Dentoskeletal and soft tissue changes in class II subdivision treatment with asymmetric extraction protocols
Janson et al. Progress in Orthodontics
Dentoskeletal and soft tissue changes in class II subdivision treatment with asymmetric extraction protocols
Guilherme Janson 0 2
Eduardo Beaton Lenza 0 2
Rodolfo Francisco 0 2
Aron Aliaga-Del Castillo 0 2
Daniela Garib 0 2
Marcos Augusto Lenza 1
0 Department of Orthodontics, Bauru Dental School, University of São Paulo , Alameda Octávio Pinheiro Brisolla 9-75, Bauru 17012-901 , Brazil
1 Department of Orthodontics, Dental School, Federal University of Goiás , Goiania , Brazil
2 Department of Orthodontics, Bauru Dental School, University of São Paulo , Alameda Octávio Pinheiro Brisolla 9-75, Bauru 17012-901 , Brazil
Background: This study cephalometrically compared the dentoskeletal and soft tissue changes consequent to one and three-premolar extraction protocols of class II subdivision malocclusion treatment. Methods: A sample of 126 lateral cephalometric radiographs from 63 patients was selected and divided into two groups. Group 1 consisted of 31 type 1 class II subdivision malocclusion patients treated with asymmetric extractions of two maxillary premolars and one mandibular premolar on the class I side, with an initial mean age of 13.58 years. Group 2 consisted of 32 type 2 class II subdivision malocclusion patients treated with asymmetric extraction of one maxillary first premolar on the class II side, with an initial mean age of 13.98 years. t test was used for intergroup comparison at the pre- and posttreatment stages and to compare the treatment changes. Results: Group 1 had greater maxillomandibular sagittal discrepancy reduction and greater maxillary first molar extrusion. Group 2 had mandibular incisor labial inclination and protrusion, and group 1 had mandibular incisor lingual inclination and retraction. Maxillary molar asymmetry increased in group 2, while mandibular molar asymmetry increased in group 1. Conclusions: The treatment changes produced by these two class II subdivision protocols are different to adequately satisfy the different needs for types 1 and 2 class II subdivision malocclusions.
Class II subdivision; Premolar extractions; Asymmetric extractions; Cephalometrics
Two main types of class II subdivision malocclusions
have been identified. Type 1 class II subdivision
malocclusions are characterized by distal positioning of the
mandibular first molar on the class II side, coincidence
of the maxillary dental midline with the midfacial plane
and deviation of the mandibular dental midline to the
class II side, in a frontal clinical view [
]. Type 2 class
II subdivision malocclusions are characterized by mesial
positioning of the maxillary first molar on the class II
side, deviation of the maxillary dental midline to the
class I side and coincidence of the mandibular dental
midline with the midfacial plane [
]. There is also a
third type, with combined characteristics of the first two
types. Consequently, in this type, the maxillary midline
is deviated to one side and the mandibular midline is
deviated to the other [
One of the treatment options for type 1 class II
subdivision malocclusions consists in extractions of two
maxillary premolars and one mandibular premolar on
the class I side, as long as the facial profile and/or the
amount of crowding allow extractions to be performed
]. For type 2 class II subdivision malocclusions, a
treatment option may consist in extracting one maxillary
premolar on the class II side [
1, 4, 6, 8, 13, 14
it is speculated that the amount of dentoskeletal and soft
tissue retraction is larger for the first treatment option.
However, this has not been investigated.
When faced with the third type of class II subdivision
malocclusion, the orthodontist may have to choose
whether to treat it is as a type 1 or type 2 class II
subdivision malocclusion, with the mentioned protocols.
Therefore, knowing the differences in the dentoskeletal
and soft tissue changes provided by both treatment
protocols, it will be possible to select the best
protocol to address the characteristics of the specific
Therefore, the objective of this work is to test the
following null hypothesis: dentoskeletal and soft tissue
changes are similar between type 1 class II subdivision
malocclusions treated with two maxillary and one
mandibular premolar extractions to type 2 class II
subdivision malocclusions treated with one maxillary
This study was approved by the Ethics Committee of
Bauru Dental School, University of São Paulo, Brazil.
