Advanced imaging as orthodontics Aids

Advanced Imaging AsAdvanced Imaging As
Orthodontic AidsOrthodontic Aids
www.indiandentalacademy.comwww.indiandentalacademy.com

Advanced Imaging As Orthodontic AidsAdvanced Imaging As Orthodontic Aids
IntroductionIntroduction ..
Historical perspective on imaging in orthodontic.Historical perspective on imaging in orthodontic.
Imaging goals and strategiesImaging goals and strategies
General imaging goalsGeneral imaging goals
Clinical imaging goalsClinical imaging goals
Conventional Craniofacial Imaging MethodsConventional Craniofacial Imaging Methods
 Hard tissue ImagingHard tissue Imaging ::
Cephalometric radiographyCephalometric radiography
Panoramic projectionsPanoramic projections
Periapical projectionsPeriapical projections
Tomography / C T ScansTomography / C T Scans
Corrected Tomography of the TMJCorrected Tomography of the TMJ
 Soft tissue Imaging:Soft tissue Imaging:
C TC T
MRIMRI
ArthrographyArthrography
Contemporary and Evolving Imaging TechniquesContemporary and Evolving Imaging Techniques
Digital ImagingDigital Imaging
Volumetric imagingVolumetric imaging
Structured light imagingStructured light imaging
Laser scanningLaser scanning
StereophotogrammetryStereophotogrammetry www.indiandentalacademy.comwww.indiandentalacademy.com

Contemporary and Evolving Imaging Techniques
 Digital Imaging
 Volumetric imaging
 Structured light imaging
 Laser scanning
 Stereophotogrammetry
Current status of Three Dimensional Facial Imaging.
 Dental crowns / Dentition
 Tooth roots
 Craniofacial skeleton
 Face
 Facial expression
Image Calibration and Registration.
Database.
Clinical utility and implications
 Orthodontic Records
 TMJ evaluation
 Orthodontic Boundary Condition
 Implants
 Impaction
 Esthetics
 Orthognathic Surgery and Distraction Osteogenesis
Summary.
Bibliography. www.indiandentalacademy.comwww.indiandentalacademy.com

IntroductionIntroduction
 Images of Craniofacial region are important components of the orthodonticImages of Craniofacial region are important components of the orthodontic
patients records attempted to achieve the accurate replication or portrayalpatients records attempted to achieve the accurate replication or portrayal
of the anatomic truth.of the anatomic truth.
 Anatomic truths are the accurate 3-dimensional anatomy, static and inAnatomic truths are the accurate 3-dimensional anatomy, static and in
function as it exist in vivo.function as it exist in vivo.
 Imaging is most commonly used by orthodontist to measure and recordImaging is most commonly used by orthodontist to measure and record
the size & form of craniofacial structures.the size & form of craniofacial structures.
 Imaging presently used in practice have been adopted in an effort toImaging presently used in practice have been adopted in an effort to
balance the anticipated benefits with associated cost & risks to the patient.balance the anticipated benefits with associated cost & risks to the patient.
 Because of these considerations, orthodontist routinely uses an array of 2-Because of these considerations, orthodontist routinely uses an array of 2-
D anatomy of the craniofacial region.D anatomy of the craniofacial region.

 For example:For example:
 Anatomy captured by site-specific images including panoramicAnatomy captured by site-specific images including panoramic
and periapical radiographs and photographs for teeth;and periapical radiographs and photographs for teeth;
Tomography & MRI for TMJ & Cephalometric radiograph for theTomography & MRI for TMJ & Cephalometric radiograph for the
facial skeletonfacial skeleton
 Although site-specific imaging enhances detail, it also segmentsAlthough site-specific imaging enhances detail, it also segments
anatomy by creating a patchwork of separate images toanatomy by creating a patchwork of separate images to
represent an entire structure. This process of segmentingrepresent an entire structure. This process of segmenting
anatomy results in related anatomic structure beinganatomy results in related anatomic structure being
differentiated arbitrarily based on the point of view selected anddifferentiated arbitrarily based on the point of view selected and
associated imaging geometry of that view.associated imaging geometry of that view.
 This causes difficulty if not impossible responsibility on theThis causes difficulty if not impossible responsibility on the
clinician to reconstruct the true anatomy mentally.clinician to reconstruct the true anatomy mentally.

 Limitations of this approach have resulted in the developmentLimitations of this approach have resulted in the development
of standardized analyzing methodology that can be used toof standardized analyzing methodology that can be used to
describe the anatomic information contained in the images.describe the anatomic information contained in the images.
 This analysis uses linear and angular measurements that areThis analysis uses linear and angular measurements that are
generated manually and with computer assistance.generated manually and with computer assistance.
 These measurements are often incorporated into researchThese measurements are often incorporated into research
database for use in predicting growth and for evaluatingdatabase for use in predicting growth and for evaluating
treatment outcomes.treatment outcomes.
 Although cases of imaging in orthodontic has been adequate,Although cases of imaging in orthodontic has been adequate,
the fulfillment of the ideal imaging goal of replicating thethe fulfillment of the ideal imaging goal of replicating the
anatomic truth has been limited by the available technology, theanatomic truth has been limited by the available technology, the
quality of the databases used to generate data and by traditionquality of the databases used to generate data and by tradition

 The process of imaging technology and the development ofThe process of imaging technology and the development of
numerically controlled mathematical models makes it possiblenumerically controlled mathematical models makes it possible
to create 3 – D observation of maxillofacial structures.to create 3 – D observation of maxillofacial structures.
 Computer assisted simulations in medicine are closely relatedComputer assisted simulations in medicine are closely related
to the progress in industrial technology.to the progress in industrial technology.
 Computer assisted manufacturing (CAM), computer assistedComputer assisted manufacturing (CAM), computer assisted
designing (CAD), and finite element methods (FEM) weredesigning (CAD), and finite element methods (FEM) were
created to assist the manufacturing industry after World War II.created to assist the manufacturing industry after World War II.
 In medicine the utilization of digital modalities began when theIn medicine the utilization of digital modalities began when the
company, EMI developed X-ray CT in 1972, thus computercompany, EMI developed X-ray CT in 1972, thus computer
assisted simulations were invented.assisted simulations were invented.

 The advantages of simulation areThe advantages of simulation are visualization, repetition,visualization, repetition,
feedback and prediction.feedback and prediction.
 Simulated results based on collected data & logical calculationsSimulated results based on collected data & logical calculations
support diagnosis, treatment planning and assist the actualsupport diagnosis, treatment planning and assist the actual
operation.operation.
 Dental CAD/CAM programmes for prosthetic & orthodonticDental CAD/CAM programmes for prosthetic & orthodontic
simulations are commercially available.simulations are commercially available.
 Recently, dental CT has also been developed toRecently, dental CT has also been developed to
provide 3-D evaluation of the patient.provide 3-D evaluation of the patient.
 It is the time to establish new simulation methods thatIt is the time to establish new simulation methods that
will be utilized for more accurate orthodontic diagnosiswill be utilized for more accurate orthodontic diagnosis
& treatment modalities.& treatment modalities.

 At present much of the experience and knowledge in C-F health care isAt present much of the experience and knowledge in C-F health care is
documented with 2-D records a qualitative assessment. Within this systemdocumented with 2-D records a qualitative assessment. Within this system
are constraints and limitations that have bearing on outcome assessment,are constraints and limitations that have bearing on outcome assessment,
criteria for success, cost and other parameters of care. If the overall goal iscriteria for success, cost and other parameters of care. If the overall goal is
to strive for improvements in the quality, efficiency and accessibility of C-Fto strive for improvements in the quality, efficiency and accessibility of C-F
care, there is overwhelming need for accurate a effective imagingcare, there is overwhelming need for accurate a effective imaging
modalities.modalities.
 At current status CT & MRI are most commonly utilized in complex C-F careAt current status CT & MRI are most commonly utilized in complex C-F care
while more routine care such as dental treatment rely almost entirely on 2-Dwhile more routine care such as dental treatment rely almost entirely on 2-D
photographs and radiographs.photographs and radiographs. www.indiandentalacademy.comwww.indiandentalacademy.com

 In both the situations, the various imaging modalitiesIn both the situations, the various imaging modalities
are collected and assembled by the clinician toare collected and assembled by the clinician to
supplement clinical examination record.supplement clinical examination record.
 The 2-D images have certain shortcomings such as:The 2-D images have certain shortcomings such as:
Lack of perspectiveLack of perspective
Effect of projectionEffect of projection
SuperimpositionSuperimposition
Imaging artifactsImaging artifacts
Information voidsInformation voids
Lack of motion.Lack of motion.

Historical Perspective On Imaging In OrthodonticsHistorical Perspective On Imaging In Orthodontics
 X-ray radiation was invented byX-ray radiation was invented by Wilhelm ConradWilhelm Conrad
RoentgenRoentgen, Rector of Institute of Physics, Wurtzburg,, Rector of Institute of Physics, Wurtzburg,
Germany, on 8th November 1885. About 36 year’s laterGermany, on 8th November 1885. About 36 year’s later
traditional cephalometry in 2-D known astraditional cephalometry in 2-D known as
Roentgenographic cephalometry was introduced toRoentgenographic cephalometry was introduced to
dental profession bydental profession by Broadbent and BoltonBroadbent and Bolton..
 He noted fluorescence of platino cyanide plates adjacentHe noted fluorescence of platino cyanide plates adjacent
to a cathode ray tube. He placed his hands b/w the tubeto a cathode ray tube. He placed his hands b/w the tube
and the plate he was able to cast a shadow and perceiveand the plate he was able to cast a shadow and perceive
not only the hand in outline but also its bones.not only the hand in outline but also its bones.
 Roentgen introduced silver halide film as a mean toRoentgen introduced silver halide film as a mean to
record his experimental findings; however the low X-rayrecord his experimental findings; however the low X-ray
output & low sensitivity of the film made this a relativelyoutput & low sensitivity of the film made this a relatively
impractically slow procedure for diagnostic imaging.impractically slow procedure for diagnostic imaging.
Initial usages of X-radiation in medicine were primarilyInitial usages of X-radiation in medicine were primarily
fluoroscopic.fluoroscopic. www.indiandentalacademy.comwww.indiandentalacademy.com

 Medical fluoroscope was developed byMedical fluoroscope was developed by ThomasThomas
EdisonEdison,, William SteuberWilliam Steuber, a photographer from, a photographer from
Louisville, and was changed byLouisville, and was changed by George EastmanGeorge Eastman inin
1896 with developing introral X-Ray films as Edison’s1896 with developing introral X-Ray films as Edison’s
fluoroscope as it was obviously too large to place influoroscope as it was obviously too large to place in
the mouth.the mouth.
 About 90 years later,About 90 years later, Francis MouyenFrancis Mouyen, then a dental, then a dental
student at the University of Toulouse, France, decidedstudent at the University of Toulouse, France, decided
that the several flights of stairs b/w the Endodonticsthat the several flights of stairs b/w the Endodontics
department and the X-ray film processors at hisdepartment and the X-ray film processors at his
institution were an unnecessary waste of time. Heinstitution were an unnecessary waste of time. He
conceived the possibility of using a video camera chipconceived the possibility of using a video camera chip
(CCD) combined with the Scintillator normally found in(CCD) combined with the Scintillator normally found in
panoramic and other extra oral X-ray cassettes topanoramic and other extra oral X-ray cassettes to
produce an instant image.produce an instant image.www.indiandentalacademy.comwww.indiandentalacademy.com

 Francis MouyenFrancis Mouyen has essentially miniaturized Edison’s Fluoroscope to ahas essentially miniaturized Edison’s Fluoroscope to a
place in the mouth.place in the mouth.
 The 1st European versions ofThe 1st European versions of Mouyen Radiovisiography (RVG)Mouyen Radiovisiography (RVG) werewere
developed in the mid-to late 1980’s and approved for sale in end ofdeveloped in the mid-to late 1980’s and approved for sale in end of
1990.Since than additional versions of RVG developed.1990.Since than additional versions of RVG developed.

