Download THE EVALUATION OF DEHISCENCES USING CONE BEAM COMPUTED TOMOGRAPHY

THE EVALUATION OF DEHISCENCES USING
CONE BEAM COMPUTED TOMOGRAPHY
Nicholas S. Ising, D.M.D.
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2010
ABSTRACT
Introduction: Cone beam computed tomography (CBCT) has
allowed for the visualization of the entire maxillomandibular complex in three dimensions without overlap of
structures at a significantly reduced radiation dose and
cost to the patient. Purpose: The purpose of this study
was to validate the use of 3-D surface volume rendering
(SVR) images to quantify the height of alveolar
dehiscences. Materials and Methods: Twenty-four dehiscences
were created on 9 incisors, 9 canines, and 6 premolars on 4
cadaver skulls. i-CAT CBCT’s were taken of each skull at .
2mm voxel size. Each dehiscence was quantified by 21
orthodontic residents using the 3-D SVR starting at a
density value (DV) of 1365. The principal investigator
(PI) also quantified each dehiscence using the 2-D
multiplanar (MP) image and 3-D SVR image starting at 1200
DV. Results: The results of this study showed an average
method error of the residents as a group to be .57mm with
an intraclass correlation (ICC) of .77%. The resident’s
method error ranged from .45mm-1.32mm, and the ICC was from
.201-.857%. Only 4 of the residents showed significant
systematic differences compared to the direct measurement.
As a group, the paired t-test was non-significant.
Systematic error was low at -.01mm for the direct
measurement compared to the resident’s average 3-D SVR at
1365 DV measurement. The 3-D SVR at 1365 DV images were
compared to the MP and 3-D SVR images at 1200 DV with no
significant differences in the measurements and low
systematic error. The method error of the PI was .45mm, .
45mm, and .41mm for the 3-D SVR at 1365 DV, 3-D SVR at 1200
DV, and 2-D MP respectively. Conclusions: Using the 3-D SVR
image, dehiscences of the periodontium can be quantified to
a significant level.
1
THE EVALUATION OF DEHISCENCES USING
CONE BEAM COMPUTED TOMOGRAPHY
Nicholas S. Ising, D.M.D.
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2010
COMMITTEE IN CHARGE OF CANDIDACY:
Assistant Professor Ki Beom Kim,
Chairperson and Advisor
Professor Eustaquio Araujo
Adjunct Professor Peter H. Buschang
i
DEDICATION
I dedicate this thesis to my loving wife for her
patience throughout my residency, and her ability to
withstand all of the trials of pregnancy.
this to my parents and brothers.
I also dedicate
I would not be the man
that I am today without their help and guidance.
ii
ACKNOWLEDGEMENTS
I would like to acknowledge the following individuals
for their help with my thesis:
•
Dr. Ki Beom Kim for his time and efforts to guide
this thesis and serving as my chairperson.
•
Dr. Peter Buschang and Dr. Eustaquio Araujo for
their extensive contributions as committee
members.
iii
TABLE OF CONTENTS
List of Tables............................................v
List of Figures..........................................vi
CHAPTER 1: INTRODUCTION...................................1
CHAPTER 2: REVIEW OF THE LITERATURE
Dehiscences..........................................3
Orthodontics and the Periodontium....................7
Radiographic Techniques.............................14
Computed Tomography Scans of the Periodontium.......23
Cone Beam Computed Tomography and the Periodontium..26
Statement of the Research...........................31
List of References..................................33
CHAPTER 3: JOURNAL ARTICLE
Abstract............................................48
Introduction........................................50
Materials and Methods...............................53
Dehiscence Construction........................53
Imaging........................................55
Statistical Analyses................................57
Results.............................................58
Discussion..........................................66
Conclusion..........................................72
List of References..................................73
Vita Auctoris............................................79
iv
LIST OF TABLES
Table 1:
Systematic Intraobserver Error............60
Table 2:
Random Intraobserver Error................61
Table 3:
Systematic Interobserver Error............61
Table 4:
Random Interobserver Error................62
Table 5:
Comparing the Tooth Groups................65
v
LIST OF FIGURES
Figure 1:
The Partial Volume Effect.................20
Figure 2:
Computed Tomography Density Value Ranges..22
Figure 3:
Dehiscences...............................54
Figure 4:
3-D Surface Volume Rendering
Images....................................56
Figure 5:
2-D Multiplanar Images....................57
Figure 6:
Intraobserver Reliability.................60
Figure 7:
Systematic Error Mean Difference..........62
Figure 8:
Intraclass Correlation for each resident
compared to the direct measurement........63
Figure 9:
Method Error..............................64
Figure 10:
Direct Measurements compared to the
Resident’s Average measurement using the 3-D
Surface Volume Rendering Image............65
Figure 11: Human Error...............................70
vi
CHAPTER 1: INTRODUCTION
The periodontium is a dynamic and unique part of the
human body, which provides support and nutrition for the
teeth.
The alveolus, periodontal ligament, cementum, and
supporting gingiva are all parts of the periodontium.
When
pressure and tension are placed on the periodontal ligament
during orthodontics, osteoclastic and osteoblastic cells
are recruited to area.
The teeth are then able to move
within the bone by modeling and remodeling.
Orthodontic diagnosis requires a thorough exam of
the supporting periodontium.1
Dehiscences, fenestrations,
and other intra-bony defects should be included for the
orthodontic diagnosis and treatment plan.
Knowledge of
these defects could drastically affect the treatment plan.2
Ectopically positioned teeth could have periodontal defects
which could lead to the extraction of those teeth over
others.3
The biomechanics of treatment could also be
affected.
Expansion treatment and proclination of the
incisors are an acceptable alternative to extraction
treatment.
However, this biomechanical therapy could lead
to deleterious effects without proper knowledge of the
buccal and lingual bony plates.4-7
10
Identifying dehiscences before treatment and caused
from treatment is of paramount importance.
However, this
requires a surgical flap procedure or a computed tomography
(CT) radiograph.
Significant risks from flap surgery are
possible including recession, soft tissue dehiscence, and
tissue necrosis.8
CT’s have a very high dose of radiation,
large expense to the practitioner and patient, and is not
practical for dentistry.9
A newer technology, cone beam
computed tomography (CBCT), has the potential to identify
these periodontal defects.10,11
CBCT’s offer tooth and bone
assessment without obstruction from overlying structures.12
They also have a reduced radiation dosage and cost compared
to CT.9,13
The purpose of this study is to validate the
ability of an orthodontist to use the 3-D Surface Volume
Rendering (SVR) CBCT radiograph to accurately measure the
size of a dehiscence.
11
CHAPTER 2: REVIEW OF THE LITERATURE
Dehiscences
Dehiscences are bony defects of the alveolar unit.
They are located on the buccal or lingual aspect of a tooth
and can extend from slightly below normal (1.5-2mm below
the cementoenamel junction) to the apex of the root with
normal interproximal bone levels.14
There are two main types of gingiva, thin and scalloped
and thick and flat.15,16
The thin and scalloped gingiva is a
significant risk factor for developing recession and
dehiscences.
The gingiva is easily abraded away until the
base of the dehiscence is reached.
This process is called
self-limiting recession.14
The etiology of dehiscences can be attributed to many
causes.
One cause for dehiscences is ectopically
positioned teeth which are outside of the bony limits of
the alveolus are often lacking the normal amount of bone on
the overlying facial surface.3,17,18
12
This is often due to
significant anterior crowding.19
This crowding does not
allow the tooth to erupt into its appropriate position
causing it to impact or to erupt outside of the bony
limits.19
Another eruption anomaly is that the roots of a
tooth may erupt in a more buccal position compared to the
crown creating a dehiscence, especially on mandibular
incisors.17
Frenum attachments are another cause for
dehiscenses.17
They can place enough pressure on the bone in
certain areas to eventually cause recession of the bone.
The maxillary and mandibular mid-labial frenum most often
cause the recession on the associated central incisors.17
Patient habits are a frequent cause of dehiscences.
