Recent advances digital imaging /certified fixed orthodontic courses by Indian dental academy

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RECENT ADVANCES IN
Leader in continuingIMAGING
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Cephalostat in 1931

Broadbent-Bolton (USA)

Hofrath (Germany)


De Nevreze’s (1936)
profilometer
oriented to the FH

Korkhaus, 1937

Waldo, 1938


Marcolis, 1940

Weingart, 1948

Thurow, 1951


Bjork, 1951

Reboul (1954) described a simple way adjustment and simple
head-holder. User a cephalostat is well adjusted, it cannot be
expected to obtain accurate superimposition between left and
right slides.

Laster model of the
Broadbent-Bolton
Roentgenographic
Cephalometer


Elsasser 1951 - 1953 proposes the
ORTHOMETER
which measures the departure of various
points in the facial midline form
orthognathy

After the Discovery of X-rays by Roentgen in
1895,traditional 2-D cephalographs also
known as Roentgenographic cephalometry
was
introduced by Broadbent 36 years
later. With the arrival of the cephalometric
technique and its increasing popularity
clarification of the anatomic basis for
malocclusions became possible.

Limitations of 2D’s
Several reasons for limited validity of the 2D
Cephalometry’s scientific method :
1. A conventional headfilm is a 2D
representation of a 3D object.
2. Cephalometric analyses are based on the
assumption of a perfect superimposition of
the right and left sides about the mid sagittal
plane.

3.

a)
b)
c)
d)
e)

A significant amount of external error, known
as radiographic projection error, is associated
with image acquisition.
Size
Magnification
Distortion
Patient positioning
Projection distortion

4.

5.

Manual data collection and processing in
cephalometric analysis has been shown to
have low accuracy and precision.
Errors in location of landmarks due to the lack
of well defined outlines, hard edges and
shadows.


What is a digital image?


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


What is an Analog image


An analog image, such as a radiographic
film, has virtually an infinite number of
elements, with each element represented by
a continuous gray scale.


Imaging and Image acquisition

Images

Conventional
ANALOG PROCESS
Contemporary
DIGITAL PROCESS


Characteristics of digital images






A digital image is composed of picture elements (pixels) that are
arranged in a 2‑dimensional rectangular grid, with each pixel
having a specific size, color, intensity value, and location within
the image (ie, bitmapped or raster).
A pixel is the smallest element of a digitized image. Radiographic
images generally use gray color with an intensity value between
8 bits (28 or 256 shades of gray) and 12 bits (2 12 or 4096 shades
of gray).
Image resolution refers to the degree of sharpness of the image.
Resolution is determined by the number of pixels per given
length of an image (pixels/ mm), the number of gray levels per
pixel (bits), and the management of the gray levels.





The pixels in a digital image are arranged in a matrix. If a large
number of pixels are used to represent an image, their discrete
nature becomes less apparent, i.e., the spatial resolution of the
image improves as the number of pixels increases.
Each pixel has a digital value that represents the intensity of
the information recorded by the detector at that point. Each digital
value is represented as a binary number; information is recorded
in terms of a series of ones or zeros. Each one or zero is called a
“bit.” In a 6-bit image each pixel will have 64 possible values,
ranging from 0, which represents a black area on the image, to 63,
which represents a white area; an 8-bit image each pixel will have
256 possible values. The quality of an image depends on both the
number of pixels and the number of gray levels which make up
the image.





A pixel has no size or shape. At the time it's born, it's simply an
electrical charge. A pixel is only given size and shape by the
device we use to display or print it. The size of a digital photo
sensor is determined by the number of photo sites that it has on its
surface. Even though the captured pixels have no physical
dimensions, this size is usually specified in one of two ways--by
the sensor's dimen-sion in pixels, or by its total number of pixels.
For example, the same image can be said to have 1,800 X 1,600
pixels (expressed as "1,800 by 1,600"), or to contain 2.88 million
pixels (1,800 multiplied by 1,600).
When a digital image is displayed on the computer screen, its size
is determined by three factors: the screen's resolution, the screen's
size, and the number of pixels in the image.

Image enhancement









There is potential for improving the diagnostic quality of digital images by
enhancing the images using various algorithms. Digital images can be
enhanced using algorithms that mathematically manipulate the gray-level
values of the pixels.
Using enhancement algorithms it may be possible to extract information from
radiographs that previously required further additional radiographic exposure
to the patient. However, image enhancement is actually the suppression of
information that the operator deems unnecessary for a particular task, rather
than the addition of further information.
Image enhancement can be divided into three main areas:
Contrast improvement,
Smoothing and
Edge enhancement


Devices to store digital images




Magnetic tapes
Laser or optical disks
Optical tapes


Film based imaging



Film-based imaging consists of X-ray interaction with electrons in
the film emulsion, production of a latent image, and chemical
processing that transforms the latent image into a visible one. As
such, radiographic film provides a medium for recording,
displaying, and storing diagnostic information. Film-based images
are described as analog images. Analog images are characterized
by continuous shades of gray from one area to the next between
the extremes of black and white


Each shade of gray has an optical density (darkness) related
to the amount of light that can pass through the image at a
specific site. Film displays higher resolution than digital
receptors with a resolving power of about 16 lp/mm.
However, film is a relatively in efficient radiation detector
and, thus, requires relatively high radiation exposure. The
use of rectangular collimation and the highest speed film
are methods that reduce radiation exposure, but these
techniques are not practiced commonly. Chemicals are
needed to process the image and are often the source of
errors and retakes. The final result is a fixed image that is
difficult to manipulate once captured.

Specific applications of digital
imaging
DIGITAL IMAGING:
Still / video patient image acquisition and archiving
COMPUTER ACQUISITION AND ANALYSIS OF CEPHALOMETRIC FILMS:
Lateral, PA, Spiral CT cephalometry.
ELECTRONIC ORTHODONTIC STUDY MODELS
COMPUTER BASED NEWER IMAGING MODALITIES:
3D CT, MRI applications.
REAL TIME 3D RECONSTRUCTION
FUNCTIONAL GNATHOLOGICAL APPLICATIONS

Digital imaging
Digital imaging is the result of X-ray interaction with electrons in
electronic sensor pixels (picture elements), conversion of analog data
to digital data, computer processing, and display of the visible image
on a computer screen. Data acquired by the sensor is communicated to
the computer in analog form. Computers operate on the binary
number system in which two digits (0 and 1) are used to represent
data. These two characters are called bits (binary digit), and they form
words eight or more bits in length called bytes. The total number of
possible bytes for 8-bit language is 2* = 256. The analog-to-digital
converter transforms analog data into numerical data based on the
binary number system. The voltage of the output signal is measured
and assigned a number from 0 (black) to 255 (white) according to the
intensity of the voltage. These numerical assignments translate into
256 shades of gray.

