Variations in bracket placement in the preadjusted
orthodontic appliance
Nasib Balut, DDS, MS," Lewis Klapper, DMD, DScD, PhD, b James Sandrik, MS, PhD, = and
Douglas Bowman, MS, PhD '
Me.rico City, Me.rico, am/Chicago, IlL
This study was conducted to determine the accuracy of bracket placement with the direct bonded
technique. Ten orthodontic faculty members bonded a preadjusted orthodontic appliance on models
of five cases of malocclusion in a simulated clinical situation (mannequin). A total of 50 sets of
models served as the population of the study. Photographs of the models were measured to
determine vertical and angular discrepancies in position between adjacent bracket pairs from a
constructed reference line. Variations are evaluated with respect to the classification of malocclusion,
specific tooth type, and intra/inter operator differences. A mean of 0.34 mm for the vertical
discrepancies and a mean of 5.54 ~ for the angular discrepancies are found in placement of the
orthodontic brackets. (AMJ ORTHOD DENTOFACORTHOP 1992;102:62-7.)
T h e prcadjusted bracket system is the most
widely used in orthodontic therapy today. The basic
premise of the preadjusted system is that proper bracket
position allows the teeth to be positioned with a straight
wire into an ocelusal contact with excellent mesiodistal
inclinations (tips) and excellent faciolingual inclination
(torque).
Most clinicians are aware that clinically the "straight
wire" (preadjusted) appliance does not eliminate wire
bending. Variations in tooth structure and malocclusions affect the final bracket positions. Variations from
the straight wire appliance averages must be compensated by bends placed in the arch wires.
The present study was designated to evaluate variations in placement in the vertical and angular bracket
position from the ideal with a preadjusted orthodontic
appliance ("A" Company, Johnson & Johnson, San
Diego, Calif.). Variations in bracket position were evaluated with respect to the classification of maloeclusions,
specific tooth type, and intra/inter operator differences.
REVIEW OF THE LITERATURE
Bracket placement and tooth structure
Originally Angle t taught that the best position of
the band was where it fits better mechanically. Then,
if possible, the bracket should be placed at the center
of the labial surface of the tooth. Later, placement of
'Associate Professor, Universidad Intercontinental Mexico.
bAssociate Professor, Loyola University of Chicago.
'Chairman of the Department of Dental Materials, Loyola Uniser~ity of
Chicago.
aAssc,ciate Professor of Biostatistics, Lo) ola University of Chicago.
8 / I / 27285
62
the anterior bands at the junction of the middle and the
incisal thirds of the crown was recommended. 2 Ricketts 3
advocated the use of marginal ridges as guidelines for
band and bracket vertical positioning.
More recently, Andrews 47 introduced the bracketing technique of placing the straight guidelines of the
bracket (vertical tie wings) parallel to the long axis of
the clinical crown and then moving the bracket up or
down until the middle of its slot base is at the same
height as the midpoint of the clinical crown.
Thurow 8 showed that two different vertical positions
of a bracket on a tooth will cause two different buccolingual axial inclinations (torque).
Meyer and Nelson 9 showed that an error of 3 mm
vertically in bracket placement on a premolar can result
in 15~ torque alteration and 0.04 mm alteration in the
in/out adjustments.
In orthodontics, what affects the design of the orthodontic appliances and their use is the inclination of the
labial or buccal surface of the tooth crown to the long
axis of either the entire tooth or the occlusal surface of
the crown.
Kraus, t~ Taylor, 2 and Dellinger tt found great variations existed in tooth structure that can affect treatment
results.
Improvements in bracket design were made incorporating tip, ~torque, ~2rotation, and differences in base
thickness 47.13 beginning with Angle in 1928 and, more
recently, with Andrews in 1970 who introduced the
"straight wire concept" in preadjusted orthodontic appliance.
Roth 14 in 1975 evaluated the preadjusted bracket
system after he had used it for 5 years. In 1981 he
Volume 102
Nunzber I
Variations in bracket placement in preadjusted appliance
63
Fig. 2. Occlusal view of one =diagnostic set-up" showing occlusal contacts checked with articulating ribbon,
as a template for the final ideal tooth position desired for each
case.
Fig. 1. Front view of one "diagnostic set-up" showing idea! angulation where teeth were positioned.
modified the appliance by altering the amount of preadjustment built into the brackets? 5 His objectives were
to have the teeth in overcorrected positions at the end
of treatment when unbent, full-sized wires were used.
