Clinical outcome with mandibular second versus first premolar extractions in orthodontic treatment

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When the treatment plan calls for maxillary and/or mandibular premolar extrac
-
tions, it seems that many more orthodontists prefer to extract the first rather than
the second premolars.
2
In a recent (2002) survey in the US, the dominant extrac
-
tion pattern was the maxillary and mandibular first premolars.
2
The next most
common pattern was extraction of the maxillary first premolars, with no extraction
in the mandible. The removal of the maxillary first and the mandibular second pre-
molars was the preferred pattern in only 7.5% of the extraction cases, and the
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Q
BJÖRN U. ZACHRISSON
OSLO, NORWAY
Clinical outcome with mandibular second
versus first premolar extractions in
orthodontic treatment
The posttreatment anteroposterior position of the mandibular incisors apparently
can influence the facial profile. According to Holdaway,
1
the most frequent com-
ment heard in criticism of orthodontics comes from parents of prospective patients
who do not like the changes in upper lip position that they have observed in some
orthodontically treated patients. Since there is a relationship between root surface
area and anchorage potential, the choice of which mandibular teeth to be
extracted may have a direct effect on the amount of anterior segment retraction.
The extraction of 2 mandibular premolars usually gives more than enough
space to align the mandibular incisors. Orthodontic closure of the residual space
may result in the retraction of the mandibular anterior segment. This retraction
may be favorable in the orthodontic treatment of Class III malocclusion, whereas it
is usually unfavorable in Class II malocclusions. There is little information available
on prediction of the amount of incisor retraction that can be expected during the
closure of the mandibular premolar extraction spaces, and on the difference
between the outcome with extraction of the first or second premolars.
Do we have any reliable predictions and recommendations concerning the treat-
ment results following extractions of mandibular second versus first premolars
when it comes to:
(1)
amount of mandibular incisor retraction;
(2)
long-term stability
of the treatment results;
(3)
profile changes?—José M. Llamas, Sevilla, Spain

359
maxillary and mandibular second premolars in 6%. These numbers have remained remark-
ably similar for the past 10 years, or more.
2
By tradition, an obvious reason for selecting
the mandibular first rather than the second premolars for extraction is their generally
poorer morphology—commonly a smaller tooth with a diminutive lingual cusp compared to
the second premolar. However, when the extraction decisions are made, it is my opinion
that the mandibular incisor position in space after treatment, and the predicted profile
changes with different extraction alternatives, should be regarded as more important fac-
tors than the tooth morphology and the contact point relationships between the first molar
and the neighboring premolar (Fig 1). Tooth morphology can, if necessary, be improved
with new minimally invasive prosthetic enamel bonding techniques, whereas excessive
incisor retroclination (Fig 2a) and accentuation of undesirable profile characteristics as a
result of the orthodontic treatment (Fig 3) may produce irreparable damage to the patient.
Fig 1 Desirable incisor positioning and harmonious facial profile in young male ortho-
dontic patient with retraction of the incisors after mandibular second premolar extrac-
tion. Prolonged retention using gold-coated 0.030-inch lingual retainer bonded to
canines only.
a b
c
d e
f
Fig 2 Finished transfer case where the extraction of both mandibular first premolars has resulted in larger-than-intended interin-
cisal angle
(a). The undertorque may increase the likelihood for vertical relapse of the deep overbite. Safer alternative (b,c) with
extraction of mandibular second premolars in case with moderate crowding (b). Simple control of anchorage and space closure
using elastomeric chain and Class II elastics on straight mandibular archwire (c).
a b
c

360
EEffffeecctt ooff pprreemmoollaarr eexxttrraaccttiioonnss oonn mmaannddiibbuullaarr iinncciissoorr rreettrruussiioonn
Some recent studies have tried to quantify and compare the outcome of mandibular second
versus first premolar extractions during orthodontic treatment.
3–6
Crowding and profile full-
ness have been found to be the most significant factors influencing the extraction sequence
decision,
3–6
but the facial type (the ratio between posterior and anterior facial heights)
3
and
incisor overjet and molar relationship may also be influencing factors.
4
Shearn and Woods
4
reported a mean retrusive effect on the mandibular incisors of 2.4 mm with mandibular first
premolar extraction and 1.0 mm with second premolar extraction. There was generally more
forward movement of the mandibular molars than incisal retraction with the extraction of
the second premolars than with the extraction of the first premolars. However, a specific
extraction pattern did not necessarily guarantee certain amounts of incisor retraction or
molar forward movement. Steyn et al
5
found that the mandibular incisors were retracted, on
average, by 2.1 mm relative to the N-Pog line in patients with mandibular first premolar
extractions and by 1.4 mm in those with mandibular second premolar extractions. In a
recent study of 70 Class II Division 1 malocclusion patients treated with premolar extrac
-
tions when mandibular incisor retraction was not part of the treatment plan, Al-Nimri
3
reported that the mandibular incisors were retracted in only 65% of the patients. On aver
-
age, the mandibular incisors were retracted by 1.3 mm relative to the nasion-pogonion line
in subjects treated with first premolar extractions; in those treated with second premolar
extractions, it was 0.8 mm, but this difference was not statistically significant.
In each study,
3–6
it was reported that significant individual variability exists in the
response to orthodontic treatment with any of the extraction patterns investigated. Thus it
seems possible to achieve a variety of incisor changes with each pattern, although there
does appear to be some definite trends.
4
Fig 3 Undesirable flattening of facial
profiles following excessive retroclination
after mandibular first premolar extraction
in 2 young patients.
a b
c d