 Extaroral devices have been added to panoramicExtaroral devices have been added to panoramic
imaging and cephalogram and storage phosphorsimaging and cephalogram and storage phosphors
have became available for dental purpose, ashave became available for dental purpose, as
alternative to solid- state technologies and furthermorealternative to solid- state technologies and furthermore
cone beam CT was developed.cone beam CT was developed.
 The following issues question the validity of 2-DThe following issues question the validity of 2-D
cephalometry to derive clinical information used incephalometry to derive clinical information used in
treatment planning.treatment planning.
Conventional head film is a 2-D representation of 3-Conventional head film is a 2-D representation of 3-
object.When 3-D is represented in 2-D, the imagedobject.When 3-D is represented in 2-D, the imaged
structures are displayed vertically and horizontally:structures are displayed vertically and horizontally:

The amount of structural displacement is proportional to theThe amount of structural displacement is proportional to the
distance of the structure from the film / recording plane.distance of the structure from the film / recording plane.
Cephalometric analysis are based on assumption of perfectCephalometric analysis are based on assumption of perfect
super imposition of the right and left sides about thesuper imposition of the right and left sides about the
midsagittal plane.midsagittal plane.
 Perfect super imposition are observed in- frequently becausePerfect super imposition are observed in- frequently because
facial symmetry is rare and because of the relative imagefacial symmetry is rare and because of the relative image
displacement of the right and left sides. These technicaldisplacement of the right and left sides. These technical
limitations do not produce accurate assessments of C-Flimitations do not produce accurate assessments of C-F
anomalies & facial symmetriesanomalies & facial symmetries www.indiandentalacademy.comwww.indiandentalacademy.com

 Projection geometry precludes the ability to acquire accurate dimensionalProjection geometry precludes the ability to acquire accurate dimensional
information aligned in the direction of X-ray beam.information aligned in the direction of X-ray beam.
 Significant amount of external error such asSignificant amount of external error such as
 Radiographic projectionRadiographic projection  Size magnificationSize magnification
 Patient positioningPatient positioning
 Manual data collection and processing in cephalometry analysis haveManual data collection and processing in cephalometry analysis have
been shown to have low accuracy & precision.been shown to have low accuracy & precision.
 Significant error is associated with ambiguity in locating landmarksSignificant error is associated with ambiguity in locating landmarks
because of the lack of well defined anatomic feature, outlines, hardbecause of the lack of well defined anatomic feature, outlines, hard
edges, shadows and variation in patient position.edges, shadows and variation in patient position.

 VigVig reported the lack of validity ofreported the lack of validity of
Cephalometric analysis as a diagnosticCephalometric analysis as a diagnostic
instrument & demonstrated that conclusionsinstrument & demonstrated that conclusions
drawn from the some cephalogram varieddrawn from the some cephalogram varied
significantly depending on the analysis used.significantly depending on the analysis used.
 According to the biometricianAccording to the biometrician Fred Book steinFred Book stein,,
traditional Cephalometry have neither validtraditional Cephalometry have neither valid
biologic parameter nor valid biometricbiologic parameter nor valid biometric
predication.predication.

 HatcherHatcher recently reviewed and categorized sources of error inherent torecently reviewed and categorized sources of error inherent to
traditional Cephalometrics.traditional Cephalometrics.
 internal orientation errorinternal orientation error
 external orientation errorexternal orientation error
 geometric errorgeometric error
 association errorassociation error
 Computers have been used to assist in reducing these errors. HoweverComputers have been used to assist in reducing these errors. However
they may also introduce errors because of pixel size, loss of color &they may also introduce errors because of pixel size, loss of color &
contrast information and incomplete calibrations. Therefore in an attemptcontrast information and incomplete calibrations. Therefore in an attempt
to eliminate these random and systematic errors, methods have beento eliminate these random and systematic errors, methods have been
developed to provide 3-D representation of the C-F complex.developed to provide 3-D representation of the C-F complex.

Imaging Goals And StrategiesImaging Goals And Strategies
 General imaging goals:General imaging goals:
 Include anatomic feature detection and morphologicInclude anatomic feature detection and morphologic
measurement.measurement.
 Anatomic featuresAnatomic features orthodontic landmarks, anatomic descriptorsorthodontic landmarks, anatomic descriptors
that characterize normal & abnormal anatomy.that characterize normal & abnormal anatomy.
 One should take the following imaging goals into consideration duringOne should take the following imaging goals into consideration during
designing of imaging protocol.designing of imaging protocol.
 Image the entire region of interestImage the entire region of interest
 View the region of interest in atleast two planes at right angleView the region of interest in atleast two planes at right angle
to each other (3-D perspective)to each other (3-D perspective)
 Obtain images with maximum detail, minimal distortion &Obtain images with maximum detail, minimal distortion &
minimal superimposition.minimal superimposition.
 Diagnostic value of the imaging study must be in balance withDiagnostic value of the imaging study must be in balance with
the cost and risk associated to obtain the study.the cost and risk associated to obtain the study.

 Clinically determined goalsClinically determined goals::
 C-F imaging is used for independently deciphering one / more of theC-F imaging is used for independently deciphering one / more of the
following categories of information or for interpreting the complexfollowing categories of information or for interpreting the complex
interrelationships b/w C-F diagnosis, growth & treatment by derivinginterrelationships b/w C-F diagnosis, growth & treatment by deriving
information in two or more of the following categoriesinformation in two or more of the following categories ..
 Identify normal and abnormal anatomy.
 Determine root length and root alignment.
 Determine relationship b/w tooth space requirement and jaw
dimensions.
 Determine maxillomandibular spatial relationship.
 Determine status of TMJ
 Determine past, present, and expected C-F growth magnitude
and direction.
 Determine effect of treatment on the C-F anatomy.
 Identify and localize supernumeraries & impacted teeth ..

Conventional C-F Imaging MethodsConventional C-F Imaging Methods::
 The following is the brief review of imaging methods mostThe following is the brief review of imaging methods most
widely used by the orthodontic profession.widely used by the orthodontic profession.
A.A. Hard tissue imagingHard tissue imaging ::
 Cephalometric radiographyCephalometric radiography
 Panoramic projectionsPanoramic projections
 Periapical projectionsPeriapical projections
 Tomography / C T ScansTomography / C T Scans
 Corrected Tomography of the TMJCorrected Tomography of the TMJwww.indiandentalacademy.comwww.indiandentalacademy.com

 Cephalometric radiographyCephalometric radiography ::
 Despite the limitations Cephalometric radiographyDespite the limitations Cephalometric radiography
remains a vital clinical tool used for gross inspection,remains a vital clinical tool used for gross inspection,
to describe morphology and growth, to diagnosisto describe morphology and growth, to diagnosis
anomalies, to forecast future relationship to plananomalies, to forecast future relationship to plan
treatment and to evaluate growth and treatmenttreatment and to evaluate growth and treatment
results.results.
 It is only quantitative method that permits theIt is only quantitative method that permits the
investigation and evaluation of the spatial relationshipinvestigation and evaluation of the spatial relationship
b/w cranial and dental structures.b/w cranial and dental structures.

 It gives highest projectional resolution than all other imagesIt gives highest projectional resolution than all other images
including CT.including CT.
 Fine details in bony structures are evident and trained eyeFine details in bony structures are evident and trained eye
can resolve some structures smaller than 0.1mm.can resolve some structures smaller than 0.1mm.
 Lateral cephalogram provide pertinent information on skeletal,Lateral cephalogram provide pertinent information on skeletal,
dental, & soft tissue morphology & relationships.dental, & soft tissue morphology & relationships.
 PA cephalogram used primarily to assess skeletal & dentalPA cephalogram used primarily to assess skeletal & dental
asymmetries ,although substantial limitation arise fromasymmetries ,although substantial limitation arise from
internal orientation errors associated with variation in the 3-Dinternal orientation errors associated with variation in the 3-D
position of the head relation to instrumentation.position of the head relation to instrumentation.
 As a research tool cephalometry has been the most widelyAs a research tool cephalometry has been the most widely
used imaging modality in orthodontic investigations.used imaging modality in orthodontic investigations.www.indiandentalacademy.comwww.indiandentalacademy.com

 Cephalometric analysis gives:Cephalometric analysis gives:
Configuration of facial skeletalConfiguration of facial skeletal
Relationship of jaw basesRelationship of jaw bases
Relationship of the axial inclination of the incisorsRelationship of the axial inclination of the incisors
Assessment of soft tissue morphologyAssessment of soft tissue morphology
Growth pattern and directionGrowth pattern and direction
Localization of malocclusionLocalization of malocclusion
Treatment possibilities and limitationsTreatment possibilities and limitations..

 Panoramic projections:Panoramic projections:
 It is an excellent method if used with the realization that it has greaterIt is an excellent method if used with the realization that it has greater
value for screening than diagnostic purpose.value for screening than diagnostic purpose.
 Provides some information’s about mandibular symmetry, present,Provides some information’s about mandibular symmetry, present,
missing or supernumerary teeth; dental age ,retained root tipsmissing or supernumerary teeth; dental age ,retained root tips
,eruption sequence and limited information about gross periodontal,eruption sequence and limited information about gross periodontal
health, sinuses, root parallelism and the TMJs.health, sinuses, root parallelism and the TMJs.
 It can also reveal to some degree of the pathological conditions andIt can also reveal to some degree of the pathological conditions and
variation from normal.variation from normal.

 It is used in initial survey, that can provide the required insightIt is used in initial survey, that can provide the required insight
or assist in determining the need for other projections & alsoor assist in determining the need for other projections & also
useful when patient do not tolerate intraoral radiographs.useful when patient do not tolerate intraoral radiographs.
Panoramic radiograph gives a single image of the facialPanoramic radiograph gives a single image of the facial
structure that include both U/L jaws & their supportingstructure that include both U/L jaws & their supporting
structures.structures.

 AdvantagesAdvantages
 Broad coverage of the facialBroad coverage of the facial
bones and teeth.bones and teeth.
 Low patient radiation exposureLow patient radiation exposure
dosedose
 Can be used in patient unableCan be used in patient unable
to open their mouth.to open their mouth.
 Short duration of time requiredShort duration of time required
(3-4 min).(3-4 min).
 For patient education.For patient education.
 Minimal infection controlMinimal infection control
proceduresprocedures ..
 DisadvantagesDisadvantages
 Image does not display fine anatomicImage does not display fine anatomic
details that are available on intraoraldetails that are available on intraoral
periapical radiographs.periapical radiographs.
 Not useful in detecting proximal caries,Not useful in detecting proximal caries,
periapical diseases and periodontalperiapical diseases and periodontal
diseases.diseases.
 Uneven magnification and geometricUneven magnification and geometric
distortion.distortion.
 Occasionally overlapping of structuresOccasionally overlapping of structures
such as cervical spine can hidesuch as cervical spine can hide
odontogenic lesions, particularly in theodontogenic lesions, particularly in the
incisor region.incisor region.
 Cannot be used as a substitute forCannot be used as a substitute for
intraoral film.intraoral film.

 Periapical projectionPeriapical projection
 Periapical radiograph records images of the outlines, position andPeriapical radiograph records images of the outlines, position and
mesiodistal extent of the teeth and surrounding tissues.mesiodistal extent of the teeth and surrounding tissues.
 For orthodontic perspective, these images provide several benefitsFor orthodontic perspective, these images provide several benefits
 To assess overall dental & periodontal health, root length, shape andTo assess overall dental & periodontal health, root length, shape and
form.form.
 To study the integrity of the lamina dura (to rule out possibility ofTo study the integrity of the lamina dura (to rule out possibility of
ankylosis).ankylosis).
 To assess the position of impacted, erupting, supernumerary teethTo assess the position of impacted, erupting, supernumerary teeth
and root stumps.and root stumps.
 To study root parallelism.To study root parallelism.


Bitewing radiographyBitewing radiography ::
 Useful in detectingUseful in detecting
Interproximal and secondary caries.Interproximal and secondary caries.
Overhanging restoration.Overhanging restoration.
Periodontal conditions.Periodontal conditions.
Calculus deposits.Calculus deposits.
Chronic resorption of inter- alveolar bone.Chronic resorption of inter- alveolar bone.
Pulp stones in pulp chambers.Pulp stones in pulp chambers.
Occlusal relationship of the teethOcclusal relationship of the teeth..

 Occlusal radiographyOcclusal radiography ::

MaxillaryMaxillary  depicts images of hard palate, upperdepicts images of hard palate, upper
liplip,, base of the nose.base of the nose.

MandibularMandibular  depicts images of tongue, floor of thedepicts images of tongue, floor of the
mouth and lower lipmouth and lower lip
 Useful in detecting:Useful in detecting:
Expansion of palatal arch during orthodontic jawExpansion of palatal arch during orthodontic jaw
expansion procedures.expansion procedures.
The presence & relative position of impacted / embeddedThe presence & relative position of impacted / embedded
teeth (as a part of localization).teeth (as a part of localization).
To identify expansion of cortical plate in case of anyTo identify expansion of cortical plate in case of any
pathology such as cyst.pathology such as cyst.
Foreign bodies, fractures, cleft palate,.Foreign bodies, fractures, cleft palate,.
stones in salivary ducts and other gross abnormalstones in salivary ducts and other gross abnormal
condition / lesions of the jaws.condition / lesions of the jaws.

