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Three-dimensional immediate post-surgery condylar displacement

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Three-dimensional immediate post-surgery condylar displacement

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Content 1

Three-Dimensional Immediate Post-surgery
Condylar Displacement
by
Esther Moon

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

MAY 2014
Esther Moon
2

Table of Contents

I. Abstract 3
II. Introduction 4
III. Literature Review
a. 3-Dimensional Imaging 5
b. Registration & Superimpositions of 3-Dimensional Models 7
c. 3-Dimensional Imaging in Orthognathic Surgery 9
d. Condylar Positional Change After Surgery 10
e. Resorption and Stability 14
IV. Materials and Methods
a. Sample 20
b. Method 20
c. Validation 23
V. Results 30
VI. Discussion
a. Condylar displacement 34
b. Limitations 37
VII. Conclusion 39
VIII. References 40
IX. Appendix 46

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I. Abstract
Background: Two dimensional studies have shown displacement of the condyles immediately
after orthognathic surgery. Some condylar displacement that occurs with orthognathic surgery is
related with greater relapse tendencies. With the development of cone beam CT (CBCT) scans,
3-dimensional images can show a more accurate direction of condyle displacement. Objectives:
1) To establish a method to assess condylar changes in position after orthognathic surgery
relative to the position of the glenoid fossa and temporal bone. 2) To evaluate the 3-dimensional
change in position of the condyle within 2-weeks of orthognathic surgery.
Materials and Methods: Sample consisted of pre- and 2-week-post-surgical CBCT scans for 17
orthognathic surgical patients whose surgery was completed by one surgeon with a consistent
protocol. The glenoid fossa and temporal bone were registered to assess the 3-dimensional
displacement of the condyle as a result of orthognathic surgery.
Results: Semitransparencies and color maps depicting condylar displacements are shown and
direction of condylar movement is described.
Conclusion: It is possible to assess condylar movement due to orthognathic surgery in 3-
dimensions. The most frequent condyle displacement was a backwards rotation of the lateral pole
around the long axis of the condyle.

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II. Introduction
Relapse after orthognathic treatment has been related to condylar resorption and condylar
displacement during surgery. Condylar displacement appears to be related to condylar resorption,
which could lead to sagittal relapse and anterior bite opening. Because orthognathic surgery can
potentially cause displacement, it is important to observe the degree and direction of
displacement post-surgically. Many studies have used 2-dimensional radiographs to measure the
displacement of condyles. However, these images do not capture the transverse movements due
to the nature of 2-dimensional radiographs. More recently, with the introduction of cone beam
computed tomography, studies have measured the 3-dimensional displacement of the condyles
because orthognathic osteotomies can cause rotational, transverse, and anterior-posterior
displacement of the condyles. However, many of these studies observed the condyles at the 3
months, 6 months, and 1 year post-operative time points.
The purpose of this study is (1) to establish a method to assess condylar change in
position after orthognathic surgery relative to the position of the glenoid fossa and temporal
bone, and (2) to assess the condylar displacement after bi-maxillary surgery relative to the
glenoid fossa at 2-weeks, prior to remodeling of the temporomandibular complex.

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III. Literature Review
a. 3-Dimensional Imaging
With the introduction of the first practical medical computed tomography (CT) in 1971
by Dr. Hounsfield in England, CT’s have become one of the most important diagnostic tools in
radiologic examinations. Although the medical CT had great use for clinical applications in
medicine, the high radiation and cost did not justify the regular use in dentistry. However, with
the introduction of the cone beam computed tomography (CBCT) in the United States in 2000 at
Loma Linda University, its use in dentistry has become more possible (Mah et al. 2004).
As CBCT became a more prevalent tool in the realm of orthodontics, many studies have
been completed to determine the reliability of CBCT images. To determine the reliability of
CBCT images, it is important to understand the difference between medical CT and CBCT.
Medical CT has a high output rotating anode generator as opposed to the CBCT, which can have
a low energy fixed anode tube like a panoramic machine. Furthermore, unlike that of a CBCT,
the x-ray source of a medical CT radiates a fan-shaped x-ray beam and records the data on a
solid-state image detector arranged in a 360° array around the patient. For a CBCT, the x-ray
source radiates a cone-shaped x-ray beam with a special image intensifier and a solid state sensor
or an amorphous silicon plate for capturing the image. Thirdly, the medical CT captures images
slice by slice, whereas the CBCT captures images in 1 rotation sweep (Mah et al.
2004)(Halazonetis et al. 2004).
Currently in the field of orthodontics, CBCT has not been linked to a clear diagnosis
classification (Grauer et al. 2009). Because of the high radiation dosage, CBCT, especially the
large field view, is not recommended for routine orthodontic radiography, since the radiation
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dosage of a CBCT is double that of a panoramic and cephalogram. CBCT has been found to be
more accurate to the real size object unlike that of conventional radiographs such as a panoramic
radiograph. Furthermore, although the incidental findings in CBCT scans taken for various
dental and orthodontic needs is approximately 25%, some question that this percentage is not
enough to implement CBCT as a routine diagnostic tool. CBCT is still recommended for select
cases (Halazonetis et al. 2012) (HuJoel et al. 2008) (Ahmed et al. 2012). With asymmetry and
congenital malformations, measurements using conventional cephalometric radiographs are
difficult. Follow-up 2-dimensional (2D) cephalometric examination for asymmetric orthognathic
cases is not an accurate tool to measure change due to the limitation of seeing a rotational 3-
dimensional (3D) movement on a 2D radiograph. In congenital malformations, even finding a
reference point is difficult. Therefore, in the cases of asymmetry and congenital malformations,
CBCT is a recommended diagnostic tool that may change diagnosis and treatment plans for these
cases (Tarajima et al. 2009) (Haney et al. 2007) (Cevidanes et al. 2006).
CBCT imaging is also recommended for impacted teeth. The use of 2D and 3D images of
impacted maxillary canines can produce different diagnoses and treatment plans for the same
patients. (Haney 2010) In 2D radiographs, images can be enlarged, distorted, or overlapped
reducing the image quality and diagnostic accuracy. But now, these limitations can be
minimized. More specifically, one 3D image as opposed to multiple 2D radiographs is sufficient
for detailed characterization of canine impaction and systematic analysis of potential etiologic
factors from local teeth and bones (Yan et al. 2013).
Currently, CBCT is used in surgical planning for orthognathic cases. Virtual surgical
simulations can be used for surgical planning, simulations, and operation training because the
computerized plan can be transferred accurately and consistently to the patient at the time of
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surgery (Hsu et al. 2013). It is a more cost effective and efficient alternative to the traditional
training and surgical planning. Therefore, CBCT is currently an ideal option for surgical
planning.
b. Registration & Superimposition of 3-Dimensional Models
Today, longitudinal assessment of growth and treatment effects is performed with 2D
radiographs. However, 2D radiographs are limited because images can be enlarged, distorted, or
overlapped reducing the image quality and diagnostic accuracy (Yan et al. 2013). In
orthodontics, 2D cephalometric radiographs have been used to superimpose landmarks and
assess changes. However, the overlapping of multiple structures sometimes makes certain
landmarks difficult to identify.
With the introduction of CBCT in orthodontics, the overlapping of structures seen in 2D
radiographs are no longer a problem, allowing clear visualization of all structures. However,
locating landmarks in 3D models on complex curving structures is significantly more difficult.
Nonetheless, CBCT images were reported to be reliable in measurements and landmark
identification (Grauer et al. 2009).
To analyze the change of the structures of interest at different time points, a stable
reference structure needed to be identified. Cevidanes et al. found that the structures along the
cranial base for adults and the anterior cranial fossa for growing children were stable and reliable
to use as reference structures (Cevidanes et al. 2006) (Cevidanes et al. 2009) (Motta et al. 2010).
Currently, it is possible to analyze changes due to treatment, growth, aging, and relapse
by registering CBCT records from different time point with the help of verified and accurate 3-D
analysis software (Motta et al. 2010). Because the cranial base surface is a stable reference
8