The
use of smokeless tobacco products causes defects in the
location of use, and the lingual of the alveolus is prone
to recession from tongue piercings.20,21
Another study indicates that there is a strong
association of periodontal defects with traumatic
occlusion.
The trauma, along with inflammation in the
area, can cause destruction of the bone surrounding the
affected tooth.22
If this traumatic occlusion is removed,
there is a significant reduction in the further progression
of periodontal disease.22,23
13
Iatrogenic treatment has also been shown to cause
defects whether through moving teeth outside of the
alveolus or through impinging on the biologic width with a
dental restoration.4,24
The normal attachment of the gingiva
has 1mm of sulcular depth, 1mm of epithelial attachment,
and 1mm of connective tissue attachment above the crestal
bone.
If a restoration impinges on this space, the bone
and epithelial attachment will migrate apically until the
normal levels are established again.
Normal aging and traumatic tooth brushing, over the
course of time, cause recession of the gingiva and bone17.
As the gingiva is abraded, the alveolar bone recedes with
the gingiva to maintain the biologic width.14
Pathological conditions of the periodontium can cause
inflammation.
This inflammation is associated with the
breakdown of the cells and tissues causing the loss of the
gingiva and bone height.17
As seen above, the etiology of recession, dehiscence
formation, and general periodontal breakdown can be due to
one single influence or to a more complex interaction
within the periodontium.17
14
Dehiscences are widely prevalent among American
populations.
In a study of 146 adult American skulls,
40.4% of the skulls had at least one dehiscence, and 3315
teeth were evaluated in which 9% had dehiscences.
Sixty-
seven percent of dehiscences were found in the mandible.
The presence of dehiscences and fenestrations (windows in
the alveolar bone in which the root is in direct contact
with the soft tissues) were positively correlated with thin
alveolar bone and negatively correlated with attrition of
the teeth.
African American males and Caucasian females
were significantly more likely to have dehiscences, while
African American females were significantly more likely to
have fenestrations.25 Other reports place dehiscences and
fenestrations as high as 20% in the population.14
With these
rates of dehiscences, an orthodontist must consider
dehiscences in their diagnosis and treatment plan.
Often, dehiscences are present but the gingival margin
level and probing depth is normal.
This is due to a long
junctional epithelial attachment of the gingiva to the
cementum.
In a study to relate dehiscences to the
recession of the gingiva, the average depth of a dehiscence
was 5.43mm while the average recession on those teeth was
2.67mm.
15
However, the study showed that the depth of the
dehiscence does not always correlate with the depth of the
gingival recession.
Often the apical extent of the
dehiscence is significantly more than 2.76mm from the level
of the gingiva and was shown to be as great as 7.5mm
different.26
Orthodontics and the Periodontium
The biomechanic treatment plan must be tailored to each
individual patient based on the assessment of their
periodontium.
The facial and lingual bony plates need to
be evaluated so as to not impose on the limits of the
alveolus.5
The periodontium has incredible regenerative
properties from local stem cells, but iatrogenic effects
may occur during orthodontic treatment.27
The inclusion of a
Periodontal Screening and Recording (PSR) exam along with a
referral to a periodontist, if necessary, needs to be a
part of every new patient exam.1
A systematic review of the literature identified an
absence of reliable evidence describing positive effects of
orthodontic treatment on periodontal health. The existing
evidence suggests that orthodontic therapy results in small
16
detrimental effects to the periodontium overall.28
Orthodontic therapy was associated with 0.03 millimeters of
gingival recession, 0.13 mm of alveolar bone loss, and 0.23
mm of increased pocket depth when compared with no
treatment.28
One of the most important aspects of determining
periodontal tissue reaction is the thickness of the
gingiva.
Thin gingiva is at a much higher risk factor for
recession and periodontal defects.15,16
Reports show that
grafting should be done prior to orthodontics if any
gingival recession is present and anticipated to increase
or if there is less than 2mm of attached gingiva.1,29
If the
grafting is done for cosmetic reasons, then it should be
done after orthodontics.1
It has been suggested that the inclination of the lower
incisors results in gingival recession and bone loss. Using
CT’s, one study found there was no difference in bony
support of the lower incisors with different inclinations.30
However, these CT’s were from orthodontically untreated
individuals.
To examine the effects of orthodontic
proclination, another study examined the mean difference of
recession between proclined and non-proclined teeth during
treatment.
17
The mean difference of recession was 0.14 mm,
which was not significant.31
Most of the cast studies agree
with the previous cast study that proclination does not
significantly change the gingival level in adults or
children.32-36
The width of the keratinized gingiva also does
not change during orthodontic treatment even if the
clinical crown length increases.37
Wingard and Bowers showed
in-vivo on monkeys that mandibular incisor proclination
from 2-5mm does not result in gingival recession.38
However,
Steiner et al. showed on monkeys that a 3mm proclination of
maxillary central incisors produced significant recession
of the gingival margin, connective tissue level, and
marginal bone.4
Final inclination of greater than 95
degrees and free gingival-margin thickness of less than .5
mm showed greater and more severe recession.16
Faced with
the alternative between extraction and reasonable labial
movement of lower incisors, the present studies indicate
that the latter is a valuable alternative leading to no
clinically relevant recession of the gingiva.31-36
Most of
these studies were conducted using pre-treatment and posttreatment models which only looked at the gingival heights.
The underlying facial bone could have changed considerably.
Handleman determined that there were orthodontic walls
or barriers to orthodontic treatment.
18
These walls were the
palatal cortex and the lingual symphisis due to the
thickness of the bone.
The labial-lingual widths of the
alveolus should be established before treatment to
determine the amount of space available to move the teeth.
Short face type patients generally present with a greater
alveolar bone width than the long face type.39
Thin alveoli
were especially noted for mandibular incisors in high angle
cases and average class III cases.
It was noted for
maxillary central incisors in high angle class II patients.
Significant iatrogenic sequelae could be caused by
challenging the limits of the alveolus.5
Extraction treatment in which the anterior teeth are
maximally retracted may reach the bony lingual plate and
challenge this wall.
Sarikaya et al. used CT scans to
evaluate the thickness of the labial and lingual plate
after retraction of maxillary and mandibular anterior teeth
from first premolar extractions7.
The study showed there
was a reduction of the width of bone following retraction
in both arches on the lingual and at the alveolar crest on
the buccal of the mandibular incisors.
Several patients
developed dehiscences that were not visible from visual
inspection or cephalometrically.
When the available room
for tooth movement is limited, the movement may force the
19
tooth root against the cortical plate and may cause adverse
sequelae.7
Expanders have been used for over 100 years.
Whether
slow or rapid, expanders have been used to correct crossbites and increase the arch perimeter.
It has long been
thought that there is no long term effect on the
periodontium.
However, the expansive forces may cause the
teeth to displace themselves outside of the bony limits of
the alveolus causing bony dehiscences.
Greenbaum and
Zachrisson showed that rapid and slow expansion patients
compared to normal treatment groups displayed no
significant effects to the periodontium.40
Although the mean
differences were clinically small, individual variation was
evident.
Among the few persons who exhibited the more
marked periodontal breakdown at the central aspect of the
first molars, most were found in the rapid expansion group.40
Other studies also found no significant gingival recession
using slow expansion but did show marked tipping of the
teeth.41,42 The rarest complication of an expander was extreme
root resorption or bony dehiscenses.43
Garib et al. conducted a study to evaluate the effects
of a Hyrax and Haas type rapid palatal expander (RPE)
appliances using CT’s.
20
RPE reduced the buccal bone plate
thickness of supporting teeth 0.6 to 0.9 mm and increased
the lingual bone plate thickness 0.8 to 1.3 mm.
RPE
induced bone dehiscences on the anchorage teeth's buccal
aspect from 7.1 ± 4.6 mm at the first premolars to 3.8 ±
4.4 mm at the mesiobuccal area of the first molars.
