Download Orthodontic treatment time in 2- and 4-premolar

ORIGINAL ARTICLE
Orthodontic treatment time in 2- and
4-premolar-extraction protocols
Guilherme Janson,a Fábio Rogério Torres Maria,b Sérgio Estelita Cavalcante Barros,b
Marcos Roberto de Freitas,c and José Fernando Castanha Henriquesc
Bauru, São Paulo, Brazil
Introduction: The purpose of this study was to compare the treatment times of complete Class II
malocclusions treated with 2- and 4-premolar-extraction protocols. Methods: Ninety-seven patients were
selected and divided into 2 groups, according to the 2 extraction criteria. Group 1, treated with 2 maxillary
premolar extractions, consisted of 49 patients (30 male, 19 female) with a mean age of 14.35 years. Group
2, treated with 4 premolar extractions, consisted of 48 patients (27 male, 21 female) with a mean age of 13.03
years. Treatment times of the groups were compared with the t test. Results: Treatment times were
significantly shorter with the 2-premolar-extraction protocol compared with the 4-premolar-extraction
protocol. Conclusions: Treatment time will be shorter and the occlusal results more predictable with a
2-premolar-extraction protocol compared with 4 premolar extractions. (Am J Orthod Dentofacial Orthop
2006;129:666-71)
C
lass II malocclusions can require different
types of treatment when severity of the anteroposterior discrepancy, age, and patient compliance are considered.1 Options for correction of Class II
malocclusion include headgear, fixed and removable
functional appliances, fixed appliances with Class II
elastics, extractions, and orthognathic surgery.2-5 Extractions can involve 2 maxillary premolars,6 or 2
maxillary and 2 mandibular premolars.7 It has been
demonstrated that a 2-maxillary-premolar-extraction
protocol provides a better occlusal success rate than the
4-premolar-extraction protocol.8
The number of teeth extracted and the severity of
the malocclusion can influence treatment time.9 Because malocclusion severity is an inherent characteristic that cannot be controlled, efforts have been made to
quantify the influence of extractions on the duration of
orthodontic treatment.10,11 Investigations comparing
treatment times between malocclusions treated with
and without extractions demonstrated that the number
From the Department of Orthodontics, Bauru Dental School, University of São
Paulo, Bauru, São Paulo, Brazil.
a
Associate professor.
b
Graduate student.
c
Professor.
Based on research by Dr Fábio Rogério Torres Maria in partial fulfillment of
the requirements for the degree of Master of Science in Orthodontics at Bauru
Dental School, University of São Paulo.
Reprint requests to: Dr 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, July 2004; revised and accepted, September 2004.
0889-5406/$32.00
Copyright © 2006 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2005.12.026
666
of teeth removed is positively correlated to treatment
time.10-15 In spite of this evidence, Class II treatment
times of 2-maxillary-premolar-extraction and 4 premolar-extraction protocols have not been compared.
Therefore, our objective was to test the following null
hypothesis: complete Class II treatment time is similar
in the 2-maxillary and 4-premolar-extraction protocols.
MATERIAL AND METHODS
The sample was retrospectively selected from the
files of over 2000 treated patients at the Orthodontic
Department at Bauru Dental School, University of São
Paulo, Brazil. Records and the initial dental study
models of all patients who initially had complete
bilateral Angle Class II malocclusions (molar relationship) and were treated with 2 maxillary premolar
extractions or 2 maxillary and 2 mandibular premolar
extractions, and standard fixed edgewise appliances
were selected and divided into 2 groups. Sample
selection was based exclusively on the initial anteroposterior dental relationship, regardless of any other
dentoalveolar or skeletal characteristic. Additionally,
patients had all permanent teeth up to the first molars,
with no tooth agenesis or supernumerary teeth.
Group 1 consisted of 49 patients treated with 2 first
maxillary premolar extractions (30 male, 19 female) at
an initial mean age of 14.35 years (range, 9.42-27.08
years). Forty-three had Class II Division 1 malocclusions, and 6 had Class II Division 2 malocclusions.
Their treatment plans included the extraction of 2
maxillary premolars. Patients with nonextraction treatment plans were excluded.
Janson et al 667
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 129, Number 5
Group 2 consisted of 48 patients with Class II
Division 1 malocclusions, treated with 4 premolar
extractions (27 male, 21 female) at an initial mean age
of 13.03 years (range, 10.67-18.33 years). Thirty-five
were treated with 4 first premolar extractions, 11 were
treated with first maxillary premolars and second mandibular premolar extractions, 1 was treated with 4
second premolar extractions, and 1 was treated with
first and second maxillary premolar extractions on the
left and right quadrants, respectively, and first mandibular premolar extractions.
