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Comparison of facial midline landmark and condylar position changes following orthognathic surgery

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Comparison of facial midline landmark and condylar position changes following orthognathic surgery

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Comparison of Facial Midline Landmark
and Condylar Position Changes Following
Orthognathic Surgery

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)

Heather Stephens
MAY 2017

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Table of Contents

I. List of Figures.…………………………………………………………………………………………….…. 3
II. List of Tables.……………………………………………………………………………………..…….….. 4
III. Abstract.…………………………………………………………………….…………………………….…. 5
IV. Introduction.…………………………………………………………….…………………………………. 7
V. Literature Review.………………………………………………………………………………………... 8
• Digital Imaging in Orthodontics
• CBCT in Orthodontics
• CBCT in Orthognathic Surgery and Virtual Surgical Planning
• CBCT Organization, Orientation and Interpretation
• Natural Head Position (NHP)
• Condyle Position Following Orthognathic Surgery
• Methods Of Assessing Condylar Position Changes
• Surfaced Based Registration and Voxel Based Registration

VI. Materials and Methods.…………………………………………………………………………… 28
• Sample Subjects
• Surgical Technique and Postsurgical Protocol
• Data Acquisition
• Method for Generating Condyle and Fossa STL Mesh Files
• Method For Condyle Superimposition
• Method for CBCT Image Reorientation to NHP
• Method for Generating Lateral Ceph from CBCT
• Method for Tracing Lateral Ceph
• VSP Data
• Statistical Analysis

VII. Results.……………………………………………………………………………….…………………… 42
VIII. Discussion…………………..………………………………………………………………..………… 58
IX. Limitations…………………………………………………………………………………..……………. 65
X. Conclusion…………………………………………………………………………………..……….….… 66
XI. References………………………………………………………………………………..………….…… 68
XII. Appendix…………………………………………………..……………………………………………… 75
3
List of Figures

Figure 1 - Lateral Cephalometric Image……..…………………………………………………….…………………………………. 9
Figure 2 - Inferior Alveolar Nerve Tracing shown in various perspectives on a 3D image……………………. 12
Figure 3 - Virtual Pre-Surgical, Intermediate and Final Positioning Predictions……………………..…………12-13
Figure 4 - Pre and Post Surgical Soft tissue Predictions………………………………………………………………………. 14
Figure 5 - The basic 3-stage process of CBCT image acquisition and image processing…………………….…. 15
Figure 6 - Axes of coordinates in a 3-dimensional image……………………………………………………………………. 17
Figure 7 - Condyle Tomogram …………………………………..……………………………………..……………………..……….. 19
Figure 8 - Will et al (1984) Tracing of a sub mental vertex image ……………………..……………………………….. 23
Figure 9 - Will et al. (1984) - tracing of pre- and post-surgical left tomograms including condylar contour
with axis points and cross for reference, contour of glenoid fossa, cranial base detail………… 24
Figure 10 - Pullinger and Hollender method for measurement of condylar change ……………………………. 25
Figure 11 - Measurement of condylar position change on tomograms (Alder 1999).……………………….…. 26
Figure 12 - Surface distance color maps visualization showing condyle displacement………………………... 27
Figure 13 - Isolation of the region of interest for segmentation………………………………………………………….. 31
Figure 14 – Segmentation - Spheres coalesce until the structure of interest is identified………………….… 32
Figure 15 - Corrected condylar displacement …………………………………………………………………………………….. 35
Figure 16 - Cropped, superimposed condyles in bounding box re-oriented to world coordinate axis….. 36
Figure 17 - 3D image tools in Dolphin Imaging. 3D volumetric image with 3D in semi-transparent view
with x, y and z planes projected on the image…………………………………………………………………... 37
Figure 18 - 3D volumetric image with 3D in semi-transparent view from front and left side………………. 38
Figure 19 - Lateral Cephalometric Image Production Options (Dolphin Imaging) ……………………………….. 39
Figure 20 - Lateral ceph landmarks identified for lateral ceph data measurements………………………….… 40
Figure 21. Virtual Surgical Planning Final Movements Summary Table……………………………………….……… 41
Figure 22 - SNA, SNB and PFH for sample A only Increased. AFH SN-GoGn, Occl-SN and PFH for sample B
only decreased. ………………………………………………………………………………………………………….……. 47
Figure 23 - Scatter plot graph of post-surgical ceph SNB change vs. VSP predicted pogonion………….…..58
Figure 24 - Directions of force exerted by mandibular depressors and elevators and their influence on
mandibular proximal and distal fragments. ……………………………………………………………………... 63
Figure 25 - Will et al. (1984) Results - Mean skeletal changes (mm) …………………………………………………... 64

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List of Tables
Table 1 - Sample Data……………………………………………………………………………………………………………………….. 29
Table 2 - Lateral ceph landmarks identified for lateral ceph data measurements………………………………. 40
Table 3 - Descriptive statistics - Sample A: Condylar movement data ……………………………………………..… 43
Table 4 - Sample A - Condylar movement data - Analysis of variance……………………………………………. 43-44
Table 5 - Sample B descriptive statistics……………………………………………………………………………………..…….. 44
Table 6 - Sample B one-sample t-test ……………………………………………………………………………………………….. 45
Table 7 - Descriptive statistics - Sample A Ceph data (n=17) ……………………………………………………………… 46
Table 8 - Descriptive statistics - Sample B Ceph data (n=15) ……………………………………………………………… 46
Table 9 - Descriptive statistics - Sample A and B combined (n=32) ……………………………………………………. 46
Table 10 - Descriptive statistics - Sample A and B combined (n=32).…………………………………………….. 46-47
Table 11 - Descriptive Statistics - Combined Ceph (n=32).……………………………………………………………….… 48
Table 12 - Combined Data - One-Sample t-test ………………………………………………………………………………… 48
Table 13 - Group Statistics comparing Male and Female - Combined Ceph Data (n=32)………..……… 48-49
Table 14 - Independent sample tests - Male and Female - Combined Ceph Data (n=32)..………………….. 49
Table 15 - Independent Samples Test comparing males and females - Combined Ceph Data ……… 49-50
Table 16 - Descriptive statistics - comparing patient age - Combined Ceph Data …………………………….. 51
Table 17 - Independent Samples Test comparing patient age - Combined Ceph Data (n=32).……………. 51
Table 18 - Correlations comparing patient age - Combined Ceph Data (n=32).……………………………… 51-52
Table 19 - Descriptive statistics - Sample A - Comparison of condyle movement with ceph change.…. 53
Table 20 - Model Summary - Sample A - Comparison of condyle translation with ceph change……….. 53
Table 21 - Sample A - ANOVA - Sample A - comparing ceph change with condyle translation…………… 53
Table 22 - Sample A - Coefficients for condyle translation…………………………………………………………… 53-54
Table 23 - Model Summary - Sample A - Comparison of condyle rotation with ceph change……………. 54
Table 24 - ANOVA - Sample A - comparing ceph change with condyle rotation………………………………… 54
Table 25 - Sample A - Coefficients for condyle rotation……………………………………………………………………. 55
Table 26 - Descriptive statistics - Sample B ceph data (n=15) …………………………………………………………… 55
Table 27 - Model Summary - Sample B - Comparison of condyle translation with ceph change………… 55
Table 28 - ANOVA - Sample B - comparing ceph change with condyle translation……………………………. 55
Table 29 - Sample B - Coefficients for condyle translation………………………………………………………………...56
Table 30 - Model Summary - Sample B - Comparison of condyle rotation with ceph change……………. 56
Table 31 - ANOVA - Sample B - comparing ceph change with condyle rotation………………………………… 56
Table 32 - Sample A - Coefficients for condyle rotation……………………………………………………………………. 56
Table 33 - Correlation between post-surgical ceph SNB change and VSP predicted pogonion………….. 57

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Abstract
Background: CBCT imaging offers numerous advantages in orthognathic surgery case
diagnosis, treatment planning and post-surgical evaluation. In maxilla-mandibular
combination surgery, regions of the craniofacial complex are altered in all three
dimensions of space. The upper jaw, lower proximal segment and bilateral distal
segments must be separated, reoriented and then secured in the desired position. The
movements of the surgical segments must be made in concert with each other in order to
ensure a stable result.
Purpose: To evaluate the relationship between midline lateral cephalometric landmark
changes with condylar translation and rotation displacement, relative to the glennoid
fossa, following bi-maxillary surgery.
Materials and Method: Post-surgical condyle translation and rotation values were
measured for 32 patients in two groups (sample A, n=17 and sample B, n=15) by
segmenting pre- and 2 weeks post-surgery DICOM files in ITK snap. Each pair of
condyles was re-oriented to the glenoid fossa, cropped to the same size and then
superimposed with Geomagic software. Lateral cephalometric images were generated
from these same pre- and post-surgical CBCT images, oriented to natural head position,
and several midline landmarks were identified. The linear or angular change between the
pre- and post-surgical landmarks was then calculated and analyzed for statistical
significance. The condylar translation and rotation changes were then compared to the
post surgical lateral ceph changes.
Also, Virtual Surgical Planning (VSP) data for 31 of the 32 patients (one VSP report was
not available) in the sample were collected and evaluated. Pogonion values from the post-
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surgical positional change and pre-surgical VSP predicted movement were calculated and
evaluated for statistically significant correlation.
Results: For sample A (n=17) the average condylar displacement was 0.78 mm on the x-
plane, -3.80 mm on the y-plane and 0.15 mm on z-plane. The average rotation was 0.06 º
on the x-axis, 0.31º on the y-axis and -0.28º on the z-axis. Translation along the y-axis
(anteroposterior) and rotation on z-axis (superoinferior), were the only movements that
were statistically significant (p<0.008).
In sample B (n=15) the average condylar displacement was 0.05 mm on the x-plane, -
0.39 mm on the y-plane and 0.01 mm on the z-plane. The average rotation was -0.69 mm
on x-axis, 1.69 on the y-axis and -2.43 on z-axis. The movements that were statistically
significant were translation on the y-axis and rotation on the y-axis (p<0.008).
Lateral cephalometric landmark samples for SNA, SNB, AFH, SN-GoGn and Occl-SN
were all statistically significantly (p<0.05), while PFH (posterior facial height) was not
significant (t(31)=1.719, p=0.096).
No significant correlation was found between lateral ceph midline landmarks SNA, SNB,
AFH, PFH, SN-GoGn, or Occl-SN with age of patient at time of surgery, gender of
patient, condyle rotation, or condyle translation.
Pre- and post-surgical lateral ceph pogonion change and the VSP pogonion movement
estimates were strongly correlated (correlation coefficient = 0.751).
Conclusions: We saw an agreement between pre- and post-surgical changes for sample A
and sample B for all rotation and translation in the X direction; however, there was less
conformity between samples in translation for Y and Z directions.
The strong correlation between pre- and post-surgical lateral ceph pogonion movements
7
and the VSP pogonion movement estimates is to be expected, as surgical movements are
completed as planned using pre-fabricated intraoral surgical splints to aid in obtaining
planned skeletal movements.

Introduction
A novel method to quantify post surgical condylar displacement in three dimensions
(translation and rotation, in x, y and z axes) was previously developed at the University
of Southern California and used to analyze data from two sample groups (sample “A”
n=17, sample “B” n=15).

This study aims to compare the condylar displacement results of the two sample groups
from those studies with data from lateral cephalographs derived from pre- and post-
surgical CBCT volumes that have been oriented to natural head position. The pogonion
measurement for each patient’s pre-op Medical Modeling through Virtual Surgical
Planning from (VSP Orthognathics; Golden, Colorado) was also obtained and compared
to pogonion changes between the pre- and post-surgical lateral cephalometric images.

