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Operator-determined and reoriented natural head position in three-dimensional imaging

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Operator-determined and reoriented natural head position in three-dimensional imaging

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Content 1

Operator-determined and Reoriented Natural
Head Position in Three-Dimensional Imaging
By
Laura Rein, DMD

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 2016
Laura Rein, DMD

2

Table of Contents
I. Abstract 3
II. Introduction 4
III. Literature Review 5
3-Dimensional Imaging 5
Acquiring a 2D- and 3D-Cephalogram 8
Natural Head Position 12
Current and past methods to adopting NHP in CBCT 17
Operator reorientation of Cephalograms and CBCTs to NHP 23
IV. Materials and Methods 26
Sample 26
Method for CBCT Image Acquisition 27
Method for CBCT Image Reorientation 28
Statistical Analysis 32
V. Results 33
VI. Discussion 40
Limitations 48
VII. Conclusion 51
VIII. References 52
IX. Appendix 55

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I. Abstract
Background: The advent of cone bean computed tomography (CBCT) imaging presents
numerous advances in orthodontic diagnosis and treatment planning. To acquire an image, a
patient is oriented in the CBCT unit’s built-in restraints according to a horizontal reference
plane. While natural head position (NHP) is a more ideal postural position due to high
standardization and reproducibility, it is not regularly used by CBCT units due to the difficulty in
positioning each patient. Purpose: The purpose of this study is to compare different patient’s
head position as determined and imaged by radiologic technicians, to a reoriented position
modified by the use of intracranial landmarks. Materials and Methods: The sample consisted
of 151 orthodontic patient’s with current CBCT images from one practitioner’s office in Los
Angeles, CA. The Pitch, Roll, and Yaw were adjusted in Dolphin 3D Imaging until intracranial
landmarks were aligned and symmetrical. The pitch, roll, and yaw coordinates were recorded
and statistical analysis was performed to test for significance and correlation to age and gender.
Results: There was no statistically significant difference between the roll of the operator-
determined position and the reoriented images. There was a statistical difference in pitch and
yaw, in which the patient tended to look upwards and to the left within the CBCT machine.
Correlation testing demonstrated a positive linear relationship between pitch and age.
However, no relationship exists between pitch, roll, yaw and gender.
Conclusion: The results of our study demonstrate that roll is a position accurately determined
by the radiologic team. However, both pitch and yaw required modification in order to place
the patient into NHP.

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II. Introduction
Natural head position is 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. This physiologic position is said to also be a dynamic position, which
can be achieved by taking the first step forward from standing to walking. As CBCT imaging has
increased demand in the dental profession, it has become crucial to perfect techniques for
enhanced image acquisition and facial analysis. Currently, there are a variety of methods and
devices reported, which help guide a patient into NHP for CBCT image capture. However,
individual patient asymmetries or patient movement, can complicate the ease at which an
image is taken in NHP. Thus, it is essential for orthodontists to devise their own method of CBCT
image reorientation to properly align a patient for CBCT analysis and reliability.

Presented herein, is a method used by a private practitioner in Los Angeles, CA, to
reorient a CBCT image into NHP. The results of this study are compared to the position at which
the radiologic technicians captured the 151 CBCT images used within, and analyzed for
significance.

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III. Literature Review
3-Dimensional Imaging
Conventional dental radiographic imaging, such as a panoramic radiograph or a
bitewing, provides a two-dimensional image of a three-dimensional object. While these
radiographs provide helpful information regarding the mesial-distal and apical-coronal views of
an object or tooth, it is impossible to visualize the buccal-lingual plane nor assess its
relationship within the surrounding craniofacial complex. The superimposition of important
structures, in addition to background noise, can further make 2-D dental radiograph
interpretation challenging.

The first commercially available 3-dimensional imaging, a medical computed
tomography (CT) scanner, was introduced in 1972 by Sir Godfrey Hounsfield of Great Britain
(Pan et al. 2008). As CT scans were one of the first technologies to allow visualization of both
hard and soft tissues, they were quickly deemed as one of the most important clinical imaging
tools and radiological advancements. The acquisition of clear non-overlapped and cross-
sectional images similarly held great implications for the dental field (Pan et al. 2008; Shah et al.
2014). However, it wasn’t until 1987 that CT scans were first applied to the dental profession
and maxillofacial complex (Dos Santos et al. 2004).

While CT imaging is the gold standard for assessing maxillofacial fractures and pathology
(Dos Santos et al. 2004), the high radiation dosage does not warrant CT scans to be an ideal
candidate for regular dental or orthodontic diagnosis. CBCT scans have thus gained popularity
6

in the dental field, as of 1997, as the images are produced by a less expensive machine that
uses 3-20% the radiation dose of conventional CT. Similarly, the machine produces an accurate
image by a smaller machine in a fraction of the time (Machado 2015). The many advantages of
CBCT over CT scans within the dental profession, are attributed to the internal architecture and
basic function of the machines.

As depicted in Figure 1, CT scans use a narrow fan-shaped x-ray beam from a high
output rotating anode generator, which consists of an x-ray tube and a series of detectors (A).
As the x-rays pass through the patient’s body, the rays are registered by the detectors in 360 
around the patient. A series of these recordings are taken from different angles along the long
axis of the patient, as the patient is advanced through the machine for the next slice to be
recorded (Machado 2015). The internal structure of the patient’s body is then reconstructed
from the various angles and silhouettes captured. A CBCT image (B), however, utilizes a cone-
shaped x-ray beam that is centered on a 2-D detector. It rotates around the patient one time to
create a series of 2D images which are reconstructed by Aboudara’s cone-beam algorithm into
an image (Dos Santos et al. 2004; Pan et al. 2008).

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A). B).
Figure 1. Diagram of 3-D Imaging. A). Conventional CT scans are taken slice by slice by a fan
shaped x-ray beam. B). By contrast, CBCT scans are taken in one pass by a cone-shaped
x-ray beam. *Image adapted from: Saudi Dent J. 2015 Jan; 27(1): 12–21.
CBCT imaging has found varied application in all fields of dentistry. In oral and
maxillofacial surgery, CBCT scans have become routine for thorough surgical evaluation and
treatment planning of orthognathic surgery, implant surgery, orthognathic surgery
superimposition, dentofacial orthopedics, and surgical removal of impacted teeth, cysts, and
tumors (RSNA 2015). In oral and maxillofacial pathology, CBCT has helped evaluate dental and
osseous diseases in the jaws and the temporo-mandibular joint (TMJ). In endodontics, CBCT
has been used selectively to assess root canal volume, vertical fractures, multiple extra root
canals, and apical lesions (Garib et al. 2014).

Like endodontics, CBCT in orthodontics is not yet used for routine records and diagnosis.
Previous research has shown that lateral cephalograms, panoramic x-rays, anterior periapicals,
and posterior bitewing radiographs are sufficient for most adult orthodontic patients, while
cephalograms and intraoral and/or panoramic x-rays are sufficient for most adolescents (White
8

et al. 2009; Hodges et al. 2013). These 2-dimensional images usually provide sufficient
information about root anatomy/angulation, the airway, and skeletal/dental disease for most
patients (Hodges et al 2013). However, patients with suspected impacted teeth, facial
asymmetry, sleep apnea, severe root resorption, or persistent TMJ symptoms may warrant the
use of a CBCT scan. A CBCT scan, however, should only be utilized when there is a clear and
specific clinical justification for the patient, which will help provide the most clear and concise
diagnosis and treatment planning (White et al. 2009; Hodges et al. 2013; Garib et al 2014).

Acquiring a 2D- and 3D-Cephalogram
Prior to the use of 3D imaging, orthodontists relied solely upon cephalometric imaging
and analyses to study an individual’s dental and skeletal relationships. The different analyses,
such as Steiner or Rickets, have been extremely useful to describe how an individual varies from
the norm. However, the 2D imaging of 3D subjects, makes precise intracranial landmark
identification difficult, and greatly alters the consistency and reliability at which subsequent
cephalograms are taken and compared (Cevidanes et al. 2009; Weber et al. 2013).

