Original Article

The Effect of Vertical and Horizontal Head Positioning in

Panoramic Radiography on Mesiodistal Tooth Angulations

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Ian W. Mckee, DDS, MSca; Kenneth E. Glover, DDS, MSDb; Philip C. Williamson, DDS, MScc;
Ernest W. Lam, DMD, PhDd; Giseon Heo, BSc, PhDe; Paul W. Major, DDS, MScf

Abstract: The purposes of this study were to examine the effect of potentially common patient positioning
errors in panoramic radiography on imaged mesiodistal tooth angulations and to compare these results with the
imaged mesiodistal tooth angulations present at an idealized head position. A human skull served as the matrix
into which a constructed typodont testing device was fixed according to anteroposterior and vertical cephalo-
metric normals. The skull was then repeatedly imaged and repositioned five times at each of the following five
head positions: ideal head position, 58 right, 58 left, 58 up, and 58 down. The images were scanned and digitized
with custom software to determine the image mesiodistal tooth angulations. Results revealed that the majority
of image angles from the five head positions were statistically significantly different than image angles from
the idealized head position. Maxillary teeth were more sensitive to 58 up/down head rotation, with 58 up causing
mesial projection and 58 down causing distal projection of maxillary roots. Mandibular anterior teeth were
more sensitive to 58 right/left head rotation, with the projected mesiodistal angular difference between 58 right
and 58 left rotation ranging from 4.08 to 22.38. Maxillary teeth were relatively unaffected by 58 right/left head
rotation, and mandibular teeth were relatively unaffected by 58 up/down head rotation. It was concluded that
the clinical assessment of mesiodistal tooth angulation with panoramic radiography should be approached with
extreme caution with an understanding of the inherent image distortions that can be further complicated by the
potential for aberrant head positioning. (Angle Orthod 2001;71:442–451.)
Key Words: Axial inclination; Root parallelism; Head rotation; Patient positioning

INTRODUCTION ment is often performed clinically, panoramic radiography

Orthodontists critically evaluate crown and root position is frequently used to visualize root parallelism and mesio-
before, during, and after orthodontic treatment in the pursuit distal tooth angulation.1–3
of excellence of the occlusal result. Whereas this assess- In his well-known study, Andrews4 stated that normal
occlusion is dependant on, among other factors, the correct
a
Senior Orthodontic Resident, Division of Orthodontics, Faculty
mesiodistal inclination (or tip). Other investigators have
of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, found that appropriate axial inclinations and root parallel-
Canada. ism are important for proper occlusal and incisal function
b
Professor and Chairman, Division of Orthodontics, Faculty of Med- of the teeth and are an important component in maintaining
icine and Dentistry, University of Alberta, Edmonton, Alberta, Canada. a stable treatment result.1,5–10 This has special significance
c
Clinical Assistant Professor, Division of Orthodontics, University
of Alberta, Edmonton, Alberta, Canada. in the orthodontic extraction case, where extraction sites are
d
Associate Professor, Division of Radiology, Faculty of Medicine prone to open if roots are insufficiently paralleled.5,7,10
and Dentistry, University of Alberta, Edmonton, Alberta, Canada. Although panoramic radiography offers numerous diag-
e
Faculty Lecturer, Department of Mathematical Sciences, Faculty nostic and prognostic uses in orthodontic diagnosis and
of Science, University of Alberta, Edmonton, Alberta, Canada.
f
Professor, Division of Orthodontics, Faculty of Medicine and
treatment planning, the machinery produces images with
Dentistry, University of Alberta, Edmonton, Alberta, Canada. variable magnification factors (both horizontal and verti-
Corresponding author: Dr Paul Major, Faculty of Medicine and cal), resulting in angular distortion.11 Various investigators
Dentistry, Room 1043, Dentistry/Pharmacy Center, University of Al- have studied panoramic image generation in an attempt to
berta, Edmonton, Alberta, Canada T6G 2N8 quantify the dimensional accuracy of the images.2,3,12–40
(e-mail: major@ualberta.ca).
Based on a thesis submitted by Dr Mckee in partial fulfillment of the Although convenient to make, the panoramic radiograph
degree of Master’s of Science, Division of Orthodontics, Faculty of Med- is extremely technique and operator sensitive. Schiff et al22
icine and Dentistry, University of Alberta, Edmonton, Alberta, Canada. reported that the most frequent errors in panoramic radi-
Accepted: March 2001. Submitted: January 2001. ography occurred in patient positioning. In a study of 1000
q 2001 by The EH Angle Education and Research Foundation, Inc. panoramic films, the relative frequency of positioning errors