Data from sample A and sample B was analyzed independently as well as in
combination. The six midline landmarks selected for this study consisted of four angular
measurements (°) and two liner measurements (mm) collected from pre- and post-
surgical lateral cephs, which were oriented to natural head position. Linear and angular
changes from pre- to post-surgery were measured for sella-nasion-A point angle (SNA),
sella-nasion-B point angle (SNB), anterior facial height: N-Me (AFH), posterior facial
8
height:Co-Gn (PFH), sella-nasion to gonion-gnathion angle (SN-GoGn), occlusal plane
to sella-nasion angle (Occ-SN). ANS, while a midline structure, was considered but
ultimately not selected as a landmark for our study because in many of the patients it was
clipped to ensure proper nasal projection and angulation and could not be measured on
post surgical cephs.

Literature Review
Digital Imaging in Orthodontics
The era of imaging in medicine and dentistry began with the discovery of X-rays
by the German/Dutch mechanical engineer and physicist W. C. Roentgen in 1895. This
was an achievement that earned him the first Nobel Prize in Physics in 1901. (McMillan
1999) Thirty years later, in 1931 standardized methods for the production of
cephalometric radiographs in orthodontic patients were introduced by Broadbent in the
USA and by Hofrath in Germany and remained nearly unaltered until recently. Broadbent
emphasized the importance of the position and distance arrangements to achieve
distortion-free radiographs when taking lateral and postero-anterior cephalometric
radiographs. (Broadbent,1931) Cephalograms have since been widely used to evaluate
skeletal and dental changes that occur due to growth, orthodontic treatment and/or
maxillofacial surgery.

While lateral cephalometric images are an advantage over clinical evaluation alone, there
are several disadvantages of 2D cephalometry. In a lateral image, the X-ray beams are
non-parallel and originate from a small source, leading to radiographs with areas of
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magnification due to the distance between the focus, the object and the film in an attempt
to express 3D structures onto a 2D plane. Symmetry is assumed, as cephs are generated
from a superimposition of the left and right sides at the mid-sagittal plane, but symmetry
may not be present in all patients. This can lead to errors in identifying landmarks,
especially landmarks that are located on curves, as these are more prone to error than
those on anatomically formed edges. Landmarks with wider variation of anatomical
location can also be challenging to accurately identify on a ceph. (Baumrind 1971)
Patient position can also affect landmark identification, overlap of non-midline structures
and ceph orientation (pitch, roll and yaw). (Nalçaci 2010) These issues are exaggerated
when treating surgical patients, since when compared to the general population, a greater
proportion of surgical patients have asymmetric craniofacial complexes. (Baek 2012,
Sheats 1998)

Figure 1 – Lateral Cephalometric Image
Either asymmetry or poor patient positioning have resulted in duel outlines of skeletal structures in this
lateral cephalogram, making accurate and reliable landmark identification difficult.

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CBCT in Orthodontics
Cone beam computed tomography (CBCT) imaging was introduced to dentistry in 1998.
(Mozzo 1998) The information obtained from CBCT imaging provides several
advantages over 2D imaging. For example, CBCT imaging provides increased accuracy
of measurements, improves localization of impacted teeth, provides visualization of the
airway, and also allows for identification and quantification of asymmetry. CBCT
imaging can be used to assess periodontal structures, identify endodontic problems, plan
placement sites for dental implants or temporary skeletal anchorage devices, and evaluate
the temporomandibular joint (TMJ). However, CBCT imaging does involve an increase
in radiation dose relative to combined diagnostic digital panoramic and cephalometric
imaging. The specific quantity of radiation absorbed by a patient as the result of a CBCT
scan varies greatly, depending on the machine type, settings, slice number/thickness and
the size of the field of view. (Halazonetis 2005, Nalçaci 2010, Mah 2003)
Also, CBCT image quality depends on many factors including the contrast of the image,
patient movement during image acquisition, presence of metal (which creates noise),
overall signal-to-noise ratio of the image, and the threshold filters applied by the
operator. Many of these issues can also affect the quality of 2D images.

CBCT imaging in association with computer software allows anatomical structures to be
properly represented in all three viewing planes – sagittal, coronal, and transverse.
Landmark identification is also greatly enhanced in CBCT images with magnification
and filters to adjust image quality (brightness, gamma, contrast, etc.).
11
Multi-planar views are especially advantageous in identifying bilateral landmarks such as
condylion, gonion, and orbitale, which are frequently superimposed in conventional
radiographs.

Adams et al. (2004), compared the accuracy and precision of 2D and 3D radiographic
methods with caliper measurements on dry skulls. The results showed great variability
between the 2D and dry skull measurements, with the range varying from -17.68 mm
(underestimation of Gn-Zyg R) to +15.52 mm (overestimation of Zyg L-Zyg R). With the
3D method (Sculptor, Glendora, Calif) they found a -3.99 (underestimation) mm to +2.96
mm (overestimation) and concluded that the 3D evaluation was significantly more
precise, within approximately 1 mm of the dry skull measurements.

While generally agreed to be more accurate than 2D cephalometric images (Moshiri et al.
2007, Adams et al. 2004), when Periago et al. (2008) compared the accuracy of twenty
orthodontic linear measurements between anatomical landmarks on CBCT derived 3D
images to direct measurements made on human skulls, they found statistically significant
differences between the 3D-CBCT means and true dimensions for all of the midsagittal
measurements except Na-A and six of the 12 bilateral measurements. However, ninety
percent of mean differences were less than 2 mm, and 95% confidence intervals were all
less than 2 mm except for Ba-ANS (3.32 mm) and Pog-Go (2.42 mm). They concluded
that while many linear measurements between cephalometric landmarks generated from
CBCT datasets may be statistically significantly different from anatomic dimensions,
most can be considered to be sufficiently clinically accurate for craniofacial analyses.
12
From these study’s we can conclude that while measurements of craniofacial analysis
made in 3D are more precise and accurate versus those measured in 2D, they are still
only interpretations of an incredibly complex form.

CBCT in Orthognathic Surgery and Virtual Surgical Planning
CBCT data can be used in orthognathic surgery to evaluate the shape and position of the
TMJ complex, measure tooth root lengths for planning osteotomy sites, measure and
trace the inferior alveolar nerve position in the mandible, determine the location and
position of impacted teeth, identify pathologic lesions, as well as accurately determine the
length and position of skeletal structures.

Figure 2 - Inferior Alveolar Nerve Tracing shown in various perspectives on a 3D image

CBCT imaging in tandem with appropriate software, such as Medical Modeling’s Virtual
Surgical Planner, and virtual patent-specific dental models enables the examination of the
spatial relationships of hard and soft craniofacial tissues.

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Initial Position (above)

Intermediate surgical position (above)
Final surgical position (above)
Figure 3 - Virtual Pre-Surgical, Intermediate and Final Positioning Predictions

Virtual surgical planning systems provide the ability to accurately integrate 3D skeletal
imaging with occlusal data from high-resolution scans of stone models using a fiducial
registration technique. From this 3D combined skeletal and dental model, a surgeon is
able to fabricate guides, stents and other tools as needed for a surgical case using additive
manufacturing technologies to accurately plan and complete osteotomy fixation positions
or implant placement locations. (Hsu 2013)

Facial soft tissue, hard tissues and dentition, also termed a triad, have a significant
function in planning of orthodontic and orthognathic treatment. Pre- and post-treatment
evaluation of dentoskeletal relationships, craniofacial relationships and facial appearance
14
(balance and beauty), in terms of soft and underlying hard tissues is vital, but can be
difficult due to changes craniofacial complex occurring in three dimensions, as well as
over time. (Orhan 2014) Virtual anatomical models, when co-registered with other
available skeletal and soft tissue 3D image data, can be used to evaluate treatment options
prior to surgery and to create anatomically correct positioning splints critical to
determining proper segment positioning during segment fixation.

Prior to surgery, surgeons can utilize software that manipulates the 3D scan image data of
the maxillofacial soft tissues and associated hard tissues to generate virtual predictions
that replicate manipulation of the hard tissues to produce a correct deformation reaction
in the attached soft tissues. (Virtual Treatment Outcome, VTO) This method can offer a
more distinct depiction of anticipated changes subsequent to surgical treatment compared
with less sophisticated computer modeling (Schendel et al., 2009).

Figure 4 - Pre and Post Surgical Soft tissue Predictions

Moving forward, clinicians are continuing to develop methods to better integrate the
structural (soft tissue envelope, facial skeleton and dentition) and photographic 3D
15
images. (Plooij 2011) Several studies have used three-dimensional facial modeling
techniques that utilize video image capture rather than still photography to improve the
accuracy of facial landmark identification. One such technique utilizes two stereo pairs of
video cameras at each side of the patient's face. The system allows rapid capture of the
face in three dimensions and precise measurement of anatomic landmarks.
The system can be used to capture the facial image and a cephalogram almost
simultaneously, allowing more accurate superimposition of soft and hard tissues. With
the goal that this precision will facilitate absolutely identical image and radiograph
position agreement and improve existing biostereometric measurement systems ability to
predict soft tissue changes following orthognathic surgery. (Ayoub 1996)

CBCT Organization, Orientation and Interpretation
The formation of a CT image is a distinct three-phase process.
• The scanning phase produces data (but not an image)
• The reconstruction phase processes the acquired data and forms a digital image.
• The conversion phase transforms the image from digital to analog, which is
expressed as varying shades of gray.
There are adjustable factors associated with each of these phases that can have an effect
on the characteristics and quality of the image.

Figure 5 - The basic 3-stage process of CBCT image
acquisition and image processing

16
Rotating the x-ray tube completely around the head and projecting many views forms a
complete scan. The complete scan produces a Digital Imaging and Communications in
Medicine (DICOM) data set that contains sufficient three-dimensional array of intensity
information for the reconstruction of a volumetric image.

Every 3D pixel, or voxel, in the image is referenced by three coordinates, x, y, and z,
with z indicating the number of the slice to which the voxel belongs, y indicating the row
in the slice, and x indicating the column. In order to display images correctly, the
software needs to know the mapping between this x, y, z image coordinate system and
the patient coordinate system. This is important, because the mapping between
directions x, y, z and the right-left, anterior-posterior or inferior-superior directions in the
human body can vary depending on the systems settings.

While 3D image data and all the available software manipulation possibilities are
incredible, in order to be of value, proper orientation of the image is of the utmost
importance. RAI codes let you specify image orientation quickly. Each of the three letters
in the code is an abbreviation for the direction in the patient coordinate system. For
example, the code RAS means that the X corresponds to the right-left direction, Y
corresponds to the anterior-posterior direction, and the Z corresponds to the inferior-
superior direction. Many other orientation standards exist, but in radiology, RAS is the
standard orientation for most imaging applications, including those used in this study.

17

Figure 6 - Axes of coordinates in a 3-dimensional image.
The negative and positive directions in the x, y, and z axes represent left and right, forward and
backward, and up and down, respectively. RAS conveys standardized orientation information,
regardless of whether a patient is vertically or horizontally positioned.

Natural Head Position (NHP)
One of the challenges of comparing 3D CBCT (or any) images taken at different times is
that no matter the protocol for patient positioning, slight changes always exist. The sella-
nasion line and Frankfort horizontal can vary considerably in relation to a horizontal or
vertical line depending on the position if the head (pitch). In order to minimize this
variability, various protocols for positioning a patient in a reproducible stance have been
developed.

NHP is defined as the most standardized and reproducible position of the head, where a
patient is standing in an upright posture with the eyes focused horizontally on a point at
eye-level distance away. (Moorees et al. 1958; Molhave 1960, Weber et al. 2013).