The mechanics used with the standard fixed edgewise appliances included 0.022 x 0.028-in conventional
brackets (not preadjusted), associated with extraoral
headgear and lip bumpers to reinforce anchorage for the
maxillary and mandibular teeth, respectively, when
necessary. Class II elastics were also used when applicable, especially in the 4 premolar-extraction protocol,
to aid in correcting the Class II anteroposterior relationship. There was no anchorage preparation. The
usual wire sequence began with a 0.015-in twist-flex or
0.016-in nitinol wire, followed by 0.016, 0.018,
0.020-in and, finally, 0.021 ⫻ 0.025-in or 0.018 ⫻
0.025-in stainless steel wires (Unitek, Monrovia, Calif).
In extraction treatment, the canines are initially retracted a small amount to allow space for leveling and
aligning of the anterior teeth. The anterior teeth were
retracted en masse with the rectangular wire, after
leveling and aligning. If a 0.021 ⫻ 0.025-in wire was
being used, the dimensions of the rectangular wire were
electrolytically reduced in the posterior segments to
reduce the friction forces with the brackets and tubes.
The canines and anterior teeth were retracted with
elastic chains. Deep overbites were usually corrected
by reversing and accentuating the curve of Spee of the
stainless steel archwires until obtaining overcorrection.
This overcorrection was maintained by accentuating
and reversing the curve of Spee in the rectangular wire
as well. Fixed or removable functional appliances were
not used.
From the patient records, the following information
was obtained: initial age, sex, date of treatment onset,
date of treatment completion, and total treatment time.
To evaluate the initial malocclusion severity compatibility of the groups, the initial treatment priority index
(TPI)16 and the amount of mandibular crowding were
blindly calculated on the pretreatment dental study
models of each patient. 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 malocclusion. With the exception of rotation and
displacement, all TPI components were measured along
a continuous scale from positive to negative values.
Thus, mandibular overjet and open bite are entered as
negative overjet and negative overbite, respectively. A
constant corresponding to the first-molar relationship
was added to the TPI score. Total scores on the TPI
ranged from 0 to 10 or more, with higher scores
representing more severe malocclusions.17,18
TPI components were defined as follows.17,18
●
●
●
●
●
Overjet: 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.
Overbite or open bite: with the dental models in
centric (convenience) occlusion, 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.
Tooth displacement: the sum of the number of teeth
noticeably rotated or displaced from ideal alignment,
plus 2 times the number of teeth rotated more than
45° or displaced more than 2 mm.
First-molar relationship: a constant comprising the
severity of the malocclusion, based on the relationship between the maxillary and mandibular first
molars.
Posterior crossbite: buccolingual deviation in occlusion of postcanine teeth. The measurement is positive
for buccal crossbite (first molar positioned too far to
the buccal side) or negative for lingual crossbite.
Crossbite is also scored as the number of teeth
deviating from ideal cusp-to-fossa fit by cusp-to-cusp
relation or worse.17,18
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.
Error study
Twenty pairs of dental study models were randomly
remeasured by the same examiner (F.R.T.M.), for the
TPI and the mandibular-crowding evaluations. The
casual error was calculated according to Dahlberg’s
formula19 S2 ⫽ ⌺d2/2n, where S2 is the error variance
and d is the difference between the 2 determinations of
the same variable, and the systematic error with dependent t test,20 for P ⬍.05.
668 Janson et al
Table I.
American Journal of Orthodontics and Dentofacial Orthopedics
May 2006
Results of error study
Table II.
First
measurement
Second
measurement
Variable
Mean
SD
Mean
SD
P
Dahlberg
TPI
Initial MC
8.37
2.55
1.17
3.04
8.35
2.45
1.08
2.71
.804
.587
0.245
0.591
Results of t test between groups
Group 1
(n ⫽ 49)
Group 2
(n ⫽ 48)
Variable
Mean
SD
Mean
SD
t
P
MC, Mandibular crowding (mm).
Initial TPI
Initial MC
Initial age (y)
TT
7.94
0.75
14.35
23.52
1.29
1.28
2.79
5.86
8.21
3.44
13.03
28.12
1.09
2.73
1.68
7.59
⫺.11
⫺6.22
2.79
⫺3.35
.268
.000*
.006*
.001*
Statistical analyses
*Statistically significant P ⬍.05.
MC, Mandibular crowding (mm); TT, treatment time (months).