The
subjects with thinner buccal bone plates prior to expansion
were more likely to show a more marked reduction of the
alveolar crest. The Hyrax expander produced greater
reduction of first premolar buccal alveolar bone crest
level than did the Haas expander.6
Rungcharasseng
et al.
conducted a similar study using CBCT’s and found
significant reduction of the alveolar crest around the
first premolars (-4.42mm) and molars (-2.92mm).44
The amount
of alveolar bone loss displayed by the CT and CBCT scans
shows severe iatrogenic sequelae to RPE treatment if the
level of bone loss measured is accurate.
These studies
show that the overlying gingiva may not always show the
effects of treatment on the underlying bone.6,44
The formation of bony dehiscences during treatment is
caused when the limit of the biologic structure is reached
where the bone becomes too thin for the osteoprogenitor
cells to form new bone.32
Bony dehiscences produced during
excessive tooth movement may repair if the teeth are moved
21
back within the limits of the alveolus.
This is due to the
increase in tension on the alveolar crest from the
stretching of the supracrestal fibers.45
It has been shown
in-vivo on monkeys that moving the teeth back into the arch
after expansion can cause a spontaneous correction of the
dehiscence.46
The second CT in Garib et al. and
Rungcharasseng et al. study was taken at the removal of the
expander after a three month long retention period with the
RPE still in place.6,44
This would not allow for relapse of
the teeth as would be expected post-expansion and potential
bony repair of the alveolus.47
To correct the defects of the
periodontium, research is being conducted on the
reformation of bone after dehiscence formation.
Bone
morphogenic protein, enamel matrix derivative, and guided
tissue regeneration have been shown to regain bony
Support.48-50
Impacted canines also present several periodontal
complications to consider for orthodontic treatment.
position of the canine can have impacts on the future
The
periodontal health.51
Labially erupted canines (20% of
canine impactions), especially high labial, often have
recession post-orthodontic treatment.3,13,18
Positional
location prior to treatment and proper orthodontic and
22
surgical management allows for a more successful prognosis
of the supporting periodontium.51,52
Radiographic Techniques
The history of radiographs in dentistry has evolved
steadily.
Peri-apical, bitewing, and panoramic radiographs
were originally used to evaluate the periodontium.
Alterations of the interproximal crestal bone could be
determined; however, the facial and lingual aspects of the
alveolus could not be evaluated.53,54
The computed tomography
(CT) radiograph allowed for complete visualization of the
bony components of the alveolus.55
This three-dimensional
(3-D) representation of the alveolus has allowed detection
of facial and lingual bony defects.56
The first CT scanner was developed by Hounsfield in
1967.57
Since then several generations of machines have been
developed leading to the CT scanners of today.
It is a
process of using traditional tomograms and using geometric
mathematical formulas to reconstruct a 3-D image.58
The
spiral and helical CT imaging generates a continuous, fanshaped beam of photons.
The source and the sensor move
about the subject in 1mm increments taking multiple scans.
23
These individual scans are then reconstructed into the 3-D
images.
This process can be time consuming, and any
movement can distort the image.
The radiation exposure is
also very high due to the length of exposure to the
photons, which makes this technique less routinely used in
orthodontics, along with the cost of the scan.58
CBCT’s were first developed for angiography in the
early 1980s at Mayo.57
Over the past 5-10 years and several
generations of development, CBCT machines have been
popularized for its use in dentistry.
CBCT’s are captured
by using a cone shaped beam of photons which strike a
digital flat panel detector.
This allows acquisition of
the image in one pass with shorter scan times instead of
1mm slices with the conventional CT machines.
The benefits
of CBCT scans are a lower radiation dosage, shorter
acquisition time, lower cost of the machine, isotropic
voxels as small as .095mm, and the subjective image quality
is high.9,13
The scan is also not taken in a horizontal
position allowing more accurate soft tissue scans.
However, metal artifacts from restorations or implants
compromise the image quality.
These scans capture anywhere
from 160-600 images and are reduced to a volume using a
weighted, filtered program using the Feldkamp algorithm9.
24
Cone-beam images also show anatomic structures and
relationships without overlay or distortion not previously
revealed with conventional imaging. Cross-sectional images
and 3-D reconstructions may be viewed in any orientation
needed.
The practitioner can now readily examine root
inclination and the temporomandibular joint, location of
impacted and supernumerary teeth, the thickness of bone,
space available between tooth roots at sites where miniimplants can be placed to provide anchorage, and for
planning surgical cuts. It is also possible to examine
maxillo-mandibular facial asymmetries, relationships of
soft tissues, and the airway in three dimensions.13,59,60 A
particular problem orthodontist’s face is to understand the
position of impacted canines. 3-D volumetric imaging of
impacted teeth can show the presence or absence of a tooth,
size of the follicle, buccal to lingual location,
inclination of the tooth, amount of the bone covering the
tooth, potential paths of eruption into the arch, and
proximity to and resorption of roots of adjacent teeth,
especially lateral incisors.3,61-63
Such information allows for
improved treatment planning and diagnosis for bringing
these teeth into function with limited gingival
recession.3,18,61
3-D Surface Volume Rendering (SVR) images
display a 3-D reconstruction and offer an improved means
25
for assessing treatment outcomes and different patterns of
bone remodeling following orthognathic surgery.59
Superimposition of 3-D images has been developed to help
evaluate changes as a result of orthodontic treatment and
growth.
There is a need to identify orthodontic conditions
and problems most likely to benefit from the use of CBCT
scans in comparison with conventional cephalometric
radiographs.9 Therefore, the patient is subjected to the
lowest radiation dose and receives the highest quality
treatment.
In the dental community, CBCT radiographs are
rapidly changing the diagnostic and treatment planning
abilities.9,13,64,59
Many professionals are now even considering that using
a 3-D radiograph is the new standard of care for certain
situations.65,66
One study looked at the effect CT’s had on
the treatment plan of 80 children with impacted canines.
The treatment plans of 35 (43.7%) of the 80 children were
altered due to the increased information from the CT scan.
More than half (53.8%) of the treatment plans were altered
from the discovery of root resorption on the incisors
adjacent to the impacted canines. Without the CT
investigation, 13 who had no root resorption on their
incisors would have had lateral incisors extracted, and 11
26
children would not have been treated for root resorption
that had caused a pulp exposure on the incisor root.2
Another study showed that root resorption was present in
27.2% of lateral and 23.4% of central incisors with an
adjacent impacted cuspid.62
Nearly all of these resorptions
occurred where the impacted canines were in close contact
with the incisors.62
These studies show the importance that
3-D scans have on diagnosis, and the shift to these scans
becoming a standard of care.2
Radiation dosage of the computed tomography scans have
far exceeded that of panoramic and bitewing radiographs.
However, cone beam computed tomography scans have
significantly reduced this exposure to nearly that of a
full mouth series of intraoral radiographs.67,68 Using risk
calculations, the risk of fatal malignancy from a CBCT of
the jaws is between 1 in 100 000 to 1 in 350 000.69 When
considering a large imaging field, the effective dose for a
cone-beam examination ranges from 44–50 µSv for some
machines and up to 477 µSv for others depending on the
voxel size. The effective dose is about 20 µSv for a medium
size view and as low as 6–12 µSv for a 4 cm field of view.9,13
For comparison, a conventional full-mouth set of dental
radiographs is about 84-150 µSv, a panoramic view about
27
6.7-54 µSv, a conventional CT of the same region about
2,270-2,600 µSv, and a flight from Paris to Tokyo is around
137 µSv.9,13
Several studies have investigated the accuracy of CT
and CBCT images with the 2-D multiplanar (MP) reformatting
and 3-D SVR.
Direct measurements on skulls compared to CT
scans have shown to be highly accurate.
A .377mm average
difference between the CT and direct measurements was found
with no statistical difference.70
Systematic errors were
low: 0.88, 0.76, and 0.84 mm for horizontal, vertical, and
transverse measurements, respectively.71
Using the 3-D SVR
CT image, smaller slice thickness showed more accurate
measurement with an average difference to be ~.6mm to the
true value.72
These accurate reports for CT scans were then
compared to CBCT scans.
