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Use of digital models to assess orthodontic treatment progress and identify deficiencies

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Use of digital models to assess orthodontic treatment progress and identify deficiencies

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Content 1
USE OF DIGITAL MODELS TO ASSESS ORTHODONTIC TREATMENT PROGRESS AND
IDENTIFY DEFICIENCIES

By

Christopher R. Myers
1
and Eric Budiman
2

A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)

May 2015

Copyright 2015 Christopher R. Myers
1
and Eric Budiman
2

2
Table of Contents
Abstract 3
Chapter 1: Background 4
1A: History of Digital Models 4
1B: Precision and Accuracy 6
1C: Digital vs Plaster: Space Analysis 7

Chapter 2: American Board of Orthodontics Final Model Grading 9
2A: Final Model Grading System 9
2B: Common Errors in Completing the ABO Clinical Exam 11
2C: Digital Models for the Objective Grading System 11

Chapter 3: Our Current Study 13
3A: General Overview 13
3B: Align Technology iTero Intraoral Scanner 14

Chapter 4: Purpose 15

Chapter 5: Materials and Methods 16

Chapter 6: Results 32

Chapter 7: Discussion 36

Chapter 8: Conclusion 42

References 44

List of Figures and Tables 47

3
Abstract
Purpose: The objective of this study was to assess whether the iTero intraoral
scanner can be used to assess orthodontic progress and identify common
deficiencies.
Methods: In this retrospective study, 22 patients in the detailing and finishing
stages of orthodontic treatment were scanned using the iTero intra-oral scanner.
Scanned arches were then analyzed using ABO Cast-Radiograph criteria to
objectively score each virtual model. The arches were analyzed twice within one
week by the same individual using the same tools in the same location under the
same conditions. Total and category scores were determined. Correlation
statistics were used to detect statistically significant contributors to the overall
score.
Results: Occlusal contacts, occlusal relationships, and overjet were the most
highly correlated predictors (statistically significant P<.01) of the final ABO Cast
Evaluation score for the progress models. Assessing ABO grading criteria was
reliably accomplished with the exception of buccolingual inclination
Conclusion: Virtual models created using the iTero digital intraoral scanner can
reliably be used to assess orthodontic progress and visualize deficiencies.
4

1. Co-senior author
2. Co-senior author

Chapter 1. Background
1A. History of Digital Models
Intra-oral digital scanners for dentistry developed in the 1980s (Logozzo et
al. 2008) as a method for taking three-dimensional images of soft and hard tissues.
The technology was an alternative to traditional impression-taking techniques
such as alginate and VPS with resulting digital images used by CAD/CAM software
for single-unit restorations, fixed partial dentures, and implant planning (Ender et
al. 2013). More recent developments in the scanning technology and associated
software allow digital models to be used for many aspects of dentistry including
archiving, treatment planning, simulation exercises, and prosthesis fabrication.
(Peluso et al. 2004, Hajeer et al. 2004) Additionally, intraoral scanning has
benefits in user time, patient comfort, convenience, and storage compared with
traditional impression-taking and model storing methods (Yuzbasioglu et al. 2014).
This advantage of model storing is significant, reducing the need for large
amounts of physical storage. Another advantage of digital models is their ease of
retrieval from any connected workstation, allowing for quick viewing when
necessary as well as fast and convenient sharing. (Asquith et al. 2012, Dalstra et al.
2009)
5
Today, there are many manufacturers of scanning systems, each utilizing
different technologies to create the final digital model (Logozzo et al. 2008).
There are single picture systems, such as the CEREC Bluecam and Align
Technology’s iTero, where a single optical impression of 2-3 teeth is taken when
the camera is held still. Multiple images can then be stitched together to create
an entire dental arch. (Kurbad et al. 2011) The images are distortion-free so that
a full arch can be precisely captures in just a few minutes (Logozzo, et al. 2008).
There are also video systems, such as the CEREC Omnicam, which continuously
acquire hard and soft tissues as the camera moves along the arch.
Pretreatment of the tooth surface also varies amongst different scanning
technologies. Scanners such as the Lava COS and the CEREC Bluecam require
powdering of the tooth surface, which allows for a uniform reflective surface for
proper light reflection and surface registration (Logozzo, et al. 2008). This step is
time consuming for the clinician and may result in errors due to uneven
powdering or saliva contamination (Ender, et al. 2013). New intra-oral scanners,
such as the CEREC Omnicam and Align Technology’s iTero no longer require any
surface pretreatment, simplifying the process for the clinician.