The human eye is able to detect approximately 32 gray levels.
Some digital systems sample the raw data at a resolution of
more than 256 gray values such as 10 bit or 12 bit values.
The large number of gray values is reduced to
256 shades of gray with the advantage of controlling under or
overexposed images. Direct digital imaging systems produce a
dynamic image that permits immediate display, image
enhancement, storage, retrieval, and transmission. Digital
sensors are more sensitive than film and require significantly
lower radiation exposure. Dynamic range or latitude is the
range of exposures that will produce images within the useful
density range.

Resolution




The quality of a digital image depends in part on the number of
pixels used to create the image. This is referred to as
Resolution.
More pixels add detail and sharpen images. If any digital image is
enlarged enough, the pixels will begin to show an effect called
pixelization. The more pixels are there in the image, the more it
can be enlarged before the pixelization occurs.


DIGITAL PHOTOGRAPHY


Digital photography is essentially the same as
conventional photography except that in the
place of the photographic film the camera stores
all of its images onto a computer chip or a
similar storage medium in a digital format


THREE STEPS OF DIGITAL
PHOTOGRAPHY

INPUT

IMAGE
PROCESSING


OUTPUT

Resolution for orthodontic
photography


To be useful for orthodontic photography the
resolution has to be minimum of 800*600 and
1800 *1600 or to contain 2.88 million pixels
(1800 multiplied by 1600) produce excellent
pictures.


HOW A DIGITAL CAMERA WORKS


The big difference between traditional film cameras and
digital cameras is how they capture the images. Instead of
the film, digital cameras use a solid state device called an
image sensor, usually a charge couple device or
complementary metal oxide semiconductor.
On the surface of each of these finger nail sized silicon
chips is a grid containing hundreds of thousand or
millions of photo sensitive diodes called photo sites,
photo elements, or pixels. Each photo site captures a
single pixel in the photograph to be .

THE EXPOSURE
when shutter release button of a digital camera is pressed
a metering cell measures the light coming through the
lens and sets the aperture and shutter speed for the
correct exposure. When the shutter opens briefly, each
pixel on the image sensor records the brightness of the
light that falls on it by accumulating an electric charge.
The more the light that hits a pixel, the higher the charge
it records. Pixels capturing light from highlights in the
screen will have high charges. Those capturing from
shadows will have low charges

Evaluating Image Quality


When we look at a photograph, we make an overall
appraisal on two levels of detail: content and quality. In
orthodontic photography, there are many details we can
examine to determine the quality of an image. As an
example, we should look for the edges of the rectangular
wire, the contour of the rubber ligatures, the ends of the
plastic separators, and the sharpness of the premolar
brackets in the background. Other details in this type of
photograph can be saliva bubbles, mucous veins, the
hairs around the lips, and the palatal creases.

Optimal Image Sizes




There are two kinds of image sizes often termed as
resolution -- optical and interpolated.
The optical resolution of a camera or scanner is the
actual number of the image sensor's photosites. This
resolution can be improved to a limited extent by a
process called interpolat-ed resolution, which adds pixels
to the image using software. The program evaluates the
pixels surrounding each new pixel to determine what its
colors should be. For example, if all the pixels around a
newly inserted pixel are red, the new pixel will be made
red. What's important to keep in mind is that interpolated
resolution doesn't add any new information to the
image--it just adds pixels and makes the file larger..

Understanding Image Files and
Compression




JPEG (Joint Photographic Experts Group, is by far the most popular
format for display of photographic images on the Internet. Although
these files have traditionally used a ".jpg" extension, the actual file
format is called JFIF (JPEG File Interchange Format). GIF, has
been optimized for the display of type and line drawings, but
supports only 8-bit color on the computer screen, whereas JPEG
supports the more detailed 24-bit color.
The JPEG format uses a "lossy" compression scheme that makes
digital files smaller, but sacrifices image quality. Compression is
performed on blocks of pixels, eight on a side. Every time we open
one of these files and then save it again, the image is compressed. As
the image go through a series of saves, it becomes more and more
degraded. Therefore, one should not use the JPEG format to save
original images and expect to modify later. All originals should be
saved in a loss-free format such as TIFF (Tag Image File Format) or
BMP (bitmap) at maximum color depth.



A new JPEG 2000 format, not yet available
in digital cameras, uses wavelet technology
to allow higher compression with fewer
image flaws. With this type of compression,
the image is "streamed," or gradually filled
in with more detail. JPEG 2000 images can
be saved in "loss-less" files and will have
the same color scheme on any display
system



Most digital cameras have a default resolution of JPEG 72dpi,
which is good for displaying on computer screens or in
presentations (although 90dpi would be ideal), but produces
poor quality for publication . Images of this resolution become
completely distorted when enlarged, and most printed
orthodontic journals will not accept them. Some camera models
allow higher resolutions to be used in TIFF or BMP formats,
which are more suitable for publication. These non-compressed
images take up much more space, however, making it possible
to fill the camera's memory with only four to six high-resolution
photographs. Furthermore, the TIFF 300-350dpi is the ideal
format for interpo-lating without noticeably distorting the photograph, thus occupying less memory.

VIDEO IMAGING






Video capture is used less frequently for facial and
intra oral image acquisition. Video capture systems
connect video camera to a computer through a frame
grabber. A frame grabber is an interface board in a
computer that converts the analog video signal from a
video camera into a 24- bit RGB digital image.
The frame grabber grabs an image frame from the
continuous video signal.
Frame grabbers in clinical use acquire images at 640 by
480 resolution for NTSC signals and 768 by 576 for
SECAM or PAL signals.





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Image quality greatly depends on the type of
signal generated by the video camera. The three
common types are
COMPOSITE SIGNALS,
S – VIDEO SIGNALS,
RED-GREEN-BLUE (RGB) SIGNALS




Composite signals combines luminance (brightness) and
chrominance (color) information into one signal. S- video, also
known as Y-C, uses separate signals for luminance (Y) and
chrominance (C), resulting in higher over all image quality.



RGB component video separates the red, green, and blue
information into separate signals and generates the highest
quality image.



S-video or RGB video signals are the preferred for clinical
imaging.