 Tomography / CT Scan:Tomography / CT Scan:
 Tomography is a general term used for anTomography is a general term used for an
imaging technique that provides an image ofimaging technique that provides an image of
a layer of the tissue.a layer of the tissue.
 These layers / planes can be oriented toThese layers / planes can be oriented to
conform a desired slice of the anatomyconform a desired slice of the anatomy
under study.under study.
 The versatility of this technique makesThe versatility of this technique makes
tomography highly desirable for accuratetomography highly desirable for accurate
imaging of a wide variety of M-F structures,imaging of a wide variety of M-F structures,
including TMJs,for cross-sectional imaging ofincluding TMJs,for cross-sectional imaging of
the maxilla & mandible.the maxilla & mandible.

 Corrected tomography of the TMJCorrected tomography of the TMJ
 Axially corrected tomography has been usedAxially corrected tomography has been used
commonly to examine the hard tissue of the jaw jointcommonly to examine the hard tissue of the jaw joint
and assess the open & closed mouth condyle –and assess the open & closed mouth condyle –
fossa spatial relationships.fossa spatial relationships.
 Axially corrected TMJ tomography refers to theAxially corrected TMJ tomography refers to the
alignment of the tomographic beam with thealignment of the tomographic beam with the
mediolateral long axis of the condyle to producemediolateral long axis of the condyle to produce
image layers that are parallel or perpendicular to theimage layers that are parallel or perpendicular to the
mediolateral long axis of the condyle.mediolateral long axis of the condyle.
 Laterosuperior and mediosuperior surfaces of theLaterosuperior and mediosuperior surfaces of the
condyle are more difficult to image than the centralcondyle are more difficult to image than the central
2/3rd of the condyle with sagittal tomography and2/3rd of the condyle with sagittal tomography and
axially corrected coronal plane images therefore it isaxially corrected coronal plane images therefore it is
recommend for viewing these surfaces.recommend for viewing these surfaces.
 LimitationsLimitations: provides 2-D images and because of its: provides 2-D images and because of its
inability to image the disk.inability to image the disk.

B.B. Soft Tissue ImagingSoft Tissue Imaging ::
 C TC T
 MRIMRI
 ArthrographyArthrography
 Computed TomographyComputed Tomography: CT differ from traditional: CT differ from traditional
tomography by the use of a computer to aid intomography by the use of a computer to aid in
generating the images and by allowing multiplegenerating the images and by allowing multiple
CT slices to be “stacked” to represent a 3-D form.CT slices to be “stacked” to represent a 3-D form.
 CT, although better than traditional radiography, isCT, although better than traditional radiography, is
inefficient at producing suitable soft tissue contrastinefficient at producing suitable soft tissue contrast
because it is designed and optimized forbecause it is designed and optimized for
visualization of hard tissues.visualization of hard tissues.
 In 1972In 1972 Godfrey HounsfieldGodfrey Hounsfield announced theannounced the
invention of a revolutionary imaging techniqueinvention of a revolutionary imaging technique
he referred it ashe referred it as computerized axial transversecomputerized axial transverse
scanning.scanning. www.indiandentalacademy.comwww.indiandentalacademy.com

 Tomography:Tomography:
 (A)(A) Conventional film based tomographyConventional film based tomography
also calledalso called body section radiographybody section radiography
 is a radiographic technique designed to image moreis a radiographic technique designed to image more
clearly objects lying within a plane of interest.clearly objects lying within a plane of interest.
 This accomplished by blurring the images ofThis accomplished by blurring the images of
structure lying superficial and deep to the plane ofstructure lying superficial and deep to the plane of
interest through the process of motion unsharpness.interest through the process of motion unsharpness.
 Since introduction of CT and MRI which haveSince introduction of CT and MRI which have
superior low contrast resolution, film basesuperior low contrast resolution, film base
tomography has been used less frequently.tomography has been used less frequently.
 (B)(B) Conventional tomographyConventional tomography is now appliedis now applied
primarily to high contrast anatomy such as TMJs andprimarily to high contrast anatomy such as TMJs and
dental implant diagnostics.dental implant diagnostics.
 Equipment for Tomography includes an X-ray tubeEquipment for Tomography includes an X-ray tube
and radiographic film rigidly connected and capableand radiographic film rigidly connected and capable

 Examination begin with X-ray tube and filmExamination begin with X-ray tube and film
placed on opposite side of the fulcrum whichplaced on opposite side of the fulcrum which
is placed within the plane of interest (focalis placed within the plane of interest (focal
plane).plane).
 As the coordinated movement occurs theAs the coordinated movement occurs the
images of objects located within the focalimages of objects located within the focal
plane (at the fulcrum) remain in fixed positionplane (at the fulcrum) remain in fixed position
on the film throughout the length of tube & filmon the film throughout the length of tube & film
travel and are clearly imaged.travel and are clearly imaged.
 Images located away from the focal plane (i.e.Images located away from the focal plane (i.e.
superficial/deep) have continuously changingsuperficial/deep) have continuously changing
position on the films as result images areposition on the films as result images are
believed beyond recognition by motionbelieved beyond recognition by motion
unsharpness.unsharpness. www.indiandentalacademy.comwww.indiandentalacademy.com

There are atleast 5 types of Tomographic movementsThere are atleast 5 types of Tomographic movements : Linear,: Linear,
Circular, Spiral, Hypocycloidal, and Elliptical.Circular, Spiral, Hypocycloidal, and Elliptical.
Mechanically the simplest tomographic motion is the linear.Mechanically the simplest tomographic motion is the linear.

 Linear tomography can be accomplished in 2Linear tomography can be accomplished in 2
ways :ways :
 Both the X-ray tube and film move alongBoth the X-ray tube and film move along
concentric arc rather than in straight line.concentric arc rather than in straight line.
 X-ray tube and film move in opposite directionX-ray tube and film move in opposite direction
about fixed fulcrum in path of travel parallel withabout fixed fulcrum in path of travel parallel with
one another.one another.
 Both method giving similar result are used byBoth method giving similar result are used by
currently available X-ray units. But the imagecurrently available X-ray units. But the image
quality of linear tomographs has severalquality of linear tomographs has several
deficiencies compared with tomographsdeficiencies compared with tomographs
produced by other types of movements.produced by other types of movements.

 With this tomograph (linear) theWith this tomograph (linear) the image appearimage appear
streaked.streaked. These streaked calledThese streaked called parasites linesparasites lines,,
appear when the long axis of a structure lying outsideappear when the long axis of a structure lying outside
the focal plane is oriented parallel with the movementthe focal plane is oriented parallel with the movement
of the tube . As a result linear motion whether it be theof the tube . As a result linear motion whether it be the
parallel/arc type , fails to satisfy a requirement forparallel/arc type , fails to satisfy a requirement for
optimal blurring.optimal blurring.
 Distance from tubeDistance from tube patient, patientpatient, patient  film , the tubefilm , the tube
 film changes constantly and because thefilm changes constantly and because the
angulations of the X-ray beam through the focal planeangulations of the X-ray beam through the focal plane
change during exposure with the parallel type ofchange during exposure with the parallel type of
motion, inconsistent magnification, dimensionalmotion, inconsistent magnification, dimensional
instability, and non-uniform density may be seeninstability, and non-uniform density may be seen
across the linear tomographic image.across the linear tomographic image.

 If sharper tomographic images of more uniformIf sharper tomographic images of more uniform
density , consistent magnification, and dimensionaldensity , consistent magnification, and dimensional
stability are required , a multidirectional tomographicstability are required , a multidirectional tomographic
motion is necessary.motion is necessary.
 Thickness of tissue in the focal plane is called aThickness of tissue in the focal plane is called a
tomographic layertomographic layer and the location of this layer withinand the location of this layer within
the object is determined by thethe object is determined by the position of fulcrumposition of fulcrum
and its width (described numerically as the thicknessand its width (described numerically as the thickness
of cut) by tomographic angle or arc.of cut) by tomographic angle or arc.
 Relationship between thickness of the cut andRelationship between thickness of the cut and
tomographic angle is inverse.tomographic angle is inverse.
 Greater the tomographic angle, thinner the thicknessGreater the tomographic angle, thinner the thickness
of cut.of cut.
 Thus selection of the angle and hence the thicknessThus selection of the angle and hence the thickness
of cut depends on the objective of diagnostic taskof cut depends on the objective of diagnostic task
and the type of tissue being examined.and the type of tissue being examined.

(A)(A) Wide angle tomography:Wide angle tomography:
 More than 10 degreesMore than 10 degrees
 Allows visualization ofAllows visualization of finefine
structurestructure that normally would bethat normally would be
obscured by super imposition inobscured by super imposition in
conventional radiography.conventional radiography.
 Layer as thin as 1mm can beLayer as thin as 1mm can be
imagedimaged
 DisadvDisadv :Produces images of:Produces images of
decreased contrastdecreased contrast. (because. (because
from the different thickness offrom the different thickness of
adjacent structures.)adjacent structures.)
 USES:USES:
 Useful when tissues of greaterUseful when tissues of greater
physical density such as bonephysical density such as bone
are studied.are studied.
 It is excellent technique forIt is excellent technique for
evaluating maxilla and mandibleevaluating maxilla and mandible
before implant placement.before implant placement.www.indiandentalacademy.comwww.indiandentalacademy.com

(B)(B) Narrow angleNarrow angle tomography:tomography:
 Less than 10 degrees. Called asLess than 10 degrees. Called as zonographyzonography..
 Thick zone (25mm) of tissue can be sharply imaged.Thick zone (25mm) of tissue can be sharply imaged.
 USESUSES::
 Useful when the subject contrast is lowUseful when the subject contrast is low
therefore of little difference in physical densitytherefore of little difference in physical density
between adjacent structures.between adjacent structures.
 Is preferred when soft tissue are imaged.Is preferred when soft tissue are imaged.

Computed TomographyComputed Tomography ::
 Godfrey Hounsfield in 1972Godfrey Hounsfield in 1972 invented the revolutionary imaginginvented the revolutionary imaging
technique, refers astechnique, refers as computerized axial transverse scanningcomputerized axial transverse scanning..
 With this he was able to produce an axial cross sectionalWith this he was able to produce an axial cross sectional imageimage
of the head using a narrowly collimated, moving beam of x-of the head using a narrowly collimated, moving beam of x-
rays.rays.
 The remnant radiation of this beam was detected by scintillationThe remnant radiation of this beam was detected by scintillation
crystals, the resulting analog signal was fed into a computer,crystals, the resulting analog signal was fed into a computer,
digitized and analyzed by a mathematical algorithm and datadigitized and analyzed by a mathematical algorithm and data
were reconstructed as an axial tomographic image.were reconstructed as an axial tomographic image.
 Image produced are 100 times more sensitive thanImage produced are 100 times more sensitive than
conventional X-ray systems.conventional X-ray systems.
 CT scanner consists of a radiographic tube that emits a finelyCT scanner consists of a radiographic tube that emits a finely
collimated, fan shaped X-ray beam that is directed to a series ofcollimated, fan shaped X-ray beam that is directed to a series of
scintillation detection or ionization chambers.scintillation detection or ionization chambers.

 Fig 1. X-ray tube (Fig 1. X-ray tube (aa) rotates in tandem with detectors) rotates in tandem with detectors
((bb) on opposite side to image 1 thin axial slice. Bed is) on opposite side to image 1 thin axial slice. Bed is
then advanced through machine for next slice.then advanced through machine for next slice.