6
1B. Precision and Accuracy
Before digital intraoral scanners could be viewed as a mainstream device to
replace traditional impression-taking methods, precision and accuracy of the final
models had to be determined. Flugge, et al. (2013) measured the precision of the
iTero intraoral scanner under clinical conditions and compared it with the
precision of extraoral digitization. The study compared 10 full-arch iTero scans on
the same patient with 10 scans of a stone model of the same arch. Each intraoral
scan was superimposed on the other for best fit. The deviations were then
measured from the superimpositions. The process was repeated using a stone
model created from polyether impression material. The stone model was
scanned using the iTero and scanned by an extraoral model scanner (D250 by
3Shape). The scanned arches were split into 3 groups: Group 1 for the intraoral
iTero scan, Group 2 for the iTero scan of the stone model, and Group 3 for
extraoral model scanner (D250). Results showed that average deviation of the 10
intra-oral scans was 50 micrometers, while repeat iTero scans of a plaster model
showed an average deviation of 25 micrometers. The group scanned by the D250
showed deviations of 10 micrometers. The higher precision of extra-oral scanning
could be due to patient movement, limited intra-oral space, intra-oral humidity,
and saliva flow. The authors postulated that difficulty in camera placement next
7
to teeth intraorally accounted for much of the deviation between the intraoral
scans and the extraoral iTero scans. Deviations were high in the molar area,
which indicate that patient-related factors had a strong influence (Flugge, et al.
2013).
Ender, et al. (2013) studied the effect of scanning strategies on accuracy.
The study compared 3 scanning systems (3M Lava COS, CEREC Bluecam, and
Cadent’s iTero) by using the manufacturer’s recommended scanning protocol. A
reference master model was scanned and then trueness and precision of each
scanning protocol was measured. All scanning systems showed high levels of
accuracy with the iTero giving trueness of +/- 35.0 micron and a precision of +/-
30.9 micron. The team concluded that all 3 scanning systems can take full arch
impressions with a high accuracy given adequate scan strategies. The study also
concluded the powder-free systems, like iTero, can provide the same level of
accuracy compared with scanning systems with surface pretreatment.

1C. Digital versus Plaster: Space Analysis
Plaster, or stone, models have long been the standard for viewing a
patient’s dentition extraorally. In performing space analysis evaluations, digital
models or plaster models can be used. In a study where 25 plaster models were
8
fabricated from alginate impressions and then scanned into a digital model,
mesial-distal tooth widths were measured in both types of models. A space
analysis was calculated and the amount of crowding for both types of models was
measured. It was found there was a slight (0.4 mm), but statistically significant
difference in the maxillary models, but no significant difference in the mandibular
models (Leifert, et al. 2009). The finding of a statistically significant but clinically
insignificant difference is consistent with other studies. (Dalstra et al. 2009,
Zilberman et al. 2003, Mullen et al. 2007) Furthermore, the amount of time taken
to complete the space analysis was statistically significant, where the analysis was
completed 65 seconds faster with digital models. (Mullen et al. 2007)
When measuring tooth size, overbite, and overjet on plaster versus digital
models, Santoro, et al. (2003), studied 76 randomly selected pretreatment
patients. A statistically significant difference was found for tooth size and overbite,
but these differences were not clinically relevant. There was no difference found
in the measurement of overjet.