The concept of natural head position (NHP) was introduced to orthodontics in the 1950’s
in papers by Moorees and Kean, Molhave and others. It had been shown in studies to be
valid and reproducible for cephalometric diagnosis. In their 1992 study, Lundstrom and
Ludstrom found the reproducibility of NHP, assessed as the error of a single observation,
18
was close to 2 degrees - which is significantly less that the inclinations of sella-nasion,
basion-nasion, and porion-orbitale lines to a horizontal line drawn through sella which
showed standard deviations of between 4.5 and 5.6 degrees. These findings, in
combination with the fact that the NHP represents a realistic appearance of a patient’s
profile, support its use as a basis for cephalometric analysis of dentofacial anomalies.
(Ludstrom et al. 1992)

Since NHP is unique and consistent for each individual, a CBCT unit’s standard restraints
will not provide adequate, individualized guidance to obtain an image in NHP. Different
methods have been reported that range from simply positioning a mirror at eye-level on a
wall a distant from the patient to more complicated instruments, such as registration jigs
and inclinometers (Lundstrӧm et al. 1995; Weber et al. 2013; Meiyappan et al. 2015).
Recent studies by Liu et al. (2015) and Weber et al. (2013) both use horizontal and
vertical laser lines projected on the patient’s face to adjust the pitch, roll, and yaw. Some
clinicians also place four semi-permanent radiopaque positioning ink dots or adhesive
markers on the face; two vertically along the forehead and two horizontally along the pre
auricular/infrazygomatic area, to help align the laser beams and resulting ceph images.
While following patient poisoning protocols at the time of the scan allows CBCT
generated images to be as close to the patients NHP as possible, post scan digital re-
orientation is often required to correct the image alignment.

Condyle Position Following Orthognathic Surgery
When a CBCT volume is indicated for orthodontic assessment and/or orthognathic
19
surgery, it generally includes the right and left temporomandibular joints making them
available for evaluation by the clinician who prescribes the scan. With a 3D image a
clinician is able to see the unmagnified size, shape and relationship of the condylar and
articular surfaces. This allows for a more accurate evaluation of the joints versus, what is
often the only condyle imaging that is obtained as part of standard orthodontic records the
evaluation, a panoramic radiograph. (Motta et al. 2010; Larson BE 2012).

Figure 7 - Condyle tomogram

The relationship between the mandibular condyle and glenoid fossa has long been
debated and still remains a highly controversial issue in many dental sub-specialties. 3D
analysis of the distal segments of the mandible after orthognathic surgery has
significantly contributed to the understanding of the multi-directional (anterior, posterior,
medial, lateral) movements of the condyle within the TMJ. The location, magnitude, and
direction of mandibular and condylar rotations during surgery can be qualitatively and
quantitatively measured by superimposition of pre- and post-surgery 3D scans. In order
to analyze maxillofacial changes at multiple time points, we rely on relatively stable and
reliable reference structures, primarily those along the cranial base for adults and the
anterior cranial fossa for growing children. (Cevidanes et al. 2006, 2009; Motta et al.
2010).
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During orthognathic surgery, changes often occur in the position of the mandibular
condyles, articular disc, and paradiscal tissues however, this change in condylar
positional should be minimized. Inappropriate condylar positioning can lead to
postoperative complications including idiopathic condylar resorption, functional disorder,
and post-operative relapse. Factors contributing to the change in condylar position during
orthognathic surgery include the posture of the patient during surgery, muscle relaxation
while under anesthesia, positioning errors during rigid fixation, lack of stability with non-
rigid fixation methods, intra-capsular bleeding or edema of the joints, internal
derangement, or a combination of these factors. (Kim 2013)

“Condylar position is known to be affected post-operatively by factors such as the
rotational movement of the distal segment, muscle equilibrium, fixation method, and
surgeon’s experience.” (Kim et al. 2012). Small changes in the condylar position will
need to be accommodated for by the physiologic adaptation, which can lead to skeletal
relapse or condylar remodeling (Kim et al. 2011).

Multiple studies have been conducted to track the post-operative movement of the
condyles after various lengths of time, ranging from shortly after surgery to after several
years of retention. Kim et al. found that immediately after surgery, there is anterior
displacement of the condyle. At 3 months, a distal movement was seen from the axial
view and an inward rotation from the coronal view. Three to six months later there was
evidence of rotation of the condyle, after an additional 6 months the condyles were
considered to be stable. (Kim YJ et al. 2014)
21
Other studies reported different direction and magnitude results for post-surgical condylar
movement. (Chen et al. 2013, Rotskoff et al. 1991, Schendel et al. 1980, Sickels et al.
1999, Motta et al. 2011). Chen et al. reported a posterior-inferiorly movement
immediately after surgery, followed by an anterior-superior movement 3 months post-
surgery, and an overall net posterior-superior movement when comparing the pre-surgery
and three months post-surgery condyle position. Chen also reported that this position
remained stable during the 1-year follow-up. The conclusion of these researches, was that
the posterior displacement could possibly be caused by manual manipulation of the
proximal segment during surgery (Chen et al. 2013). However, they caution that their
measurements were taken from 2-dimensional images generated from a 3D volume, and
may not as accurate as if they had been measured in the original 3D image.

Condyle positional changes after orthognathic surgery remain difficult to predict, even
with 3D analysis data from a large number of cases. A wide variety of studies have been
conducted to examine the changes of the structures pre and post orthognathic surgery in
mandibular-only surgery, bi-maxillary surgery, and unilateral osteotomies. However, due
to the overwhelming number of variables, condylar displacement change is difficult to
isolate. Errors when evaluating condylar change on 2D radiography can occur because
the condyles have been displaced in all three planes of space during surgery. Modern
three-dimensional models, registered on the anterior cranial base do provide a more
reliable way to compare pre and post-surgical condylar changes since translation and
rotation may be viewed in all planes of space, but even 3D methods still face challenges
when accounting for all of the factors that could contribute to errors in the data.
22
(Cevidanes et al. 2005, De Clerck 2012)

Methods Of Assessing Condylar Position Changes
There is a long history of measuing condylar change over time in the literature. As
imaging technology has advanced an assortment of radiographic techniques have been
used to evaluate condylar displacement, including the hand tracing of and more recently,
the computer analysis of linear tomography, submentovertex radiography, lateral
cephalometric radiograph, computed tomography. Three methods byWill et al 1984,
Pullinger and Hollander 1986 and Alder et al 1999 have historical significance and will
be discussed. Presently, CBCT is the method that is most widely used in the maxillofacial
region, as it allows for accurate 3D imaging of the TMJ complex with less radiation
exposure than some of the other methods available. (Chen et. al 2013, H.J. Yang and S.J
Hwang 2014; Kim et al 2011, Carvalho et al 2012, Cevidanes et al 2007, De Clerck et al
2012).

In his 1984 article evaluating forty one mandibular advancement BSSO surgery patients,
Will et al. introduced a hand traced, 2D method of assessing changes in condylar
displacement by evaluating condylar position preoperatively and at three specific times
post-operatively (T1 - pre surg, T2 - with in 1 week post-op, T3 - with in one week of
fixation release, T4 - at least 6 weeks post fixation release) via tracings and
measurements from sub-mental vertex films, a lateral cephalogram, and right and left
temporomandibular joint tomograms.

23
Each submental vertex film was manually traced to measure the angle between the long
axis of the condyle (the line connecting the medial- and lateral-most points of the
contour) and the midsagittal plane (a “best fit” line between the internal occipital
protuberance, the posterior limit of the foramen magnum, the anterior limit of the
foramen magnum, and the frontal crest). (Figure 8)

1. Lateral pole, left condyle
2. Medial pole, left condyle
3. Medial pole, right condyle
4. Lateral pole, right condyle
5. Frontal crest
6. Anterior limit, foramen magnum
7. Posterior limit, foramen magnum
8. Internal occipital protuberance

Figure 8 - Will et al (1984) Tracing of a sub mental vertex image

Each lateral film was traced and superimposed using the ethmoid triad (nasion, posterior
cranial fossa, and the soft tissue contour of the upper face) as references. Linear change
between the center of the condyle CC and Gonion were used in order to quantify
proximal fragment movement. “Tomograms were traced and superimposed to measure
superoinferior and anteroposterior movements of the condyle and inclination of the
condyle in a sagittal plane. Inclination of the proximal condyle and distal fragment were
referred to as either clockwise, with the anterior portion moving inferiorly, or
counterclockwise, with the anterior portion moving superiorly. On the preoperative films
two arbitrary points were located along the neck of the condylar process as an axis and a
cross of perpendicular lines was constructed through the more superior point. Two
additional points were arbitrarily marked in the cranial base.” (Will et al. 1984) The
24
results of this study included no significant condylar movement during the surgical
interval, significant superior movement during intraosseous fixation, with posterior
movement of only the left condyle, followed by no change in condylar position after
release of fixation.

Figure 9 - Will et.al. 1984 - tracing of pre- and post left
tomograms including condylar contour with axis points
and cross for reference, contour of glenoid fossa, cranial
base detail.
Cranial base reference points (solid lines)
Right and left pre and post surgical condyle super
impositions.

Then in 1986, Pullinger and Hollender did a study that compared different methods of
evaluating condyle change on tomograms The first was a subjective evaluation of change
using a rating system from -2 (posterior change) to +2 (anterior change) to score the
amount of movement (with 0 used for no change). These results were compared to
measurements from a microcomputer and graphics tablet. They analyzed radiographs
placed on a view box at 14x magnification through a video camera, then collected linear
and area measurements with the use of a graphics tablet. They were able to use the
computer commands lines and distances to generate linear distances measurements
between two markers and remove some of the human error from the data collection
process. Linear measurements of the posterior and anterior joint space; horizontal
displacement of condylar midpoint from the fossa’s midpoint; posterior inter-articular
dimension and the anterior inter-articular dimension were used to evaluate condyle
25
position. Their sample was made up of 10 patients of record at a dental school TMJ
clinic.

Figure 10 - Pullinger and
Hollender method for
measurement of condylar
change

“Line A was drawn through the most superior surface of the glenoid fossa parallel to the
FH plane. Line B and C were drawn to the most anterior and posterior aspects of the
condyle. Anterior, superior, and posterior spaces were measured in millimeters. The
anterior space (AS) and posterior space (PS) values were determined and ln(PS/AS) was
calculated to assess the anteroposterior relation of the condyle to the fossa. An ln(PS/AS)
higher than 0.25 indicated the anterior position of condyle in the glenoid fossa. An
ln(PS/AS) lower than -0.25 indicated the posterior position and all values in between
indicated the concentric position.” (Pullinger 1986) These results were then compared to
those from the visual scoring system.

A decade later, in 1999, Alder et al. used computed tomography to determine condylar
position changes, in all three planes of space (X, Y, and Z), between pre-surgical and 8-
week post-surgical condyle positions for 21 consecutive patients who underwent BSSO
advancement with rigid fixation. They described CT imaging and analysis as superior to
26
other available radiographic techniques due to increased consistency and accuracy of
measurements between timepoints. Landmarks, outside of the surgical area, including the
orbital walls, zygomatic arches, and external auditory meatus were superimposed in order
to compare pre- and post-surgery CT scans. For some measurements, reformatted 2D
images were generated from the 3D volumes. The condylar positions evaluated included:
medio-lateral condylar position (axial view), medio-lateral condylar angulation (axial
view), superior-inferior condylar position (reformatted sagittal view), rotational changes
(sagittal view) and anterior-posterior condyle movement (sagittal view).
To determine superior-inferior condylar position on the reformatted sagittal image, “a
plane through mid-condyle and coronoid process was drawn from head of condyle to tip
of coronoid process (line A). Second line was drawn from articular eminence to superior
border of glenoid fossa (line B). A third line (line C) was drawn beginning at most
superior part of glenoid fossa and extending parallel to line A; this third line represents
distance between head of condyle and top of glenoid fossa. Distance was measured
perpendicular to lines A and C.”

Figure 11 - Measurement of condylar position change on
tomograms. (Alder 1999)

These three different methods of calculating condyle position changes from images taken
at multiple time points (utilizing the imaging and measurement technology available at
the time) highlights some of the many challenges in the ongoing pursuit to understand
27
and predict changes in condylar position over time, and especially after maxillofacial
surgery.

Surfaced Based Registration and Voxel Based Registration
Other techniques, besides radiographic image analysis, such as color mapping or surface
and voxel-based registration, can also be used to evaluate pre- to post-surgical structure
changes. In color mapping distance data points from two superimposed scans are
compared and software calculates thousands of color-coded point-to-point comparisons
using the surface distances in millimeters between the 3D images, so that the difference
between T0 and T1 surfaces at any location can be quantified. In 2010 Carvallo et al.
evaluated pre-surgery, splint removal (4–6 weeks post-surgery), and 1-year post-surgery
cone-beam computed tomography scans for 27 patients and color mapped the resulting
craniofacial changes at nine areas, including the condyles.

