Holography in orthodontics

INTRODUCTION
Holography is the name given to the
process of wave front reconstruction and
comes from the Greek words ‘holos’,
meaning whole and ‘gramma’ meaning
message. So it gives whole message.
www.indiandentalacademy.com

Holography is a photographic technique
for recording and reconstructing images in
such a way that the three-dimensional
aspect of an object can be retained.
The recorded image is called a hologram.
In recent years, holography has been
used increasingly in biomechanical
research in dentistry, especially in
orthodontics.

METHOD OF RECORDINGMETHOD OF RECORDING
Experimental apparatus consists of a
flat optical table with air suspension.
The illumination for recording and
reconstruction of holograms was
provided by a 15 mW He-Ne laser.

The laser, the optical components for
steering and shaping of object and
reference beams, the experimental
model, and the photosensitive
material used for recording of
holograms were rigidly mounted on
top of the optical table by means of
magnetic bases.

Holographic set-up

The highly coherent and
monochromatic light from
the laser source is split into
two beams by means of a
beam splitter .

One of the beams is directed by
mirrors, expanded by means of a
spatial filter (microscope objective
and a pinhole assembly), and is
used to illuminate the experimental
model to be recorded.

Holographic set-up
a: Laser.
b: Beam splitter.
c: Beam expander.
d: Holographic plate.
e: Spatial filter.
ob: Object beam.
rb: Reference beam

This beam, referred to as the object
beam, is modulated by a reflection from
the experimental model and carries all the
information about the instantaneous
condition of the it’s surface.
The second beam is known as the
reference beam and is not modulated by
any intervening object.

If both of these beams are
allowed to impinge on some
kind of a surface, they will
produce a set of fringes, on
that surface, as a result of their
mutual interference.

The fringe pattern resulting from the
Superposition of two beams can be
recorded in the photographic emulsion
which, upon photographic processing,
becomes a hologram.
The holographic plate consists of a
highly sensitized emulsion that coated
on a glass plate.

Double exposure holographic
interferometry
First the normal state of the object was
recorded.On the same record plate before
processing, another exposure
corresponding to the deformed portion of
the object
(for example: skull with an activated
appliance in palate)was recorded.

This double exposed plate was processed
after reconstruction, one corresponding to
the original position and another
corresponding to the deformed position of
the experimental model.
These two reconstructed image waves
interfered giving rise to an image with
number of bright and dark fringes on the
image.

Bright & dark fringes on the image
From the fringe pattern the magnitude and direction of displacement
can be calculated.

Holography being recorded on
macerated human skull

Upon recording holography,the
plates were developed & the
images were recorded with a
camera in 2-Dimensional
photographs.

INTERPRETATION OF RESULTS
Holographic interpretations can be
done in two ways.
1.qualitative analysis:
By direct observation of the
fringes.

2. Quantitative analysis:
By making measurements either by
directly counting the no. of fringes or
fringe spacing on the hologram or by
making measurements on the
photographs
The interpretation of photos can be done
by following a method put forward by
RYSZARD J PRYPUTRIEWICZ (1969).

A grid of 3 horizontal & 3 vertical
lines which represent the
projections, if the planes in
which the deformations &
displacement of the sutures
were measured,were drawn on
the photo of interferograms.

A-In the horizontal
plane
B- In the vertical plane

The displacements were calculated from the
no. of fringes using the following formula.
nλ
d = -------
2
Where d = Displacement in mm.
n = no. of fringes.
λ = He- Ne laser wavelength = 632.8×10¯ 9
nm
----------
2

INTERPRETATION OF PHOTOS

THE INITIAL REACTION OF A MACERATED HUMAN SKULL CAUSED
BY ORTHODONTIC CERVICAL TRACTION DETERMINED BY LASER
METROLOGY
1982 Jan Kragt, Dute,AJO
Forces were applied to the maxilla of a
macerated human skull in a backward
direction 10 degrees below the occlusal
plane.
The skull was fixed to a heavy metal
support at the occipital and parietal
bones.

These forces were applied near the first
permanent molars via a rigid stainless
steel bar, which was fitted to a cast-
metal splint attached to the palatal
surface and buccal region of the
maxillary arch.
Using a holographic configuration,
double-exposure holograms were
made.

Forces were increased step by step

Fringe shifts in different points of the
hologram were measured and the x, y, and
z components of the displacement were
calculated for eight points located on
various bones of the skull.
Viewed from the frontal, force application to
the maxilla resulted in a downward and
backward rotation.

A, Frontal section with a force increase from 2.00 to 2.50 N per side. B, Left lateral
section with a force increase from 2.00 to 2.50 N per side. C, Frontal section with a force
increase from 6.25 to 7.25 N per side. D, Left lateral section with a force increase from
6.25 to 7.25 N per side. www.indiandentalacademy.com

INITIAL EFFECTS OF ORTHOPEDIC FORCES - A STUDY OF
ALTERATIONS IN THE CRANIOFACIAL COMPLEX OF A MACERATED
HUMAN SKULL OWING TO HIGH-PULL HEADGEAR TRACTION
Kragt and Duterloo 1982 Jan AJO
The initial reaction of components of the
craniofacial skeleton of a macerated
human skull was studied after high-pull
headgear traction. The applied forces
were increased step by step from 0.5 N to
3.25 N per side
(1N = 100 grams).

Laser holography was used for
measuring displacements in three
dimensions in seventeen indicator
points on the skull. These points
were located near sutures or on the
outer surface of individual bones.