 Depending on the scanners ,mechanical geometry,Depending on the scanners ,mechanical geometry,
both the radiographic tube and detector may rotateboth the radiographic tube and detector may rotate
synchronously about the patient. Or the detector maysynchronously about the patient. Or the detector may
form a continuous ring about the patient and the x-rayform a continuous ring about the patient and the x-ray
tube may move in circle within the detection ring.tube may move in circle within the detection ring.
 Regardless of the mechanical geometry, theRegardless of the mechanical geometry, the
transmission signals recorded by the detectorstransmission signals recorded by the detectors
represent a composite of the absorption chacteristicsrepresent a composite of the absorption chacteristics
of all element of the patient in the path of x-ray.of all element of the patient in the path of x-ray.
 The CT image is reconstructed by the computer whichThe CT image is reconstructed by the computer which
mathematically manipulates the transmission datamathematically manipulates the transmission data
obtained from multiple projections.obtained from multiple projections.
 For example: If one Projection is made every 1/3rd ofFor example: If one Projection is made every 1/3rd of
a degree, 1080 projection is made during the coursea degree, 1080 projection is made during the course
of a size 360-degree rotation of the scanner about theof a size 360-degree rotation of the scanner about the
patient.patient.
 Data derived from 1080 projections constitute oneData derived from 1080 projections constitute one
scan, containing all the information necessary toscan, containing all the information necessary to
construct one image.construct one image. www.indiandentalacademy.comwww.indiandentalacademy.com

CT images are recorded & displayed as a matrix of individual blocksCT images are recorded & displayed as a matrix of individual blocks
calledcalled voxels (volume elements). Each square of the image matrix is a(volume elements). Each square of the image matrix is a
pixel.pixel.
Size of a pixel about 0.1mm is determined partly by the computerSize of a pixel about 0.1mm is determined partly by the computer
programme used to construct the image , the length of voxel about 1—programme used to construct the image , the length of voxel about 1—
20mm is determined by width of X-ray beam, which in turn controlled by20mm is determined by width of X-ray beam, which in turn controlled by
the pre patient and post patient collimation.the pre patient and post patient collimation.

 For image display each pixel is assigned a CTFor image display each pixel is assigned a CT
no. (Known as Hounsfield unit) representingno. (Known as Hounsfield unit) representing
density.density. This no. is proportional to the degree toThis no. is proportional to the degree to
which the material within the voxel haswhich the material within the voxel has
attenuated the X-ray beam.attenuated the X-ray beam.
 It represents the absorption characteristics orIt represents the absorption characteristics or
linear attenuation coefficient of that particularlinear attenuation coefficient of that particular
volume of tissue in the patient.volume of tissue in the patient.
 The CT no. range from -1000 to +1000The CT no. range from -1000 to +1000
Hounsfield units. Each constituting differentHounsfield units. Each constituting different
level of optical density. This scale of densitieslevel of optical density. This scale of densities
is base on air (-1000), water (0) and denseis base on air (-1000), water (0) and dense
bone (+1000).bone (+1000).

 Advantages:Advantages:
 Different planes can be visualized
(saggittal, coronal, transverse)
once the scan is completed
viewing the subject at different
levels can be done by computer
 Greater sensitivity (changes less
than 1 % can be visualized).
 Superimposition of anatomical
structure is not an issue to
confuse diagnosis.
 (Prederisken et al 1995 have
reported that the effective dose for
M-F complex range from 0.11—20
mSv)
 DisadvantagesDisadvantages::
 CT has great difficulty in
imaging metallic objects
anything denser than
enamel producing serous
artifacts giving rise to SUN
RAY ARTIFACTS.
 Expensive

• CT has advantages over conventional film radiographyCT has advantages over conventional film radiography andand
film tomography.film tomography.
 CT completely eliminates the superimposition of images of structures
superficial/deep to the area of interest. (Blurring)
 Because of high contrast resolution of CT difference between tissues
that differ in physical density by less than 1% can be distinguished.
Whereas conventional radiography requires 10% difference in physical
density to distinguish between tissues.
 Data from single CT imaging procedure consisting of multiple
contiguous scans can be viewed as images in the axial, coronal, or
saggittal planes depending on the diagnostics task. This is reformed as
multiplanar reformatted imaging.
 Useful in evaluations of patient before placement of endoessous
implants.
 Primarily because of high contrast resolution and ability to demonstrate
small differences in soft tissues density, it has become useful in
diagnosis and treatment plan in the craniofacial complex. [Salivary
gland, TMJ, disease].

 As the invention of MRI which proved superior to CT for
depicting soft tissue, the use of CT scanning for assessment of
internal derangement of the TMJ has decreased significantly.
 Despite the fact that similar information about maxillary &
mandibular anatomy can be obtained with film tomography, CT
allows reconstruction of cross sectional images of the entire
maxilla or mandible or both from single imaging procedure.
 Multiplanar CT imaging has made significant contribution to
diagnosis; however these images are 2-D and require a certain
degree of mental integration by the viewer for interpretation;
this limitation has led to the development of computer programs
that reformat data acquired from axial CT scan into 3 –D CT
images.
 3-D CT requires that each voxel shaped as a rectangular
parallelepiped or rectangular solid be dimensionally altered into
multiple cuboidal voxels. This is called interpolation, creates set
of evenly spaced cuboidal voxel (cuberille) that occupy the
same volume as the original voxel.

 TheThe CT numbersCT numbers (Hounsfield Unit) of the cuboidal voxel(Hounsfield Unit) of the cuboidal voxel
represent the average of the original voxel CT numbersrepresent the average of the original voxel CT numbers
surrounding each of the new voxels. Creations of this newsurrounding each of the new voxels. Creations of this new
cuboidal voxels allow the image to be reconstructed in anycuboidal voxels allow the image to be reconstructed in any
plane without loss of resolution by locating their position inplane without loss of resolution by locating their position in
space relative to one another.space relative to one another.
 Only the cuboidal voxel (cuberille) representing the surfaces ofOnly the cuboidal voxel (cuberille) representing the surfaces of
the object scanned are projected onto the viewing monitorthe object scanned are projected onto the viewing monitor
during reconstruction of 3-D CT image.during reconstruction of 3-D CT image.
 The surface formed by these cuberilles then appears as ifThe surface formed by these cuberilles then appears as if
illuminated by a light source located behind the viewer.illuminated by a light source located behind the viewer.
 In this manner the visible surface of each pixel is assigned aIn this manner the visible surface of each pixel is assigned a
gray level value, depending on its distance from and orientationgray level value, depending on its distance from and orientation
to the light source. Thus pixel faces the light source and / or areto the light source. Thus pixel faces the light source and / or are
closer to it appear brighter than those that are turned away fromcloser to it appear brighter than those that are turned away from
the source and / or are farther away.the source and / or are farther away.
 Once constructed, 3-D CT images may be further manipulatedOnce constructed, 3-D CT images may be further manipulated
by rotation about any axis to display the structure imaged fromby rotation about any axis to display the structure imaged from
many angles, also external portions of the image can bemany angles, also external portions of the image can be
removed electronically to reveal concealed deeper anatomy.removed electronically to reveal concealed deeper anatomy.

 First study using this 3 – D CT was done on patient withFirst study using this 3 – D CT was done on patient with
suspected intervertebral disk herniation & spiral stenosis. Sincesuspected intervertebral disk herniation & spiral stenosis. Since
than 3-D CT was applied to C-F complexes, i.e.than 3-D CT was applied to C-F complexes, i.e. reconstructivereconstructive
surgery, treatment of congenital & acquired deformities forsurgery, treatment of congenital & acquired deformities for
evaluation of intracranial tumors, benign & malignant lesions ofevaluation of intracranial tumors, benign & malignant lesions of
M-F complex; cervical spine injuries, pelvic fractures,M-F complex; cervical spine injuries, pelvic fractures,
deformities of the hands & feet also helpful in patient with TMJdeformities of the hands & feet also helpful in patient with TMJ
ankylosis.ankylosis.
 It can also be used in construction of life size models that canIt can also be used in construction of life size models that can
be used for trial surgeries and the construction of surgicalbe used for trial surgeries and the construction of surgical
stents and creation of accurate implanted prosthesis.( helpful instents and creation of accurate implanted prosthesis.( helpful in
identifying available bone for C-F & cochlear implants ).identifying available bone for C-F & cochlear implants ).
 It is superior to conventional CT & plain film tomography inIt is superior to conventional CT & plain film tomography in
elucidating skeletal structures.elucidating skeletal structures.
 CT technology is being advanced continuously .CT technology is being advanced continuously .ImatranImatran
(Sanfrancisco) has developed a CT scanner capable of(Sanfrancisco) has developed a CT scanner capable of
acquiring data upto 10 times faster than conventional CT.acquiring data upto 10 times faster than conventional CT.

 It’s ultra fast CT which has scan time on the order of 50 mIt’s ultra fast CT which has scan time on the order of 50 m
sec, enhancing quality without motion artifacts.sec, enhancing quality without motion artifacts.
 Other manufactures have developed spiral CT scanners.Other manufactures have developed spiral CT scanners.
 Gantry containing the X- ray tube & detectors revolvesGantry containing the X- ray tube & detectors revolves
around the patient, the table on which the patient is lyingaround the patient, the table on which the patient is lying
continuously advances through the gantry. This results incontinuously advances through the gantry. This results in
acquisition of continuous spiral of data as the X-ray beamacquisition of continuous spiral of data as the X-ray beam
moves down the patient.moves down the patient.

 Compared with conventional CT, spiral CTCompared with conventional CT, spiral CT
provides multiplanar image reconstruction,provides multiplanar image reconstruction,
reduced examination time (12 sec. Vs 5 Min.)reduced examination time (12 sec. Vs 5 Min.)
and a reduced radiation dose (upto 75 %).and a reduced radiation dose (upto 75 %).
 Despite significant advances in other aspect ofDespite significant advances in other aspect of
CT technology the radiation dose has remainedCT technology the radiation dose has remained
essentially unchanged. For this reason and foressentially unchanged. For this reason and for
those associated with cost, access & training,those associated with cost, access & training,
the use of traditional CT examination inthe use of traditional CT examination in
dentistry has remained low and is restricted todentistry has remained low and is restricted to
C-F anomalies & comprehensive treatments.C-F anomalies & comprehensive treatments.
However situation is evolving rapidly with theHowever situation is evolving rapidly with the
advert of cone beam CT for dentistry.advert of cone beam CT for dentistry.

CONE BEAM VOLUMETRIC TOMOGRAPHYCONE BEAM VOLUMETRIC TOMOGRAPHY
(CBVT / CBCT)(CBVT / CBCT)
 The principle differences in distinguishing fromThe principle differences in distinguishing from
traditional CT are thetraditional CT are the type of imaging sourcetype of imaging source
detector complex & method of data acquisitiondetector complex & method of data acquisition..
The X-ray source for CT is aThe X-ray source for CT is a high –output rotating anodehigh –output rotating anode
generator, where as for CBVT can be agenerator, where as for CBVT can be a low energy fixedlow energy fixed
anodeanode tube similar to that used in dental panoramictube similar to that used in dental panoramic
machines.machines.
CT usesCT uses fan shaped X-ray beamfan shaped X-ray beam from its source to acquirefrom its source to acquire
images and records the data on aimages and records the data on a solid state imagesolid state image
detectors arranged in a 360 degree array around thedetectors arranged in a 360 degree array around the
patient. CBVT usespatient. CBVT uses cone shaped X-ray beamcone shaped X-ray beam with awith a
special image intensifier andspecial image intensifier and solid state sensors or ansolid state sensors or an
amorphous silicon plateamorphous silicon plate for capturing the imagesfor capturing the images

 The main difference b/w CBCT & traditional CT areThe main difference b/w CBCT & traditional CT are
the type of imaging source- detector complex & thethe type of imaging source- detector complex & the
method of data acquisitionmethod of data acquisitionwww.indiandentalacademy.comwww.indiandentalacademy.com

 Conventional CTConventional CT images the patients in a series ofimages the patients in a series of
axial plane sliceaxial plane slice that are captured as individual stackedthat are captured as individual stacked
sliced or from a continuous spiral motion over axialsliced or from a continuous spiral motion over axial
plane. CBVT usesplane. CBVT uses one sweepone sweep of the patient similar toof the patient similar to
that for panoramic radiography.that for panoramic radiography.
– Image data collected for complete dental / M-FImage data collected for complete dental / M-F
volume or limited regional area of interest. Scanvolume or limited regional area of interest. Scan
time varies from 10 – 90 seconds, dose 40 – 50time varies from 10 – 90 seconds, dose 40 – 50
uSv (similar to conventional dental radiograph).uSv (similar to conventional dental radiograph).
– In comparison to radiation dose from aIn comparison to radiation dose from a
panoramic examination is in the range of 2.9 –panoramic examination is in the range of 2.9 –
9.6 uSv and that from a complete mouth series9.6 uSv and that from a complete mouth series
ranges from 33- 84 uSv and 14 -100uSv.ranges from 33- 84 uSv and 14 -100uSv.

