ORIGINAL ARTICLE

Assessment of skeletal and dental changes by maxillary

protraction

Sang J. Sung, DDS, MSD,a and Hyoung S. Baik, DDS, MSD, PhDb
Seoul, Korea

To further evaluate the effect of maxillary protraction on facial growth, cephalometric changes in 129
subjects with conditions diagnosed as skeletal Class III malocclusion and who had been treated with
maxillary protraction were compared to 9 male and 12 female subjects with annual cephalometric records
from the Yonsei growth study sample. The control subjects had Angle Class I malocclusions with normal
overjet and overbite. More maxillary forward displacement and mandibular growth inhibition were observed
in the protraction group during treatment, and the difference from the untreated controls was statistically
significant. When changes due to treatment according to ages were compared, there was no statistical
difference. The direction of maxillary growth was similar in the untreated and protraction groups. Maxillary
protraction had a growth-stimulating effect on the maxilla during the treatment period. (Am J Orthod
Dentofacial Orthop 1998;114:492-502)

T here have been many studies on morpho- pubertal and pubertal period can shorten treatment
logic features, developmental features, and growth pat- time, and if mandibular growth is properly controlled
tern of skeletal Class III malocclusion.1-3 Camouflage after the treatment, favorable anterior occlusion can be
treatment is possible in mild to moderate skeletal Class obtained.11,20 Nonetheless, improvement of the facial
III cases; however, for growing patients with moderate profile is inferior to what can be achieved in surgical-
to severe skeletal problems, orthopedic appliances orthodontic patients because the actual length of
such as chin cup and maxillary protraction headgear mandible, which is excessive in skeletal Class III
are indicated.4-20 patients, cannot be reduced.14,28
Maxillary protraction is recommended for skeletal The effects of maxillary protraction that are seen on
Class III patients with maxillary deficiency.5-7 The the lateral cephalogram include forward and downward
principle of maxillary protraction is to apply tensile movement of the maxillary bone and dentition, lingual
force on the circumaxillary sutures and thereby stimu- inclination of mandibular teeth, and downward and
late bone apposition in the suture areas; in doing so, the backward rotation of the mandible.12,13,18 These effects
maxillary teeth become the point of force applica- tend to turn Class III malocclusion into Class I occlu-
tion,9,11 and the face (forehead, chin, zygoma) or occip- sion and produce an orthognathic profile in a short
ital area becomes the anchorage source.8,15 In ani- period of time. Nevertheless, whether maxillary pro-
mal21-23 and biomechanical studies,24,25 histologic traction can actually stimulate growth is still obscure,
changes and stress distribution in suture areas strongly and questions have been raised as to the orthopedic
suggest the application in human subjects. effect in prepubertal or pubertal subjects.14,16
One of the most important factors to consider in The purpose of this study was to examine whether
treating skeletal Class III patients with orthopedic force maxillary protraction brings skeletal changes, how
is the optimal treatment timing.26,27 Early intervention skeletal and dental changes progress with aging, and
facilitates growth modification, but there may be diffi- whether growth is actually stimulated by maxillary
culty in retaining treatment effects through the growth protraction, by comparing control and maxillary pro-
period, necessitating long-term treatment and patient traction groups during and after treatment.
cooperation.10,16 Orthopedic treatment during the pre-
MATERIAL AND METHODS
From the Department of Orthodontics, College of Dentistry, Yonsei University, Subjects
Seoul, Korea.
aResearch Fellow. The protraction group consisted of 129 subjects age
bProfessor and Chairman. 7 to 13 years, who were treated at Youngdong-Sever-
Reprint requests to: Dr. Hyoung S. Baik, Department of Orthodontics, College ance Hospital, Yonsei University. Their conditions
of Dentistry, Yonsei University, CPO Box 8044, Seoul, Korea.
Copyright 1998 by the American Association of Orthodontists. were diagnosed as skeletal Class III malocclusion with
0889-5406/98/$5.00 + 8/1/87875 a deficient maxilla as compared to the Korean norm.19
492
American Journal of Orthodontics and Dentofacial Orthopedics Sung and Baik 493
Volume 114, Number 5

Table I. Age and sex distribution of untreated and protraction subjects

Untreated group Protraction group
Age interval
(Years) Male Female Subtotal Male Female Subtotal

7-8 9 12 21 12 6 18
8-9 9 12 21 8 12 20
9-10 9 12 21 6 14 20
10-11 9 12 21 7 23 30
11-12 9 12 21 7 16 23
12-13 9 12 21 11 7 18
Total 129

For the untreated group, annual follow-up of 9-male and 12-female subjects was done from age 7 to 13.

Table II. Comparison of initial cephalometric values of the untreated and protraction groups
Age 7 Age 12

Untreated Protraction Untreated Protraction

Mean SD Mean SD Mean SD Mean SD

Angular ()
SNA 80.17 3.01 * 78.56 2.59 80.43 1.76* 78.35 2.76
SNB 74.93 2.54*** 78.97 1.98 76.44 1.88 ** 78.65 2.64
ANB 5.22 1.57*** .49 1.88 3.98 1.37 *** .31 2.10
MP 32.98 3.40** 30.58 2.68 31.46 3.40 32.37 3.94
Linear (mm)
MxL 46.20 2.49* 43.53 2.49 49.42 2.32 ** 47.44 1.40
MnL 96.02 3.38 * 101.29 5.90 111.30 3.55 114.41 5.83
Wits 1.48 4.08 *** 6.92 2.72 2.73 1.74 *** 7.05 3.35
Number 22 18 21 18

Paired t test between the untreated group and protraction group: *, P < .05; **, P < .01; ***, P < .001.