Angle Orthodontist, Vol 71, No 6, 2001 442

PANORAMIC HEAD POSITION AND TOOTH ANGULATIONS 443

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FIGURE 1. Initial typodont testing device.

was as follows: 14% chin too low, 4% head tilted, 4% head lif) with an idealized occlusion from second molar to sec-
turned, and 1% chin too high.22 In conventional panoramic ond molar (Figure 1). For each tooth, two chromium steel
radiography, the image layer is significantly narrower in the balls (Commercial Bearing, Edmonton, Alberta, Canada)
anterior region, and blurring and distortion are least in the measuring 1.58 mm in diameter were glued into position
center of the image layer.18,24,25,27,29,39 Failure to position the following preparation with a #2 round bur. The occlusal
patient’s dental arches accurately causes variation in both ball was placed in the buccolingual and mesiodistal mid-
vertical and horizontal magnification, resulting in angular point of the crown on the occlusal/incisal surface, whereas
distortion of the image.25 Investigations into the effect of the placement of the apical ball into the root surface de-
vertical and horizontal rotation of a skull or testing device pended on the tooth being prepared. Excluding maxillary
on angular measurements revealed that the canine/premolar and mandibular first and second molars and maxillary first
region of both arches expressed the largest amount of dis- bicuspids, the apical ball was placed into the buccolingual
tortion.17,38 Xie et al40 assessed the accuracy of vertical mea- and mesiodistal midpoint of the root in the apical third. For
surements taken from panoramic radiographs. They rec-
teeth displaying dilaceration in the apical third, the apical
ommended selecting a horizontal reference line that is lo-
dilaceration was removed with a diamond disc to remove
cated anatomically directly above or below the point being
the effect of dilaceration on long axis determination. For
measured and in the plane of the center of the image layer,
rather than a reference plane distant from the site of mea- the remaining teeth, the apical ball was placed in the center
surement.40 of the bifurcation/trifurcation. These steel balls served as
Considering that the inherent dimensional inaccuracy of reference markers for image angle determination, and an
panoramic images is compounded by the variability of pa- imaginary line joining the centers of the occlusal and apical
tient positioning, it seems reasonable to believe that the balls was used to represent the long axis of each typodont
assessment of mesiodistal angulations of teeth cannot be tooth.
reliably performed on panoramic films. The purposes of this The maxillary and mandibular typodont was then bonded
study were to examine the effects of varying horizontal and with 0.022-inch-slot clear orthodontic brackets (Spirit,
vertical head rotations of an anatomic typodont/skull testing Ormco Corporation) to idealized bracket positions, and a
device on image mesiodistal angulations from the Ortho- passive 0.020-inch round stainless steel archwire (Permach-
pantomograph (OP 100; Instrumentarium, Munich, Ger- rome resilient/Orthoform III, 3M Unitek, Monrovia, Calif)
many) and to compare these findings to the image mesio- was ligated into position with elastomeric modules (Figure
distal angulations from an idealized head position. 2).
MATERIALS AND METHODS
Typodont positioning into skull
Test device design
The test device consisted of a clear anatomic maxillary A dried adult human skull with complete natural denti-
and mandibular typodont (Ormco Corporation, Orange, Ca- tion and class I skeletal and dental relation served as the

Angle Orthodontist, Vol 71, No 6, 2001

444 MCKEE, GLOVER, WILLIAMSON, LAM, HEO, MAJOR

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FIGURE 2. Modified typodont testing device.