Sample size calculation, considering an 80% of test power
at a significance level of 5%, with a minimum mean
difference to be detected of 0.85 mm in 1-NB, with a
standard deviation of 1.19 mm, revealed that 31 individuals in
each of the two groups were the minimum amount
Therefore, 63 patients, of White Mediterranean ancestry,
initially presenting with class II subdivision malocclusions
were retrospectively selected from the files of the Orthodontic
Department at Bauru Dental School, University of São Paulo,
Brazil. These patients were treated between 1998 and
2012 and were divided into two groups, according to
their treatment approach. Group 1 consisted of 31
patients with type 1 class II subdivision malocclusions, with
initial and final mean ages of 13.58 and 16.83 years,
respectively, and a mean treatment time of 3.25 years,
treated with asymmetric extractions of two maxillary
premolars and one mandibular premolar on the class
I side. Group 2 consisted of 32 patients with type 2
class II subdivision malocclusions, with initial and final
mean ages of 13.98 and 16.90 years, respectively, and a
mean treatment time of 2.92 years, treated with
asymmetric extraction of one maxillary premolar on
the class II side (Figs. 1 and 2).
The primary selection criterion was that patients
presented a full class II molar relationship on one side and
class I molar relationship on the opposite side.
Additional selection criteria were: presence of all maxillary
and mandibular permanent teeth up to the first
molars, absence of supernumerary and impacted teeth,
agenesis and anomalies of size and/or shape of the
teeth, no facial trauma or medical history that could
have altered the normal growth of their apical bases,
no previous orthodontic treatment, initial and final
records in satisfactory conditions, and good occlusal
All patients were treated with conventional edgewise
or preadjusted fixed appliances (Roth prescription), both
with 0.022 × 0.028 in. metalic brackets, by graduate
students supervised by the same clinical instructor (GJ). Fixed
or removable functional appliances were not used. The
usual wire sequence began with 0.014 in. Niti archwires,
followed by 0.016 in. Niti and 0.018, 0.020, and finally
0.018 × 0.025 in. stainless steel archwires. Thereafter,
enmasse retraction of the anterior teeth was performed.
Anchorage reinforcement with cervical extraoral
headgear and lip bumpers (at the gingival margin of
] were used in all patients to maintain the
original posterior teeth anteroposterior relationships.
Class II elastics were used 18 h a day, for minor
anteroposterior adjustment in the final stages, with
0.018 × 0.025 in. stainless steel archwires. Deep bites
were usually corrected with accentuated and reversed
curve of Spee on the archwires. As retention, the patients
in both groups used Hawley plates on the maxillary arch
and canine-to-canine bonded retainers.
The pretreatment and posttreatment lateral
cephalograms were obtained from each patient and scanned
to allow the acquisition of images by Dolphin®
Imaging 11.5 (Patterson Dental Supply, Inc., Chatsworth,
CA). The magnification factors of the radiographic
images that varied from 6 to 9.8% were corrected by
the cephalometric software. Subsequently, 35
landmarks in the dentoskeletal facial structures and 17
landmarks in the soft tissue were marked (Figs. 3 and
4, Table 1).
For dental asymmetry assessment, two digital tracings
were performed for each patient at T1 and T2. In the
first tracing, linear measurements were made from
the mesial point of the most mesial maxillary and
mandibular molar, perpendicularly, to the Svert Line
(6-Svert). In the second tracing, linear measurements
were made from the mesial point of the most distal
maxillary and mandibular molar, perpendicularly, to
the same vertical reference line (6-Svert). Asymmetry
was calculated as the difference between the most
mesial and distal molars for the maxillary and
mandibular molars [
The Little irregularity index [
] was used to calculate
crowding at the pretreatment stage. This index was
originally used to evaluate anterior mandibular dental
crowding, and has been adapted to also quantify
maxillary anterior crowding [
Twenty-two lateral cephalograms were randomly
selected and remeasured by the same examiner (EBL),
after a 30-day interval. Random errors were calculated
according to Dahlberg’s formula (Se2 = ∑d2/2n) [
where S2 is the error variance and d is the difference
between 2 determinations of the same variable and the
systematic errors were evaluated with dependent t tests,
at P < 0.05 [
The means and standard deviations (SD) for each
variable were calculated for both groups.