As early as the 1860’s, craniologists and anatomists realized that for ideal craniometric
studies, a skull had to be oriented in each person’s most natural manner (Solow et al. 1971;
Bansal et al. 2012; Meiyappan et al. 2015). To determine this most ideal position, both
horizontal and vertical intra- and extra-cranial reference lines were used and compared in
various genders and races (Meiyappan et al. 2015). After considerable trial and error for
9

standardization, it was agreed in Frankfort, Germany in 1884, that the horizontal plane that
traversed the left and right porion and the left orbitale was the best orientation of skulls for
craniometric evaluation. This horizontal reference plane known as Frankfort Horizontal (Figure
2), was adopted by many orthodontists and has since been used worldwide in many
cephalometric analyses (Houston 1991; Huh et al. 2014). However, as intracranial reference
points are not always stable and visible landmarks, the variability of these reference lines in
conjunction with non-standardized cephalometric imaging techniques, complicated
cephalometric reliability.

(A). (B).

Figure 2. (A). Skeletally, Frankfort Horizontal represents the horizontal line made from
Porion (the most superior point of the external acoustic meatus) to Orbitale (the
most inferior point of the left orbit). (B). Facially, Frankfort Horizontal (plane) can
be determined from the lower margin of the eye socket (Orbitale, O) to the notch
above the tragus of the ear (Tragion, T)
*Images adapted from Eur J Orthod. 2006; 28; 319-326.

In 1931, Birdsall Holly Broadbent advocated the use of cephalostats to help position a
patient with a stable base, for which subsequent accurate cephalograms could be taken. He
stated that this head immobilizer, as depicted in Figure 3, could help determine accurate
orthodontic changes in growth and development by eliminating the uncertainty in patient
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positioning (Jiang et al. 2007). Broadbent also believed that the use of a cephalostat would
allow the visualization of landmarks currently unable to be seen before (Silva et al. 2003).

During this decade, Broadbent imaged skulls with lead pieces marking relevant
landmarks. To image each cranium, he first used a head restraint with ear rods in both the right
and left external acoustic meatus to align the trans-meatal axis (Figure 3A). He then used
Frankfort horizontal to align the vertical position of the head, by placing the horizontal
reference plane parallel to the floor. Lastly, to achieve three-point fixation, a nasal rest and
nasion pointer were used to secure the patient for image acquisition (Figure 2B) (Schuler et al.
2008). While slight cephalostat variations may exist from machine to machine, these three
principles are still employed by modern day cephalometric imaging machines (Lundstrӧm et al.
1995).
(A). (B).

Figure 3. (A) Patient positioning from a frontal position demonstrating mid-sagittal plane is
perpendicular to the x-ray beam. The ear rods are placed in both the left and right
external acoustic meatus to hold the trans-meatal axis parallel to the x-ray beam.
(B) Patient positioning from an anterio-posterior view demonstrating a nasion
pointer and nasal rest to maintain secure patient positioning.
*Images adapted from Br Dent J. 2001: 190; 16 - 22
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In contrast to 2-D cephalogram imaging, modern CBCT units do not have rigid
cephalostats which place a patient into a very particular orientation. To acquire a 3D image, a
patient is simply guided into the machine and the chin is rested on a chin base for support. A
laser light is used to align the patient’s mid-sagittal plane perpendicular to the x-ray beam
(Figure 4A) (Huh et al. 2014). A second laser light is used to align either Frankfort horizontal or
the occlusal plane parallel to the floor. The patient is then secured with an auricular support to
hold the head in place as the image is taken (Figure 4B) (Kim et al. 2015). Dissimilar to 2D
cephalometric imaging, CBCT units do not generally employ a 3-point fixation method.
(A) (B)
Figure 4. (A) The mid-sagittal plane of a patient is defined as a ‘line’ that passes through the
midline structures of the face. (B) A patient is guided into proper position for taking a
CBCT image with the use of a chin support and head rest. The laser guide lights are also
demonstrated.
*Images adapted from http://medical.tpub.com/14275/css/14275_21.htm and
http://tekitronics.com/site/products/Rotograph-Evo-D-Panoramic-with-Ceph.html

Despite the relatively fast exposure time of CBCT, it is not uncommon that patient
movement can alter the diagnostic quality of an image. Even with best attempts to align a
patient with lasers and supports, a patient’s head can translate in anteroposterior, lateral, and
vertical directions, as well as rotate around the x, y, and z axes (Damstra et al. 2010). The
rotations around the x, y, and z, axes are respectively referred to as pitch, yaw, and roll (Figure
12

5) (Kim et al. 2015). Pitch, roll, and yaw can be adjusted in any acquired CBCT image to realign a
patient into ideal position, or compensate for any underlying skeletal asymmetry. To maintain
the consistency that Broadbent proposed, the x, y, and z coordinates should be recorded in
each patient’s initial CBCT and matched in subsequent imaging.

Figure 5. A 3D analysis of the orientation of the head, jaws, and teeth is incomplete without
considering the 3D rotations in all 3 axes; the pitch, roll, and yaw.
*Image adapted from J Craniomaxillofac Surg. 2015: 43(2); 264-273.

Natural Head Position
While Frankfort horizontal has helped advance the field of orthodontics in diagnosis and
treatment planning, the inherent flaws in relying upon intracranial structures as reference
planes were quickly exposed (Jiang et al. 2007). In 1955, William B Downs demonstrated how
three children with nearly the same facial profile, or typing, had drastic variations in their
cephalometric analyses (Figure 6). Downs attributed these craniometric inconsistencies to each
individual’s cant of the Frankfort horizontal reference plane, seen as the patient gazes forward
13

(Downs 1956; Houston 1991). Similarly in the 1950’s Arne Bjork demonstrated two individuals
with nearly identical facial typing that had great discrepancies in the anatomy of their cranial
base (Houston 1991; Jiang et al. 2007). These drastic variations in intracranial reference lines
led anatomists and orthodontists to explore extra-cranial landmarks as stable cephalometric
reference planes (Schmidt 1958).

Figure 6. Downs study of 100 students demonstrated inherent flaws of using intracranial
landmarks as stable reference plane. All three students are gazing into their ‘NHP’
with variable FH angles.
*Image adapted from Angle Orthod. 1956;26(4):191-212.

Interestingly enough, extra-cranial landmarks were employed in craniometric studies
prior to the introduction of intra-cranial landmarks. Natural head position, or NHP, was such a
reference plane used by anthropologists even prior to the invention of Broadbent’s cephalostat
(Houston 1991; Jiang et al. 2007). Broca first described NHP in 1862 as a physiologic position in
which ‘a man is standing and his visual axis is horizontal (Cooke 1990; Weber et al. 2013;
Meiyappan et al. 2015). This position was further explained by Molhave, as an ‘intention
position,’ in which it is the stable natural manner achieved by taking one step forward from
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standing to walking (Molhave 1960). Downs also described NHP by ‘the use of a mirror in front
of the patient, who should be directly looking into his own reflected pupils’ (Lundstrӧm 1995;
Silva et al. 2003).

Today, NHP is defined as a standardized and reproducible upright posture where the
head is oriented in a position while focusing on an eye-level point at a horizontal distance away
(Schmidt 1958; Weber et al. 2013). Some anatomists further define NHP as a position of
‘maximum comfort,’ based upon a patient’s self-perception and horizontal gaze (Silva et al.
2003). Furthermore, it is widely accepted that NHP is not a single angular measurement. NHP
is a posture that is characterized as a dynamic position, defined by a range of angles around the
natural head’s position (Lundstrӧm 1990; Üsümez et al. 2001; Silva et al. 2003).

Throughout the years, anatomists have attempted to further explore and explain the
extrinsic factors that contribute to the stability of NHP. Research has demonstrated that the
upright position of the head is reproducible and stable because it is balanced by the post-
cervical and masticatory suprahyoid and infrahyoid muscle groups (Ӧzbek et al. 1998; Weber et
al. 2013). These muscle groups attach directly to the hyoid bone (Figure 7), which are directly
responsible for the fluctuation in mandibular inclination (Weber et al. 2013). Cranial posture is
also controlled by the neuromuscular systems that influence normal functions, such as
respiration and mastication.

