Download Influence of cephalometric characteristics on the occlusal success

ORIGINAL ARTICLE
Influence of cephalometric characteristics on
the occlusal success rate of Class II
malocclusions treated with 2- and 4-premolar
extraction protocols
Guilherme Janson,a Marcos Janson,b Alexandre Nakamura,b Marcos Roberto de Freitas,a
José Fernando Castanha Henriques,a and Arnaldo Pinzanc
Bauru, Brazil
Introduction: The objectives of this investigation were to compare the initial cephalometric characteristics of
complete Class II Division 1 malocclusions treated with 2 or 4 premolar extractions and to verify their
influence on the occlusal success rate of these treatment protocols. Methods: A sample of 98 records from
patients with complete Class II Division 1 malocclusion was divided into 2 groups with the following
characteristics: group 1 consisted of 55 patients treated with 2 maxillary first premolar extractions at an
initial mean age of 13.07 years; group 2 included 43 patients treated with 4 premolar extractions, with
an initial mean age of 12.92 years. Initial and final occlusal statuses were evaluated on dental casts with
Grainger’s treatment priority index (TPI), and the initial cephalometric characteristics were obtained from
the pretreatment cephalograms. The initial cephalometric characteristics and the initial and final occlusal
statuses of the groups were compared with the t test. A multiple regression analysis was used to
evaluate the influence of all variables in the final TPI. Results: The 2-premolar extraction protocol provided
a statistically smaller TPI and consequently a better occlusal success rate than the 4-premolar extraction
protocol. The 4-premolar extraction group had statistically smaller apical base lengths, more vertical facial
growth patterns, and greater hard- and soft-tissue convexities at pretreatment than the 2-premolar extraction
group. However, the multiple regression analysis showed that only the extraction protocol was significantly
associated with the final occlusal status. Conclusions: The initial cephalometric characteristics of the groups
did not influence the occlusal success rate of these 2 treatment protocols. (Am J Orthod Dentofacial Orthop
2008;133:861-8)
C
lass II malocclusion extraction treatment can
involve 2 maxillary premolars1 or 2 maxillary
and 2 mandibular premolars.2 The extraction of
only 2 maxillary premolars is generally indicated when
there is no crowding or cephalometric discrepancy in
the mandibular arch.3,4 Extraction of 4 premolars is
indicated primarily for crowding in the mandibular
arch, cephalometric discrepancy, or a combination in
growing patients.3-5 It was demonstrated that complete
From the Department of Orthodontics, Bauru Dental School, University of São
Paulo, Brazil.
a
Professor.
b
Graduate student.
c
Associate professor.
Based on research by the second author in partial fulfillment of the requirements for the degree of master of science in orthodontics at Bauru Dental
School, University of São Paulo, Brazil.
Reprint requests to: Guilherme Janson, Department of Orthodontics, Bauru
Dental School, University of São Paulo, Alameda Octávio Pinheiro Brisolla
9-75, Bauru, SP, 17012-901, Brazil; e-mail,[email protected].
Submitted, November 2005; revised and accepted, April 2006.
0889-5406/$34.00
Copyright © 2008 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2006.04.045
Class II malocclusion treatment with 2 maxillary premolar extractions produces a better occlusal success
rate than the 4-premolar extraction protocol,6 because
obtaining a Class I molar relationship requires more
anchorage reinforcement with removable appliances
and patient compliance.6-10 Treatment time is also
shorter with the 2-premolar than the 4-premolar extraction protocol11 because molar relationship correction,
inherent to nonextraction and 4-premolar extraction
protocols, is considered to increase Class II treatment
time.12-15 However, these groups were selected based
exclusively on the initial anteroposterior dental relationship, regardless of any other dentoalveolar or skeletal characteristic.6,11 Consequently, some cephalometric characteristics could have influenced the results, in
spite of the treatment protocol.16,17 Therefore, the
objectives of this investigation were to compare the
initial cephalometric characteristics of complete Class
II Division 1 malocclusions treated with 2 or 4 premolar extractions and to verify their influence on the
occlusal success rate of these treatment protocols.