All modifications and improvements in orthodontic
appliances were predicated on the ability of the clinician
to accurately visualize and correctly place the bracket
on the tooth. No one has actually studied how well this
is accomplished clinically.
METHODS AND MATERIALS
Pretreatment models of five orthodontic patients re'presenting different types of malocclusion were selected. One
Class I, two Class II, Division 1, and two Class II, Division
2 malocclusion cases were taken from the Orthodontic Department at Loyola University School of Dentistry. The models were duplicated and a "diagnostic set-up" was fabricated
from the duplicate models (Fig. 1). The teeth were positioned
to "ideal" angulation (agreed ideal according to Andrew.'s six
keys of occlusion, as modified by Roth) and occlusal contact
and checked with articulating ribbon (Accu-Film, Parkell,
Farmingdale, N.Y.) (Fig. 2).
An acrylic occlusal registration key (upper and lower)
was fabricated from each diagnostic set-up. The key served
Ten faculty members from the Orthodontic Department
of Loyola University School of Dentistry were the subjects
of this study. Each faculty member was asked to place preadjusted brackets ("A" Company) on five duplicated pretrcatment orthodontic patient models, from first molar to first
molar, inclusively. The models were mounted on a mannequin
to simulate the patient (Fig. 3).
A total of 50 bonded cases of malocclusions served as
the population for this study (10 faculty members • 5 cases).
After the brackets were placed in the untreated models,
the teeth Were sectioned from the base. The sectioned teeth
were transferred to the occlusal registration made from the
diagnostic set-up for that patient and secured in place with
adhesive (cyanoacrylate).
The sectioned teeth secured with adhesive to the occlusal
registration were designated at the "transfer set-up." This
represents the ideala relationship of teeth desired in the finished case (Fig. 4).
Five photographs were taken of each transfer set-up oriented perpendicular to the crown of the teeth at a fixed distance
with a 90 mm macro lens (Panagor) and Minolta 35 mm
single lens reflex camera body. The lens was set on a 1:1
magnification ratio.
The resulting photographs were digitized on a Houston
Instrument Hi-Pad digitizer. The outer edges of each bracket
slot were used as reference. The vertical and angular differences in brackets positions were measured between tooth pairs
by digitizing the outer edges of each bracket with a program
written for an IBM mainframe computer (IBM Corp., White
Plains, N.Y.).
The measurements were calculated from a reference line
that was formed by connecting the outer edges of adjacent
bracket pairs. The vertical measurements were calculated by
measuring the difference between the perpendicular distance
64
Balut e t a / .
Am. J. Orthod. Dente~w. Onhvp.
July 1992
Fig. 3. Duplicate model mounted on mannequin showing direct bonded brackets in place.
A
B
Fig. 4. Transfer set-up.
of the adjacent slot edges to the reference line (Fig. 5). The
angular measurements were calculated from the difference
between the arctangents of the slopes of the individual brackets to a reference line connecting the outer occlusal edges of
the slots of the adjacent bracket pair (Fig. 5).
If the four points ',,,'ere on the reference line, the linear
and angular values would be "zero" for each tooth pair: (This
would indicate ideal bracket placement on the models.) Any
linear or angular differences observed represent errors in
bracket placement.
Two-way analysis of variance was used to determine
whether differences exist, and multiple comparison procedures were made by a Tukey's HSD test to determine where
the differences exist. The experimental error of this study was
determined by repeating measurements of two facult2r members (10 cases) with a paired t test for the linear and angular
measurements. A mean of 0.005 mm of linear difference ',,,'as
found, and a mean of 0.087 ~ of angular difference was found,
which was not statistically significant.
Fig. 5. Independence of vertical and angular relationships between adjacent bracket pairs. A, Bracket pair with both vertical
(line A not equal to line B) and angular differences to the reference line. B, Bracket pair with vertical difference but no angular difference to the reference line. C, Bracket pair with angular difference but no vertical difference (line E equals line F)
to the reference line.