9
Chapter 2. American Board of Orthodontics Final Model Grading
2A. Final Model Grading System
In 1996, the American Board of Orthodontics (ABO) implemented an
objective grading system for their final certification exam. The ABO Model
Grading System contains eight criteria: alignment, marginal ridges, buccolingual
inclination, occlusal contacts, occlusal relationships, interproximal contacts, and
root angulation. Proper alignment is characterized by the alignment of the lingual
incisal edges of maxillary anterior teeth and labial incisal edges of mandibular
anterior teeth. In the posterior quadrants, the mesiobuccal and distobuccal cusps
should be in the same alignment in the mandible. For the maxilla, the central
grooves should all be in the same plane.
Marginal ridges for both maxillary and mandibular posterior teeth should
be on the same level or within 0.5 mm from each other. The canine premolar
contact and the mandibular 1
st
premolar are not graded. Buccolingual inclination
of posterior teeth shall be assessed by using a flat surface that is extended
between the occlusal surfaces of the right and left poster teeth. The straight edge
should contact the cusps and the buccal/lingual cusps should be within 1mm of
the straight edge.
10
The buccal cusps of the mandibular premolars and molars and the lingual
cusps of the maxillary premolars and molars should be contacting the occlusal
surfaces of opposing teeth. To measure occlusal relationship, the maxillary canine
cusp tip should align with the embrasure or contact between the mandibular
canine and adjacent premolar. The buccal cusps of the maxillary premolars should
align with the embrasures or contacts between the mandibular premolars and
first molar. The mesiobuccal cusps of the maxillary molars should align with the
buccal groves of the mandibular molars.
Overjet in the anterior region is characterized by the mandibular canines
and incisors contacting the lingual surfaces of the maxillary canines and incisors.
Interproximal contacts are assessed by viewing the models from an occlusal
perspective. The mesial and distal surfaces of the teeth should be in contact with
each other. Root angulation is assessed through a panoramic radiograph and the
roots should be parallel to one another and oriented perpendicular to the occlusal
plane.
Any discrepancy is given either 1 point or 2 points, depending on severity.
The points are tallied to arrive at the final score for the Cast Evaluation-
Radiograph evaluation. As we are not evaluating radiographs as part of this study,
11
we will refer to this assessment as the ABO Cast Evaluation, or simply Cast
Evaluation.

2B. Common errors in preparing for and completing the ABO clinical exam
The Cast-Radiograph Evaluation is a measure of the results of treatment
based on the analysis of the final dental casts and dental radiographs. The most
common deficiencies found are alignment, buccolingual inclination inadequacies,
marginal ridge discrepancies, and root angulation problems. Lateral incisors and
second molars most often lack adequate alignment (English, et al. 2011).

2C. Digital Models for the Objective Grading System
Using digital models to submit for the American Board of Orthodontics Final
Model Exam has not yet been approved. There are currently two preliminary
studies that evaluated the accuracy of scoring digital models with OrthoCAD’s
ABO objective grading system software. A study by Costalos et al. 2005, evaluated
48 models for 24 patients and found that similar scores were found for both
models in marginal ridges, occlusal contacts, occlusal relationships, overjet, and
interproximal contacts. Scores for alignment and buccolingual inclination were
found to be significantly different. (Costalos et al. 2005) Another study by
12
Hildebrand, et al. evaluated 36 cases and found that the total scores were
significantly different between plaster and digital models, which differed by 9
points on average. The differences were due to alignment, occlusal contact, and
overjet. (Hildebrand et al. 2008) Future advancements in software will be
necessary for improved accuracy for digital scoring for the ABO.

13
Chapter 3. Our Current Study
3A. General Overview
In evaluating the progress of orthodontic treatment for ABO qualified cases,
it is common for orthodontic residents, and experienced orthodontists, to take
impressions for progress models. This allows the resident and the supervising
faculty to assess what modifications are needed according to the grading criteria
stated above. The downside of this process is that due to the setting time of the
plaster the patient is often sent home before any model evaluation can be done.
This results in a lag time for any adjustments and contributes to longer treatment
times.
Using the iTero (Align Technology, Inc., San Jose, CA) digital intra-oral
scanner will allow the digital impression and resulting model to be viewed while
the patient is still present. Resulting adjustments to the fixed appliance can be
made on the same day increasing the efficiency of the practitioner and aiding in
reduced treatment time.