Loubele et al. compared CBCT and
CT scans, and both yielded sub-millimeter accuracy for
linear measurements.73
The volumetric data rendered with
CBCT systems provided highly accurate data compared with
the physical measures directly from the skulls, with around
1% relative error.74,75
The systematic error in the x, y, and
z spacial planes is 0.19, 0.21, and 0.19 mm respectively.76
The i-CAT CBCT machine has been shown to be accurate to ±1
voxel.77 Other studies also found small differences in
28
linear measurements comparing i-CAT CBCT’s to dry skulls
using the 3-D SVR image in Dolphin 3-D imaging.
These
errors were due to a lack of fiducial markers, but were
still clinically accurate with an approximate measurement
error of .8mm.78,79
Baumgertal et al. found that both the 3-D
SVR CBCT image and the caliper measurements were highly
reliable (r >0.95).80 The CBCT measurements tended to
slightly underestimate the anatomic truth.79-81
This
underestimation only became clinically significant when
multiple measurements are added together, i.e. measuring
tooth space-arch length discrepancy.
The measurements from
CBCT volumes can still be used for quantitative analysis;
however, an adjustment for this error allows for improved
accuracy.
This was accomplished by adding a voxel size to
the measurement to account for the underestimation due to
“the partial volume effect” (Figure 1).80
Figure 1: The Partial Volume Effect80
29
This effect appears as blurring over sharp edges on CT
and CBCT scans. It is due to the scanner being unable to
differentiate between a small amount of high-density
material (bone) and a larger amount of lower density (soft
tissues) in the same voxel. The processor tries to average
out the two densities or structures, and information is
lost.
This can be partially overcome by scanning using
thinner slices or a smaller voxel size; however, Hassan et
al. state that smaller voxels can lead to more distortion
on the 3-D SVR image.82
Another strategy to prevent this
information loss is the “full width half maximum” (FWHM)
method for CT scans.83,84
This is accomplished using the mid-
density value between the bone and soft tissue or air and
setting the density value (DV) accordingly.
This is
accomplished for CT scans because each tissue type has a
known DV range (Figure 2), although absolute DV vary
between machines.85,86
However, the densities are
inconsistent in CBCT images; therefore, finding a threshold
range is more difficult.87,88
In a study to determine bone
densities for implant placement, the Hounsfield Units (HU)
and DV for CBCT were consistently higher than for the CT HU
and DV’s.89
30
Figure 2: CT Density Value Ranges90
Schlueter et al. measured dry mandibular condyle
widths using the 3-D SVR view in Dolphin imaging.
The
density values were adjusted into the soft tissue range in
order to visualize the low density bone of the condyle.
The measurements were found to be accurate with this
adjustment.90
If soft tissues were present, the ability to
determine the condyle size would be compromised.
Therefore, more accurate bony measurements should be made
on higher density cortical bone when soft tissues are
present on the 3-D SVR image.
31
Also, an open-mouth scan
position coupled with a voxel size of <.4 mm is recommended
when creating 3D reconstructions of the dental arches.82
Ballrick et al. showed that the smaller the voxel size
accounted for the best measurement accuracy and spatial
resolution followed by increased scan times and finally the
size of the scan.91
Spatial resolution is the ability to
separate 2 objects in close proximity.
Theoretically, this
resolution should be equal to the voxel size; however this
was found not to be the case.
The detector’s ability to
reduce the noise (energy from other sources not from the xray tube including light and scatter) along with the voxel
size, scan time, scan size, and human error make the
spatial resolution .86mm.91
The study also found that the
measurement error was .1mm, and 94.4% of the measurements
were slightly smaller, but not clinically significant.91
So
if the measurement is greater than .86mm, then the
measurement could be within .1mm.
Overall, the scans had a
1:1 image to reality ratio,92,93 and the direct measurements
of dry skulls or phantoms were found to be accurate to
measurements made on the CBCT images and conventional CT
images.
CT Scans and the Periodontium
32
A thorough knowledge of the periodontium is of primary
importance for an orthodontist to create a problem list and
diagnosis.
CT scans of the head and neck have been the
gold standard for indentifying periodontal defects.94
Several studies have been done to validate the accuracy of
these scans compared to direct measurements.
Pisorious et
al. studied whether probing depths could be detected by CT
scans, but the values for the CT were on average 2mm
different than for direct probing.95
The results did show
better diagnostic findings for furcal defects.95
Naito et
al. conducted an in-vivo study on 31 teeth and 186 sites of
periodontal breakdown.
These sites were measured with a
periodontal probe to the cementoenamel junction after flap
surgery and served as the direct measurement.
Then CT’s
were conducted and the same sites were measured.
The
results showed that the mean difference between CT and the
true bone level was 0.41 ± 2.53 mm with a correlation of .
75.55
The results of this study indicate that CT has the
potential to allow precise assessment of bone defects
caused by periodontal disease.
The previous studies looked at periodontal breakdown
as a whole.
33
Fuhrmann conducted a series of studies using
CT scans to study dehiscences, labial-lingual bone width,
and orthodontic treatment effects.
Seventy percent of the
60 artificially made dehiscences could be identified on the
scans using the multiplanar sections.12
The ability to
identify the dehiscence often was determined by the ability
to detect the periodontal ligament space.
Of the defects
identified, the CT’s were nearly identical to the direct
measurement measurements, 4.2mm to 4.0mm respectively.12
In
the study of labial-lingual bony dimensions, 80% of the
dehiscences were identified in the area of the mandibular
incisors.96
The labial bone width was measureable in the
apical and middle sections of the root.
However, when the
bone overlying the root became less than .5mm thick, the
thickness of the bone was not observable.
A visible
periodontal ligament space was found to improve the
reliability of the measurement of buccal or lingual bone
plates up to 0.2mm.97
This study also showed that regular
cephalograms were not accurate to determine labial bone
thickness on lower incisors.
Only one dehiscence was
observed using a lateral cephalogram and the thickness was
often overestimated by 1mm.96
Orthodontic treatment effects
were studied in Fuhrmann’s third study.
taken before and after treatment.
CT scans were
No noticeable
dehiscences or periodontal breakdown were observed in the
34
fixed appliances group.
However, in the quad-helix
expansion group, significant buccal dehiscences were
observed on the posterior teeth.19
The Pre-treatment CT’s
showed several dehiscences in the mandibular incisor region
which correlated with a small symphisis, reduced labiolingual bone width, anterior crowding, thin bone plates, or
eccentric tooth positions.19
Micro CT scans are also becoming available to
determine the finer details of the alveolus due to a voxel
size in the micrometer range.98,99
One author developed
methods to allow for highly accurate and reproducible
measurements of tooth-supporting alveolar bone using Micro
CT100.
However, the micro CT scan is not currently practical
for orthodontists due to the small field of view, large
dose, and high cost of the scan.
CBCT and the Periodontium
CBCT technology has become increasingly popular for
reasons mentioned above.
This new radiographic technique
has to be validated compared to conventional CT scans.
Vandenberghe et al. investigated periodontal bone
35
architecture using conventional intraoral radiography and
3D CBCT images.
The conclusions of this study found that
traditional radiography images provided more bone details,
but CBCT provided a better morphologic description of the
alveolus and periodontal defects.101
Intraoral radiography
scored significantly better for contrast, bone quality, and
delineation of lamina dura, but CBCT was superior for
assessing crater defects and furcation involvements.101
In
the follow up study, CBCT scans with 0.4 mm thick crosssections demonstrated more accurate values, indicating
enhanced assessment of periodontal bone loss.56
Another
study simulated the ability to detect intrabony defects and
showed that CBCT has better detection properties than
traditional intraoral radiography.102
Agbaje et al. studied
the ability to determine the volume of bony defects using
CBCT scans.
Seventy-one defects were filled with water and
measured to be 227mm3 on average.
volume to be 225mm3.103
CBCT scans determined the
This shows that CBCT scans permit
imaging of anatomical structures in three planes and allows
for reliable volume estimates.
Mol and Balasunduram
studied the ability to accurately determine bone levels
circumferentially around a tooth, and CBCT scans were found
to be more accurate in the premolar and molar areas
compared to anterior teeth.104
36
The scans were not perfect,
but better than conventional radiographs.