MANGENTIC RESONANCE IMAGING (MRI)MANGENTIC RESONANCE IMAGING (MRI)
 In contrast to CT, which uses X- rays for acquisition ofIn contrast to CT, which uses X- rays for acquisition of
information pertaining to an object studied, MRI usesinformation pertaining to an object studied, MRI uses
NONIONIZING RADIATION FROM THENONIONIZING RADIATION FROM THE
RADIOFREQUENCY (RF) BAND OF THERADIOFREQUENCY (RF) BAND OF THE
ELECTROMAGNETIC SPECTRUM.ELECTROMAGNETIC SPECTRUM.
 MR image is produced by placing the patient inside a largeMR image is produced by placing the patient inside a large
magnet, which induces a relatively strong external magneticmagnet, which induces a relatively strong external magnetic
field.field.
 This causes the nuclei of many RF signal, energy isThis causes the nuclei of many RF signal, energy is
released from the body, detected & used to construct thereleased from the body, detected & used to construct the
MR image by computer.MR image by computer.
 High contrast sensitivity of MRI to tissue difference &High contrast sensitivity of MRI to tissue difference &
absence of radiation exposure is the advantage over CT forabsence of radiation exposure is the advantage over CT for
imaging soft tissuesimaging soft tissues. Although CT remains an important. Although CT remains an important
technique for imaging bony tissue. Theory of MRI is basedtechnique for imaging bony tissue. Theory of MRI is based

 Atomic nuclei spin about their axis much as earth spins aboutAtomic nuclei spin about their axis much as earth spins about
its axis.its axis.
 Atomic nucleiAtomic nuclei  proton & neutrons (nucleons). each posesproton & neutrons (nucleons). each poses
spin or angular momentum.spin or angular momentum.
 In nucleiIn nuclei where proton & neutron arewhere proton & neutron are paired evenlypaired evenly, the spin, the spin
of each nucleon (proton & neutron) cancels that of anotherof each nucleon (proton & neutron) cancels that of another
producingproducing a net spin of zeroa net spin of zero..
 In nucleiIn nuclei  where proton & neutron arewhere proton & neutron are not evenly pairednot evenly paired
(unpaired)(unpaired)  aa net spin is creatednet spin is created..
 Spin is associated with an electrical charge; a magnetic fieldSpin is associated with an electrical charge; a magnetic field
is generated in nuclei with unpaired nucleons, causing theseis generated in nuclei with unpaired nucleons, causing these
nuclei to act as a magnet with north and south polesnuclei to act as a magnet with north and south poles
(magnetic dipoles).(magnetic dipoles).

 M R imaging is based on the principle that the nuclei of someM R imaging is based on the principle that the nuclei of some
atoms are capable of spinning and they generate a magneticatoms are capable of spinning and they generate a magnetic
field in the process. MRI mainly makes use of hydrogen. Thefield in the process. MRI mainly makes use of hydrogen. The
tissues to be analyzed are placed in a strong magnetic field.tissues to be analyzed are placed in a strong magnetic field.
Since the large no. of hydrogen atoms present in the tissuesSince the large no. of hydrogen atoms present in the tissues
behave like tiny magnets, they get aligned with the magneticbehave like tiny magnets, they get aligned with the magnetic
field. When a radio signal is used, these tiny magnets flip 90field. When a radio signal is used, these tiny magnets flip 90
or 180 degrees depending on the amplitude and duration ofor 180 degrees depending on the amplitude and duration of
the signal and get misaligned with respect to the magneticthe signal and get misaligned with respect to the magnetic
field. When the RF is stopped, the nuclear magnets relax andfield. When the RF is stopped, the nuclear magnets relax and
flip back in alignment with the magnetic field. As these nucleiflip back in alignment with the magnetic field. As these nuclei
relax, they transmit a radio signal whose frequency is uniquerelax, they transmit a radio signal whose frequency is unique
to the element and a signal strength that is indicative of theto the element and a signal strength that is indicative of the
elements abundance. An image or MR image is constructedelements abundance. An image or MR image is constructed
by a computer using these radio signals.by a computer using these radio signals.

 Best resolution of tissue of lowBest resolution of tissue of low
inherent contrast (diagnosis ofinherent contrast (diagnosis of
suspected internal derangement ofsuspected internal derangement of
TMJ & evaluating the treatment ofTMJ & evaluating the treatment of
internal derangement afterinternal derangement after
surgery)surgery)
 Identitifying & localizing oro facialIdentitifying & localizing oro facial
soft tissue lesions, and providingsoft tissue lesions, and providing
images of salivary glandimages of salivary gland
parenchyma.parenchyma.
 Make use of non-ionizing radiationMake use of non-ionizing radiation
 Because the region of the bodyBecause the region of the body
imaged in MRI is controlledimaged in MRI is controlled
electronically, direct multiplanarelectronically, direct multiplanar
imaging is possible without re-imaging is possible without re-
orienting the patient.orienting the patient.
 Disadvantages:Disadvantages:
 Long imaging timeLong imaging time
 Potential hazard imposed by presence ofPotential hazard imposed by presence of
ferromagnetic metals in the vicinity of theferromagnetic metals in the vicinity of the
imaging patient.imaging patient.
 Auditory effect of noiseAuditory effect of noise noise from thenoise from the
vibration in the gradient coil and other parts ofvibration in the gradient coil and other parts of
the scanner due to the varying magnetic field.the scanner due to the varying magnetic field.
noise may read upto 95 dB causing temporary ornoise may read upto 95 dB causing temporary or
permanent hearing loss.permanent hearing loss.
 Contraindicated in patient with pacemakers,Contraindicated in patient with pacemakers,
cerebral aneurysm clips / implants.cerebral aneurysm clips / implants.
 Some patient suffers from claustrophobia whenSome patient suffers from claustrophobia when
positioned in MRI machine.positioned in MRI machine.
 As it is expensive, its use in dentistry is limited.As it is expensive, its use in dentistry is limited.
 Magnetic field may cause minor physiologicalMagnetic field may cause minor physiological
changes in the length of cardiac cycle, changeschanges in the length of cardiac cycle, changes
in red cell morphology, alteration in growthin red cell morphology, alteration in growth
pattern.pattern.
 Magnetophosphans are visual flashes seen byMagnetophosphans are visual flashes seen by
subjects due to direct stimulation of the opticsubjects due to direct stimulation of the optic
pathway.pathway.

ArthrographyArthrography
 It is a technique in which an indirect image of theIt is a technique in which an indirect image of the
disk is obtained by injecting adisk is obtained by injecting a radio opaque dyeradio opaque dye intointo
one or both joint space under fluoroscopic guidance.one or both joint space under fluoroscopic guidance.
 Perforation is detected by the flow of contrast agentPerforation is detected by the flow of contrast agent
into the superior joint space from the lower spaceinto the superior joint space from the lower space
and adhesions are detected by the manner in whichand adhesions are detected by the manner in which
contrast agent fills the joint space.contrast agent fills the joint space.
 After both the spaces are filled it is studied usingAfter both the spaces are filled it is studied using
fluoroscopy during open & closing movements andfluoroscopy during open & closing movements and
fluoroscopic study is supplemented by tomographyfluoroscopic study is supplemented by tomography

Although Arthrography has contributed in understanding the diskAlthough Arthrography has contributed in understanding the disk
position, in recent years MRI has replaced TMJ Arthrographyposition, in recent years MRI has replaced TMJ Arthrography
for clinical use completely.for clinical use completely.
 Information of theInformation of the
position, function,position, function,
morphology & integritymorphology & integrity
of the disk attachmentof the disk attachment
which is required forwhich is required for
treatment planning.treatment planning.
 Disadvantage:Disadvantage:
 Allergic to the dyeAllergic to the dye
(nonionic iodine) and(nonionic iodine) and
infection, radiationinfection, radiation
dose risk,dose risk,
percutaneous injectionpercutaneous injection
into the TMJ.into the TMJ.

Contemporary and Evolving Imaging TechniqueContemporary and Evolving Imaging Technique
A.A. Digital ImagingDigital Imaging::
 used for imaging specific tissues. For example face,used for imaging specific tissues. For example face,
skeleton, muscles.skeleton, muscles.
 In general these methods can be noninvasive by usingIn general these methods can be noninvasive by using
magnetic resonance, ultrasound, visible light and laser ormagnetic resonance, ultrasound, visible light and laser or
invasive using radiography.invasive using radiography.
 Initially orthodontic professional used photography,Initially orthodontic professional used photography,
panoramic, cephalometrics and periapical imaging.panoramic, cephalometrics and periapical imaging.
 Replacement of film based imaging with digital imagesReplacement of film based imaging with digital images
created the potential to increase productivity, improvedcreated the potential to increase productivity, improved
quality, reduced X-ray dose, reduced regulatory burdens.quality, reduced X-ray dose, reduced regulatory burdens.
 Digital technique produce a dynamic rather than static,Digital technique produce a dynamic rather than static,
image in which the visual characteristic of density, contrastimage in which the visual characteristic of density, contrast
can be manipulated after acquisition to meet specificcan be manipulated after acquisition to meet specific
diagnostic tasks or to correct errors in exposure techniques.diagnostic tasks or to correct errors in exposure techniques.

 Digital imaging require number of componentsDigital imaging require number of components
like electronic sensor or detector, computerlike electronic sensor or detector, computer
with an analog to digital converters , monitorwith an analog to digital converters , monitor
or printer for image display.or printer for image display.
 Data obtained by an electronic sensor isData obtained by an electronic sensor is
presented to the computer as analogpresented to the computer as analog
information. This information is converted intoinformation. This information is converted into
discrete units, since computers function onlydiscrete units, since computers function only
with digital information represented by either 0with digital information represented by either 0
or 1.or 1.
 Computer language is based on theComputer language is based on the binary no.binary no.
system in which two digits are used to representsystem in which two digits are used to represent
informationinformation (0 & 1)(0 & 1) these two character arethese two character are
calledcalled BITSBITS for binary system.for binary system.
 In typical computer language, these characterIn typical computer language, these character
form words 8 or more bits in length calledform words 8 or more bits in length called
BYTESBYTES .With every bit of an 8-bit word being.With every bit of an 8-bit word being
either 0 or 1, the no. of possible words or bytes,either 0 or 1, the no. of possible words or bytes,
in this language is 2 8 (256).in this language is 2 8 (256).
 Analog-to –digital converter (A/D convention)Analog-to –digital converter (A/D convention)
used to change the analog output signal fromused to change the analog output signal from
these detector system to a numericthese detector system to a numeric
representation based on the binary no. systemrepresentation based on the binary no. system
recognizable by the computer.recognizable by the computer.

 This task is accomplished by measuring the voltage of theThis task is accomplished by measuring the voltage of the
output signal at discrete intervals and then assigning a no. tooutput signal at discrete intervals and then assigning a no. to
intensity of the voltage. Thus 256 voltage levels may beintensity of the voltage. Thus 256 voltage levels may be
discriminated that ultimately are displayed in image form, afterdiscriminated that ultimately are displayed in image form, after
computer manipulation as 256 shades of gray.computer manipulation as 256 shades of gray.
 The sensitivity that can be achieved with even this relativelyThe sensitivity that can be achieved with even this relatively
short 8-bit system can be appreciated when one considersshort 8-bit system can be appreciated when one considers
that the human eye can distinguish only about 32 shades ofthat the human eye can distinguish only about 32 shades of
gray.gray.
 The methods by which digital images are produced,The methods by which digital images are produced,
manipulated, stored , retrieved and transmitted are similar formanipulated, stored , retrieved and transmitted are similar for
all technique, from CT to intraoral radiography , differing onlyall technique, from CT to intraoral radiography , differing only
in the means by which they are acquired.in the means by which they are acquired.
 Digital images are considered eitherDigital images are considered either DIRECT OR INDIRECTDIRECT OR INDIRECT
radiographyradiography

 Direct radiographyDirect radiography ::
 Image is acquired by some detector that isImage is acquired by some detector that is
sensitive to electromagnetic energy either insensitive to electromagnetic energy either in
the range of visible light or X- rays.the range of visible light or X- rays.