361
It should be pointed out that orthodontic treatment with extraction of mandibular pre-
molars need not always cause mandibular incisor retraction. Mandibular incisor proclina-
tion may result from labial movement of these teeth during alignment if the mandibular
canines were buccally positioned, from prolonged use of Class II traction, or if the amount
of mandibular arch crowding exceeds the extraction spaces.
3,4
PPrreeddiiccttiioonn ooff pprrooffiillee cchhaannggeess wwiitthh eexxttrraaccttiioonnss ooff mmaannddiibbuullaarr sseeccoonndd vveerrssuuss ffiirrsstt pprreemmoollaarrss
Although it may be difficult to make accurate soft tissue profile predictions in individual
cases, we still have to try to foresee what are pleasing and harmonious soft-tissue
changes with the orthodontic corrections (see Figs 1 and 7), as well as those which are not
(Fig 3). In my opinion, the most useful and adequately detailed advice in this regard comes
from Holdaway’s soft-tissue analysis and recommendations.
1
This implies that the before-
treatment soft tissue thickness at point A should be used as a guide. If it is within the nor-
mal range (14 to 16 mm) in adolescents, the upper lip will follow the maxillary incisor in a
one-to-one ratio once the lip strain is eliminated. However, if the tissue at point A is very
thin (9 to 10 mm), the lip may follow the incisor immediately and still retain the taper.
Adult lips may react similarly to that of thin lips in adolescent patients. On the other hand,
if the soft tissue at point A is very thick (18 to 20 mm) at the start of orthodontic treat
-
ment, the lip may not follow the incisor movement at all.
EExxcceessssiivvee rreettrraaccttiioonn ooff mmaannddiibbuullaarr ccaanniinneess aanndd iittss ccoonnsseeqquueenncceess
The mandibular canines may sometimes be retracted too far in adolescent and adult cases
with moderate crowding if retraction of the mandibular incisor is not wanted, and the
mandibular first premolars have been extracted as part of the orthodontic treatment plan.
This is because the combined posterior anchorage of the root surface area of the second
premolar plus the first and second molars is indeed a solid block in comparison with the
anterior anchorage of only 1 canine and 2 more or less crowded incisors. Excessive canine
retraction can easily occur, for example, if Class II elastics are not worn properly, if there is
a root resorption problem in the maxillary incisors that prevents the use of intermaxillary
elastics, or if the first and second molars do not move mesially as readily as expected.
Excessive retraction of the mandibular canines starts a vicious circle (Fig 4). Since the max-
illary canines must occlude properly with the mandibular canines, these teeth will also be
excessively retracted. Next, the maxillary and mandibular incisors will move too far back,
increasing the need for labial crown and lingual root torque. Such torque is not always easy
to achieve, and, at best, takes a long time. Therefore, mandibular first premolar extraction
cases can end up with larger-than-intended interincisal angles (Fig 2a). The upright incisors
may cause vertical relapse and mandibular incisor crowding (see below).
Fig 4 Vicious cycle of excessive retraction.
Extraction of mandibular first premolars
Excessive retraction of
mandibular incisors
Excessive retraction of
maxillary incisors
Large interincisal angle
Vertical relapse
Mandibular incisor crowding