Figure 12 - Surface distance color maps visualization showing condyle
displacement.
A. superimposed models pre-surgery (white) and at splint removal
(semitransparent mesh; B. superimposed models pre-surgery (white) and
at 1 year post-surgery (semitransparent mesh). C/E. Surface distances
between pre-surgery to splint removal D/F. Surface distances between
splint removal and the 1-year follow-up. Color map ranges between −3.6
mm (dark blue) and +3.6 mm (dark red).

For the condyles, positive values represent posterior-superior displacement, and negative
values anterior-inferior displacement. Displacements of the inferior and superior regions
of the ramus in opposite directions or with different magnitudes indicate torque
movement of this structure. (Carvalho 2010, Motta 2011)
28
Surface based registration (SBR) was the initial method described for 3D image
superimposition. The principle involves approximating two surfaces by selecting
corresponding landmarks on the two images and translating and rotating one of the
images so the landmarks align. This is followed by an iterative process (Iterative Closest
Point (ICP) algorithm), which minimizes the surface distance between the two surfaces.
Another, similar method of superimposition utilized in the medical research field known
as voxel based registration (VBR). It has been widely used for various medical
applications and research purposes, including diagnoses, treatment planning and
assessment of a variety of cases utilizing CT, CBCT, MRI, and 3D ultrasound. Voxel
based registration utilizes the grey scale difference of the voxels to align the two DICOM
images to the best superimposition achieving the least total grey scale density difference
between the two images. Voxel-based registration uses the intensities throughout the
entire selected volume and therefore uses the image content as the basis of the
registration and is useful were it is difficult to detect distinct surface topography features.
A study by Almukhtar (2014) found no statistically significant differences between the
voxel based and surface based registration methods. However, voxel based registration
showed more consistency in representation of the actual soft and hard tissue positions as
indicated by lower mean standard deviation.

Materials and Methods
Sample Subjects
The subjects of the present study included two data sets. The first (sample A) was
29
17 consecutive patients (10 female, 7 male) diagnosed with skeletal malocclusion (14
skeletal class II patients and 3 skeletal class III) with an age range of 20-53 years. The
second (Sample B) included 15 consecutive patients (6 male and 9 female) diagnosed
with skeletal malocclusion (11 skeletal class II patients and 4 skeletal class III) with an
age range of 17 – 36 years.

Patients Male Female Class II Class III Age
Sample A 17 7 10 14 3 20-53
Sample B 15 6 9 11 4 17-36
Table 1 – Sample Data

Surgical Technique and Postsurgical Protocol
VSP Medical Modeling (VSP Orthognathics; Golden, Colorado) was used to
virtually treatment plan each of the surgeries. Virtual Surgical Planning Data tables from
31 of 32 patients (VSP table for one pt could not be located) showing predicted surgical
movements were obtained. VSP data tables included a list of bony and occlusal
anatomical landmarks and their summarized movements from pre-operative position,
with the mandible auto rotated closed, to simulate the post operative position. Values
listed on the final movements summary table included: midline of lower incisor (IsL1),
lower left incisor (IsL1L), lower right incisor (IsL1R, lower left canine (LK9L), lower
left posterior molar (mesio buccal cusp) (L7L), lower right canine (LK9R), Lower right
posterior molar (mesiobuccal cusp) (L7R), and pogonion (pog).

All patients in this study received pre-surgical orthodontic treatment. All
underwent bi-maxillary orghognathic surgery by the same surgeon with a maxillary Le
Fort I osteotomy and mandibular Bilateral Sagittal Split Osteotomy (BSSO). In all cases,
30
segments were secured with rigid fixation plates.

Data Acquisition
Cranial CBCT scans were taken prior to, as well as two weeks after two jaw
orthognathic surgery. Scans were acquired on a single machine (iCat 3D dental imaging
system,) to a standard protocol (120 kVp; 5 mA; 23cm x 17 cm field of view; with a
scanning time of 67 seconds; and image acquisition at 0.4mm voxel size). Scans included
both condyles and both glenoid fossas in order to accurately compare the pre- and post-
surgical condylar positions.

The scanned data were then exported as DICOM files. The age, sex and Angle
molar classification of each patient was recorded. Other personal information was not
recorded. The DICOM files were then imported into ITK-SNAP software to segment the
3D images for further analysis.

Method for Generating Condyle and Fossa STL Mesh Files
Two DICOM files for each patient (pre-surgical and 2-week post-surgical) were loaded
into ITKSnap (version 2.4.0; www.itksnap.org) to segment the temporomandibular joint
(TMJ) regions of interest.
The imported image summary dimensions were x:
400, y: 400, z: 544 slices, Voxel spacing x: 0.40mm,
y: 0.40mm, z: 0.40mm, and the orientation was set to
RAI (RAI = x: right to left, y: anterior to posterior, z: inferior to superior). The crosshairs
31
mode was used to view the condyle on the orthogonal axial, coronal, and sagittal planes.
The image contrast of the isolated grayscale image was then adjusted to show the greatest
contrast between the glenoid fossa and the condylar head. The active drawing label color
was set as red for the condylar head and green for the fossa.
The semi-automatic segmentation mode was then used on each temporomandibular joint
complex to isolate the region of interest (Figure 13).

Figure 13 - Isolation of the region of interest for segmentation

The isolated region of interest was defined as follows:
• Posterior margin - the most inferior border of the mastoid process seen on the
sagittal slice
• Anterior margin - frontal bone of the cranial base from the sagittal slice
• Medial margin - apex of the petrous temporal bone seen on the frontal slice
• Lateral margin - the outermost layer of the skin
• Superior margin - frontal bone of the cranial base
• Inferior margin - body of the ramus just above the lingual foramen
32

Once the selection box contained the structures of interest, the auto-segmentation process
was initiated.
1. Pre-processing
• The intensity regions were adjusted so that the hard tissue could be delineated
from soft tissue and scan artifacts.
• The upper threshold was set to its maximum and the lower threshold and
smoothness was adjusted so that the border of the condylar head and glenoid
fossa was clearly defined.
2. Geodesic snake initialization
• Initialization centers (nucleoids) were placed evenly throughout the structure
of interest. The radii of the spheres were adjusted to stay within the structure
of interest.

Figure 14 - Segmentation. Spheres coalesce until the structure of interest is identified.
3. Segmentation
• Computer generated segmentation was run until the spheres grew to coalesce
33
with one another and fill the structure of interest, and the process was stopped
once the structure of interest’s voxels were labeled. (Figure 14)
4. Refinement
• To refine the segmentation, the mesh was edited using the scalpel and lasso
tools to cut the gross structures segmented from areas where the nucleoids had
extended past the desired boarders. Starting with the axial view and using the
coronal and sagittal view as verification, each CBCT image slice was
reviewed. The polygon tool was used to either fill a void in the area of interest
with the appropriate label color over a clear label, or to erase an unwanted
area by drawing over the label color with a clear label.
5. Export
• Once properly segmented and refined, the segmentation of the object of
interest was saved as a .GIPL and then exported as an “.stl" format mesh.

Method For Condyle Superimposition
Superimposition of the pre and post surgery scans was completed in Geomagic Studio
Software (Version 10; Geomagic U.S., Research Triangle Park, NC). Using the glenoid
fossa as the superimposition reference structure, quantitative measurement of condylar
post surgical movement was possible.

The glenoid fossa was not moved or altered during orthognathic surgery and could
therefore be used as a reference structure to isolate and identify true post surgical
condylar movement, while eliminating the effect of head position changes during the
34
scans.
1. File Import
• For each patient’s left and right sides, four segmented “.stl” files were
imported into the Geomagic Studio Software – the pre-surgical condyle
(PreC), pre-surgical glenoid fossa (PreGF), post-surgical condyle (PostC) and
post-surgical glenoid fossa (PostGF).
2. Fossa Matrix
• The pre surgical glennoid fossa was “pinned” to avoid any movement relative
to the coordinate system. The post surgical glennoid fossa was manually
registered onto the preGF using 3 landmarks visible on both condyles,
selected upon the visual judgment of the evaluator, then globally registered.
The transformation matrix of the PostGF translation and rotation in three
planes of space was recorded and saved.
• Fossa images were then hidden from view
3. Condyles Cropped
• The PreC was “pinned” to prevent any movement of this object. The post-
surgical condyle was manually registered to the pre-condyle, using 3
landmarks visible on both condyles, selected upon the visual judgment of the
evaluator and then globally registered.
• Once superimposed, the condylar neck was simultaneously cropped from both
images, creating similar volumes.
• The cropped post condyle was then reset to its initial position relative to the
pinned pre condyle.
35
4. Condyle Superimposition
• The cropped post condyle was then “reoriented” to it’s “0” position. Before
continuing with the superimposition process, it was verified that the
coordinates of the PostC were back to (0,0,0) to avoid errors in the measuring
process.
• With the pre-surgical glenoid fossa (PreGF) pinned, the post-surgical glenoid
fossa (PostGF) was then globally registered to PreGF.
• The transformation matrix describing the movement of Post GF was loaded to
move the 2 week post-surgical condyle the same distance and direction as its
corresponding 2 week post-surgical glenoid fossa. This way the true
displacement of the condyles pre-surgery and postsurgery was revealed.

Figure 15 - Corrected condylar displacement: Pre-surgery (blue) and post-surgery (red)

36
5. Measurement of Condylar Displacement
• The data from the transformation matrix for the post surgical condyle
movement (accounting for the positional changes that occurred between the
pre- and post- surgical scan glenoid fossa’s) was then recorded for analysis. x,
y and z values for both translation and rotation were collected.
6. Method Alteration for Sample B, Move to Origin
• Egregiously erroneous results were generated when this method was applied
to the second data set. Values ranging from -5 to 17 millimeters of movement
were seen in the final data table. Multiple theories to resolve this issue were
developed and pursued, and after many attempts, the solution of altering the
method to move the condyle images to the origin (0,0) of the axis system after
cropping them to the same level, but prior to applying the fossa transformation
matrix. (Figure 16)

Figure 16 - Cropped,
superimposed condyles in
bounding box re-oriented to
world coordinate axis

37
Method for CBCT Image Reorientation to NHP
Pre and post surgical DICOM file CBCT scans were imported into dolphin imaging
(Dolphin Imaging Plus v.11.9, Patterson Dental Supply Inc., Chatsworth, CA) for 32
patients (64 scans). The cranial base, orbitale and pogonion were used as landmarks in
order to orient the images into Natural Head Position (NHP).

Figure 17 – 3D image tools in Dolphin Imaging. 3D volumetric image with 3D in semi-transparent view
with x, y and z planes projected on the image.

Image orientation
• Under the ‘orientation’ mode, the images were first viewed from the right
side. In a ‘semi-transparent’ mode, the yaw and the roll were adjusted, until
the right and left orbits and zygomatic buttresses were coincident (Figure 18).
The same protocol was followed for the CBCT image as seen from the left.
Lastly, the same procedure was followed from a frontal view, to align the base
of the orbits symmetrically.
• To ensure that the roll was properly aligned, in solid mode, each CBCT was
looked at in a coronal clipping slice from the ‘top facing down’ view. The
38
sagittal and coronal symmetries were assessed by using the crista galli
alignment with the center of foramen magnum and internal occipital
protuberance. Similarly, the distances from the major foramina to the sagittal
and coronal reference lines were adjusted until both the right and left sides
were coincident.
• The image was then checked one more time in the frontal view for any
modifications of roll.
Figure 18 - 3D volumetric image with 3D in semi-transparent view from front and left side

• Finally, in the ‘top facing down’ view, the image is adjusted for any further
necessary roll modifications
• Changing back to the transparent mode, the CBCT image is assessed from the
right side, left side, and frontal view. The orbits and zygomatic buttresses
were again assessed for symmetry. The clinical midlines were checked again
against the CBCT image midlines before the image was assessed for both the
hard and solid tissues together.
39
• The pitch was adjusted after all other planes had been set. The pitch of the
image was modified until the patient was looking in the most natural head
position, with eyes gazing straightforward at the horizon.
• The corrected CBCT image is saved as ‘position zero’.
Method for Generating Lateral Ceph from CBCT
Once the CBCT images were oriented to NHP, lateral cephalometric images were
generated. Left orthogonal views with the ruler set to 100mm and placed on the left side
of the image were created. These NHP corrected ceph images were then exported into the
Dolphin layout.