within the same patient, 3-dimentional (3D) segmentations of anatomic structures, such as the
airway, have been used to compare the orientation of structures relative to this reference
structure (Grauer et al. Dec 2009).
Commercial packages are available for registration and superimpositions such as Dolphin
Imaging, InVivoDental, and 3dMDvultus (Grauer et al. 2009). Semi-automatic segmentation
with interactive and fixed threshold protocols of ITK-Snap was tested against other volume
segmentation imaging software programs and concluded that they were more accurate than that
of InVivo Dental and Ondemand3D for upper airway assessment (Weissheimer et al. 2012).
Furthermore, the fully automated voxel-wise registration helps in avoiding observer-dependent
location of points identified from the overlapping of anatomic landmarks (Motta et al. 2010).
However, because the gray level between imaging machines may have some
discrepancies although very similar, the CBCT images should be used with caution for the
evaluation and interpretation of density values (Azeredo et al. 2013). Because the visual
perception of the operator defines the rendered image of bone and soft tissue by the threshold
value set by the operator, quantitative assessment may present to be challenging (Macchi et al.
2006) (Grauer et al. 2009); CBCT image use for qualitative assessments are appropriate as it
does not rely on the operator (Grauer et al. 2009). Therefore, it may be necessary to validate the
intra- and inter-observer error with quantitative assessment.
Nonetheless, when compared to “medical” tomography, CBCT has been considered the
method of choice for maxillofacial imaging because the machine and scans cost less, CBCT has
lower radiation dose and faster acquisition time, there is good contrast for facial bones and teeth,
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and one exam can capture all of the conventional orthodontic images such as panoramic
radiographs and conventional cephalograms (Motta et al. 2010).
c. 3-Dimensional Imaging in Orthognathic Surgery
CBCT scans and superimpositions have been used to analyze numerous structures
ranging from occlusion (Macchi et al. 2006) to craniofacial deformities (Tarajima et al.
2009)(Haney et al. 2007) (Cevidanes et al. 2006) and palatal expansion (Hino et al. 2014).
Furthermore, for orthognathic surgery, condyle position before and after surgery has been
studied for years with both 2D radiographs and with 3D CBCT scans.
For orthognathic surgical cases, long-term follow-up has relied on serial 2D
cephalometric radiographic superimpositions. However, this 2D view is a less accurate method
of superimposition because it is a representation of a 3D structure. Projections of anatomical
structures are overlapped, are magnified, and cause loss of information such as transverse
deviations, which can lead to errors in analysis. Chen et al concluded that CBCT provides an
accurate 3D image of the TMJ complex and is possibly the best choice for evaluating condylar
displacement after orthognathic surgery (Chen et al. 2013) and a more accurate and useful tool
for the estimation of condylar resorption (Kobayashi et al. 2012).
Instead of trying to examine projected superimposed structures on a 2D image such as a
cephalogram, a 3D image of anatomic structures with real size and form allows for a more
realistic examination of bilateral structures (Motta et al. 2010). Furthermore, 3D CBCT images
have very minimal projection errors due to the way the x-ray beams are projected unlike that of
traditional dental imaging used in orthodontics, such as a cephalogram and a panoramic
radiograph (Mah et al. 2004).
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The registration process and semitransparent superimpositions of 3D images have played
a great role in the analysis of short-term and long-term orthognathic surgical stability, and have
been a great instrument for clinical, scientific, and educational orthodontics and surgical
application (Motta et al. 2010).
With the introduction of 3D registration, superimpositions of models and calculated
surface distances clearly exhibit the localization, magnitude and direction of the mandibular
rotations, allowing for the quantification of anteroposterior, transverse, and vertical movements
of craniofacial structures involved in orthognathic surgery (Motta et al. 2010).
CBCT has become a great tool in studying the position, movement, stability, and
remodeling of the condyles before and after orthognathic surgery. Volumetric studies have been
completed to analyze the potential change in condyles after orthognathic surgery (Maal et al.
2012). Because change in structures can be induced, it is important to study the
temporomandibular complex and its response to change.
d. Condylar Positional Change after Surgery
Condylar position has been assessed in order to determine the optimal
temporomandibular joint position (TMJ) for the minimizing of temporomandibular disorders
(Corday et al. 2006). The study of condylar position is important in orthodontic treatment
because the neuromusculature positions the mandible to its maximum intercuspation regardless
of the position of the condyle (Corday et al. 2006). Furthermore, bite forces change due to the
static and dynamic loading of mandibular condyle changes after surgery (Dicker et al 2012).
Therefore, clinicians may mistake this mandible position to be the seated condylar position.
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Many studies have been conducted to examine the changes of the structures before and
after orthognathic surgery in mandibular-only surgery, bi-maxillary surgery, and unilateral
osteotomies. Recent 3-D analysis of the distal segments of the mandible after orthognathic
surgery has greatly contributed to the understanding of the anterior, posterior, medial, and lateral
movements of the condyle within the TMJ (Cevidanes et al 2005). The location, magnitude, and
direction of mandibular rotations during surgery can be clearly visualized by 3-D model
superimpositions and surface distance calculations. Furthermore, 3-D imaging has allowed for
the quantification of vertical transverse and anteroposterior ramus rotation for mandibular
surgery (Cevidanes et al. 2005).
Condylar position is known to be affected postoperatively by factors such as the
rotational movement of the distal segment, muscle equilibrium, fixation method, and surgeon’s
experience. Because sagittal split ramus osteotomy of the mandible is known to affect the
condylar positioning postoperatively, it is important to accurately assess the position of the
condyles to maximize the stability of the surgery and predict treatment (Kim et al. 2012).
The small changes in the condylar position can be accommodated by the physiologic
adaptation leading to later skeletal relapse or condylar remodeling (Kim et al. 2011). To increase
skeletal stability and prevent relapse, the control of the proximal segment is always important.
Some of the surgical risk factors for postoperative condylar resorption is the
counterclockwise rotation of the distal and proximal mandibular segments as well as surgically
induced posterior condylar displacement (Chen et al. 2013). Ultimately, improper condylar
position and condylar axial changes can lead to TMJ disorders (Kim et al. 2011).
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Condylar displacement was frequently found with sagittal splitting procedures.
Displacement accompanied with rotation or tilting of the condylar long axis predominated.
Furthermore, the direction and amount of condylar displacement was influenced by the type of
osteosynthesis and direction of the fragments bearing teeth (Kundert et al. 1980).
Compared to patients who underwent split sagittal ramus osteotomy (SSRO), those that
received intraoral vertical ramus osteotomy (IVRO) showed a significantly higher incidence of
condylar remodeling. When looking at the positional change in the condyle, those of the IVRO
group had a specifically altered long axis postoperatively as well as an outward rotation of the
condylar long axis. Furthermore, the degree of rotation in the condyles that remodeled was
significantly larger on average than those without bone formation (Katsumata et al. 2006).
Nonetheless, condylar displacement and the condylotomy effect was minimized with the
intraoral vertico-sagittal ramus osteotomy (IVSRO) surgical technique therefore decreasing the
symptoms of postoperative laterogenic temporomandibular joint disorder (Kim et al 2013).
Multiple studies were conducted to track the post-operative movement of the condyles
after certain periods of time. 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. There was evident rotation of the condyle 3-6 months
later, and condylar stability 6 months later (Kim et al. 2014).
Other studies found different condylar movements. Immediately after surgery, the
condyles had moved posterior-inferiorly (Chen et al. 2013) (Rotskoff et al. 1991) followed by an
anterior-superior movement 3 months after surgery. However, ultimately, there was a net
posterior-superior movement when comparing the condyle position pre-surgery and 3 months
13