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It has, thus, been generally concluded that each individual’s deviation from NHP has
been guided primarily by the need to maintain a patent pharyngeal airway, and a proper sight,
hearing, and vestibular orientation (Ӧzbek et al. 1998, Peng et al 1999). It is thus, not surprising,
that current studies on subjects with obstructive sleep apnea or enlarged tonsils/adenoids,
demonstrate an altered NHP due to the necessity to maintain each individual’s function
(Molhave 1960; Ӧzbek et al. 1998; Weber et al. 2013).

Figure 7. The suprahyoid muscles (geniohyoid, digastric, mylohyoid, and stylohyoid muscles)
attach superiorly to the hyoid bone and help elevate the bone and widen the
esophagus when swallowing. The infrahyoid muscles (thyrohyoid, omohyoid,
sternohyoid, and sternothryoid) attach inferiorly to the hyoid to aid in speech and post-
swallowing [12].
*Image adapted from: http://oerpub.github.io/epubjs-demo-
book/content/m46484.xhtml

Despite the early use of NHP, it wasn’t until the mid-1950’s that NHP was introduced to
orthodontics for craniofacial diagnosis and treatment planning. Soon thereafter, numerous
studies evolved that supported the use of NHP as a reproducible and stable reference plane
(Solow et al. 1971; Weber et al. 2013). Downs in 1956, Bjerin in 1957, and Moorrees and Kean
16

in 1958 all demonstrated the reproducibility of NHP in both adults and children of varying race
and ethnicity, with only slight (4 ) variation (Solow et al. 1971; Cooke 1990; Lundstrӧm et al.
1995; Jiang et al. 2007; Bansal et al. 2012). In 1988, Michael S. Cooke was one of the first to
report the reproducibility of NHP during lateral cephalometric radiography on orthodontically
aged children. Cooke radiographed 217 random 12-year old children with both supporting ear
rods and mirrors at a vertical distance eye height away. He reported NHP reproducibility was
increased when a mirror was used as an external eye source rather than when stabilizing ear
rods were used. Similarly, in 1999, Cooke demonstrated in a 15 year longitudinal study that
NHP was remarkably reproducible with a 2.2  method error. The variance of NHP after 15 years
was found to be 4.8 , which was significantly less than the 25 -36  variance of intracranial
reference planes.

Despite providing a more reproducible position for craniometric studies, NHP is an
invaluable tool in orthodontic diagnosis. As NHP positions a patient in their ‘true life’
appearance, all orthodontic records should be taken and further evaluated in that orientation.
Referencing a more stable profile, in which the patient naturally carries themselves, will provide
a more meaningful view of a patient and their growth, which provides a more accurate
treatment plan and orthodontic outcome (Jiang et al. 2007; Damstra et al. 2010).

17

Current and past methods to adopting NHP in CBCT
As NHP is a position that is unique and consistent for each individual, CBCT unit’s built-in
restraints do not provide individualized guidance to obtaining an image in NHP. Over the years,
it has become necessary for each operator to adopt their own technique of recording NHP.
Different methods are 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).

One of the very first methods of guiding a patient into NHP was reported by Moorrees
and Kean in 1958. Unknowingly, Moorrees and Kean replicated a technique that was first
reported by Schmidt in 1876. As Schmidt sought to understand the disagreement among
observers regarding the correctness of the head position (1956), he studied patients in both a
self-position and corrected position. In his investigations, Schmidt used a wood frame with a
protractor and plumb line attached, to study the relationship between a vertical reference,
Frankfort Horizontal, and the patient’s ‘corrected position’, or NHP (Figure 8) (Jiang et al. 2007;
Schuler 2008).

Figure 8. A light wooden frame with protractor and plumb line was used to study the
relationship between Frankfort Horizontal and NHP in 20 individuals.
*Image adapted from Am J Phys Anthropol. 1958: 16; 213-234.
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Moorrees and Kean also used the concept of a ‘protractor and plumb line’ to record
NHP and true vertical on each cephalometric film. As seen in Figure 9, a brass bow with a
stainless steel ligature wire was stretched between the cassette holder and base plate, aligned
in a vertical plane. Since the wire was placed directly in front of the cassette, the resulting
image was recorded with a true vertical registered reference line on each radiograph. To allow
the patient to posture themselves in a natural position, the left ear plug was removed from the
cephalostat and the patient gazed into a mirror at pupillary height 170 cm in front of them.
Moorrees and Kean found that when replicating radiographs, the true vertical used was a more
preferable reference line, as the biologic variation of intracranial lines varied greatly. (Schmidt
1958; Lundstrӧm et al. 1995).

Figure 9. Moorrees and Kean devised one of the first modifications of the cephalostat to guide
a patient into NHP for cephalometric imaging. Not pictured is the mirror placed 170 cm
away at pupillary height.
*Image adapted from Am J Phys Anthropol 1958: 16; 213-234.

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In addition to introducing a true vertical reference line into cephalometric imaging,
Moorrees and Kean also published their method on how a patient is oriented into NHP for
image acquisition. First the patient should be looking at his own eyes as reflected into a mirror.
Next, the operator examines and adjusts the patient until the pupil is exactly in the middle of
the eye. The ear support is then placed in front of the tragus, as the patient relaxes into a
comfortable position, and the head is assessed for any rotation/tilting. From the frontal view,
the head posture is confirmed, corrected, and secured lightly with an auricular support. A final
verification is made in both views and the image is captured. This method of positioning is still
widely used today in CBCT imaging (Schmidt 1958).

Following Moorrees and Kean’s techniques, additional contributions were made that
sought to find alternate ways of transferring NHP to the cephalostat and registering NHP on
lateral cephalograms. In 1983, K. J. Showfety, described a device which was able to record
standing natural head position and transfer the specific orientation to a cephalometric head
film. Showfety used an instrument called a fluid-level device, which was based upon the
principles of physics and fluid systems. The device was fixed to the patient’s temple (between
the eyebrow and hairline) and the patient was asked to stand upright and gaze down a long
hall. The patient also took a step forward from standing, and the fluid level rotated until the
meniscus was aligned with the horizontal wire, as seen in Figure 10. These steps were repeated
two times to ensure reproducibility. The patient was then placed in the cephalometric head
holder with ear rods to maintain the position, and a vertical reference chain was used.

20

The clinical trial results of Showfety’s study demonstrated that on 28 individuals, the
horizontal wire was 89.75  to the vertical reference chain with an error of .25 . This method
was exceptionally close to the ideal 90  relationship of the horizontal wire to the vertical
reference chain, which indicates Showfety’s successful method of obtaining NHP (Showfety et
al. 1983).

Figure 10. Fluid-level device in which the air bubble meniscus is aligned with the .030 inch
diameter wire on top of the ends of the bubble, thus indicating a perpendicular to a
gravity-defined true vertical [24].
*Image adapted from Am J Orthod Dentofacial Orthop. 1983: 83; 495–500

As NHP is considered a dynamic position, many orthodontists recognized the
importance of capturing NHP not as a static movement, as Moorrees and Kean and Showfety
did, but rather as a dynamic recording. Cleall et al. (1966) were the first to record dynamic
changes in head posture with the use of cinefluorography (Murphy et al. 1991; Üsümez et al.
2001). However, the high use of irradiation did not make this technique acceptable for
everyday NHP positioning. Murphy et al. in 1991, introduced a measuring device called an
inclinometer. The intent of the instrument was to be able to record reproducible cranial
posture during swallowing and mastication. When Murphy et al.’s recordings were compared
to the study’s plumb-line control, the inclinometer demonstrated analogous NHP
21

measurements, suggesting an inclinometer was an effective technique for registering NHP
(Cleall et al. 1966; Üsümez et al. 2001).