Rungcharassaeng
et al. investigated the effects of expansion and showed the
creation of bony dehiscences around the anchor teeth as
discussed earlier.44
Misch et al. investigated the ability to determine
artificial osseous defects that were intrabony and
dehiscence type comparing the multiplanar views from a
CBCT, peri-apical radiographs, and periodontal probing to a
digital caliper.
The defects had gutta percha markers from
the cementoenamel junction to the base of the defects and
were on dry skulls.
Thirty-three percent of the
dehiscences could not be visualized and were therefore not
included.
The systematic errors for all defects were .
34, .27, and .41mm (Probe, PA, CBCT) comparing the CBCT
measurements to the direct measurements.
No systematic
error was reported for dehiscences alone, but the
interproximal defects difference was .36mm.
Therefore CBCT
fared well to traditional measurement styles, but was no
more accurate.
Several dehiscences were not included in
the study but the ones that were included had markers to
show the most apical extent.10
Mengel et al. created 14 dehiscences, 14
fenestrations, and 14 intrabony defects on dry pig and
37
human skulls.
Conventional CT scans, CBCT scans, and
intraoral radiography were compared.
4cm and .125mm voxel size.
The scans were 3cm by
All of the defects were
measured on the multiplanar views in three planes of space
for the CT and CBCT scans.
The mean difference for all
defects was .16+/-.1mm for the CT scans, and .19+/-.11mm
for CBCT scans. For dehiscences of a known size (12mm high,
3mm wide), the deviations were .28, .21, and .88 for
height, width, and depth on the CBCT image.11
Mengel et al. duplicated the prior study using dental
implants placed into dry pig mandibles.
11 fenestrations,
dehiscences, and intrabony defects each were created around
the implants.
The multiplanar image measures compared to
the direct peri-implant defect measurements showed a mean
deviation of 0.17 ± 0.11 mm for the CBCT’s and 0.18 ± 0.12
mm for the CT’s.
For dehiscences of a known size (6mm
height, 4mm width), the deviations were .22, .14, and .16
for the height, width, and depth.
The quality of the
dehiscence construction in both studies may distort the
findings of these studies because the bone was not thinned
at the margins to simulate natural dehiscences.
Between
the two studies, the CT and CBCT scans displayed only a
slight deviation in the extent of the defects. Both
38
radiographic imaging techniques permitted imaging of periimplant defects in three planes without overlay or
distortion. Mengel et al. concluded that CBCT scans have
better imaging quality than CT scans.105
To determine the incidence of dehiscences, a study
performed mandibular anterior flap surgery and CBCT
radiographs on 32 untreated patients.
alveolar defect.
78% had at least one
Dehiscences were the most common defect
and were found most often on the mid-labial of the
mandibular canines.
had dehiscences.
However, all mandibular anterior teeth
This report determined a need to validate
CBCT scans for the detection and measurement of dehiscences
prior to orthodontic treatment.106
CBCT have also been used to quantify the amount of
available soft tissue (ST), ST-CBCT.
Retracting the lip
away from the alveolus during the scan permitted
visualization of the soft tissue.
This CBCT technique
allowed for measurements from the gingival margin to the
facial bone crest, the gingival margin to the CEJ, and
width of the facial gingiva. These scans allowed for a
clear visualization, measurement of the dimensions, and
analysis of the relationship of the structures of the
39
periodontium.
However, this study needs to be verified due
to the use of only three scans.15
Dentoalveolar CBCT scans provide an improvement for the
planning of orthodontic biomechanics based on the presence
and size of pre-treatment dehiscences.
The mechanics
employed would reduce the movement of teeth outside of the
bony envelope.
The scans will also help to determine any
iatrogenic effects caused by orthodontic treatment.
Kasaj
and Willerhausen conclude that the low dosage and superior
image quality of CBCT’s are promising for periodontal
applications, especially in the area of dehiscence,
fenestration, intra-bony defect, and cyst recognition.107
CBCT has the potential to replace conventional radiography
and to make diagnostic decisions based on the bony
architecture found on the scan.108
Statement of the Research
CBCT scans have been shown to be a clinically accurate
representation of the skull and its anatomy.92,93
These scans
can be used by an orthodontist to make diagnostic and
treatment decisions for the patient.9,13,59
40
The scans also have
the ability to determine the effects of treatment
especially of the bone. The 3-D SVR view is often used by
orthodontists to evaluate the dentition and make treatment
decisions.
This is due to the ease of use of the software
and the ability to view the entire skull in 3-D.
This study is being undertaken to determine the ability
of orthodontists to evaluate the alveolus especially the
bone covering the roots of the teeth using CBCT’s.
Prior
studies have shown that measuring dehiscence size on the
CBCT multiplanar views has been clinically accurate on dry
skulls without soft tissues.10,11,105
Prior studies have also
shown that measurements made on the CBCT scans, multiplanar
and 3-D SVR, are clinically accurate78-80,90,91.
This study will
reconstruct natural dehiscences with the soft tissues
present.
Then CBCT’s will be captured at .2mm voxel size
and the measurements of the dehiscences will be carried out
by 21 orthodontic residents.
All dehiscences will be
marked and evaluated using the 3-D SVR view in Dolphin 3-D
(Dolphin Imaging 10.5 Premium Chatsworth, CA).
The
hypothesis is that dehiscences can be measured by
orthodontic residents to a clinically significant level
comparing direct to CBCT measurements.
41
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2008;78:387-395.
80. Baumgaertel S, Palomo JM, Palomo L, Hans MG.
Reliability and accuracy of cone-beam computed tomography
dental measurements. Am J Orthod Dentofacial Orthop.
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81. Lascala CA, Panella J, Marques MM. Analysis of the
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82. Hassan B, Couto Souza P, Jacobs R, de Azambuja Berti S,
van der Stelt P. Influence of scanning and reconstruction
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83. Halazonetis DJ. Commentary. American Journal of
Orthodontics and Dentofacial Orthopedics. 2009;136:25-28.
84. Spoor CF, Zonneveld FW, Macho GA. Linear measurements
of cortical bone and dental enamel by computed tomography:
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85. Levi C, Gray JE, McCullough EC, Hattery RR. The
unreliability of CT numbers as absolute values. AJR Am J
Roentgenol. 1982;139:443-447.
86. Shapurian T, Damoulis PD, Reiser GM, Griffin TJ, Rand
WM. Quantitative evaluation of bone density using the
Hounsfield index. Int J Oral Maxillofac Implants.
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87. Katsumata A, Hirukawa A, Okumura S, Naitoh M, Fujishita
M, Ariji E, Langlais RP. Effects of image artifacts on
gray-value density in limited-volume cone-beam computerized
tomography. Oral Surg Oral Med Oral Pathol Oral Radiol
Endod. 2007;104:829-836.
88. Yamashina A, Tanimoto K, Sutthiprapaporn P, Hayakawa Y.
The reliability of computed tomography (CT) values and
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cone beam CT: comparison with multidetector CT.
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89. Aranyarachkul P, Caruso J, Gantes B, Schulz E, Riggs M,
Dus I, Yamada JM, Crigger M. Bone density assessments of
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2005;20:416-424.
90. Schlueter B, Kim KB, Oliver D, Sortiropoulos G. Cone
beam computed tomography 3D reconstruction of the
mandibular condyle. Angle Orthod. 2008;78:880-888.
91. Ballrick JW, Palomo JM, Ruch E, Amberman BD, Hans MG.
Image distortion and spatial resolution of a commercially
available cone-beam computed tomography machine. Am J
Orthod Dentofacial Orthop. 2008;134:573-582.
92. Lagravère MO, Carey J, Toogood RW, Major PW. Threedimensional accuracy of measurements made with software on
cone-beam computed tomography images. Am J Orthod
Dentofacial Orthop. 2008;134:112-116.
93. Lagravère MO, Carey J, Ben-Zvi M, Packota GV, Major PW.
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Hounsfield conversion in a NewTom 3G cone beam computed
tomography unit. Dentomaxillofac Radiol. 2008;37:305-308.
