabling a
lower dose of radiation to be given to the pt.
Disadvantage



Inferior image quality


RADIOGRAPHIC IMAGE
CHARACTERSTICS
(i) Radiographic Density (ii) Contrast

-

atomic no)

(iii) Radiographic Speed
Fast film requires
Slow
(iv) Image Quality

∞ Exposure time (x)
∞ Subject Thickness
∞ Subject Density
Subject contrast (Subject’s
thickness, density and
Film contrast (Intensity of
the remnant beam)
Scattered radiation.

-

exposure
exposure
by using Grid.
(Reduces the amount of
scattered radiation).


RELATIVE RADIATION EXPLOSURE


RADIATION BIOLOGY


Radiation effects at the tissue and
organ level








The radio sensitivity of a tissue or organ is
measured by its response to radiation.
Short term effects
Of radiation on a tissue is determined primarily
by the sensitivity of its parenchymal cells. Cells
are lost primarily by mitosis linked death.
Extent of cell loss depends on – damage to the
stem cell pools & proliferative rate of cell
population.
Long term effects
The long term deterministic effects of radiation on
tissues and organs depend primarily on the
extent of damage to the fine vasculature.

Radiation effects of oral tissues

Oral mucous membrane
• mucositis
• secondary candida albicans infection
• long term – atrophic changes due to progressive
obliteration of fine vasculature and fibrosis
Taste buds Extensive degeneration.
Salivary glands
• Xerostomia
• Ph ↓ to 5.5
• Progressive fibrosis, adiposis, loss of fine vasculature
and parenchymal degeneration
Teeth
• radiation caries.
Bone
• Normal marrow may be replaced with fatty marrow and
fibrous connective tissue
• Osteoradionecrosis

Late somatic effects
• Carcinogenesis and leukemia


ALARA
The most recent recommendations involving the establishment
of permissible doses and dose limits to occupational and
nonoccupational groups can be summarized in the principle of
ALARA (As low as reasonably achievable).
This means that every available method for reducing exposure
to ionizing radiation will be implemented to minimize
potential risks and adverse consequences


Protective measures that aim to minimize the radiation exposure to
the patient are:
•Utilization a high sped film and intensifying screens to reduce
the dose of radiation and the exposure time.
•Filtration of secondary radiation or scatter radiation produced
by low energy x-ray photons by an aluminum filter.
•Collimation by a diaphragm made of lead in order to achieve
optimal beam size

•Proper exposure technique and processing in order to avoid
unnecessary repetition of the procedure.
•The patient’s wearing a lead apron in order to absorb scatter
radiation.
•In order to avoid scatter radiation the operator must stand at least 6
feet behind the tube head or should stand behind a lead protective
barrier while making the x-ray exposure.


TYPES OF RADIOGRAPIC TECHNIQUES
I
II

Intra oral
Extra Oral

-

IOPA, Bitewing, Occlusal.
Oblique lateral, various
skull projections OPG.

INTRA ORAL PERIAPICAL RADIOGRAPH:It shows 2 to 4 teeth & provides detailed information
about the teeth and surrounding alveolar bone.









Indications:Detection of apical Infection / Inflammation.
Periodontal status detection.
Assessment of pressure & position of unerupted teeth.
Evaluation of implants post operatively.
Techniques:Paralleling tech
Bisected angle tech

PARALLELING TECH
( Right angle intra oral tech )
(or)
(Long cone tech.)
Procedure:- X Ray film in supported to
the long axis of the teeth
by film holder & the central
beam in directed at right
angle to the teeth & the
film
– To further reduce
geometric distortion X Ray
source be located relatively
distant from the teeth.


BISECTING ANGLE TECH
• Based on the simple geometric
theorem (i.e.) (ieszynski’s rule
of isometry), which states the 2
angles are equal when they
share one complete side & have
2 equal angles.
• The plane of the film & long axis of the teeth form an
angle with its apex at the point where the film is
in contact with the teeth. When this angle is bisected by an
imaginary line or plane, 2 congruent angles with a
common side (Imaginary bisector) formed. central ray is
directed at a right angle to the plane that bisects the
angle
between the long axis at the tooth & the film.

