Download Treatment Effects of Cervical Headgear and Lower Utility Arch

ARAŞTIRMA (Research)
Hacettepe Dişhekimliği Fakültesi Dergisi
Cilt: 30, Sayı: 3, Sayfa: 74-84, 2006
Treatment Effects of Cervical Headgear
and Lower Utility Arch Mechanics in Angle
Class II Division 1 Low-Angle Patients
Angle Sınıf II Bölüm 1 Malokluzyona Sahip
Low-angle Hastalarda Servikal Headgear ve Alt
Utility Ark Mekaniğinin Tedavi Üzerine Etkileri
*Müge AKSU DDS, PhD, *Filiz YUKAY DDS, PhD
*Hacettepe University, Faculty of Dentistry, Department of Orthodontics
ABSTRACT
ÖZET
Objective: A prospective study was performed to
evaluate the effects of cervical headgear and lower
utility arch (CHG+LUA) in Class II division 1 lowangle patients and to determine whether reverse
response occurred during the upper first molar distalization period.
Subjects and Methods: Thirty patients were included
in the study and were divided in two groups. The first
group was treated with CHG+LUA while the second
group was treated only with cervical headgear (CHG).
After achieving Angle class I molar relation, the
cephalograms were taken.
Results: The assessment of cephalometric findings
showed that significant reduction of maxillary protrusion, molar distalization, and extrusion were obtained
in both groups. LUA influenced the lower molar
uprighting and the lower incisor intrusion significantly. The rotation of the mandible showed a significant
increase in CHG group while it remained constant in
CHG+LUA group.
Conclusion: These results showed that reverse
response effect, which may be an effective way of
controlling the mandibular rotational response, could
be achieved by CHG+LUA.
Amaç: Sınıf II bölüm 1 malokluzyona sahip lowangle hastalarda servikal headgear ve alt utility
ark (CHG+LUA) uygulamasının etkilerini incelemek ve üst birinci molar distalizasyonu sırasında
mandibulada “ters yanıt” etkisinin olup olmadığını
araştırmaktır.
Bireyler ve Yöntem: Tedaviye dahil edilen toplam
30 birey iki gruba ayrılmış, birinci gruba CHG+LUA,
diğer gruba sadece CHG uygulanmıştır. Angle sınıf
I molar ilişkisi elde edildikten sonra lateral sefalogramlar alınmıştır.
Bulgular: Sefalometrik değerlendirmelerden elde
edilen bulgular, her iki grupta da maksiller protrüzyonda azalma, molar distalizasyonu ve ekstrüzyonu
elde edildiğini göstermektedir. Alt utility ark, alt
molarda anlamlı dikleşmeye ve alt kesicilede anlamlı
intrüyona neden olmuştur. Mandibuler rotasyon
CHG grubunda anlamlı şekilde artarken, CHG+LUA
grubunda sabit kalmıştır.
Sonuç: Araştırma sonuçları, mandibular rotasyonun
kontrolünde etkin bir yol olan “ters yanıt” etkisinin
CHG+LUA uygulaması ile elde edilebileceğini göstermiştir.
KEYWORDS
Cervical headgear, lower utility arch, Class II division 1
ANAHTAR KELİMELER
Servikal headgear, alt utility ark, Sınıf II bölüm 1
118
Introduction
Extraoral traction is the most reliable method
for management of maxillary protrusion and still
continues to be a major treatment alternative for
the orthodontists.