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RReellaattiioonnsshhiipp bbeettwweeeenn vveerrttiiccaall rreellaappssee aanndd mmaannddiibbuullaarr aanntteerriioorr ccrroowwddiinngg
Deep anterior overbite may be caused by overeruption of the maxillary incisors, overerup-
tion of the mandibular incisors, or a combination of both. To achieve ideal functional and
esthetic orthodontic results, it is important to determine, before orthodontic treatment is
started, which teeth and dentition are overerupted. Except for careful analysis of the
study casts and cephalograms, important information may then come from examining the
maxillary central incisor display in relationship to the upper lip at speech and with the lips
at rest,
7–13
and by analyzing the lower lip–maxillary incisor relationship in deep overbite
situations.
14,15
It is also important to establish an optimal interincisal angle by obtaining adequate
torque of the maxillary and mandibular incisors at the end of treatment. The long-term sta-
bility of deep overbite correction after orthodontic treatment appears to be related to the
torque or axial inclination of the incisors.
16–23
The deep overbite may return if the maxillary
and/or mandibular incisors continue to erupt following appliance removal. When the maxil-
lary and mandibular incisors have been positioned too upright, relative to one another
after orthodontic treatment, they will have an increased tendency to overerupt following
appliance removal.
16–18
As demonstrated by Swain (Swain BF, personal communication),
the available space for the mandibular anterior teeth will automatically decrease as the
overbite increases (Fig 5).
If the deep bite returns in a treated malocclusion, the incisal edges of the mandibular
incisors will occlude against a labiolingually thicker portion of the maxillary
Incisors
19,20
(Figs 5a to 5c). This will restrict their space and produce incisor crowding or,
more rarely, spacing of the maxillary incisors with the mandibular arch intact.
Fig 5 With relapse of deep overbite, incisal edges of mandibular incisors occlude against labiolingually thicker portion of maxillary
incisors and canines (a to d). Small pieces of wire placed where 6 mandibular teeth occlude on maxillary cast, with various
degrees of overbite relapse (e). Note dramatic difference in length of wires (f) when stretched and measured (reprinted by permis-
sion of B.F. Swain). [Author: Were these actually printed somewhere, or are you just giving him credit (the reference was
personal communication)]
a
b
c
d
e

363
AAddvvaannttaaggeess ooff mmaannddiibbuullaarr sseeccoonndd pprreemmoollaarr eexxttrraaccttiioonn
When mandibular premolar extractions are necessary, and little, if any, change of
mandibular incisor position in space is desired, it is frequently better and safer to extract
the mandibular second rather than the first premolar. The orthodontic treatment then
becomes easier and more predictable with regard to anchorage control (see Figs 2b and
2c). In addition, the achievement of proper maxillary and mandibular incisor torque is
more easily obtained and undesired flattening of the facial profile can be avoided (see Fig
1). Prolonged retention with fixed retainers
19,24,25
is recommended in adolescents (see Figs
1e and 7g), as well as adult patients.
OOvveerrccoommiinngg tthhee ssiizzee pprroobblleemm ooff tthhee mmaannddiibbuullaarr ffiirrsstt pprreemmoollaarr
There is an interesting way to get around the problem of premolar size when a decision is
made to extract a mandibular first premolar in a case with mild to moderate crowding and
a weak profile. If the first premolar is extracted (Fig 6a), the second premolar can be
moved mesially, with coil springs, against the first and second mandibular molars during
the first phase of treatment (Figs 6b to 6f). The 2 mandibular molars will probably not
move distally, due to lack of space and the presence of thick cortical bone in the retromo-
lar area. When the second premolar contacts the canine (Figs 6c and 6f), the case can be
treated like a mandibular second-premolar extraction case, in terms of anchorage.
A similar approach, without using anterior anchorage, can be used to move the first
molars mesially (Fig 7).
26
Of course, the temporary insertion of mini-implants will also allow
such tooth movements.
ab
c
d
e
f
Fig 6 Mesial movement of mandibular second premolars with coil springs against the first molars after extraction of first premo-
lars. When the second premolars contact the canine, the anterior anchorage is reinforced and the situation is similar to that when
the second premolars have been extracted.

364
CClliinniiccaall iimmpplliiccaattiioonnss
1.
When mandibular premolar extractions are necessary in an orthodontic treatment plan,
and maintenance of the pretreatment mandibular incisor position in space is desired,
the second premolars are often a better and safer choice than the first premolars.
Orthodontic treatment then becomes easier and more predictable with regard to
anchorage control and achievement of proper anterior torque, and undesired flattening
of the facial profile is more easily avoided.
2.
If the mandibular first premolars are extracted, and incisor retraction is unwanted, it may
be useful to move the second premolar into contact with the canine as the first phase of
treatment, to avoid harmful effects on mandibular incisor position and facial profile.
3.
To correct and maintain the correction of an excessive overbite, the orthodontist should
analyze which teeth are overerupted, intrude such teeth and establish an optimal maxil
-
lary incisor to upper and lower lip relationship, and secure an adequate interincisal
angle. The mechanical means may include selecting proper bracket torque, bending
additional torque into rectangular archwires, and, if necessary, using auxiliary torquing
springs to deliver extra lingual root torque.
4.
The relationship between vertical anterior relapse and increased mandibular incisor
crowding should be known and respected.
ab
c
d
e
f
g
h
i
Fig 7 Mandibular second premolar extraction case in male adolescent patient. The first molars were moved mesially to contact
the first premolars, using coil springs against the second molars (a to d). Next, the second molars were moved mesially with elas-
tomeric chain (d,e). Class II elastics to the first molars supported the anterior anchorage (e). Note the intraoral results (f,g) and
good facial appearance after treatment (h,i).

365
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T. M. Graber, Editor-in-Chief
University of Illinois at Chicago,
College of Dentistry
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Chicago, Illinois 60612, USA