post-surgery (Chen et al. 2013) (Schendel et al. 1980) (Sickels et al. 1999) (Motta et al. 2011).
More specifically, Chen et al. stated that the condyles moved posterior-inferiorly after surgery,
anterior-superiorly at 3 months, and remains stable during the 1-year follow-up. For class I cases,
the condyles were located in the center of the fossa, whereas the condyles for class II, Division 1
cases were positioned more anteriorly than those in class I or III (Chen et al. 2013).
Chen et al concluded that the posterior displacement may be caused by the manual
manipulation of the proximal segment during surgery. During the early postoperative period in
patients treated by mandibular subcondylar osteotomy, magnetic resonance imaging verified the
presence of intra-articular edema. Also, condyles tended to move back anterior-superiorly after
splint removal during the 3-months post-surgical period (Chen et al. 2013).
In class III malocclusion surgical patients, Kim YJ et al also stated that the condyles
moved anteriorly during the surgery and posteriorly after the surgery. They also stated that the
initial anterior displacement of the condyles could be related to the surgical edema or
hemarthrosis. When examined more carefully, they found that, up until 3 months after surgery,
the condyle moved more distally, and the mesio-lateral distance decreased causing the narrowing
of the intercondylar distance. After 3 months for asymmetric cases, the undeviated side moved
towards the midline whereas the deviated side moved pack to its presurgical position. Also, the
tendency of the proximal segment to autorotate may cause the mandibular condyle or ramus after
surgery to autorotate anteriorly. This may be related to the direction of surgical relapse.
However, after 6 months, the condylar positions were relatively stable (Kim et al. 2013).
Not only was there movement on the sagittal plane but there was inward rotation along
the coronal condylar axis after surgery (Kim et al. 2011). Carvalho found torqueing of the ramus
14