For facial and intra oral shots, video –captured image resolution
is low compared with images acquired with mega pixel digital
cameras. Video captures chief advantage over digital
photography is immediacy; images need not to be transferred via
a flash memory card from the camera to a computer. However,
optimal video lighting is difficult to achieve, especially for intra
oral views. Further more, video capture systems are tethered by a
video cable to a computer, where as digital cameras are portable
and easy to use in several locations

Digital Radiograph (RVG)
sensor head

object

x-ray
source
scintillator

CCD

fibre optic
layer

transmitter
converter
amplifier


PC

quantizer
amplifier
receiver

Direct Digital Imaging



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



A number of components are
required for direct digital image
production. These components
include
X-ray source,
Electronic sensor, a
Digital interface card,
Computer with an analog todigital converter (ADC),
Screen monitor,
Software, and
Printer.


DIGITAL RADIOGRAPH


Digital radiograph

• Amorphous Selenium
• CCDs
• Amorphous Silicon

• Phosphor plates

Direct digital sensors









are either a CHARGE-COUPLED DEVICE (CCD)or
COMPLEMENTARY METAL OXIDE SEMICONDUCTOR
ACTIVE PIXEL SENSOR (CMOS-APS).
The CCD is a solid-state detector composed of an array of X-ray or light
sensitive pixels on a pure silicon chip. A pixel or picture element consists of a
small electron well into which the X-ray or light energy is deposited upon
exposure.
The individual CCD pixel size is approximately 40µ with the latest versions in
the 20µ range. The rows of pixels are arranged in a matrix of 512 x 512 pixels.
Charge coupling is a process whereby the number of electrons deposited in
each pixel are transferred from one wall to the next in a sequential manner to a
read-out amplifier for image display on the monitor.
There are two types of digital sensor array designs: AREA AND LINEAR.
Area arrays are used for intra oral radiography, while linear arrays are used in
extraoral imaging. Area arrays are available in sizes comparable to size 0, size
1, and size 2 film, but the sensors are rigid and area for image acquisition.







thicker than radiographic film and have a smaller sensitive area for image
capture. The sensor communicates with the computer through an electrical
cable. Area array CCDs have two primary formats:
Fiber optically coupled sensors and
direct sensors
Fiber optically coupled sensors utilize a scintillation screen coupled to a
CCD. When X-rays interact with the screen material, light photons are
generated, detected, and stored by CCD. Direct sensor CCD arrays capture
the image directly.


X-RAY IMAGING WITH CCD
SCINTILLATOR
- converts x-radiation to photons
(light)
FIBRE OPTIC LAYER
- conducts photons to CCD
- stops x-radiation
CCD
- converts photons to electrons
(charge)
ELECTRONIC CIRCUIT
- amplifies the signal
- converts the analog signal to digital



The complementary metal oxide semiconductor active pixel
sensor (CMOS-APS) is the latest development in direct digital
sensor technology. Externally, CMOS sensors appear identical to
CCD detectors but they use an active pixel technology and are
less expensive to manufacture. The APS technology reduces by a
factor of 100 the system power required to process the image
compared with the CCD. In addition, the APS system eliminates
the need for charge transfer and may improve the reliability and
lifespan of the sensor. In summary, CMOS sensors have several
advantages including design integration, low power
requirements, manufacturability, and low cost. However, CMOS
sensors have more fixed pattern noise and a smaller active area
for image acquisition.

Indirect or Scanned Digital
Imaging


Indirect digital imaging implies
the image is captured in an analog
or continuous format and then
converted into a digital format. As
with any data conversion, this
analog to digital conversion (ADC)
results in the loss and alteration of
information.




Instead of capturing the border that traverses a particular pixel,
the pixel value is averaged. This is called partial volume
averaging. Consequently, many edges are lost or distorted in an
analog to digital conversion. The original indirect digital
imaging technique was to optically scan a conventional film
image (analog) and generate a digital image. Obviously, this
technique required an optical scanner capable of processing
transparent images as well as the appropriate software to
produce the digital image.


Indirect Photostimuable Phosphor
Plates


Imaging using a photostimulable phosphor (PSP) can also be described as an
indirect digital imaging technique. The image is captured on a phosphor plate
as analog information and is converted into a digital format when the plate is
processed. The PSP consists of a polyester base coated with a crystalline halide
emulsion that converts X-radiation into stored energy. The crystalline emulsion
is made up of a europium-activated barium fluoro halide compound (BaFBrEu
2+). The energy stored in these crystals is released as blue fluorescent light
when the PSP is scanned with a helium-neon laser beam. The emitted light is
captured and intensified by a photomultiplier tube and then converted into
digital data. Not all of the energy stored in the PSP is released during scanning
and consequently, the imaging plates must be treated to remove any residual
energy. PSP technology is used for intra oral as well as extra oral imaging


Principle of phosphor plate
imaging


For CCD-based digital radiography, panoramic units and
combination units (in which both panoramic images and
cephalograms can be recorded) are available . Cross-sectional
tomography, which is sometimes useful in the management of
orthodontic patients, cannot be performed with the CCD-based
digital units. Some companies offer to rebuild a conventional
panoramic unit to work with a CCD sensor. If this is done, film
can no longer be used in the system because the CCD receptor
works in a very different manner than the film. Only the Digi Pan
(Trophy Radiology, France) unit allows the CCD-based receptor to
be exchanged with a conventional film cassette system.




CCD receptors are more sensitive to x- rays so
the exposure can be lower with the film. Where
as most of the SP systems recommend using the
same dose as with film


The SP imaging plate systems can, in principle,
work with any available conventional
radiographic equipment because the plates are
installed in the same cassette type as film. The
only difference between SP and film radiography
is that the SP plate replaces the film and the
intensifying screen in the cassette. After exposure
the plate is read into the scanner. The plates are
sensitive to light and highly sensitive to the infra
red light.

Advantages of digital radiography
over conventional radiography are:









Working time from image exposure to image display is reduced .
Chemical processing is avoided, so there are fewer hazards to
the environment and no image errors because of processing.
Exposure to radiation is reduced . Greater dynamic range is
available compared with film; overexposure and underexposure
are less apt to occur, contrast and density can be enhanced, size
can be changed, and colors added.
Cephalometric measurements and analyses can be more easily
performed with the aid of task dependent software.
Storage and communication are electronic, so copies of an image
can be sent to others without losing the original.

CEPHALOMETRIC APPLICATIONS


Cephalometric soft ware is routinely used for case
diagnosis and treatment planning. These applications
replace manual acetate tracings with computer
generated tracings derived from digitized head films.
During the process of digitization, the X-Y coordinates
of cephalometric landmarks are recorded and stored in a
dataset from which various cephalometric
measurements are made. The datasets are also the
starting point for formulation of VTO’S and STO’S .
Cephalograms are two dimensional representations of
three dimensional anatomy.