matrix into which the typodont dentition was fixed for sub- on lateral cephalometric image). (Modification of the
sequent panoramic imaging (Figure 3). McNamara analysis measurements was calculated by
The glenoid fossa was remodeled with cold-cure acrylic adding the 14-year-old norm for nasion perpendicular to
resin to provide positive seating of the condyle. This en- Frankfort horizontal to A-point (3.8 mm) to the 14-year-
sured reproducible mandibular opening/closing and a stable old norm for A-point parallel to nasion perpendicular to
centric occlusion supported by both typodont tooth inter- Frankfort horizontal to facial surface of upper incisor
cuspation and condyle/glenoid fossa fit. Chromium steel (1.2 mm); total distance nasion perpendicular to Frank-
balls measuring 1.58 mm in diameter were fixed to the skull fort horizontal to facial surface of upper incisor 5 5
at the following positions to confirm that the vertical, an- mm.
teroposterior, and transverse positions of the typodont den- 3. Vertical
tition conformed to pre-established norms: a. Nasion to maxillary central incisor edge 5 76 mm
(linear distance measured on skull).
1. Nasion—the junction of the nasal and frontal bones at
b. Occlusal plane cant to Frankfort horizontal (PoOr) to
the most posterior point on the curvature of the bridge
occlusal plane 5 98 (measured on lateral cephalo-
of the nose.
metric image).
2. Right and left anatomic porion—the most superior point
of the external auditory canal (anatomic porion).
The maxillary typodont was then rigidly fixed to
3. Pogonion—the most anterior point on the contour of the
the skull
chin.
The position of the mandibular typodont dentition in all
The natural maxillary dentition, supporting bone, and
three planes of space was determined by its centric occlu-
portions of the skeletal maxilla were removed, and the max-
sion articulation with the maxillary typodont. The dental
illary typodont dentition was temporarily wired into place
relationship of the articulated typodont was a fully inter-
with ligature wires. Multiple anthropometric, lateral, and
digitated class I molar and cuspid relation with 2-mm over-
postero-anterior (PA) cephalometric measurements were
jet, 2-mm overbite, and coincident dental midlines. The
made with subsequent movements of the maxillary typo-
mandibular typodont dentition was firmly ligature-tied to
dont until the following positions were obtained:
the maxillary typodont dentition, and the natural mandib-
1. Transverse—bisection of the midpoint of the incisal steel ular dentition, supporting bone, and portions of the skeletal
balls on typodont teeth #11 and 21 with a line joining mandible were removed. The skeletal mandible was then
the steel balls placed at nasion and pogonion (measured rotated upward (ensuring full seating of the condyle in the
on PA cephalometric image). glenoid fossa) until the pre-existing vertical dimension of
2. Anteroposterior—nasion perpendicular to Frankfort hor- the skull was achieved (distance nasion to pogonion 5 108
izontal (PoOr) to upper incisor edge 5 5 mm (measured mm). The mandibular typodont was then rigidly fixed to

Angle Orthodontist, Vol 71, No 6, 2001

PANORAMIC HEAD POSITION AND TOOTH ANGULATIONS 445

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FIGURE 3. Typodont/skull testing device.

the skeletal mandible, and the intermaxillary ligature wires 3. Camera tripod—fully adjustable vertical and horizontal
were released. Lateral and PA cephalometric analyses of controls.
the finalized movements revealed attainment of positioning
goals and a remarkably ‘‘normal’’ dental-to-skeletal and Panoramic radiographs
dental-to-dental relation as shown: The skull and head holder assembly was positioned into
1. Upper incisor to Frankfort horizontal (PoOr) 5 1088. an Orthopantomograph OP 100 at five separate times at
2. Lower incisor to mandibular plane (GoMe) 5 948. each of the following five head positions and exposed:
3. Interincisal angle 5 1328. 1. Ideal position: 08 horizontal rotation, 08 vertical rotation.
2. 58 right: 58 ‘‘right’’ horizontal rotation, 08 vertical rota-
Head holder tion.
3. 58 left: 58 ‘‘left’’ horizontal rotation, 08 vertical rotation.
A custom-designed radiolucent head holder (Mechanical 4. 58 up: 08 horizontal rotation, 58 ‘‘head up’’ vertical ro-
Engineering, University of Alberta, Edmonton, Alberta, tation.
Canada) was constructed to ensure the validity of the hor- 5. 58 down: 08 horizontal rotation, 58 ‘‘head down’’ vertical
izontal and vertical head rotation about a reproducible axis rotation.
of rotation (Figure 4). The head holder consisted of three
components: Optimum image density and contrast was achieved at
exposure settings of 57 KVP, 2.0 mA, and 17.6 seconds.
1. Hollow cylinder—permanently attached to the exterior The object was to position the skull to simulate the desired
surface of the skull at foramen magnum. position of the patient’s head in the panoramic unit and to
2. Solid cylinder—precision-machined end attached into represent common patient positioning errors (Figure 5). For
hollow cylinder and connected at its base via internal the idealized head position, the Frankfort horizontal was
screw threads to the mounting screw on the camera tri- aligned with the horizontal light guide, the midsagittal
pod. plane was aligned with the vertical light guide, and the