In 2001, Üsümez and Orhan introduced a modified inclinometer that could record NHP
and that could also be transferred to a cephalostat for clinical use. The inclinometer was
incorporated into a pair of eyeglass frames that had tilt sensors that could measure pitch and
roll (Figure 11) (Orhan et al. 1996). After establishing a ‘self-balance’ position, the patients
looked into their own eyes in a mirror and pitch and roll were recorded. The subjects were then
placed into the cephalostat and instructed to move their heads until the pitch and roll readings
coincided with their original recordings. The replicated cephalograms taken with the recorded
pitch/roll demonstrated highly repeatable and accurate patient positioning into NHP.

(A) (B)
Figure 11. Üsümez et al.’s device (A) The eyeglass frame with inclinometers on both arms
attached to a conversion module instrument. (B) The eyeglasses with the right sensor
parallel to the sagittal plane for pitch measurement and the L sensor perpendicular to
the sagittal plane for roll measurement. The eyeglasses wear a total of about 22
grams [33, 34].
*Images adapted from Am J Orthod Dentofacial Orthop. 2001: 120(6); 664-670

22

The most recently reported modified method of recording NHP was reported by Liu et al
in 2015. In this study, a laser level was used to project a horizontal reference line on a physical
model, and a 3D image was obtained with a multi-camera system (Figure 12). Digitally, the
recorded NHP was reproduced by registering the coordinate axes with the horizontal reference
on both the frontal and lateral views (Liu et al. 2015; Tian et al. 2015). First, the z coordinate, or
roll, was adjusted until it was parallel to the laser beam. Secondly, the y axis, or pitch, was
adjusted in the lateral view until the laser beam was parallel with the y-coordinates. The
alterations in the pitch and roll angles were noted, and with reproducibility, the method
deemed an accurate and clinically feasible method of orienting the head in NHP.

Figure 12. Horizontal (A) and vertical (B) laser beams are demonstrated in both the frontal and
lateral view on the physical model.
*Image adapted from Am J Orthod Dentofacial Orthop. 2015: 147(6); 781-787

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Operator reorientation of Cephalograms and CBCTs to NHP
While countless methods, such as those suggested above, have been devised to
properly image a patient in NHP, often times a patient’s position is captured deviant from their
true NHP. Most commonly, a patient seems to have the tendency to flex or extend their head
in relation to the cervical vertebrae or even true vertical. This alteration in ‘pitch’ can cause the
patient to appear with a reduced posterior facial height, reduced AP dimension, appearance of
facial retrognathism, and reduced nasopharyngeal space (Brodal 1972; Silva et al. 2003).

It has thus become essential that both operators and orthodontists are perceptive to
any alterations in NHP and can confidently modify this position into an ideal ‘corrected’ one.
For these alterations, the operator, or orthodontist, will commonly use their best judgment to
modify pitch, roll, and yaw to orient the CBCT or cephalogram into NHP. However, as
techniques in taking cephalograms vary, the landmarks which are used for the basis of
CBCT/cephalogram reorientation, vastly differ.

For the reorientation of these images, the superimposing reference line is very
important (Cleall et al. 1966; Dvortsin et al. 2011). Conventional reference lines used in
cephalogram analyses, utilize landmarks that may change as a patient progresses through their
orthodontic treatment. Examples of these soft tissue reference lines include the V-line, a soft
tissue line connecting nasion and subnasale. Rickett’s E-line, similarly, is an extra-cranial soft
tissue reference line that goes from the tip of the nose to soft tissue pogonion (Figure 13). In
24

addition to variation with growth, the soft tissue lines can vary tremendously as lip posture is
changed in imaging or treatment (Bister et al. 2002; Dvortsin et al. 2011).

Figure 13. The upper line represents the ‘V-line’, and the lower line represents Rickett’s E line’.
*Image adapted from Eur J Orthod. 2002: 24; 457-470.

In 1974, David Feuer discussed the importance of using an intracranial reference line,
rather than the extracranial soft tissue lines, for consistent NHP guidance. Feuer discusses
Enlow et al.’s analysis method which was based on three vertical and four horizontal equivalent
dimensions of the face (Feuer 1974; McCarthy et al. 2001) The proposed analysis uses a
posterior nasomaxillary vertical plane, PM, which traverses the intersection of the great wings
of the sphenoid with the planum sphenoidum tangent to the maxillary tuberosities (Figure 14).
This PM line is claimed to be approximately perpendicular to the line of vision, which suggests
its use as a consistent reference line for NHP (Feuer 1974; McCarthy et al. 2001).
25

Figure 14. Enlow’s PM line has a perpendicular relationship with the NHA (neutral line of
vision).
*Image adapted from Anat Rec. 2001: 264; 247-260

In 2011, Dima et al continued exploring other options for superimposition reference
lines. As the upper part of the facial profile is considered more stable than the lower facial
profile, the ‘N-line’ was devised which was hypothesized to be constant and reproducible
(Bister et al. 2002; Dvortsin et al. 2011). As seen in Figure 15, the ‘N-line’ is centered on the
nose and involves five landmarks along the nasal bridge; soft tissue nasale, subnasale, labius
inferius, labius superius, and soft tissue supramentale. On both photographs and
cephalometric radiographs, the N-line was traced and the angle of the N-Line to the true
vertical was registered and compared to the E- and V-line. Unsurprisingly, the N-line was found
to be a preferred superimposition reference line to both the E- and V-line.

26

Figure 15. The 5 landmarks used in the ‘N-line’: TV – true vertical, NFL – nose-frontal line, Sn –
subnasale, Li – labius inferius, Ls – labius superius, sm – soft tissue supramentale
*Image adapted from Angle Orthod. 2011: 81(5); 889-894.

IV. Materials and Methods
Sample
189 consecutive patients were screened for this study. Patients were anonymized by
assigning an arbitrary code number that corresponded to their patient record number. Of the
189 patient’s screened, 151 patients with current CBCT images on file were selected from July
24
th
, 2012 and February 17
th
, 2015. All patients were chosen from one practitioner’s office in
Los Angeles, CA. All CBCT images were taken by the Los Angeles Center for Oral and
27

Maxillofacial Surgery radiologic team. All 151 images were captured on the same iCAT CBCT
machine (Imaging Sciences International, Hatfield, PA), to minimize environmental error.

Method for CBCT Image Acquisition
All patients were told to stand aside the iCAT machine and look straight forward at the
horizon to assess symmetry. The patient was then guided and seated into the machine. The
head was first supported by a temple support that goes across the forehead and rests on either
side of the temple (Figure 16).

Figure 16. iCAT Temple support being guided onto the patient. *Note: this patient is standing
not sitting.
*Image adapted from: http://www.adirondackoralsurgery.com/meet-us/office-tour/

Next, horizontal and vertical laser light beams were projected on the patient to register true
horizontal and vertical lines. Adjustments to the seating heights were made to accommodate
subjects in achieving proper alignment on their faces. The horizontal line was placed in front of
the condyle on both the right and left side, with best attempts to align the heights. The light
was projected on and off until a stable repeatable position was achieved. The vertical line was
28

then projected on the patient to align the mid-sagittal plane. Lastly, the chin was supported on
the chin rest prior to image capture.

Method for CBCT Image Reorientation
The resulting DICOM files were imported into Dolphin 3D Imaging (Patterson Dental;
Chatsworth, CA). Prior to adjusting the images, each patient’s diagnostic photographs were
assessed for any major asymmetries, particularly the eyes being level. If patients appeared
relatively symmetrical, the files were then opened in edit mode in Dolphin 3D, and the
segmentation for both the hard and soft tissues in both solid and translucent mode was
adjusted (Figure 17).

Figure 17. Adjustment of segmentation of hard and soft tissues in both solid and translucent
mode to appropriately visualize anatomical structures.

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
29

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 (Figure 19).

(A)
(B)
Figure 18. (A) Yaw and Roll were adjusted on the Right sided view until the orbital rims and
zygomatic buttresses were aligned (B).