OBJECT LOCALIZATION
TUBE SHIFT TECHNIQUE (Buccal
object rule, Clark' rule)






The relative positions of radiographic
images of two separate objects change
when the projection angle at which the
images were is changed.
If the object in question appears to
move in the same direction with respect
to the reference structures as does the
X-ray tube, it is on the lingual aspect of
the reference object.
If it appears to move in the opposite
direction of the X-ray tube, it is on the
buccal aspect. If it does not move with
respect to the reference object ,it lies at
the same depth (in the same vertical
plane) as the reference object

RIGHT ANGLE TECHNIQUE


Two projections taken at
right angles to one another
localize an object. In
clinical practice the
position of an object on
each radiograph is noted
relative to the anatomical
land marks. This allows an
observer to determine the
position of the object or an
area of interest.


Stanley A. Jacobs et al (AJO 2000).
A rotational panoramic radiograph with an ant occlusal
radiograph is a preferred combination of radiographs to
localize unerupted mandibular anterior teeth. This
combination uses a tube shift in the vertical plane. The
rotational panoramic radiograph is taken at an effective
angle of +7°C to the occlusal plane & anterior occlusal
radiograph is taken at -55°C.
Conor Armstrong (EJO - 2003).
States that localization of ectopic maxillary canines
was significantly more successful with horizontal parallax
than with vertical parallax. But both radiographic
techniques were poor at localizing buccal EMC (success rate
is only 63%).


BITE WING RADIOGRAPH
Film in designed to show the crowns of the premolar &
molar teeth on one side of the jaw.
Indications:




To detect proximal Dental Caries.
Monitoring the progression of Dental Caries.
Assessment of existing restoration.
Assessment periodontal status.
Technique:-





Film in placed between tongue & teeth, close to the
lingual surface of the teeth & parallel to the long axis.
Film tab should be centered in occlusal line.
X Ray is projected to the center of the film through
contact areas (angle 5 degree)

OCCLUSAL RADIOGRAPHY
Maxillary occlusal
(a) Topographical
- Ant
Maxilla & dentition, ant
nasal fossa.
(b) Cross Sectional - Palate,
Zygomatic Process of
Maxilla, nasolacrimal Canal
Nasal Septum, 2nd Molar
to 2nd Molar.
( c) Lateral Topographical
• Half of the ridge of
Maxilla,
Inferio Lateral aspect of
the antrum, tuberosity,
teeth from lateral
incisor to molar. www.indiandentalacademy.com

MANDIBULAR OCCLUSAL
(a ) Cross Sectional
Lingual & Buccal Plates of the jaw bone 2nd molar to 2nd
molar.
(b) Lateral cross section
Soft palate, half of the floor of the mouth, buccal &
lingual cortical plate (Lateral incisor to 3rd molar).
Uses:



To Precisely locate roots, supernumery unerupted &
Impacted teeth (canine to 3rd molar)
To aid in examining – pt with trismus who can open the
mouth only a few mm.


EXTRA ORAL RADIOGRAPHIC
TECHNIQUES
•
•
•
•

Lateral cephalometric projection ( sagital (or) Median)
submento Vertex ( Transverse (or) horizontal)
Water’s projection
Postero anterior ( Frontal view)

I. SUBMENTO VERTEX:It reveals the position and orientation of the
condyle, curvature of the mandible.
II. WATERS PROJECTION:Used to evaluate orbit, nasal cavity and
maxillary sinus.

POSTERO ANTERIOR VIEW
The X ray passes in a posterior anterior direction through the
skull.
A cassette is positioned vertically in a holding device. A grid
is used
Head is centered in front of the cassette with the cantho
meatal line.
Uses








To detect developmental abnormalities like facial
asymmetries.
Used to examine the skull for presence of disease, trauma,
developmental abnormalities.
Used to detect progressive change in the mediolateral
dimensions of the skull.
It offers good visualization of facial structures including
frontal, ethmoidal sinus, nasal fossa and orbits.

POSTERO ANTERIOR VIEW


LATERAL CEPHALOMETRY
“Cephalometry” the term may mean a simple consideration of
anatomic part of the skull in the head plate or the treatment of
measurements by the use of analytic geometry.
History:









1922 – Pacini Introduced a method for standardized head
radiography.
1931 – Broad Bent in the US
Hofrath in Germany-introduced modern cephalometry.
Pacini – Large fixed distance from the X Ray source to the
cassette. The head of the subject is placed adjacent to a stand
holding the cassette and war immobilized with a gauge
bandage wrapped around both the face and the cassette, after
the pt’s midsagittal plane was carefully oriented parallel to the
cassette.
Broad Bent;- Involves a constant focal spot to object distance
(5 feet) &constant object to film distance (9cm)
Lucien de coster – was the first to publish an analyses based
on proportional relationships in the face conforming to the
principles used in antiquity.