RESULTS
Discrepancies w e r e found in p l a c e m e n t o f the orthodontic brackets in height and angulation. A m e a n o f
0.34 m m for the linear m e a s u r e m e n t s and a mean o f
5.54 ~ for the angular m e a s u r e m e n t s were found (Table
Volume 102
Variations in bracket placement in preadjusted appliance
Number I
65
Table I. Mean, standard deviation, range, maximum values and minimum values of the linear and
angular discrepancies
Standarddeviation
(SD)
Range
0.34
0.29
5.54
4.32
Mean = X
Linear discrepancies
(mm)
Angular discrepancies
(degrees)
I
I
Maximum
value
Minbnum
value
1.80
1.80
0.00
29.10
29.10
0.00
Table II. Mean, standard deviation range of the vertical and angular discrepancies by faculty
Mean
Faculty
N = 110
Linear
1
2
0.38
0.35
3
4
5
6
0.26
0.33
0.34
0.34
7
8
9
10
0.31
0.32
0.42
0.36
]
Range
SD
Angular
Linear
6.02
4.87
5.77
5.12
6.76
4.48
5.21
5.40
6.33
5.48
0.28
0.30
0.22
0.26
0.29
0.28
0.27
0.29
0.34
0.31
I) between adjacent bracket pairs (all faculty members,
all teeth).
Table II shows the mean, standard deviation, and
range of the linear and angular discrepancies by faculty,
indicating statistically significant differences in angular
bracket position among faculty no. 2, no. 5, and no.
6. For the linear measurements, statistically significant
differences were found between faculty no. 3 and no.
9 (P --< 0.01).
When the linear and angular discrepancies among
the five models were analyzed, there was no significant
difference among them in vertical discrepancy
(P -> 0.05). Model no. 2 (Class II) showed significantly
less angular discrepancy than Model no. 5 (Class II)
(P -< 0.01).
Tables III and IV indicate that the lower anterior
teeth presented the least variation in bracket placement, in both angular and vertical measurements
(P ~ O.OOl). The teeth that showed the most angular
discrepancy were the upper anterior teeth and the upper
and lower canines (P ~ O.OOl). The upper second premolars were the teeth which presented the most vertical
discrepancy in bracket placement (P < O.OOl).
DISCUSSION
Toward the end of the treatment, the teeth must be
brought as close as possible to their final and functional
I
Angular
Linear
4.54
4.11
4.47
3.71
5.12
3.21
4.07
3.85
5.07
4.31
1.30
1.62
1.03
1.11
1.56
1.11
1.25
1.36
1.79
i.55
I
Angular
20.79
21.20
23.61
17.06
24.30
13.06
18.26
17.25
29.01
19.63
positions before debonding. This necessitates a perfect
alignment of the marginal ridges, contact points, and
roots of the teeth. Factors such as error in bracket placement, tooth irregularities, and variations in tooth structure make it difficult to achieve these goals accurately
with the preadjusted orthodontic appliance.
In this study, model no. 2 had significantly less
angular discrepancy than model no. 5. The reason was
that model no. 5 had a lower right first premolar severely
malposed. The crowding and the size of the clinical
crown of that specific tooth made it impossible to place
the bracket correctly. In addition, model no. 2 had
larger clinical crowns, not severely rotated teeth, making it less difficult for the operator to place the orthodontic brackets. There is no correlation between the
type of malocclusion and the error in bracket placement.
The error in placement seems to be more related to
the skill of the operator, tooth structure, size of clinical
crowns, and malposition of the tooth in the dental arch.
In some cases, the operator has to compromise and
place the bracket more gingivally because of interference with the long cuspal heights on opposing posterior
teeth. Since any effect o f bracket/tooth interference was
exchuted fronz this study, tile actual clinical accuracy
of bracket positioning on the posterior teeth wouhl be
much worse on a patient than was shown here.
It appears that it was easier for the operators to
66
Balut el al.
Am. J. Orthod. Dentofiw. Orthop.
