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ORIGINAL ARTICLE
Dentoskeletal and soft-tissue changes with
cervical headgear and mandibular protraction
appliance therapy in the treatment of Class II
malocclusions
Danilo Furquim Siqueira,a Renato Rodrigues de Almeira,b Guilherme Janson,c Analu Giampietro Brandão,a
and Carlos Martins Coelho Filhod
Bauru, São Paulo, and São Luís, Maranhão, Brazil
Introduction: In this study, we cephalometrically compared changes in the dentoskeletal and soft tissues
after orthodontic treatment of Class II Division 1 malocclusions between the cervical headgear (CHG) and the
mandibular protraction appliance (MPA) followed by fixed appliances. Methods: The sample consisted of 50
patients divided into 2 groups of 25 patients each (13 male, 12 female). Group 1 patients were treated with
CHG and fixed appliance, and group 2 patients were treated with the MPA and fixed appliances. The patients
were matched according to sex, age, treatment time, and initial cephalometric variables. The groups were
compared regarding pretreatment stage and treatment changes, with t tests, at P ⬍.05. Results: The CHG
group showed statistically greater restriction of the anterior displacement of the maxilla, improvement of the
skeletal Class II relationship, decreased facial convexity, extrusion and distalization of the maxillary first
molar, and extrusion of the mandibular incisors. The MPA group had statistically greater increases in
maxillary length, mandibular protrusion, maxillary incisor retrusion, mesial displacement of the mandibular
first molars, and protrusion of the lower lip. Conclusions: The changes in Class II malocclusion correction
between the CHG and the MPA were that the CHG corrected the Class II malocclusion primarily through
greater action on the maxillary skeletal and dentoalveolar structures as compared with the MPA, which
corrected the malocclusion through greater action on the mandibular dentoalveolar structures. (Am J Orthod
Dentofacial Orthop 2007;131:447.e21-447.e30)
M
any appliances are designed to correct Class
II malocclusions with a nonextraction approach. One of the most used and studied
mechanisms is the extraoral appliance that restricts the
anterior displacement of the maxillary first molar and
the maxilla and produces improvement in the maxillomandibular relationship.1-5
The choice of the best appliance depends on many
factors, including patient compliance. The mandibular
protraction appliance (MPA) is a fixed functional appliance that maintains continuous mandibular advancea
Graduate student, Department of Orthodontics, Bauru Dental School, University of São Paulo, Bauru, São Paulo, Brazil.
b
Associate professor, Department of Orthodontics, Bauru Dental School,
University of São Paulo, Bauru, São Paulo, Brazil.
c
Professor, Department of Orthodontics, Bauru Dental School, University of
São Paulo, Bauru, São Paulo, Brazil.
d
Private practice, São Luís, Maranhão, Brazil.
Reprint requests to: Analu Giampietro Brandão, Department of Orthodontics,
Bauru Dental School, University of São Paulo, Alameda Octávio Pinheiro
Brisolla 9-75, Bauru, São Paulo, 17012-901, Brazil; e-mail, analugb@uol.
com.br.
Submitted, August 2005; revised and accepted, April 2006.
0889-5406/$32.00
Copyright © 2007 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2006.04.029
ment to correct Class II anteroposterior discrepancy and
therefore does not depend on patient compliance.6-9 It
has important features: easy chairside construction with
ordinary and inexpensive wires; no special bands,
crowns, or wire attachments; easily inserted, adjusted,
and removed; and versatility. It is also an excellent
mechanism for preserving maxillary molar and mandibular incisor anchorage.6-9
Investigations with the MPA demonstrated that the
changes it produces are primarily dentoalveolar, with
distalization of the maxillary dentoalveolar process and
mesial displacement of the mandibular molars.6-9 Studies comparing removable functional appliances with
headgear demonstrated that both appliances are effective in correcting Class II malocclusions, and reducing
overjets and apical base discrepancies.10-12 Headgear
showed distal effects on the maxilla and moved the
maxillary first molars farther distally and occlusally,5,10,12 whereas removable functional appliances
caused greater mandibular protrusion, and greater increases in mandibular length and mandibular molar
extrusion.5,10,12 However, comparisons of headgear
447.e21
447.e22 Siqueira et al
American Journal of Orthodontics and Dentofacial Orthopedics
April 2007
Fig 1. MPA III.
with fixed functional appliances have not been conducted. Similarly, the effects of the MPA have not been
compared with other appliances, especially extraoral
headgear, to demonstrate the different effects in the
correction of Class II malocclusions. Therefore, the
objective of this study was to cephalometrically compare the dentoskeletal and soft-tissue changes after
treatment of Class II Division 1 malocclusions with
cervical headgear (CHG) and the MPA followed by
fixed appliances.