The decision as to which type of headgear to use in the treatment of growing patients
with skeletal and dental class II malocclusion has
been discussed by many investigators1-6. Cervical headgear has been most frequently used in
cases of skeletal maxillary protrusion, producing
distal displacement of the maxilla, increasing
the vertical dimension and generating mandibular clockwise rotation7,8. Because some studies have shown the upper molar extrusion and
the opening rotation of the mandible besides
the distalization effect of cervical headgear5,910,
many orthodontists tend to avoid using cervical
headgear when a patient with class II maxillary
protrusion has a vertical growth pattern. Some
investigators have stated that mandibular plane
angle opens with the cervical headgear11,12, while
others have disagreed with this statement, believing that mandibular plane closes or does not
change with treatment1,13. Many authors have
reported significant changes in vertical parameters when patients treated with cervical headgear
compared to patients treated without the use of
headgear14-16, or patients treated with occipital
or high-pull headgear4,12,16,17. However, Ricketts
et al18 suggested that the effect of cervical headgear did not occur as it has been accepted in
the literature. According to the authors18, when a
cervical headgear is used in high-angle patients,
the extrusion of both maxillary molar and maxilla causes a reciprocal clockwise rotation of the
mandible, resulting in a higher face height. On
the contrary, in low-angle patients, the authors
stated that the extrusive forces of cervical headgear cause changes in the dentition rather than
in the facial proportions. In those cases, where
a cervical headgear is used in combination with
a lower utility arch, the mandible may rotate in
a counterclockwise direction. This effect is called
“reverse response” of the mandible and the mandibular arch. This is almost entirely a functional
response and adverse to the common concepts.
The purpose of this prospective study was (1)
to evaluate the skeletal and dental effects of cervical headgear and lower utility arch (CHG+LUA)
in Class II division 1 low-angle patients whether reverse response occurs (2) and to compare the dental and skeletal differences between
CHG+LUA and CHG during the upper first molar distalization.
Subjects and Method
The sample consisted of thirty patients (14
boys and 16 girls) either in the late mixed or permanent dentition ranging in age from 9.08 to
13 years. The inclusion criteria for the patients
in the study were as follows: (1) Class II division
1 skeletal maxillary protrusion with a low-angle growth pattern (SNA>80o, ANB>4o, maxillary depth angle>90o, lower facial height< 47o,
FMA<25o, GoGnSN < 32o) (2) Half to one full
cusp upper molar deviation (3) None or minimal
crowding (4) Good cooperation
The subjects were divided into two groups
randomly. The first group consisted of 15 patients (8 boys and 7 girls) with a mean age of
10.54 ± 1.05 years, whose treatment included
an orthopedic cervical headgear in conjunction
with a lower utility arch18,19. The second group
consisted of 15 patients (6 boys and 9 girls) with
a mean age of 10.52 ± 0.96 years, whose treatment included an orthopedic cervical headgear
only. These patients did not wear any other appliances during the distalization. The first group
was closely matched for age and dentoskeletal
characteristics with the patients in the second
group (Table I).
The headgear used for both groups was Kloehn type (GAC International, Bohemia, NY) with
a long outer bow. All the patients were instructed
to wear the CHG 14-16 hours per day with an
orthopedic force of 500 gm18.
The lateral cephalograms were taken at the
start of treatment (T1) and after molar distaliza-
119
tion was completed (T2). The radiographs were
traced by one investigator (M.A.) to verify anatomic landmarks (Figure 1A). The duration of distalization was 1.23 ± 0.42 years in the CHG+LUA
group and 1.17 ± 0.30 years in the CHG group.
The skeletal and dentoalveolar effects of CHG +
LUA and CHG were then compared by cephalometric analysis.
Maxillary and mandibular skeletal responses
were documented by comparing the means of
cephalometric measurements at T1 and T2 (Figure 1B).