As untreated controls, 9 males and 12 females with lon- appliance with bands on first molars, was used as the
gitudinal records who showed Angle Class I molar intraoral appliance, and Delaires face mask was used
relationship on lateral cephalograms along with normal as the extraoral appliance. The RPE appliance was
anterior overbite and overjet were selected from the used for expansion in patients with a constricted max-
Yonsei growth study sample. Both the protraction and illa. It was also used in some patients who needed no
untreated groups were divided into six age groups maxillary expansion because it holds the maxilla as
(Table I). one rigid unit. In the primary dentition of patients who
In addition, 22 children 10 to 12 years of age who needed expansion, primary canines and primary molars
came for follow-up checks after maxillary protraction were banded for the RPE placement. The La/Li appli-
were chosen as follow-up subjects. They were com- ance was used only for mixed dentition patients who
pared with the untreated group of age 11 patients for needed no expansion. Force from the face mask was
treatment effects, and with the untreated group of age applied to a hook that was positioned about 8 mm
12 patients for 1 year posttreatment changes. In almost superior to the occlusal plane and at the mesial side of
all the patients in the follow-up protraction group, night maxillary first premolar of RPE appliances, or at the
wear of a chin cup was recommended after crossbite posterior side of the deciduous canine of La/Li appli-
correction, and was continued until the initiation of ances. The force vector was about 25 downward and
fixed appliance treatment. forward to the occlusal plane. The face mask was used
for more than 12 hours a day, with about 300 to 400 gm
Methods forces on each side.
Maxillary protraction device and methods. A rapid Analysis of lateral cephalograms. For the protrac-
palatal expansion (RPE) appliance with bands on first tion patients, lateral cephalograms were taken before
molars and first premolars and a soldered palatal and after anterior crossbite correction, which required
framework with jackscrew, or a labiolingual (La/Li) 8 to 9 months for most children. For the untreated con-
494 Sung and Baik American Journal of Orthodontics and Dentofacial Orthopedics
November 1998

Fig 2. Assessment of direction of jaw displacement and

rotation.

value were taken. The palatal plane angle (PP) and

mandibular plane angle (MP) were measured to the X-
axis. For the measurement of the direction of maxillary
displacement, the angular displacement of point A to
X-axis (A-angle) was calculated as Arctangent [(verti-
cal changes of point A) / (horizontal changes of point
Fig 1. X-Y axis and cephalometric landmarks. A)] * 57.3 (Fig. 2).
After the landmark location, the measurements
were digitized and calculated by the Yonsei cephalo-
trol, cephalograms were taken annually from the age of metric analysis program on an IBM-compatible PC.
7 to 13. The S-N (sella-nasion) plane was used as a ref- Statistical analysis. Annual growth amounts were
erence for overall superimposition; in consideration of measured by superimposition of cephalograms in the
the growth changes of sella and nasion, stable struc- untreated group, and treatment changes were measured
tures of the anterior cranial base were also used.12,29 by the difference in landmark location before and after
Cephalometric measurements were taken by one per- correction of anterior crossbite in the protraction
son, and to validate reproducibility of the measure- group. The mean and standard deviation of the changes
ments, 20 randomly selected cephalograms were in all cephalometric measurements of all groups were
retraced after a 1-week interval. Correlations between calculated.
the double measurements were then analyzed in terms Paired t tests were performed to observe the signifi-
of vertical, horizontal, and angular measurements. The cance of differences between the amounts of growth or
correlation coefficients between the double measure- treatment change within each group. A group t test was
ments in all three cases were over 0.9.30 performed to compare growth of the untreated and pro-
A horizontal reference plane (X-axis) was created traction groups, to evaluate the orthopedic effect of max-
for the linear and angular measurements. This refer- illary protraction. Analysis of variance (ANOVA) was
ence plane was set up from the point sella with a 6 done among the different age groups of untreated and
downward inclination to S-N line. A line perpendicular protraction patients to examine differences due to age.
to the X-axis at point sella was constructed as the ver-
tical reference plane (Y-axis) (Fig. 1). RESULTS
Vertical and horizontal linear measurements were There were statistically significant differences (p <
made for the following seven points: point A, PNS, 0.001) in growth amount of the untreated and protrac-
point B, incisal edge of the maxillary incisor (MxI), tion groups in the six groups that were divided accord-
mesial cusp tip of the maxillary first molar (MxM), ing to ages.
incisal edge of the mandibular incisor (MnI), and
mesial cusp tip of the mandibular first molar (MnM). Comparison of initial cephalometric values of the
Maxillary length (MxL) was measured by the distance untreated and protraction groups (Table II)
along the X-axis between ANS and PNS, and mandibu- At the ages of 7 and 12 years, the protraction group
lar length (MnL) was measured by the distance showed maxillary deficiency with decreased SNA
between condylion (Co) and pogonion (Pog). Measure- angle and maxillary length, and moderate to severe
ments of the SNA, SNB, and ANB angles and the Wits skeletal Class III malocclusion tendency by the Wits
American Journal of Orthodontics and Dentofacial Orthopedics Sung and Baik 495
Volume 114, Number 5