94. Holberg C, Steinhäuser S, Geis P, Rudzki-Janson I.
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limitations. J Orofac Orthop. 2005;66:434-444.
95. Pistorius A, Patrosio C, Willershausen B, Mildenberger
P, Rippen G. Periodontal probing in comparison to diagnosis
by CT-scan. Int Dent J. 2001;51:339-347.
96. Fuhrmann R. Three-dimensional interpretation of
labiolingual bone width of the lower incisors. Part II. J
Orofac Orthop. 1996;57:168-185.
54
97. Fuhrmann RA, Wehrbein H, Langen HJ, Diedrich PR.
Assessment of the dentate alveolar process with high
resolution computed tomography. Dentomaxillofac Radiol.
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98. Butz F, Ogawa T, Chang T, Nishimura I. Threedimensional bone-implant integration profiling using microcomputed tomography. Int J Oral Maxillofac Implants.
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99. Kuhn JL, Goldstein SA, Feldkamp LA, Goulet RW, Jesion
G. Evaluation of a microcomputed tomography system to study
trabecular bone structure. J. Orthop. Res. 1990;8:833-842.
100. Park CH, Abramson ZR, Taba M, Jin Q, Chang J, Kreider
JM, Goldstein SA, Giannobile WV. Three-dimensional microcomputed tomographic imaging of alveolar bone in
experimental bone loss or repair. J. Periodontol.
2007;78:273-281.
101. Vandenberghe B, Jacobs R, Yang J. Diagnostic validity
(or acuity) of 2D CCD versus 3D CBCT-images for assessing
periodontal breakdown. Oral Surg Oral Med Oral Pathol Oral
Radiol Endod. 2007;104:395-401.
102. Noujeim M, Prihoda T, Langlais R, Nummikoski P.
Evaluation of high-resolution cone beam computed tomography
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103. Agbaje JO, Jacobs R, Maes F, Michiels K, van
Steenberghe D. Volumetric analysis of extraction sockets
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vivo jaw bone. J. Clin. Periodontol. 2007;34:985-990.
55
104. Mol A, Balasundaram A. In vitro cone beam computed
tomography imaging of periodontal bone. Dentomaxillofac
Radiol. 2008;37:319-324.
105. Mengel R, Kruse B, Flores-de-Jacoby L. Digital volume
tomography in the diagnosis of peri-implant defects: an in
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2006;77:1234-1241.
106. Mostafa YA, El Sharaby FA, El Beialy AR. Do alveolar
bone defects merit orthodontists' respect? World J Orthod.
2009;10:16-20.
107. Kasaj A, Willershausen B. Digital volume tomography
for diagnostics in periodontology. Int J Comput Dent.
2007;10:155-168.
108. Tyndall DA, Rathore S. Cone-beam CT diagnostic
applications: caries, periodontal bone assessment, and
endodontic applications. Dent. Clin. North Am. 2008;52:825841, vii.
56
CHAPTER 3: JOURNAL ARTICLE
Abstract
Introduction: Cone beam computed tomography (CBCT) has
allowed for the visualization of the entire maxillomandibular complex in three dimensions without overlap of
structures at a significantly reduced radiation dose and
cost to the patient.
Purpose: The purpose of this study
was to validate the use of 3-D surface volume rendering
(SVR) images to quantify the height of alveolar
dehiscences. Materials and Methods: Twenty-four dehiscences
were created on 9 incisors, 9 canines, and 6 premolars on 4
cadaver skulls.
2 mm voxel size.
i-CAT CBCT’s were taken of each skull at .
Each dehiscence was quantified by 21
orthodontic residents using the 3-D SVR starting at a
density value (DV) of 1365.
The principal investigator
(PI) also quantified each dehiscence using the 2-D
multiplanar (MP) image and 3-D SVR image starting at 1200
DV. Results: The results of this study showed an average
method error of the residents as a group to be .57 mm with
an intraclass correlation (ICC) of .77%.
The resident’s
method error ranged from .45 mm - 1.32 mm, and the ICC was
from .201 - .857%. Only 4 of the residents showed
significant systematic differences compared to the direct
57
measurement. As a group, the paired t-test was nonsignificant.
Systematic error was low at -.01 mm for the
direct measurement compared to the resident’s average 3-D
SVR at 1365 DV measurement.
The 3-D SVR at 1365 DV images
were compared to the MP and 3-D SVR images at 1200 DV with
no significant differences in the measurements and low
systematic error.
The method error of the PI was .45 mm, .
45 mm, and .41 mm for the 3-D SVR at 1365 DV, 3-D SVR at
1200 DV, and 2-D MP respectively. Conclusions: Using the 3D SVR image, dehiscences of the periodontium can be
quantified to a significant level.
58
Introduction
Traditionally, practitioners have used conventional
bitewings, peri-apical, lateral cephalograms, and panoramic
radiographs to evaluate the teeth, roots, and periodontium
for diagnosis and treatment planning.
These radiographs
are limited due to the inherent overlap of bony structures
and inability to determine buccal and lingual bony
defects.1-3
To be able to visualize the entire bony support of the
teeth, computed tomography (CT) has been utilized to allow
three-dimensional evaluation without distortion.
However,
CT’s are not practical for dentistry due to the high cost
of the machine4,5 and large radiation dose to the patient.6,7
A newer technology, cone beam computed tomography
(CBCT) is now being used to image the head and neck.
The
radiation dose is significantly less than a conventional CT
and is approximately equivalent to a conventional full
mouth series.6,7
The lower cost of the machine, lower
radiation dosage of the scan, and high image quality make
the CBCT more practical for use in dentistry.8,9
59
CBCT’s have been used to evaluate root angulations,
position of canine and supernumerary impactions, the
temporomandibular joint, placement of mini-implants,
assessing maxillo-mandibular facial asymmetries, and the
alveolar morphology of the periodontium.4,8,10
These
capabilities enhance an orthodontist’s information to make
more accurate diagnostic and treatment decisions.8,11
Some
authors have even stated that CBCT’s have become the
standard of care for certain situations such as canine
impactions.12,13
The periodontium provides support and nutrition to the
teeth and allows for orthodontic tooth movement.
Therefore, it is crucial to consider the periodontium in
the diagnosis and treatment plan of each individual
patient.14
Dehiscences are one of the major bony defects to
consider because it is difficult to determine their
presence.15
One study showed that 40% of American skulls had
at least one dehiscence with 67% of dehiscences in the
mandible.16
Mostofa et al. performed anterior mandibular
flaps and CBCT’s on 32 patients.
Seventy-eight percent of
the patients had at least one dehiscence with the highest
rates on the canines.17
60
With these rates of dehiscences,
orthodontists must factor this in when creating a treatment
plan.
A systematic review of the literature has shown that
orthodontic treatment has very small detrimental effect on
the periodontium.18
A significant risk factor for this is
the gingival biotype.
Thin and scalloped gingiva is more
prone to recession than thick and flat.19,20
Some orthodontic
mechanics, proclination and expansion, have been used to
alleviate crowding without showing significant negative
effects on the level of the gingiva.21,22
However, study
models and lateral cephalograms do not adequately show the
effects of treatment on the alveolar bone.23
Löst related
the level of the gingiva to the level of the alveolar bone
for dehiscences.
The bone was on average 2.76 mm more
apical than the overlying gingiva; however, there was a
wide variation with some distances as great as 7.5 mm.24
Steiner showed in-vivo on monkeys that excessive movement
of the incisors outside of the alveolus leads to
dehiscences.25
Rungcharassaeng et al. took CBCT’s pre and
post expansion and found reduction of the alveolar crest
around the first premolars (-4.42 mm) and molars (-2.92
mm).26
Other studies have shown crestal alveolar bony
changes from extraction treatment as well.27
61
The limits of
the alveolus as well as the ability to accurately quantify
the alveolar bone levels pre and post treatment need to be
verified.
Traditionally, 2-D multiplanar (MP) images have been
used to interpret CBCT’s using the sagittal, axial, and
coronal planes.
