orthodontics

1. EARLY TREATMENT SYMPOSIUM
Serial extraction revisited: 30
years in retrospect
Jimmy C. Boley, DDS, MS
Richardson, Tex
O
ne of the most
common prob-
lems in ortho-
dontics is tooth size-arch
length discrepancy
(TSALD). The contro-
versy over whether to re-
solve this discrepancy by
increasing the size of the
dental arch or by reduc-
ing the amount of tooth
structure persists to this
day. Because virtually
any approach to resolving TSALD can align the teeth,
the long-term stability of competing approaches is of
paramount importance. The effect on the face is also a
major consideration. Of the various aspects of occlu-
sion such as molar relationship, overbite, and overjet,
mandibular anterior alignment is the area of relapse
most noted by patients. Therefore, it has been the focus
of many stability studies.
The most common unit of measurement for man-
dibular anterior tooth alignment is the irregularity index
as suggested by Little1
in 1975. The irregularity index
is defined as the sum of the distance between the
contact points of the 6 permanent anterior teeth. It is not
the same as TSALD. An irregularity index of less than
3.5 mm is judged to be minimal and thus clinically
satisfactory. An irregularity index score greater than 6.5
mm indicates severe irregularity.
There are few reports in the literature on long-term
postretention stability of TSALD patients treated in the
mixed dentition. Four studies at the University of
Washington reported on both approaches—increasing
arch length and extracting premolars.2-5
The study of
resolving the TSALD in the mixed dentition by increas-
ing arch length (expansion) was especially discourag-
ing. Seven and a half years postretention, 89% of the
patients studied had unsatisfactory results, with a mean
irregularity index score of 6.06 mm. The 3 studies in
which premolars were extracted in the mixed dentition
found an irregularity index 10 years postretention of
4.39, 3.15, and 3.09 mm, respectively.
Foster and Wiley found that extraction of deciduous
canines had no detrimental effect on the eventual width
of the permanent canines. Numerous studies have
documented that mandibular incisors tip lingually as a
result of serial extraction, but not excessively.7-10
So, is extracting in the mixed dentition, followed by
multibanded treatment in the permanent dentition and a
retention phase of approximately 3 years, a better
choice in the long term? In one study, researchers
examined a subsample of 30 serial extraction patients
from the 114 studied by Scott Franklin in his 1995
“AAO Award of Merit” thesis. The subsample included
8 males and 22 females with a mean T1 age of 10.44
years and a mean postretention (T3) age of 30.3 years.
T2 records were collected shortly after the end of active
treatment. Long-term postretention crowding in these
serial extraction patients was minimal.
The mean T3 irregularity index of 2.7 mm was
below the cut-off level of 3.5 mm considered to be
satisfactory. The range was 0.31 to 5.9 mm, and 70% of
the patients were in the minimally irregular category,
and none was in the severe category (over 6.5 mm).
Evaluation of the facial profiles at the end of treatment
and 15 years later by using the Holdaway line showed
that profiles were within the normal range at both
periods. Numerous studies have found that premolar
extractions do not produce poor facial balance.12-16
In her thesis at the University of Toronto, Julianne
Peterson17
found similar results. She examined 20
serial extraction patients (3 males and 17 females) with
a mean T1 age of 10.5 years and a mean postretention
age of 30.8 years. Nearly 16 years posttreatment, the
mean T3 irregularity index score was 2.4 mm (range,
0.5 to 4.95 mm). Seventy-five percent of the patients
fell into the minimal category, and none was severe.
In these stable cases, the mandibular intercanine
expansion was minimal (1.2 mm), and the mandibular
Associate professor, Baylor College of Dentistry, Texas A&M University
System, Dallas, and in private practice.
Presented at the International Symposium on Early Orthodontic Treatment,
February 8-10, 2002; Phoenix, Ariz.
Am J Orthod Dentofacial Orthop 2002;121:575-7
Copyright © 2002 by the American Association of Orthodontists.
0889-5406/2002/$35.00 ϩ 0 8/1/124685
doi:10.1067/mod.2002.124685
575