Fig 3. Superimposition of protraction cases of different age groups (before and after treatment).

analysis. In the untreated groups, there was a tendency untreated group according to ages, so the data for
for SNA and SNB to be smaller than the Korean norms, males and females were combined.
but the ANB angle and Wits value were within normal
range.19 Comparison of the changes in the untreated and
protraction groups (Table III)
Statistical significance of the changes and gender The duration of treatment was between 7.8 and 9.1
difference months, and changes that occurred during this period
When the protraction group and untreated group were compared with the annual growth amount of the
were divided according to ages to make comparisons, untreated group. The growth rate of the untreated
significant differences were noted between the amount group was similar to that of the Ann Arbor samples.26
of changes and annual growth. There was almost no When the protraction and untreated groups of the same
gender difference in either the protraction group or the age were compared, vertical changes of point A were
496 Sung and Baik American Journal of Orthodontics and Dentofacial Orthopedics
November 1998

Table III. Comparison of the changes of untreated and protraction groups according to ages
Age 7 Age 8 Age 9

Untreated Protraction Untreated Protraction Untreated Protraction

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

Horizontal (mm)
A 0.3 0.9*** 2.8 1.4 0.4 0.7*** 2.0 1.2 0.8 0.8** 2.1 1.4
PNS 0.3 1.1*** 1.1 0.9 0.2 1.0*** 0.7 1.2 0.4 1.0*** 1.0 1.0
B 0.2 1.4* 1.7 1.6 0.5 1.0* 2.1 1.8 0.9 1.5* 2.6 2.7
MxI 1.8 1.5*** 4.8 2.8 1.9 1.4** 3.7 1.9 1.6 1.0 2.4 2.3
MxM 0.2 1.1*** 3.6 1.7 0.5 1.1*** 3.0 1.9 1.1 1.0** 3.3 2.7
MnI 1.6 1.8*** 0.8 1.9 1.4 1.3*** 1.5 1.6 1.2 0.9*** 2.4 2.2
MnM 0.9 1.0*** 0.2 1.3 0.7 l.1** 0.7 1.7 1.0 1.1* 0.4 2.1
Vertical (mm)
A 1.4 0.7 1.3 1.3 1.7 0.8* 0.8 1.0 1.4 0.8 1.2 0.9
PNS 1.3 0.7 1.7 0.9 1.4 1.0 1.4 1.1 1.0 0.6** 1.8 1.1
B 2.5 1.3 2.8 2.4 2.5 0.9 2.7 1.5 2.6 0.9 3.2 2.3
MxI 3.2 4.5 2.6 3.4 3.3 3.6 1.6 1.4 2.7 1.8 2.1 1.6
MxM 3.7 2.1 3.5 1.9 2.7 1.4 3.0 1.5 2.1 0.6* 3.2 2.1
MNI 1.2 2.1 2.1 2.4 1.8 1.1 1.9 1.5 1.3 0.9 1.8 2.0
MnM 0.8 2.0 1.8 1.7 2.2 0.7* 1.6 1.0 2.0 0.6 2.4 1.8
Angular ()
SNA 0.5 1.0*** 2.1 1.5 0.6 1.0*** 1.7 1.1 0.2 1.0** 1.7 1.4
SNB 0.0 0.7*** 1.4 1.1 0.1 0.7*** 1.3 1.0 0.4 0.9*** 1.3 1.4
ANB 0.4 0.7*** 3.4 1.4 0.5 0.7*** 2.9 1.2 0.1 0.7*** 3.0 2.0
PP 0.1 1.1 0.4 1.3 0.3 1.2** 0.8 1.5 0.2 0.9** 0.9 1.3
MP 0.0 1.2*** 2.2 1.6 0.1 0.8*** 1.7 1.1 0.3 0.9*** 1.6 1.4
Linear (mm)
MxL 0.5 1.2*** 1.5 1.5 0.7 1.1** 1.3 1.3 0.9 1.0* 1.3 1.2
MnL 3.3 0.8*** 1.2 2.0 2.6 1.1*** 0.6 1.9 2.4 1.4* 1.2 1.3
Wits 0.1 2.9*** 4.7 3.1 0.1 2.9*** 4.2 1.8 0.3 1.6*** 4.8 2.9
Age (yrs) 7.0 0.0 7.8 0.9 8.0 0.0 8.6 0.4 9.0 0.0 9.6 0.3
Period (mo) 12.0 0.0 8.4 2.4 12.0 0.0 7.8 3.9 12.0 0.0 8.9 3.8
Number 21 18 2l 20 21 20

Group t test between the untreated group and protraction group: *, P < .05; **, P < .01; ***, P < .001.