Figure 19 – Lateral Cephalometric Image Production Options (Dolphin Imaging)

Method for Tracing Lateral Ceph
• The “University of North Carolina Cephalometric Tracing and Analysis” was
completed on pre- and post-surgical cephalograms for all 32 patients in the
sample. Landmarks identified included orbitale, key ridge, sella, porion,
condylion, PTM, ANS, PNS, nasion, A point, B point, lower incisor, upper
incisor, lower first molar, upper first molar, pogonion, menton, gnathion, and
gonion (see descriptions in Table 2).
40
• Image contrast adjustment tools were used to better visualize the image and
the precise location of the landmarks that were identified for this analysis.
• Skeletal AP, Dental AP, Skeletal vertical, Dental vertical and Soft tissue
profile values were generated in dolphin.
• Six midline structure values (SNA, SNB, anterior face height, posterior face
height, SN-GoGn and Occlusal plane to SN) were recorded for analysis.

Figure 20 - Lateral ceph landmarks identified
for lateral ceph data measurements

Table 2 - Lateral ceph landmarks identified for lateral ceph data measurements

Landmark Description
Porion Most superior point of external auditory meatus
Orbitale Lowest point on inferior orbital rim
A point Innermost point on the contour of the maxilla between incisor tooth and ANS
B point Innermost point on the contour of the mandible between incisor tooth and bony chin
Condylion Most posterosuperior point on head of condyle
Gnathion Lowest, most anterior midline point on the symphysis of the mandible
Sella Center of the bony chamber in the cranial base surrounding the pituitary gland
Nasion Juncture of the internasal suture with the nasofrontal suture in the midsagittal plane
Gonion Most inferior, posterior, and lateral point on the angle of the mandible
Menton Most inferior midline point on the symphysis of the mandible
41
VSP Data
Virtual surgical planning was completed for each patient prior to surgery. Data tables
showing the expected changes in landmark positions were collected for all but one
(n=31/32) patients, since one patient’s record could not be located. Pogonion was the
only midline skeletal structure for which data was utilized for this study.

Figure 21 - Virtual Surgical Planning Final Movements Summary Table

Statistical Analysis
Descriptive statistics, including mean, median, range, standard deviation, minimum, and
maximum were evaluated for sample A condyle data, sample B condyle data as well as
for the lateral ceph data for both data sets combined and sample A lateral ceph data
separately.

Pearson correlation tests were run in order to determine if the observed condylar changes
42
were statistically significant as well as, if there was a relationship between age and
gender and condylar movement. Results were considered significant at P<0.008. An
ANOVA test was used to see if there was any relationship between groups or within
groups. A one-sample t-test was used to see if there were any statistically significant
differences between right and left condyles. An Intraclass Correlation Coefficient of 99%
was achieved when 11 random cases were selected from the first sample of 17 patients
and measured a second time four weeks after the data was collected, validating the
reproducibility of measurements.

A Bonferroni correction (p<0.008) was applied in order to avoid Type I Error due to
multiple comparisons. All statistical analyses were performed with SPSS software (SPSS
Inc. of IBM, Chicago, IL). Raw data of our study can be found in the Appendix.

Results
The sample of the present study included two subsample data sets. The first (A) was 17
consecutive patients (10 female, 7 male) diagnosed with skeletal Class II or Class III
malocclusion (14 skeletal class II patients and 3 skeletal class III) with an age range of
20-53 years. The second (B) included 15 consecutive patients (12 male and 18 female)
diagnosed with skeletal Class II or Class III malocclusion (11 skeletal class II patients
and 4 skeletal class III) with an age range of 17 - 36 years.

The amount of condylar displacement between pre-surgical and 2 week post-surgical
CBCT scans is collected and the descriptive statistics for all patients is displayed in Table
43
10. Six measurements were collected for the right and left condyles of each patient
(translation and rotation on the 3 planes of space).
Sample A results
For sample A (pt# 1-17) the average condylar displacement was 0.78 mm on the x-plane,
-3.80 mm on the y-plane and 0.14 mm on the z-plane. As for rotation, the average
movement was 0.06 º on the x-axis, 0.30º on the y-axis and -0.27º on the z-axis. The
greatest displacements were translation in the y-plane (anteroposterior) and rotation on
the z-axis (superoinferior), which were also the only movements statistically significant
(p<0.008). (Table 3 and Table 4)

Table 3 - Descriptive statistics - Sample A: Condylar movement data

n Mean Range Minimum Maximum Std. Deviation
T_X 34 0.7836 6.90 -3.51 3.39 1.53770
T_Y 34 -3.8036 15.46 -12.96 2.49 3.91872
T_Z 34 0.1498 12.50 -7.90 4.60 2.49749
R_X 34 0.0631 10.10 -4.16 5.94 2.229175
R_Y 34 0.307 11.77 -6.46 5.31 2.68439
R_Z 34 -0.2778 25.62 -13.99 11.63 7.17404
n = 34 condyles, 17 right and 17 left

Table 4 - Sample A - Condylar movement data - Analysis of variance

Sum of
squares
df
Mean
Square
F Sig
T_X
Between
Groups
1.663 1 1.663 0.697 0.41

Within Groups 76.366 32 2.386

Total 78.029 33

T_Y
Between
Groups
144.641 1 144.641 12.782 0.001

Within Groups 362.12 32 11.316

Total 506.761 33

T_Z
Between
Groups
2.432 1 2.432 0.383 0.541
44

Within Groups 203.404 32 6.356

Total 205.836 33

R_X
Between
Groups
4.071 1 4.071 0.77 0.387

Within Groups 169.248 32 5.289

Total 173.319 33

R_Y
Between
Groups
0.095 1 0.095 0.013 0.911

Within Groups 237.702 32 7.428

Total 237.797 33

R_Z
Between
Groups
1131.336 1 113.336 63.842 0.000

Within Groups 567.071 32 17.721

Total 1698.406 33

Sample B results
Sample B (pt # 18-32) consisted of 15 patients (30 condyles). The average condylar
displacement was 0.05 mm on the x-plane, -0.39 mm on the y-plane and 0.01 mm on the
z-plane. The average rotation was -0.69 mm on x-axis, 1.69 on the y-axis and -2.43 on z-
axis. The movements that were statistically significant were translation on the y-axis and
rotation on the y-axis (p<0.008). The greatest displacements were translation in x-axis
and rotation on z plane. The movements that were statistically significant were translation
on y-axis and rotation on the y-axis (p<0.008). (Tables 5-6).

Table 5 - Sample B descriptive statistics

N Mean Range Minimum Maximum
Std.
Deviation
T_X (mm) 30 0.0448 5.18 -2.07 3.11 1.1116
T_Y (mm) 30 -0.3922 2.46 -1.63 0.83 0.5776
T_Z (mm) 30 0.0106 2.01 -0.96 1.06 0.4341
R_X (°) 30 -0.6847 10.49 -4.48 6.01 2.5101
R_Y (°) 30 1.6847 11.79 -5.92 5.87 2.8148
R_Z (°) 30 -2.4253 20.53 -12.18 8.35 6.069

45
Table 6 - Sample B one-sample t-test

Test Value = 0

95% Confidence interval
of the difference

t df sig (2 tailed) Mean difference Lower Upper
T_X 0.221 29 0.827 0.0448 -0.3703 0.4598
T_Y -3.719 29 0.001 -0.3922 -0.6079 -0.1765
T_Z 0.134 29 0.894 0.01062 -0.1515 0.1727
R_X -1.494 29 0.146 -0.6847 -1.622 0.2526
R_Y 3.225 29 0.003 1.6573 0.6063 2.7084
R_Z -2.189 29 0.037 -2.4253 -4.6916 -0.1591

When comparing sample A and sample B, the range for rotation values in all planes was
similar, as was the range for translation in the x plane (6.90 in sample A and 5.18 in
sample B). The range for translation in the Y and Z plane, however, do not match as well
as the other variables, the minimum and maximum values are different by several orders
of magnitude, 15.46 (T_Y) and 12.96 (T_Z) in Sample A and 2.46 (T_Y) and 2.01 (T_Z)
translation in Sample B.

Lateral Ceph Data Statistical Analysis
The pre- and post-surgical CBCT data for patients from sample A and sample B was
further analyzed once the images were oriented to natural head position and lateral
cephalograms were created. Data from sample A and sample B was analyzed
independently as well as in combination. Anterior posterior as well as vertical changes
were evaluated for 6 midline landmarks – SNA, SNB, AFH, PFH, SN-GoGn, Occ-SN.
ANS could not be used, as it was clipped to ensure proper nasal projection and angulation
in many of the patients and could not be measured on post surgical cephs. These values
consist of both angular and linear variables.
46
Table 7 - Descriptive statistics - Sample A Ceph data (n=17)
count mean
sample
standard
deviation
sample
variance minimum maximum range
SNA 17 3.400 2.253 5.078 -0.9 7.9 8.8
SNB 17 6.582 2.830 8.012 1.2 11.6 10.4
AFH (N-Me)
(mm) 17 -3.859 3.231 10.443 -10.6 2.7 13.3
PFH (Co-Gn)
(mm) 17 4.382 7.258 52.680 -2.4 19.6 22
SN - GoGn 17 -10.235 6.372 40.609 -23.3 -0.3 23
Occl to SN 17 -7.629 4.530 20.522 -16.7 -0.1 16.6

Table 8 - Descriptive statistics - Sample B ceph data (n=15)
count mean
sample
standard
deviation
sample
variance minimum maximum range
SNA 15 2.893 2.214 4.902 -2.1 6.7 8.8
SNB 15 4.073 3.414 11.652 -2.7 8.4 11.1
AFH (N-Me)
(mm) 15 -2.647 3.309 10.947 -10.7 2.6 13.3
PFH (Co-Gn)
(mm) 15 -0.593 4.947 24.476 -12.3 8.7 21
SN - GoGn 15 -3.933 3.908 15.275 -10 4.4 14.4
Occl to SN 15 -1.827 4.528 20.505 -11.5 3.3 14.8

Table 9 - Descriptive statistics - Sample A and B combined (n=32)
count range minimum maximum mean
sample
standard
deviation
sample
variance
SNA 32 10 -2.1 7.9 3.163 2.214 4.900
SNB 32 14.3 -2.7 11.6 5.406 3.319 11.015
AFH (N-Me)
(mm) 32 13.4 -10.7 2.7 -3.291 3.273 10.711
PFH (Co-Gn)
(mm) 32 31.9 -12.3 19.6 2.050 6.679 44.608
SN - GoGn 32 27.7 -23.3 4.4 -7.281 6.170 38.067
Occl to SN 32 20 -16.7 3.3 -4.909 5.339 28.508

Table 10 - Descriptive statistics - Sample A and B combined (n=32)
count
low
extremes
low
outliers
high
outliers
high
extremes
SNA 32 0 0 0 0
SNB 32 0 0 0 0
Total Anterior
Face Ht (N-Me)
(mm) 32 0 0 0 0
47
Posterior Facial
Ht (Co-Gn) (mm) 32 0 1 4 0
SN - GoGn 32 0 2 0 0
Occ Plane to SN 32 0 0 0 0

In both sample A and sample B, and the combined data the greatest variation of values
were seen in the SN-GOGN and Occ plane to SN values. The smallest range in both
samples and the combined data was in SNA.