Cephalometric work flow
DIGITIZATION

DISPLAY

ANALYSIS

TREATMENT PLANNING

HARD COPY


DIGITIZATION






Digitization is a process by which analog
information is converted into digital format
Methods of digitization:
POINT MODE DIGITIZATION,
STREAM MODE DIGITIZATION.


Point mode digitization


It refers to the discrete location of individual landmarks.
The user sequentially locates landmarks in a predetermined order, recording one coordinate pair for each
landmark. A visual representation of cephalogram is
generated by connecting discretely digitized landmarks
with lines or curves. If the digitizing landmarks have
been suitably selected and are in reasonable proximity,
the resulting vector tracing is an effective representation
of the original radiographic contours.


Stream mode digitization


It is a process in which a stream of coordinate pairs is
recorded as the user traces a radiographic contour. The
stream of points is controlled by programmable options;
points may be recorded at a specified number of
coordinate pairs per second or after the cursor has
moved a minimal distance. A large number of adjacent
points are transmitted, and these when joined in a
simple point- to –point fashion, provide a credible
representation of radiographic contours.

With the advent of DIGIGRAPH, work station Sonic
digitization provides a new measuring technique For
registering linear distances. The original concept Was to
eliminate or minimize the need for radiation
Exposure in obtaining lateral cephalometric measurements for
Patients diagnosis. It also includes a module for doing space
analysis utilizing study casts.
In this way comprehensive records for diagnosis and treatment
planning were obtained

SONIC DIGITIZATION


Point mode digitization

Stream mode digitization

More time consuming

Less time consuming

More accurate landmark
locations

Less accuracy

Less technique sensitive

Highly technique sensitive
needs a digitizing cursor or
mouse

Reliable and precision

less reliable

CRITERIA IN SELECTING A
CEPHALOMETRIC SOFTWARE
CONVERGENCE
The software database should integrate cephalometric
digital images both photographic and personal data of
the patient ,dental chart etc. this will basically ensure
that each patient has only one file, and all elements can
be accessed there from . In the ideal scenario it must be
possible to access other office management functions
like scheduling , fee management , correspondence and
the like also from the patient file .

RELIABILITY
Software programmes contain “bugs” causing the
programmes to malfunction or to “crash”. It is typical to
custom made software's, as big companies often have a
β version and is field tested before marketing. It is good
idea to first check with an user before actually buying
the software to check out “run time error”


RELEVENCE
This is a major aspect in evaluating cephalometric
software. Most commercial programmes offer most of
the better-known cephalometric analysis for both lateral
& PA views. Most programmes have a fixed no of
cephalometric landmarks, typically between 50 to 200
and various permutation combinations of planes and
angles based on these which can be user determined.
Some programmes have the facility to define new
landmarks and offer the maximum flexibility in this
regard.

ACCURACY
It is another major aspect, given the error prone nature of
cephalometrics. There are basically two type of inputs
i.e. the digitizer & the scanner. The digitizer is definitely
more accurate as it is a direct transfer, but the digitizer is
a costly piece of equipment. Scanners are cheap but tend
to have magnification problems, but can be easily over
come by placing a calibrated ruler over the cephalogram.
Accuracy of +0.25/ mm is to be ensured in the input
device, whether it be a digitizer or scanner.


ON-SCREN MEASUREMENTS

Most programmes offer an electronic caliper to measure
distances and or angles on the screen.

INTEGRATION WITH DIGITAL
PHOTOGRAPHS
Most of the newer versions of the software permits
superimposition of the digital photograph over the "ceph
tracing" producing a photo cephalometric montage for
clinical visualization. Most often the superimposition is
accomplished by superimposing on the FHP registering
at Po or Or.

IMPORT/EXPORT FEATURE
Most programmes will have an import/export feature
permitting data to be imported and exported. Exporting
of the data to statistical programmes are valuable when
studies are being conducted and batch processing of data
is necessary. Likewise export to graphic display like
charts is also a desirable feature.


WINDOWS BASED CONTROLS
The programming language usually comes with an array of
controls for image editing such as exposure, zoom, quality
adjustment controls etc. Most of the current software's offer image
enhancement features, for adjusting under/over exposure of the
cephalogram.

IMAGE SMOOTHENING
The computer image many years ago when printed used to have a
dotted appearance because of the pixel pattern of the display.
Current programmes use, image smoothing technology called "anti
aliasing" and Bezier curves, for print outs so that print outs
produce outlines that are smooth and more like the manual tracing.
A perusal of the print out will show the adequacy of the soft ware
in this respect.

COLOUR CODING

Color coding is essential for designating cephalograms
taken at different time points. ie; T, and T2 etc. This
should be user determinable.

UPGRADABILITY

computer technology is fast advancing and hence the
soft ware should be upgradeable and the company that
offers it should be around, and capable of performing
the upgrade. Most companies offer up gradation through
internet connectivity, which is very useful for adding
newer versions or downloading “patches” that are
offered from tie to time

COST
Budgetary considerations are also important. A
particular aspect is the licensing policy of the
company for multiple copies/sites for those
having satellite clinics. Over the year prices of
most software’s has dropped and they have
become affordable and is a real time saving tool


DIGITAL PROCEDURE TO
ASSESS FACIAL ASYMMETRY




screening facial skeleton asymmetries and
distinguishing growth discrepancies from simple
rotations of the mandible can be difficult.
Conventional panoramic, frontal, and submental
vertical radiographs, computed tomography (CT)
scans, and magnetic resonance imaging have been
used to determine facial harmony and skeletal
deviation before dental treatment to avoid possible
iatrogenic temporo-mandibular disorders.





A frontal view of the subject's face was recorded with
a digital camera, when useful, the subject's frontal
cephalogram was also photographed. The subject was
positioned face forward with both ears clearly visible
to the photographer.
The mid sagittal reference plane for the frontal
photograph is a vertical line that crossed the midpoint
of a virtual line joining the pupils; it is located with a
ruler on the screen. The vertical plane had to be
perpendicular to the upper border of the computer
screen and the bi pupilar line. If the lines diverged,
the nose and pupils were examined; any deviation of
the nose tip with or without an irregularity in the
transverse or vertical location of the pupils was
considered a sign of possible upper and midface
asymmetry. In such cases, no correction of head
tipping to obtain parallelism between the pupils and
the screen border was attempted.