RADIOGRAPHIC CEPHALOMETRIC
TECHNIQUE
Simplest procedure to

Simplest procedure to
obtain head radiographs in
natural head position is to
instruct the patients to sit
upright and look straight
ahead to a point at eye
level on the wall in front of
them.

Patient is positioned within
the cephalostat using
adjustable bilateral ear rods
placed within each auditory
meatus, usually while the
patient is in the standing
position. The midsagital plane
of the patient is vertical and
perpendicular to the X Ray
beam. It is also parallel to the
film plane which in turn
perpendicular to the X Ray
beam.

OREINTATION IN NATURAL HEAD
POSITION
Orientation of pts in natural head position
will result in only a small range of error. Such
differences have only minor effect on the
interpretation of facial morphologic features &
facial disharmony


LATERAL CEPHALOGREM


CLINICAL USES
(i) GROSS INSPECTION
To observe gross anatomic relations of skeletal & soft tissues
in the lateral & frontal films in order to determine major
dysplasias.
use of 3 ‘p’ s
Growth assessment of Physical morphology
Search for Pathological Phenomenon
The interpretation of Physiologic condition.


(ii) DESCRIPTION
gives mathematical measurement & description .4 ‘c’ s
Characterization or description comes first.
Comparison of one individual to another is made possible
Classification of factors.
Communication of the problems.
(iii) GROWTH AND TREATMENT
It is used to record and measure changes.
(iv) PLANNING AHEAD
Treatment Planning
More useful to make a “Cephalometric set up”


TRACING & IDENTIFICATION OF
CEPHALOMETRIC LANDMARKS
Steps








Soft tissue profile, external cranium, Vertebra.
Cranial base, internal border of cranium, frontal sinus & ear
rods.
Maxilla & related structures including nasal bone &
pterygomaxillary fissures.
The mandible.


CEPHALOMETRIC SUPERIMPOSITIONS
Growth and mechano therapy contribute to the outcome
of orthodontic treatment to different degrees.
cephalometric superimpositions demonstrate the combined
effects of growth and mechanotherapy.
Regional cephalometric superimpositions are performed
to evaluate three basic components of skeletal and dento
alveolar development:-maxillary ,mandibular and overall
facial changes.
Superimposition of cranial base yields information about
the movements of facial bones away from the cranial
structures.
Superimposition of maxillary structures can be used to
evaluate changes in the maxillary dento alveolar complex
(PNS-ANS line).
Mandibular superimposition on relatively stable
anatomical structures can be used to evaluate dento
alveolar changes.

Methods of superimposition
1.Superimposition on S-N at S.
2.Superimposition natural reference structures such as cranial
base.
3.Using a subtraction technique where a positive copy is
made of one of the radiographs and overlaid on the other.
Areas of radiograph where no change has taken place
appear uniformly grey.
4.Using a “blink comparator”. Two radiographs are illuminated
alternately in rapid succession, giving an impression of
the changes that have occurred between the radiographs.
5.Using digital images tracings of cephalometric radiographs
can be superimposed either on landmarks or structures
that have out lined by the operator.

V. Gavel & L.Dermant (EJO – 2003).
To identify position of unerupted canine by
using lateral cephalogram, 3 different
displacements were stimulated. 10 mm frontally,
10 mm sagitally, 5mm vertically.
They concluded that the degree of vertical &
sagittal displacement of the incisor point of the
impacted canine, angulation, length of the teeth
measured on cephalogram appeared to give an
accurate representation.


COMPUTERIZED CEPH
With introduction of digital imaging, automated and
semi-automated landmark identification directly from the
digital images can be done. This would avoid the
•
•

need for manual tracing
removes operator subjectivity

but at present automated systems are unable to match
human operators in the accuracy of landmark identification.
Yi Jane chen et al (AO 2000), compared the traditional
and computer aided digital cephalometric landmarks and
concluded that the inter observer error for each landmark
in digital images was generally larger than that in the
original radiograph. Mostly seen in Po, Ar, ANS, UM.