July 1992
Table III. Mean of angular discrepancies of each faculty by tooth pair in degrees
Tooth pair
(n = 5)
Mttrillary arch
i-I
1-2
2-1
2-3
3-2
3-4
4-3
4-5
5-4
5-6
6-5
Mandibular arch
1-1
1-2
2-1
2-3
3-2
3-4
4-3
4-5
5-4
5-6
6-5
5
10.30
7.14
5.87
6.97
6.61
6.24
8.20
4.76
6.03
3.95
2.90
13.29
2.96
5.45
4.76
5.54
4.14
4.95
2.21
5.87
5.52
3.72
7.42
6.40
4.32
7.72
7.09
3.95
5.49
3.64
5.27
3.84
8.34
6.46
3.56
4.04
3.13
4.08
4.87
5.58
2.62
5.36
3.86
6.80
7.16
7.10
4.93
8.33
8.89
13.17
7.05
6.23
8.31
3.24
9.93
4.80
4.52
6.91
7.41
1.96
5.95
5.53
3.25
3.18
3.56
3.99
2.95
4.12
4.02
6.60
6.96
5.58
6.52
1.91
7.69
3.94
3.32
6.27
3.32
4.92
6.01
9.43
4.44
7.93
5.23
7.30
6.05
7.57
7.76
3.51
5.32
6.88
3.73
7.12
5.39
5.89
5.56
5.48
8.50
8.69
3.61
6.16
4.32
6.14
11.61
5.98
5.64
4.13
7.69
6.49
7.56
4.62
5.19
6.21
6.04
6.90
6.26
4.13
5.87
4.71
6.15
4.11
5.33
5.92
5.22
6.56
5.72
11.16
4.29
4.24
4.15
4.80
3.37
2.98
3.56
5.58
5.55
3.00
7.01
3.82
2.28
7.99
3.54
3.72
2.27
4.28
3.68
4.79
5.99
9.32
8.44
8.39
6.77
5.34
4.74
3.09
2.32
7.77
5.38
9.70
6.28
7.02
5.20
8.46
2.24
3.11
3.21
7.12
4.31
6.08
6.63
6.97
7.00
7.56
4.72
7.65
2.14
4.13
6.44
4.05
2.48
4.66
5.55
4.11
4.21
3.86
5.90
2.93
4.66
2.10
5.78
5.83
7.52
7.77
7.89
4.45
7.73
4.44
3.85
4.52
3.29
7.24
4.25
3.65
5.14
4.39
4.82
6.19
2.92
5.94
7.12
5.66
11.63
9.30
9.10
7.83
7.59
3.26
4.47
2.32
2.35
2.74
4.35
4.62
3.48
6.61
6.10
5.69
5.63
9.95
3.51
3.62
4.00
4.50
5.98
5.37
6.25
7.31
6.02
5.00
5.93
4.26
Table IV. Mean of vertical discrepancies by tooth pair in millimeters
Fact~
Tooth pair
(n = 5)
Mttrillary arch
1-1
I-2
2-1
2-3
3-2
3-4
4-3
4-5
5-4
5-6
6-5
0.27
0.57
0.67
0.54
0.66
0.52
0.33
0.37
0.24
0.62
0.55
0.24
0.44
0.57
0.18
0.63
0.39
0.66
0.45
0.30
0.75
0.30
0.27
0.24
0.60
0.16
0.27
0.28
0.40
0.19
0.24
0.30
0.28
0.11
0.44
0.51
0.23
0.30
0.44
0.19
0.35
0.34
0.61
0.36
0.14
0.46
0.31
0.26
0.17
0.42
0.47
0.48
0.28
0.63
0.63
0.33
0.40
0.39
0.33
0.13
0.46
0.19
0.44
0.31
0.87
0.65
0.06
0.21
0.16
0.23
0.33
0.50
0.31
0.52
0.35
0.82
0.32
0.18
0.21
0.36
0.18
0.12
0.45
0.37
0.55
0.69
0.82
0.57
0.13
0.28
0.48
0.58
0.41
0.54
0.21
0.33
0.44
0.63
0.38
0.21
0.55
0.33
0.29
0.30
0.49
0.20
0.36
0.23
0.99
0.28
0.19
0.37
0.44
0.30
0.33
0.44
0.33
0.40
0.34
0.70
0.43
Mandibular arch
I-I
I-2
2-1
2-3
3-2
3-4
4-3
4-5
5-4
5-6
6-5
0.22
0.19
0.19
0.31
0.31
0.33
0.33
0.37
0.31
0.18
0.22
0.22
0.06
0.17
0.41
0.26
0.11
0.44
0.39
0.30
0.30
0.23
0.13
0.06
0.11
0.28
0.42
0.18
0.29
0.35
0.34
0.20
0.23
0.16
0.21
0.22
0.29
0.27
0.34
0.39
0.46
0.34
0.45
0.20
0.11
0.26
0.26
0.27
0.40
0.22
0.34
0.37
().47
0.21
0.34
0.19
0.19
0.14
0.14
0.50
0.34
0.34
0.30
0.33
0.24
0.31
0.19
0.14
0.17
0.29
0.31
0.19
0.37
0.22
0.45
0.43
0.43
0.22
0.14
0.23
0.18
0.21
0.28
0.37
0.26
0.39
0.13
0.06
0.37
0.25
0.42
0.82
0.69
0.68
0.37
0.28
0.38
0.34
0.23
0.31
0.15
0.19
0.30
0.47
0.31
0.48
0.51
0.44
0.40
0.18
0.21
0.16
0.21
0.33
0.38
0.29
0.37
0.35
0.37
0.28
0.21
Volume 102
Number 1
visualize the long axes of the lower incisors and to
place the bracket appropriately and at the correct height.