3B. Align Technology iTero Intraoral Scanner
Align Technology, Inc. has provided the Orthodontic Department at the
University of Southern California Herman Ostrow School of Dentistry a current
14
model iTero intraoral scanner for use in this study. The iTero system uses a laser
scanning protocol known as “parallel confocal,” that allows the scanner to
measure the distance from the scanner’s sensor tip to the object. (Garg et al.
2008, van der Meer et al. 2012, Henkel et al. 2007) Single 3D frames are captured
on each scan and are stitched with other frames to compile a complete 3D model
(Fig 1). The clinician takes several scans throughout both arches that result in a
model with over 100,000 data points. (Garg et al. 2008)
The iTero was tested on 1,600 cases in multiple offices over a 24

month
period, and was introduced nationally in 2007. Double blind studies revealed that
patients were able to recognize a difference in time for impressions with the iTero
versus the conventional PVS impression. Patients also reported overall
satisfaction with the reduction of gagging, anxiety, poking, stretching, and post
impression discomfort. (Garg et al. 2008)

15
Chapter 4. Purpose
We hypothesize that digital models made with the iTero intraoral scanner can be
used to reliably determine Cast-Radiograph Evaluation scores, as measured by the
American Board of Orthodontics (ABO) final model grading system, and to identify
common deficiencies. Through the identification of common deficiencies we
expect to use the information supplied to improve orthodontic finishes per ABO
standards.

16
Chapter 5. Materials and Methods
Twenty two patients from the University of Southern California’s Advance
Orthodontic Program were randomly selected to participate in the study. The
inclusion criteria included: (1) Full size stainless steel or beta-titanium wire (equal
to or greater than 0.016 x 0.022 for 0.018 bracket slots, equal to or greater than
0.019 x 0.025 for 0.022 bracket slots), (2) patients required comprehensive
orthodontic treatment, and (3) treatment was at the detail and finishing stages of
orthodontic treatment, per each treating resident. The exclusion criteria were: (1)
surgical orthodontic treatment, (2) two phase orthodontic treatment, (3) transfer
patients from outside orthodontists or orthodontic programs, (4) interdisciplinary
patients, and (5) craniofacial dysmorphology patients.
Each patient was scanned with the iTero intra-oral scanner using the
iRecords option. The maxillary arch, mandibular arch, and occlusion were scanned
with the full fixed appliance in place. Once the scan was completed and the digital
model was constructed by the iTero software, the treating resident and
supervising faculty member used the information from the digital models to make
detailing adjustments to the fixed appliance.
17
The twenty two scans were then evaluated by a single resident who applied
ABO Cast-Radiograph Evaluation criteria (Figure 1) to the digital models, omitting
the radiograph portion of the scoring (Cast Evaluation).
18
Figure 1. American Board of Orthodontics Cast-Radiograph Evaluation

19
The models were manipulated into configurations that allowed for easy and
accurate evaluation. Frontal view is the default view when the iTero software is
running, and the first image seen when evaluating a model (Figure 2).

Figure 2. Frontal View

It is convenient to evaluate overjet next, as it requires minimal
manipulation to achieve this view. Per the ABO Grading System for Dental Casts
and Panoramic Radiographs (2012), overjet is used to assess the relative
transverse relationship of the posterior teeth, and the anteroposterior
relationship of the anterior teeth. In the posterior region, the mandibular buccal
20
cusps and maxillary lingual cusps are used to determine proper position within
the fossae of the opposing arch. In the anterior region, the mandibular incisal
edges should be in contact with the lingual surfaces of the maxillary anterior
teeth.