Automatic computerized radiography
identification of cephalometric Landmarks. D
J Rudolph et al.
This study compared manual identification on a
computer monitor and Spatial Spectrometry
automatic method for landmark identification on
minimum resolution image. Fifteen landmarks
were selected on set of 14 test images. The
results showed no statistical difference (p>0.05)
in mean landmark identification errors between
manual identification on a computer display and
automatic identification using SS

THREE DIMENSIONAL CEPHALOMETRIC
ANALYSIS
It is a valuable tool in assessment of skeletal remodeling,
contour changes, and changes in proportion that occur
with aging. Computed assisting tomographic data can be
used in either coronal or axial direction.
Advantages:•
•
•
•

Precise anatomic data unobtainable by other methods
can be acquired from a 3D radiological image.
Improved diagnostic accuracy.
Contours & surface detail are rendered in fine detail.
Ability to correlate soft tissue and hard tissue points
directly on the computer.
Constrains:Lack of uniformity www.indiandentalacademy.com
in viewing the reconstructed image.

Method:



Both axial & coronal slices were obtained.
Slice 3mm (or) less is used.
CT scans were reconstructed in 3 D by reformatting
process.
Uses:-





Especially useful in patient with marked dentofacial
asymmetries.
To improve preoperative diagnostic capabilities including
volumetric analysis.


XERORADIOGRAPHY
It is the process of recording a latent radiographic
image on a selenium coated aluminum plate ,the image is
then transferred to a specially treated paper for
visualization. The whole process is fully automatic , taking
90 seconds to complete.
Advantages
1) Soft tissues, bone, teeth, and air passages are clearly
visible because of a large recording latitude , high
resolution and the “ edge enhancement phenomenon”
2) more pronounced definition and contrast
Davis and associates and Johnson conclude
Xeroradiography is superior to conventional radiography

ORTHOPANTOMOGRAPHY


It is a technique for producing a single tomographic image
of the facial structures that includes both the maxillary and
mandibular arches and their supporting structures.
ADVANTAGES











Broad coverage of the facial bones & teeth.
Low pt radiation dose.
Convenience of the examination for the pt.
Ability to be used in pts unable to open their mouth.
DISADVANTAGES
Unequal magnification.
Geometric distortion.

INDICATIONS






Need to know the State of the dentition and the presence /
absence of teeth.
Unerupted tooth.
Periodontal tooth support.
Destructive disease of the articular surface of TMJ.
PRINCIPLE



Two adjacent disks rotate at the same speed in opposite
direction as an X Ray beam passes through their centers of
rotation.
IMAGE LAYER



It is a 3 – dimensional curved zone (focal trough) in which
the structures lying with in the layer are reasonably well
defined on final panoramic image.

PATIENT POSITIONING
Mid sagital plane must be centered with in the image layer.
Patient ‘s chin and occlusal plane is aligned so that it is lower
anteriorly, angled 20-30 degrees below the horizontal plane. Line
from the tragus of the ear to the outer canthus of the eye is
parallel with the floor.
POSITIONING ERROR
1) Pt. too far from the film.
2) Pt. too close to the film
3)
4)
5)

Ant teeth magnified in
width and out of focus.

Ant teeth narrowed and out
of focus.
Pt. Asymmetrically turned
Post teeth enlarge on one
right or left
side and decreased on other
side.
Pts. Wearing earrings
Artefactual shadow.
Failure to instruct the pt
Vertical (or) horizontal
to keep still throughout
distortion of the part
the cycle
of the image being produced
at the time of the movement.

SPECIALISED IMAGING TECHNIIQUES


Conventional tomography



Stereoscopy



Scanography



Computed tomography



Magnetic resonance Imaging



Ultrasonography



Arthrography



Digital radiography

COMPUTED TOMOGRAPHY


CT image is a display of a thin slice of the body, developed
from multiple X ray absorption measurements made
around the periphery.
ADVANTAGES:-









Cross Sectional Image
Superior contrast resolution
Geometric accuracy
Tissue Characterization
Image windowing
Digital image processing
Quick and Non invasive


TECHNIQUES
 Xenon CT – To study blood flow.
 Quantitative CT – Determination of bone mineral content.
 Dynamic CT (Rapid sequence CT) - to study physiology.
 High Speed resolution CT.