Means and standard deviations for each variable
were calculated to enable characterization of both
groups. T tests were used to compare initial age, TPI,
mandibular crowding, and the treatment times of the
groups. Because mandibular anterior crowding can influence extraction decisions in the mandibular arch21-24 and
treatment times,25-27 the groups were divided into subgroups without crowding. Therefore, these subgroups
were similarly compared to eliminate the influence of
crowding in the treatment-time results. Results were
considered significant at P ⬍.05.
RESULTS
There were no systematic errors in the TPI and initial
mandibular crowding evaluation (Table I). The casual
errors were within acceptable levels. The groups were
compatible regarding initial TPI, but the subjects in
group 2 had more crowding and younger initial ages
than those in group 1. Treatment times were also longer
in group 2 (Table II). When the groups were divided
into noncrowded subgroups, their initial age and TPI
were compatible, but treatment time in subgroup 2 was
longer than in subgroup 1 (Table III).
DISCUSSION
The subjects were selected on the basis of having
complete bilateral Class II malocclusions, independently of cephalometric skeletal characteristics. Because both groups were similarly chosen, it could be
expected that these characteristics would be evenly
distributed among them. Usually, it is not the skeletal
characteristics of a Class II malocclusion that primarily
determine whether it should be treated with 2 or 4
premolar extractions but, rather, the dentoalveolar characteristics.
Regarding the initial compatibility of the 2 groups,
Table II shows no statistically significant differences in
initial TPI between groups. However, the statistically
significant difference between the initial crowding of
both groups might influence the decision between the
treatment protocols and perhaps treatment time. The
greater the mandibular crowding, the greater the ten-
Table III.
Results of t test between subgroups without
crowding
Subgroup 1
(n ⫽ 35)
Subgroup 2
(n ⫽ 14)
Variable
Mean
SD
Mean
SD
t
P
Age (y)
Initial TPI
TT
14.10
7.94
24.35
2.26
1.35
5.64
13.23
7.78
30.13
1.83
0.82
8.89
1.28
0.40
⫺2.72
.204
.687
.008*
*Statistically significant P ⬍.05.
TT, Treatment time (months).
dency for a 4-premolar-extraction protocol. For that
reason, the groups were divided into subgroups without
crowding; they were compared with the t test to
investigate any interference of this initial difference in
the results. The 6 Class II Division 2 subjects in group
1 and none in group 2 should not cause incompatibility
of the groups, because the larger score of the TPI from
a larger overjet in the Division 1 subjects would be
compensated by the larger overbite of the Division 2
subjects. Accordingly, the anchorage reinforcement
would also be similar because of the greater labial
crown torque that should be applied to the maxillary
incisors to correct their inclination and to retract them
in the Class II Division 2 subjects.
Group 1 had a significantly shorter treatment time
than group 2 (Table II). This result corroborates the
findings of several studies in which shorter treatment
times were related to protocols with fewer extractions.10,11,13-15,28,29 Group 1 patients had a significantly
higher age range than group 2; this tends to make Class
II treatment more difficult and consequently longer, as
found in previous studies.30,31 However, the results
suggested otherwise, and this age difference even
corroborated them. Comparing the subgroups without
initial crowding demonstrated a similar tendency
(Table III). Treatment time in the noncrowded subgroup
2 tended to be slightly greater than that in group 2 (Tables
II and III). This tendency opposes previous speculations
Janson et al 669
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 129, Number 5
that crowding increases treatment time.25-27 Generally, it
might be reasonable to expect that crowding would
increase treatment time because it increases the severity of
the malocclusion, which is more difficult to treat.11,32-34
However, this might not apply in every situation,
especially when complete Class II malocclusion treatment protocols are being compared, such as in this
study. It could be speculated that there was a tendency
for treatment time to be shorter in group 2 than in the
noncrowded subgroup 2 because, after the mandibular
extractions in the crowded subjects, most of the spaces
are used to correct crowding during the leveling and
alignment phase, leaving minor spaces to be closed
during the anterior en-masse retraction phase. On the
other hand, in noncrowded subjects, in whom mandibular extractions were performed to correct incisor
proclination, only small amounts of the spaces are
closed during leveling and alignment, and most of the
spaces are closed during the retraction phase. This
would increase retraction time and overall treatment
time. Further specific studies are necessary to confirm
this speculation.