with mandibular advancement (Carvalho et al. 2011). On the contrary, Kim et al found that
condylar angulations in all dimensions did not change after single-jaw surgery unlike that of
those that received double-jaw surgery, who showed a forward and medial rotation in the sagittal
and axial planes respectively (Kim et al. 2012). Cevidanes concluded that condylar displacement
associated with 2-jaw surgery was not significant when compared to maxillary only surgery
(Cevidanes et al. 2005)
Condyle positional changes after orthognathic surgery is difficult to predict. Condylar
displacement is difficult to differentiate from errors in conventional 2D radiography because the
condyles may have been displaced in more than one plane during surgery in both position and
inclination (Cevidanes et al. 2005). After studying the condyles with 2D radiography, Motta et al
ultimately concluded that there is still not enough evidence to ascertain if condylar remodeling
due to the transverse displacement post mandibular surgical advancement would interfere with
post-treatment stability although studies have revealed an associated (Motta et al. 2010).
e. Resorption and Stability
In the eighties, it was first reported that condylar resorption led to relapse. According to
Park et al, condylar resorption is the physiologic process which structurally alters the
temporomandibular complex and that it is based on the interaction between the mechanical
forces sustained by the TMJ and the adaptive capacities of the condyle (Park et al. 2012).
However, the definition of resorption itself was being questioned.
Many researchers have defined condylar resorption differently. Cutbirth et al. defined
progressive condylar resorption to be a change in shape of the condyle with loss of condylar
height (Cutbirth et al. 1998). Similarly, Hoppenreijs et al described progressive condylar
15

resorption as an extreme structural change of the condyle which leads to the decrease in ramus
height and therefore decrease in posterior facial height (Hoppenreijs et al. 1999). Kobayashi et al
not only described condylar resorption to be of an obvious reduction in the height of the ramus,
but also a posterior rotation of the proximal segment or both in the cephalometric radiograph.
Furthermore, Kobayashi et al stated that progressive condylar resorption as an appreciable
condylar resorption on the CT of patients who have occlusal change postoperatively consisting
of either an increase in overjet or a decrease in overbite, or both (Kobayashi et al. 2012).
However, Moore et al. claims that the term condylar resorption should be defined as total
condylar resorption in the presence of systematic disease (Moore et al. 1991).
Not only is the definition of condylar resorption a topic of debate, the cause of the
condylar resorption is still under study. Researchers have tried to connect condylar resorption
with different factors. Certain condyle shapes and deformities were found to be more susceptible
to condylar resorption (Bouwman et al. 1994) (O’Ryan et al. 1984).
The etiology of progressive condylar resorption is still unclear (Kobayashi et al. 2012)
(Park et al. 2012). It can be caused by patient factors such as systemic diseases and disorders,
anatomy-dependent factors, and also surgical factors (Hoppenreijs et al. 1998). Furthermore,
remodeling of the condyles has been associated with prosthodontic rehabilitation, orthodontic
treatment, condylar fractures, and osteotomies of the mandibular ramus (Lambert et al. 1986)
(Hoppenreijs et al. 1998).
In orthognathic surgeries, there are multiple theories of what causes condylar resorption.
Kobayashi et al concluded that condylar resorption may occur when mechanical loading exceeds
the adaptive capacity of the condyle when the surrounding soft tissue components are stretched,
16

which this tension will ultimately cause a retrusive force into the fossa (Kobayashi et al. 2012).
Hoppenreijs et al claimed that many predisposing and contributory factors can result in
progressive condylar resorption. One important factor in the etiology of condylar resorption is
the mechanical loading during or after bilateral sagittal split osteotomy (BSSO) and impediment
of blood flow in the condyle and the capsule of the TMJ. Furthermore, the interdigitation of an
unstable occlusion can produce loading of the condyles. Therefore, the stabilization of the
occlusion will allow for the TMJ to be restored to a functional equilibrium (Hoppenreijs et al.
1999) (Chen et al. 2013). Although Park et al believed that pre-existing unrecognized and
untreated TMJ pathologic features or orthognathic surgery-incurred TMJ conditions such as joint
damage may lead to postoperative instabilities, they believed that morphologic changes and
dysfunction of the TMJ will not occur as long as the condylar displacement is within the
physiologic capability of the adaptive mechanics (Park et al. 2012).
Apart from morphologic changes of the condyle due to the change in position and forces
of the hard and soft tissue, other factors were found to make certain groups more prone to
condylar resorption. Posteriorly inclined condylar necks were considered a nonsurgical risk
factor for resorption (Chen et al. 2013). Furthermore, resorption was found to be more prevalent
in women, especially those with high mandibular plane angles, preoperative temporomandibular
dysfunction, a large mandibular advancement, and a distal segment counterclockwise rotation
(Cutbirth et al. 1998). Hoppenreijs et al also reported progressive condylar resorption to be more
prevalent in females with preexisting TMJ dysfunction, within the age range from 20-30, and
those that have undergone large advancements of the mandible (Hoppenreijs et al. 1999).
Additionally, hormonal changes may also be a prominent factor in condylar resorption
(Kobayashi et al. 2012). Even the predisposed occlusal relationship can cause certain patients to
17

be prone to resorption. Isolated resorption of the superior part of the condyles was a tendency in
patients with a deep bite (Hoppenreijs et al. 1999). However, even with all the association with
progressive condylar resorption, the etiology is still unclear (Kobayashi et al. 2012) (Park et al.
2012).
Relapse can occur for many reasons. Worms et al expressed that condylar resorption
contributes to relapse (Worms et al. 1980) (Hoppenreijs et al. 1999). Kim et al concluded that
condylar positional changes and soft-tissue tension are frequent findings in early post-surgery
instability. However, even if the condylar position is controlled, the increase in muscle and soft
tissue tension may cause future relapse (Kim et al. 2011). Epker agreed that skeletal relapse may
occur even though skeletal stabilization is employed and the proximal segment is controlled. The
two reasons were one of dental nature and the other of skeletal growth. Dental compensations
before surgery may relapse after surgery therefore compounding the situation which is inherently
a post-surgical problem. Furthermore, delayed skeletal relapse may also cause relapse due to
growth of the mandible or maxilla or condylar degeneration (Epker et al. 1982).
The importance of determining the change in position of the condyle has been a topic of
interest because of the possibility of condylar resorption and surgical relapse. Kim et al believed
that postoperative occlusion and positional change of the condyle are major factors related to
surgical relapse (Kim et al. 2012). Peterson and Wilmar-Hogeman found that the degree of post-
operative condylar displacement and the incidence of resorption had a positive correlation
(Peterson et al. 1989), which Park et al later confirmed that condylar positional change can
induce postoperative early or later skeletal relapse as well as TMJ symptoms (Park et al. 2012).
18