similar or less, but horizontal changes in the protraction were similar to those of the untreated group (1.6 to
group were twice to four times those of the untreated 3.7 mm).
group (P < .05). The horizontal changes of point B in
the protraction group were from 1.7 to 2.7 mm, Comparison of follow-up subjects in the protrac-
which were opposite to those of the untreated group tion and untreated groups (Table IV)
(0.2 to 2.2 mm) (Figs. 3 and 4B). The mandibular plane The horizontal changes of point A in the protrac-
angle decreased with age in the untreated group, and tion group during the first year posttreatment
increased in the protraction group (P < .001). The decreased to one half of the amount during the active
palatal plane angle decreased slightly in the protraction protraction period. The vertical changes of point A
group at all ages, but increased slightly or stayed the during posttreatment were similar to those during
same in the untreated group. protraction, but one third of the amount in the 12-
The horizontal changes of maxillary central year-old untreated group. Mandibular length in the
incisors were from 2.4 to 4.8 mm in the protraction protraction group showed only a 0.4 mm increase dur-
group, which were greater than those of the untreated ing treatment, but it increased 2.7 mm during the
group (1.0 to 1.9 mm). In addition, the horizontal posttreatment period. Nonetheless, it was still less
changes of the maxillary central incisors in the pro- than the annual growth amount of untreated group of
traction group were greater than those of A point (1.7 age 12.
to 2.8 mm). The vertical changes of maxillary molars The mandibular plane angle increased 2.1 during
in the protraction patients were 2.5 to 3.5 mm, which treatment period, but it decreased 1.1 during 1 year
American Journal of Orthodontics and Dentofacial Orthopedics Sung and Baik 497
Volume 114, Number 5

Age 10 Age 11 Age 12

Untreated Protraction Untreated Protraction Untreated Protraction

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

0.6 0.8*** 2.2 1.2 1.3 1.0* 2.1 1.3 0.6 1.2* 1.7 0.6
0.2 l.0*** 1.2 1.3 0.6 1.0*** 0.8 0.9 0.3 1.3* 0.8 0.7
0.7 l.0*** 2.3 2.3 2.2 1.4 2.0 2.5 0.4 1.8 2.7 3.1
1.0 1.0*** 3.1 2.2 1.9 1.3 2.9 2.8 1.0 1.4** 3.3 2.2
0.8 0.9*** 3.9 2.7 2.1 1.5 3.4 2.6 1.0 1.8 2.1 1.5
1.2 1.0*** 1.8 1.9 1.9 1.3*** 1.3 1.8 0.5 1.6* 1.4 2.5
1.1 0.7** 0.3 1.8 2.4 1.3*** 0.4 1.3 1.9 1.6* 0.3 2.2

1.4 0.7* 0.9 1.0 1.0 0.9 0.9 0.9 2.7 1.3* 1.3 1.1
1.1 1.0 1.6 1.0 1.3 0.9 1.4 1.2 1.5 0.7 1.4 0.6
2.4 1.0 2.9 1.5 1.9 1.0 2.8 1.8 4.7 2.2 4.1 2.5
1.9 0.9 1.3 1.1 1.1 0.9 1.3 1.4 3.5 1.0 2.2 2.0
1.6 0.6** 3.0 1.5 2.0 0.8 2.5 1.9 3.5 1.0 3.0 1.5
1.8 1.1 1.9 1.3 1.1 0.9** 2.4 1.8 3.3 1.2 3.0 2.3
1.8 0.8 2.1 1.1 1.9 1.0 2.0 1.5 2.1 1.0 2.8 1.9

0.0 0.9*** 1.7 1.4 0.5 0.8*** 2.0 1.3 0.3 1.0 1.0 0.9
0.2 0.6*** 1.4 1.0 0.8 0.6*** 1.1 1.1 0.5 0.7** 1.6 1.6
0.2 0.7*** 3.1 1.6 0.3 0.8*** 3.0 1.8 0.2 0.5 2.5 2.0
0.3 1.4** 1.1 1.9 0.2 1.1 0.4 1.5 0.4 1.0 0.4 2.1
0.0 0.7*** 1.5 1.2 1.1 0.9*** 1.7 1.7 0.5 1.1*** 2.1 1.4

0.7 1.1* 1.2 1.0 0.7 1.2** 1.3 1.3 0.5 1.5* 1.2 1.0
2.6 1.6*** 0.8 1.4 2.9 1.5*** 0.4 1.5 4.8 2.4 *** 0.6 1.5
0.6 1.3*** 4.9 2.9 0.1 1.2*** 4.7 2.9 0.0 1.1** 4.2 3.9
10.0 0.0 10.6 0.3 11.0 0.0 11.5 0.5 12.0 0.0 12.7 0.4
12.0 0.0 7.9 2.2 12.0 0.0 8.3 3.4 12.0 0.0 9.1 3.6
21 30 21 23 21 18