Angle Orthodontist, Vol 71, No 6, 2001

446 MCKEE, GLOVER, WILLIAMSON, LAM, HEO, MAJOR

Palo Alto, Calif, Hewlett Packard Desk Scan II, Palo Alto,
Calif, Corel Photopaint 6.0 Ottawa, ON, Canada, Crusher-
soft Software, Edmonton, AB, Canada) on a Dell Dimen-
sion XPS D433 PII IBM-compatible PC. The order of land-
mark identification was standardized for all radiographs and
involved the following 4 points for each tooth angle deter-
mination:

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1. TC9 (tooth crown): the center of the occlusal steel ball.
2. TR9 (tooth root): the center of the apical/furcal steel ball.
3. WD9 (wire distal): intersection of a computer-generated
vertical midpoint between adjacent teeth (on the distal
side of the tooth being measured) and the image of the
reference archwire.
4. WM9 (wire mesial): intersection of a computer-generated
vertical midpoint between adjacent teeth (on the mesial
side of the tooth being measured) and the image of the
reference archwire.
Upon completion of digitization of each panoramic im-
age, the program generated an Excel spreadsheet of the im-
age mesiodistal angulation (determined as the angle formed
by lines constructed between the reference points TC and
TR and between WD and WM) for the 24 teeth.

Error of the method and statistical analysis

The principal investigator undertook all typodont/skull
modifications, skull positioning, and image angle measure-
FIGURE 4. Skull and head holder. ments.
The total error of each image angle measurement was a
incisal edges of the maxillary and mandibular incisors were combination of the error of measurement (ie, digitization)
placed into the notched bite block. For the horizontal (right and the error of repeated head positioning for each of the
and left) rotations, markings placed on the frontal bone of five head positions. To determine the error of digitization,
the skull at 58 ‘‘right’’ and 58 ‘‘left’’ assisted in alignment one of the 25 images was randomly selected, and each tooth
with the panoramic unit’s vertical light guide while keeping was digitized five consecutive times. The error of digiti-
the Frankfort horizontal aligned with the horizontal light zation ranged from 0.458 to 0.868. The average total error
guide. For the vertical (up and down) rotations, markings and standard deviation for each head position’s image angle
placed on the lateral surface of the skull at 58 ‘‘head up’’ measurements were as follows: ideal, 0.968 (0.578); 58 right,
and 58 ‘‘head down’’ assisted in alignment with the pano- 1.328 (1.038); 58 left, 1.388 (0.978); 58 up, 0.998 (0.478); 58
ramic unit’s horizontal light guide while keeping the mid- down, 2.288 (3.058).
sagittal plane aligned with the vertical light guide. Paired t-tests were completed for each tooth to detect
The combined head holder and tripod assembly ensured angular differences between the idealized head position and
that the right and left rotation occurred about the center of each of the four head positions (58 right, 58 left, 58 up, and
foramen magnum (ie, vertical axis of rotation) and that the 58 down). Significance levels of less than .05 were consid-
up and down rotation occurred about the incisal edges of ered to be statistically significant.
the maxillary and mandibular incisors and bite block as-
sembly (ie, horizontal axis of rotation). RESULTS
The mean and standard deviation values for the image
Image angle determination
mesiodistal angulations for all 24 teeth are presented in Ta-
Custom-designed software (Mechanical Engineering, ble 1. Paired t-tests comparing the idealized head position
University of Alberta) was utilized to calculate the mesio- individually to 58 right, 58 left, 58 up, and 58 down head
distal angulation of the typodont teeth relative to the ref- positions are presented in Table 2.
erence archwire from the 25 panoramic images. The radio- The majority of maxillary and mandibular image angles
graphs were scanned with a resolution of 600 dpi and mag- (64%) from the 4 head positions were statistically signifi-
nification of 200% (Hewlett Packard Scan Jet 6100 C/T, cantly different from image angles from the idealized head

Angle Orthodontist, Vol 71, No 6, 2001

PANORAMIC HEAD POSITION AND TOOTH ANGULATIONS 447

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FIGURE 5. Panoramic images from the Orthopantomograph OP 100 at each of the 5 head positions. (A) Ideal head position. (B) 58 right. (C)
58 left. (D) 58 up. (E) 58 down.