 Indirect radiographyIndirect radiography ::
 Uses radiographic film as the image receptor ,imageUses radiographic film as the image receptor ,image
is digitized from the output signal of either a videois digitized from the output signal of either a video
camera, a charged coupled device (CCD) scannercamera, a charged coupled device (CCD) scanner
or a laser scanner that views the processedor a laser scanner that views the processed
radiographradiograph

DIGITAL SUBRACTION RADIOGRAPHYDIGITAL SUBRACTION RADIOGRAPHY
 Require two identical imagesRequire two identical images
 Subtracted image is a composite of these two,Subtracted image is a composite of these two,
representing their differing densities.representing their differing densities.
 Although visual examination of standard radiographyAlthough visual examination of standard radiography
cannot detect a 0.85 mm change in the thickness ofcannot detect a 0.85 mm change in the thickness of
cortical bone digital subtraction radiography is socortical bone digital subtraction radiography is so
sensitive it cansensitive it can detect a 0.12 mm changedetect a 0.12 mm change..
 The ability of digital subtraction to record minuteThe ability of digital subtraction to record minute
difference depends on the degree of matching of thedifference depends on the degree of matching of the
two images. However techniques have beentwo images. However techniques have been
developed to correct difference in image contrastdeveloped to correct difference in image contrast
projection geometry & hardening of X-ray beamprojection geometry & hardening of X-ray beam
caused by tissues through which the X-ray travels.caused by tissues through which the X-ray travels.www.indiandentalacademy.comwww.indiandentalacademy.com

 Useful in diagnosis ofUseful in diagnosis of
periodontal and cariousperiodontal and carious
lesions.lesions.
 Also has been reported toAlso has been reported to
have potential for evaluationhave potential for evaluation
of small changes in theof small changes in the
mandibular condyle positionmandibular condyle position
and integrity of the articularand integrity of the articular
surface, as well as forsurface, as well as for
assessment of osseousassessment of osseous
remodeling around granularremodeling around granular
hydroxyapatite implants.hydroxyapatite implants.
 Disadvantages:Disadvantages:
 Difficult to use in clinicalDifficult to use in clinical
practice because eachpractice because each
occasion requiresoccasion requires
reproducible alignment of thereproducible alignment of the
central ray of the x- raycentral ray of the x- ray
beam, the teeth, and the film.beam, the teeth, and the film.

B.B. Structural light ImagingStructural light Imaging
 Principle behind structured light system is the projection of aPrinciple behind structured light system is the projection of a pattern ontopattern onto
a surface that is distorted and interpreted as 3-D information to produce aa surface that is distorted and interpreted as 3-D information to produce a
surface map.surface map.
 Patterns used vary fromPatterns used vary from lines, stripes, grids, circles and other designslines, stripes, grids, circles and other designs..
 An e.g.: of this basic system from eyeronics that uses a 35mm slideAn e.g.: of this basic system from eyeronics that uses a 35mm slide
projector to project a grid pattern and a common digital camera to recordprojector to project a grid pattern and a common digital camera to record
images.images.
 Because these system capture images from only one perspective orBecause these system capture images from only one perspective or
camera viewpoint, several images are taken to obtain front, left, rightcamera viewpoint, several images are taken to obtain front, left, right
views of face.views of face.
 To produce full face model (ear to ear) with these systems, differentTo produce full face model (ear to ear) with these systems, different
perspective are combined in a process calledperspective are combined in a process called stitching to produce onestitching to produce one
model.model.

 STRUCTUREDSTRUCTURED
LIGHT IMAGING .ALIGHT IMAGING .A
to C, The basicto C, The basic
system fromsystem from
Eyetronics uses aEyetronics uses a
35 mm slide35 mm slide
projector to projectprojector to project
a grid pattern & aa grid pattern & a
common digitalcommon digital
camera to recordcamera to record
images of front andimages of front and
side angles of theside angles of the
faces and create afaces and create a
surface map. D to Fsurface map. D to F
, different, different
perspective areperspective are
combined in acombined in a
process calledprocess called
stitching to producestitching to produce
one model.one model.

 Stitching can be done manually / semi automatically.Stitching can be done manually / semi automatically.
 Developments are underway to develop automaticDevelopments are underway to develop automatic
process.process.
 Because a pattern is projected onto the face, theBecause a pattern is projected onto the face, the
texture map (color information) contains this patterntexture map (color information) contains this pattern
information and can be distracting.information and can be distracting.
 For this reason, a 2nd image taken with identicalFor this reason, a 2nd image taken with identical
position with out projected pattern.position with out projected pattern.
 In this way the surface map, derived from theIn this way the surface map, derived from the
projected pattern, is used with a clean texture mapprojected pattern, is used with a clean texture map
to produce more realistic 3-D images. However atto produce more realistic 3-D images. However at
this time only one of these structured light imagingthis time only one of these structured light imaging
systems has been validated for clinical use.systems has been validated for clinical use.

C.C. Laser Scanning:Laser Scanning:
 Another technology for 3-D facial imaging involves the useAnother technology for 3-D facial imaging involves the use
of lasers.of lasers.
 Laser scanner are capable of producing detailed models ,Laser scanner are capable of producing detailed models ,
however the scanning process requires the object/subjecthowever the scanning process requires the object/subject
toto remain stillremain still for a period of seconds to minute or morefor a period of seconds to minute or more
while scanner revolves around the subjects head.while scanner revolves around the subjects head.
 Laser provides only theLaser provides only the surface mapsurface map andand cannot providecannot provide
color informationcolor information for the texture, a color camera that isfor the texture, a color camera that is
registered with the laser scanner provides this information.registered with the laser scanner provides this information.
 In studies of laser scanning of plaster and plasterIn studies of laser scanning of plaster and plaster
mannequin heads investigation reported a 0.6mm variationmannequin heads investigation reported a 0.6mm variation
of localization in 3 axes, when using prelabledof localization in 3 axes, when using prelabled
anthropometric land marks. However more comprehensiveanthropometric land marks. However more comprehensive
studies using laser for anthropometric measurementsstudies using laser for anthropometric measurements
reported that more than half of these were unreliable i.e.reported that more than half of these were unreliable i.e.
error higher than 1.5mm.error higher than 1.5mm.www.indiandentalacademy.comwww.indiandentalacademy.com

D.D. Stereophotogrammetry:Stereophotogrammetry:
 It is similar to human visual process, uses two imagesIt is similar to human visual process, uses two images
separated in viewpoint by a small distance.separated in viewpoint by a small distance.
 Images from human eye are interpreted by the brain toImages from human eye are interpreted by the brain to
provide images with depth.provide images with depth.
 The use of Stereophotogrammetry for CF imaging has beenThe use of Stereophotogrammetry for CF imaging has been
reported using dry skull, cleft lip and palate for quantificationreported using dry skull, cleft lip and palate for quantification
and validation of the linear and angular facial measurements.and validation of the linear and angular facial measurements.
 In the latter the absolute value of the reproducibility error forIn the latter the absolute value of the reproducibility error for
localizing the landmarks reported 1mm for distance and 1.1localizing the landmarks reported 1mm for distance and 1.1
degree for the angles.degree for the angles.
 Recently Stereophotogrammetry with 2-infrared CCD (chargeRecently Stereophotogrammetry with 2-infrared CCD (charge
couple device) cameras are used to locate facial landmarkscouple device) cameras are used to locate facial landmarks
automatically and provide anthropometric information (linearautomatically and provide anthropometric information (linear
distance and angles).distance and angles). www.indiandentalacademy.comwww.indiandentalacademy.com

 Error in reproducibility of a land mark and marker location wasError in reproducibility of a land mark and marker location was
less than 2mm.less than 2mm.
 It can also be applied to CF skeleton reconstructions usingIt can also be applied to CF skeleton reconstructions using
multiple planar radiographs.multiple planar radiographs.
 Radiographs use common registration points to produce a 3-Radiographs use common registration points to produce a 3-
D coordinate system. In this approach, image information isD coordinate system. In this approach, image information is
insufficient to generate a 3-D volume similar to that generatedinsufficient to generate a 3-D volume similar to that generated
with CT or CBVT.with CT or CBVT.
 However advantage with this method is the ability to useHowever advantage with this method is the ability to use
existing equipment and to obtain image views that are inexisting equipment and to obtain image views that are in
current use & congruent with the existing knowledge base ofcurrent use & congruent with the existing knowledge base of
Cephalometric and growth & development.Cephalometric and growth & development.
 Additionally radiation dose of planar films is much lower theAdditionally radiation dose of planar films is much lower the
CT / volumetric imaging and favorable cost benefit analysis.CT / volumetric imaging and favorable cost benefit analysis.
 Conventional Cephalometric images showed a wide variabilityConventional Cephalometric images showed a wide variability
in the standard deviation ranging from an underestimation of –in the standard deviation ranging from an underestimation of –
17.68mm to an over estimation of +15.52mm.17.68mm to an over estimation of +15.52mm.

Current Status Of 3-D Facial ImagingCurrent Status Of 3-D Facial Imaging
 Acquiring dimensionally accurate facial images using any ofAcquiring dimensionally accurate facial images using any of
the foregoing approaches is demanding because of tissuesthe foregoing approaches is demanding because of tissues
reflectance, interference of hair and eyebrows, change ofreflectance, interference of hair and eyebrows, change of
posture between different views and movement duringposture between different views and movement during
imaging therefore certain structures such as eyes and earsimaging therefore certain structures such as eyes and ears
do not image well because of extreme reflectance or underdo not image well because of extreme reflectance or under
cuts where light and laser cannot enter.cuts where light and laser cannot enter.
 Compounding these is the post processing complexity duringCompounding these is the post processing complexity during
which the computer process these images to reduce artifactswhich the computer process these images to reduce artifacts
and smooth surfaces while retaining detail.and smooth surfaces while retaining detail.
 In addition errors are introduced during the stitching togetherIn addition errors are introduced during the stitching together
of the multiple perspectives to form a complete facial mould.of the multiple perspectives to form a complete facial mould.
 Given these limitation and others, no systems is in commonGiven these limitation and others, no systems is in common
clinical use, although there are ongoing developments andclinical use, although there are ongoing developments and
techniques to eliminate these limitation.techniques to eliminate these limitation.

a)a) Dental crownsDental crowns
 Two general methods to produce 3-D models of theTwo general methods to produce 3-D models of the
dental crowns aredental crowns are
 Direct methodDirect method
 Indirect methodIndirect method
 The latter begins with an accurate impression withThe latter begins with an accurate impression with
alginate or polyvinyl siloxane materials.alginate or polyvinyl siloxane materials.
 From here the impression is poured with plaster or stoneFrom here the impression is poured with plaster or stone
and imaged in aand imaged in a destructive or non destructive mannerdestructive or non destructive manner
 Destructive imaging involves the removal of a thin layerDestructive imaging involves the removal of a thin layer
of material, alternating with image capture to generate aof material, alternating with image capture to generate a
stack of images that are rendered in three dimensions.stack of images that are rendered in three dimensions.
 Nondestructive scanning involves the use of a laserNondestructive scanning involves the use of a laser
based system with a multi-axis robot to obtain severalbased system with a multi-axis robot to obtain several
perspectives of the plaster model.. The perspectives areperspectives of the plaster model.. The perspectives are
combined to render a complete model.combined to render a complete model.

 Another approach to non-destructive scanningAnother approach to non-destructive scanning
involves the use of micro- CT methods to image theinvolves the use of micro- CT methods to image the
plaster model or alternatively, image the dentalplaster model or alternatively, image the dental
impression directlyimpression directly. Within these processes are the. Within these processes are the
abilities to generate models with qualitativeabilities to generate models with qualitative
information as well as models that are dimensionallyinformation as well as models that are dimensionally
accurate for production of dental appliances andaccurate for production of dental appliances and
other demanding applications.other demanding applications.
 A direct method of producing 3-D models of theA direct method of producing 3-D models of the
dentition involves the use of an intra oral cameradentition involves the use of an intra oral camera
based on structured light principles.based on structured light principles.
 After isolating the dentition and application of anAfter isolating the dentition and application of an
opaquing agent, small postage-stamp sized imagesopaquing agent, small postage-stamp sized images
of the dentition are taken with a video camera whileof the dentition are taken with a video camera while
a light pattern is strobed onto the teeth. .a light pattern is strobed onto the teeth. .

 The images are streamed to a computer where they areThe images are streamed to a computer where they are
registered and the data are processed to remove artifacts andregistered and the data are processed to remove artifacts and
redundant points. The complete dental arch is imaged inredundant points. The complete dental arch is imaged in
approximately 90 sec.approximately 90 sec.
 Once the data are obtained, the next step is to produceOnce the data are obtained, the next step is to produce
models of the dentition for diagnosis and treatmentmodels of the dentition for diagnosis and treatment
simulation / planning. For diagnostic purposes, the entire archsimulation / planning. For diagnostic purposes, the entire arch
can be treated as a single object, however for treatmentcan be treated as a single object, however for treatment
simulation, particularly involving tooth movement; the singlesimulation, particularly involving tooth movement; the single
arch must be segmented into individual teeth. Because thearch must be segmented into individual teeth. Because the
contact points between teeth do not image well, segmentingcontact points between teeth do not image well, segmenting
the teeth is a formidable challenge.the teeth is a formidable challenge.