MATERIAL AND METHODS
The sample consisted of 50 patients divided into 2
groups of 25 patients each (13 male, 12 female). The
primary selection criteria for both groups were a Class II
Division 1 malocclusion with at least an end-to-end
bilateral Class II molar relationship, all maxillary and
mandibular teeth up to the second molars, a convex
facial profile, and an accentuated overjet.
Group 1 comprised patients with an initial mean age
of 12.40 years (range, 10.00-13.83 years), treated with
CHG and fixed appliances, from the files of the Orthodontic Department, Bauru Dental School, University
of São Paulo. The mean treatment time was 2.39 years
(range, 1.58-4.42 years). Patients used the CHG 16
hours per day, for a mean time of 16 months, with a
mean force of 450 g on each side. After molar relationship correction, 0.022 ⫻ 0.028-in standard edgewise
fixed appliances were placed. The usual wire sequence
began with a 0.016-in nickel-titanium wire followed by
0.016, 0.018, 0.020, and finally 0.021 ⫻ 0.025-in
stainless steel archwires (Unitek, Monrovia, Calif).
Then the fixed appliances were removed, and Hawley
retainers were used in the maxillary arches, and canineto-canine retainers were bonded in the mandibular
arches.
Group 2 consisted of patients with an initial mean
age of 12.30 years (range, 9.25-16.08 years) treated
simultaneously with the MPA and fixed appliances at
the private practice of the fifth author in São Luís,
Maranhão, Brazil, with a mean treatment time of 2.80
years (range, 1.33-4.00 years). The MPA (Fig 1) is an
intraoral fixed appliance that induces continuous mandibular protrusion.6 It requires stainless steel edgewise
archwires in both arches. The length of the appliance is
determined by the distance from the mesial aspect of
the maxillary tube to the stop on the mandibular
archwire. Three versions were used in this study: MPA I,
II, and III. The only difference between them was the
protrusive mechanism. MPA III was a variation of the
earlier versions, with a tube-and-plunger mechanism
with 0.032-in stainless steel wire.8 MPA I and II were
constructed with 0.032-in stainless steel wires as shown
in Figure 2. However, their modes of action were
similar.6-9 Previous use of fixed orthodontic appliances
is indispensable to all types of MPA. Before placement
of the MPA, 0.022 ⫻ 0.028-in edgewise fixed appliances were placed, and leveling progressed up to
rectangular 0.021 ⫻ 0.025-in stainless steel archwires (Unitek). Then the MPA was placed to correct
the Class II anteroposterior discrepancy. The rectangular arches must have enough extension distal to the
molar tubes for the bend-down tieback and to support
elastic chains.6 The mandible was advanced to an
edge-to-edge incisor position. The mean MPA treatment time was 7 months; then the appliances were
removed. At this stage, the molar relationship was
corrected and the overjet reduced. Finishing of the
occlusion was obtained with fixed appliances. Retainers
consisted of Hawley plates in the maxillary arches and
bonded canine-to-canine lingual arches in the mandibular arches.
Lateral radiographs of the groups were obtained
from each patient at pretreatment (T1) and posttreatment (T2), in different machines, which produced
magnification factors between 6% and 9.8%. The lateral cephalograms were traced on acetate paper, and the
cephalometric tracings and landmark identifications
were performed by 1 investigator (D.F.S.) and then
digitized with a digitizer (DT-11, Houston Instruments,
Siqueira et al 447.e23
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 131, Number 4
Fig 2. A, MPA I; B, MPA II; C, MPA III.