Figure 3. Overjet

The left and right buccal segments were then scored for occlusal contacts
and occlusal relationship. Per the ABO Grading System for Dental Casts and
Panoramic Radiographs (2012), occlusal contacts are measured to assess the
adequacy of the posterior occlusion. Again, a major objective of orthodontic
21
treatment is to establish maximum intercuspation of opposing teeth. Therefore,
the functioning cusps are used to assess the adequacy of this criterion; i.e., the
buccal cusps of the mandibular molars and premolars, and the lingual cusps of the
maxillary molars and premolars. If cusp form is small or diminutive, that cusp in
not scored.

Figure 4. Occlusal Contacts – Buccal Cusps of Lower Teeth

22
Figure 5. Occlusal Contacts – Palatal Cusps of Upper Teeth

Per the ABO Grading System for Dental Casts and Panoramic Radiographs
(2012), occlusal relationship is used to assess the relative anteroposterior position
of the maxillary and mandibular posterior teeth. In order to achieve accuracy and
reliability in measuring this relationship, results of previous tests have shown that
the most verifiable method of scoring this criterion is to use Angle’s relationship.
Therefore, the buccal cusps of the maxillary molars, premolars, and canines must
align within 1mm of the interproximal embrasures of the mandibular posterior
teeth. The mesiobuccal cusp of the maxillary first molar must align within 1mm of
the buccal groove of the mandibular first molar.
23
Figure 6. Occlusal Relationship

The models can now be disarticulated to view the maxillary and mandibular
arches separately. Alignment and Interproximal Contacts were scored. Per the
ABO Grading System for Dental Casts and Panoramic Radiographs (2012),
alignment is usually a fundamental objective of any orthodontic treatment plan.
Therefore, it seems reasonable that any assessment of quality or orthodontic
result must contain an assessment of tooth alignment. In the anterior region, the
incisal edges and lingual surfaces of the maxillary anterior teeth and the incisal
edges and labial-incisal surfaces of the mandibular anterior teeth were chosen
and the guide to assess anterior alignment. These are not only the functioning
24
areas of these teeth, but they also influence esthetics if they are not arranged in
the proper relationship. In the maxillary posterior region, the mesiodistal central
groove of the premolars and molars is used to assess adequacy of alignment. In
the mandibular arch, the buccal cusps of the premolars and molars are used to
assess proper alignment. These areas were chosen since they represent easily
identifiable points on the teeth, and represent the functioning areas of the
posterior teeth. The results of the four field tests show that the most commonly
malaligned teeth were the maxillary and mandibular lateral incisors and second
molars, with accounted for nearly 80% of mistakes.
Per the ABO Grading System for Dental Casts and Panoramic Radiographs
(2012), interproximal contacts are used to determine if all spaces within the
dental arch have been closed. Persistent spaced between teeth after orthodontic
therapy are not only unesthetic, but can lead to food impaction. In past field tests,
spacing is generally not a major problem with ABO cases.

25
Figure 7. Alignment and Interproximal Contacts

Marginal ridges are the next criterion to be scored as the disarticulated
views can be easily manipulated to provide the valuable information. Per the
ABO Grading System for Dental Casts and Panoramic Radiographs (2012),
marginal ridges are used to assess proper vertical positioning of the posterior
teeth. In patients with no restorations, minimal attrition, and no periodontal
bone loss, the marginal ridges of adjacent teeth should be at the same level. If
the marginal ridges are at the same relative height, the cementoenamel junctions
will be at the same level. In a periodontally healthy individual, this will result in
flat bone level between adjacent teeth. In addition, if marginal ridges are at the
26
same height, it will be easier to establish proper occlusal contacts, since some
marginal ridges provide contact areas for opposing cusps. Based upon the four
field tests, the most common mistakes in marginal ridge alignment occurred
between the maxillary first and second molars. The second most common
problem area was between the mandibular first and second molars.