Merging of 3D setups and CT scan givesMerging of 3D setups and CT scan gives ::
 Position of the maxillary incisors root relative to thePosition of the maxillary incisors root relative to the
lingual cortical border of the palate to plan retraction /lingual cortical border of the palate to plan retraction /
torque.torque.
 Amount of bone in posterior maxilla for molarAmount of bone in posterior maxilla for molar
distalization.distalization.
 Amount of bone lateral to buccal segment available forAmount of bone lateral to buccal segment available for
space closure or dental / skeletal expansion.space closure or dental / skeletal expansion.
 Root proximity to maxillary sinusRoot proximity to maxillary sinus
 3-D volume of an atrophied alveolar ridge3-D volume of an atrophied alveolar ridge
 Position of mandibular incisor roots relative to thePosition of mandibular incisor roots relative to the
buccal cortical bone.buccal cortical bone.
This procedure can be of great help for the clinican inThis procedure can be of great help for the clinican in
diagnosis and treatment planning to assess variousdiagnosis and treatment planning to assess various
treatment options, monitor changes over time, predicttreatment options, monitor changes over time, predict
and display final treatment results and measureand display final treatment results and measure
treatment outcomes accurately.treatment outcomes accurately.

b)b) Tooth rootsTooth roots
 Traditional method of obtaining details are panoramic or periapical
radiographs. Although these images give useful information such as
root position, morphology, the information is 2-D and subject to
projection errors.
 Recently studies on use of panoramic images to assess root
parallelism, found variation b/w different panoramic devices and that
the majority of image angles from panoramic units was statistically
significantly different from the true angle measurements & concluded
that clinical assessment of mesio-distal tooth angulations with
panoramic radiography should be approached with extreme caution.
 3-D root information is necessary for comprehensive patient specific
models which can be obtained with conventional CT /CBVT.
 Tooth roots reside within the volume and need to be separated /
segmented out of the volume to produce independent objects for
treatment simulation & therapy purposes . (Currently under
development). Additionally root information needs to be integrated with
highly accurate 3-D dental crown information ..www.indiandentalacademy.comwww.indiandentalacademy.com

c)c) Craniofacial skeleton:Craniofacial skeleton:
a)a) PhotogrammetryPhotogrammetry
b)b) Volumetric imaging deviceVolumetric imaging device
d)d) Face:Face:
a)a) LaserLaser
b)b) Structure lightStructure light
e)e) Facial Expression & Mandibular MotionFacial Expression & Mandibular Motion ::
– Relatively less information are available on recordingRelatively less information are available on recording
attributes of facial expression and mandibular motion.attributes of facial expression and mandibular motion.
– Within the realm of recording facial expression the twoWithin the realm of recording facial expression the two
general approaches aregeneral approaches are tracking markers placed onto thetracking markers placed onto the
skin and tracking facial features such as the corners ofskin and tracking facial features such as the corners of
the eyes and mouth or folds of the tissue.the eyes and mouth or folds of the tissue.
– Both the methods make use of video cameras.Both the methods make use of video cameras.www.indiandentalacademy.comwww.indiandentalacademy.com

 System using markers are generally more reliable, howeverSystem using markers are generally more reliable, however
their placement can be tedious and their position are difficulttheir placement can be tedious and their position are difficult
to replicate for comparisons b/w sessions.to replicate for comparisons b/w sessions.
 RecentlyRecently jaw tracking devicejaw tracking device have been developed to trackhave been developed to track
the mandibular range of motion and its position relative tothe mandibular range of motion and its position relative to
maxilla & cranium as well as velocity of opening & deviation ofmaxilla & cranium as well as velocity of opening & deviation of
opening and closing in 3-D.opening and closing in 3-D.
 Two basic approaches areTwo basic approaches are
Optic –electric methodOptic –electric method
Ultrasonic based methodUltrasonic based method
 Optic –electric methodOptic –electric method::
 Utilizes an array ofUtilizes an array of video camerasvideo cameras to record markers that areto record markers that are
positioned on the patient.positioned on the patient.
 Ultrasonic based methodUltrasonic based method::
 Utilizes an array ofUtilizes an array of microphonesmicrophones secured to the patients headsecured to the patients head
to record changes in ultrasonic frequency with different jawto record changes in ultrasonic frequency with different jaw
position.position. www.indiandentalacademy.comwww.indiandentalacademy.com

Image Calibration & RegistrationImage Calibration & Registration
 Image Calibration & Registration of C-F anatomy is integral to understandingImage Calibration & Registration of C-F anatomy is integral to understanding
biomechanical relationships in face & jaws.biomechanical relationships in face & jaws.
 Presently computer assisted imaging has created the opportunity for the orthodonticPresently computer assisted imaging has created the opportunity for the orthodontic
profession to visualize and study the C-F anatomy better.profession to visualize and study the C-F anatomy better.
 Digital patient models can be used to assess the C-F & dental anatomy inDigital patient models can be used to assess the C-F & dental anatomy in staticstatic
andand dynamic statesdynamic states . (Study and simulate the functional relationship b/w various. (Study and simulate the functional relationship b/w various
tissues).tissues).
 Newer interactive imaging tools allow the orthodontic practitioner to manipulate theNewer interactive imaging tools allow the orthodontic practitioner to manipulate the
digital patient model to simulate treatment and dynamically test feasibility of variousdigital patient model to simulate treatment and dynamically test feasibility of various
approaches.approaches.
 Knowledge gained through simulation can be used during the clinical phase ofKnowledge gained through simulation can be used during the clinical phase of
treatment, which will improve treatment efficacy and efficiency. Image data for eachtreatment, which will improve treatment efficacy and efficiency. Image data for each
type of anatomy being modeled is calibrated & co-registered to the same 3-D matrixtype of anatomy being modeled is calibrated & co-registered to the same 3-D matrix
which can be used to construct models, spatially stitch together various image setswhich can be used to construct models, spatially stitch together various image sets
& populate a morph metric data base with 3-D locations of selected anatomic& populate a morph metric data base with 3-D locations of selected anatomic
structures.structures.

 When data from 2 or 3-D image sets are combined into a 3-DWhen data from 2 or 3-D image sets are combined into a 3-D
matrix they are assigned concurrently a common Cartesianmatrix they are assigned concurrently a common Cartesian
coordinate system.coordinate system.
 To create the model, the relevant anatomy displayed in theTo create the model, the relevant anatomy displayed in the
images is reduced to a point cloud with each point beingimages is reduced to a point cloud with each point being
numerically described on the Cartesian coordinate system.numerically described on the Cartesian coordinate system.
 Then the points are connected and textured to transform toThen the points are connected and textured to transform to
vertices on a polygon meshvertices on a polygon mesh. This mesh is tiled, smoothed and. This mesh is tiled, smoothed and
textured to create a realistic rendering of the anatomic surfaces.textured to create a realistic rendering of the anatomic surfaces.
 Polygon mesh segment anatomically relevant objects, such asPolygon mesh segment anatomically relevant objects, such as
maxilla, mandible and teeth. Surface subdivisions are amongmaxilla, mandible and teeth. Surface subdivisions are among
other available rendering options.other available rendering options.
 Multiple calibrated images permit simultaneous 3-DMultiple calibrated images permit simultaneous 3-D
measurements of selected anatomic structures.measurements of selected anatomic structures.

 Analysis of images in a calibrated environmentAnalysis of images in a calibrated environment
creates the opportunity to extract accurate C-F 3-Dcreates the opportunity to extract accurate C-F 3-D
morphmetric data.morphmetric data.
 A calibrated environment is 3-D, true and accurateA calibrated environment is 3-D, true and accurate
visualization and analysis space or volume where allvisualization and analysis space or volume where all
modes of diagnostic bioimaging can be calibrated; comodes of diagnostic bioimaging can be calibrated; co
registered and correlated and simultaneously viewedregistered and correlated and simultaneously viewed
and analyzed and over comes the significant shortand analyzed and over comes the significant short
comings of multiplane radiographic images andcomings of multiplane radiographic images and
photographs through the calibrations & cophotographs through the calibrations & co
-registration process to enable accurate 3-D-registration process to enable accurate 3-D
measurements.measurements.
 Accurate morphmetric data have great value inAccurate morphmetric data have great value in
developing a database of CF form and to initiatedeveloping a database of CF form and to initiate
cross sectional and longitudinal studies in growth,cross sectional and longitudinal studies in growth,
development , and environment has the potential todevelopment , and environment has the potential to
advance global knowledge and education relative toadvance global knowledge and education relative to
advance CF anatomy.advance CF anatomy.

DATABASE:DATABASE:
 CF imaging database programmes currently in clinical use are designedCF imaging database programmes currently in clinical use are designed
primarily to be an image management system forprimarily to be an image management system for storage , retrieval andstorage , retrieval and
viewing of 2-D patient imageviewing of 2-D patient image. Dolphin imaging.); Quick Cephalometric. Dolphin imaging.); Quick Cephalometric
systems.systems.
 These systems allow for 2-D measurements on uncalibarated andThese systems allow for 2-D measurements on uncalibarated and
uncorrelated cephalopmetric image for the purpose of orthodonticuncorrelated cephalopmetric image for the purpose of orthodontic
assessment.assessment.
 Several sources of error are known to occur in standard 2-DSeveral sources of error are known to occur in standard 2-D
Cephalometric measurements technique.Cephalometric measurements technique.
 Measurements guide clinician in developing a plan to transform the size,Measurements guide clinician in developing a plan to transform the size,
shape, location and orientation of the teeth, jaws and adjacent facial softshape, location and orientation of the teeth, jaws and adjacent facial soft
tissues.tissues.
 These measurements are stored in the patient data record.These measurements are stored in the patient data record.
 These techniques are time consuming and highly dependent on operatorThese techniques are time consuming and highly dependent on operator
interaction.interaction.
 Foregoing scenario do provide some advantage by containing algorithmsForegoing scenario do provide some advantage by containing algorithms
for computing angles and distances between land marks and allows forfor computing angles and distances between land marks and allows for
rapid editing location of land marks.rapid editing location of land marks.

 Necessity exists to develop on standard database that canNecessity exists to develop on standard database that can
store multiple source modes of calibrated 2-D and 3 –Dstore multiple source modes of calibrated 2-D and 3 –D
bioimages, analysis data and simulation models and maintainbioimages, analysis data and simulation models and maintain
current statistical data.current statistical data.
 An active database software function is currently underAn active database software function is currently under
development that will enhance the patient specific anatomicdevelopment that will enhance the patient specific anatomic
model; by automatically identifying anatomy and associatedmodel; by automatically identifying anatomy and associated
landmarks, perform volumetric analysis characterizing eachlandmarks, perform volumetric analysis characterizing each
individual tooth and other C-F components, perform standardindividual tooth and other C-F components, perform standard
measurement for patient diagnosis and assessment andmeasurement for patient diagnosis and assessment and
compare the anatomy or object to archetype models.compare the anatomy or object to archetype models.
 Assigning a common cartesian coordinate system centeredAssigning a common cartesian coordinate system centered
within the patients anatomy can optimize the visualization andwithin the patients anatomy can optimize the visualization and
analytical process with the calibrated environment.analytical process with the calibrated environment.
Simultaneous visualization and analysis of multiple imagesSimultaneous visualization and analysis of multiple images
correlated to the common coordinate system of an anatomiccorrelated to the common coordinate system of an anatomic
model creates the opportunity to extract the best features of themodel creates the opportunity to extract the best features of the
combined image set to aid in land mark identification, definingcombined image set to aid in land mark identification, defining
and segmenting tissues, evaluating anatomic structures,and segmenting tissues, evaluating anatomic structures,
building patient specific models and providing accuratebuilding patient specific models and providing accuratewww.indiandentalacademy.comwww.indiandentalacademy.com

 Accurate 3-D CF morphmetric data can aidAccurate 3-D CF morphmetric data can aid
the clinician in making informed decisionsthe clinician in making informed decisions
regarding the initial condition of the patient,regarding the initial condition of the patient,
aid in treatment decisions, assist in underaid in treatment decisions, assist in under
standing the anatomic effect of time and orstanding the anatomic effect of time and or
treatment and compare data to a referencetreatment and compare data to a reference
data source to determine current status anddata source to determine current status and
predictions about growth & development.predictions about growth & development.

CLINICAL UTILITY AND IMPLICATIONCLINICAL UTILITY AND IMPLICATION
 It is clear that no. of new imaging techniquesIt is clear that no. of new imaging techniques
and approaches are available or soon will beand approaches are available or soon will be
available for patient care.available for patient care.
 The challenge is for the clinican to decide on aThe challenge is for the clinican to decide on a
particular imaging modality as a function of theparticular imaging modality as a function of the
information or diagnostic yield Vs patient risk &information or diagnostic yield Vs patient risk &
cost benefit analysis.cost benefit analysis.
 To make this decision, clinican need to have aTo make this decision, clinican need to have a
working knowledge of the technology as well asworking knowledge of the technology as well as
its capabilities.its capabilities.