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




LIMITATIONS
High dose of radiation.
Geometric (or) Contrast miss.
Artifacts.
INDICATIONS
Bone lesions affecting the TMJ.
Implant planning.
COMPONENTS
Gantry – Consists of a) Detector array
b) X Ray source.
c) Pt. Support couch.
Computer.
Control console – This allows the operator to dictate the
parameters of the CT scan.

IMAGE ACQUISITION

CT images are acquired
in the axial, coronal, or
sagital planes. These
images are taken in
succession and are
generally referred to as
slices. The information
form these multiple slices
can then be reformatted to
produce images in other
planes.


CT NUMBERS OR HOUNSFIELD
UNITS
The numeric data in each
pixel is called a CT number.
The CT number corresponds to
the linear attenuation
coefficient of a particular tissue
at a designated kilo voltage.
Air
Fat
Water
CSF
Muscle
Bone

=
=
=
=
=
=

-1000
-100
-0
+1
+50
+1000


Gary yip et al (seminar
in ortho 2004).
Concluded that micro
tomography is particularly
useful for the technically
demanding task of assessing
mineral density patterns of
bone, supporting titanium
implants.
The expediency,
nondestructive nature, & 3D
imagery of this technique
used to evaluate quantity,
quality & mechanical
properties of bone.


MAGNETIC RESONANCE IMAGING
(MRI)
Discovered by Purcell and Loch in 1946.
PRINCIPLE:







MRI uses non-ionizing radiation from the
radiofrequency (RF) band of the Electromagnetic
spectrum.
Unpaired Neutron/Proton  Magnetic Dipoles
in biological tissues- H2 atom is the most
common.
Natural state – Net magnetization is zero.
Application of External Magnetic field.
•
•



Spin-up (Lower energy state).
Spin -down (Higher energy state ).

MRI reflects the magnetic properties of mobile H2.

IMAGING PROCESS
1)Patient placed in the magnetic field.
The protons act like small magnets ,align themselves with in the
magnetic field and begin to rotate at a precise frequancy. This is
called ‘Precession’ ( Larmor Frequency)
Protons align in external magnetic field.a new magnetic
vector is induced. That is Net Magnetic vector in Longitudinal
Magnetization
Superconductive magnet – field strength 0.1 – 2 Telsa.
2)Radio wave sent in.
New Magnetic vector excited by RF wave.
Tipping of Bulk magnetic vector in space.
Duration of RF wave determinates Angle of tip.
the tipping of new magnetic vector results in a decrease in its
size and a new magnetic vector- Transverse Magnetization
appears.
3)Radio wave turned off.
Protons calm down/relax www.indiandentalacademy.com
to original position.
Recovery via T1 & T2 relaxation times.

4)Patient emits signal ( as T1, T2).
Rotation of bulk magnetic vector to pre-excitation state 
Induction of electric current in wire coils .Signal received and
processed.
T1  measures the longitudinal return of protons to align with the
external magnet after the RF pulse has stopped.
Small water molecules takes long time to transfer energy.leads to
long T1- appear black on T1 weighted images.
Larger fat molecules-shorter T1- White or Bright.
T1 - Shows Anatomy
T2  measures the energy transfer between interacting protons
after excitation. For water, CSF, saliva – Long T2 – White or
bright. For fat – short T2 – bright signal suppressed.
T2 - Shows Pathology
5)Reconstruction of picture.
Most common –spin echo pulse sequence
Application of RF pulses-localization of signals-Fourier
transformation-reconstruction of image.

MR CONTRAST AGENT


Injected contrast agents change the signal intensity by
altering T 1 and T 2 relaxation times. Paramagnetic GdDTPA-Most popular
(Gaddolinium diethylene
Triamine pantothenic acid).

SAFETY CONSIDERATIONS




Contraindicated in pts with Ferromagnetic materials
like Cardiac pacemaker.
Safety in Pregnancy not established.


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










ADVANTAGES
It offers best resolution of tissues of low inherent
contrast.
No ionizing radiation in involved with MRI.
Because e at the region of the body Imaged in MRI in
controlled electronically, direct multiplannar imaging is
possible without reorienting the patient.
DIS ADVAVTAGES
Relatively long imaging times and the potential hazard
imposed by the presence of ferromagnetic metals in the
vicinity of the imaging magnet.
Ex – Cardiac pacemakers, cerebral aneurysm clips
Some patients suffer from claustrophobia when
positioned in a MRI Machine.
INDICATIONS
It gives excellent soft tissue contrast resolution.
Diagnosing a suspected internal derangement of the
TMJ and evaluating the treatment of that derangement
after surgery.
Identifying and Localizing orofacial soft tissue lesions.
Gives Images of salivary gland parenchyma.