Figure 8. Marginal Ridges

The final criteria to be scored was buccolingual inclination. Per the ABO
Grading System for Dental Casts and Panoramic Radiographs (2012), buccolingual
inclination is used to assess the buccolingual angulation of the posterior teeth. In
27
order to establish proper occlusion in the maximum intercuspation and avoid
balancing interferences, there should not be a significant difference between the
heights of the buccal and lingual cusps of the maxillary and mandibular molars
and premolars. When measured on an actual stone model, a special gauge is
used to assess this relationship. Some latitude is allowed, however in past field
tests significant problems were observed in the buccolingual inclination of the
maxillary and mandibular second molars.

Figure 9. Buccolingual Inclination

A flow chart was created to show the most efficient method of analyzing
the virtual model on a screen.
28
Figure 10. Flow Chart
Frontal View

Overjet

Occlusal Relationships

Occlusal Contacts (Buccal and Lingual)

Upper Arch Alignment and Rotations

Upper Arch Marginal Ridges

Upper Arch Buccolingual Inclination

Lower Arch Alignment and Rotations

Lower Arch Marginal Ridges

Lower Arch Buccolingual Inclination

29
There can be difficulty in making objective measurements when viewing
digital models on a computer screen. The iTero software provides a reasonable
solution to this in the form of an overlay grid. This grid can be switched on and
off as needed and overlays the entire screen with 1mm increments.

Figure 11A. 1mm Measurement Grid

30
Figure 11B. 1mm Measurement Grid, Alternate View

The measurements were made twice within the same week by the same
operator. Data was collected according to the Guidelines for Evaluating and
Expressing the Uncertainty of NIST Measurement Results, meaning that certain
conditions need to be fulfilled in the establishment of repeatability:
 The same experimental tools
 The same observer
 The same measuring instrument, used under the same conditions
 The same location
 Repetition over a short period of time
31
 Same objectives
These repeatability methods were developed by Bland and Altman. (Bland JM,
Altman DG. 1983)
The data for each category was tabulated and reliability of the operator in
determining the Average ABO Cast Score was calculated using the intraclass
correlation coefficient. A correlation analysis was then utilized to determine the
significance of each category in relation to the total score.
This study was submitted to, and approved by, the University of Southern
California Health Sciences Campus Institutional Review Board ID: HS-14-00455.

32
Chapter 6. Results
Table 1. Total ABO Score and Category Measurements for Cast Evaluation

33
Figure 12. Graphical Illustration of Cast Evaluation Data

34
Table 2. ABO Score for each Run

To test the reliability of these measurements, an intraclass correlation coefficient
was calclulated to be 0.956, suggesting that the scores are highly correlated and
the measurements reliable.

35
Table 3. Correlation and Critical Values

Results showed a statistically significant correlation (p< .01, critical value = .537)
between Total ABO Cast Score and three individual categories: Occlusal Contacts
(.889), Occlusal Relationships (.549), and Overjet (.572). Marginal ridges were
also found to be statistically correlated with the Total ABO Cast Score (p<.05).

36
Chapter 7. Discussion
With Intra-oral scanners getting faster and more accurate, they are
becoming more common as a replacement for alginate impressions and plaster
models. Digital models eliminate the need for large amounts of physical storage
space to keep patient records. The real time scan also allows the doctor to
evaluate the models and make the proper treatment adjustments on the same
day, creating more efficient treatment. Full mouth scans and the digital
construction of the models can be ready for analyzing in under 10 minutes, a
significant advantage over plaster models. With plaster models, the patient is
usually dismissed from the office before the models are ready, and any
adjustments are performed at the next visit – potentially the next month.
In order to use the digital model for Cast Evaluation scoring, manipulation
of the model is critical, but no easy task. Proper orientation of the model is rather
difficult to achieve with the same measurement appearing differently depending
on orientation. Figure 13 shows 4 images of occlusal relationships for the same
digital model.