Austin, Tex) (Table I, Fig 3). These data were stored on
a computer and analyzed with Dentofacial Planner 7.02
(Dentofacial Planner Software, Toronto, Ontario, Canada), which corrected the image magnification factors
of the groups.
Sixteen patients were randomly selected, and the
radiographs were retraced, redigitized, and remeasured
by the same examiner after a 2-month interval. Systematic errors were estimated by paired t tests (P ⬍.05),
and casual errors were calculated according to Dahlberg’s formula, Se2 ⫽ ⌺d2/2n, where d is the difference
between duplicate measurements, and n is the number
of double measurements.13,14
Statistical analysis
Means and standard deviations for each variable were
calculated to enable characterization of the groups.
Normal distributions were verified by the KolmogorovSmirnov test (for the initial and final stages and for
treatment changes). Results of this test showed that all
variables were normally distributed. Therefore, the
t test was used for comparison between the groups at T1
and T2 and for treatment changes, at P ⬍.05. All
statistical analyses were performed with software (Statistica for Windows 6.0, Statsoft, Tulsa, Okla).
RESULTS
Of the 29 variables, only 1 had a systematic error:
L6-MP. The range of casual errors varied from 0.34
(SNB angle) to 2.64 (NLA angle) (Table II).
The groups were compatible regarding initial ages,
treatment times, and almost all cephalometric variables.
Only U6-PP was statistically greater in group 1 than in
group 2 (Table III).
The cervical headgear group had statistically
greater restriction of the anterior displacement of the
maxilla (SNA angle), improvement of the skeletal
Class II relationship (ANB angle), decreased facial
convexity (NAP angle), extrusion (U-6PP), distalization of the maxillary first molar (U6-Fperp), and extrusion of the mandibular incisors (L1-MP). The MPA
group had a statistically greater increase in maxillary
length (Co-A), mandibular protrusion (SNB angle),
maxillary incisor retrusion (U1-NA), mesial displacement of the mandibular first molars (L6-Fperp), and
protrusion of the lower lip (LL-Fperp; Table IV).
At T2, the CHG group showed a significantly
retruded maxilla (SNA angle), smaller anteroposterior
basal discrepancy (ANB angle), and mandibular protrusion (NAP angle), protruded maxillary incisors (U1NA), greater maxillary first molar dentoalveolar height
(U6-PP), retruded maxillary molars (U6-Fperp), uprighted and greater dentoalveolar height of the mandibular incisors (IMPA, L1.NB, L1-MP), and retruded
mandibular first molar crown (L6-Fperp) in relation to
the MPA group (Table V).
DISCUSSION
When analyzing the results, one must bear in mind
that they were obtained from the use of the CHG or the
MPA with fixed appliances. Distinctions between the
separate effects of the MPA were not possible because
the treatment rationale of this appliance requires initial
leveling and alignment up to a rectangular stainless
steel archwire before placement of the Class II correction appliance.6-9
447.e24 Siqueira et al
American Journal of Orthodontics and Dentofacial Orthopedics
April 2007
Table I. Definitions of less usual lines, planes, and
variables used
Planes and lines
Frankfort horizontal plane (FH): constructed by subtracting 7°
from SN line, registered on S41,45
Mandibular plane Go-Me: constructed from Go to Me
Palatal plane: constructed from ANS to PNS
SN: line constructed from S to N
NA: line constructed from N to A
NB: line constructed from N to B
AP: line constructed from A to P
Fperp (Frankfort perpendicular): line constructed perpendicular
to Frankfort horizontal plane, through S
