/

University of Southern California Dissertations and Theses

/

Premolar extraction influence on third molar angulation and retromolar length

(USC Thesis Other)

Premolar extraction influence on third molar angulation and retromolar length

PDF

Transcript (if available)

Content 1

Premolar
Extraction
Influence
on
Third
Molar
Angulation
and
Retromolar
Length

by

Sean
Gardner

A
Thesis
Presented
to
the

FACULTY
OF
THE
USC
GRADUATE
SCHOOL

UNIVERSITY
OF
SOUTHERN
CALIFORNIA

In
Partial
Fulfillment
of
the

Requirements
for
the
Degree

MASTER
OF
SCIENCE

(CRANIOFACIAL
BIOLOGY)

MAY
2016

Sean
Gardner

2

Table
of
Contents

Abstract

3

List
of
Tables
and
Figures

4

Chapter
1.
Extraction
vs.
Nonextraction
Treatment

5

Chapter
2:
Third
Molar
Impactions

14

Chapter
3:
Our
Current
Study

22

Chapter
4:
Hypotheses

23

Chapter
5:
Methods

24

Chapter
6:
Results

28

Chapter
7:
Discussion

44

Chapter
8:
Conclusions

46

Bibliography

47

3

Abstract.
Premolar
extraction
influence
on
3
rd

molar
angulation
and
retromolar
length.

Introduction:
Previous
studies
evaluating
premolar
extraction
influence
on
third
molar

angulation
have
always
evaluated
the
changes
of
the
3
rd

molar
by
examining
the
long
axis
of
the

tooth.

However
many
orthodontic
patients
begin
treatment
when
root
formation
has
not

begun
on
3
rd

molars.

This
study
will
examine
the
angulation
changes
in
3
rd

molars
using
a

horizontal
axis
in
the
occlusal
plane.

Retromolar
length
has
been
found
as
a
contributing
factor

to
impaction
versus
eruption.

This
study
will
examine
the
change
in
retromolar
length
before

and
after
orthodontic
treatment
in
extraction
and
non-‐extraction
cases.

Methods:
In
this

retrospective
study,
90
patients
were
divided
into
3
groups
of
30
patients
each.
Groups
were

compared
using
one-‐way
ANOVA
by
extraction
pattern
(nonextraction,
first
premolar
extraction,

second
premolar
extraction).
The
horizontal
axes
of
the
second
and
third
molars
were
traced
on

initial
and
final
panoramic
radiographs.
The
angulation
change
between
the
molars
was

determined
between
initial
and
final
angulations.

The
retromolar
length
was
determined
by

comparing
the
width
of
the
3
rd

molar
to
the
space
available
from
the
distal
of
the
2
nd

molar
to

the
ramus.

The
initial
and
final
proportions
were
compared
using
chi-‐square
analysis
to

calculate
the
proportional
change
over
the
treatment
period.

Results:

The
mean
third
molar

angulation
change
in
the
non-‐extraction
group
was
3.1±11.6°,
first
premolar
extraction
group
was

10.0±16.7°,
and
second
premolar
extraction
group
was
6.3±13.1°.

The
final
retromolar
length
to
third

molar
width
proportion
among
the
three
groups
was:
non-‐extraction
1.88±1.38,
first
premolar

extraction
group
1.26±0.53,
and
second
premolar
extraction
group
1.19±0.37.

Discussion:
There
was

not
a
significant
difference
in
3
rd

molar
angulation
changes
among
the
three
groups.

Extraction

orthodontic
treatment
did
not
help
improve
eruption
angles
of
third
molars.

There
was
a
highly

4

significant
difference
(p
value<
0.01)
between
the
extraction
groups
and
non-‐extraction
group

in
the
proportion
of
third
molar
width
to
retromolar
length.

Extraction
orthodontic
treatment

results
in
mesial
movement
of
the
mandibular
dentition
and
more
space
distal
to
second

molars
for
eruption
of
third
molars.

Conclusion:
Further
studies
could
be
performed
using
CBCT

images
pre-‐
and
post-‐treatment
to
calculate
accurately
the
positional
changes
in
mandibular

third
molars
and
retromolar
length.