position. Examination of Figures 6 and 7 reveals a common 42, and 43. As mentioned previously, 58 up and down had
pattern between the varying head positions. For the max- less of an effect on mandibular root projection than did 58
illary teeth, 58 up and 58 down head rotations had a much right and left rotations.
more pronounced effect on deviations from idealized head Table 3 reports the total envelope of angulation error sep-
position than did 58 right and 58 left head rotations. Where- arately for horizontal head rotation and vertical head rota-
as 58 up resulted in a mesial projection of all maxillary tion. Horizontal head rotation had the greatest distorting
roots (teeth #11 and 21 remained unchanged), 58 head down effect on the mandibular anterior teeth, with a perceived
resulted in a distal projection of all maxillary roots. The angular difference between 58 right and 58 left rotation of
maxillary canine and first and second premolars displayed 48 to 22.38. Vertical head rotation had the greatest distorting
the most distortion, and the maxillary central incisor the effect on the maxillary anterior and posterior teeth (exclud-
least distortion for the up and down head rotations. For the ing teeth #11 and 21), with a perceived angular difference
mandibular teeth, 58 right caused the anterior roots to in- between 58 up and 58 down rotation of 7.68 to 14.98.
cline to the right, thereby increasing the mesiodistal angu-
lation of teeth #41, 42, and 43 while decreasing the mesio- DISCUSSION
distal angulation of teeth #31, 32, and 33. Similarly, 58 left
caused the anterior roots to incline to the left, thereby in- Considering that only one panoramic unit was used in
creasing the mesiodistal angulation of teeth #31 and 32 this study, the results can only be applied to the Orthopan-
while decreasing the mesiodistal angulation of teeth #41, tomograph OP 100. However, a companion study imple-

Angle Orthodontist, Vol 71, No 6, 2001

448 MCKEE, GLOVER, WILLIAMSON, LAM, HEO, MAJOR

TABLE 1. Mean and Standard Deviation Value for the Image Mesiodistal Angulations by Tooth Number (in Degrees)a
Image Angles (5 Head Positions)
Ideal Position 58 Right 58 Left 58Up 58 Down
Tooth No. Mean SD Mean SD Mean SD Mean SD Mean SD
16 97.1 0.4 98.9 0.5 96.5 1.0 92.7 0.4 102.8 0.6
15 98.3 0.9 101.3 0.9 99.9 1.1 92.7 0.6 105.3 0.9

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14 98.0 0.4 99.1 0.7 101.0 1.4 90.7 0.8 104.9 0.9
13 97.0 0.9 97.2 0.7 99.2 0.7 91.2 0.7 101.7 0.7
12 92.6 0.7 92.2 0.6 94.3 0.8 90.1 0.6 97.7 0.6
11 90.0 0.9 89.3 0.8 89.9 0.3 89.6 1.0 91.1 0.7
21 94.1 1.2 94.0 0.6 93.8 0.6 94.0 0.9 95.4 0.6
22 94.0 0.8 96.1 0.6 95.2 0.8 91.2 0.6 98.9 0.6
23 93.1 1.0 94.5 1.4 95.9 1.2 87.9 1.2 100.4 1.3
24 98.2 0.6 99.0 1.2 100.9 0.8 91.3 0.8 106.2 1.1
25 93.0 0.8 91.4 0.6 96.4 0.6 86.9 0.6 99.6 0.4
26 94.7 0.6 93.9 0.7 97.9 0.8 90.6 1.3 100.0 0.5
36 85.3 0.6 88.7 0.6 81.1 0.6 87.5 0.7 84.3 1.4
35 87.0 0.6 89.3 0.6 82.9 0.9 89.8 0.8 86.0 1.0
34 86.3 0.7 86.6 1.1 82.9 0.6 88.5 1.4 86.3 1.1
33 84.5 1.1 80.5 2.3 84.5 0.7 87.8 1.4 87.1 1.8
32 89.1 1.6 80.8 3.9 95.3 2.8 89.8 1.4 97.1 5.5
31 92.7 2.3 85.6 3.2 102.9 2.1 92.8 2.0 101.6 9.1
41 91.7 2.4 100.3 3.9 78.0 3.1 89.8 2.2 90.4 12.0
42 90.0 1.9 94.6 2.3 75.9 2.2 87.6 1.4 91.0 7.4
43 87.8 1.2 89.4 1.6 76.0 3.5 89.3 1.3 90.2 2.6
44 86.8 0.3 85.1 1.1 80.9 3.3 89.4 0.9 87.3 0.8
45 89.3 0.9 86.7 0.8 91.8 2.2 93.3 0.5 89.2 1.7
46 86.0 0.5 83.4 1.0 89.4 0.8 89.0 0.5 84.8 1.3
a
A mesiodistal angulation value greater than 908 indicates a distal inclination to the root. A mesiodistal angulation value less than 908
indicates a mesial inclination to the root.