Skeletal cephalometric variables
SNA: SN to NA angle
SNB: SN to NB angle
ANB: NA to NB angle
NAP: NA to AP angle
FMA (Sn.GoMe): Frankfort mandibular plane angle
SN.PP: SN to palatal plane angle
Go-Gn: distance between Go and Gn
Co-A: distance between Co and A-point
Co-Gn: distance between Co and Gn
UAFH (upper anterior face height): distance from N to ANS
LAFH (lower anterior face height): distance from ANS to Me
PFH (posterior face height): distance from S to Go
LPFH (lower posterior face height): distance from Ar to Go
Dental cephalometric variables
U1.NA: maxillary incisor long axis to NA angle
U1-NA: distance between most anterior point of crown of
maxillary incisor and NA line
U1-PP: perpendicular distance between incisal edge of maxillary
central incisor and palatal plane
U6-PP: perpendicular distance between mesiobuccal cusp of
maxillary first molar and palatal plane
U6-Fperp: perpendicular distance between mesiobuccal cusp of
maxillary first molar and Fperp
L1.NB: mandibular incisor long axis to NB angle
L1-NB: distance between most anterior point of crown of
mandibular incisor and NB line
IMPA: incisor mandibular plane angle
L1-MP: perpendicular distance between incisal edge of
mandibular incisor and mandibular plane GoMe
L6-MP: perpendicular distance between mesiobuccal cusp of
mandibular first molar and mandibular plane GoMe
L6-Fperp: perpendicular distance between mesiobuccal cusp of
mandibular first molar and Fperp
Soft-tissue cephalometric variables
NLA: nasolabial angle
UL-Fperp: distance between upper lip and Fperp
LL-Fperp: distance between lower lip and Fperp
Dentoskeletal and soft-tissue changes
and T2 status
The CHG showed statistically greater restriction of
the anterior displacement of the maxilla than did the
MPA (Tables IV and V; Fig 4). This result could be
expected because the MPA is similar to the Herbst
appliance, which was shown to have no significant
Fig 3. Cephalometric landmarks: S, sella turcica; N,
nasion; A, subspinale; B, supramentale; P, pogonion;
Me, menton; Go, gonion; Gn, gnathion; Co, condylion;
Ar, articulare; ANS, anterior nasal spine; PNS, posterior
nasal spine; UL, upper lip; LL, lower lip; Prn, pronasale;
Sn, subnasale; Prn=, nasal columella; U1, most anterior
point of maxillary incisor crown; L1, most anterior point
of mandibular incisor crown; U6, point located on
maxillary first molar mesial cusp; L6, point located on
mandibular first molar mesial cusp.
effect in forward maxillary displacement,15 whereas the
CHG does.2,4,5,16-18 Probably, this greater restriction
effect on forward maxillary displacement is consequent
to the longer time that the CHG was used (16 months)
compared with the MPA (7 months). Consequently, the
effect on the increase in maxillary effective length was
statistically smaller for the CHG, and the maxilla at T2
was significantly more retruded in group 1.
The MPA produced greater mandibular protrusion than did the CHG, as is usually observed when
comparing the treatment effects of functional appliances and headgears.10,12,19 This greater mandibular
protrusion is consequent to the greater increase in
mandibular length usually produced by functional appliances.15,20-24 Although this effect is still controversial, some have shown that it is possible.15,20-24 However, the mandibular length increase was greater but not
statistically significant in group 2. Therefore, what
could have accounted for this smaller mandibular
protrusion in group 1 was the cumulative effects of a
nonsignificant smaller increase in mandibular length
Siqueira et al 447.e25
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 131, Number 4
Table II.