posttreatment. The mandibular teeth and point B be affected along with the maxilla, both must be con-
moved more anteriorly during the posttreatment period sidered. Sakamoto et al.5 and Sugawara et al.7 reported
(Fig. 4A). that although chin cup treatment temporarily reduces
mandibular growth rate and alters growth direction, the
DISCUSSION treatment effect may be unstable because catch-up
In respect to the relationship between facial growth growth occurs once the application of orthopedic force
and development of malocclusion, Enlow31 studied the stops.
prevalence of brachycephalic and prognathic facial
profiles in the Far East and Central Europe. In the Changes in length of the jaws
patient population at Youngdong-Severance Hospital, In untreated children, the maxilla is displaced for-
the prevalence of Angle Class III malocclusion is about ward and downward from the anterior cranial base, the
40%.32 In many cases, both patients and parents prefer posterior portion of maxilla shows constant downward
trying orthopedic treatment during growth to waiting movement and there is an increase in maxillary body
for orthognathic surgery after growth completion; thus, length.33,34 The sutural reaction to protraction can be
maxillary protraction has become the first choice in estimated by analyzing changes in the maxillary length
orthopedic treatment of growing skeletal Class III mal- on the lateral cephalogram; this can be obtained by
occlusion patients. either directly measuring the distance between anterior
The effect of growth modification by maxillary pro- and posterior landmarks on maxilla10,16 or comparing
traction can be interpreted in terms of changes in size, the spatial changes of anterior and posterior land-
position, and growth rate.26 Because the mandible can marks.17,18 In this study, maxillary length was obtained
498 Sung and Baik American Journal of Orthodontics and Dentofacial Orthopedics
November 1998

Fig 4. Comparison of protraction case and untreated case. A, Protraction case with before and after
treatment and follow-up. B. Changes of untreated case age from 7 to 12.

by measuring the distance between points ANS and was less than 1.2 mm during treatment period (Table
PNS along the X-axis. The mean changes of maxillary III). So the protraction group showed an inhibition of
length in protraction group ranged from 1.2 mm to 1.5 mandibular growth.13,16,20 This is probably due to the
mm compared with 0.5 mm to 0.9 mm in the untreated retractive anchorage status of the chin cup of the face
group, with a statistically significant difference (Table mask.
III). Thus, maxillary length increased more in the pro-
traction group. This may be caused by more bone appo- Changes as a function of age
sition occurring in the posterior portion of maxilla, Delaire8 recommended that extraoral traction
indicating an orthopedic effect of maxillary protraction should start early, in the primary dentition stage if
(Fig. 3B, 3D and 3E).13,18 possible. Other investigations have suggested that the
Mandibular length in the untreated group showed a most suitable time for maxillary protraction can be
growth rate of 2.4 mm to 4.8 mm per year, and this sur- selected based on the eruption of maxillary teeth,11,17
passed the growth amount of maxilla; however, in the the developmental status of circumaxillary sutures,27
protraction group, the increase in mandibular length and the amount of growth potential.26 The juvenile
American Journal of Orthodontics and Dentofacial Orthopedics Sung and Baik 499
Volume 114, Number 5

Table IV. Comparison of follow-up subjects in the protraction and untreated groups
Age 11 Age 12 Protraction

Protraction Protraction
Untreated (during treatment) Untreated (posttreatment) During treatment Posttreatment

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

Horizontal (mm)
A 1.3 1.0* 2.0 0.9 0.6 1.2 0.8 1.2 2.0 0.9*** 0.8 1.2
PNS 0.6 1.0 0.9 0.7 0.3 1.3 0.0 1.2 0.9 0.7** 0.0 1.2
B 2.2 1.4*** 1.2 1.9 0.4 1.8* 1.9 2.1 1.2 1.9*** 1.9 2.1
MxI 1.9 1.3 2.6 1.2 1.0 1.4 1.9 2.2 2.6 1.2 1.9 2.2
MxM 2.1 1.5 2.3 0.8 1.0 1.8 0.9 2.2 2.3 0.8* 0.9 2.2
MnI 1.9 1.3*** 1.4 1.8 0.5 1.6* 2.1 1.6 1.4 1.8*** 2.1 1.6
MnM 2.4 1.3*** 0.1 1.2 1.9 1.6 1.9 2.3 0.1 1.2*** 1.9 2.3
Vertical (mm)
A 1.0 0.9 0.8 0.5 2.7 1.3*** 0.8 1.2 0.8 0.5 0.8 1.2
PNS 1.3 0.9 0.8 0.6 1.5 0.7* 0.6 1.2 0.8 0.6 0.6 1.2
B 1.9 1.0 2.1 1.2 4.7 2.2*** 1.2 2.1 2.1 1.2 1.2 2.1
MxI 1.1 0.9 0.9 0.8 3.5 1.0*** 0.4 1.2 0.9 0.8 0.4 1.2
MxM 2.0 0.8 1.5 0.9 3.5 1.0** 0.7 1.9 1.5 0.9 0.7 1.9
MnI 1.1 0.9 1.8 1.7 3.3 1.2*** 0.5 1.1 1.8 1.7** 0.5 1.1
MnM 1.9 1.0 2.0 1.6 2.1 1.0*** 0.4 1.2 2.0 1.6*** 0.4 1.2
Angular ()
SNA 0.5 0.8** 1.5 1.0 0.3 1.0 0.3 1.1 1.5 1.0*** 0.3 1.1
SNB 0.8 0.6*** 1.1 1.3 0.5 0.7 0.8 1.1 1.1 1.3*** 0.8 1.1
ANB 0.3 0.8*** 2.5 0.9 0.2 0.5 0.5 1.1 2.5 0.9*** 0.5 1.1
PP 0.2 1.1 0.1 1.2 0.4 1.0* 0.0 1.4 0.1 1.2 0.0 1.4
MP 1.1 0.9*** 2.1 1.9 0.5 1.1* 1.1 1.3 2.1 1.9*** 1.1 1.3
A-angle 24.1 35.1 20.1 14.1 22.6 64.8 3.9 52.1 20.1 14.l 3.9 52.1
Linear (mm)
MxL 0.8 1.2* 1.2 0.5 0.5 1.5* 0.9 1.5 1.2 0.5 0.9 1.5
MnL 2.9 1.5*** 0.4 0.9 4.8 2.4* 2.7 1.9 0.4 0.9*** 2.7 1.9
Wits 0.1 1.2*** 3.0 2.2 0.0 1.1 0.9 2.2 3.0 2.2*** 0.9 2.2
Period (mo) 12*** 8.0 2.9 11.9 5.4 8.0 2.9 11.9 5.4
Number 21 22 21 22 22 22