The changes in force and anatomy after surgery combined with the joint anatomy
variations in different dentofacial anatomy have an effect on condyles (Cutbirth et al. 1998).
Some studies revealed remodeling and resorption of the anterior-superior area of the condylar
head after orthognathic surgery using lateral cephalometric analysis (Park et al. 2012). Other
studies found remodeling activity in the posterior part of the condylar head if it was accompanied
by a postoperative anterior-inferior displacement of the condylar head (Katsumata et al. 2006).
Nevertheless, the movement of certain anatomical structures caused patients to have resorption at
specific regions of the condyle.
The movement of the maxilla, mandible, or both can highly influence the incidence of
condylar resorption. With bimaxillary orthognathic surgery, there was a decrease in the condylar
heights and condylar head remodeling (Park et al. 2012). However, long-term stability studies
revealed that maxillary advancement surgery was more stable than bi-maxillary orthognathic
surgery (Cevidanes et al. 2005). Nonetheless, Kim et al. stated that the extent of maxillary
movement may highly influence the vertical relapse rate (Kim et al. 2011).
With mandibular advancement, the incident of progressive condylar resorption can be up
to 31% depending on the population studied (Bouwman et al. 1994) (Kobayashi et al. 2012). The
immediate relapse subsequent to a mandibular advancement surgery with rigid fixation has been
well documented (Cutbirth et al. 1998). Hoppenreijs et al found that progressive condylar
resorption occurs after sagittal split advancement osteotomies regardless of whether it is
accompanied by maxillary surgery or not (Hoppenreijs et al. 1999).
Post-surgical relapse has been a major concern in orthognathic surgical corrections. With
the introduction of rigid internal fixation, some of the problems have been resolved (Strauss et al.
19

1993). Furthermore, the incidence of condylar resorption after bimaxillary osteotomies was
reduced after intermaxillary fixation was avoided (Bouwman et al. 1994). Hoppenreijs confirmed
that progressive condylar resorption did not exclusively occur in patients treated with rigid
fixation (Hoppenreijs et al. 1999).
Skeletal relapse due to resorption is apparent at specific time points post-surgery.
Condylar resorption can be first seen radiographically starting at 6 months after surgery (Cutbirth
et al. 1998) (Hoppenreijs et al. 1998) (Katsumata et al. 2006). Therefore, with the presence of
resorption, open bites can be seen within the first 6 months postoperatively (Hoppenreijs et al.
1998). Not only is skeletal relapse a change that can be seen after 6 months but also occlusal
changes can be seen (Kobayashi et al. 2012). Franco et al observed that small condylar changes
continue beyond one year post-surgery with variation in the direction of change. However, over a
3-year period, mandibular advancement surgery was stable (Franco et al. 2013).
The change in position of the condyle can cause certain areas of the condylar head to remodel
or resorb and ultimately cause relapse post-surgery. In 1992, Arnett et al suggested that condylar
resorption and late relapse may occur if rigid fixation results in mediolateral torqueing or
posterior positioning (Arnett et al. 1992). Because inappropriate condylar positioning can lead to
postoperative complications such as idiopathic condylar resorption, functional disorder, and post-
operative relapse, it is important to study the condylar positional change after surgery (Kim et al.
2013) (Chen et al. 2013)

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IV. Materials and Methods
a. Sample
The sample consisted of 21 consecutive patients treated by only one surgeon. The surgeon used
Medical Modeling (VSP Orthognathics; Golden, Colorado) to virtually treatment plan the
surgeries. There were 16 skeletal class II patients and 5 skeletal class III patients. The patients
received pre-surgical orthodontic treatment and underwent bi-maxillary surgery. For each
patient, the pre-surgical and 2-week post-surgical cone-beam computed tomography (CBCT)
DICOM files were collected, anonymized, and stored in a directory by a code. The age and sex
of the patients were the only information collected. Other personal information was not recorded.
Of the 21 CBCT scans collected, 4 patients (2 class II, 2 class III) were excluded because the
CBCT scans did not fully capture both condyles pre-surgery and post-surgery. Of the 17 patients,
2 patients (class II) were analyzed differently due to improper seating of the condyles upon pre-
surgical CBCT record.
b. Method
Each pre-surgical and 2-week post-surgical DICOM file was uploaded into ITK-Snap (version
1.8.0; www.itksnap.org). The image summary on the wizard for loading a grayscale image had
dimensions set at 400, 400, 547 slices, spacing set at 0.40mm, 0.40mm, 0.40mm, and the
orientation was set at RAJ. The crosshairs 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
curve control point was set at 1 point. Prior to initiating segmentation, the label color was set.
21

The active drawing label color was set to draw over a clear label to allow the condyle to be
drawn in red and the glenoid fossa in green.
The semi-automatic segmentation mode was then used per temporomandibular joint complex to
isolate the region of interest. This area isolated was defined as follows:
 the posterior margin of the region of interest was set to include the most inferior border
of the mastoid process seen on the sagittal slice
 the anterior margin was set to include the frontal bone of the cranial base from the
sagittal slice
 the medial margin was set to include the apex of the petrous temporal bone seen on the
frontal slice,
 the lateral margin was set to include the outermost layer of the skin
 the superior margin included the frontal bone of the cranial base
 the inferior margin was set to include the body of the ramus just above the lingual.
Once the selection box exhibited the structures of interest, the segmentation process was
initiated. For step 1, pre-processing, the intensity regions were adjusted. With the selection of the
combined display, the hard tissue can be seen more clearly. 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. For step 2, geodesic snake initialization, the
initialization centers were placed evenly spaced throughout the structure of interest. The radii of
the spheres were adjusted to stay within the structure of interest. Then step 3, segmentation, was
initiated until the spheres grew to coalesce with one another and fill the structure of interest, and
ultimately finalized when the structure of interest was identified.
22