Systematic and casual errors
Groups
Variable
Maxillary component
SNA (°)
Co-A (mm)
Mandibular component
SNB (°)
Go-Gn (mm)
Co-Gn (mm)
Maxillomandibular relationship
ANB (°)
NAP (°)
Vertical component
SN.GoMe (°)
SN.PP (°)
UAFH (mm)
LAFH (mm)
PFH (mm)
LPFH (mm)
Maxillary dentoalveolar component
U1.NA (°)
U1-NA (mm)
U1-PP (mm)
U6-PP (mm)
U6-Fperp (mm)
Mandibular dentoalveolar component
IMPA (°)
L1.NB (°)
L1-NB (mm)
L1-MP (mm)
L6-MP (mm)
L6-Fperp (mm)
Dentoalveolar relationship
Overjet (mm)
Overbite (mm)
Soft-tissue profile
NLA (°)
UL-Fperp (mm)
LL-Fperp (mm)
First measurement
(n ⫽ 16)
Second measurement
(n ⫽ 16)
Mean
SD
Mean
SD
Casual errors
(Dahlberg)
Systematic
errors (P)
84.6
85.0
3.82
3.86
84.30
85.10
3.58
3.68
0.614
0.529
.178
.357
79.50
70.40
105.90
3.01
3.90
5.10
79.30
70.10
106.10
2.95
3.83
5.00
0.340
0.615
0.554
.064
.314
.083
5.10
7.50
2.25
6.17
5.00
7.30
2.27
6.25
0.375
0.705
.491
.617
31.40
4.80
46.70
60.10
68.80
39.60
4.52
3.21
3.99
5.08
4.04
3.16
31.60
5.00
46.60
60.20
68.80
39.60
4.58
3.27
4.03
5.46
4.55
2.90
0.542
0.550
0.398
0.386
0.753
0.788
.389
.393
.706
.800
.968
.791
27.10
5.70
26.50
20.70
39.50
7.24
1.49
2.44
1.91
3.51
26.40
5.50
26.70
20.70
39.10
6.97
1.66
2.43
1.84
3.41
1.351
0.406
0.449
0.424
0.729
.120
.204
.139
.842
.459
95.90
27.10
5.10
37.00
25.90
38.80
7.56
7.79
2.59
3.40
2.58
4.11
96.10
26.90
4.90
37.20
26.40
38.50
7.22
8.00
2.55
3.70
2.93
3.91
1.632
1.463
0.381
0.458
0.544
0.853
.756
.763
.205
.228
.006*
.447
7.65
4.44
3.26
2.41
7.34
4.87
3.36
2.47
0.467
0.637
.060
.052
108.60
4.60
2.40
8.93
2.25
2.75
108.40
4.20
2.60
9.06
2.24
2.92
2.645
0.704
0.244
.843
.105
.231
*Statistically significant at P ⬍.05.
associated with a statistically significant greater increase in maxillary first molar extrusion in this group;
this caused clockwise rotation of the mandible with a
consequent retrusive effect.1,5,16,25,26 Despite the
greater mandibular protrusion produced by the MPA,
there were no significant differences in the mandibular
components between the groups at T2; this means that
these appliances do not have discernible effect differences in these areas.
The CHG produced a statistically greater improvement in the maxillomandibular relationship and consequently a greater reduction in facial convexity than did
the MPA, in spite of the greater mandibular protrusion
it produced, as discussed above. These differences in
effect amounts between headgears and functional appliances were also observed previously.10,12,19 They are
consequent to the greater restriction of maxillary forward displacement with headgear.1-5,16,25 Consequently, the CHG group finished with a smaller apical
base anteroposterior discrepancy and a smaller facial
convexity than did the MPA group; this is positive in
Class II malocclusion treatment.
Treatment changes in both groups were similar
in the vertical components, which had similar char-
447.e26 Siqueira et al
Table III.
American Journal of Orthodontics and Dentofacial Orthopedics
April 2007
Intergroup comparison at T1 (t test)
Groups
CHG (n ⫽ 25)
MPA (n ⫽ 25)
Variables
Mean
SD
Mean
SD
P
Initial age (y)
Treatment time (y)
Maxillary component
SNA (°)
Co-A (mm)
Mandibular component
SNB (°)
Go-Gn (mm)
Co-Gn (mm)
Maxillomandibular relationship
ANB (°)
NAP (°)
Vertical component
SN.GoMe (°)
SN.PP (°)
UAFH (mm)
LAFH (mm)
PFH (mm)
LPFH (mm)
Maxillary dentoalveolar component
U1.NA (°)
U1-NA (mm)
U1-PP (mm)
U6-PP (mm)
U6-Fperp (mm)
Mandibular dentoalveolar component
IMPA (°)
L1.NB (°)
L1-NB (mm)
L1-MP (mm)
L6-MP (mm)
L6-Fperp (mm)
Dentoalveolar relationship
Overjet (mm)
Overbite (mm)
Soft-tissue profile
NLA (°)
UL-Fperp (mm)
LL-Fperp (mm)
12.40
2.39
0.90
0.90
12.30
2.80
1.76
0.73
.788
.052
83.15
84.88
3.05
4.07
83.50
84.21
4.66
4.07
.753
.562
77.55
70.46
105.55
3.12
4.25
5.38
77.42
69.06
102.83
3.33
3.77
4.52
.886
.225
.059
5.60
8.64
1.38
4.42
6.08
10.25
2.76
6.16
.441
.296
33.84
6.82
48.00
60.36
67.27
39.29
3.73
3.97
3.36
4.69
3.69
2.71
32.71
7.22
46.93
58.10
65.51
38.02
5.48
3.91
3.11
5.90
3.88
3.25
.399
.721
.251
.140
.108
.141
29.11
6.11
25.94
20.80
37.90
8.83
2.08
2.47
1.79
3.80
30.74
6.16
24.74
19.40
38.86
6.71
2.20
3.22
1.79
4.61
.464
.942
.147
.008*
.426
94.87
26.23
5.14
37.60
26.04
36.93
5.44
5.56
1.37
2.11
1.72
3.86
95.48
25.60
5.08
36.82
26.27
37.43
7.75
8.22
2.34
3.08
2.55
4.71
.746
.752
.901
.302
.708
.681
8.05
4.78
2.45
1.82
8.72
5.13
2.68
2.06
.359
.525
105.66
82.90
77.50
9.96
4.26
4.99
106.07
83.06
76.31
12.85
5.14
5.42
.900
.905
.424
*Statistically significant at P ⬍.05.