30

Figure 19. Yaw and Roll were adjusted on the Frontal view until the base of the orbital rims
were aligned.

To ensure that the roll is properly aligned, in solid mode, each CBCT was looked at in a
coronal clipping slice from the ‘top facing down’ view (Figure 20). The 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. Lastly, in the ‘top facing down’ view, the image is adjusted for any further
necessary roll modifications.
31

Figure 20. From a ‘top down view,’ the midline structures, as well as foramina, are used to
adjust roll until they are equidistant from the sagittal and coronal planes.

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 are assessed again for
symmetry, as are the base of the orbits. The clinical midlines were checked again against the
CBCT image midlines before the image was assessed for both the hard and solid tissues
together (Figure 21). The pitch is lastly adjusted, until the patient is looking in the most natural
head position, with eyes gazing straightforward at the horizon. The corrected CBCT image is
saved as ‘position zero,’ and the pitch, roll, and yaw coordinates are recorded for statistical
analysis.
32

Figure 21. The hard and soft tissues are aligned and the image is assessed for final adjustments
in yaw, roll, and pitch.

Statistical Analysis
Descriptive statistics, including mean, median, range, standard deviation, minimum, and
maximum, were calculated for pitch, roll, and yaw. Histograms of the data were made, to test
for data normalcy. For an accuracy test, a 1-sample t test was performed to determine whether
the pitch, roll, and yaw reoriented coordinates were statistically different from 0 . A Levene’s
test was then performed to determine a relationship between pitch, roll, yaw, and gender.

To evaluate whether, generally, there was any correlation between pitch, roll, yaw, and
age, Pearson correlation tests were used. Results were considered significant at P<0.01. All
statistical analyses were performed with software (SPSS Inc. of IBM, Chicago, IL). Raw data of
our study can be found in the Appendix.

33

Results were considered significant at P<.05. However, as pitch, roll, and yaw are
simultaneous and related, a Bonferroni correction test was performed to reduce Type 1 error.
Our α was set at .01666.

V. Results
The demographic characteristics of the subjects for our study can be found in Table 1.
Aside from the number of male and female subjects, the range and averages for the male and
females in this study are not significantly different. The male to female ratio is 1:2.
N Range of Age (years) Average Age (years)
Male 50 13 to 65 38
Female 101 12 to 70 35

Table 1. Demographic characteristics

Table 2 represents the summary statistics for the data. Pitch has the largest range in
coordinate values, followed by yaw. Roll has the smallest variation and range in coordinate
points. Both roll and yaw have a negative mean, while pitch has a positive mean. Yaw has the
largest standard deviation and roll has the smallest.

34

Sample Range ( ) Minimum ( ) Maximum ( ) Mean ( ) Standard
Deviation
Pitch 151 20.89 -10.43 10.46 2.15 3.04
Roll 151 8.58 -4.32 4.26 -0.19 1.60
Yaw 151 15.21 -11.71 3.50 -4.21 3.06
Table 2. Descriptive statistics of Pitch, Roll, and Yaw.
Descriptive statistics were also performed on the data, when the data was differentiated
by gender (Table 3). The female group for both pitch and yaw had the greatest standard
deviation. The yaw for male and female were almost identical.

N Mean Standard Deviation Standard Error Mean
Pitch Female 101 2.01 3.10 0.31
Male 50 2.42 2.93 0.41
Roll Female 101 -0.18 1.55 0.15
Male 50 -0.22 1.72 0.24
Yaw Female 101 -4.21 3.11 0.31
Male 50 -4.22 3.01 0.43
Table 3. Descriptive statistics of Pitch, Roll, and Yaw for male and female.
35

The histograms below (Figure 22) demonstrate that the collected data follows a
distribution that is close to normal. This means that for pitch, roll, and yaw, 95% of the
observed data will fall within 2 standard deviations of the mean.

A)

B)

36

C)

Figure 22. A). The histogram of Pitch, in degrees, with distribution plot B). The histogram of
Roll, in degrees, with distribution plot. C). The histogram of Yaw, in degrees, with
distribution plot. All curves are normally distributed.

As the data visually appear to be normal, one-way t-tests were performed (Table 4).
Pitch and yaw are both seen to be statistically significant with P values of .000. Roll, with a P
value of .142, does not have any statistical significance. The null hypothesis was thus rejected
for pitch and yaw, which suggests an association between pitch, yaw, and our method of
reorientation.
T Degrees of Freedom Significance 95% Confidence Interval
Pitch 8.69 150 .000 1.66 to 2.64
Roll -1.48 150 .142 0.45 to .065
Yaw -16.89 150 .000 -4.71 to -3.72
Table 4. T-test comparisons of pitch, roll, and yaw. *Statistically significant at P<.0167
37

F Significance
Pitch .62 .43
Roll .41 .52
Yaw .19 .67

Table 5. Levene’s Test of Equality of Variances for pitch, roll, and yaw. Equal variances assumed
for gender. *Statistically significant at P<.05.

To test the relationship of pitch, roll, and yaw with gender, a Levene’s test for equality
of variances was performed. The P value of pitch, roll, and yaw were .43, .52, and .67
respectively. The null hypothesis is accepted, suggesting there is no relationship or association
between pitch, roll, yaw and gender (Table 5).

A Correlation analysis was then performed to determine the strength of association
between age, pitch, roll, and yaw. Pitch was the only variable that was found to be statistically
significant (Table 6). The relationship between pitch, roll, yaw, and age is graphically depicted in
Figures 23-25. Pitch has a positive linear relationship with age, demonstrating a correlation
coefficient of .085. While the data on roll and yaw appears to be extremely scattered, a very
slight weak positive linear relationship is demonstrated, with correlation coefficients of 0.0072
and 0.014 respectively.

38

Age
Pitch Pearson Correlation 0.29
Significance 0.000
N 151
Roll Pearson Correlation 0.09
Significance 0.302
N 151
Yaw Pearson Correlation 0.12
Significance 0.143
N 151
Table 6. Correlation analysis for pitch, roll, yaw, and age.*Correlation is significant at .01 level.

Figure 23. Correlation between pitch and age. Circles indicate observed data, dotted line
represents best linear fit (Pearson correlation coefficient estimate 0.085).
y = 0.0627x - 0.1297
R² = 0.0833
-15.00
-10.00
-5.00
0.00
5.00
10.00
15.00
0 20 40 60 80
Pitch ( )
Age (years)
Pitch versus Age
39

Figure 24. Correlation between roll and age. Circles indicate observed data, dotted line
represents best linear fit (Pearson correlation coefficient estimate 0.0072).

Figure 25. Correlation between yaw and age. Circles indicate observed data, dotted line
represents best linear fit (Pearson correlation coefficient estimate 0.014).
y = 0.0097x - 0.5427
R² = 0.0072
-15.00
-10.00
-5.00
0.00
5.00
10.00
15.00
0 20 40 60 80
Roll ( )
Age (years)
Roll versus Age
y = 0.0261x - 5.1598
R² = 0.0143
-15
-10
-5
0
5
10
15
0.00 20.00 40.00 60.00 80.00
Yaw ( )
Age (years)
Yaw versus Age
40

VI. Discussion
CBCT scans within the dental profession have tremendous applications that range from
detecting osseous lesions to treatment planning precise orthognathic surgery. In order to obtain
the most reliable, accurate, and diagnostic image, it is essential that the patient is positioned in a
consistent way. It is widely accepted that NHP is the most physiologic, standardized, and
reproducible position, from which a CBCT image could be taken. Data has shown that using a
natural coordinate system, such as NHP, is an ideal reference plane when evaluating facial
asymmetries, or obtaining an accurate facial analysis (Weber et al. 2013). The ideal method for
recording and reproducing NHP should be repeatable, accurate, and independent of the
operator. Most importantly, the technique employed should not influence the patient’s natural
position when the scan is taken (Liu et al. 2015).