The reference plane for the frontal cephalogram
was perpendicular to the midpoint of the
intersection of a line joining the 2 lateroorbital
points and the base of the crista galli . In cases of
upper and midface asymmetry, a perpendicular
line drawn from the base of the crista galli on the
tangential projection of the planum sphenoidal
defined the vertical and horizontal coordinates of
the reference planes.

Reference lines used to define midsagittal plane in photographic
(PHP) and radiographic (RHP) images. PHIP is perpendicular at
midpoint of line between pupils; RHIP is perpendicular from base
of crista galli through line joining 2 lateroorbital points.

In cases of severe upper face and midface asymmetry,
sagittal reference plane should follow upper portion of nasal
crest. Horizontal plane is perpendicular to nasal line through
its midpoint.







Each cropped half face was then inverted to obtain an
inverted right or left half face.
Next, either the half faces were merged, or I inverted half
face was superimposed on the original photograph. To
merge, each half face was combined with its inverted half
Both photographs were then compared with the original
full photograph. For superimposition the original
photograph was outlined and transformed as a negative to
produce black contours on a white background. Each
half‑face photograph was also outlined but kept positive
with white contours on a black background





All outlined photographs were made 30% to 40%
less opaque to achieve good superimposition.
Inverted outlined half faces were superimposed
separately on the inverted, contoured, and
negatively transformed originals..
When necessary, cephalograms were examined
by merging the half faces with or without
inversion and with or without transformation
from negative to positive.

Superimposition of transparent original and inverted half faces
helps to define growth deficit. Original outline is black, and
inverted outline is white.

right

left

Electronic digital study models:

Advantages:







Production is easy, routine and predictable.
relatively in expensive to produce
Easy to examine and measure.
Can be mounted /articulated in a variety of ways
to simulate occlusal relationships
True 3D medium that accurately represents
normal/ malocclusions

Disadvantages:






Storage a major problem- because of physical
size and weight
Labor intensive cataloging and retrieving
Easily lost or damaged
Bulky to transfer




Very accurate three-dimensional geometric crown models are
now commercially available from different sources.
Destructive scanning methods (Orthocad from Cadent) slice
the dental impression of the patient as it is scanned producing a
stack of images that are rendered to produce the final model.
Laser systems are also used to directly image the stone model
of patient’s dentition (e-Models from GeoDigm Corp.). A direct
imaging method (OraScanner from OraMetrix) also exists
wherein an intra-oral camera capable of generating highly
accurate 3D crown models is used after applying an opaquing
agent to the teeth. However all these methods provide data on
the tooth crowns only and nothing on root form.



Even so, the only true 3D information routinely used
today is plaster study models of the teeth, and the
models are not accurately merged or calibrated with the
other diagnostic information. Some techniques exist to
create 3D digital study models that can be viewed on a
computer screen. Although these might be accurate
representations of the occlusal anatomy, they still have
the limitation of showing only the crowns and occlusal
surfaces of the teeth, and they cannot show the true
size, location, or relationships of the roots of the teeth
and other anatomy



Current methods to produce 3-dimensional tooth root models
involve conversion from radiographic means (computed
tomography) or creation using computer-assisted design (CAD)
software. The CT lacks detail while the CAD is manually
fabricated and can bear little resemblance to the original. Thinplate splines have been used in morphometrics to define changes
of shape between subjects of the same species . Thin-plate
splines are used to deform a 3D geometric prior model of a tooth
to match 2D patient radiographs, producing a “best-fit” patient
specific 3D geometric polygonal mesh of the tooth.


Peri apical radiograph
of the
second bicuspid;

View of the 3D
prior
geometric tooth;


Both the radiograph
and the
3D model overlaid

Landmarks interactively selected by the user in the 3D prior
model image (+) and the radiograph the overlaid image of the
shell of the tooth 3D model (before fitting)
and the shaded warped image of the fitted 3D model.


Features of a scanner











When scanning photographs or other orthodontic records, we need
resolution of 600 dots per inch (dpi),.
When scanning slides with higher details we need 1200 dots per inch
(dpi).,
When scanning a cephalogram we need min of 150 -300 dpi.
For printing of cephalogram we need to scan in 300 dpi.
For placing pictures in slide shows the resolution of 150 dpi is enough
The scanner should have a transparency adapter to scan slides and
radiographs.
The higher the optical density, the better will be the detail in the dark
part of images, especially the radiographs, a value of 3.4 or above is
ideal. This is measured on a logarithmic scale, so a difference of 1unit
means 10 times better. A scanner with density 3.3 is 2 times better
than a scanner with density 3.0.

LASER SCAN


In a laser scan, a positive model is first created, and laser
light is then reflected from the surface of the model. The
resulting scatter pattern is captured by an optical sensor,
and the original shape is reconstructed with
mathematical algorithms. Laser scanning is relatively
inexpensive, but the process is slow, and the resolution is
limited to about 300 microns. Only 1object can be
scanned at a time; this limits the number of models that
can be processed per day. Laser scanning cannot be used
to accurately scan impressions directly, because
undercuts in the impression create hidden surfaces that
are inaccessible by the laser beam

DESTRUCTIVE SCAN


In a destructive scan, a positive model is created and encased in a
contrasting urethane resin. Paper‑thin slices of the encased object
are incrementally removed by a computer numerical‑controlled
machine cutter. After each increment is removed, a digital picture
of the exposed area is captured. The scanned layers are
electronically combined to recreate the original geometry.
Destructive scanning technology is accurate to about 50 microns,
but the object is destroyed in the process (hence the name). The
preprocessing step (encasing) can be messy, but many objects can
be encased together and scanned at once for efficiency.
Impressions and bite registrations are not typically scanned
directly because (1) rubbery materials such as PVS are difficult to
slice cleanly in the scanner, (2) the wide variety of PVS colors
available makes calibration difficult, and (3) the destructive
process allows only 1 chance to correctly acquire the scan.

WHITE LIGHT SCAN


A white‑light scan is similar to a laser scan, but
white‑light interference patterns (moir6
patterns) are reflected instead of laser light; this
improves resolution and reduces scan time.
Direct line‑of‑sight of all surfaces of the object
is still required for accuracy, so a plaster model
must first be made.


CT SCAN


In a CT scan, a series of digital radiographs of the
object is captured, and the images are electronically
processed to generate an extremely detailed
3‑dimensional reproduction of the object. The scanner
can scan both stone models and impressions (if the tray
is not steel or other high‑density material), because any
undercuts are completely visible to the scanner. Many
objects can be scanned at once for maximum efficiency.
PVS bite registrations can also be scanned.