The dental measurements (Figures 1C and
1D) were obtained through maxillary and mandibular superimpositions, respectively18-20. Maxilla
was superimposed on the palatal plane at ANS
and mandible was superimposed on the corpus axis at Pm. The long axis of maxillary and
FIGURE 1b
1 SNA (°)
6 GoGnSN (°)
2 SNB (°)
7 FMA (°)
3 Palatal plane-FH (°)
8 Lower facial height (°)
4 Maxillary depth (°)
9 Cant of occlusal plane (°)
5 Facial depth (°)
FIGURE 1a
1
Nasion
14 L6 mesial apex
2
3
Sella
Orbitale
15 L6 bifurcation
16 B point
4
Porion
17 Pm
5
A point
18 Pogonion
6
U1 crown
19 Menton
7
U1 apex
20 Gonion
8
U6 mesiobuccal cusp tip
21 Xi point
9
U6 mesiobuccal apex tip
22 R1
10 U6 trifurcation
23 R3
11 L1 crown
24 ANS
12 L1 apex
25 PNS
13 L6 mesiobuccal cusp
FIGURE 1c
1 Palatal plane
2 Line perpendicular to palatal plane from ANS
3 U6, distalization of the crown (mm)
4 U6,distalization of the trifurcation (mm)
5 U6, angulation (°)
6 U6, vertical displacement (mm)
7 U1, horizontal displacement of the crown (mm)
8 U1, horizontal displacement of the apex (mm)
9 U1, angulation (°)
10 U1, vertical displacement (mm)
120
axis respectively. The vertical movements of the
maxillary and mandibular first molars and incisors were determined by measuring the perpendicular distances between the mesiobuccal cusp
tip of the maxillary molar, mesial cusp tip of the
mandibular first molar and incisal edges of the
maxillary and mandibular incisor teeth relative to
the palatal plane and corpus axis at T1 and T2.
Statistical analysis
FIGURE 1d
1 Corpus axis
2 Line perpendicular to corpus axis from Pm
3 L6, distalization of the crown (mm)
4 L6, distalization of the bifurcation (mm)
5 L6, angulation (°)
6 L6, vertical displacement (mm)
7 L1, horizontal displacement of the crown(mm)
8 L1, horizontal displacement of the apex (mm)
9
L1, angulation (°)
The means and standard deviations were calculated for each cephalometric variable. Paired
t-test was performed in each group to analyze
the changes from T1 to T2. Student t-test was
used to evaluate intergroup differences at different periods (T1-T2). To determine the accuracy
of the method, 15 cephalograms were retraced
and recalculated by the same investigator. The
reliability coefficients were between 0.93 and
0.99 for linear measures, and between 0.91 and
0.97 for angular measures, indicating a high level of consistency.
10 L1, vertical displacement (mm)
Results
mandibular first molar teeth were constructed by
drawing a line through the apexes and the mesiobuccal and mesial cusp tips for the upper and
lower first molars. The long axes of incisor teeth
were constructed through the incisal edge and
apex. The angular differences in teeth positions
were measured as the angles between the long
axis of each maxillary and mandibular tooth and
the lines perpendicular to palatal plane and corpus axis at T1 and T2. To determine the amount
of molar distalization, the distances between the
cusp tip of the maxillary first molar and the line
perpendicular to palatal plane from ANS and
the cusp tip of the mandibular first molar and
the line perpendicular to corpus axis from Pm
were used. The distances of the trifurcation and
the bifurcation were also measured to determine the amount of tipping after distalization. The
amount of horizontal displacements of maxillary and mandibular incisors was measured on
a line parallel to the palatal plane and corpus
Maxillary depth angle decreased significantly in CHG+LUA and CHG groups with a mean
change of 1.87o and 1.93o respectively (p<0.05,
Table II). The mean changes in SNA angle did
not indicate a significant reduction in both groups
(p>0.05, Table II) while palatal plane angle decreased significantly in CHG group (p<0.05, Table II).
The upper first molar (U6) in CHG + LUA
and CHG groups moved distally with respect to
its crown (4 mm, and 1.77 mm respectively, p<
0.05, Table III). However, the distalization of the
trifurcation of the upper first molar showed significant difference in CHG + LUA group (2.4 mm,
p< 0.05, Table III), while there was no significant difference in the CHG group (0.77 mm, p>
0.05, Table III) during cervical headgear therapy.
The change in the angulation of the U6 was statistically different in the CHG+LUA group, indicating that the tooth was distalized by tipping
of the crown rather than the bodily movement.