5

Tables
and
Figures

Figure
1.
Buccal
view
of
TSALD

11

Figure
2.
Occlusal
view
of
TSALD

12

Figure
3.
Anchorage
Considerations

13

Figure
4.
Horizontal
reference
plane
and
horizontal
axes
of
2
nd

and
3
rd

molar

25

Figure
5.
Measurement
of
the
width
of
the
3
rd

molar

25

Figure
6.
Measurement
of
retromolar
length

26

Table
1.
Initial
group
comparisons

27

Table
2.
Greater
than
5°
or
less
than
5°angulation
change

28

Figure
7.
3rd
molar
angulation
change
(Non-‐Ext)

29

Figure
8.
3rd
molar
angulation
change
(1
st

premolar
ext)

29

Figure
9.
3rd
molar
angulation
change
(2
nd

premolar
ext)

30

Table
3.
Extraction
of
First
Premolars
with
Unfavorable
Angulation
Change

30

Table
4.
Extraction
of
Second
Premolars
with
Favorable
Angulation
Change

30

Table
5.
Extraction
of
Second
Premolars
with
Unfavorable
Angulation
Change

30

Table
6.
Final
Mean
Proportion
of
Third
Molar
Width
to
Retromolar
Length

31

Figure
10.
Example
of
favorable
outcomes
with
2
nd

premolar
ext

31

Figure
11.
Example
of
favorable
outcomes
with
2
nd

premolar
ext

32

6

Figure
12.
Example
of
favorable
outcomes
with
1
st

premolar
ext

33

Figure
13.
Example
of
favorable
outcomes
with
1
st

premolar
ext

34

Figure
14.
Example
of
unfavorable
angulation
change
with
2
nd

premolar
ext

35

Figure
15.
Example
of
unfavorable
angulation
change
with
2
nd

premolar
ext

36

Figure
16.
Example
of
unfavorable
angulation
change
with
1
st

premolar
ext

37

Figure
17.
Example
of
unfavorable
angulation
change
with
1
st

premolar
ext

38

Figure
18.
Example
of
no
angulation
change
with
2
nd

premolar
ext

39

Figure
19.
Example
of
no
angulation
change
with
1
st

premolar
ext

40

Figure
20.
Example
of
no
angulation
change
with
non-‐ext

41

Figure
21.
Example
of
unfavorable
angulation
change
with
non-‐ext

42

Figure
22.
Example
of
favorable
angulation
change
with
non-‐ext

43

7

Chapter
1:
Extraction
vs.
Nonextraction
Treatment

History

“The
best
balance,
the
best
harmony,
the
best
proportions
of
the
mouth
in
its
relation
to
the
other

features
require
that
there
shall
be
a
full
complement
of
teeth.”
(Angle
1907)

Edward
Angle
believed

that
every
patient
should
be
treated
with
nonextraction
treatment,
however
many
of
his
successors

spent
their
career
in
orthodontics
arguing
for
extraction
treatment.

Calvin
Case
defended
his
extraction

treatment
by
stating
that
the
treatment
would
be
less
prone
to
relapse
(Pollock
1964).

Charles
Tweed,
a

student
of
Dr.
Angle,
started
treating
all
of
his
cases
with
a
nonextraction
philosophy.

After
seeing
the

relapse
and
protrusive
profiles
associated
with
nonextraction
treatment
he
decided
to
retreat
relapsed

cases
using
4
premolar
extractions
(Tweed
1944).

Tweed
stated
that
carefully
planned
extractions

would
increase
post-‐treatment
stability
and
improve
facial
esthetics.

Despite
the
popularity
of
Tweed’s

treatment
philosophy
the
debate
over
extraction
and
nonextraction
treatment
still
continues.

Arch
Length
Considerations

The
main
complaint
from
orthodontic
patients
is
their
“crooked
teeth,”
which
as
we
know
is
a
result
of
a

lack
of
space
to
align
teeth
within
the
patient’s
bone.

This
problem
presents
to
orthodontists
as
Tooth

Size
Arch
Length
Discrepancy
(TSALD),
which
is
defined
as
the
sum
of
mesial-‐distal
lengths
of
the

individual
crowns
being
greater
than
the
linear
bone
available.

Misalignment
of
the
dentition,
the

crown
lengths
are
discontinuous,
allows
for
all
of
the
teeth
to
be
present
in
the
bone.

Orthodontic

treatment
will
align
these
teeth
and
will
require
a
greater
amount
of
space
than
is
currently
present.

Orthodontic
treatment
does
not
only
align
teeth,
we
also
correct
the
curve
of
spee
by
leveling.

Leveling

requires
arch
length
because
as
teeth
are
leveled
on
a
flat
plane
additional
space
will
be
needed
to
fit
all

of
the
teeth.

8

Molar
and
canine
correction
of
inter-‐arch
relationships
will
also
require
arch
length.

For
example
in

class
II
dentitions
the
lower
dentition
will
need
to
move
anteriorly
to
correct
to
a
class
I
relationship.

The
forward
movement
of
the
lower
dentition
is
confined
to
the
limits
of
the
alveolar
bone,
the
amount

of
space
required
for
alignment
affects
how
much
space
is
available
for
class
II
correction.