CT impression scanning is the preferred method
because of its speed and accuracy. To create a virtual
dental model directly from the impression with CT
scanning, the impression is mounted on a platform that
rotates in front of an amorphous silicon x‑ray sensor.
Hundreds of digital radiographs of the impression are
captured as it rotates 360'. These radiographs are
converted to images called sinograms , which represent
the data from a horizontal line of the detector as the part
rotates .




A 16 central‑processing‑unit fiber‑optically linked computing
cluster uses the sinograms and a series of mathematical
algorithms to create 116‑micron thick reconstruction slices of
the object . These slices are stacked electronically and inverted,
and the resulting surface is smoothed to yield a raw electronic
study model




Upon the prescribing clinician's approval of the diagnostic setup
and the treatment animation (staging), each stage of treatment is
converted into a physical model with a machine called a
stereolithography apparatus (SLA). These SLA resin models are
loaded into an automated aligner‑forming system that heats,
forms, and laser‑marks sheet plastic over each plastic model.
These parts are transported on a conveyor belt to a robotic arm
that loads each part into an automated cutting machine for
trimming Automation enables aligner trimming to be completed
in less than 30 seconds. Once trimmed, the part is ejected, and
the aligner is separated, polished, disinfected, and packaged for
shipment .


INVISALIGN
INVISALIGN is the process of straightening teeth in
invisible way without braces.
 Uses a series of clear removable aligners to straighten
teeth without metal wires or brackets.
 Co founded by ZIACHISTI and KELSY WIRTH in
1997
ALIGN TECHNOLOGY:
 The treatment procedure is handled by the computer
technicians in Pakistan – process takes 3 weeks to a
month
 After approval from the orthodontist specifications are
transmitted to the manufacturing plant in Mexico.



Patient gets the first aligner after 6 weeks of the
first visit. Most treatments require 20 – 60
aligners worn for 2 weeks each.
 Should be taken of only for eating and
brushing.
CONTRAINDICATIONS:
 Patients with severe malocclusions
 All children- growing jaws and erupting teeth,
too complicated for the computer to model.



Impressions are
made using
Polyvinyl Siloxane

Impression and bite
send along with a
detailed treatment
plan.

Advanced imaging
technology transforms
plaster models into a
highly accurate 3-D
digital image.

A computerized movie called ClinCheck® depicting the movement of
teeth from the beginning to
the final position is created.

INVISALIGN

Customized set of aligners
are made from these
models, sent to the doctor,
and given to the patient. Pt
to wear each aligner for
about two weeks.

From the approved file,
laser scanning to build
a set Invisalign® uses
of actual models that
reflect each stage of the
treatment plan.

Using the Internet, the
doctor reviews the
ClinCheck file - if
necessary, adjustments to
the depicted plan are made.

DESTRUCTIVE
SCANNING

STEREO LITHOGRAPHIC
MACHINE

INVISALIGN READY
FOR USE

INVISALIGN CUTTER

PACKING OF
INVISALIGN

OraScanner a light‑based
imaging device

Diagnosis and
treatment planning

Obtaining a
Virtual model

SURE SMILE
TECHNOLOGY

Wire bending robot
Producing arch wires

"virtual bracket placement"

and selection of the
www.indiandentalacademy.com sequence and progression
archwire

3D IMAGING


Selected digital imaging devices can produce
digital volumes or 3D images. The volume
element (voxel) is the smallest element of a
3‑ dimensional image. A voxel volume can be
thought of as a 3D array or stack of
bitmapped images, with each voxel having
height, width, and thickness.

Why do we need a three dimensional
record???


In clinical orthodontics it is not enough just to
accurately image the facial shape but essential to
be able to detect changes in the image. When
evaluating the success of appliance therapy it is
also important to be able to distinguish between
changes in morphology due to treatment and
changes due to other factors such as growth and
normal variation.



In traditional cephalometry 3D craniofacial structures
are projected onto 2D radiographic film. This process
creates cephalometric landmarks that do not exist in
patient. These structures are effectively optical illusions
of craniofacial anatomy. Ex are mandibular symphysis,
pterygoid fossa, and the key ridge. Although we refer to
these structures are anatomical landmarks, they are in
fact, artifacts of the cephalometric technique. Another
problem arises when bilateral structures are averaged to
create a unified anatomic outline. Averaging the
structures results in a loss of parasagittal information and
any true asymmetry of the patient is lost.

BASIC PRINCIPLES TO MEASURE IN
THREE DIMENSIONS


There are two geometric strategies for measuring
in three dimensions. They are
ORTHOGONAL MEASUREMENT
MEASUREMENT BY TRIANGULATION


ORTHOGONAL MEASUREMENT


The general characteristic of orthogonal systems is that they
locate the third dimension (Z) by a technique separate from that
used to measure the other two dimensions (X and Y). In most
measurements the object to be measured is sliced into layers,
either physically or optically. Ex: serial section of histology and
pathology. Here the specimen is sliced into a number of layers of
known thickness. The X and Y dimensions are measured on the
slice surface and the Z Dimension is measured by tallying how
many slices into the specimen lies. The common feature of all
orthogonal measuring systems is that X and Y distances are
captured by some method other than that used for capturing Z.
Ex: CT scanner

COMPUTED TOMOGRAPHY
Computed to-mography (CT) machines
acquire image data by using either a single
narrow x‑ ray beam or a thin, broad,
fan‑ shaped x‑ ray beam. These beams rotate
around the patient in a circular or spiral path
as the patient moves through the scanning
machine or as the rotating beam passes over
the patient.


CT SCAN


The advent of computerized transverse axial scanning,
computed tomography, or CT greatly facilitated access to the
internal morphology of soft tissue and skeletal structures.
Conventional CT scanning is accomplished by acquiring a series
of individual images. Typically, the images represent crosssections through the body. The image slices are from 1 to 10
millimeters thick and the distances between them are from 1 to
10 or 20 millimeters. Projection data are acquired and
reconstructed into images as the patient is moved incrementally
through the CT gantry (that is, an image is obtained; the patient
is moved to the next scanning position, and the next image is
obtained). CT scans possess no magnification errors caused by
geometric distortions. Such errors are common in conventional
radiographs.