menting four different panoramic units with the same test- and buccolingual inclinations represented in the human
ing device at a standardized head position revealed striking dentition.
similarities and trends between panoramic units in their The results of this study revealed that most of the image
overestimation and underestimation of tooth angulations.41 angulations from the four aberrant head positions were sta-
In addition, although the results can only be applied to the tistically significantly different from the image angulations
typodont tooth angulations represented, the skull/typodont at the ideal head position. The application of clinically sig-
testing device was reasonably anatomic in design. The arch nificant tolerance limits should be applied to this research.
form, arch dimensions, and positioning of the dentition Previous investigators have reported that for clinical pur-
within the skull could represent a clinical situation. Al- poses, variations of as much as 2.58 (in either direction)
though the true buccolingual angulations of the typodont between a tooth and an established reference plane does not
were not determined, lateral cephalometric measurements constitute a serious objection to the use of the radio-
graph.12,17,38 Application of these clinically significant tol-
of the upper and lower incisor angulations revealed posi-
erance limits revealed that 53% of the maxillary and man-
tioning well within a range of normal.
dibular image angles from the four head positions were still
This testing device is in contrast to previous studies using
clinically significantly different from the image angles at
nonanatomic tooth angulations with considerably less atten-
ideal head position.
tion to jaw positioning within the panoramic unit’s image The relative sensitivity of the maxillary tooth angulations
layer.2,17,38 Lucchesi et al2 used a Plexiglas mandibular mod- to up/down skull rotation and of the mandibular tooth an-
el with steel pins placed at mesiodistal angulations selected gulations to right/left rotation is difficult to explain. Hori-
randomly but confined to a range of 220 to 120 degrees. zontal head rotation alters the object-film and source-object
Three-dimensional positioning of the model into the pan- distances, resulting in varying degrees of horizontal and
oramic unit used not a skull, but rather placement within vertical magnification, and therefore angle distortion. Hor-
the unit’s chin rest. Other investigators have relied on steel izontal head rotation also alters beam projection angle. With
wire meshes to depict arch form and dimension.17,38 The the image layer being narrowest in the anterior dental re-
lead shot utilized to represent tooth angulations was usually gion, it is possible that the mandibular anterior teeth are
orientated with total disregard for the unique mesiodistal less tolerant of horizontal rotation.

Angle Orthodontist, Vol 71, No 6, 2001

PANORAMIC HEAD POSITION AND TOOTH ANGULATIONS 449

TABLE 2. Paired t-test Comparisons of Mesiodistal Tooth Angulations at Varying Vertical and Horizontal Head Positions vs Idealized Head
Position (Mean Difference in Degrees)a
58 Right vs Ideal 58 Left vs Ideal 58 Up vs Ideal 58 Down vs Ideal
Mean Mean Mean Mean
Tooth No. Difference P Value Difference P Value Difference P Value Difference P Value
16 1.9 .001* 20.6 .191 24.4 .001* 5.7 .001*
15 3.0 .014* 1.6 .090 25.6 .001* 7.0 .001*

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14 1.2 .031* 3.0 .004* 27.2 .001* 6.9 .001*
13 0.2 .736 2.2 .023* 25.8 .001* 4.7 .001*
12 20.4 .454 1.7 .008* 22.4 .004* 5.2 .001*
11 20.7 .372 20.1 .820 20.4 .372 1.0 .168
21 20.1 .903 20.4 .617 20.1 .925 1.3 .072
22 2.2 .014* 1.2 .088 22.8 .009* 4.9 .001*
23 1.4 .053 2.8 .012* 25.2 .001* 7.3 .001*
24 0.9 .243 2.8 .001* 26.9 .001* 8.0 .001*
25 21.6 .014* 3.4 .001* 26.1 .001* 6.6 .001*
26 20.8 .038* 3.2 .002* 24.1 .006* 5.3 .001*
36 3.5 .001* 24.1 .002* 2.2 .002* 20.9 .069
35 2.3 .005* 24.1 .001* 2.8 .004* 21.0 .126
34 0.3 .563 23.4 .002* 2.2 .062 0.0 .988
33 24.0 .005* 0.0 .987 3.3 .005* 2.6 .068
32 28.3 .008* 6.2 .006* 0.8 .290 8.0 .044*
31 27.2 .006* 10.2 .001* 0.1 .906 8.9 .119
41 8.6 .019* 213.7 .003* 21.9 .261 21.3 .798
42 4.6 .042* 214.1 .001* 22.4 .122 1.0 .725
43 1.6 .208 211.8 .003* 1.5 .198 2.4 .035*
44 21.7 .013* 25.9 .016* 2.6 .003* 0.4 .383
45 22.5 .021* 2.6 .054 4.1 .001* 20.1 .958
46 22.6 .003* 3.4 .003* 3.0 .001* 21.2 .069
a
Mean difference 5 (deviated head position, ie, 58 right, 58 left, 58 up, or 58 down) 2 (idealized head position).
* A P value of less than .05 is considered statistically significant.