121
TABLE I
Pretreatment variables
Variables
CHG+LUA
(n=15)
CHG
(n=15)
Mean SD
Mean SD
P
SNA (º)
T1
81.90 ± 3.34
81.33 ± 3.02
NS
ANB (º)
T1
5.67 ± 1.33
5.76 ± 1.67
NS
Maxillary depth (º)
T1
91.60 ± 1.53
91.13 ± 1.89
NS
Lower facial height (º)
T1
42.73 ± 3.58
42.97 ± 2.66
NS
FMA (º)
T1
22.87 ± 1.9
23.73 ± 1.76
NS
GoGnSN (º)
T1
32.30 ± 1.11
32.63 ± 2.66
NS
Age
T1
10.54 ± 1.05
10.52 ± 0.96
NS
* p<0.05
SD: standard deviation NS: not significant
TABLE II
T1 (pretreatment) and T2 (after the distalization period) values of maxillary skeletal measurements
Variables
Maxillary depth (º)
T1
CHG+LUA
(n=15)
CHG
(n=15)
Mean SD
P
91.60 ± 2.53
Mean SD
81.90 ± 3.34
0.008*
SNA (º)
0.000*
T2
89.73 ± 2.56
89.20 ± 1.69
T1
81.90 ± 3.34
81.33 ± 3.02
NS
Palatal plane-FH (º)
NS
T2
80.80 ±3.78
80.50 ±2.63
T1
1.97 ±3.07
3.07 ±3.58
0.002*
NS
T2
0.93 ±3.22
P
0.87 ±3.59
* p<0.05
SD: standard deviation NS: not significant
(5.6º, p< 0.05, Table III). On the other hand,
the angulation of the U6 in CHG group did not
change significantly (-0.17º, p> 0.05, Table III).
In both groups, the upper first molar showed significant vertical change (1.07 mm, and 1. 43 mm
respectively, p< 0.05, Table III). The only significant change of the upper incisor (U1) in the
CHG +LUA group was found in the horizontal
displacement of the upper incisor’s apex (0.93
mm lingually, p< 0.05, Table III). The horizontal,
the angular and the vertical changes in the position of the U1 did not differ in the CHG group
(p>0.05, Table III).
122
TABLE III
T1 (pretreatment) and T2 (after the distalization period) values of maxillary dental measurements
Variables
U6, distalization
T1
CHG+LUA
(n=15)
CHG
(n=15)
Mean SD
P
-36.17 ± 3.41
of the crown (mm)
U6, distalization
0.015*
T2
-40.17 ± 3.72
-40.63 ± 3.68
T1
-37.13 ± 2.69
-38.40 ± 2.48
0*
NS
T2
-39.53 ± 2.76
-39.17 ± 2.91
T1
15.27 ± 6.52
19.70 ± 2.91
0.014*
U6, vertical
U1, horizontal
NS
T2
20.87 ± 7.42
19.87 ± 9.36
T1
20.90 ± 2.93
20.37 ± 1.58
displacement (mm)
0.046*
0.001*
T2
21.97± 2.71
21.80 ± 1.68
T1
-1.17 ± 3.26
-1.63 ± 3.11
displacement of
NS
NS
the crown (mm)
T2
-1.70 ± 3.50
-0.83 ± 2.76
U1, horizontal
T1
-10.33 ± 2.09
-11.60 ± 1.76
displacement of
0.019*
NS
the apex (mm)
T2
-11.27 ± 1.94
-10.93 ± 2.80
U1, angulation (º)
T1
21.40 ± 6.43
23.10± 7.08
NS
U1, vertical
NS
T2
21.90 ± 7009
25.00 ± 6.71
T1
29.37 ± 2.62
28.47 ± 1.89
displacement (mm)
NS
T2
30.03 ± 2.27
P
-38.87 ± 2.86
0*
of the trifurcation (mm)
U6, angulation (º)
Mean SD
NS
28.53 ± 2.46
* p<0.05
SD: standard deviation NS: not significant
The mandibular skeletal measurements
showed no statistically significant changes in
both groups (SNB, facial depth angle) (p>0.05,
Table IV). The measurements such as GoGnSN,
FMA, lower facial height did not show any signifi-
cant difference in the CHG+LUA group (p>0.05,
Table IV) while there was a significant increase in
FMA, and lower facial height in the CHG group
(p<0.05, Table IV).