Using Magnetic resonance imaging, temporo mandibular
joint Effects of activator treatment are analyzed by Sabine
et al , Angle Orthodontist 6; 72, 2002 he concluded the
following:
During the one year treatment period the sagital dental
arch relationship improved .On average, the physiologic
position of disc, condyle and fossa was present both
present and after one year activator treatment.
A pretreatment physiological disc condyle relationship
was unaffected by activator therapy. The prevalence of sub
clinical capsulitis of the inferior stratum of posterior
attachment during activator treatment.
Using magnetic resonance imaging and cephalometric
investigation , temporo mandibular joint remodeling in
adolescent and young adults during Herbst treatment was
analyzed by sabine et al
The increase in mandibular prognatism accomplished
by Herbst therapy is found to be a result of codylar and
glenoid fossa remodeling.

ULTRASONOGRAPHY
The phenomenon perceived as sound is the result of
periodic changes in the pressure of air against the eardrum.
Periodicity of these changes lies anywhere between 1500 and
20,000 cycles per second.
PRINCIPLE
 Electrical impulses generated by the scanner causes the
dipoles in the crystal to realign themselves and to the
electrical field and thus suddenly change the crystal’s
thickness. This abrupt change begins a series of vibrations
that produce the sound waves that are transmitted in to the
tissues being examined.
ADVANTAGES
 Does not require special facilities.
 Can be used to view the joint in a continuum with out
invasion, discomfort.
DISADVANTAGES
 Noise signal.
 Size of the transducer.
 Meniscus not seen.

Chien_Lun peng et al (EJO – 2003).
To differentiate infantile and mature swallow. He used
B +ve mode ultrasonography movements of the tongue tip
& submental musculature during swallowing were recorded
on video cassette.
It provides a noninvasive visualization of tongue
movements & no foreign body is required in the oral cavity
allowing more natural swallowing behaviour.


DIGITAL RADIOGRAPHY


A digital image is a matrix of square pieces or picture elements
(pixels), that form a mosaic pattern from wherein original image can
be reconstructed for visual display.
Analog Image



1) Conventional radiographic
Image



2) Silver halide grain



3) Randomly dispersed



4) Continuous Spectrum

Digital Image
1) a) Light sensitive
elements to record
the image.
b) Shades of gray to
display the Image
2) Light sensitive
elements
3) Regular grid of rows
and Columns
4) Numeric and Discrete.


PIXELS AND VOXELS


Pixel
2-D Digital Images – Composed of Picture elements.



Voxel
3-D Digital Images – Composed of volume elements.

PRODUCTION OF DIGITAL IMAGE
Analog to Digital conversion (ADC).




Sampling

- Small range of voltage values grouped
together.

Quantization - Every sampled signal is assigned a value.
Pixels are arranged in proper locations and given a
shade of gray corresponding to quantization
number.

ADVANTAGES OF DIGITAL RADIOLOGY










Reduces time and effort needed for chemical processing
error.
Eliminates faulty radiographs due to processing error.
Eases image transfer for electronic communication.
Eases storage, back up and retrieval.
Permits computed optimization at image.
Facilities pt communication.
Lowers radiation dose to the pt.
Ability to manipulate image contrast and density.

DISADVANTAGES





Initial expenditure high.
X-ray receptor in IO systems –susceptible to rough
handling.
Risk of system becomes obsolete.

TECHNIQUES


Single step system (CCD/C MOS).



2 step wireless system (PSP Plated).

CCD (Charge coupled device)






The CCD uses a thin wafer of silicon as the
basis for image recording.
Associated read out and amplifying
electronics.
Scintillating layer-Gadolinium oxybromide or
cesium iodide.

IMAGE PRODUCTION IN CCD SENSOR
Radiation
Breakage of silicon bonds
Production of electron hole pairs
Creation of Charge pockets
Charge pocket in each pixel
forms latent image
Bucket brigade transfer
Read out amplifier
ADC

IMAGE

ADVANTAGES




It is a part of the direct sensor system. Image is displayed
on the monitor in a few seconds.
It has the lowest noise.