861
862 Janson et al
American Journal of Orthodontics and Dentofacial Orthopedics
June 2008
MATERIAL AND METHODS
The sample was retrospectively collected from the
files of the orthodontic department at Bauru Dental
School, University of São Paulo. Ninety-eight patients
(56 male, 42 female), who satisfied the inclusion
criteria were selected. The sample was divided into 2
groups according to the extraction protocol. Group 1
consisted of 55 patients (31 male, 24 female) treated
with 2 maxillary first premolar extractions at an initial
mean age of 13.07 years (SD 1.42; range, 9.42-15.17
years). Group 2 included 43 patients (25 male, 18
female) with an initial mean age of 12.92 years (SD
1.73; range, 10.67-18.33 years). These patients were
treated with the following extraction combinations: 30
were treated with 4 first premolar extractions, 11 were
treated with maxillary first premolar and mandibular
second premolar extractions, 1 was treated with 4
second premolar extractions, and 1 was treated with
maxillary first and second premolar extractions in the
left and right quadrants, respectively, and mandibular
first premolar extractions. The groups were well
matched by age and sex. Specific inclusion criteria
required all patients initially to have complete (fullcusp) bilateral Class II malocclusion (molar relationship),7,18,19 regardless of any other dentoalveolar or
skeletal characteristic. Additionally, the subjects had all
permanent teeth up to the first molars and no dental
anomalies of number, size, or form.
Lateral headfilms were obtained in centric occlusion with passive lip posture at the pretreatment stage.
The lateral cephalograms for each subject in both
groups were traced on acetate paper by 1 investigator
(M.J.) and digitized (Accugrid XNT, model A30TL.F,
Numonics, Montgomeryville, Pa). These data were
then stored on a personal computer and analyzed with
Dentofacial Planner software (version 7.02, Dentofacial Software, Toronto, Ontario, Canada) (Fig 1). Because the headfilms had been taken with different
machines, the enlargement factors, from 6% to 9.8%,
were corrected with the cephalometric software.
It was not possible to use every subject from our
previous study, because the initial ages of the groups
had to be matched for the cephalometric study, and the
initial lateral cephalograms of some subjects were not
available.6 Therefore, a new comparison of the initial
and final occlusal statuses of these subjects had to be
conducted. We used Grainger’s treatment priority index20 (TPI). The TPI index provides weighted subscores for overjet, vertical overbite or open bite, tooth
displacement, and posterior crossbite, as well as summary scores reflecting the overall severity of the malocclusion. With the exception of rotation and displace-
Fig 1. Unusual cephalometric measurements: 1, Mx1PP: perpendicular distance from the maxillary central
incisor edge to the palatal plane; 2, Mx6-PP: perpendicular distance from the mesial cusp tip of the maxillary
molar to palatal plane; 3, Mx6-ANSperp: distance between the mesial point of the maxillary first molar and
the anterior nasal spine-perpendicular line; 4, Md1-MP:
the perpendicular distance from mandibular central
incisor edge to the mandibular plane; 5, Md6-MP: the
perpendicular distance from the mesial cusp tip of the
mandibular molar to mandibular plane; 6, Md6-Pogperp: distance between the mandibular first molar mesial point and the pogonion-perpendicular line; 7, overjet: the horizontal distance from the maxillary incisor
edge to the mandibular incisor edge, measured parallel
to the Frankfort horizontal plane; 8, overbite: the vertical
distance from the maxillary incisor edge to the mandibular incisor edge, measured perpendicular to the Frankfort horizontal plane; 9, molar relationship: distance
between the mesial surface of maxillary first molar and
the mandibular first molar, measured parallel to the
Frankfort horizontal plane (positive value when the
maxillary molar was anterior to the mandibular molar);
10, canine relationship (OP): distance between the
maxillary canine cusp tip and the mandibular canine
cusp tip, measured parallel to the functional occlusal
plane; 11, NAP angle formed by nasion, A-point, and
pogonion (not illustrated).
ment, all TPI components are measured along a
continuous scale from positive to negative values.
Thus, mandibular overjet and open bite are scored as
negative overjet and negative overbite, respectively. A
constant corresponding to the first molar relationship is
added to the TPI score. Total scores on the TPI range
Janson et al 863
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 133, Number 6
from 0 to 10 or more, with higher scores representing
more severe malocclusions.21,22
The TPI components are defined as follows.21,22
1. Overjet is the anterior distance from the most
mesial part of the labial surface of the maxillary
central incisor to the labial surface of the opposing
mandibular incisor, measured perpendicularly to
the coronal plane.
2. Overbite or open bite (with the dental models in
centric [convenience] occlusion) is the amount of
vertical overlap of the maxillary central incisor over
the mandibular central incisor taken as a ratio of the
total crown height (cervix to incisal edge) of the
mandibular incisor.
3. Tooth displacement is the sum of the number of
teeth noticeably rotated or displaced from ideal
alignment, plus twice the number of teeth rotated
more than 45° or displaced more than 2 mm.
4. First molar relationship is a constant comprising the
severity of the malocclusion, based on the relationships between the maxillary and mandibular first
molars.