The mesh was then edited using the scalpel to cut the gross structures segmented due to the
leakage of the nucleoids. Starting with the axial view and using the coronal and sagittal view as
verification, the polygon option was then used to refine the segmentation. The labels were
adjusted to either draw in the un-segmented object of interest with the appropriate label color
over a clear label, or it was used to erase an unwanted area by drawing over the label color with a
clear label. Once the object of interest was segmented and refined, the segmentation was saved in
a “.gipl” and “.stl" format, the condyles separate from the glenoid fossa.
Geomagic Studio Software (Version 10; Geomagic U.S., Research Triangle Park, NC) was used
to superimpose and analyze the movement of the condyles using the glenoid fossa as the
reference structure. Because the CBCT was taken at different orientations relative to the CBCT
machine as it is nearly impossible to take radiographs in exactly the same position at different
time points, the glenoid fossa needed to be registered as a reference. This in turn brought the
condyles with the glenoid fossa revealing the true movement of the condyles without the effect
of head positioning.
For each patient, the “.stl” format of the segmented pre-surgical and post-surgical condyles and
glenoid fossa were imported into the Geomagic Studio Software (Version 10; Geomagic U.S.,
Research Triangle Park, NC). The glenoid fossa was hidden until the registration of the
structures.
The right and left condyles were registered separately to prevent one condyle from affecting the
registration of the other condyle. With only the pre-surgical (PreC) and post-surgical condyles
(2wkPostC) of one side visible, a copy (2wkPostC
copy
) was made of 2wkPost. PreC and
2wkPostC were pinned to prevent any movement of these two objects. 2wkPostC
copy
was then
23

globally registered to the pinned PreC and then cropped at the same level to allow for very
similar volumes. If necessary, to get the condyles in close proximity for the program to
automatically register the condyles, the condyles were manually registered using 3 landmarks
visible on both condyles. These points were selected upon the visual judgment of the evaluator.
2wkPostC
copy
was then globally registered to the pinned 2wkPostC to move the cropped object to
its original position.
The pre-surgical glenoid fossa (PreGF) was “pinned,” a software program option preventing any
movement of the object. The post-surgical glenoid fossa (2wkPostGF) was then globally
registered to PreGF. The transformation matrix describing the movement of 2wkPost GF was
then saved and loaded to 2wkPost C
copy
to move 2wkPost C
copy
the same distance and direction
as its corresponding 2wkPostGF. Therefore, the displacement of the condyles pre-surgery and
post-surgery compared to the glenoid fossa was revealed.
c. Validation
Five cases were randomly selected and their DICOM images were imported into ITK-Snap
(version 1.8.0; www.itksnap.org). The pre-surgical and post-surgical condyles were segmented
twice by the primary evaluator and once by a secondary evaluator. These segmented images in
the “.stl” format were imported into Geomagic Studio Software (Version 10; Geomagic U.S.,
Research Triangle Park, NC), globally registered, and cropped to the same level. A 3-
dimentional analysis tool in Geomagic Studio Software (Version 10; Geomagic U.S., Research
Triangle Park, NC) was then run.
For intra-evaluator validation, the second set of segmentations of the condyle by the primary
evaluator was tested against the first set of segmentations by the primary evaluator, the reference
24

segmentations. The maximum distance (positive and negative), the average distance (positive
and negative) and the standard deviation of change were recorded. A color map was obtained
using 15 color segments with a maximum and minimum critical difference of ±1.0mm and
maximum and minimum nominal of ±0.05mm.
For inter-evaluator validation, the set of segmentations of the condyle by the secondary evaluator
was tested against the first set of segmentations by the primary evaluator, the reference
segmentations. The maximum distance (positive and negative), the average distance (positive
and negative) and the standard deviation of change were recorded. A color map was obtained
using 15 color segments with a maximum and minimum critical difference of ±1.0mm and
maximum and minimum nominal of ±0.05mm.

Copy of the post-surgery condyle
Pre-surgery condyle position
25

Copy of the post-surgery condyle
registered to pre-surgery condyle position
Both pre- and post- surgery condyles
cropped at same level
Copy of the post-surgery condyle
Post-surgery condyle position
26

Copy of the post-surgery condyle
registered to original post-surgery
condyle position
Copy of the post-surgery condyle
position (cropped)
Pre-surgery condyle position (cropped)
27

Movement (transformation) of the post-surgery glenoid fossa to the position of the pre-surgery
glenoid fossa saved.

Post-surgery
Glenoid Fossa

Pre-surgery
Glenoid Fossa

Registration of post-
surgery Glenoid Fossa to
pre-surgery Glenoid Fossa
28

Post-surgery condyle position
before transformation of glenoid
fossa applied
Pre-surgery condyle position
Post-surgery condyle
position after
transformation of
glenoid fossa applied
29

Post-surgery condyle position
Pre- and post- surgery
condyle position after
registration with glenoid
fossa as reference
30

V. Results
Seventeen consecutive patients (5 male, 12 female; mean age, 28.5; range 18-51 yr) were
included in this retrospective study. Twelve of the patients were skeletal class II, 6 of whom had
a high mandibular plane angle. Three of the patients were skeletal class III.