The upper anterior teeth and the upper and lower
canines showed the most angular discrepancy. It appears that the operators have difficulty in judging root
angulation of these teeth.
The teeth that presented the most difficulty in vertical bracket placement were the upper second premolars, possibly because of the length of their clinical
crowns (which are sometimes short). This is exacerbated by the molar arch wire slot being gingivally positioned on the molar as a result of the headgear tube
being occlusally positioned.
The observed mean angular discrepancy of 5.54 ~
plus the standard deviation of 4.32 ~ indicates that a
bracket error of 10~ between bracket pairs, with the "A"
Company appliance, would occur with the same frequency as a bracket pair placed in perfect alignment.
This is somewhat surprising when one considers that
few orthodontists request more than 10~ of tip be built
into their preadjusted appliance prescriptions.
Although 3 of the 10 faculty members differed statistically in their angular bracket placement measurements, their vertical measurements were statistically
indistinguishable (means of 0.35 mm, 0.34 ram, and
0.34 mm). Those two faculty members who differed
statistically in their vertical bracket placement showed
no statistical differences in their angular bracket placement measurements (means of 5.77 ~ and 6.33~
No faculty member was statistically different from
any of the other faculty members in both vertical and
angular discrepancies in bracket placement. This indicates that there is no systematic difference among the
faculty members in bracket placement. It would be reasonable to assume that the errors of the faculty represent
what would be expected of orthodontic practitioners in
general. These can be seen as independent variables in
this study because of the method with which the measurements were referenced and the manner in which
bracket positional variation may occur. Figs. 5, A to C
illustrate the manner in which vertical and angular .discrepancies may occur independently of each other.
The fact that the majority of the faculty members
were so similar in their results seems to indicate a basic
human limitation in direct placement of the brackets in
the mouth.
The clinical implications in the error of bracket
Variations bl bracket placenlent in preadjltsted appliance
67
placement in this study are unstable tooth positions,
lack of root paralleling, food impaction because of marginal ridge discrepancies, and failure to establish the
very specific occlusal scheme of canine rise or mutually
protected occlusion.
It should not be interpreted froth this study that
achievement of acceptable orthodontic results is impossible with straight wire therapy. With proper wire
bending or rebonding bracket positions, an excellent
result can certainly be achieved; however, increased
time and effort must be expended by the orthodontist
and the patient to accomplish these goals.
REFERENCES
1. Angle HE. The latest and best in orthodontic mechanism. Dental
Cosmos 1928;70:il43; 1929;71:164.
2. Taylor RMS. Variations in morphology of teeth. New York:
Charles C. Thomas, 1978.
3. Ricketts MR. Biopr~gressive therapy. Denver: Rocky Mountain
1979.
4. Andrews FL. The Straight Wire Appliance origin, controversy,
commentary. J Clin Orthod 1976;10:99.
5. Andrews FL. Straight Wire Appliance, arch form, wire bending
and experiment. J Clin Orthod 1976;10:8.
6. Andrews FL. The S.W.A. explained anad compared. J Clin
Orthod 1976;10:174.
7. Andrews FL. The S.W.A. syllabus of philosophy and techniques. San Diego: LF Andrews Foundation for Orthodontic
Education and Research, 1974.
8. Thurow CR. Edgewise orthodontics. 3rd. ed. St. Louis: CV
Mosby, 1972.
9. Meyer M, Nelson G. Preadjusted edgewise appliance, theory
and practice. AM J OR'nlOD 1978;73:485.
10. Kraus SB. Dental anatomy and occlusion. Chapter I. Baltimore:
Williams and Wilkins, 1969.
11. Dellinger LE. A scientific assessment of the straaight wire appliance. AM J OR'IIIOD 1978;73:290.
12. Jarabak RL. Development of a treatment plan, in the light of
one's concept of treatment objectives. AM J ORTHOD
1969;36:481.
13. Andrews FL. The six keys to normal occlusion. AM J OR.'RIOD
1972;62:296.
14. Roth HR. Five years clinical evaluation of the Andrews S.W.A.
J Clin Orthod 1981;11:175.
15. Roth HR. Functional occlusion for the orthodontists, part i11.
J Clin Orthod 1981;11:175.
Reprint requests to:
Dr. Nasib Balut
Manuel E. Izaguirre 11-601-602
CTO Comercial Satelite
EDO de Mexico City
Mexico 53100