5. Posterior crossbite is the buccolingual deviation in
occlusion of the postcanine teeth. The measurement
is positive for buccal crossbite (first molar positioned too far buccally) and negative for lingual
crossbite. Crossbite is also scored as the number of
teeth deviating from ideal cusp-to-fossa fit by a
cusp-to-cusp relationship or worse.21,22
In the 2-premolar extraction subjects, it was assumed that a Class II molar relationship at the end of
treatment would be classified as a neutral relationship
in the TPI because this is the correct posterior tooth
arrangement in a normal relationship of the anterior
teeth in this treatment approach.
Mandibular crowding of the initial dental study
models was calculated as the difference between arch
length (circumference, from left to right first molars)
and the sum of tooth widths from first molar to first
molar, in millimeters. In a well-aligned arch, arch
length was equal to the sum of the tooth widths.
Negative values indicated crowding.23
Forty pairs of dental study models (20 of each
group) were remeasured by the same examiner (data
obtained from the previous study6), and 20 randomly
selected radiographs were retraced and redigitized by
the same examiner (M.J.). The casual error was calculated according to Dahlberg’s formula (S2 ⫽ ⌺d2/2n),24
where S2 is the error variance and d is the difference
between the 2 determinations of the same variable. The
systematic error was evaluated with dependent t test25
at P ⬍0.05.
Statistical analyses
Intergroup compatibility for initial age and sex
distribution was evaluated with t and chi-square tests,
respectively. The cephalometric variables at pretreatment were compared between the groups with t tests. A
multiple regression analysis was used to evaluate the
influence of all variables in the final TPI (FTPI).
Statistical analyses were performed with Statistica software (Statistica for Windows, version 6.0, Statsoft,
Tulsa, Okla) at P ⬍0.05.
RESULTS
Of the 29 variables, only 4 had systematic errors:
Md6-Pogperp, overbite, canine relationship, and nasolabial angle (definitions are given in Fig 1). Four
variables showed casual errors greater than 1 mm or 1°,
and only 2 variables were greater than 2°.
The groups were compatible for initial age, sex
distribution, and initial TPI (ITPI) (Table I).
Group 1 had larger basal bones (Co-A, Co-Gn,
Go-Gn, Co-Go), more protrusive mandible (SNB angle), more horizontal growth pattern (FMA, SNGoGn), less protruded mandibular incisors (Md1-NB),
larger Class II canine anteroposterior discrepancy (canine relationship OP), and less convex profile (NAP)
than group 2 (Table II, Fig 2, A).
Of all variables, only the extraction protocol was
significantly associated with the FTPI, according to the
multiple regression analysis (Table III).
DISCUSSION
The purpose of this investigation was to evaluate
whether the initial cephalometric characteristics of the
groups in a previous study, whose occlusal outcomes
were compared, could have influenced the results.6 In
that study, the results showed a better occlusal success
rate for the 2-premolar extraction protocol compared
with the 4-premolar extraction protocol. The groups in
the previous study were chosen primarily for complete
bilateral Class II malocclusion, independently of the
associated cephalometric skeletal characteristics.
Therefore, the same subjects were selected for this
evaluation, except those without an initial cephalometric radiograph. Additionally, to match the groups’
initial ages, some other records were discarded. This
resulted in the records of 98 patients. Table I shows that
the groups were compatible for initial age, sex distribution, and ITPI. Although the groups were not compatible for initial amount of crowding, this variable was
taken into account in the multiple regression analysis.
The FTPI of group 1 was statistically smaller than that
of group 2, demonstrating a greater occlusal success
864 Janson et al
Table I.
American Journal of Orthodontics and Dentofacial Orthopedics
June 2008
Compatibility and results of the occlusal comparison between the groups
Group 1 (n ⫽ 55) 2 extractions
Group 2 (n ⫽ 43) 4 extractions
Variable
Mean (SD)
Mean (SD)
P value
Crowding (mm)
Age (y)
Sex
0.76 (1.30)
13.02 (1.42)
3.44 (2.69)
12.92 (1.73)
0.000*†
0.773†
Male
31 (56.36%)
ITPI
FTPI
Female
24 (43.63%)
Male
25 (58.13%)
8.17 (1.80)
0.67 (0.72)
Female
18 (41.86%)
8.16 (1.04)
1.87 (1.66)
0.843‡
0.970†
0.000*†
*Statistically significant: †t test; ‡chi-square test.
Table II.