Condylar Movement on the Coronal Plane
When comparing the pre- and post- surgical condylar movements from the coronal view,
the most common movement seen was the outward rotation of the lateral pole. For the right
condyle, all 15 condyles indicated an outward rotation of the lateral pole. For the left condyle, 13
of the 15 condyles indicated an outward rotation of the lateral pole. Cases 498 and 897 was
analyzed separately due to improper seating of the condyle upon evaluation (See Table 1)

Condylar Movement on the Frontal Plane
When comparing the pre- and post- surgical condylar movements from the frontal view,
the most common movement seen is the superior rotation of the lateral pole for both the right and
the left condyles. Cases 498 and 897 was omitted due to improper seating of the condyle upon
evaluation (See Table 1 for all movements)

Condylar Movement on the Lateral Plane
When comparing the pre- and post- surgical condylar movements from the lateral view,
the most common movements for the right condyle were both the posterior rotation and the
posterior bodily movement. For the left condyle, the posterior rotation was the most common
31

movement. Cases 498 and 897 was omitted due to improper seating of the condyle upon
evaluation (See Table 1 for all movements)

Class II vs Class III
No trend pattern of movement was identifiable between the skeletal class II correction
surgeries and the skeletal class III correction surgeries.

Validation
The average discrepancy between the inter-evaluator segmentation was less than 0.3mm, with a
maximum difference of 1.2mm. The average discrepancy between the intra-evaluator
segmentation was less than 0.26mm, with a maximum difference of 1.1mm. Because the average
discrepancy between the inter- and intra- evaluator segmentation is less than 0.4mm, the size of
one voxel, the discrepancy is within the margin of error of the CBCT image. The data for
measured differences are shown in Table 2.

Degree of Movement
Of the 17 patients, two patients had condyle seating problems pre-surgically. Five
patients had moderate displacement of both condyles. Of the five patients, one patient had severe
displacement of one condyle. Four patients had moderate displacement of one condyle. Six
patient had minimal displacement of both condyles. (See Table 3)
32

Table 1. Summary of movement of the condyles from the coronal, frontal, and lateral view.
33

Table 2. Validation results inter- and intra- evaluators

Table 3. Degree of movement
34

VI. Discussion
a. Condylar displacement
An unwanted effect of orthognathic surgery is condylar displacement because of the
potential condylar resorption that can result in post-surgical relapse. Controlling the position of
the proximal segment is always important when it comes to skeletal stability and the prevention
of relapse. In this study, condylar displacement within 2 weeks post-surgery, through the
segmentation of CBCT images and registration of the condyles over the glenoid fossa, was
examined before remodeling of the glenoid fossa and condylar head could occur.
This study controlled for the following factors.
1. Displacement due to growth. The subjects ranged from 18 to 51 years of age, which is
beyond their adolescent growth spurt. The structures along the cranial base is a stable
structure that can be used as a reference for adults. Therefore, the glenoid fossa was used
as a site of reference (Park et al. 2012) (Cevidanes et al. 2006) (Cevidanes et al. 2009)
(Motta et al. 2010).
2. Displacement due to condyle and glenoid fossa remodeling. Resorption is first detectable
radiographically at 6 months (Papadaki et al 2007).
Many studies have been completed to track the condylar displacement after orthognathic
surgery. Kim YJ et al. and Kim YJ et al. observed an anterior displacement immediately after
surgery, (Kim YJ et al. 2014)(Kim YJ et al. 2013) as opposed to Chen et al and Rotskoff who
observed a posterior-inferior displacement immediately after surgery (Chen et al 2013)(Rotskoff
et al 1991). In other studies, the type of osteotomy there was a rotation or tilting of the condyle
35

along the long axis and displacement differences depending on the type of osteotomy (Kundert et
al. 1980) (Katsumata et al. 2006) (Carvalho et al. 2011).
In our study, the view was analyzed from 3 different planes, the coronal, frontal, and lateral
plane. The outward rotation of the lateral condylar pole visible from the coronal view, is
inevitable for symmetric mandibular advancements surgeries, the wider portion of the mandible
also advances forward, which causes the anterior portion of the lateral portions to flare outwards
to accommodate for the width of the wider portion of the mandible. As for class III corrective
surgery, no pattern was evident form the coronal view. (See Table1)
From the frontal view, the lateral pole of the condyle rotates superiorly. Because the
intercondylar width cannot change since the glenoid fossa is the limiting factor, the inferior
portion of the proximal segment may need to accommodate for the width change of the body of
the mandible. No pattern was evident from the frontal view for class III corrective surgery. (See
Table 1)
The movement of the condyle seen from the lateral view is also affected by the type of
osteotomy. Because the lower border of the mandible needs to be flush between the body of the
mandible and the proximal segment, the movement of the mandible, which is guided by
occlusion, determines the degree of displacement of the proximal segment. Therefore, the
rotational displacement of the condyle seen from the lateral view may have a certain pattern of
movement dependent on the type of osteotomy. (See Table 1)
The stretched soft tissue in 2-jaw surgery with counter clockwise rotation of the mandible
creates tension leading to a retrusive force on the mandible. This happens more often in a
mandibular advancement for a class II surgical correction, the chances of future condylar
36

resorption and surgical relapse is greater (Kobayashi et al. 2012) (Chen et al. 2013) (Kim et al.
2011). In our study, the posterior movement of condylar heads in class II surgical corrections
was not present in all individuals. The degree of advancement may play a large role in how much
the condylar head is distalized. A rotation of the occlusal plane, therefore the rotational
correction of the mandible, may affect the tissue tension that can potentially distalize the
condyles. More research needs to be done to see if the type of class II correction will affect how
much or even if the condyle will be distalized.
When examining the anatomy of the condylar head, those that were larger had minimal
displacement compared to the smaller condylar heads that had lost anatomical structure pre-
surgically. The smaller condylar heads allow for more movement within the glenoid fossa.
Furthermore, if the glenoid fossa also lost anatomical structure and the borders are less defined,
the condylar head seating can be affected greatly during surgery. The condyles that resulted in
greater post-surgical movement had smaller condylar heads or a less defined glenoid fossa.
Six of the 17 cases had minimal movement. Upon examination of these condyles, they
presented with a lot of anatomical structural characteristic prior to surgery which would prevent
much displacement during surgery. Of the 9 patients with one or both moderate condylar
displacement, one condyle with severe displacement presented with a large degree of structural
loss prior to surgery. Two of the cases could not be compared pre- to post- surgery due to the
inability of proper condylar seating. Upon examination of one case with great posterior condylar
displacement, the glenoid fossa had lost most of its posterior border, therefore causing the
condyles to slip further posteriorly. (See Table 3)
37