These images have been shown to be able to
evaluate the periodontium9,28; however, the 3-D surface volume
rendering (SVR) images are becoming more popular to
interpret CBCT’s. The aim of this study is to evaluate the
usage of 3-D SVR images from CBCT’s to quantify bony
dehiscences.
Materials and Methods
Dehiscence Construction
Four human cadaver heads with soft tissues present and
dentate maxillary and mandibular arches were obtained from
the Anatomy Department at Saint Louis University.
Twenty-
four dehiscences were created on the buccal aspect of 9
canines, 9 mandibular incisors, and 6 premolars.
Before
the defect construction, a surgical flap was made to allow
access to the bone (Figure 3).
62
A 1/4 round carbide bur and
handpiece was used to remove the bone overlying the roots.
The margins of the bone were thinned to simulate natural
dehiscences (Figure 3).
The dehiscences were made at all
different heights from the cementoenamel junction so that
there was no standardization.
To reduce method error, a
metallic marker was placed at the cementoenamel junction
for a consistent fiducial marker. The dehiscences were
measured from the metallic marker to the base of the
dehiscence directly with a digital caliper to the nearest .
01mm.
Each dehiscence was measured twice with 2 weeks
between measurements to assess reliability.
All metallic
restorations were removed from the dentition to reduce
scatter radiation.
Then the soft tissues were replaced and
sutured tightly to simulate natural soft tissues.
a
b
Figure 3: (a) Completed Dehiscences with thinned margins,
(b) Soft tissues sutured back into place.
63
Imaging
CBCT’s of the 4 skulls were acquired with the i-CAT
scanner (Imaging Sciences International, Hatfield, Pa).
The skulls were positioned using a head holder.
A single
25 second scan comprising 306 basic projections with a 16
cm (Width) by 6 cm (Height) field of view and .2 mm voxel
size was captured.
The CBCT data was imported into
Dolphin 3-D (Dolphin Imaging Version 10.5 Premium
Chatsworth, CA).
All image reconstructions and
measurements were performed on a 20.1-inch flat panel LCD
monitor (FlexScan S2000, Eizo Nanao Technologies Inc,
Cypress, Calif) with a resolution of 1600 × 1200 and a
0.255 mm dot pitch.
The principal investigator (PI) used the 3-D SVR image
generated in Dolphin 3-D imaging to make measurements from
each metallic marker to the most apical extent of the
dehiscence starting at a density value (DV) of 1200 and
1365 (Figure 4).
The PI also used the 2-D MP images to
measure each dehiscence (Figure 5).
Measurements were made
twice for the 2-D MP and SVR at a DV of 1200 images and
three times for the SVR DV at 1365 images, with 1 week
between measurements to assess reliability.
64
Twenty-one orthodontic residents (including the PI) at
Saint Louis University with at least 1 year of experience
manipulating CBCT images in Dolphin imaging, measured the
dehiscences using the 3-D SVR image starting at the DV of
1365.
The DV of 1365 and lighting adjustments of the
images reduced glare and allowed visualization of the fine
bony architecture.
Each resident was given the same
tutorial on use of the software to manipulate the images.
All dehiscences were measured in the same order for each
skull.
The PI was available during the measurements but
only answered questions on the use of the software.
a
b
Figure 4: (a) 3-D Surface Volume Rendering (SVR) image at
1365 density value, (b) Measurement on 3-D SVR image
65
Figure 5: The 2-D Multiplanar images using the coronal,
sagittal, and axial planes.
Statistical Analyses
A standard statistics software program (SPSS Version
17, Chicago, IL) was used to analyze the data.
To
determine reliability, single measure Intraclass
Correlation Coefficients (ICC) was determined for all
multiple sets of direct and CBCT measurements.
The average
of the multiple measurements was then used as the true
value.
To determine intraobserver error, the direct
measurements were compared to the average of the PI’s MP
and 3-D SVR (At 1200 and 1365 DV) measurements and to
66
compare the 3-D SVR at 1365 DV to the MP and the 3-D SVR at
1200 DV measurements in three ways: a 2-tailed paired
student’s t-test at <.05 significance level, method error,
and single measure ICC’s.
To determine interobserver
error, the three tests were also used to compare the direct
measurements to the 3-D SVR at 1365 DV for each resident
and the average of all the residents.
The teeth were then
separated into three groups: incisors, canines, and
premolars.
ICC, method error, and Wilcoxon Signed Rank
tests were used to compare the direct measurements to each
tooth group.
Results
The ICC of the multiple sets of measurements all
showed reasonable correlations (figure 6).
The 3-D SVR
image at 1365 DV showed the lowest correlation due to the
experience of the PI manipulating the images and
quantifying the dehiscences.
The systematic intraobserver
error showed low mean differences between the direct
measurements compared to the MP and 3-D SVR at 1200 and
1365 DV; as well as, comparing the different CBCT images to
67
each other with no significant differences (table 1).
The
random intraobserver error comparing the direct
measurements to the different CBCT images showed high
intraclass correlations and similar method errors of .45
mm, .45 mm, and .41 mm for the 1365 DV 3-D SVR, 1200 DV 3-D
SVR, and 2-D MP respectively (table 2).
The systematic difference between the direct and 3-D
SVR measurements was -.01 mm for the average of the
residents (table 3).
Four residents, out of 21, showed a
significant difference between the direct and 3-D SVR
measurements with systematic differences ranging from
negative .44 mm to .89 mm (table 3 and figure 7).
The ICC
and ME for the average of the residents was .77% and .57 mm
(table 4 and figure 8).
The ICC range was from .20-.86%,
and the method error ranged from .45 mm - 1.32 mm (table 4
and figure 9).
The resident’s average measurement was not
consistently above or below the direct measurement (figure
10).
The tooth groups were then compared with incisors
showing the best method error at .336 mm and ICC of .906%
(table 5).
All tooth groups were not significantly
different from the direct measurements using the Wilcoxon
Signed Rank test (table 5).
68
Figure 6: Intraobserver Intraclass Correlation showing
reliability of multiple direct, 3-D Surface Volume
Rendering (1365 density value and 1200 density value), and
2-D Multiplanar measurements.
Table 1: Systematic Intraobserver Error using a Paired ttest
Direct vs 3-D
Surface Volume
Rendering (SVR) at
1365 Density
Value(DV)
Measurement
Direct vs SVR at
1200 DV
Measurement
Direct vs 2-D
Multiplanar
Measurement
SVR at 1365 DV vs
SVR at 1200 DV
Measurement
SVR at 1365 DV vs
2-D Multiplanar
Measurement
Mean
Difference
Standard
Deviation
t
Probability
-0.13mm
0.63mm
-1.003
0.33
0.00mm
0.65mm
0.002
0.99
-0.2mm
0.56mm
-1.758
0.09
0.13mm
0.36mm
1.747
0.09
-0.07mm
0.45mm
-0.769
0.45
Table 2: Random Intraobserver Error
Single
Measure
Intraclass
Correlation
Direct vs
Surface Volume
Rendering (SVR)
at 1365 density
value (DV)
measurement
69
0.86
Method Error
Probability
0.000
1 and 2 Standard
Deviations
68%
95%
0.45mm
0.89mm
Direct vs SVR
at 1200 DV
measurement
0.84
0.000
0.45mm
0.89mm
Direct vs
Multiplanar
measurement
0.88
0.000
0.41mm
0.82mm
Table 3: Systematic Interobserver Error
* Indicates Paired t-test was statistically significant
(p<.05)
Pair
ed
ttest
Mean
Standard
Prob
Difference Deviation
abil
Residents (mm)
(mm)
t
ity
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
-0.048
-0.23
0.18
0.89
-0.16
0.09
-0.44
0.48
0.17
-0.39
-0.11
-0.44
0.19
-0.014
0.23
1.22
1.31
0.91
1.67
0.85
1.15
1.40
1.27
1.03
0.94
0.97
0.90
1.03
1.39
1.04
-0.19
-0.85
0.98
2.59
-0.95
0.38
-1.54
1.85
0.79
-2.06
-0.54
-2.41
0.92
-0.05
1.07
0.85
0.41
0.34
0.016*
0.35
0.71
0.14
0.077
0.44
0.051
0.60
0.024*
0.37
0.96
0.30
Table 3 continued
16
17
18
19
20
21
Average
70
-0.29
0.62
-0.16
-0.29
-0 .36
-0.13
-0.01
0.9
1.14
0.85
0.88
0.83
0.63
0.82
-1.54
2.65
-0.93
-1.64
-2.16
-1.00
-0.058
0.14
0.014*
0.36
0.11
0.041*
0.33
0.95
Figure 7: Systematic error mean difference for each
resident and the resident’s average on the 3-D Surface
Volume Rendering at 1365 density value measurement compared
to the direct measurement (* denotes Paired t-test <.05).