123
TABLE IV
T1 (pretreatment) and T2 (after the distalization period) values of mandibular skeletal measurements and facial pattern
Variables
SNB (º)
T1
CHG+LUA
(n=15)
CHG
(n=15)
Mean SD
P
76.23 ± 2.92
Mean SD
75.57 ± 2.33
NS
Facial depth (º)
NS
T2
76.67 ± 3.68
76.07 ± 2.80
T1
86.93 ± 2.28
86.37 ± 2.23
NS
GoGnSN (º)
NS
T2
86.73 ± 2.22
85.90 ± 2.19
T1
32.30 ± 1.11
33.63 ± 2.66
NS
FMA (º)
NS
T2
33.27 ± 4.71
33.63 ± 6.17
T1
22.87 ± 1.9
23.73 ± 1.76
0.016*
NS
Lower facial height (º)
T2
23.30 ± 3.60
24.90 ± 4.60
T1
42.73 ± 3.58
42.97 ± 2.66
0.047*
NS
T2
43.40 ± 3.89
P
43.83 ± 3.51
* p<0.05
SD: standard deviation NS: not significant
The crown of the lower first molar (L6) in the
CHG+LUA group was distalized and tipped back
significantly (with a mean difference of 2.5 mm
and 8.3˚, p< 0.05, Table V).The vertical change
in the position of the L6 was not shown to be
significantly different in CHG+LUA group. The
crown of the lower incisor (L1) in the CHG+LUA
group retroclined and intruded significantly with
a mean difference of 4.73˚ and 1.13 mm respectively (p<0.05, Table V).The cant of occlusal
plane increased 2.47˚ (p<0.05, Table V) in the
CHG+LUA group while there was no significant
change in the CHG group. In CHG group, all
the variables determinig the L6 and L1 positional changes, did not also show any significant
difference during distalization (p>0.05, Table V).
Within all the skeletal measurements regarding the maxilla and the mandible, neither of
the variables showed any significant difference
between the two groups. The distalization of the
U6 was significantly different between the two
groups (p<0.05, Table VI). In CHG+LUA group,
both the crown and the trifurcation moved distally with a mean difference of 4 mm and 2.4
mm respectively. On the other hand, in the CHG
group, the distalization of the crown and the trifurcation was 1.77 mm and 0.97 mm respectively. The horizontal displacement of the U1 was
significantly different between the two groups
(p<0.05, Table VI). In the CHG+LUA group,
U1 moved 0.53 mm lingually while in the CHG
group, U1 moved 0.8 mm labially. For the L6,
the distalization of the crown (2.5 mm for the
CHG+LUA group and 0 mm for the CHG group)
and the bifurcation (2.4 mm for the CHG+LUA
group and 0.97 mm for the CHG group) and the
124
TABLE V
T1 (pretreatment) and T2 (after the distalization period) values of mandibular dental measurements
Variables
L6, distalization
T1
CHG+LUA
(n=15)
CHG
(n=15)
Mean SD
P
-32.80 ± 2.41
of the crown (mm)
L6, distalization
NS
T2
-35.30 ± 2.70
-33.77 ± 2.40
T1
-33.80 ± 0.74
-34.37 ± 0.16
NS
NS
T2
-34.56 ± 2.70
-34.46 ± 0.16
T1
-10.33 ± 10.49
11.20 ± 7.0
0*
L6, vertical
L1, horizontal
NS
T2
18.77 ± 6.15
11.0 ± 4.45
T1
13.23 ± 1.49
12.87 ± 1.43
displacement (mm)
NS
NS
T2
13.60 ± 1.65
12.77 ± 2.41
T1
-6.13 ± 1.87
-5.70 ± 1.87
displacement of
0.011*
NS
the crown (mm)
T2
-7.53 ± 2.83
-6.27 ± 1.72
L1, horizontal T1
-8.70 ± 1.87
-7.67 ± 1.03
displacement of
NS
NS
the apex (mm)
T2
-8.30 ± 2.83
-7.63 ± 1.16
L1, angulation (º)
T1
6.47 ± 5.72
4.80 ± 4.56
0.012*
L1, vertical
Cant of occlusal
NS
T2
1.73 ± 8.91
25.40 ± 1.80
T1
25.50 ± 2.0
26.50 ± 2.24
displacement (mm)
0.017*
T2
24.37 ± 2.57
T1
18.13 ± 0.98
plane (º)
NS
19.10 ± 3.84
0.019*
T2
*p<0.05
SD: standard deviation NS: not significant