acteristics at T2. Increases in lower anterior face
height (LAFH) with these appliances are usually
greater than those of normal growth, as previously
shown.1,9,15,16,21,23,27-29 Therefore, similar concerns apply when using these appliances in patients who do not
need increases in the LAFH.1,27,28 Appliances with the
opposite effect would be preferable for those patients.1,28,30
The maxillary incisors had a statistically greater
linear retrusion with the MPA appliance in relation to
A-point, as compared to the CHG. This retrusion was
greater in relation to A-point. The maxillary first molars
were distalized in group 1, whereas they had mesial
displacement in group 2, with a statistically significant
difference. If the maxillary molars were distalized in
group 1, it would follow that the incisors should have
had statistically greater retrusion in group 1 as well.
However, because of the skeletal effect of the CHG’s
greater restriction of maxillary forward displacement,
the incisor retrusion relative to A-point was smaller in
group 1.
Maxillary first molar extrusion was statistically
greater with the CHG than with the MPA; this was
expected because of the known predominant extrusive
Siqueira et al 447.e27
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 131, Number 4
Table IV.
Intergroup comparison of treatment changes (T2-T1, t test)
Groups
CHG (n ⫽ 25)
Variables
Maxillary component
SNA (°)
Co-A (mm)
Mandibular component
SNB (°)
Go-Gn (mm)
Co-Gn (mm)
Maxillomandibular relationship
ANB (°)
NAP (°)
Vertical component
SN.GoMe (°)
SN.PP (°)
UAFH (mm)
LAFH (mm)
PFH (mm)
LPFH (mm)
Maxillary dentoalveolar component
U1.NA (°)
U1-NA (mm)
U1-PP (mm)
U6-PP (mm)
U6-Fperp (mm)
Mandibular dentoalveolar component
IMPA (°)
L1.NB (°)
L1-NB (mm)
L1-MP (mm)
L6-MP (mm)
L6-Fperp (mm)
Dentoalveolar relationship
Overjet (mm)
Overbite (mm)
Soft-tissue profile
NLA (°)
UL-Fperp (mm)
LL-Fperp (mm)
MPA (n ⫽ 25)
Mean
SD
Mean
SD
P
⫺2.46
0.64
1.77
2.04
⫺0.17
2.54
2.10
2.01
.000*
.002*
0.26
3.06
6.39
1.17
3.06
2.90
1.36
3.25
6.38
1.96
2.87
3.03
.020*
.824
.996
⫺2.71
⫺5.97
1.25
2.93
⫺1.53
⫺3.57
1.43
2.65
.003*
.004*
0.31
1.26
2.81
4.04
5.30
4.04
1.48
1.71
1.51
2.33
2.18
2.24
⫺0.63
0.37
2.34
2.92
4.95
3.97
2.86
2.35
2.31
2.29
2.64
2.30
.151
.131
.393
.092
.614
.911
⫺6.41
⫺0.98
1.33
2.20
⫺0.78
9.40
2.46
1.82
1.67
2.55
⫺11.16
⫺2.86
1.13
1.00
1.26
7.79
2.03
1.88
1.45
2.60
.058
.005*
.705
.009*
.007*
2.03
2.62
0.85
1.10
2.65
2.50
6.26
6.11
1.37
1.99
1.08
2.69
5.23
5.98
0.92
⫺0.12
3.02
4.99
8.38
7.73
1.32
2.23
1.01
2.87
.133
.095
.859
.046*
.216
.003*
⫺5.24
⫺2.23
2.73
2.10
⫺5.93
⫺2.63
2.70
1.88
.372
.477
3.54
0.78
2.62
7.43
2.42
2.42
4.54
0.96
4.54
9.94
2.49
2.66
.688
.805
.010*
*Statistically significant at P ⬍.05.