Table 4: Random Interobserver Error
Residents
Intraclass Correlation
1
2
3
4
5
6
7
8
Method Error (mm)
0.65
0.42
0.70
0.20
0.79
0.66
0.58
0.61
0.85
0.92
0.64
1.32
0.60
0.80
1.02
0.94
0.71
0.75
0.72
0.75
0.69
0.34
0.74
0.74
0.50
0.80
0.77
0.76
0.86
0.77
0.72
0.71
0.67
0.70
0.73
0.96
0.74
0.66
0.90
0.60
0.64
0.63
0.45
0.57
Table 4 Continued
9
10
11
12
13
14
15
16
17
18
19
20
21
Average
Figure 8: Single Measures Intraclass Correlation comparing
the direct measurements to each resident’s and the
71
resident’s average measurements on the 3-D Surface Volume
Rendering.
Figure 9: Method error comparing the direct measurements
against the 3-D Surface Volume Rendering at 1365 density
value measurement for each resident and the resident’s
average.
Figure 10: Direct measurements compared to the resident’s
average on the 3-D Surface Volume Rendering (SVR) starting
at 1365 density value (DV).
Table 5: Comparing the different tooth groups with
Intraclass Correlation, method error, and Wilcoxon Signed
Rank test.
Wilcoxon
Intraclass
Method
signed Rank
Correlation
Error
test
Canines
0.759
0.62
0.953
Premolars
0.532
0.739
0.917
Incisors
0.828
0.336
0.779
Discussion
Understanding the alveolar bone morphology using the
images derived from a CBCT has been of great interest in
the dental community.
Comparing CBCT images to traditional
intraoral radiography, it was found that CBCT had better
72
potential to represent the alveolus, especially detecting
the 3-D volume of intrabony defects.1,29,30
The detection of
dehiscences through traditional radiography or direct
evaluation is nearly impossible.
However, the CBCT images
offer a real advantage in the detection of these defects.
The results of this study show that dehiscences can be
accurately measured using the 3-D SVR from CBCT’s.
The
residents as a group showed only a .57 mm method error and
a .77% intraclass correlation.
However, the method error
range was from .445 mm to 1.36 mm.
The incisors had the
best method error at .336 mm.
Mengel et al. showed that dehiscence height could be
measured with only a .28 mm systematic difference.9
Mengel
et al. conducted another study measuring dehiscences on
implants and found the systematic difference to be .22 mm.31
These two studies compared traditional CT to CBCT at
.
125 mm voxel size with both showing similar results.
The
authors state that the CBCT showed better image quality.
Misch et al. conducted a study measuring intrabony and
dehiscence defects using CBCT at .4 mm voxel size.
The
systematic difference in height of both defects combined
was found to be .41 mm.28
73
Fuhrmann used traditional CT with
1 mm slices and determined a .2 mm systematic difference of
dehiscence height.3
The prior studies used the 2-D MP images on dry skulls
with a known dehiscence size, were interpreted by only a
few individuals, and only found systematic differences.
The current study has no standardized size of the
dehiscences, the soft tissues were present, systematic and
random differences were found, and the dehiscences were
measured by 21 individuals.
These methods better represent
the normal anatomy of a random patient and interpretation
of the bony morphology on a CBCT by a random observer.
The
ability to quantify the dehiscence varies on the skill of
the practitioner due to the wide variation in method error
amongst the residents.
There appears to be a learning
curve to detecting dehiscences on the image.
The PI had
the most experience manipulating the images, quantifying
the dehiscences, and showed the lowest error of .445 mm.
The interpretation of the 2-D MP images has been shown
to be highly accurate with a systematic difference as low
as .1 mm and a 1:1 image to reality ratio.32-34
The 3-D SVR
image has not shown the same accuracy from some of the
current studies, but these studies did not use definite
fiducial markers.35,36
74
Baumgaertel et al. measured the 3-D
SVR images and showed very high correlations for single
measurements compared to the direct measurement.
When
multiple measurements were added together, the measurement
sum became significantly smaller than the true value.
The
smaller measurement’s sum is due to the “partial volume
effect”.32
A voxel may only show 1º of density.
The density
of the voxel is the average of the respective densities
within the voxel.
If bone and soft tissue are in the same
voxel and the density value is set to show bone and not
soft tissue, information is lost and the measurement is
smaller than the true value.
In the current study, the
measurements varied from larger than the direct measure to
smaller (figure 10) and were only single measures.
So this
effect was negligible.
The small amount of error within the study is mainly
attributable to human error.
This error is due to the
ability to distinguish between very thin bone and the root
of the tooth (Figure 11).
The voxel size and cadaver bone
quality play a smaller role as well.
According to Ballrick
et al., 50% of error is attributable to voxel size alone.33
The smaller the voxel the clearer the image; however, it is
at an increased radiation dose to the patient.
residents that were significantly different, the
For the 4
75
correlation may be higher than other residents, but the
measurements are further from the correlation line making
the measurements for those residents significantly
different.
a
b
c
d
Figure 11: Human Error. Dehiscences with thinned margins on
the direct evaluation (a and c). Difficulty determining the
junction between bone and tooth on the 3-D surface volume
rendering at 1365 density value(b and d).
76
The 2-D MP images have been the standard for
interpreting CBCT images.
However, the 3-D volumetric
rendering is becoming more popular due to the user-friendly
software.
This study also examined the difference in the
measurements between the 2-D MP images and the 3-D SVR
images at different density values.
The method error was
nearly equivalent for each, with good correlations to the
direct measurements.
The 2-D MP was the most reliable and
had the lowest random error.
However, there was no
significant difference between the three image
reconstructions. The 3-D SVR starting at 1365 DV was used
to measure the dehiscences because it offered the clearest
view of the alveolar bone without interference from
adjacent tissues.
With conventional CT, there are definite
known density values of different tissues.
The density
value range is then set accordingly to only visualize the
tissues of interest, i.e. bone.37
With CBCT, the density
values are inconsistent based on the field of view.38
The CT
DV starts at 1200 for the lowest density bone,39 but CBCT
values may be slightly higher.40
Therefore, the selection of
1365 DV as the lowest DV would be within the normal range
of low density bone and the interpreter could visualize the
fine, low density bony architecture.
77
For evaluating surface defects including dehiscences of
the periodontium, either the 2-D MP or 3-D SVR images may
be used for interpretation.
The 3-D SVR image from a CBCT
with .2mm voxel size has the ability to accurately quantify
dehiscences with sub-millimeter accuracy.
Conclusions
Using the 3-D SVR image, dehiscences of the
periodontium can be quantified to a significant level.
The 3-D SVR image can be used for orthodontic
diagnosis, treatment planning, and post-treatment
evaluation for dehiscences.
78
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VITA AUCTORIS
Nicholas Steven Ising was born December 13th, 1981 in
Louisville, Kentucky.
He is the second child of Steven and
Karen Ising both of Louisville, Kentucky where he was
raised.
Nicholas graduated from Saint Xavier High School in
2000.
He then attended the University of Kentucky until
2003 when he was accepted to dental school.
He received
his D.M.D. degree from the University of Louisville Dental
School in 2007 and is planning to receive his M.S.D. from
Saint Louis University in January, 2010.
From there, he
will enter into private practice in his hometown of
Louisville, Kentucky.
Nicholas is happily married to his wife, Natalie, and
they are due for their first child, Noelle, in December,
2009.
85