20.60 ± 0.86
P
-33.77 ± 2.35
0.006*
of the bifurcation (mm)
L6, angulation (º)
Mean SD
NS
20.73 ± 2.63
125
TABLE VI
Comparison of pre and post-distalization differences between groups
CHG+LUA
(n=15)
CHG
(n=15)
Mean SD
Mean SD
P
U6, distalization of the crown (mm)
-4.0 ± 2.65
-1.77 ± 2.46
0,02*
U6, distalization of the trifurcation (mm)
-2.4 ± 1.48
-0.97 ± 1.93
0,03*
U1, horizontal displacement
of the crown (mm)
-0.53 ± 1.42
0.8 ± 1.80
0,03*
L6, distalization of the crown (mm)
-2.5 ± 3.01
0 ± 1.57
0,008*
L6, distalization of the bifurcation (mm)
-2.4 ± 1.48
0.97 ± 1.93
0,03*
L6, angulation (º)
8.43 ± 5.47
-0.20 ± 7.52
0,001*
L1, vertical displacement (mm)
-1.13 ± 1.62
1.10 ± 2.75
0,01*
Variables
*p<0.05
SD: standard deviation NS: not significant
angulation (8.43o for the CHG+LUA group and
-0.20o for the CHG group) were significantly different between the study groups (p<0.05, Table VI). The vertical displacement of L1 was also
significantly different between the two groups
(p<0.05, Table VI). (L1 intruded with a mean
difference of 1.13 mm in the CHG+LUA group
while extruded with a mean difference of 1.10
mm in the CHG group).
Discussion
A prospective investigation was undertaken
to determine the effects of CHG+LUA in Class
II division 1 low-angle patients. The orthopedic
effect of CHG has previously been the subject
of many studies1-3,5-7,14. In contrast with the common concepts about the mandibular rotational
effects, Ricketts et al18 suggested that a reverse
response could occur when a CHG was used
with a LUA in low-angle patients. According to
the authors,18 the extruding upper molar picks
up the lower molar, uprighting that tooth in a
distal rotation. This action allows the maxilla to
be compressed and rotated distally without rotation of the mandible and is referred to as the
reverse response of the LUA18. However, CHG
therapy accompanying by LUA has been rarely
investigated20. The only investigation reported in
the literature was the retrospective study of Cook
et al20, which was performed in high-angle patients. The purpose of this study was not to focus
on posttreatment effects but to evaluate pure effects of CHG+LUA during the molar distalization
period as the overall change for the entire period
of treatment may hide the CHG effect.
In this study, the maxilla moved distally in
terms of maxillary depth angle. Our finding is
in accordance with the finding of many studies
indicating the restriction of the maxilla with the
use of CHG4,9,21,22. However, SNA angle did not
show any significant difference during the distalization while some authors interpreted differences in SNA reduction7,21,23. The observation period in this study included only the distalization
period, which might be insufficient to achieve an
orthopedic movement.
The literature regarding the effect of CHG on
the palatal plane angle is still unclear. Although
many authors reported that anterior nasal spine
to be positioned downward more than posterior
nasal spine1,3,5,11,18,24, rotation of the palatal plane was changed significantly only in CHG group.
Boecler13 et al reported no change in the angulation of the palatal plane with CHG therapy in
contrast to our finding.
126
The results of this study indicate that there was
a significant distalization of U6 in both groups.