FIGURE 6. Mean angular difference of the image (4 varying head FIGURE 7. Mean angular difference of the image (4 varying head
positions) vs image (idealized head position) mesiodistal angulations positions) vs image (idealized head position) mesiodistal angulations
for maxillary teeth by tooth number. for mandibular teeth by tooth number.

The possibility that aberrant head positioning or mea- validity of the horizontal and vertical head rotation about a
surement error could have been responsible for true/image reproducible axis of rotation. In addition, the skull posi-
angle differences must be considered. However, great care tioning was repeated five times for each machine to estab-
was taken in the use of all machine guides for skull posi- lish a data set of five measurements for each tooth. Sub-
tioning. Use of a custom-designed head holder ensured the jectivity of landmark identification on the scanned panto-

Angle Orthodontist, Vol 71, No 6, 2001

450 MCKEE, GLOVER, WILLIAMSON, LAM, HEO, MAJOR

TABLE 3. Total Envelope of Error for Combined Horizontal (58 CONCLUSION

Right/58 Left) and Combined Vertical (58 Up/58 Down) Head Rotation
(Mean Angular Difference in Degrees) The following conclusions can be drawn from this study:
Horizontal Head Rotation Vertical Head Rotation
1. The majority of maxillary and mandibular image angles
Mean Mean
(64%) from the 4 head positions were statistically sig-
Angular Angular
Tooth No. Difference SD Difference SD nificantly different from image angles at the idealized
head position.

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16 2.5 0.6 10.1 0.8
15 1.4 1.1 12.6 1.2
2. Vertical head rotation (58 up and 58 down) had a much
14 1.8 1.2 14.1 1.5 more pronounced effect on the deviation of maxillary
13 2.0 0.7 10.5 0.7 angle projection. Conversely, horizontal head rotation
12 2.1 1.1 7.6 0.4 (58 right and 58 left) had a much more pronounced effect
11 0.6 0.6 1.4 1.2 on the deviation of mandibular anterior angle projection
21 0.3 0.6 1.4 1.1
22 1.0 0.7 7.7 1.2
from truth.
23 1.4 2.3 12.5 2.1 3. Application of clinically significant tolerance limits of
24 1.9 1.6 14.9 1.2 2.58 revealed that 53% of the maxillary and mandibular
25 5.0 0.8 12.7 0.6 image angles from the four head positions were still clin-
26 4.0 1.0 9.4 1.6 ically significantly different from the image angles at
36 7.6 0.7 3.1 1.4
35 6.4 1.3 3.8 0.6
ideal head position.
34 3.7 1.4 2.2 1.7 4. The clinical assessment of mesiodistal tooth angulation
33 4.0 2.3 0.7 3.0 with panoramic radiography should be approached with
32 14.5 3.0 7.2 6.9 extreme caution, with an understanding of the inherent
31 17.4 1.8 8.8 10.7 image distortions that are further complicated by the po-
41 22.3 2.4 0.6 13.6
42 18.7 0.5 3.4 8.6
tential for aberrant head positioning.
43 13.4 3.1 0.9 3.7
44 4.2 3.7 2.2 1.2 ACKNOWLEDGMENT
45 5.1 2.0 4.2 1.9
46 6.0 1.3 4.2 1.5
The Rayburn McIntyre Memorial Fund supported this study. We
acknowledge the mathematical and software design assistance of Kent
West, BSc, MSc.
mography images was reduced by using the center of the
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Angle Orthodontist, Vol 71, No 6, 2001