The adopted method of acquiring each patient’s CBCT image herein, is in line with
current research used to record NHP with the least amount of external interference and
greatest reproducibility. Current comparable studies that test their patient positioning
techniques, use 3D camera systems in place of CBCTs, to help minimize the subject’s radiation
exposure. 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. Weber et
al. also place four semi-permanent positioning ink dots on the face; 2 vertically along the
forehead and 2 horizontally along the pre-auricular/infrazygomatic area, to help align the laser
beams (Figure 26). Both studies also used cephalostats that provided only temple and chin
support without any other type of guidance. These studies both demonstrated the ability to
41

accurately reproduce NHP through various time points. Similarly, they both found that of all the
3 coordinates, pitch had the greatest variation while roll had the least (Weber et al. 2013; Liu et
al. 2015).

Figure 26. Weber et al.’s technique of NHP orientation – 4 semi-permanent dots placed on the
face to help align the horizontal and vertical laser beams
*Image adapted from: Am J Orthod and Dentofacial Orthoped. 2013;143(5):738-44.

Our study herein demonstrated similar results to Liu et al. and Weber et al., as pitch was
the coordinate with the greatest variability within our patient population. This is unsurprising,
when the physiology of the head and neck is examined. Maintaining the sagittal plane (Figure
27) while upright, requires a combination of positional memory, muscle memory, muscle tone,
and visual memory. This muscular support is required from the trunk, as well as the muscles of
the head and neck. The heavy weight of the head, additionally, can contribute to the variation
42

in NHP, as gravity influences the balance of the head and the spine. The equilibrium in the
sagittal plane can also be affected by daily occupation. Some of our subjects may be
students/workers that are required to look downwards at books/computers throughout the
day, and others may not have any kind of daily positional influence. This variation in head
position can cause the habitual position of the head in the sagittal plane to become unbalanced
and thus, variabilities in positioning are captured throughout time (Brodal et al. 1972; Weber et
al. 2013; Liu et al. 2015).

Figure 27. The 3 planes of space: sagittal, coronal, and transverse. Movement in the sagittal
plane alters pitch, movement in the coronal plane affects roll, and movement in the
transverse plane results in a change in yaw.
*Image adapted from: https://en.wikipedia.org/wiki/Anatomical_terms_of_location.

While our results did not show that roll was a predicted coordinate that differed
between our study and as captured by the radiologic team, roll was still the coordinate in our
study that had the least variation amongst subjects. Our findings are in sync with the results of
43

Weber et al. and Liu et al. who also found roll was the least variable coordinate when
reproducing NHP over time. As previously mentioned, the head is supported by the large infra-
and supra-hyoid muscles that allow slight flexion/extension across the vertical axis (sagittal
plane). When the patient is asked to gaze forward into his/her own eyes, the patient is guided
by neuromuscular systems that control the interactions between their eye position, head
position, and muscles.

The vestibular system plays a large role in responding to this motion and spatial
orientation. The inner ear, specifically, is not only responsible for changing sound into
neurological signals which then travel to the brain, but also detecting motion in 3 planes of
space. The anatomy of the inner ear includes a utricle, a saccule, and 3 semi-circular fluid-filled
canals oriented in a sagittal, transverse, and coronal plane (Figure 28). As a patient tilts their
head from side-to-side, hair bundles within the coronal plane are stimulated after motion is
sensed by the posterior semi-circular canal. Additionally, the eyes move in the opposite
direction as the head tilt, in order to maintain visual focus on an object (Brodal 1972).

The natural avoidance of a side-to-side tilt, demonstrates the body’s protective instinct
to maintain the head position centered over the vertical axis of the spine. Of all 3 planes of
space, the coronal plane is the axis most heavily influenced by the vestibular, neural, and
muscular system (Brodal 1972). This is most likely necessary to maintain a patent pharyngeal
airway, and a proper sight, hearing, and vestibular orientation. It is thus not surprising, that the
44

coronal axis, or roll, is the most repeatable position when the patient attempts to maintain or
duplicate a past posture (Cleall et al. 1966; Brodal 1972; Peng et al. 1999).

Figure 28. The components of the right inner ear
*Image adapted from: https://classconnection.s3.amazonaws.com/184/flash
cards/1904184/jpg/51352566999599.jpg

The stability of roll and the variation of pitch anatomically, is also seen when we
examine our patient’s within the cephalostat. In our study, the iCAT cephalostat uses a head
strap as a temple support. It is thus, not surprising, that the roll does not have drastic variation
as the head is fairly immobilized in the z coordinate. Similarly, yaw is fairly easy to assess for
reproducibility and symmetry. When the y coordinate is assessed, the laser lights are projected
onto the patient, which help the operator determine symmetry. However, movement in the x
coordinate or pitch, has the least support by the cephalostat. The flexion/extension of the head
is not restricted, and instead is solely up to the operator to assess pupillary symmetry with the
use of a mirror, to eliminate any unwanted movement.

45

In addition to pitch having the greatest variation in our study, it was also the only
coordinate that had a positive number for a mean. As our images were manipulated within
Dolphin Imaging, a positive pitch was seen when the head was adjusted downwards along the
sagittal plane. Thus, a positive pitch coordinate suggests that within the iCAT machine, the
patient is more commonly looking upwards and the reorientation of the image requires a
downwards movement. In contrast to pitch, both the roll and yaw coordinates had negative
averages and less variation in position. When roll and yaw were adjusted, a more negative
coordinate was obtained as the patient’s head was either tilted or axially moved to the right.
Thus, in addition to generally gazing more upwards, our patient population had a tendency to
favor their left side within the iCAT machine. It is possible that since the patient enters the
machine to the left, the patient naturally favors this side.

Our study also evaluated the relationship between pitch, roll, yaw, and gender of our
subject. While we did not find any correlation, a study conducted by Ferrario et al. (1993)
demonstrated that their male and female subjects had statistically significant differences in
pitch. They found that female subjects had a more extended sitting head position, which
affected their studied lateral Fox and Camper planes (Figure 27). This difference in seating
posture was also seen in the Frankfort horizontal plane, which was measured to be 8  for
females and about 5  for males. When both subjects were standing, the horizontal plane
measured 13.2  in females and 13.1  in males, making the difference in standing-seated
Frankfort planes about 5.2  for females and 8.1  for males. These results suggest that male
subjects have a greater extension while standing, and they also tend to be more affected by
46

changes in the standing-to-sitting position than females (Ferrario et al. 1993). Similarly, the
effect of a stronger muscular support system could influence their flexion and neck extension
(Brodal 1972).

Figure 27. The camper line is defined as the tragus-nasal ala line, here depicted by the line
indicated by the arrow.
*Image adapted from Am J Orthod Dentofacial Orthop 1993;103:327-37.

It is also plausible that the difference between our study and Ferrario et al.’s study in
relation to gender, could be due to the variation in our subject’s age. Ferrario et al.’s study used
subjects that were between 20 and 27 years old, with an average age of about 22. However, in
our study, our subject’s, ranged between 12 and 70 years old with an average age of about 35
for females and 38 for males. Ferrario et al. postulates in his study, that the significant
extension of the head is likely due to patient age and a subconscious flexion of the neck. In a
study by Preston et al., they suggest that the tipping back of the head from seating to standing
could also be due to the necessity of an individual to be aware of his/her surroundings and to
enhance the visual field while upright (Ferrario et al. 1993; Preston et al. 1997).

47

When we further examined the correlation between age and pitch, roll, and yaw in our
study, we unsurprisingly found that pitch was the only coordinate that was statistically
significant. The positive linear relationship and coefficient correlation of 8.5% suggests that as
age increases, the pitch coordinate becomes less negative or increasingly more positive. These
results also suggest that as our subject’s age increases, there is an increased tendency to
position the head upwards, and a greater requirement to reorient an imaged head downward
to attain NHP. While a linear correlation exists, these results may not be necessarily clinically
significant.