37
Figure 13. Orientation
A

B

C

D

Figures 13A and 13B show the same model and portray the same
relationship of upper canine to lower canine and lower first premolar. The only
difference is the rotation of the images along a vertical axis at the center of the
arch. Note that in 13A, the upper canine cusp fits nicely between the
interproximal embrasure between the lower canine and lower first premolar. Per
ABO grading, this is an expected finish and receives no point deduction. However,
13B shows the same image simply rotated clockwise along the same vertical axis.
38
In this image, we see a definite discrepancy between the upper canine cusp and
the interproximal embrasure of the lower canine and lower first premolar. This
discrepancy is greater than the 1mm allowed by ABO grading and would be given
a 1-point deduction.
A possible way of reducing this particular error is to orient the digital
models in such a way that a tangent line can be drawn at the canine. When the
model is rotated so the tangent is horizontal on the viewing screen, then the
occlusal relationship can be properly scored. The application of a tangent line is
shown in Figures 13C and 13D. However, solutions such as this are not as easy
when parts of the digital model need to be cut or sliced away in order to achieve
the correct orientation of the model, such as when viewing marginal ridge
discrepancies.

39
Figure 14. Marginal Ridge Evaluation Difficulties
A

B

Figures 14A and 14B show the view used to determine marginal ridge
discrepancies. The ABO grading criteria only allow for 0.5mm of marginal ridge
variation before points are given for the deficiency. For the purpose of
understanding the relationship of one tooth to another, as is the case when
detailing to finish orthodontic treatment, the orientation shown in 14A is good
enough, and the grid can be overlaid to assist in a more objective measurement.
However, for the purpose of ABO grading, the contralateral side needs to be
“sliced” away so that the marginal ridge relationships can be easily seen. Figure
14B shows the shortcoming of the current software in achieving this goal.
The most difficult category to measure was buccolingual inclination. The
ABO provides a special measuring instrument with 1mm “steps” to accurately and
objectively measure this dimension on a stone model.
40
Figure 15. ABO Measuring Instrument

Using the iTero software, this proved to be rather difficult, even when
using the 1mm overlay grid provided by the software. The ability to accurately
and precisely measure buccolingual inclination within the iTero software was so
difficult as to render any statistical data as insignificant. With the exception of the
previously discussed marginal ridge height, all other objective measurements
were relatively easily obtained with the aid of proper positioning and utilization of
the 1mm grid.
Three grading categories correlated strongly to the total ABO Cast
Evaluation score: occlusal contacts, occlusal relationships, and overjet. This is in
contrast to English et al. (2011), who listed common deficiencies in the Cast-
Radiograph Evaluation as: alignment, buccolingual inclination inadequacies, and
marginal ridge discrepancies. One must remember, though that we are
comparing progress models undergoing ABO scoring with finished cases. The
progress models certainly had their deficiencies with alignment, and consistent
41
with English et al. (2011), the errors were predominantly with second molars.
Buccolingual inclination inadequacies and marginal ridge discrepancies can also
largely be attributed to second molars on finished cases.
When examining orthodontic cases still in progress, however, we found the
common errors centered on occlusion: occlusal contacts, occlusal relationships,
and overjet. Orthodontic treatment requires a great deal of planning and control.
Orthodontists begin by aligning teeth within the arch while leveling the arch. One
of the final relationships to be corrected is the patient’s occlusion, in most cases
requiring cooperation from the patient to wear elastics. Anterior overjet
generally follows the occlusal relationships, so if the relationships are correct then
anterior overjet should also be correct. The final step in finishing an orthodontic
case is to use vertical elastics and/or remove the archwires to allow the patient’s
occlusion to settle into place. All of this occurs in the final months of treatment
and explains the differences seen between grading a progress model and grading
a final model.