This finding is in accordance with the findings reported in the literature1,9. However, the amount
of distalization in CHG group was less than that
of CHG + LUA group. Although the duration of
distalization was almost the same, a difference
between the amounts of distalization occurred.
This might be due to the variation in the amount
of molar cusp deviation at the start of treatment.
Another possible explanation for this might be
the angular changes between the two groups during the distalization period. To investigate the
type of molar movement, distalization of the trifurcation of U6 was also evaluated. The amount
of distalization of the trifurcation was less than
the crown movement in contrast with the studies reported in the literature20,25. Furthermore,
Schiavon Gandini et al25 showed that the distal
relocation of U6 was more significant in the apex
due to the 20o upward angulation of the external
bow. Additionally, Cook et al20 did not observe
any distal tipping when the outer bows of the
CHG were bent upward. The downward vector of
the extraoral force produced a more downward
movement of U6 in both groups. Cook et al20
reported the upper molar extrusion either with
or without treatment, suggesting that the molar
extrusion could not be attributed to only cervical
headgear due to the ongoing downward growth
of the maxilla.
In this study, the lower first molar moved
distally and the lower incisors intruded and retroclined significantly in the CHG+LUA group as
described by Ricketts et al.18 The bioprogressive
theory of cortical anchorage hypothesizes that
bends in the utility arch will move the roots of
the first lower molars toward the buccal cortical
bone of the mandible, leading to the extrusion of
the lower first molars and the intrusion of lower
incisors. The upper molar in the CHG+LUA
group extruded, then uprighted the lower first
molar in a distal rotation, confirmig the reverse
response effect of the LUA. In contrast with our
findings, Cook et al did not find any reverse response effect in their study group.
Additionally, L1 and the cant of the occlusal
plane were also changed by the LUA. The LUA
might have a reaction at the molar to upright it
however, cortical anchorage might prevent the
significant molar extrusion even when the incisor intrusion mechanics were used. Meanwhile,
Cook et al20 did not find any molar response while they found a significant intrusion and proclination of the lower incisors.
Since no other appliances were worn by the
patients in our study during the period of the investigation, it can be stated that CHG+LUA used
in this study produced Class II correction without
producing an opening rotation of the mandible.
GoGnSN, FMA and lower facial height angles did
not demonstrate any significant changes between
T1 and T2 in CHG+LUA group, confirming that
when a CHG is used in conjunction with a LUA,
the mandible may remain constant without any
rotation. Ricketts et al18 also suggested that the
extrusive forces of CHG was translated through
the utility arch to the lower dentition, allowing
maxilla to move distally without rotation of the
mandible. Cook et al20 reported different results
with our findings regarding mandibular rotation,
this might be due to their study group which was
different from that of our study.
A limitation of this study was that the groups
were relatively small. However, the characteristics of the patients and the application of the
appliances were highly homogeneous and the
study was designed prospectively. Most of the
studies pertaining to CHG are either retrospective or CHG has been combined with edgewise appliances; functional appliances, bite plates,
extractions and the groups in these studies are
not usually homogeneous. Additionally, there
is only one study in the literature, investigating
the speculation of Ricketts et al.18 Future studies
including larger study groups and posttreatment
effects should be undertaken for the long-term
effects of CHG+LUA.
Conclusion
Both CHG+LUA and CHG groups restricted maxillary sagittal growth and resulted in an
127
extrusion of upper first molars. The lower first
molar uprighted and moved distally with LUA,
however, it could not prevent the extrusion but
might restrict the excessive extrusion of the upper first molar. The reverse response of the LUA
did not affect the mandibular rotation in lowangle patients thus, mandible remained stable
without any rotation in the CHG+LUA group.
However, opening rotation of the mandible occurred in the CHG group.
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CORRESPONDING ADDRESS
Müge AKSU DDS, PhD
Hacettepe University, Faculty of Dentistry, Department of Orthodontics 06100 Sıhhiye-Ankara/TURKEY
Tel: +90 312 3116461 Fax: +90 312 3091138 e-mail: [email protected]