The results of our findings are similar to a study done by Üsümez et al. (2006) to
determine if there was a statistically significant difference between the means of a static and
dynamic head posture position. The study did not analyze for differences in gender, but their
sample consisted of 25 males and 25 females ranging between 20-25 years old. Üsümez et al.
reported that the mean NHP is less tipped backwards when standing than when seated by
about a 2  average. Furthermore, 41 of their 50 subjects (82%), showed flexed walking head
postures, with their heads tipped forward during walking or when relatively constrained.
Üsümez et al. contribute their findings to the fact that the younger subjects may need to see
where he or she is stepping immediately in front of them, and there is less of a need to be
aware of a distant surrounding.

In either case of the head being tipped forward or backward, the results of our study
and the studies preceding us, demonstrate that NHP is a distinct dynamic position. It is thus
48

essential that each patient be captured in this manner to attain the most ideal diagnostic CBCT
image. While best attempts are made to capture the subject in this natural reference plane,
reliable methods of reorientation are often required to place the patient into this harmonious
natural position for CBCT evaluation and interpretation. Our method presented herein, is a
reliable technique to reorient a patient’s CBCT scan into NHP producing reproducible pitch and
yaw coordinates.

Limitations
One of the biggest limitations of our study, is that the reorientation of the pitch, roll,
and yaw into an ideal position is solely based upon the perception of the operator. While all
the images were reoriented by one operator, it is possible that there is bias and variability in
the data. Similarly, the CBCTs captured are done by radiology technicians trained to the best of
their ability to assess patient asymmetries, abnormalities, and positions. However, it would not
be unlikely that inaccurate positioning occurred, especially in patients with severe mandibular
or other facial asymmetries.

While our sample was of reasonable size, especially in comparison to preceding
research, we did not have equal numbers of male and female subjects. It is possible that our
1:2 ratio of male:female did not permit us to see a relationship between pitch, roll, yaw, and
gender due to the unbalanced sample. However, this male to female ratio is the common trend
seen in the majority of orthodontic offices and samples.

49

The CBCT scans used in our study were all taken by the same machine in the same office
to eliminate environmental error. However, it is possible that the position of the machine in the
room, in addition to the way the patient enters the machine, could affect the orientation of the
patient within the cephalostat. This is especially a plausible error for yaw, in which a patient
may turn one way or another for operator communication. Roll could also be greatly affected,
as the temple/forehead guide in the cephalostat prevents the head from tipping side to side
along the coronal axis. If a patient’s most habitual position is tipped towards the right or left,
the patient would be forced into an unnatural posture for image acquisition.

In contrast to the studies discussed above, no data was captured to compare the patient
in subsequent CBCT images or with multiple repeated time points. Thus, our data was collected
at one point in time, which allowed us to capture NHP in a more static than dynamic position.
Additional information regarding patient positioning while standing or while walking would be
valuable information for future studies. Similarly, it would be valuable to have sequential 3D
images (or CBCTs) without the influence of cranial support (cephalostats).

Since the time that 3D images were taken, the Los Angeles Center for Oral and
Maxillofacial Surgery has modified their imaging technique. Prior to the patient being seated in
the machine, the patient is asked to stand and gaze forward at the horizon. Similar to Weber et
al. (2013), 3 radiopaque stickers are placed on the patient: two in front of the tragus on either
side and one below the iris on the cheek on the right side. The third sticker is used to achieve a
3-point reference. The patient is then guided and seated into the machine before the head is
50

supported by both a temple and chin support. After these xrays are captured, the resulting
images are modified in Dolphin Imaging from a DICOM to a DAC file, utilizing the 3 radiopaque
stickers as references for NHP reorientation. A future study would be especially interesting,
that compares the positional difference between the radiologic team’s reoriented NHP with the
use of extracranial landmarks, to our reorientation method described above.

51

VII. Conclusion

The goal of this study was to compare the method in which 151 CBCT scans were taken,
to a reoriented operator-determined natural head position. The study presented herein,
suggest:
-Roll is a reliable position as captured by the radiologic team.
-Pitch is a position which required operator reorientation to a corrected position – our
patient’s most naturally looked upwards and their heads were reoriented downwards
into ideal position.
-Yaw is also a position which was not accurately positioned by the radiologic team and
required operator modification – our patient’s favored their left side and were
reoriented along the x axis to their right.
-No relationship was seen between pitch, roll, yaw, and gender.
-A weak positive correlation was seen between pitch and age; however, these results
may not be clinically significant.

Further research is required to assess if the new method of clinically determining a
patient’s NHP with radiopaque markers, is a reliable technique in comparison to our method of
NHP orientation.

52

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55

IX. Appendix
Patient
Code
Anonymized
Code Gender DOB Pitch Roll Yaw Age
D1018 1 1 1/31/1976 1.25 -3.75 0.43 40
D1022 2 1 3/14/1987 -1.47 -0.30 -1.99 28
D1032 3 0 3/2/1972 0.74 0.78 2.24 43
D1062 4 0 2/15/2002 0.76 -2.69 -5.53 13
D1100 5 1 8/11/1973 -0.03 1.00 -1.50 42
D1101 6 1 12/25/1975 0.00 0.00 -1.00 40
D1102 7 1 10/22/1989 6.25 0.22 -2.24 26
D1103 8 1 1/31/1996 6.77 -0.96 -0.37 20
D1201 9 1 7/22/1994 0.75 -0.26 0.50 21
D1202 10 1 1/2/1989 4.50 0.00 0.00 27
D1203 11 0 5/24/1956 7.25 -1.25 0.00 59
D1207 12 1 9/3/1988 1.22 -1.18 -3.53 27
D1208 13 1 5/19/1970 -0.05 -1.50 1.75 45
D1209 14 0 11/25/1979 0.01 -3.00 -2.50 36
D1211 15 1 8/28/1994 5.50 0.53 2.31 21
D1212 16 1 9/2/1960 10.00 0.00 0.00 55
D1213 17 0 7/2/1979 0.24 0.75 0.00 36
D1214 18 0 10/20/1970 7.79 -0.65 -2.61 45
D1215 19 1 1/6/1973 0.12 2.25 3.50 43
D1216 20 1 3/8/1979 0.00 0.50 -1.00 36
D1218 21 1 6/30/1951 6.59 1.45 2.68 64
D1219 22 1 8/14/1972 0.01 -2.75 -1.50 43
D1222 23 1 5/30/1998 0.07 -2.25 -1.25 17
D1223 24 1 9/30/1971 4.88 -2.09 -1.93 44
D1225 25 1 8/20/1996 2.25 -1.27 0.45 19
D1226 26 0 10/29/1953 2.99 3.25 0.17 62
D1227 27 1 5/1/1983 4.75 -0.46 -0.54 32
D1228 28 1 4/22/1975 2.00 0.23 0.51 40
D1229 29 1 2/26/1953 0.00 -0.50 -0.25 62
D1230 30 1 9/27/2000 0.00 -1.00 -0.25 15
D1231 31 0 12/5/1997 1.51 -2.29 1.44 18
D1233 32 0 9/7/1953 7.00 0.00 -3.75 62
D1234 33 0 8/9/1997 4.03 0.54 3.04 18
56