The mean values were similar in both samples for SNA, SNB and anterior facial height
(N-Me) with minimum and maximum values of similar scale and agreement of
positive/negative sign. However they were different for posterior facial height (Co-Gn),
SN-GoGn and occlusal plane, with larger discrepancies between mean values for each
sample and a sign discrepancy for posterior facial height, (4.382 for sample A versus -
0.593 for sample B).

Figure 22 - SNA, SNB and PFH for sample A only Increased. AFH SN-GoGn, Occl-SN and PFH for sample B
only decreased.

The data for the combined sample was then
analyzed with one sample T-tests to determine the
significance of the values. All values were
significant except for posterior face height, the
sample for which the range was the highest in
both samples and there was the greatest number of
high/low outliers from the data set (4 high and 1 low). The results showed an overall
48
increase in posterior face height, SNA and SNB and an overall decrease in SN-GoGn,
Occl-SN and anterior face height.

Table 11 - Descriptive Statistics - Combined Ceph Data (n=32)

N Mean Std Deviation
Std Error
Mean
SNA 32 3.1625 2.2137 0.39133
SNB 32 5.4063 3.31895 0.58671
AFH 32 -3.2906 3.2728 0.57855
PFH 32 2.0313 6.68481 1.18172
SN_GOGN 32 -7.2688 6.18502 1.09337
OCC_SN 32 -4.9094 5.33929 0.94386

Table 12 - Combined Data - One-Sample t-test

Lowest Value = 0

95% Confidence interval of the
difference

t df sig (2 tailed)
Mean
difference Lower Upper
SNA 8.081 31 0.000 3.1625 2.3644 3.9606
SNB 9.214 31 0.000 5.4063 4.2096 6.6029
AFH -5.688 31 0.000 -3.2906 -4.4706 -2.1107
PFH 1.719 31 0.096 2.0313 -0.3789 4.4414
SN_GOGN -6.648 31 0.000 -7.2688 -9.4987 -5.0388
OCC_SN -5.201 31 0.000 -4.9094 -6.8344 -2.9844
P=<0.05. Value of 0 indicates less than 0.05.

Ceph data for male and female patients showed no significant difference in any variable
for gender.

Table 13 - Group Statistics comparing Male and Female - Combined Ceph Data (n=32)

F=1, M=0 N Mean
Std
Deviation
Std Error
Mean
SNA 1 21 3.4571 2.286 0.4988

0 11 2.6 2.0513 0.6185
SNB 1 21 6.3 3.029 0.66106

0 11 3.7 3.304 0.99608
AFH 1 21 -3.433 3.35266 0.73161

0 11 -3.018 3.2557 0.98163
PFH 1 21 2.576 5.98497 1.30603

0 11 0.991 8.0669 2.43226
49
SN_GOGN 1 21 -7.8476 5.7177 1.2477

0 11 -6.164 7.15252 2.15657
OCC_SN 1 21 -5.486 5.3308 1.16327

0 11 -3.809 5.4324 1.63793

Table 14 - Independent sample tests - Male and Female - Combined Ceph Data (n=32)

Levene's Test of Equality of
Variances

F sig
SNA
Equal variances
assumed 0.428 0.518

Equal variances
not assumed
SNB
Equal variances
assumed 0.096 0.759

Equal variances
not assumed
AFH
Equal variances
assumed 0.284 0.598

Equal variances
not assumed
PFH
Equal variances
assumed 0.419 0.522

Equal variances
not assumed
SN_GOGN
Equal variances
assumed 0.04 8.43

Equal variances
not assumed
OCC_SN
Equal variances
assumed 0.001 0.978

Equal variances
not assumed

Table 15 - Independent Samples Test comparing males and females - Combined Ceph Data

t-test for Equality of Means
t df
sig (2
tailed)
Mean
difference
SNA
Equal variances
assumed
1.042 30 0.306 0.8571

Equal variances not
assumed
1.079 22.486 0.292 0.8571
SNB
Equal variances
assumed
2.236 30 0.033 2.6

Equal variances not 2.175 18.914 0.043 2.6
50
assumed
AFH
Equal variances
assumed
-0.336 30 0.739 -0.4152

Equal variances not
assumed
-0.339 20.961 0.738 -0.41512
PFH
Equal variances
assumed
0.631 30 0.533 1.5853

Equal variances not
assumed
0.574 15.935 0.574 1.5853
SN_GOGN
Equal variances
assumed
-0.726 30 0.474 -1.6839

Equal variances not
assumed
-0.676 16.87 0.508 -1.6839
OCC_SN
Equal variances
assumed
-0.84 30 0.408 -1.6766

Equal variances not
assumed
-0.835 20.078 0.414 -1.6766

Combined lateral ceph data for male and female patients showed no significant difference
(p=.05) in any variable for gender. Sample A patients (n=17) consisted of 10 Females
and 7 males, sample B patients (n=15) consisted of 9 females and 6 males. (Ratios of
1.43 to 1 and 1.5 to 1 respectively. Combined, all patients (n=32) totaled 19 females and
13 males, an overall ratio of 1.46 to 1.

Combined lateral ceph data was also analyzed for correlation with patient age at time of
surgery. Sample A patients (n=17) ranged in age from 20-53, sample B patients (n=15)
ranged in age from 17-36 years old at time of surgery. Combined, all patients (n=32)
ranged in age from 17-53 with a mean age of 26.28. No significant difference was found
between age at time of surgery and any of the lateral ceph variables.

51
Table 16 - Descriptive statistics - comparing patient age - Combined ceph data

N Range Min Max Mean SD
Age 32 36 17 53 26.28 9.003
Valid N (listwise) 32

Table 17 - Independent Samples Test comparing patient age - Combined Ceph Data (n=32)

t-test for Equality of Means

95% Confidence interval of the difference

Std. Error Lower Upper
SNA Equal variances assumed 0.8228 -0.8232 2.5375

Equal variances not
assumed
0.7946 -0.78875 2.503
SNB Equal variances assumed 1.1625 0.22579 4.9742

Equal variances not
assumed
1.1955 0.09705 5.1029
AFH Equal variances assumed 1.2359 -2.9393 2.1089

Equal variances not
assumed
1.2243 -2.9615 2.1312
PFH Equal variances assumed 2.5126 -3.54605 6.7166

Equal variances not
assumed
2.7607 -4.2691 7.4397
SN_GOGN Equal variances assumed 2.3198 -6.4216 3.0537

Equal variances not
assumed
2.4915 -6.9437 3.5757
OCC_SN Equal variances assumed 1.9968 -5.7546 2.4013

Equal variances not
assumed
2.0089 -5.8663 2.513

Table 18 - Correlations comparing patient age - Combined Ceph Data (n=32)

Age SNA

Age PFH
Age
Pearson
Correlation
1 0.202

Age
Pearson
Correlation
1 0.122

Sig (2
tailed)
0.267

Sig (2 tailed)

0.507

N 32 32

N 32 32
SNA
Pearson
Correlation
0.202 1

PFH
Pearson
Correlation
0.122 1

Sig (2-
tailed)
0.267

Sig (2-tailed) 0.507

N 32 32

N 32 32

Age SNB

Age
SNGOG
N
Age Pearson 1 0.271

Age Pearson 1 -0.177
52
Correlation Correlation

Sig (2
tailed)
0.133

Sig (2 tailed)

0.333

N 32 32

N 32 32
SNB
Pearson
Correlation
0.271 1

SNGOGN
Pearson
Correlation
-0.177 1

Sig (2-
tailed)
0.133

Sig (2-tailed) 0.333

N 32 32

N 32 32

Age AFH

Age OCCSN
Age
Pearson
Correlation
1 -0.018

Age
Pearson
Correlation
1 -0.199

Sig (2
tailed)
0.923

Sig (2 tailed)

0.275

N 32 32

N 32 32
AFH
Pearson
Correlation
-0.018 1

AFH
Pearson
Correlation
-0.199 1

Sig (2-
tailed)
0.923

Sig (2-tailed) 0.275

N 32 32

N 32 32

Combined lateral ceph data for male and female patients showed no significant
correlation (p=0.05) in any variable for age.

Condyle movement and lateral ceph data comparison
A proxy value, the sum of the absolute values for condyle rotation/translation, was used
for condyle translation and rotation in order to compare condyle movement to
cephalometric post-surgical change. A proxy is an indirect measure of the desired
outcome which is itself strongly correlated to that outcome. It is commonly used when
direct measures of the outcome are unobservable and/or unavailable.

53
Table 19 - Descriptive statistics - Sample A - Comparison of condyle movement with ceph change

N range minimum maximum mean
standard
deviation variance
SNA 17 8.80 -0.9 7.9 3.400 2.253 5.078
SNB 17 10.4 1.2 11.6 6.582 2.830 8.012
Total Anterior
Face Ht (N-Me)
(mm) 17 13.3 -10.6 2.7 -3.859 3.231 10.443
Posterior Facial
Ht (Co-Gn) (mm) 17 22 -2.4 19.6 4.382 7.258 52.680
SN - GoGn 17 23 -23.3 -0.3 -10.235 6.372 40.609
Occ Plane to SN 17 16.6 -16.7 -0.1 -7.629 4.530 20.522

Regression of Condyle Translation – Sample A

Table 20 - Model Summary - Sample A - Comparison of condyle translation with ceph change
Model R R Square
Adjusted R
Square Std. Error of the Estimate
1 0.348 0.121 -0.074 4.52772
a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN

R is the correlation between the observed and predicated value of the dependent variable.
R square is the portion of the variance of the dependent variable (translation proxy) that
can be explained by the independent variables (lateral ceph values). The adjusted R
square is the adjustment for the number of predictors.

Table 21 - Sample A - ANOVA - Sample A - comparing ceph change with condyle translation
Model
Sum of
Squares
df
Mean
Square
F sig.
1 Regression 76.333 6 12.722 .621 0.712
a

Residual 553.506 11 20.500

Total 629.838 16

a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN
b. Dependent Variable: P_Trans

Table 22 - Sample A - Coefficients for condyle translation

Unstandardized
Coefficients
Standardized Coefficients

Model

B Std. Error Beta t Sig.
1 (Constant) 4.688 2.314

2.026 0.053

SNA 0.419 0.376 0.213 1.114 0.275
54

SNB 0.232 0.416 0.148 0.558 0.581

AFH 0.270 0.355 0.196 0.760 0.454

PFH 0.101 0.257 0.166 0.394 0.697

SN_GOGN 0.298 0.505 0.428 0.591 0.560

OCC_SN -0.441 0.408 -0.450 -1.080 0.290
a. Dependent Variable: P_Trans

Values for B are the regression evaluation for predicting the dependent variable from the
independent variable. Beta coefficients are the estimates resulting from a regression
analysis that have been standardized so that the variances of dependent (proxy
translation/rotation) and independent variables are one. Therefore, standardized
coefficients refer to how many standard deviations a dependent variable will change, per
standard deviation increase in the predictor variable. Significance tests whether an
investigator may conclude that that effect reflects the characteristics of the whole
population if the p-value of an observed effect is less than the significance level, the null
hypothesis is rejected.