COMPUTED TOMOGRAPHY
Parts of the Equipment;
1.
Scanner ( movable x
ray table + gantry)
2.
Computer system
3.
A display console




A limitation of conventional CT is that although it has a high
degree of accuracy within individual slices, it has relatively low
between-slice accuracy even with relatively narrow collimation
(2 mm) and no interslice gaps. CT scans avoid the
superimposition of structures and are, therefore, more desirable
than conventional radiography as a morphometric tool. Since its
inception, computed tomography has provided quantitative
measurements for many different biological systems and has
been used in pre- and post-surgical mapping procedures, the
evaluation of developmental and regressive dental
abnormalities, facial trauma, and temporo mandibular joint
disorders.

RADIATION DOSAGE FOR CT

Radiation dosage

1.536 rad for
a single section
1.8432 rad for

multiple sections
Estimated dose to the centre of the condyle
with CT is 180mR

NEW TOM SCANNER
The NewTom 900 scanner uses a cone‑ shaped x‑ ray
beam that is large enough to encompass the region of
interest. This type of beam uses the x‑ ray emissions
very efficiently, thus reducing the absorbed dose to
the patient. This type of beam also allows for the
acquisition of the image data in 1 revolution of the
x‑ ray source and detector without the need for patient
movement. These attributes make this system more
efficient and mechanically simpler than others, and
thus it can be designed for specific purposes, such as
imaging the maxillofacial region.

The NewTom 9000 volume imaging technique uses the
principle of tomo synthesis or cone‑ beamed CT because of the
shape of the x‑ ray beam
In a single scan, the x‑ ray source and a reciprocating x‑ ray
sensor rotate around the patient's head and acquire 360
pictures (1 image per degree of rotation) in 17 seconds of
accumulated exposure time. The entire maxillofacial volume
(13‑ cm‑ diameter field of view) is enraged, and the patient
receives an absorbed dose similar to a peri apical survey of the
dentition.


The 360 acquired images undergo a
primary reconstruction to
mathematically
replicate the patient's anatomy into
a single 3D volume that comprises
voxels similar to those of a Rubik's
cube. Each voxel is small
(0.29 mm for each of the cube faces),
thus the image has a relatively high
resolution.






The New Tom 9000 Volume scan has been extremely valuable for
investigating impacted teeth, temporo mandibular joints, implant
planning, and pathology.
Three-dimensional scans can give valuable information about
areas of the dentition, such as the position of the maxillary incisor
roots relative to the lingual cortical border of the palate to plan
retraction, the amount of bone in the posterior maxilla available
for distalization, the amount of bone lateral to the maxillary
buccal segments available for dental rather than skeletal
expansion, airway information on the pharynx and nasal passages,
maxillary root proximity to the maxillary sinus, and the position
of the mandibular incisor roots in bone.






These scans also allow 3D visualization of bony
defects and supernumerary teeth in patients with cleft
lips or palates.
axially corrected tomograms of the temporo
mandibular joints can be obtained from the same scan.


Magnetic Resonance Imaging
Principles:
Magnetism is a dynamic invisible
phenomenon consisting of discrete
fields of forces.
Magnetic fields are caused by moving
electrical charges or rotating electric
charges.
Images generated from protons of the
hydrogen nuclei.
Essentially imaging of the water in
the tissue.







Magnetic Resonance Imaging

The technique is based on the presence of specific magnetic
properties found within atomic nuclei containing protons and
neutrons,
Inherent property of rotating about their axis
Causes a small magnetic field to be generated around the
electrically charged nuclei.






When dipoles exposed within a strong electric field
Orientation in response to the field
Depending on density and spatial relation
Signal interpreted and image produced


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


Equipment;
1.
The Gantry ;houses the
patient. Patient is
surrounded by magnetic
coils
2.
Operating console ;
where the operator
controls the computer
and scanning procedure
3.
Computer room
network.

The objectives of MRI imaging of the TMJ are;











Determine relationship between the disc and Temporal and
mandibular components of the TMJ
Detect inflammation, hematoma and effusion for the soft tissue
components
MRI clearly differentiates the soft tissue components .
Short and long echo imaging of the TMJ enables identification
of the positional relationships between the disc and the condyle
The contrast and appearance of images can be varied by
selecting the field strength and other factors.
Special head holders have been designed which facilitates
orientation of the patient and reduces patient movement during
imaging



Complications;

Magnetic forces and radio waves - not know to produce any
biological side effects in man.
Non invasive technique and can be used in most patients.


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.*


















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

Short comings
Inability to identify ligament tears or perforations
Dynamics of tissue joint not possible
Cannot be used in patients suffering from claustrophobia.


The limiting factor in the use of MRI in
Orthodontics


Apart from economic cost, the functional modality of
MRI depends on the presence of large numbers of
hydrogen nuclei in the tissues being imaged. Because
hard tissues such as bone, enamel and dentin contain few
if any free hydrogen nuclei, the use of this diagnostic
tool is restricted in orthodontics to the visualization of
the cartilaginous components of temporo mandibular
joint


SPIRAL CT


Recently, a new CT technique, spiral CT (SCT or volume
acquisition CT), has been developed. This method has several
advantages over standard CT imaging. By employing
simultaneous patient translation through the x-ray source with
continuous rotation of the source-detector assembly, SCT
acquires raw projection data with a spiral sampling locus in a
relatively short period. Without any additional scanning time,
these data can be viewed as conventional trans axial images, as
multiplanar reconstructions, or as three-dimensional (3D)
reconstructions. Such images provide an opportunity to obtain
accurate images at any arbitrary location within the volume
data set.



The unique arrangement of the gantry and rotating x-ray source
assembly radically reduces scan times. Partial body scans can
be completed during a single breath hold. With standard
incremental CT, small objects can be missed or their detection
compromised if the patient's degree of inspiration and
expiration varies from scan to scan. Moreover, multi planar and
3D image reconstructions of structures from standard
incremental CT data are degraded by motion-induced
misregistration artifacts


MEASUREMENT BY TRIANGULATION


Systems that measure by triangulation analogize
the geometry of mammalian stereoscopic vision.
Typically such systems view the object to be
measured from two positions in space and
capture images from both positions on film or
some digital medium either simultaneously or in
rapid succession. Both biplanar and coplanar
stereo systems are examples of triangulation
geometry.



All the 3D measuring systems must be able to identify
the same anatomical structure in all three dimensions.
To meet this obvious requirement is frequently not as
easy as it sounds, especially in stereoscopic X-ray
systems. The greater the separation between the X-ray
sources for two of the images of any stereo pair, the
more difficult is to identify the same landmark in both
images. When other factors are equal, the most powerful
geometric solution for any stereoscopic measurement
occurs when the angle between the two emitters and the
object being imaged approximately 90 degrees.