D1235 34 0 6/19/1983 2.27 -0.46 -1.02 32
D1236 35 0 7/16/1951 3.12 1.76 -4.66 64
D1237 36 1 2/22/1985 1.01 -3.72 -1.57 30
D1238 37 0 11/13/1976 5.26 0.00 -2.76 39
D1239 38 0 6/12/1970 9.49 0.14 -4.50 45
D1240 39 1 1/7/1999 2.87 -1.22 -5.32 17
D1242 40 0 6/22/1977 2.90 1.08 -6.45 38
D1243 41 1 1/30/1976 9.73 0.77 -1.24 40
D1244 42 0 6/17/1966 6.94 0.94 -7.69 49
D1245 43 1 2/10/1999 -10.43 0.57 -7.98 16
D1247 44 0 9/3/1975 1.99 0.15 -4.25 40
D1248 45 0 11/20/1950 10.46 -3.40 1.91 65
D12489 46 0 7/14/1956 5.74 -1.47 -8.41 59
D1249 47 1 7/12/1960 5.74 0.94 -1.92 55
D1250 48 1 1/21/1986 4.46 -2.04 -6.17 30
D1251 49 0 10/24/1970 2.38 1.69 -4.45 45
D1252 50 1 4/3/1996 -1.00 -1.68 -8.97 19
D1253 51 1 8/17/1986 2.29 -1.33 -4.31 29
D1254 52 1 7/3/1968 8.98 -2.26 -0.10 47
D1255 53 1 1/15/1977 0.84 2.08 -4.97 39
D1256 54 0 10/25/1969 2.04 -0.27 -6.51 46
D1257 55 0 9/15/1986 1.89 -1.84 -5.06 29
D1258 56 0 3/26/1958 0.75 -2.94 -4.54 57
D1259 57 1 2/26/1979 4.92 1.80 -3.36 36
D1260 58 1 5/22/1998 1.68 -0.89 -3.78 17
D1261 59 0 4/15/1991 4.30 -0.21 -7.29 24
D1262 60 0 12/28/1982 -7.61 -1.68 -7.61 33
D1263 61 0 1/17/1993 -0.35 2.22 -8.51 23
D1264 62 0 5/21/1986 1.94 0.70 -5.73 29
D1265 63 1 7/9/1959 1.25 0.09 -4.25 56
D1267 64 1 2/13/1979 0.63 1.31 -5.23 36
D1268 65 1 1/6/1960 5.61 -0.40 -8.83 56
D1270 66 1 9/22/1964 10.18 0.82 -3.98 51
D1272 67 1 1/30/1980 -0.06 1.75 -4.50 36
D1274 68 0 1/8/1962 3.94 -1.84 -6.14 54
D1275 69 1 5/23/1963 0.63 1.80 -4.48 52
57

D1277 70 1 11/25/1997 7.00 0.10 -4.75 18
D1278 71 1 3/22/1978 3.39 0.28 -3.99 37
D1279 72 0 2/21/1992 0.79 -0.71 -3.26 23
D1280 73 1 12/20/1981 4.95 0.84 -3.94 34
D1281 74 1 4/6/2000 2.24 0.25 -6.75 15
D1282 75 1 8/22/1980 -3.18 0.05 -2.39 35
D1283 76 1 1/11/1966 5.40 -2.44 -3.51 50
D1285 77 1 12/10/1984 5.70 0.90 -3.93 31
D129 78 1 9/14/1980 10.23 0.80 -7.22 35
D1290 79 1 12/28/1980 0.80 -1.20 -3.77 35
D1292 80 0 5/18/1988 2.51 -0.13 -2.26 27
D1294 81 1 12/31/1997 1.58 -0.88 -4.53 18
D1295 82 1 10/7/1980 3.29 -0.09 -7.27 35
D1296 83 1 7/24/2000 1.16 1.77 -11.71 15
D1297 84 1 5/10/1971 3.23 0.38 -6.74 44
D1298 85 1 10/3/1963 0.75 0.06 -4.50 52
D1299 86 1 12/28/1982 3.73 -1.30 0.17 33
D1301 87 1 11/15/2003 4.73 0.41 -4.98 12
D1303 88 1 5/20/1962 1.63 -0.78 -8.02 53
D1304 89 1 7/10/1979 2.15 -2.17 -9.58 36
D1305 90 1 12/27/1977 2.44 -3.10 -4.88 38
D1306 91 1 6/2/1985 0.14 -0.99 -8.00 30
D1307 92 1 10/6/1963 1.21 -3.12 -7.05 52
D1308 93 1 11/30/1962 -0.07 1.50 -2.50 53
D1309 94 0 9/20/1962 4.92 1.55 -2.42 53
D1310 95 1 11/6/1982 -0.03 0.50 -4.25 33
D1311 96 1 12/24/1952 0.60 1.57 -6.50 63
D1312 97 1 12/2/1964 1.99 0.20 -5.75 51
D1314 98 1 9/27/1985 -0.07 0.75 -4.75 30
D1316 99 1 1/29/1993 0.00 -3.50 0.00 23
D1317 100 1 12/6/1991 3.83 1.74 -7.15 24
D1318 101 1 1/8/1979 6.92 1.31 -5.70 37
D1319 102 0 5/9/1987 2.58 -0.42 -7.03 28
D1322 103 0 8/6/1982 3.00 0.00 -7.00 33
D1323 104 1 6/3/1977 0.41 0.80 -6.75 38
D1324 105 1 1/13/1989 0.00 0.00 -7.50 27
58

D1325 106 0 6/5/1997 0.69 0.81 -4.49 18
D1326 107 1 3/31/1979 1.24 0.14 -6.75 36
D1327 108 0 9/26/1960 1.64 -4.32 -7.61 55
D1328 109 1 1/23/1983 -0.16 3.00 -3.50 33
D1329 110 0 12/11/1987 2.18 0.74 -6.23 28
D1330 111 1 1/31/1979 0.29 -1.98 -8.75 37
D1333 112 1 1/19/1966 0.10 -1.00 -5.00 50
D1334 113 0 7/15/1955 -0.09 1.00 -3.75 60
D1336 114 0 10/17/2002 0.13 -0.99 -7.75 13
D1337 115 0 8/30/1985 -0.06 0.75 -4.25 30
D1338 116 1 4/18/1979 -0.25 3.74 -3.76 36
D1339 117 1 5/22/1983 0.05 -0.50 -6.00 32
D1340 118 1 2/5/1971 -0.02 0.25 -5.25 44
D1342 119 1 8/7/1998 1.27 -1.57 -9.03 17
D1343 120 0 8/9/1984 1.22 -2.61 -7.55 31
D1344 121 1 5/19/1988 0.05 -0.50 -5.50 27
D1346 122 1 11/27/1959 2.24 0.24 -6.50 56
D1347 123 0 7/18/1970 0.00 0.00 -5.00 45
D1349 124 1 12/29/1953 0.99 0.13 -7.50 62
D1352 125 1 3/30/1974 1.00 4.26 -0.68 41
D1353 126 0 8/31/1975 2.26 2.99 0.57 40
D1354 127 1 9/22/1969 0.01 0.00 -3.00 46
D1355 128 0 1/29/1999 0.82 -0.96 -2.76 17
D1356 129 1 2/4/1998 0.18 -1.49 -6.75 17
D1357 130 1 7/3/1982 0.72 0.55 -3.99 33
D1358 131 1 6/10/1983 0.37 1.06 -7.49 32
D1359 132 1 6/2/1990 1.37 2.59 -3.44 25
D1360 133 0 11/14/1997 0.06 -0.50 -6.50 18
D1361 134 0 11/17/1978 0.87 3.55 -2.94 37
D1363 135 1 4/20/1996 1.97 -1.23 -8.29 19
D1364 136 0 8/17/1959 1.99 0.17 -4.75 56
D1365 137 0 7/21/1983 0.37 1.54 -5.98 32
D1366 138 0 2/6/2001 1.99 0.21 -7.00 14
D1367 139 1 8/31/1983 -0.04 1.00 -3.25 32
D1368 140 0 6/29/1996 1.10 -0.86 -7.52 19
D1369 141 1 11/4/1987 1.43 -1.57 -8.04 28
59

D1370 142 1 2/1/1945 4.50 -0.66 -7.72 71
D1371 143 0 8/8/1955 2.44 -2.85 -4.12 60
D1372 144 1 9/22/1990 -1.27 -2.19 -7.70 25
D1373 145 1 4/2/1972 0.31 2.53 -4.50 43
D1375 146 1 2/7/1993 0.08 -1.00 -5.50 22
D1376 147 1 12/24/1985 1.16 -1.65 -5.53 30
D1377 148 1 8/26/1979 4.88 -0.90 -8.74 36
D1378 149 1 6/24/1975 3.81 -0.35 -7.09 40
D1379 150 1 7/28/2000 -4.23 -0.41 -6.48 15
D1380 151 1 7/16/1978 0.33 -1.48 -5.25 37

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Core Title Operator-determined and reoriented natural head position in three-dimensional imaging

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Defense Date 02/26/2016

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