KolmogorovSmirnov tests were applied to verify normal
distribution of the variables. The results of the tests were
nonsignificant for all variables. Therefore, intergroup
comparability was evaluated with t tests regarding the
initial and final ages, treatment time and the
cephalometric characteristics at the pretreatment stage.
Chisquare test was used to compare sex distribution in
t tests were also used to compare the treatment
changes and the cephalometric status at the
posttreatment stage. All tests were performed with Statistica
software (Version 7, StatSoft Inc., Tulsa, OK, USA),
at P < .05.
The random errors ranged from 0.44 (overbite) to
1.38 mm (CoGn) and from 0.77 (SND) to 1.45°
(Cm.Sn.Ls). Only two variables (LAFH and Z angle)
presented significant systematic errors. The groups
were comparable regarding the initial age, treatment
time, sex distribution, and initial occlusal
characteristics (Table 2). At the pretreatment stage, group 2 had
significantly smaller maxillary incisor dentoalveolar
development, greater maxillary molar asymmetry, smaller
mandibular molar asymmetry, greater nasal prominence,
and smaller lower lip protrusion (Table 3).
During treatment, there was significantly greater
maxillomandibular relationship improvement, decrease
in facial convexity, and increase in molar dentoalveolar
height in group 1 (Table 4). Group 2 presented
significantly greater increase in maxillary molar asymmetry.
There was significant differences regarding mandibular
incisor behavior. While group 2 had labial tipping
Mandibular skeletal components
Maxillary dentoalveolar components
and protrusion of the incisors, group 1 had lingual
tipping and retrusion. Group 1 had greater increase
in mandibular molar asymmetry.
At the posttreatment stage, group 1 demonstrated
significantly greater LAFH, smaller labial tipping, and
greater dentoalveolar height of the maxillary incisors
(Table 5). Group 1 also presented greater maxillary
molar dentoalveolar height and smaller maxillary
molar asymmetry. Group 2 presented greater labial
tipping and protrusion of the mandibular incisors,
smaller mandibular molar asymmetry, and greater
Only class II subdivision malocclusion patients, with
complete class II on one side and class I on the other,
independently of the associated cephalometric factors
were included [
]. Group 1 had significantly greater
maxillary incisor dentoalveolar height, smaller maxillary
molar asymmetry, and greater mandibular molar
asymmetry (Table 3). The greater maxillary incisor
dentoalveolar height suggests a slightly more accentuated
vertical growth pattern and the differences in molar
asymmetry are characteristics of the two types of
subdivision malocclusions [
4–6, 11, 20
]. Group 1 had also
greater lower lip protrusion which might also have
contributed for the extraction treatment in this group.
However, these slight differences should not interfere
with the comparison.
Treatment changes and posttreatment status
The greater reduction in maxillomandibular relationship
in group 1 may be consequent to the greater number of
extractions in the maxillary arch, and increased need
for class II elastics or headgear, to reinforce
anchorage, that consequently produced a non-significantly
Mx Molar asymmetry Difference in the distance between
most mesial points of right and left
maxillary first molars, perpendicular
to Svert Line (Mx6-Svert)
Mandibular dentoalveolar components
Md Molar asymmetry Difference in the distance between
most mesial points of right and left
maxillary first molars, perpendicular
to Svert Line (Md6-Svert)
Distance between incisal edges of
maxillary and mandibular central incisors,
parallel to occlusal plane
Distance between incisal edges of maxillary
and mandibular central incisors, perpendicular
to occlusal plane
Distance from the upper lip to Steiner’s S
line (line from Pg’ to Cl)
greater maxillary retraction [
], Table 4. Group 1
also had a non-significantly greater increase in
mandibular growth. These non-significant greater changes
in group 1, when associated, might have contributed
for a significantly greater reduction in
maxillomandibular relationship than group 2. Additionally, these
associated greater non-significant changes might have
also contributed for a greater reduction in skeletal
facial convexity in group 1. However, these greater
treatment changes of group 1 were not enough to
produce intergroup differences at the posttreatment
stage (Table 5).