A-angle, The angular displacement of point A to X-axis.

Group t test between the untreated group and protraction group or between the protraction groups during treatment versus posttreatment: *, P <
.05; ** P < .01; ***, P < .001.

growth spurt that exists in some individuals can act as Table V. ANOVA test for protraction group according
an accelerating factor in general and skeletal to ages
growth.6,36 During the pubertal growth, maxillofacial Measurements Age group
growth proceeds actively even though the increase in
Vertical changes of MxI 7 > 8,11.12
sutural complexity of the palatomaxillary area after
Horizontal changes of MxI 7 > 9,11,12
the juvenile period can resist maxillary protraction
force.27,37 Thus, in order to get the maximum ortho- The greater than sign indicates relative amount of change (P < .05).
pedic effect with minimum forward sliding of the
dental arch on the maxillary base,12 the growth period
must be considered as an important variable that can cally significant, but changes of the maxillary central
affect treatment results. In most previous studies, only incisors in the group of age 7 were greater than any
subjects in juvenile period were selected, and subjects other group (Fig. 3 and Table V).
in prepubertal and pubertal period were combined in It is our opinion that greater changes in tooth posi-
others. For this study, comparisons were made with tion of the age 7 group resulted from two factors: (1)
clear distinctions between all age groups. The results tooth eruption is very active in the age 7 group, and
showed that the amount of skeletal change among the (2) the measurements of change in tooth position
protraction groups subdivided by age was not statisti- included maxillary movement, because the maxilla
500 Sung and Baik American Journal of Orthodontics and Dentofacial Orthopedics
November 1998

Fig 5. Comparison of time-related changes of point A between follow-up treated group and untreat-
ed group by box-and-whisker plot. A, Horizontal changes. B, Vertical changes.

Table VI. Comparison of the changes during treatment with other studies
Protraction Control

Wisth13 Chong20 Sarns12 Sung & Baik Wisth Chong Sung & Baik

SNA 0.03 0.9 1.5 1.5 0.1 0.31 0.5

SNB 0.9 1.13 0.85 1.1 0.4 0.19 0.8
PP 0.1 0.41 0.1 0.3 4.38 2.9
MP 0.9 0.94 0.7 2.1 0 0.77 1.1
Wits (mm) 1.9 3.0 0.13 0.1
MnL (mm) 0.7 1.87 0.4 2.6 4.38 2.9
Age (yr) 5-10 6.8 11.8* 11 4-9 6.36
Period (mo) 3-12 7.3 8 8 12 19.9* 12
Subjects 22 16 7 22 40 13 21
Device Quad-hlix La/Li Cap splint RPE or La/Li
(With Quad-hlix)

* Estimated period or ages according to measuring unit.

was not the reference object in measuring tooth move- According to animal experiments, biomechanical
ment. studies, and clinical reports on maxillary protraction,
upward and forward rotation of the maxilla occurs
Direction of jaw displacement and rotation when protraction force on molars is applied parallel to
Maxillary protraction is indicated when an antero- the occlusal plane. This type of maxillary rotation can
posteriorly deficient maxilla needs to be displaced for- be minimized when the force is applied in the canine
ward. It will work most effectively when the potential area, 20 to 30 below the occlusal plane.22-25
growth direction of patients correlates with the direc- The clinical point of force application depends
tion of maxillary protraction.9 Bjrk33 reported that in largely on the anchor teeth and appliance design. The
untreated cases, point A moves 51 on the average maxillary canine is the last to erupt during the second
(range, 0 to 82) forward and downward in relation to transitional period, and it is positioned labially in the
anterior cranial fossa, and there are individual varia- presence of crowding. In such cases, it becomes hard to
tions such as to move solely forward or downward, band these teeth for the placement of rigid intraoral
Brodie38 said that there is no change in SN-palatal appliances. Naturally, maxillary first premolars are
plane angle during growth period. often selected as the anchor teeth for RPE.
American Journal of Orthodontics and Dentofacial Orthopedics Sung and Baik 501
Volume 114, Number 5