ORTHODONTIC RECORDSORTHODONTIC RECORDS ::
 Recent inclusion of 3-D digitalRecent inclusion of 3-D digital
imaging data into the orthodontic records.imaging data into the orthodontic records.
Ultimately 3-D records replacing 2-D records,Ultimately 3-D records replacing 2-D records,
next generation CBCT / volumetric CTnext generation CBCT / volumetric CT
promises to produce in a single scan enoughpromises to produce in a single scan enough
information to eliminate the need forinformation to eliminate the need for
conventional panoramic, Occlusal,conventional panoramic, Occlusal,
Cephalometric, selected periapical & TMJCephalometric, selected periapical & TMJ
tomographic studies.tomographic studies.

 TMJ EVALUTIONTMJ EVALUTION::
 For individual seeking orthodonticFor individual seeking orthodontic
treatment to have TMJ conditions that may alter thetreatment to have TMJ conditions that may alter the
size, form, quality and spatial relationship of thesize, form, quality and spatial relationship of the
osseous joint components is not uncommon, whenosseous joint components is not uncommon, when
these conditions occur during development they maythese conditions occur during development they may
alter the growth of the ispsilateral half of the mandiblealter the growth of the ispsilateral half of the mandible
with compensations in the maxilla, tooth position,with compensations in the maxilla, tooth position,
occlusion and cranial base.occlusion and cranial base.
 Skeletal & dental changes occur in vertical, horizontalSkeletal & dental changes occur in vertical, horizontal
& transverse directions thus making them difficult to& transverse directions thus making them difficult to
characterize accurately with conventional 2-D imaging,characterize accurately with conventional 2-D imaging,
such as Cephalometric, tomographic & panoramicsuch as Cephalometric, tomographic & panoramic
projections. There by CBCT has created theprojections. There by CBCT has created the
opportunity to visualize and quantify the local &opportunity to visualize and quantify the local &
regional effects associated with the TMJregional effects associated with the TMJ
abnormalities.abnormalities. www.indiandentalacademy.comwww.indiandentalacademy.com

 ORTHODONTIC BOUNDARY CONDITION:ORTHODONTIC BOUNDARY CONDITION:
 Anatomy sets some of the boundaryAnatomy sets some of the boundary
conditions for tooth position.conditions for tooth position.
 Identification & visualization of these boundaryIdentification & visualization of these boundary
conditions can be performed by applying volumetricconditions can be performed by applying volumetric
CT during initial stage.CT during initial stage.
 In some instance, tooth movement is prevented orIn some instance, tooth movement is prevented or
diminished because of anatomic boundaries such asdiminished because of anatomic boundaries such as
cortical margins, adjacent teeth, dense bone, andcortical margins, adjacent teeth, dense bone, and
expansion of the dental arch form or the labial &expansion of the dental arch form or the labial &
buccal cortical margins of the alveolar bone.buccal cortical margins of the alveolar bone.
 These boundaries are difficult to visualize without theThese boundaries are difficult to visualize without the
aid of cross sectional or 3-D imaging technique.aid of cross sectional or 3-D imaging technique.

 IMPLANTIMPLANT::
 Implants used for anchorage to mobilize teeth orImplants used for anchorage to mobilize teeth or
dental segments and in some cases can be restoreddental segments and in some cases can be restored
to optimize function and esthetics.to optimize function and esthetics.
 Implants need to be located where they will have theImplants need to be located where they will have the
best chance for success.best chance for success.
 3-D imaging technique can play a significant role in3-D imaging technique can play a significant role in
revealing the anatomic consideration and linking themrevealing the anatomic consideration and linking them
to the prosthetic & biomechanical treatment option.to the prosthetic & biomechanical treatment option.
 IMPACTION:IMPACTION:
 3-D imaging contributes greatly in localizing3-D imaging contributes greatly in localizing
impacted teeth, identifying associated pathologicalimpacted teeth, identifying associated pathological
conditions, assist planning surgical access & assistconditions, assist planning surgical access & assist
with designing the traction mechanics for moving thewith designing the traction mechanics for moving the
impacted teeth into the dental arch & occlusion.impacted teeth into the dental arch & occlusion.

 ESTHECTIC:ESTHECTIC:
 Volumetric CT captures the spatial relationship b/wVolumetric CT captures the spatial relationship b/w
the M-F hard & soft tissues. Software can aid in visualizationthe M-F hard & soft tissues. Software can aid in visualization
and quantification of hard & soft tissue relationship.and quantification of hard & soft tissue relationship.
 Anatomic models can be constructed from the CT volume andAnatomic models can be constructed from the CT volume and
co registered with other available 3-D image data.co registered with other available 3-D image data.
 Anatomic model in a way that they provide the modeled tissuesAnatomic model in a way that they provide the modeled tissues
with attributes that will predict and simulate tissue response towith attributes that will predict and simulate tissue response to
growth, treatment, and function.growth, treatment, and function.
 ORTHOGNATHIC SURGERY & DISTRACTIONORTHOGNATHIC SURGERY & DISTRACTION
OSTEOGENESIS:OSTEOGENESIS:
 C-F hard & soft tissues and their spatial relationship can beC-F hard & soft tissues and their spatial relationship can be
analyzed on patient specific models using appropriate software.analyzed on patient specific models using appropriate software.
 The analyzed model then can be used to simulate or testThe analyzed model then can be used to simulate or test
treatment option & ultimately will be used to assist at the time oftreatment option & ultimately will be used to assist at the time of
treatment.treatment.

SUMMARYSUMMARY
 Orthodontic imaging has come a long way since theOrthodontic imaging has come a long way since the
‘‘plaster eraplaster era’ during the times of Edward Angle &’ during the times of Edward Angle &
Calvin case when plaster was the recording mediumCalvin case when plaster was the recording medium
for the dentition as well as facial form.for the dentition as well as facial form.
 Although plaster provided 3-D information, there wereAlthough plaster provided 3-D information, there were
limitations.limitations.
 With the advent of dental impression materials &With the advent of dental impression materials &
radiographic film, the orthodontic patient recordradiographic film, the orthodontic patient record
evolved into ‘evolved into ‘film era’.film era’.
 Since then use of photography & radiography hasSince then use of photography & radiography has
evolved in orthodontic practice.evolved in orthodontic practice.
 Despite their limitation these methods have servedDespite their limitation these methods have served
orthodontic well as research tool, diagnostic aid &orthodontic well as research tool, diagnostic aid &
medico-legal records.medico-legal records. www.indiandentalacademy.comwww.indiandentalacademy.com

 Now we are in ‘Now we are in ‘digital eradigital era’ in which new digital imaging’ in which new digital imaging
methods are being used to resolve previous limitation.methods are being used to resolve previous limitation.
 Imaging has evolved from merely a diagnostic aid toImaging has evolved from merely a diagnostic aid to
advanced functions such as patient specific modelingadvanced functions such as patient specific modeling
& virtual treatment simulation.& virtual treatment simulation.
 3-D information has allowed for computer assisted3-D information has allowed for computer assisted
design (CAD) approaches to orthodontic, enabling thedesign (CAD) approaches to orthodontic, enabling the
manufacturing of surgical models, guides, othermanufacturing of surgical models, guides, other
patient specific appliances.patient specific appliances.
 Upcoming developments allow the technique forUpcoming developments allow the technique for
hypothesis testing and biomechanical analysis of 3-Dhypothesis testing and biomechanical analysis of 3-D
patient data. In this manner orthodontic materials canpatient data. In this manner orthodontic materials can
be selected and tested on the virtual patient beforebe selected and tested on the virtual patient before
appliance fabrication and patient treatment.appliance fabrication and patient treatment.

BIBLIOGRAPHYBIBLIOGRAPHY
 Orthodontics: Current principles & techniques, 4Orthodontics: Current principles & techniques, 4thth
editionedition
:Thomas M. Graber ,Robert L. Vanarsdall Craniofacial:Thomas M. Graber ,Robert L. Vanarsdall Craniofacial
imaging in orthodontics , chapter 2,pg 71-100.imaging in orthodontics , chapter 2,pg 71-100.
 Oral radiology :Principles and interpretation; Stuart C. White,Oral radiology :Principles and interpretation; Stuart C. White,
Michael J. Pharoah; pg 169-243.Michael J. Pharoah; pg 169-243.
 Dentofacial deformities ,integrated orthodontic and surgicalDentofacial deformities ,integrated orthodontic and surgical
correction :2 edn.Vol III, &IV, Pg. 1718,1865-66.2308. Brucecorrection :2 edn.Vol III, &IV, Pg. 1718,1865-66.2308. Bruce
N Epkes,John P Stella, Leward C Fish.N Epkes,John P Stella, Leward C Fish.
 current status and future needs in C-F imaging: Orthodcurrent status and future needs in C-F imaging: Orthod
Craniofacial Res 6(suppl.1),2003;10-16.Mah J, Hatcher D.Craniofacial Res 6(suppl.1),2003;10-16.Mah J, Hatcher D.
 Taking stock : a critical perspective on contemporaryTaking stock : a critical perspective on contemporary
orthodontics ; Orthod Craniofacial Res 7,2004;150-156,orthodontics ; Orthod Craniofacial Res 7,2004;150-156,
Baumrind S.Baumrind S.
 Computer assisted simulations in orthodontic diagnosis andComputer assisted simulations in orthodontic diagnosis and
the application of a new cone beam X-ray CT: Orthodthe application of a new cone beam X-ray CT: Orthod
Craniofacial Res 6(suppl.1),2003;95-101, Maki K,Takanishi A,Craniofacial Res 6(suppl.1),2003;95-101, Maki K,Takanishi A,
Miller AJ.Miller AJ.
 Advance in imaging : impact on studying C-F bone structure:Advance in imaging : impact on studying C-F bone structure:
Orthod Craniofacial Res 6(suppl.1),2003;48-51,Majumdar S.Orthod Craniofacial Res 6(suppl.1),2003;48-51,Majumdar S.www.indiandentalacademy.comwww.indiandentalacademy.com

 Comparison of CT scanograms and Cephalometric radiographsComparison of CT scanograms and Cephalometric radiographs
in C-F imaging: Orthod Craniofacial Res 5,2002;104-113 ,in C-F imaging: Orthod Craniofacial Res 5,2002;104-113 ,
Chidiac JJ, Shofer FS, AL-Kutoubi A, Laster LL,Ghafari J.Chidiac JJ, Shofer FS, AL-Kutoubi A, Laster LL,Ghafari J.
 3-D visualization of the C-F patient : volume segmentation, data3-D visualization of the C-F patient : volume segmentation, data
integration and animation: Orthod Craniofacial Resintegration and animation: Orthod Craniofacial Res
6(suppl.1),2003;66-71, Enciso R,Memon A, Mah J.6(suppl.1),2003;66-71, Enciso R,Memon A, Mah J.
 Fundamentals of image acquisition and processing in the digitalFundamentals of image acquisition and processing in the digital
era: Orthod Craniofacial Res 6(suppl.1),2003;17-22, Farmanera: Orthod Craniofacial Res 6(suppl.1),2003;17-22, Farman
AGAG
 Image analysis and superimposition of 3-D CBCT models :AJO-Image analysis and superimposition of 3-D CBCT models :AJO-
DO ,May 2006,Vol.129,No.5,Pg.611-618.Lucia H SDO ,May 2006,Vol.129,No.5,Pg.611-618.Lucia H S
Cevidanes,Martin A Stynes and William R Proffit.Cevidanes,Martin A Stynes and William R Proffit.
 3-D digital modeling and setup: AJO-DO ,May3-D digital modeling and setup: AJO-DO ,May
2006,Vol.129,No.5,Pg.605-610.AldoMachi, Gianpaolo2006,Vol.129,No.5,Pg.605-610.AldoMachi, Gianpaolo
Carrafiello,VittorioCacciafesta and Antonio Norclni.Carrafiello,VittorioCacciafesta and Antonio Norclni.
 Evaluation of internal derangement of the TMJ by panoramicEvaluation of internal derangement of the TMJ by panoramic
radiographs compared with MRI: AJO-DO ,Mayradiographs compared with MRI: AJO-DO ,May
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Kim,Dong-seok Nahm. www.indiandentalacademy.comwww.indiandentalacademy.com

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