Despite there were no significant intergroup differences
in maxillary incisor treatment changes, they were
significantly more palatally tipped and had greater dentoalveolar
height in group 1, at the posttreatment stage (Tables 4
and 5). The greater palatal inclination was probably
consequent to the non-significant greater palatal tipping
that occurred during treatment in this group because
of incisor retraction to close the two maxillary
premolar extraction spaces. Group 1 already had greater
dentoalveolar height at the pretreatment stage and
because the vertical treatment changes were similar in
the groups, the initial intergroup pretreatment
difference was maintained.
The greater increase in molar dentoalveolar height
in group 1 was probably due to greater need of
intermaxillary elastics and/or headgear use, associated with
the slightly greater vertical growth pattern of this
7, 9, 24
], Table 4. The three premolar
extraction protocol performed in group 1 requires greater
amount of anchorage reinforcement during anterior
retraction, compared to the one premolar extraction
protocol performed in group 2. Therefore, this may
have contributed to more extrusion in group 1.
Consequently to this, LAFH and maxillary molar
dentoalveolar height were significantly greater in
group 1, at the posttreatment stage, which usually
], Table 5.
Because group 2 had only one maxillary premolar
extraction, it is quite obvious that maxillary molar
asymmetry had greater increase in this group than in group
1, which increased even more the significant initial
intergroup difference in molar asymmetry (Tables 4 and 5).
Nevertheless, this amount of asymmetry between the
maxillary molars in group 2 is not clinically relevant
and does not bring any decrease in smile
13, 25, 26
The significant intergroup differences in mandibular
incisor behavior was consequent to the non-extraction
treatment in group 2 and one premolar extraction
treatment in group 1 (Table 4). Therefore, there was
mandibular incisor labial inclination and protrusion
resulting from correction of the anterior crowding
and leveling of the curve of Spee without mandibular
premolar extraction in group 2 [
11, 27, 28
]. In group
1, there was retraction and lingual inclination of the
mandibular incisors as a result of space closure of
one mandibular premolar extraction [
Consequent to these different changes, the mandibular
incisors of group 1 were significantly more lingually
tipped and retruded than those of group 2 at the
posttreatment stage (Table 5).
Similarly to the maxillary molars because group 1
had only one mandibular premolar extraction, it is
quite obvious that mandibular molar asymmetry had
greater increase in this group than in group 2, which
increased even more the significant initial intergroup
difference in molar asymmetry, at the posttreatment
stage (Tables 4 and 5).
Group 1 presented a significantly smaller facial
convexity at the posttreatment stage, probably because of
the non-significanly greater upper lip retrusion, with
treatment, than group 2 [
The two treatment protocols for class II subdivision
malocclusions produced significantly different changes
in certain dentoalveolar variables. This is reasonable
because each of these protocols are indicated for
different types of class II subdivision malocclusions.
For type 1, three premolar extractions are indicated
1, 6–9, 11–13
]. This is the case when maxillary
incisor protrusion or crowding is accentuated and there
is also some mandibular crowding or incisor
7, 9, 11, 12, 33
]. Therefore, this protocol will
solve these problems [
8, 13, 24
]. For type 2, there is
usually less maxillary incisor protrusion and there is
no mandibular crowding, with the incisors
labiolingually well positioned. Therefore, the treatment
changes will be favorable according to each
The null hypothesis was rejected because the treatment
changes had the following differences:
1. There was greater maxillomandibular sagittal
discrepancy reduction in group 1;
2. There was greater maxillary first molar extrusion in
3. Maxillary molars asymmetry increased in group 2
and decreased in group 1.
4. There was greater mandibular incisor labial
inclination and protrusion in group 2, and
mandibular incisor lingual inclination and retrusion
in group 1;
5. There was greater increase of mandibular molar
asymmetry in group 1.
The authors would like to thank São Paulo Research Foundation—FAPESP
(Process Number 09/15135-3) for their financial support.
GJ contributed in the study conception, research supervision, and scientific
and English revision. EBL contributed to the data collection, statistical
analyses, and project development. RF and AADC contributed to data
checking and manuscript drafting. DG contributed to scientific and English
revision. MAL contributed to scientific revision. All authors read and
approved the final manuscript.
Ethics approval and consent to participate
This study was approved by the Ethics in Research Committee of Bauru
Dental School, University of São Paulo, Brazil.
Consent for publication
Written informed consent was obtained from the patients for publication of
this research and accompanying images.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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