Table VII. Comparison of the changes during post-treatment with other studies
Protraction Control

Wisth13 Chong20 Sarns12 Sung & Baik Wisth Chong Sung & Baik

SNA 0.1 0 0.2 0.3 0 1.31 0.3

SNB 0.6 1.63 0.5 0.8 0.4 1.96 0.5
MP 1.3 1.75 0.65 1.1 0.9 0.73 0.5
PP 0.6 1.44 0 0.3 0 0.4
Wits (mm) 0.79 0.9 0.6 0
MnL (mm) 2.8 9.3 2.7 1.9 10.46 4.8
Period (mo) (SD) 6-48 42.8* (24.8)* 11.9 (5.4) 12 44.6* (6)* 12

SD, Standard deviation.

*Estimated period or ages according to measuring unit.

In this study, the angular displacement of point A Changes in growth rate during treatment and fol-
(A-angle) and the palatal plane angle were considered low-up periods
for the purpose of predicting maxillary rotation and Growth acceleration involves a quantitative in-
displacement. In the untreated group, the A-angle was crease in size as well as less time to attain a given size.
24.1 at age 11 and 22.6 at age 12 in relation to the In this study, the protraction group revealed significant
X-axis, and the palatal plane angle showed an average annual increases in the SNA angle and maxillary
annual increase of 0.2 to 0.4 (Table IV). In the pro- length, compared with the control group during treat-
traction group, A-angle was 20.1, and the palatal ment.14,16 A larger increase in maxillary length was
plane angle decreased by 0.1 during treatment peri- also observed in the follow-up protraction group, 1.2
od. So the maxillary displacement of the protraction mm during both the treatment period and 0.9 mm dur-
group during treatment was similar to that of the ing the posttreatment period (Table IV).13
untreated group of age 11, but the changes in the A- The rate of horizontal change of point A in the fol-
angle during 1 year posttreatment were various low-up protraction group during treatment was greater
(range, 78.6 to 88) with no changes in palatal than the untreated group of age 11, but after treatment,
plane angle (Table IV). the two groups showed similar changes. Nonetheless,
Although the millimeter changes represented by the rate of the vertical change of point A in the follow-
these angular changes are small, there is a distinct sta- up protraction group was significantly smaller than the
tistical significance between the untreated and pro- untreated group of age 12 both during treatment period
traction group of age 11; this data will be valuable in and posttreatment period (Fig. 5A and B, Table IV). So
validating the center of resistance of the maxilla, maxillary protraction can bring a retruded maxilla for-
which is estimated with the use of biomechanical ward in a short period of time.
studies. In Tables VI and VII, changes during and after
The mandibular plane angle tended to decrease in treatment with maxillary protraction are compared
the untreated group but markedly increased in the pro- with the results from other studies. The duration of fol-
traction group during treatment,12,13,16,18 and the dif- low-up in studies by Chong20 and Wisth13 were longer
ference was significant (Fig. 4A and B, Table III). The than our study; overall measurements studies showed
increase in mandibular plane angle with treatment similar results, but Chongs study samples showed
may be due to incomplete compensation of the short- greater increases in mandibular length during as well
term downward displacement of maxilla by the verti- as after treatment. In this study, the chin cup that was
cal growth of the ramus. One year after protraction, worn during the follow-up period was not so effective
the mandibular plane angle decreased,12,13,20 and this in restricting the linear growth of mandible; the growth
value was significantly smaller than that of the amounts were similar with other studies that used no
untreated group of age 12 (Fig. 4A, Table IV). The chin cups.
increase in the mandibular plane angle with treatment
may be due to (1) the relapse of the treatment that Other considerations
induces vertical increase of anterior facial height and This study differs from some others in that an esti-
clockwise rotation of the mandible, and (2) chin cup mated true horizontal line (6 below the S-N plane)
effects after protraction. was used to measure the displacement of jaws and
502 Sung and Baik American Journal of Orthodontics and Dentofacial Orthopedics
November 1998