However most skull structures of orthodontic
interest look very different, when viewed from
the lateral and frontal projections. Hence the
trade off between coplanar and biplanar methods.
In effect, the coplanar method sacrifices some of
the mathematical power of the 90- degree ray
intersection of the biplanar system to obtain a
pair of images on which it is possible to locate
the same physical point on both images with
reduced error.



Stereophotogrammetry has evolved from old photogrammetric
techniques to provide a more comprehensive and accurate
evaluation of the captured subject. This technique uses one or
more converging pairs of views to build up a 3D model that can be
viewed from any perspective and measured from any direction.
The earliest clinical use of stereophotogrammetry was reported by
Thalmann - Degan in 1944 who recorded change in facial
morphology produced by orthodontic treatment.


Note that the film
plane of the camera
is parallel to the surface
of the ground.

The plane flies some desired
distance and another photograph
is taken, again with the camera
pointing straight down

figure precisely analogizes
with each position of the
aircraft being the
equivalent
of one eye.

COPLANAR STEREO CEPHALOMETRY

Schematic two-dimensional
representation distance
The region of terrain
a perpendicular is dropped
between the the blue lines
captured by the camera
along the central axis of
meeting at the top is less
in each of the two
the camera from each of
than the distance between
www.indiandentalacademy.comlocations is shown..
the red lines meeting at the bottom . the two viewing positions

FACIAL IMAGE ACQUISITION
A standard stereo camera setup is used to capture the facial
image pairs. The two cameras
are attached to a specially
designed stereo base which sits
on a tripod. Each camera can
translate and rotate along this
base so that the convergence
angle, baseline separation and
height are adjustable. Digitally
controlled slide projectors are
used to flash separate random
texture and structured light
patterns onto the subject's face.



The CCD cameras used have a resolution of 768 x 576
pixels and these are digitized in a frame grabber able to
store up to sixteen 8 bit grey level images in RAM. The
cameras are pre-calibrated using precisely defined
circular control point targets.



Random texture is used to aid the search for point
correspondences in the matching phase. Without this
large areas of the face are relatively featureless and
stereo-correlation produces many false matches.





Image pairs acquired using texture (IL, IR) and structured
light (SL, SR) projection are taken. Using digitally
controlled switching between cameras and projectors, the
time between capture is less than one second. Any slight
subject movement is unimportant since the structured light
pair is used only at the image partitioning stage.
Clearly, it is not possible to capture the entire face with only
one stereo pair. An additional stereo pair for the left and
right sides of the face, is required followed by a step to
register the three facial models.

Image light
projection

SL projection

How is 3D information about the
surface of the face obtained?

Ranging the location of two
representative points on the
face from a pair of cameras
located a known distance
apart.

A known pattern is
projected upon the
subject from a light
source (A) and
photographed by a digital
camera (B)



In a more recent development, a second digital camera
(C), mounted between the fixed projector (A) and
digital camera (B) captures a true-color image a few
milliseconds after the primary image. The 3D
information from the primary-camera-light-projector
assembly is synchronized with the 2D pixel map from
Camera C and is stored in a kind of look-up table. In
this way, the location of each pixel on the monitordisplayed image from Camera C uniquely identifies the
three dimensional coordinates of a particular point on
the surface map generated by Camera B and its
associated projector (A).





A dedicated computer chip built into the
digital camera has the ability to distinguish
different frequencies of light and hence
can tell, from the color of each light ray,
the direction in which that particular ray
has traveled from the light projector.
The projected pattern falling upon the
subject is photographed by Camera 1
which is mounted a known distance from
the Projector. When viewed from the
perspective of the Projector, the shape of
the projected pattern remains unaltered
regardless of the shape of the object it falls
upon

The reconstructed
representation of the face can
be rotated on a standard
computer monitor and the 3D
coordinates of any visible
point can be captured by
pointing and clicking with a
standard mouse or other
similar device



The system is capable of generating dense 3-D surface maps by
an image partitioning strategy and stereo
matching phase, The accuracy of euclidean reconstruction
has been established by analyzing images of a plaster cast
model of a human face containing 13 simulated facial
landmarks. This model was placed at nine different orientations
and locations within the calibration space. Stereo image pairs
were captured at each pose and the corresponding landmark
features were detected using a centroid detection algorithm.
These landmark points were then reconstructed to produce nine
independent 3-D point sets. The point sets were then registered
to a common coordinate frame using a standard approach, and
the mean landmark positions determined.

Stereo pairs of plaster cast model of human face bearing 13 simulated
landmarks using for estimating reconstruction accuracy.

AUTOMATIC 3-D LANDMARK
EXTRACTION


The method developed for automatic facial shape
change analysis is a combination of stereo-assisted
feature detection and morphometric techniques. One
advantage of using a stereo-based image acquisition
system is that the surface texture is captured which
facilitates robust 3D landmark extraction. Coupled
with this, the use of morphometric techniques provides
a geometrically and statistically meaningful way to
characterize the shape change.



An active shape model (ASM) is a statistically-based technique
for building geometric models of the shape and grey level
appearance of a variable object in order to automatically locate
new instances of the object in 2D images. It has been used
successfully to locate the main facial features in images
obtained under widely varying conditions . This technique is
now extended to 3-D facial landmark extraction by using stereo
correspondence search and surface map interpolation.




One-hundred and seven (107) landmark points in the stereo image were
defined to represent the facial features. Some points corresponded to true
landmarks, such as corners of eyes and mouth, and other points were
generated automatically by sampling at equally spaced intervals along the
hand digitized contour. They were manually digitized on 25 training images
from the facial database and aligned to compute a mean shape and build a
point distribution model (PDM). Principal component analysis on
the covariance matrix of deviations from the mean shape was carried out to
yield a set of basis vectors describing the main modes of shape variation. At
the same time, the grey level appearance model at each shape point was
constructed in the same way as for the PDM. This completes the ASM training
procedure.


METHODS OF 3D FACIAL IMAGING:
 LASER SCANNERS
 STRUCTURED LIGHT PATTERNS
METHODS OF THREE DIMENSIONAL CRANIO
FACIAL SKELETAL IMAGING:
 COMPUTED TOMOGRAPHY
 NEWTOM
METHODS OF 3D INTRA ORAL DENTAL IMAGING:
 INTRA ORAL 3D CAMERA
METHODS OF CAPTURING MANDIBULAR
MOTION IN 3D:
 ULTRA SONIC MOTION CAPTURE

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Recent advances digital imaging /certified fixed orthodontic courses by Indian dental academy

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