DISADVANTAGES






Bulk of the sensor.
Electronic cable is necessary to transfer the data from the
senior to the ADC.
Detectors are expensive.


C-MOS (Complementary Metal oxide

sensors)

Semiconductor

It is also silicon-based semiconductors.
ADANTAGES





“Design Integration”.
ADC control functions are built in with in the sensor.
Easy manufacturability.
Less expensive than CCD.

DISADVANTAGES




C-Mos sensors may not perform well in low light conductors.
More noise than CCD.
Less active area for image acquisition than CCD sensors.

2 STEP WIRELESS SYSTEM
PSP plates (Phosphostimulable
phosphor plates)
COMPOSITION
Contains “Europium – doped” Barium
fluorohalide
europium creates imperfections.
PRINCIPLES
PHOSPHORESENCE

 Quantified as a measure of X
ray energy absorbed by
material





IMAGE FORMATION

Radiation  movement of Valance electron into Conduction
band  migration into nearby Halogen vacancies
(‘F’ Centers) Formation of Latent images.
Stimulation by Red light  Return of electrons into the Valence
band  Release of energy in green spectrum  Fibro optics 
Photomultiplier tube  Conversion of light into Electrical
energy. Removal of stimulatory light by Red filter 
conversion of remaining green light into varying voltage—
Quantification in ADC  Storage and display.


ADVANTAGES





It can be used indefinitely.
Can be used with existing sources.
Linear or Logarithmic response to radiation.
Wide exposure range.

DISADVANTAGES



High Initial cost.
Poor spatial resolution.

INDICATION





Caries detection.
Alveolar bone imaging.
To study trabecular Pattern of jaw bones.
Cephalometric radiography.

IMAGE QUALITY CONSIDERATIONS
• Active area.
• Signal to noise ratio.
• Contrast resolution.
• Spatial resolutions.
• Radiation dose.
• Detector latitude.
• Detector sensitivity.

TMJ PROJECTIONS
HARD TISSUE
PANORAMIC PROJECTION



Gross osseous changes in the condyle may be identified.
Ex – Asymmetries, extensive erosions changes in articular
eminance.

TRANSCRANIAL PROJECTION


Lateral aspect of the condyle, and temporal component and
range of motion.

TRANSPHARYNGEAL (PARMA) PROJECTION



Sagital view of the medial pole of the condyle.
Erosive changes of the condyle.

SUBMENTOVERTEX VIEW
• skull base and condyles superimposed on the condylar
necks and mandibular rami
• Facial asymmetries, condylar displacement, rotation of the
mandible.
CONVENTIONAL TOMOGRAPHY
•
•
•

erosive changes of the condyle
Entire condylar head is visible in the mediolateral plane
Depicting true condylar position and revealing osseous
changes

COMPUTED TOMOGRAPHY
• Gives 3 dimensional shape and internal structure of the
osseous components of the joint and soft tissue
structures

TMJ SOFT TISSUE
ARTHROGRAPHY
•

Information about disk position, function, morphology
and integrity of diskal attachments.

MRI
•

demonstrate osseous and diskal tissues.

•

Inflammation and joint effusion

•

MEDIAL DISK displacement are best detected.


MAXILLARY CANINE IMPACTION
In Radiograph
• To determine size and shape of the teeth.
• To determine position of the teeth.

CANINE LOCALISATION
Parallax in horizontal plane.
Required Radiography :
 2 IOPA
 Upper occlusal.

Parallax in Vertical Plane.



OPG
Upper occlusal.


Vertex occlusal






X-Ray Tube is positioned above the patient , in
the mid line, aiming downwards through the
vertex of the skull.
Buccal or palatal position of an unerupted teeth
can be identified.
Dis Adv: Radiation to eyes, gonads and
pitutarygland.

True lateral & PA Jaws.
Steroscopic Views.
Cross sectional spiral
tomography.

CONCLUSION
Radiology is one of the rapidly changing field in diagnostic imaging.
Systematic approach is necessary to evaluate the complex
anatomical relationships displayed on the CT & MRI and other
specialized images.
For a long time, radiographic film was the most important medium
with which to acquire & archive the diagnostic image.
In the future conventional radiographs will become obsolete and will
be replaced by digital images.


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Radiology in orthodontics dr.kavitha /certified fixed orthodontic courses by Indian dental academy

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