Regression of Condyle Rotation – Sample A

Table 23 - Model Summary - Sample A - Comparison of condyle rotation with ceph change
Model R R Square
Adjusted R
Square Std. Error of the Estimate
1 0.570
a
0.325 0.174 4.00744
a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN

Table 24 - ANOVA - Sample A - comparing ceph change with condyle rotation
Model
Sum of
Squares
df
Mean
Square
F sig.
1 Regression 208.317 6 34.719 2.162 0.079
a

Residual 433.608 11 16.060

Total 641.925 16

a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN
b. Dependent Variable: P_Rot

55
Table 25 - Sample A - Coefficients for condyle rotation

Unstandardized
Coefficients Standardized Coefficients
Model

B Std Error Beta t Sig
1 (constant) 4.282 2.048 2.091 2.091 0.046

SNA 0.125 0.333 0.377 0.377 0.709

SNB 0.758 0.368 2.058 2.058 0.049

AFH 0.366 0.314 0.264 1.167 0.254

PFH -0.086 0.227 -0.139 -0.377 0.709

SN_GOGN -0.135 0.447 -0.193 -0.303 0.764

OCC_SN -0.095 0.361 -0.096 -0.264 0.794

a. Dependent Variable: P_Rot

Table 26 - Descriptive statistics - Sample B ceph data (n=15)
count mean
sample
standard
deviation
sample
variance minimum maximum range
SNA 15 2.893 2.214 4.902 -2.1 6.7 8.8
SNB 15 4.073 3.414 11.652 -2.7 8.4 11.1
AFH (N-Me)
(mm) 15 -2.647 3.309 10.947 -10.7 2.6 13.3
PFH (Co-Gn)
(mm) 15 -0.593 4.947 24.476 -12.3 8.7 21
SN - GoGn 15 -3.933 3.908 15.275 -10 4.4 14.4
Occl to SN 15 -1.827 4.528 20.505 -11.5 3.3 14.8

Regression of Condyle Translation – Sample B

Table 27 - Model Summary - Sample B - Comparison of condyle translation with ceph change
Model
R R Square
Adjusted R
Square
Std. Error of the Estimate
1 0.785
a
0.616 0.328 0.76374
a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN

Table 28 - ANOVA - Sample B - comparing ceph change with condyle translation
Model
Sum of
Squares
df
Mean
Square
F sig.
1 Regression 7.484 6 1.247 2.138 0.158
a

Residual 4.666 8 0.583

Total 12.15 14

a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN
b. Dependent Variable: P_Trans

56
Table 29 - Sample B - Coefficients for condyle translation

Unstandardized
Coefficients
Standardized Coefficients

Model

B Std. Error Beta t Sig.
1 (Constant) 1.330 0.583

2.282 0.052

SNA -0.167 0.121 -0.396 -1.381 0.205

SNB 0.05 0.071 0.183 0.697 0.505

AFH -0.146 0.109 -0.517 -1.333 0.219

PFH 0.079 0.078 0.4117 1.012 0.341

SN_GOGN -0.85 0.081 -0.359 -1.047 0.326

OCC_SN 0.001 0.078 0.004 0.011 0.991
a. Dependent Variable: P_Trans

Regression of Condyle Rotation – Sample B

Table 30 - Model Summary - Sample B - Comparison of condyle rotation with ceph change
Model
R R Square
Adjusted R
Square
Std. Error of the Estimate
1 0.172
a
0.029 -0.699 4.64164
a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN

Table 31 - ANOVA - Sample B - comparing ceph change with condyle rotation
Model
Sum of
Squares
df
Mean
Square
F sig.
1 Regression 5.225 6 0.871 0.04 1.000
a

Residual 172.358 8 21.545

Total 177.584 14

a. Predictors (constant): SNA, SNB, AFH, PFH, SN-GoGn, Occl-SN
b. Dependant Variable: P_Rot

Table 32 - Sample A - Coefficients for condyle rotation

Unstandardized
Coefficients Standardized Coefficents
Model

B Std. Error Beta t Sig.
1 (Constant) 7.366 3.544

2.079 0.071

SNA -0.153 0.734 -0.095 -0.209 0.84

SNB 0.165 0.435 0.158 0.379 0.714

AFH -0.026 0.664 -0.024 -0.04 0.969

PFH 0.088 0.472 0.122 0.186 0.857

SN_GOGN -0.014 0.492 -0.015 -0.028 0.978

OCC_SN 0.07 0.476 0.088 0.146 0.887

a. Dependant Variable: P_Rot

57
In the comparison of the translational and rotational movement of the condyles and the
pre- to post-surgical lateral ceph changes, no correlation was statistically significant for
any measures in sample A or sample B. Since condylar translation was the values that we
are least confident about, the combined data for sample a and b together was not
analyzed. Our conclusion is that there is no relationship between surgical movement and
condyle translation and no relationship between condylar rotation and surgical
movement.

VSP Data Analysis
There was a significant correlation of .751 between the SNB change from pre to post
surgical lateral ceph measurements and the virtual surgical plan’s predicted pogonion
change.

Table 33 - Correlation between post-surgical ceph SNB change and VSP predicted pogonion

SNB PogAP
SNB
Pearson
Correlation 1 .751**

Sig (2 tailed)

<0.001

N 31 31
PogAP
Pearson
Correlation .751** 1

Sig (2-tailed) <0.001

N 31 31
** Correlation is significant at the .01 level (2-tailed)

58

Figure 23. Scatter plot graph of post-surgical ceph SNB change vs. VSP predicted pogonion

Discussion
The predictability, accuracy and stability of surgical change are complex and multi-
faceted. Great care needs to be made in treatment planning, setting up and performing
orthognathic surgery. Both 3D and 2D imaging is used to aid orthodontist and surgeons
in developing and implementing a plan to obtain the best result. Post-operative changes
of the condyles, as well as middle and lower facial landmarks are of great interest to both
orthodontist and oral surgeons.

Direction of condyle movement post surgery - translation
Many researchers have studied the effect of orthognathic surgery on condylar position,
traditionally on 2D radiographs and more recently in 3D. However, there are several
30.00 20.00 10.00 0.00
PogAP
12.00
9.00
6.00
3.00
0.00
-3.00
SNB
59
challenges in conducting 3D measurements of condylar position changes. There are
inherent limitations associated with studying both liner and angular changes of a structure
in the three dimensions of space.

In the present study, CBCT scans of 32 patients were taken prior to, as well as, 2 weeks
following bi-maxillary surgery to assess immediate condylar positional changes, midline
landmark position changes and actual vs expected change of pogonion versus the VSP
estimate. Challenges with obtaining accurate condyle translation results for the second
sample group led up to evaluate the two groups “sample A” and “sample B”
independently as well as combined. The mean movements for translation and rotation
were measured separately in three planes of space for right and left condyles (Table 8 and
Table 9) using the glenoid fossa as registration surfaces for two sample groups (A and B).

For sample A the average condylar displacement was 0.78 mm on x plane, -3.80 mm on y
and 0.14 mm on z plane. As for rotation, the average movement was 0.06 º on x plane
R_X, 0.31º on R_Y and -0.28 on R_Z. The only significant translation movement was on
Y plane (anteroposterior changes), and rotation on z plane (superoinferior).

For sample B The average condylar displacement was .045 mm on x plane, -0.39 mm on
y plane and 0.01 mm on the z plane. For rotation, the average movement was -0.68 mm
on x plane, 1.66 on y plane and -2.43 on z plane. The greatest displacements were
translation in x-axis and rotation on z plane. The movements that were statistically
60
significant were translation on y-axis (anteroposterior), and rotation on the y-axis
(anteroposterior), (p<0.008).

The direction of condylar displacement reported by previous studies immediately after
orthognathic surgery is variable. Chen et al. and Rotskoff et al. both found
posterioinferior condyle movement post surgery. Rotskoff et al. obtained full head
tomograms one day after surgery and made linear measurements on these.
Chen et al. calculated the amount of movement in 2-dimensions by the method of
Pullinger and Hollender for 27 patients. They found no significant difference between the
right and left condyles. In their study condyles moved inferoposteriorly immediately after
surgery (T0 to T1) followed by anterosuperior movement 3 months after surgery (T1 to
T2). The superimposed effect showed posterosuperior movement compared with the
initial position before surgery (T0 to T2) and this position remained stable at 1-year
follow-up.

Sample A and B results coincide with this result in Y axis, as both our samples showed a
mean posterior condyle movement, however while sample A showed a mean inferior
movement, sample B showed and average superior movement of 1.66mm. (Chen et al
2013, Rotskoff et al. 1991). Posterior displacement can be attributed to the manual
manipulation of the proximal segment during surgery, and inferior displacement can be a
result of intra-articular edema immediately after surgery.

Since a superior movement would result in a decreased joint space, the vertical
61
translation measurement results for sample B are questionable. However, Will et al. in a
1984 study of 41 patients aged 11 to 47 years (mean, 25 years) did report a significant
superior movement, following surgery, as well as posterior movement of the left condyle.
However, cases in this study were treated with a period of maxillomandibular fixation
following surgery. The study describes that the condyles were moved into what was felt
by the surgeon to be the most posterior and superior positions in the glenoid fossa.
Intraosseous wires were placed on the superior border of the ramus, farther anteriorly and
inferiorly on the proximal fragment than the distal fragment, and tightened, ensuring the
condyle was fully seated in the glenoid fossa, which is likely to be the cause of the post
surgical superior condylar movement.

In contrast, Yeon-Joo Kim et al. found that condyles moved anteriorly during surgery,
which they also related to surgical edema or hemarthrosis. Their results coincide with
Kim YI et al. in 2010. Han et al (2016) found that in their sample of 50 patients linear
condylar displacement after orthognathic surgery occurred predominantly in the anterior,
medial, and inferior directions, with minimal changes (<1 mm) observed. Most angular
condylar changes were smaller than 4° and occurred in the inward direction in the axial
plane and the posterior direction in the sagittal plane.

Three-dimensional imaging allows for direct measurement of structures over time. As
technology continues to advance, more accurate and direct ways of generating
measurement data from medical imaging have been developed. Previously a widely used
method of measuring post-surgical condyle change on tomograms was one that Pullinger
62
and Hollender developed in 1986.

Will et al in 1984 studied 41 BSSO surgery patients. A radiological survey including a
submental vertex film, a lateral cephalogram, and right and left temporomandibular joint
tomograms was completed prior to surgery, 1-week, 6-weeks and 12-weeks post surgery.
They analyzed sub-mental films to determine the angle between the long axis of each
condyle and the midsagittal line. Tomograms were traced and superimposed to measure
superoinferior and anteroposterior movements of the condyle and inclination of the
condyle in a sagittal plane.

They found that the greatest mean net condylar movement in any direction was less than
1 mm, but noted that although the changes observed were small, the movements were
statistically significant. They found that during fixation, both condyles moved superiorly.
Posterior movement of the left condyle was significant during fixation and during the
entire observation period. The left condyle also showed significant net counterclockwise
inclination. They explained this result as a pattern of change that is consistent with what
might be expected from masticatory muscle pull in the immediate postoperative period
and during fixation.

They found that the anterior portion of the distal fragment relapsed posteriorly and
inferiorly, perhaps due to suprahyoid muscle forces, as the posterior portion is pulled
anteriorly and superiorly by the internal pterygoid muscle, resulting in clockwise rotation
of the distal fragment. As the portion of the distal fragment bearing the intraosseous wire
63
moves anterosuperiorly, it causes posterior movement and counterclockwise inclination
of the condyle.

Figure 24 - Directions of force exerted by mandibular
depressors and elevators and their influence on mandibular
proximal and distal fragments.

Will et al’s 1984 study also reported data for post-surgical lateral ceph changes. They
found significant (P < 0.001) increases in gonial angle and anterior facial height and
significant (P < 0.001) decreases in overjet and overbite, which they attribute to
clockwise direction rotation of the mandible as it was surgically advanced (x = 5.5 mm),
increasing the SNB and mandibular plane angles. This is quite different to our findings,
where all pre- to post-operative lateral ceph value changes were significant, except for
posterior face height. However, our study had a mix of class II and Class III patients who
all were treated with two jaw surgery, with Will’s study consisted of patients treated with
mandibular advancement surgery.

64

Figure 25 - Will et al. (1984) Results - Mean skeletal changes (mm)

Gender
Combined lateral ceph data for male and female patients showed no significant difference
(p=.05) in any variable for gender. Sample A patients (n=17) consisted of 10 females and
7 males, sample B patients (n=15) consisted of 9 females and 6 males. (Ratios of 1.43 to
1 and 1.5 to 1, respectively). Combined, all patients (n=32) totaled 19 females and 13
males, an overall ratio of 1.46 to 1.

65
This is in agreement with the findings of a large retrospective study by Chow et al (2007)
of 1,294 patients who underwent orthognathic surgery between January 1990 and
December 2004. Which found that the ratio between genders was 62% female and 38%
male (or 1.63:1) Another study by Parton et al. in 2011, reported that their study of
orthognathic surgery patients had a female preponderance and 1.6 to 1 female to male
ratio.