2. incisors were maintained virtually where they were at
the end of the serial extraction phase. These 2 charac-
teristics are shared with numerous other samples and
subsamples in which a minimal mean irregularity was
found. Meeting these 2 treatment objectives is believed
to enhance environmental equilibrium for the dentition,
and thus they are essential for stability in most patients.
DIAGNOSIS AND EXTRACTION SEQUENCE
If there appears to be a TSALD or if the patient’s
profile is on the full side of normal, complete records
should be taken. Usually, the mandibular laterals are at
least half erupted. A total space analysis is performed
by summing the space required to resolve the TSALD
and reposition the mandibular incisors to their desired
position. Two millimeters of arch length is subtracted
for each millimeter of posterior movement desired or,
in rare instances, added if advancement of the incisors
is indicated. Rarely is the curve of Spee an issue in the
mixed dentition. I allow for a loss of E-space as noted
by Nance22
and others2,23-25
as inevitable. The reason-
ing is that if nature is allowed to take its course, the first
molars will migrate mesially, and the TSALD will be
more severe at maturity.
In an immature (less severe) TSALD in the mixed
dentition, if the total discrepancy is 8 mm or more,
and if the first premolars are where they can be
removed without adverse sequelae, I prefer to have
the patient sedated to remove all 4 deciduous ca-
nines, the first deciduous molars, and the first pre-
molars, all at once. The more common approach is to
remove all 4 deciduous canines and then to wait until
the first premolars are fairly close to erupting or have
erupted. At this time, any combination of 4 premo-
lars can be extracted, depending on the total discrep-
ancy. If in doubt, take progress records. If still in
doubt, wait until the second premolars begin to erupt.
The patient should be evaluated every 4 months
during the serial extraction phase. Usually, once I am
sure that I have 5 mm of total discrepancy, I extract
the second premolars—the earlier the better. How-
ever, if you are just starting to use this approach, err
on the side of caution and wait until all permanent
teeth have erupted if still in doubt. You can always
remove the teeth later if indicated and obtain a
comparable result; it will simply take longer. Expe-
rience will remove most of the doubt, but not all.
A full banded-bonded edgewise appliance is placed
after the eruption of the remaining teeth, and, in most
instances, a concerted effort is made to maintain the
mandibular incisors in the position they assumed during
the serial extraction phase. Tweed7
contended that
serial extraction would permit the mandibular incisors
to tip lingually into a position of functional balance,
and he believed they should be maintained in this
position through treatment. Also, numerous studies26-29
have shown that proclined mandibular incisors tend to
Fig. A and B, Posttreatment photos show good facial
balance and pleasing smile; C, composite tracings
show effects of growth and repositioning of mandibular
incisors as result of serial extraction and treatment.
American Journal of Orthodontics and Dentofacial Orthopedics
June 2002
576 Boley

3. rebound. I also make a conscious effort to maintain the
original arch form.
A treatment time of 15 months is typical. My
treatment goals are balance and harmony of facial
features and a healthy, functional, and stable dentition.
One essential aspect of facial balance is lack of men-
talis strain when closing the lips. It has been my
experience that serial extraction does not have to be
limited to patients with severe TSALD and Class I
skeletal patterns.
I have used this approach to treatment for over 30
years and have been pleased with the results the vast
majority of the time (Fig). This is a brief summary of a
brief presentation of a complex subject. If you need
more information, Jack Dale contributed an excellent
chapter on serial extraction in the last several editions
of Orthodontics—Current Principles and Techniques
by Graber and Vanarsdall.
REFERENCES
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2. Little RM, Riedel RA, Stein A. Mandibular arch length increase
in the mixed dentition: postretention evaluation of stability and
relapse. Am J Orthod Dentofacial Orthop 1990;97:393-404.
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premolars: postretention evaluation of stability and relapse.
Angle Orthod 1990;60:255-62.
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American Journal of Orthodontics and Dentofacial Orthopedics
Volume 121, Number 6
Boley 577