42
Chapter 8. Conclusions
The iTero digital intraoral scanner has many benefits including reducing the
time take an impression and create a model, increased patient comfort, and
reduced need for storage space (and associated costs) for stone models. The
purpose of this study was to determine whether an iTero-created digital model
could be used as a progress model for preliminary ABO Cast Evaluation scoring
and if common deficiencies could be identified.
Measuring casts for ABO scoring is no simple task. Much time and effort is
expended to properly calibrate the testers, and special tools have been designed
to aid in the objectivity and repeatability of scoring. To date, there is no software
program that can replicate a properly calibrated human in scoring plaster models
for ABO grading. Measuring digital models to assess progress does not require
the accuracy, and for certain measurements, the objectivity required of ABO
grading. More important for progress models is the ability to see relationships so
that corresponding adjustments to the fixed appliance can be performed.
It was found that grading digital models per ABO Cast Evaluation grading
criteria using the iTero software, and the supplied 1mm overlay grid, can be
accomplished with a high degree of reliability. The only criteria that could not be
accurately and precisely measured was buccolingual inclination due to both the
43
inability of the digital model to be properly manipulated and the lack of a
specialized measuring instrument. Marginal ridge height measurements are also
problematic, but can be used to assess progress models. Every other grading
criteria was able to be accurately and reliably assessed on the digital models, and
an ABO score can be calculated. As a result, we can conclude that the iTero intra-
oral scanner is useful to assess orthodontic progress. We were also able to
determine the most strongly correlated deficiencies out of our sample of models:
occlusal contacts, occlusal relationships, and overjet. All of these measurements,
including marginal ridge height, can be beneficial in aiding the orthodontist in
better understanding deficiencies.

44
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American Board of Orthodontics Grading System for Dental Casts and Panoramic
Radiographs (Revised 2012)

47
Figures and Tables
Figure 1. American Board of Orthodontics Cast-Radiograph Evaluation 18
Figure 2. Frontal View 19
Figure 3. Overjet 20
Figure 4. Occlusal Contacts – Buccal Cusps of Lower Teeth 21
Figure 5. Occlusal Contacts – Palatal Cusps of Upper Teeth 22
Figure 6. Occlusal Relationships 23
Figure 7. Alignment/Rotation and Interproximal Contacts 25
Figure 8. Marginal Ridges 26
Figure 9. Buccolingual Inclination 27
Figure 10. Flow Chart 28
Figure 11A. 1mm Measurement Grid 29
Figure 11B. 1mm Measurement Grid, Alternate View 30
Figure 12. Graphical Illustration of Cast Evaluation Data 33
Figure 13. Orientation 37
Figure 14. Marginal Ridge Evaluation Difficulties 39
Figure 15. ABO Measuring Instrument 40

Table 1. ABO Score and Category Measurements for Cast Evaluation 32
Table 2. ABO Score for each Run 34
Table 3. Correlation and Critical Values 35

Abstract (if available)

Abstract Purpose: The objective of this study was to assess whether the iTero intraoral scanner can be used to assess orthodontic progress and identify common deficiencies. Methods: In this retrospective study, 22 patients in the detailing and finishing stages of orthodontic treatment were scanned using the iTero intraoral scanner. Scanned arches were then analyzed using ABO Cast-Radiograph criteria to objectively score each virtual model. The arches were analyzed twice within one week by the same individual using the same tools in the same location under the same conditions. Total and category scores were determined. Correlation statistics were used to detect statistically significant contributors to the overall score. Results: Occlusal contacts, occlusal relationships, and overjet were the most highly correlated predictors (statistically significant P<.01) of the final ABO Cast Evaluation score for the progress models. Assessing ABO grading criteria was reliably accomplished with the exception of buccolingual inclination. Conclusion: Virtual models created using the iTero digital intraoral scanner can reliably be used to assess orthodontic progress and visualize deficiencies.

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Asset Metadata

Creator Myers, Christopher R. (author)

Core Title Use of digital models to assess orthodontic treatment progress and identify deficiencies

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 04/22/2015

Defense Date 03/09/2015

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag digital models,digital scan,intraoral scan,iTero,OAI-PMH Harvest

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Advisor Sameshima, Glenn T. (committee chair), Grauer, Dan (committee member), Paine, Michael L. (committee member)

Creator Email ChristopherMyersDDS@gmail.com,myerscr@usc.edu

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