Holographic measurement of incisor extrusion
(Burstone, Every, and Pryputniewicz 1982 Jul AJO )
A technique based on pulsed laser hologram
interferometry was used to study the
dynamics of incisor extrusion.
Maxillary central incisors of four subjects
were loaded with forces acting along the long
axis of the tooth, and the resulting motions
were measured noninvasively in three
dimensions. The incisor translations and
rotations were used to determine centers of
rotation. www.indiandentalacademy.com

Mechanical reactions of facial skeleton to maxillary expansion
determined by laser holography
Pavlin and Vukicevic AJO 1984
The experiments were carried out on a
macerated human skull which had a
perfectly preserved, normally aligned
maxillary dental arch and intact alveolar
processes.
The soft palatal and periodontal tissues
were reconstructed with a semielastic
material.

The specimen was loaded gradually by
widening of a split acrylic appliance with
an expansion screw.
Interferograms were taken simultaneously
on the left and right sides of the maxillary
complex, using the 10 mV He - Ne laser
and the double-exposure method.

expansion
screw

Interferograms
are being taken

A STUDY DONE IN OURDEPARTMENT
USING HOLOGRAPHY
An in-vitro study was carried out in our
department regarding mechanical reaction
of facial skeleton to rapid palatal
expansion devices using laser
holography,which was done by using the
facility available in ANNA UNIVERSITY.

A freshly macerated human skull taken & then
fastened to heavy metal framework.With the
help of preformed bands hyrax appliance
secured and holography was performed.Then
spring jet appliance secured and holography
done,up-on activations.

hyrax appliance secured

spring jet appliance

Experimental determination of the center of resistance of the upper
first molar in a macerated, dry human skull submitted to horizontal
headgear traction
Dermaut, Kleutghen, and De Clerck -1986 Jul AJO
Laser speckle interferometry, recently
developed for noninvasive measurement of
small displacements (microns), was used to
study the movement of maxillary molars
submitted to extraoral traction.
Using an antenna-headgear at different
horizontal levels, loadings of 700 gm were
applied perpendicular to the long axes of
these teeth. www.indiandentalacademy.com

ANTENNA-HEADGEAR

Bodily movement was observed when
the traction line passed slightly
occlusal to the trifurcation of the roots.
Therefore, the center of resistance of
the upper molar was experimentally
localized at this level.

The center of resistance of anterior teeth during intrusion using the
laser reflection technique and holographic interferometry
Vanden Bulcke, Dermaut, Sachdeva, and Burstone AJO1986 Sep
The aim of this investigation was to define the
location of the center of resistance of various
consolidated units of the maxillary anterior
dentition using a dry human skull when
subject to intrusive forces.
The units studied consisted of
(a) two central incisors,
(b) four incisors, and
(c) six anterior teeth.www.indiandentalacademy.com

splints

 The objective of this study was to determine the
location of the center of resistance for different rigid
units of the anterior maxillary dentition when intrusive
forces were applied to them.
 The experiments were performed on a dry human
skull
 skull stabilized
 Araldit, displaying elastic properties somewhat
similar to the periodontium was used to fix the teeth
into the sockets.

 Silicone impressions of skull dentition taken, working
models made, and splints fabricated.
 The splints were cast in chromium-cobalt alloy.
 The splints were rigidly cemented to the teeth with zinc
oxyphosphate.
 V-shaped hooks positioned along the splints served as
points of attachment for force application
 Two forces, equivalent in magnitude and perpendicular to
the occlusal plane, were generated by dead weights and
applied at points symmetric to the midline. At the midpoint
of the segment (that is, between the two central incisors),
only a single force was applied.www.indiandentalacademy.com

Holograms as substitutes for
study casts
A hologram not only provides two-
dimensional information about an object,
as found in photographs, but also depth
information. This transforms the image
of the object into three dimensions.

Plaster casts are mainstay of clinical
orthodontic records since many years.
DISADVANTGES
 Fragile & prone for fracture
 Bulky & expensive to store and
transport.
 Need to keep for long periods.

LEGAL REQUIREMENTS
The minimum legal requirement in British
hospitals is to
 retain study casts for 8 years after
completion of treatment,
 or until the patient reaches the age of 25
for treatment carried out on minors
 or until the patient attains age of 25
years ,for medico legal reasons.
In U.S, the patient records should be kept until
10 years after orthodontist retires from practice.

Advantages of holograms
Schwaninger et al (1977) proposed potential
advantages of holograms as a substitute for study
casts.
They are
 Holograms are very resistant to damage.
 Better suited to transport by post.
 Can be stored with patient’s clinical records.
 Accurate measurements such as intercanine
width can be measured.

HOLOGRAMS
The
chairside
viewer
holographic
camera
HOLOGRAM

In a study by Harradine et al ( 1990 Aug
AJO) with four clinicians and 56 patients,
three of the clinicians found the
holograms to be acceptable alternatives
to study casts in routine clinical
orthodontic practice.
Current holographic cameras enable
those who are not experts to produce
holograms very simply, but careful clinical
and laboratory techniques are required to
ensure that these holograms correctly
record the occlusion.www.indiandentalacademy.com

disadvantages
 significant consideration is the
consequence of incorrect occlusion of
the models when the holograms are
being made.
 Once made, a hologram cannot be
adjusted as a set of study casts .

Conclusion
Holography is a remarkable tool
with extensive research
potential for clinical application.
The further enlightenment with
this tool is a question, which has
to yield positive results.

Holography in orthodontics

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (8)

Similar to Holography in orthodontics

Similar to Holography in orthodontics (20)

More from Indian dental academy

More from Indian dental academy (20)

Recently uploaded

Recently uploaded (20)

Holography in orthodontics