Upon examining the CBCT of one of the patients with condylar displacement after 7.5
months post-surgery, not only condylar resorption but also remodeling of the glenoid fossa can
be seen at the site of displacement.

b. Limitations
This pilot study had a small sample size. Given the variability in condylar anatomy, the
different surgical corrections, and other confounding variables, a larger sample will be needed to
establish statistical correlations. This is an ongoing project at University of Southern California
Department of Orthodontics.
The qualitative nature of this study reduces the power to detect patterns in displacement.
In future studies, a mathematical description of displacement will be implicated.
Geomagic Studio Software (Version 10; Geomagic U.S., Research Triangle Park, NC)
has limitations in its calculation of measuring the change in position of the condyles pre- and
post- surgery. The Geomagic Studio Software (Version 10; Geomagic U.S., Research Triangle
Park, NC) calculates the shortest distance between the pre- and post- structures, the directional
deviations. The version of the software did not allow for calculation of the planar deviations. In
38

future studies, a version of this software that allows for the calculation of the planar deviations
should be used because it will calculate a more accurate measurement of displacement.
The great variation of pre-surgical condylar relationship introduced more variability. The
protocol of the surgeon was consistent. The mandible was manipulated for optimal condylar
seating within the glenoid fossa. However, asymmetry of the mandible, pre-orthodontic
resorption of the condyles, and the strong musculature of the patient makes it difficult to analyze
condylar displacement because proper seating of the condyles within the glenoid fossa cannot be
captured in the pre-surgical CBCT.
Finding a consistent level at which the condyles were cropped was difficult; and even
more difficult for the glenoid fossa. The difference in glenoid fossa and temporal bone
segmentation could have marginally affected the registration process surface to surface based on
glenoid fossa anatomy. Even though the software only accounts for homologous surfaces during
the registration process, the more similar are these surfaces, the more stable and accurate is the
registration process.
Furthermore, the type of osteotomy as well as post-surgical swelling may affect the
direction as well as the degree of condylar displacement after bi-maxillary surgery. However, the
sample size was not large enough to reveal potential association between the types of
osteotomies. There were maxillary and mandibular advancements and setbacks as well as
clockwise and counterclockwise rotations of the occlusal plane. These osteotomies can definitely
affect the direction of condylar displacement. Although we did not account for the orthodontic
treatment differences due to doctor skill, it may be necessary to do so in future studies because
this may dictate the type of osteotomy.
39

VII. Conclusion
We were able to establish a method to assess condylar displacement after orthognathic
surgery relative to the position of the glenoid fossa and temporal bone. Because the structures of
the cranial base do not change in adults and within the 2-weeks after surgery, the glenoid fossa
can be used as a reference structure to assess the condylar displacement.
When analyzing condylar displacement after bimaxillary surgery relative to the glenoid fossa
2-weeks post-surgically, which is prior to the remodeling of the temporomandibular complex,
certain tendencies were found.
1. From the coronal view, there is an outward rotation of the lateral pole
2. From the frontal view, there is a superior rotation of the lateral pole
3. From the lateral view, there is a posterior rotation of the lateral pole
4. 6 of the 17 cases displayed minimal post-surgical displacement and minimal pre-surgical
loss of anatomical structure of both condyle and glenoid fossa
5. 9 of the 17 cases displayed moderate post-surgical displacement and noticeable pre-
surgical loss of anatomical structure of both condyle and glenoid fossa
6. The sample size was not large enough to reveal a difference between class II and class III
surgical correction osteotomies
7. Software that allows for planar deviation measurements is needed to accurately measure
condylar displacement
8. More research is needed to determine correlation of condylar displacements and class II
and class III surgical correction osteotomies

40

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45

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46

IX. Appendix
039

47

195

48

265

49

344

50

455

51

498 – improper pre-surgical condylar seating

52

683

53

770

54

783

55

877

56

897 – improper pre-surgical condylar seating

57

911

58

925

59

927

60

965

61

972

62

994

Abstract (if available)

Abstract Background: Two dimensional studies have shown displacement of the condyles immediately after orthognathic surgery. Some condylar displacement that occurs with orthognathic surgery is related with greater relapse tendencies. With the development of cone beam CT (CBCT) scans, 3‐dimensional images can show a more accurate direction of condyle displacement. ❧ Objectives: 1) To establish a method to assess condylar changes in position after orthognathic surgery relative to the position of the glenoid fossa and temporal bone. 2) To evaluate the 3‐dimensional change in position of the condyle within 2 weeks of orthognathic surgery. ❧ Materials and Methods: Sample consisted of pre‐ and 2‐week‐post‐surgical CBCT scans for 17 orthognathic surgical patients whose surgery was completed by one surgeon with a consistent protocol. The glenoid fossa and temporal bone were registered to assess the 3‐dimensional displacement of the condyle as a result of orthognathic surgery. ❧ Results: Semitransparencies and color maps depicting condylar displacements are shown and direction of condylar movement is described. ❧ Conclusion: It is possible to assess condylar movement due to orthognathic surgery in 3‐dimensions. The most frequent condyle displacement was a backwards rotation of the lateral pole around the long axis of the condyle.

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Asset Metadata

Creator Moon, Esther (author)

Core Title Three-dimensional immediate post-surgery condylar displacement

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 04/10/2015

Defense Date 04/10/2014

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

Tag cbct,condylar displacement,immediate post-surgery,OAI-PMH Harvest

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Grauer, Dan (committee chair)

Creator Email ms.emoon@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-374592

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