effect of the CHG.1,2,4,16-18,25,31 Usually, the forces
generated by the MPA tend to cause maxillary first
molar intrusion or, at least, restriction of its downward
development.6-9,15,23
The maxillary first molar crown in group 1
experienced statistically significant distalization in
relation to group 2 as was previously observed in
comparisons between headgears and removable functional appliances.10,12 This result shows that distalization with the CHG is also greater than that with a fixed
functional appliance. Therefore, it can be concluded
that the CHG has a greater molar distalizing effect.
These different changes in the maxillary component
during treatment were reflected at T2: group 1 showed
statistically protruded maxillary incisors, greater maxillary first molar dentoalveolar height, and retruded
maxillary molars in relation to group 2.
The mandibular incisors had similar anteroposterior
behavior. However, the MPA tended to displace the
mandibular incisors farther labially than did the CHG.
This is in accordance with the effects of similar
functional appliances.15,20-23,32-34 The nonsignificantly
greater labial displacement of the incisors was reflected
in restriction of their vertical development, whereas in
group 1 the incisors experienced statistically significant
vertical development compared with group 2. As the
447.e28 Siqueira et al
Table V.
American Journal of Orthodontics and Dentofacial Orthopedics
April 2007
Intergroup comparison at T2 (t test)
Groups
CHG (n ⫽ 25)
Variables
Maxillary component
SNA (°)
Co-A (mm)
Mandibular component
SNB (°)
Go-Gn (mm)
Co-Gn (mm)
Maxillomandibular relationship
ANB (°)
NAP (°)
Vertical component
SN.GoMe (°)
SN.PP (°)
UAFH (mm)
LAFH (mm)
PFH (mm)
LPFH (mm)
Maxillary dentoalveolar component
U1.NA (°)
U1-NA (mm)
U1-PP (mm)
U6-PP (mm)
U6-Fperp (mm)
Mandibular dentoalveolar component
IMPA (°)
L1.NB (°)
L1-NB (mm)
L1-MP (mm)
L6-MP (mm)
L6-Fperp (mm)
Dentoalveolar relationship
Overjet (mm)
Overbite (mm)
Soft-tissue profile
NLA (°)
UL-Fperp (mm)
LL-Fperp (mm)
MPA (n ⫽ 25)
Mean
SD
Mean
SD
P
80.69
85.52
3.25
4.86
83.34
86.75
4.56
4.52
.022*
.361
77.81
73.52
111.94
3.21
4.80
6.58
78.78
72.32
109.21
3.44
3.34
4.89
.307
.306
.103
2.89
2.68
1.32
3.99
4.55
6.68
2.54
6.47
.006*
.011*
34.15
8.08
50.81
64.40
72.57
43.33
4.13
3.73
3.28
6.14
4.64
3.25
32.08
7.59
49.27
61.01
70.46
41.99
6.37
3.18
3.93
5.76
4.45
4.37
.179
.618
.139
.050
.108
.225
22.70
5.13
27.27
23.00
37.12
5.08
1.78
3.27
2.45
5.02
19.58
3.30
25.88
20.40
40.12
8.44
2.22
2.57
1.44
4.03
.120
.002*
.100
.000*
.024*
96.90
28.85
6.00
38.70
28.68
39.42
5.32
4.52
1.44
2.92
2.42
4.93
100.71
31.58
6.00
36.69
29.29
42.42
6.82
4.09
1.98
3.88
2.57
4.17
.032*
.030*
1.000
.044*
.396
.025*
2.82
2.55
0.60
1.00
2.80
2.50
0.58
0.69
.905
.831
109.20
83.69
80.12
10.37
5.28
5.40
110.62
84.02
80.85
11.36
5.31
5.25
.647
.826
.629
*Statistically significant at P ⬍.05.
incisors are labially displaced, the distance to the
mandibular plane decreases.15 These nonsignificantly
greater labial displacements of the mandibular incisors
in group 2 caused them to show statistically significant
protrusion in relation to group 1 at T2.