teeth. This would reduce the vertical skeletal changes 6. Ritucci R, Nand R. The effect of chin cup therapy on the growth and development of
the cranial base and midface. Am J Orthod Dentofacial Orthop 1986;90:475-83.
and increase the horizontal changes in comparison to 7. Sugawara J, Asano T, Endo N, Mitani H. Long-term effects of chincap therapy on
other data sets. Projecting changes to the true horizon- skeletal profile in mandibular prognathism. Am J Orthod Dentofacial Orthop
1990;98:127-33.
tal, however, provides the most realistic profile changes 8. Delaire J. Considerations sur la croissance faciale (en particulier du maxillaire
and therefore is preferred for the studies of skeletal suprieur). Dductions thrapeutiques. Rev Stomatol 1971;72:57.
9. Cozzani G. Extraoral traction and Class III treatment. Am J Orthod 1981;80:638-50.
change. For the comparison of the treatment changes in 10. Simonsen R. The effect of face mask therapy [abstract]. Am J Orthod 1982;82:439.
the protraction group and the growth changes of the 11. Campbell PM. The dilemma of Class III treatment: early or late? Angle Orthod
1983;53:175-91.
untreated groups, an untreated Class III control group 12. Sarns KV, Rune B. Extraoral traction to maxilla with face mask: a follow-up of 17
would be most ideal, enabling us to estimate the treat- consecutively treated patients with and without cleft lip and palate. Cleft Palate J
1987;24:95-103.
ment effect directly. But, because of the ethical con- 13. Wisth PJ, Tritrapunt A, Rygh P, Boe OE, Norderval K. The effect of maxillary pro-
cerns, we were not able to form such a control traction on front malocclusion and facial morphology. Acta Odont Scand
1987;45:227-37.
group.5,6,20 The protraction group of the present study 14. Mermigos J, Full CA, Andreasen G. Protraction of the maxillofacial complex. Am J
consisted of cases in which the anterior crossbite was Orthod Dentofacial Orthop 1990;98:47-55.
15. Hickham JH, Miethke RR. Protraction: its use and abuse. Praktische Kieferorthopadie
corrected and the posterior occlusion was stabilized. 1991;5:115-32.
Severe crossbite or poor patient cooperation with face 16. Takada K, Petdachai S, Sakuda M. Changes in dentofacial morphology in skeletal
Class III children treated by a modified maxillary protraction headgear and a chin cup:
mask therapy may lead to longer treatment time and a longitudinal cephalometric appraisal. Eur J Orthod 1993;15:211-21.
reduced treatment effects. Thus, the results might be 17. Tindlund RS. Skeletal response to maxillary protraction in patients with cleft lip and
palate before age 10 years. Cleft Palate-Craniofacial J 1994;31:295-308.
different from the average values of this study. Finally, 18. Buschang PH, Porter C, Genecov E, Genecov D, Sayler KE. Face mask therapy of
it should be noted that the authors considered annual- preadolescents with unilateral cleft lip and palate. Angle Orthod 1994;64:145-50.
19. Baik HS. Clinical results of maxillary protraction in Korean children. Am J Orthod
ized analysis of the changes in protraction group Dentofacial Orthop 1995;108:583-927.
unnecessary, because the result from the direct com- 20. Chong YH, Ive JC, rtun J. Changes following the use of protraction headgear for
early correction of Class III malocclusion. Angle Orthod 1996;66:351-62.
parison was obvious enough to demonstrate the treat- 21. Kambara T. Dentofacial changes produced by extraoral forward force in the Macaca
ment effects of protraction; the changes produced by irus. Am J Orthod 1977;71:249-76.
22. Nanda R. Protraction of maxilla in rhesus monkey by controlled extraoral forces. Am
protraction over less than a year were greater than the J Orthod 1978;74:121-41.
annual growth amount in the untreated group.6 23. Jackson GW, Kokich VG, Shapiro PA. Experimental and postexperimental response
to anteriorly directed extraoral force in young Macaca nemsestrina. Am J Orthod
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CONCLUSIONS 24. Kang HS. A laser holographic study on the initial reaction of maxillofacial complex
to maxillary protraction. Korean J Orthod 1988;18:367-81.
1. Maxillary forward displacement and mandibular 25. Miyasaka-Hiraga J, Tanne K, Nakamura S. Finite element analysis for stress in the
growth inhibition were observed in the protraction craniofacial sutures produced by maxillary protraction forces applied at the upper
canines. Br J Orthod 1994;21:343-8.
group compared with the untreated group, and there 26. Proffit WR. Contemporary orthodontics. St Louis: CV Mosby; 1992. p. 91-2, 229-44.
was a statistically significant difference. 27. Melsen B, Melsen F. The postnatal development of palatomaxillary region studied on
human autopsy material. Am J Orthod 1982;82:329-42.
2. When the measurements of treatment effect according 28. Athanasiou AE. Morphologic and functional implications of the surgical-orthodontic
to ages were compared, there was no statistically sig- management of mandibular prognathism: a comprehensive review. Am J Orthod
Dentofacial Orthop 1993;103:439-47.
nificant difference. 29. Bjork A, Skieller V. Normal and abnormal growth of the mandible: a synthesis of lon-
3. The direction of maxillary growth was similar in both gitudinal cephalometric implant studies over a period of 25 years. APPENDIX; Super-
imposition of profile radiographs by the structural method. Eur J Orthod 1983;5:1-48.
the untreated and protraction groups. 30. Houston WJB. The analysis of errors in orthodontic measurements. Am J Orthod
4. Maxillary protraction had a growth stimulating effect 1983;83:382-90.
31. Enlow DH. Handbook of facial growth. Philadelphia: W.B. Saunders; 1992. p. 5,198.
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year study of 2155 patients from YDSH. Korean J Orthod 1995;25:87-100.
33. Bjrk A. Sutural growth of the upper face studied by the implant method. Trans Eur
We thank Dr. William R. Proffit for review of the Orthod Soc 1964;40:1-17.
manuscript and editorial assistance. 34. Baumrind S, Korn EL, Ben-Bassat Y, West EE. Quantitation of maxillary remodeling
2. Masking of remodeling effects when an anatomical method of superimposition is
used in the absence of metallic implants. Am J Orthod Dentofacial Orthop
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