Pretreatment comparison between groups (t test)
Variable
Maxillary component
SNA angle (°)
Co-A (mm)
Mandibular component
SNB angle (°)
Co-Gn (mm)
Go-Gn (mm)
Co-Go (mm)
Maxillomandibular relationship
ANB angle (°)
Facial pattern
FMA (°)
SN.GoGn (°)
Sn.PP (°)
LAFH (mm)
Maxillary dentoalveolar component
Mx1.NA (°)
Mx1-NA (mm)
Mx1-PP (mm)
Mx6-PP (mm)
Mx6-ANSperp (mm)
Mandibular dentoalveolar component
Md1.NB (°)
Md1-NB (mm)
Md1-MP (mm)
Md6-Pogperp (mm)
Md6-MP (mm)
Dentoalveolar relationships
Overjet (mm)
Overbite (mm)
Molar rel (mm)
Canine rel OP (mm)
Hard- and soft-tissue profile
Nasolabial angle (°)
NAP (°)
Group 1 (n ⫽ 55) 2 extractions
Mean (SD)
Group 2 (n ⫽ 43) 4 extractions
Mean (SD)
P value
81.13 (3.92)
85.40 (5.96)
79.84 (3.86)
82.77 (4.67)
0.108
0.020*
76.74 (2.75)
107.71 (6.32)
69.68 (4.40)
50.81 (4.60)
74.52 (2.83)
104.03 (5.33)
67.52 (4.54)
48.03 (4.02)
0.000*
0.003*
0.020*
0.002*
4.39 (2.81)
5.33 (3.02)
0.115
26.60 (4.94)
32.84 (5.55)
5.66 (3.33)
64.28 (5.68)
30.51 (5.17)
37.24 (5.44)
7.02 (3.38)
65.73 (5.55)
0.000*
0.000*
0.050
0.210
26.11 (9.98)
6.51 (3.95)
28.25 (2.87)
23.48 (2.86)
⫺27.13 (2.66)
27.84 (7.51)
6.83 (3.12)
28.80 (2.63)
23.30 (2.46)
⫺26.66 (3.15)
0.345
0.657
0.333
0.752
0.420
24.74 (6.00)
4.77 (2.37)
38.89 (2.88)
⫺30.95 (2.49)
27.93 (2.21)
25.69 (5.30)
6.13 (2.21)
39.94 (2.77)
⫺29.61 (3.25)
28.88 (2.19)
0.419
0.005*
0.071
0.023*
0.036*
7.21 (2.73)
4.15 (2.82)
3.69 (0.77)
4.04 (1.52)
7.36 (2.67)
4.27 (2.00)
3.81 (0.58)
3.30 (0.94)
0.776
0.812
0.377
0.006*
111.07 (13.32)
6.41 (6.79)
108.51 (13.76)
9.37 (6.73)
0.355
0.034*
*Statistically significant; rel, relationship.
rate for the former, as was obtained in the previous
study.6
There could be some criticism in using Grainger’s
TPI20 for evaluation of the pretreatment and posttreat-
ment occlusal statuses rather than the more recent and
currently mostly used peer assessment rating (PAR)
index.26-30 The first reason for this was that the TPI was
used in the previous study and because the PAR index
Janson et al 865
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 133, Number 6
Table III. Results of the multiple regression analysis
with FTPI as the dependent variable
Variable
1. Extraction protocol
2. Initial age
3. Mandibular crowding
4. Mx1-NA
5. Sex
F ⫽ 6.982
R
0.441
0.467
0.497
0.515
0.524
R2
P
0.194
0.000
0.218
0.092
0.247
0.062
0.265
0.127
0.275
0.284
P ⫽ 0.000014
FTPI ⫽ 0.44 (number of extracted premolars) ⫹ 0.16 (initial age) ⫹
0.11 (mandibular crowding) ⫹ 0.04 (Mx1-NA) ⫹ 0.26 (sex score *)
⫺ 3.12.
*Male ⫽ 1; female ⫽ 2.
A
B
Fig 2. The software (Dentofacial Planner version 7.02),
used to measure the variables, can create a mean tracing
for each group at each stage; therefore, A and B are based
on superimpositions of these mean tracings to illustrate
pretreatment and posttreatment differences between the
groups. A, Superimposition on the sella-nasion line at sella
of pretreatment mean tracings for group 1 (black) and
group 2 (red); B, same superimposition of posttreatment
mean tracings for group 1 (black) and group 2 (red).
has some limitation in evaluating the posterior segment’s anteroposterior relationship, as pointed out earlier.31-33 To overcome this deficiency, it has been
suggested that there should be a different PAR index to
separately evaluate Class I, Class II, and Class III
malocclusions.34 In this study, an efficient index to
evaluate the posterior segment’s anteroposterior discrepancy was crucial because this is where the major
differences are between the treatment success rates of
these 2 treatment protocols.6,11
The initial cephalometric difference between the
groups that could have increased treatment difficulty
for the 4-premolar extraction group would be the more
vertical growth pattern (FMA and SN.GoGn) of group
2 (Table II).35,36 The apical bases were also statistically
larger in group 1 and could have influenced the occlusal
success rate. This is why a multiple regression analysis
was conducted, with the FTPI as the dependent variable, as will be discussed.