The mandibular first molars in the MPA group had
a statistically greater crown mesial displacement than
those in the CHG group. This is consequent to the
mesial forces acting on the mandibular teeth from the
forward mandibular displacement dictated by the appliance; this also helps in correcting the anteroposterior
discrepancy.6-9,15,20,21,33,34 Mesial molar displacement
in group 1 was within the normal developmental range
because no mesial forces were applied to these
teeth.17,26,35,36 Similar to the incisors, the statistically
greater mesial displacement of the mandibular molars
in group 2 placed their crowns significantly mesial to
those of group 1 at T2.
The amounts of reduction of overjet and overbite
were similar between the appliances, and therefore
there was also similarity in these variables at the end of
treatment in both groups, showing that both appliances
have equivalent potential in correcting these Class II
malocclusion characteristics.
As would be expected in Class II nonextraction
treatment, both appliances produced similar increases
Siqueira et al 447.e29
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 131, Number 4
Fig 4. Superimposition of average cephalometric tracings of groups 1 and 2 at T2: A, total superimposition on
SN line, registered on S; B, maxillary partial superimposition on palatal plane, registered on ANS; C, mandibular partial superimposition on mandibular plane
(Go-Me), registered on symphysis.
in the nasolabial angles, primarily consequent to palatal
tipping and retrusion of the maxillary incisors.37-40
Group 2 had statistically greater lower lip protrusion,
consequent to the statistically greater mesial mandibular molar displacement and to the nonsignificant greater
mandibular incisor labial displacement, as previously
observed with similar fixed functional appliances.41,42
Despite the statistically greater lower lip protrusion in
group 2, no significant differences were found in the
soft-tissue profile at T2 between the groups, probably
because of the great variability in the soft-tissue structures.43
Even though the differences in this variable and in
many other variables were statistically significant, but
small, between the groups, they can be considered
clinically relevant when one attempts to deliver the best
results to patients with specific characteristics.41-43
Clinical considerations
Correction of Class II malocclusions in the groups
treated with the MPA and the CHG, followed by fixed
appliances, was consequent to distinct and specific
dentoskeletal changes of each protocol. Clinically, the 2
appliances produced satisfactory results by reducing
facial convexity; this is important in Class II malocclusion treatment.15,22,30,34,41-43
Although the primary changes of the MPA, as
compared with normal growth, consisted of distalization of the maxillary dentoalveolar process,6-9 we
showed that patients treated with the CHG and fixed
appliances had greater skeletal changes in the maxilla
because of the orthopedic action of this mechanism in
restricting its anterior displacement. Consequently,
there was also greater improvement in the skeletal
Class II relationship. Maxillary molar distalization was
also greater with the CHG. The MPA produced smaller
skeletal changes and greater mandibular molar mesialization and labial displacement of the incisors that
resulted in greater protrusion of the lower lip, as
compared with the CHG group. From these effects,
their indications can be derived. Patients who need
greater effects on the maxilla and the maxillary teeth
are the best candidates for the CHG, whereas those who
can accept labial mandibular incisor tipping to compensate their Class II malocclusions will be better treated
with the MPA, which has the advantage of not depending on compliance.6-9,23,41,44
CONCLUSIONS
The different changes in Class II malocclusion
correction between the CHG and the MPA were that the
CHG corrected the Class II malocclusion primarily
through greater restriction of the anterior displacement
of the maxilla and distalization of the maxillary molars
as compared with the MPA, which corrected the malocclusion through mesial displacement of the mandibular first molars, with consequent protrusion of the
lower lip.
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