According to Fink and Smith,10 each premolar
extraction accounts for an additional 0.9 months of
treatment. Our study demonstrated that treatment
time in the 4-premolar-extraction group was longer
than the treatment time in the 2-maxillary-premolar
protocol than would be expected, based on the study
of Fink and Smith (Tables II and III). This suggests
that other variables might influence treatment time in
this comparison. It is speculated that this variable is
the anteroposterior molar Class II relationship correction that is necessary in group 2. Patients must
comply in using extraoral headgear or Class II
elastics to correct Class II anteroposterior discrepancies.8,35-38 If the necessary compliance level is not
obtained, the occlusal results are compromised,35,39
and treatment time will be increased.32 Previous
studies that compared treatment times in extraction
and nonextraction subjects did not distinguish between Class I and Class II malocclusions and did not
compare 2- and 4-premolar-extraction protocols in
complete Class II malocclusion corrections.10,11,1315,28,29 According to this rationale, it would be
expected that a Class II malocclusion treated with 2
premolar extractions could have a treatment time
similar to that of 4-premolar extraction Class I
treatment.40,41 The required time to close the maxillary extraction spaces in Class II patients would be
similar to the time necessary to simultaneously close
the maxillary and mandibular spaces in Class I
patients. However, if 4 premolars are extracted in
Class II malocclusions, treatment time is increased
not because of the greater amount of space to be
closed, but because of the Class II anteroposterior
relationship that must be corrected9; this depends on
patient compliance in using headgear or Class II
elastics.8,35,38,40
Group 2 and subgroup 2 had treatment times that
were 4.6 and 5.78 months longer than group 1 and
subgroup 1, respectively. This might not be considered clinically significant, but, when patients or
parents are very demanding, it might represent a
doctor/patient/parents relationship problem. To be
efficient, one must consider every aspect that can
influence treatment time. The treatment protocol is
only 1 aspect. If other variables that also cause minor
treatment time increases act simultaneously, the
overall increase could be clinically significant. Additionally, the patients were not selected based on
excellent treatment outcomes. It has been suggested37,40 and demonstrated8 that in Class II patients the
4-premolar-extraction protocol has more complicated orthodontic mechanics, and therefore its occlusal success rate is lower than the 2-premolar-extraction protocol, especially in complete Class II
malocclusions. The most difficult aspect to be corrected in the 4-premolar-extraction protocol is the
Class II anteroposterior discrepancy. Therefore, because correction of anteroposterior discrepancies in
complete Class II 4-premolar-extraction protocols
requires more patient compliance, presumably treatment time in well-finished patients would be even
longer, when compared with well-finished patients
with 2-maxillary-premolar extractions; this should
be investigated in the future.
Treatment times for both groups in this study were
longer than reported in the literature.13,28,42 Perhaps
this can be explained because graduate students treated
them, whereas in the other investigations the patients
were treated in private practices. It is speculated that
treatment times are usually shorter in the hands of more
experienced clinicians.32,43
Clinical implications
Considering that the 4-premolar-extraction protocol for Class II malocclusion treatment usually has
longer treatment times and less satisfactory occlusal
success rates,8 because greater compliance is needed
for the treatment mechanics than the 2-premolarextraction protocol, it should be used in carefully
selected patients. The decision in every treatment
plan depends on a cost-benefit ratio.44 The orthodontic treatment goals usually include obtaining good
facial balance, an optimal static and functional occlusion, and stable treatment results.12,45 Four pre-
670 Janson et al
molar extractions in complete Class II patients are
usually used to correct crowding and incisor proclination, leading to these objectives. Nevertheless,
because of the great orthodontic discrepancies and
the patients’ primary concerns, optimal objectives
cannot always be attained.12 Therefore, when considering the several variables involved, one must also
consider the greater difficulty and time in obtaining a
good occlusal result in complete Class II malocclusion treatment with the 4premolar-extraction protocol. For example, it may be that to provide an
optimal facial balance, a 4-premolar-extraction protocol in a complete Class II malocclusion would be
the best option. However, because of the patient’s
advanced age and poor compliance attitude, along
with increased treatment time, a 2-premolar-extraction protocol would provide greater benefits and
would be the selected treatment option. If the benefits of a 4-premolar-extraction protocol in Class II
malocclusion treatment outweigh the time and the
greater mechanical difficulty costs,8 it should be
undertaken. Otherwise, a 2-premolar-extraction protocol should be preferred. The treatment objectives
might be compromised, but treatment time will be
shorter, and the occlusal results more predictable.
CONCLUSIONS
The null hypothesis was rejected because complete
Class II treatment time with the 2-premolar-extraction
protocol was significantly shorter than treatment time
with the 4-premolar-extraction protocol.
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