The more vertical growth pattern and the more
protruded mandibular incisors in group 2 help to
explain why these patients were preferably treated with
4-premolar extractions, as usually indicated in these
situations.37-39 Nevertheless, more protruded incisors
would not affect the occlusal success rates of the 2
treatment protocols. This parameter refers to the relationship of the mandibular incisors to the mandible and
the cranial base, and not to the interdental maxillomandibular relationship.
The mandibular molars were more anteriorly positioned and had greater dentoalveolar height in group 2.
Probably, the anterior positioning of the first molars
was a factor for greater crowding in this group. Because
group 2 had a greater vertical growth pattern, greater
dentoalveolar height would also be expected.40-44
The initial Class II intercanine anteroposterior
relationship was statistically greater in group 1 and
differs from the previous results in the dental casts
that showed similar anteroposterior discrepancies.6
This might have resulted from difficulty in locating
the canines in the lateral headfilms.45,46 However,
this would increase treatment difficulty in group 1
866 Janson et al
and would not help to explain the smaller occlusal
success rate of group 2.
The more convex skeletal facial profile (NAP) in
group 2 was consequent to its statistically nonsignificant greater anteroposterior basal bone discrepancy and
greater mandibular retrusion. Although greater facial
convexity might be considered less attractive than a
straighter profile,47-49 it is unlikely to play a role in the
occlusal success rate in the correction of Class II
malocclusions.
Results of the multiple regression analysis showed
that only the extraction protocol was significantly
associated with the FTPI (Table III). Other variables
that helped to explain the variation in the FTPI were
initial age, mandibular crowding, linear anteroposterior
position of the maxillary incisors (Mx1-NA), and sex.
However, individually, the association of these variables with the FTPI was not statistically significant.
These results demonstrate that it is not the cephalometric characteristics that play a primary role in complete
Class II treatment success rate but, rather, the treatment
protocol. The 4-premolar extraction treatment protocol
demands more anchorage reinforcement to correct the
anteroposterior molar relationship than the 2-premolar
extraction protocol.2,50 Usually, anchorage reinforcement is provided by removable extraoral appliances
that require patient compliance. Consequently, the
4-premolar extraction protocol requires more patient
compliance than the 2-premolar protocol.51,52 Therefore, the treatment success rate will greatly depend on
patient compliance.
It is known that malocclusions associated with a
vertical growth pattern or a severe skeletal Class II
basal relationship have poorer prognoses in orthodontic
treatment.35,53-55 This poor prognosis refers to the final
esthetic result and not specifically to the occlusal success
rate in correcting the posterior segment Class II anteroposterior discrepancy, as previously suggested6,9,56 and as
shown by our results. Group 2, with a statistically
significant more vertical growth pattern, initially had a
more convex facial profile and also ended up similarly;
this was less esthetically pleasing than a straighter
profile57-60 (Fig 2). Therefore, these results do not
contradict any concept but, rather, show that these
cephalometric parameters do not influence the occlusal
success rate of Class II malocclusions treated with 2- or
4-premolar extraction protocols.
When deciding between these 2 protocols, one must
remember that these cephalometric variables will influence the esthetic prognosis but not the occlusal success
rate. Although it is reasonable that an accentuated
vertical facial pattern and a skeletal Class II relationship have poorer prognoses for facial balance, it is
American Journal of Orthodontics and Dentofacial Orthopedics
June 2008
misleading to think that these factors will also influence
the occlusal success rate in complete Class II malocclusions treated by the investigated treatment protocols.
Our results show that the most important factor in a
better occlusal success rate in the treatment of complete
Class II malocclusions is the treatment protocol and not
any cephalometric parameter. Therefore, when the
clinician must decide between these 2 treatment protocols for a complete Class II malocclusion, the greater
difficulty of the 4-premolar extraction protocol will
play a greater role in the decision than the cephalometric parameters—ie, growth pattern and apical base
discrepancy.
CONCLUSIONS
The most relevant differences between the groups
were that the 4-premolar extraction group had statistically smaller apical base lengths, more vertical facial
growth pattern, and greater hard- and soft-tissue convexities at pretreatment than did the 2-premolar extraction group.
These different cephalometric characteristics of the
groups did not influence the occlusal success rates of
the 2 treatment protocols.
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