Age
Han et al (2016) reported a sample of 50 patients ranging in age at the time of
orthognathic surgery from 18-38 years (23+/- 4 yr). Chow et al also reported that the age
at time of surgery in their sample ranged from 16 to 54 years (mean, 24.1 years). Our
sample A patients (n=17) ranged in age from 20-53, sample B patients (n=15) ranged in
age from 17-36 years old at time of surgery. Combined, all patients (n=32) ranged in age
from 17-53 with a mean age of 26.28. Which is very similar to Chow et al’s study
sample, and the general demographics for all orthognathic surgery patients. No
significant difference was found between age at time of surgery and any of the lateral
ceph variables.

Limitations
Limitations of this study include small sample size, issues with reliability of condyle
translation data from second sample set (B) and limited midline ceph data points. ANS
was often clipped during surgery to allow for proper soft tissue draping, which eliminated
this as a landmark that could be measured on post surgical ceph and CBCT images.
66
Genioplatsy was completed on several patients in the sample. Bone graft material was
added, and/or bone segment positions were altered, changing the pognion, menton and
gnathion points in addition to the surgical change in mandible position. Pogonion was
still used for the lateral ceph to VSP data comparison, as the VSP did take into account
the planned surgical pogonion change.

Conclusion
For this study, 3D translation and rotation measurements pre- and post-surgery were
determined for 32 patients in two groups (sample A, n=17 and sample B, n=15). Lateral
cephs were generated from pre- and post-surgical CBCT images and traced using the
UNC cephalometric analysis (n=64 ceph images). The anterior-posterior change between
the pre- and post-surgical tracings was then calculated and analyzed for statistical
significance. VSP data for 31 of the 32 patients (one VSP report was not available) in the
sample were collected and evaluated. Pogonion values from the post surgical positional
change and pre-surgical VSP predicted movement were calculated and evaluated for
statistical significant correlation.

From this data, we found a strong correlation (correlation coefficient = 0.751) between
pre- and post-surgical lateral ceph pogonion movements and the virtual surgical planning
pogonion movement estimates. This is to be expected, as surgical movements are
completed as planned using pre-fabricated intraoral surgical splints to aid in obtaining
planned skeletal movements.

67
We saw an agreement between pre and post surgical changes for sample A and sample B
for all rotation and translation in the X direction, however, there was less agreement
between samples in translation for Y and Z directions.

No significant correlation was found between lateral ceph midline values SNA, SNB,
AFH, PFH, SN-GoGn, or Occl-GN with age of patient at time of surgery or gender of
patient. Analysis of this data showed no relationship between surgical movement and
condyle translation and no relationship between condylar rotation and surgical
movement.

68
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75
Appendix

Pre- to Post-Surgical Condylar Change Data (all patients)
Pt
Number
Condyle
Translation
(mm)
Rotation
(degrees)

X Y Z

X Y Z

1 R 0.206 -3.573 2.168

-2.220 1.290 5.030
L 2.812 -4.186 0.195

-0.022 1.023 -8.512

2 R -0.125 -1.951 2.379

-2.620 0.480 1.430
L 0.254 0.786 -0.606

-3.453 -0.382 -0.108

3 R 1.378 -2.383 3.926

-3.000 4.060 3.380
L 0.710 -2.035 0.348

-3.940 -2.680 -9.280

4 R 1.817 -3.295 3.363

2.722 2.550 2.029
L -3.505 2.493 1.847

-0.130 -5.130 4.750

5 R 0.369 -12.390 -2.028

2.919 -1.776 8.788
L 2.579 -2.024 0.442

1.950 2.800 -4.950

6 R 2.512 -9.086 -1.953

0.318 -1.636 8.708
L -1.348 -1.596 1.876

0.510 -2.380 -13.990

7 R 1.202 -7.298 0.900

-1.870 0.420 7.900
L 0.478 -0.431 -1.528

-0.755 5.307 -6.831

8 R -0.370 -8.876 -0.259

4.220 -0.650 7.680
L 2.128 -2.808 -1.285

-1.505 1.388 -8.630

9 R -1.296 -12.962 -7.896

2.653 -6.462 11.633
L 1.991 -1.961 -0.620

-0.980 -0.010 -7.310

10 R 0.559 -5.539 -0.345

-0.586 0.035 5.957
L 2.015 -7.819 -0.393

5.940 2.334 -13.172

11 R -0.129 -10.583 -3.975

0.950 -2.609 11.296
L -0.501 -2.033 -0.520

-4.157 -0.569 -8.228

12 R 1.661 -7.771 0.564

1.520 0.194 6.874
L -0.536 -2.028 2.094

2.263 -3.748 -3.687
76

13 R 0.375 -2.042 2.441

0.902 2.075 2.072
L 1.328 -0.759 -0.956

0.275 1.684 -3.074

14 R -2.602 -5.003 -3.413

0.754 -2.925 3.760
L 2.591 -1.142 -0.815

0.894 2.981 -2.339

15 R 1.096 -0.533 3.678

0.434 3.011 0.449
L 1.684 -0.896 -1.390

-1.563 2.362 -3.354

16 R 2.485 1.877 4.602

-1.650 4.056 -0.419
L 1.010 -1.762 0.196

0.887 -0.375 -4.082

17 R 0.424 -8.316 2.941

1.509 2.208 6.774
L 3.392 -1.396 -0.885

-1.024 1.512 -9.988

18 L 0.395 0.011 0.209

6.010 4.140 -9.150
R -0.038 0.149 0.326

0.650 3.040 4.370

19 L 0.164 -0.062 -0.183

-2.330 -5.920 -1.660
R -0.128 -0.066 0.229

-0.470 -0.980 1.850

20 L -0.101 0.007 -0.164

0.740 3.360 -6.830
R 0.064 0.046 -0.160

-4.040 2.820 0.840

21 L 0.033 0.047 0.088

-3.550 -0.660 -10.470
R -0.200 0.381 -0.162

-1.220 4.240 2.330

22 L 0.055 0.088 -0.105

-2.300 2.240 -2.820
R -0.032 -0.101 0.003

-0.570 4.940 -4.550

23 L 1.344 -0.129 0.045

-0.280 -3.140 -12.180
R 0.014 0.379 -0.488

-1.780 0.350 2.750

24 L 0.666 0.186 -0.138

-2.410 -0.530 -7.760
R -0.538 -0.081 0.008

0.310 -0.510 6.320

25 L -0.076 -0.701 -0.257

1.240 5.100 -12.180
R -0.267 0.510 -0.883

-2.990 4.490 -0.720

77
L -0.167 -0.128 -0.044

-4.07 4.51 -10.28
26 R -0.387 0.399 -0.127

-4.48 1.69 2.64

L -0.587 0.23 -0.308

2.01 5.87 -3.48
27 R -0.585 0.29 0.083

2.25 2.02 3.06

28 L -0.041 0.24 0.004

-0.38 0.75 -3.55
R -0.435 0.315 -0.046

0.52 2.69 2.09

29 L 0.17 -0.37 -0.36

-4.37 2.32 -10.53
R -0.283 0.0457 0.302

-3.63 5.34 7.22

30 L -0.056 0.108 -0.017

-0.910 1.690 -10.21
R -0.303 -0.062 -0.016

0.13 -2.26 8.35

31 L 0.003 -0.052 0.041

1.76 3.14 -6.35
R -0.04 -0.02 -0.073

3.98 -1.97 1.36

32 L -0.059 0.076 -0.01

-0.42 0.94 -3.06
R -0.131 0.172 -0.121

0.06 0.01 -0.16

Lateral Cephalometric Pre- to Post-Surgical Change Data (all patients)
Pt # SNA SNB
Total Anterior
Face Ht (N-Me)
(mm)
Posterior
Facial Ht
(Co-Gn)
(mm)
SN - GoGn
Occ Plane
to SN
1 3.3 7.8 -4 19.3 -23.3 -12.9
2 2.9 6.1 -6.6 13.4 -12.6 -3.4
3 1.3 9.2 -2.1 -0.9 -12.2 -10
4 2.6 1.2 -3.1 1.4 -8.3 -7.9
5 5.1 6 2.7 0.2 -0.3 -0.4
6 6.5 11.6 -10.6 13.5 -22.2 -16.7
7 1.2 8.4 -7.8 4.6 -15.5 -10.1
8 3 5.6 -3.5 0.5 -7.2 -3.7
9 4.7 8.1 -5.2 2.2 -12.6 -13.3
10 -0.9 7.2 -1.3 19.6 -14.7 -8
11 7.9 10.1 -4.7 2.4 -12 -9.8
12 4.2 6.7 -0.9 -0.1 -6 -3.6
13 4.9 2.3 -5.1 1.4 -5.3 -4.6
14 5.9 2.1 -2.2 0.2 -1.9 -0.1
78
15 2.3 5.2 -6.2 1.6 -7.4 -8.3
16 1.3 5.6 0.7 -2.4 -4.4 -8.5
17 1.6 8.7 -5.7 -2.4 -8.1 -8.4
18 1.5 3.1 -10.7 -12.3 4.4 3.3
19 6.7 8.1 -2.3 -1.3 -3.9 -3
20 4.4 5.4 -0.9 -1.4 -1.4 -2.2
21 1.6 7.7 -0.1 4.1 -8.1 -6.3
22 3 -1.8 -3.7 -4.3 0.4 2.3
23 -0.3 5.9 -6.5 -2.2 -10 -11.5
24 -2.1 3.5 -4.2 -6 -7.3 -8
25 1.6 4.5 -1.8 -0.4 -5.6 2.4
26 4.9 5.3 -1.8 0.6 -1.8 1.7
27 5.2 -2.7 -3.5 -1.1 -6.7 0.2
28 2.9 3 -0.4 4 -4.2 -0.1
29 3.1 7.4 2.6 4.4 -4.4 -7.4
30 3.6 8.4 -6 -2 -8.4 -1.2
31 4.1 0.5 -1.3 8.7 -1.8 2.5
32 3.2 2.8 0.9 0.3 -0.2 -0.1

Virtual Surgical Planning #'s

Pt # Pogonion
1 27.43
2 -0.14
3 24.6
4 5.21
5 8.75
6 24.76
7 21.75
8 14.85
9 17.23
10 11.73
11 16.19
12 15.12
13 9.04
14 N/A
15 11.46
16 13.54
17 18.41

79
18 5.11
19 14.14
20 10.35
21 20.44
22 1.92
23 21.17
24 18.54
25 11.03
26 8.51
27 4.57
28 4.08
29 15.58
30 14.96
31 0.3
32 7.01

80

Lateral Cephalometric Tracing Images Pre- and Post-Orthognathic Surgery

Pt #1

Pt #2

81

Pt #3

PT #4

82
Pt #5

Pt#6

83
Pt #7

Pt #8

84
Pt #9

Pt #10

85
Pt #11

Pt #12

86
Pt #13

Pt #14

87
Pt #15

Pt #16

88
Pt #17

Pt #18

89
Pt #19

Pt #20

90
Pt # 21

Pt#22

91
Pt # 23

Pt #24

92
Pt # 25

Pt # 26

93
Pt # 27

Pt #28

94
Pt #29

Pt #30

95
Pt #31

Pt # 32

96

Abstract (if available)

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Asset Metadata

Creator Stephens, Heather (author)

Core Title Comparison of facial midline landmark and condylar position changes following orthognathic surgery

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 05/03/2017

Defense Date 03/03/2017

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

Tag cbct,condyle rotation,condyle translation,lateral cephalometric landmarks,natural head position,OAI-PMH Harvest,orthognathic surgery

Language English

Contributor Electronically uploaded by the author (provenance)

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

Creator Email hstephe@usc.edu,hstephens475@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c40-370491

Unique identifier UC11258207

Identifier etd-StephensHe-5311.pdf (filename),usctheses-c40-370491 (legacy record id)

Legacy Identifier etd-StephensHe-5311.pdf

Dmrecord 370491

Document Type Thesis

Rights Stephens, Heather

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA