Class II treatment efficiency in maxillary premolar extraction and nonextraction protocols.

Abstract

In this study, we compared the efficiency of nonextraction and 2-maxillary-premolar-extraction protocols in complete Class II malocclusion treatment.
A sample of 112 records from patients with complete Class II malocclusion was divided into 2 groups with the following characteristics: group 1, comprising 43 patients treated nonextraction with an initial mean age of 12.63 years; and group 2, comprising 69 patients treated with extraction of 2 maxillary premolars with an initial mean age of 13.91 years. To compare the efficiency of each treatment protocol, the initial and final occlusal statuses were evaluated on dental casts with the peer assessment rating (PAR) index, and the treatment time of each group was calculated from the clinical charts. Treatment efficiency was calculated by the ratio between the percentage of PAR reduction and the treatment time. PAR scores, treatment times, and treatment protocols' efficiencies of the groups were compared with the t test.
The 2-maxillary-premolar-extraction protocol had a smaller final PAR score, a greater percentage of PAR reduction, and greater treatment efficiency than the nonextraction protocol of complete Class II malocclusion.
The 2-maxillary-premolar-extraction protocol has greater treatment efficiency than the nonextraction protocol of complete Class II malocclusion.

Full text

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ORIGINAL ARTICLE
Class II treatment efficiency in maxillary
premolar extraction and nonextraction
protocols
Guilherme Janson,aSérgio Estelita Cavalcante Barros,bMarcos Roberto de Freitas,a
José Fernando Castanha Henriques,aand Arnaldo Pinzanc
Bauru, Brazil
Introduction: In this study, we compared the efficiency of nonextraction and 2-maxillary-premolar-extraction
protocols in complete Class II malocclusion treatment. Methods: A sample of 112 records from patients with
complete Class II malocclusion was divided into 2 groups with the following characteristics: group 1,
comprising 43 patients treated nonextraction with an initial mean age of 12.63 years; and group 2, comprising
69 patients treated with extraction of 2 maxillary premolars with an initial mean age of 13.91 years. To
compare the efficiency of each treatment protocol, the initial and final occlusal statuses were evaluated on
dental casts with the peer assessment rating (PAR) index, and the treatment time of each group was
calculated from the clinical charts. Treatment efficiency was calculated by the ratio between the percentage
of PAR reduction and the treatment time. PAR scores, treatment times, and treatment protocols’ efficiencies
of the groups were compared with the t test. Results: The 2-maxillary-premolar-extraction protocol had a
smaller final PAR score, a greater percentage of PAR reduction, and greater treatment efficiency than the
nonextraction protocol of complete Class II malocclusion. Conclusion: The 2-maxillary-premolar-extraction
protocol has greater treatment efficiency than the nonextraction protocol of complete Class II malocclusion.
(Am J Orthod Dentofacial Orthop 2007;132:490-8)
I
ment.1-9 Because malocclusion severity is an inherent
characteristic that cannot be controlled, efforts have been
made to evaluate the influence of treatment protocol on
the efficiency of orthodontic treatment.3,10,11 Efficiency is
defined as the capacity of producing the best results with
the least time expense.12 It was demonstrated that com-
plete 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 in the 4-premolar-
extraction protocol requires more anchorage reinforce-
t is known that treatment protocol and malocclusion
severity can influence the results, the duration, and,
consequently, the efficiency of orthodontic treat-
ment with removable appliances and more patient com-
pliance than maintaining Class II molar relationship in the
2-maxillary-premolar-extraction protocol.2,5,6,13,14 Treat-
ment time is also shorter in the 2-maxillary-premolar
protocol than in the 4-premolar-extraction protocol15 be-
causemolarrelationshipcorrection,inherenttononextrac-
tion and 4-premolar-extraction protocols, is considered to
increase Class II treatment time.3,8,11,16 According to this
rationale, it could be speculated that probably a 2-premo-
lar-extraction protocol also has a better occlusal success
rate and a shorter treatment time than a nonextraction
protocol in complete Class II malocclusion patients. Al-
though treatment results and treatment times have been
compared between treatment protocols, the amounts of
changeinatimeperiodhavenotbeenrelatedtoeachother
to evaluate treatment efficiency.
The purpose of this study was to test the following
null hypothesis: complete Class II malocclusion treatment
efficiency is similar in nonextraction and 2-maxillary-
premolar-extraction protocols. Therefore, occlusal results,
treatment times, and efficiency index values were com-
pared between the 2 groups treated with these protocols.
MATERIAL AND METHODS
The sample was retrospectively selected from the
files of the Department of Orthodontics at Bauru Dental
From the Department of Orthodontics, Bauru Dental School, University of São
Paulo, Bauru, Brazil.
aProfessor.
bGraduate student.
cAssociate professor.
Based on research by the second author in partial fulfillment of the require-
ments for the degree of master of science in orthodontics at Bauru Dental
School, University of São Paulo.
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, jansong@travelnet.com.br.
Submitted, January 2005; revised and accepted, October 2005.
0889-5406/$32.00
Copyright © 2007 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2005.10.031
490

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School, University of São Paulo, Brazil; the files
include 3592 documented and treated patients. Records
and the initial and final dental study models of all
patients who initially had complete bilateral Angle
Class II malocclusion (molar relationship) and were
treated without extractions or with 2 maxillary premo-
lar extractions and standard fixed edgewise appliances
were selected and divided into 2 groups. Sample
selection was based exclusively on the initial antero-
posterior (AP) dental relationship, regardless of any
other dentoalveolar or skeletal characteristic. Addition-
ally, the patients selected had all permanent teeth up to
the first molars and no dental anomalies of number,
size, and form. Group 1 consisted of 43 patients (21
male, 22 female) treated nonextraction at an initial
mean age of 12.63 ? 1.45 years (range, 9.39-16.03
years). Thirty-six of these patients had Class II Division
1 malocclusions, and 7 had Class II Division 2 maloc-
clusions. Group 2 consisted of 69 patients (38 male, 31
female) treated with extraction of 2 maxillary first
premolars at an initial mean age of 13.91 ? 2.71 years
(range, 9.42-27.08 years). Fifty-one of these patients
had Class II Division 1 malocclusions, and 18 had
Class II Division 2 malocclusions.
Orthodontic mechanics included fixed edgewise
appliance, with 0.022 ? 0.028-in conventional brackets
and the usual wire sequence characterized by an initial
0.015-in Twist-Flex or a 0.016-in Nitinol, followed
by 0.016, 0.018, 0.020, and 0.021 ? 0.025 or 0.018 ?
0.025-in stainless steel wires (all from 3M Unitek,
Monrovia, Calif). Deepbite was corrected with accen-
tuated and reverse curve of Spee. In the 2-maxillary-
premolar-extraction patients, the anterior teeth were
retracted en masse with a rectangular wire and elastic
chains for overjet and Class II canine correction.
Extraoral headgear was used to correct the Class II AP
relationship in the nonextraction group, whereas, in the
extraction group, an extraoral appliance was used to
reinforce anchorage and maintain the Class II molar
relationship. When necessary, Class II elastics were
used in the nonextraction group to help obtain a Class
I molar relationship; in the extraction group, this
procedure was used to help maintain a Class II molar
relationship.
The patients’ records were used to determine initial
age (IAge), sex, date of treatment onset, date of
treatment completion, and total treatment time (TT).
During this procedure, it was observed that 21 of the 43
patients (48.8%) treated without extractions received
2-phase treatment and used the combined headgear-
activator appliance for 11.2 ? 6 months before treat-
ment with a fixed appliance. On the other hand, 22 of
the 69 patients (31.8%) treated with extractions of
maxillary premolars had the extractions because of the
unsuccessful attempt of Class II malocclusion treatment
without extractions. Because the nonextraction group’s
2-phase treatment and the extraction group’s delayed
extractions could influence the occlusal results and
TT,17-23 the nonextraction patients were divided into 1-
and 2-phase treatment subgroups (subgroups 1A and
1B), whereas the extraction patients were divided into
immediate-extractions and delayed-extractions sub-
groups (subgroups 2A and 2B). These subgroups were
also compared to investigate whether 2-phase treatment
and delayed extractions affect the results.
The peer assessment rating (PAR) index24 was
calculated on the pretreatment and posttreatment study
models of each patient, according to the American
weightings suggested by DeGuzman et al.25 Initial and
final occlusal characteristics were ranked by scores for
molar and premolar AP relationship, overjet, overbite,
midline, crossbite, and crowding to quantify the initial
malocclusion severity (I-PAR), the occlusal treatment
results (F-PAR), and the percentage of PAR reduction
(PcPAR),3,7,26 which is a better estimate of occlusal
improvement.10
Because the PAR index analyzes a set of occlusal
characteristics at the same time and does not discrimi-
nate the participation degree of each in the total score,
the posttreatment scores obtained for each PAR com-
ponent were individually compared to determine the
success rate achieved. Therefore, the PAR score at the
end of treatment was again separated into its several
components to allow an individual evaluation.
Thetreatmentefficiencyindex(TEI)wasevaluatedby
the relationship between PcPAR and TT in months,
expressed as TEI ? PcPAR/TT. The TEI increased when
a greater PcPAR was associated with a shorter TT.
Initial and final PAR scores were recalculated by
the same examiner (S.E.C.B.) in the pretreatment and
posttreatment study models of 30 randomly selected
patients. The casual error was estimated by Dahlberg’s
formula (Se2? ?d2/2n), where S2is the error variance
and d is the difference between the 2 determinations of
the same variable; the systematic error was calculated
with dependent t tests, at P ?.05.27,28
Statistical analyses
Compatibility of the groups regarding the propor-
tions of Class II Divisions 1 and 2 malocclusions and
sexes was evaluated with chi-square tests. T tests were
used to compare the groups regarding IAge, I-PAR,
F-PAR, PcPAR, TT, and TEI. Because there was a
statistically significant difference in the IAges that
could influence F-PAR and TT,3,18,20,22,29-32 some pa-
tients were eliminated from both groups to match the
American Journal of Orthodontics and Dentofacial Orthopedics
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Janson et al 491

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IAges, and the groups were compared again with the t
test. Descriptive statistical analysis was used to show
the patient distribution according to the F-PAR. The
occlusal results obtained for each component of the
PAR were individually compared between the groups
with the Mann-Whitney U-test. A nonparametric test
was used because the values of each PAR component
did not have normal distribution, according to the
Kolmogorov-Smirnov test.33
To investigate whether 2-phase treatment or de-
layed extractions had influenced F-PAR and TT, the
following comparisons were made: group 1 and sub-
groups 2A and 2B were compared with each other with
ANOVA, followed by Tukey tests; subgroup 1B was
compared with group 2, and subgroups 1A and 2A were
compared with t tests.
RESULTS
The I-PAR and F-PAR did not have significant
systematic errors, and the casual errors were within
acceptable levels (Dahlberg: I-PAR ? 0.8062, F-PAR ?
0.5916). The groups were similar regarding the
proportion of Class II Divisions 1 and 2 malocclusion
types and sexes (?2? 1.4696 and P ? .2254; ?2?
0.4131 and P ? .5204, respectively). IAge, Pc PAR,
and TEI were statistically greater and the F-PAR was
statistically smaller for the extraction group (the
smaller the F-PAR score, the greater the occlusal
success rate) (Table I). Similar results were obtained
when IAge was matched in the groups (Table II). At the
posttreatment stage, the extraction group had a greater
percentage of patients with PAR scores equal to zero
and a smaller PAR range (Table III). When several
occlusal characteristics of the F-PAR index were indi-
vidually compared between the groups, a better AP
relationship of the buccal occlusion was observed in the
extraction group (Table IV). The immediate-extractions
subgroup had a statistically shorter TT and a higher TEI
than the delayed-extractions subgroup and the nonex-
traction group. The F-PAR score and the PcPAR were
similar between the immediate and the delayed-extrac-
tions subgroups, and statistically greater and smaller in
the nonextracion group, respectively (Table V). The
2-phase nonextraction subgroup had a greater F-PAR
score, a smaller PcPAR, and a smaller TEI than the
extraction group (Table VI). A statistically longer TT
and a smaller TEI were found for the 1-phase nonex-
traction subgroup compared with the immediate-extrac-
tions subgroup (Table VII).
Table I. Results of independent t test between groups 1 and 2
Variable
Group 1 (n ? 43)
(nonextraction)
Group 2 (n ? 69)
(maxillary premolar
extractions)
df
P
Mean SDMean SD
IAge
I-PAR
F-PAR
PcPAR
TT
TEI
12.63
24.32
5.67
72.69
30.14
2.95
1.45
7.67
5.62
31.38
9.74
1.32
13.91
23.95
2.42
88.87
26.99
3.78
2.71
7.40
2.88
13.91
10.16
1.27
110
110
110
110
110
110
.0053*
.8008
.0001*
.0002*
.1078
.0013*
*Statistically significant at P ?.05.
Table II. Results of independent t test between groups 1 and 2 with comparable initial ages
Variable
Group 1 (n ? 36)
(nonextraction)
Group 2 (n ? 58)
(maxillary premolar
extractions)
df
P
Mean SDMean SD
IAge
I-PAR
F-PAR
PcPAR
TT
TEI
12.92
24.08
5.27
73.78
29.72
2.78
1.09
7.93
5.80
33.33
9.65
1.52
13.21
23.91
2.37
88.94
26.72
3.74
1.29
7.18
2.88
14.28
10.53
1.39
92
92
92
92
92
92
.2639
.9151
.0017*
.0030*
.1700
.0022*
*Statistically significant at P ?.05.
American Journal of Orthodontics and Dentofacial Orthopedics
October 2007
492 Janson et al

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DISCUSSION
Our subjects were selected primarily on the basis of
a complete bilateral Class II malocclusion, independent
of the associated cephalometric skeletal characteristics.
Since both groups were similarly chosen, it could be
expected that these characteristics would be evenly
distributed between them. Usually, it is not the skeletal
characteristics of a Class II malocclusion that primarily
determine whether it should be treated with or without
2 maxillary premolar extractions but, rather, the pa-
tient’s development stage, because maxillary-premolar-
extraction treatment has been preferentially used in
nongrowing Class II patients.2,14,34-37 Nevertheless, the
similarity of the malocclusion types and the initial
malocclusion severity points toward cephalometric
compatibility of the groups.38 Additionally, the primary
objective was to investigate whether there was a dif-
ference in the final occlusal success rate between these
2 treatment protocols. Further studies on the influence
of skeletal pattern on our results are being conducted.
At the beginning of treatment, the groups were
similar, except for IAge (Table I). Even though a
younger age would favor Class II treatment of the
nonextraction group,31,39 the extraction group had more
favorable occlusal results (Table I). Nevertheless, to
eliminate any concern, the groups were divided into
subgroups with matching IAges, which were compared
with the t test (Table II).
The F-PAR and the PcPAR results had statistically
significant differences between groups 1 and 2, with
more favorable results for group 2, as shown in Table I.
This demonstrates that Class II malocclusion treatment
with extraction of 2 premolars not only allows a better
occlusal success rate, but also produces a greater
Table III. Descriptive analysis of the patients’ percentages in groups 1 and 2 according to F-PAR
F-PAR (score)023456789 10111214 15161820
Cumulative %, group1
(nonextraction)
Cumulative %, group 2
(maxillary premolar
extractions)
30.2 37.241.851.153.462.767.4 7281.3 81.3 86 8688.3 90.695.3 97.6 100
44.962.365.2 81.186.9 89.894.2 95.6 95.698.5 98.5100 100100 100100100
Table IV. Results of the comparison of the F-PAR individual components between groups 1 and 2 (Mann-Whitney
U test)
Variable
Group 1 (n ? 43) (nonextraction) Group 2 (n ? 69) (maxillary premolar extractions)
Z
P
Mean rankMean rank
AP
OVJ
OVB
ML
CB
C
64.97
61.86
62.04
57.60
60.30
55.48
51.21
53.15
53.04
55.81
54.13
57.11
?2.180
?1.379
?1.426
?0.284
?0.978
?0.257
.0292*
.1679
.1536
.7762
.3280
.7969
OVJ, overjet; OVB, overbite; ML, midline; CB, crossbite; C, crowding.
*Statistically significant at P ?.05.
Table V. Results of ANOVA and Tukey tests between group 1 and subgroups 2A and 2B
Variable
Group 1 (n ? 43)
(nonextraction)
Subgroup 2A (n ? 47)
(maxillary premolar
extractions, immediate
extractions)
Subgroup 2B (n ? 22)
(maxillary premolar
extractions, delayed
extractions)ANOVA
Mean SDMean SDMean SDF
P
I-PAR
F-PAR
PcPAR
TT
TEI
24.32a
5.67a
72.69a
30.14a
2.69a
7.67
5.62
31.38
9.74
1.43
24.34a
2.80b
87.41b
23.60b
3.95b
7.47
3.13
14.40
6.31
1.26
23.13a
1.59b
91.99b
34.21a
3.08a
7.35
2.08
12.56
12.93
1.28
0.223
8.82
7.27
11.37
10.31
.8002
.0002*
.0010*
.0000*
.0000*
Different letters represent statistically significant differences.
*Statistically significant for P ?.05.
American Journal of Orthodontics and Dentofacial Orthopedics
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proportion of changes in the initial improper dental
relationships. Results of the subgroups’ comparison
with matching IAges showed a similar tendency of the
groups (Table II). The better occlusal success rate of
group 2 is also shown by the greater percentage of
patients with a PAR score equal to zero in relation to
group 1 at the end of treatment. According to Rich-
mond et al24 and Buchanan et al,40 when the PAR index
at the end of treatment is smaller than or equal to 5, the
occlusion is considered almost perfect. The extraction
group had 86.9% and the non-extraction group had 53.4%
of the patients in this correction range (Table III).
To determine which PAR components had primar-
ily contributed to the occlusal success rate difference
between the groups, they were individually compared.
The extraction group had a statistically smaller post-
treatment score and, consequently, a greater occlusal
success rate of molar and premolar AP relationship
correction than group 1. This showed that AP relation-
ship correction was the primary component that con-
tributed to the poorer occlusal results in group 1 (Table
IV). This seems logical because nonextraction Class II
treatment requires twice as much anchorage reinforce-
ment and consequently more patient compliance to
achieve a molar Class I relationship than the 2-maxillary-
premolar-extraction protocol to maintain the Class II
molar relationship.13 Therefore, these results support the
findings of other studies that suggest that treatment
difficulty increases when a full-cusp Class II molar
relationship must be completely corrected.2,4-6,8,9,13,14
The following paragraphs theoretically illustrate the
greater difficulty of the nonextraction approach.
Treatment of complete Class II malocclusions with
extraction of only 2 maxillary premolars requires an-
chorage reinforcement to avoid mesial movement of the
posterior segment during retraction of the anterior
teeth. Because the average mesiodistal diameter of
premolars is 7 mm, the anterior teeth should therefore
be distalized through this distance.13 Appliances that
provide this anchorage reinforcement are primarily
extraoral, thus requiring patient compliance for a suc-
cessful treatment result.
In complete Class II therapy without premolar
extractions, the need for anchorage reinforcement is
even greater, because the posterior segment must be
distalized 7 mm to achieve a Class I molar relationship
at the end of treatment.41,42 Afterwards, all anterior
teeth must be distalized 7 mm (or “space units”13),
corresponding to the distalization of the posterior seg-
ment. Therefore, there will be 7 mm of distalization of
the posterior segment added to 7 mm of the anterior
segment, for a total of 14 mm of distalization for both
posterior and anterior segments; this is twice the
amount required for Class II correction with extraction
Table VI. Results of independent t test between subgroup 1B and group 2
Variable
Subgroup 1B (n ? 21)
(nonextraction, 2-phase)
Group 2 (n ? 69)
(maxillary premolar
extractions)
df
P
MeanSD MeanSD
I-PAR
F-PAR
PcPAR
TT
TEI
26.42
4.95
77.89
31.96
2.74
7.84
5.75
26.69
10.53
1.42
23.95
2.42
88.87
26.99
3.67
7.40
2.88
13.91
10.16
1.33
88
88
88
88
88
.1899
.0078*
.0144*
.0548
.0067*
*Statistically significant at P ?.05.
Table VII. Results of independent t test between subgroups 1A and 2A
Variable
Subgroup 1A (n ? 22)
(nonextraction, 1-phase)
Subgroup 2A (n ? 47)
(maxillary premolar
extractions, immediate
extractions)
df
P
Mean SDMean SD
I-PAR
F-PAR
PcPAR
TT
TEI
22.31
6.36
67.73
28.40
2.65
7.11
5.53
35.19
8.82
1.48
24.34
2.80
87.41
23.60
3.95
7.47
3.13
14.40
6.31
1.26
67
67
67
67
67
.2917
.0011*
.0015*
.0121*
.0003*
*Statistically significant at P ?.05.
American Journal of Orthodontics and Dentofacial Orthopedics
October 2007
494 Janson et al