The
ideal

correction
for
class
II
would
involve
a
lower
arch
that
has
an
excess
of
length
and
spacing
of
the

dentition
to
allow
the
forward
movement
of
the
dentition
and
class
II
correction.

Nonextraction
Treatment

Nonextraction
treatment,
as
the
name
implies
requires
the
clinician
to
preserve
the
complete
dentition.

Traditionally,
this
treatment
would
be
done
for
cases
with
spacing,
non-‐crowded
cases,
and
cases
with

minor
TSALD
(many
of
these
cases
require
interproximal
filing
of
the
teeth
to
reduce
crown
width).

In

order
to
gain
space
in
a
minor
crowding
case
Lusterman
proposed
the
technique
of
Interproximal

Reduction
(IPR).

In
this
technique
the
mesial
and
distal
sides
of
the
anterior
teeth
are
reduced
and

thereby
decreasing
the
total
amount
of
tooth
length
(Lusterman
1954).

Sheridan
proposed
the

reduction
of
the
size
of
posterior
teeth
through
a
process
called
Air-‐Rotor
Stripping
(ARS)
(Sheridan

1985).

IPR
and
ARS
are
limited
by
the
amount
of
interproximal
enamel
present
therefore
are
limited
to

only
correcting
minor
TSALD.

Arch
Expansion
in
Nonextraction
Treatment

Williams
proposed
that
arch
width
expansion
posterior
to
the
canines
is
stable
and
a
valuable
treatment

method.

(Williams
2005)

Sabri
proposed
treating
patients
with
severe
arch
length
deficiency
with
rapid

palatal
expansion
and
lip
bumper.

He
showed
that
he
was
able
to
achieve
stable
results
with
fixed
lower

retention
5
years
post
treatment.

(Sabri
2010)

However
Rinchuse
challenged
the
rationale
of
many

“expansionist”
who
predict
expansion
treatment
“based
on
the
degree
of
facial-‐lingual
inclination
of
the

mandibular
molars.”
(Rinchuse
2008)

Andrews
stated
that
the
facial
crown
lingual
inclination
of

mandibular
first
molars
is
-‐30
degrees;
proponents
of
arch
expansion
believe
this
should
be
more

9

upright
allowing
for
more
room
for
the
tongue.

However
an
uprighting
mandilbular
first
molar
to
-‐12

degrees
moves
it
from
its
natural
position
of
-‐30
degrees.

(Rinchuse
2008)

Another
tradeoff
for
nonextraction
treatment
is
the
possibility
of
bone
loss
on
teeth
that
are
being

expanded
to
the
outermost
limits
of
the
alveolus.

Using
CBCT
to
measure
the
levels
of
bone
from
the

alveolar
crest
to
the
CEJ
before
and
after
treatment,
Castro
concluded
that
apical
migration
of
the
bone

is
seen
with
expansion
orthodontic
treatment.

In
the
study
11%
of
the
subjects
had
distances
of
the

alveolar
bone
to
CEJ
greater
than
2mm
prior
to
treatment
and
after
treatment
19%
of
the
subjects
had

distances
greater
than
2mm.

(Castro
2015)

Arch
Distalization

With
the
advent
of
miniscrews
the
possibilities
of
treatment
mechanics
have
greatly
increased.

Previously
it
would
have
been
almost
impossible
to
achieve
true
arch
distalization,
but
now
these

mechanics
are
possible.

Jang
et
al.
reported
using
miniscrews
to
correct
an
anterior
crossbite
with
4mm

of
distalization.

They
did
not
report
the
need
for
any
extractions
of
premolars
or
third
molars,
where
as

previously
this
amount
of
retraction
could
have
only
been
done
with
premolar
extraction.

They
also

reported
their
results
to
be
stable
one
year
after
retention.

(Jang
et
al.
2013)

Chung
et
al.
also
reported

using
nonextraction
and
miniscrew
treatment
to
correct
a
class
III.

(Chung
2010)

However,
the
patient

did
not
have
third
molars
present
at
the
start
of
treatment.

Miniscrews
are
invaluable
in
treatment
of
class
III
nonextraction
cases,
however
there
are
cases
of
using

Bioprogressive
techniques
to
accomplish
the
same
correction.

Kondo
has
reported
several
cases
where

by
using
Bioprogressive
techniques
class
III
correction
was
achieved.

Patients
maxillas
were
expanded

and
molars
extruded
causing
a
clockwise
rotation
of
the
mandible.

Patient
lower
facial
height
increased

slightly,
but
he
stated
that
this
actually
improved
the
facial
balance
because
of
their
pretreatment
facial

balance.

Maxillary
expansion
was
accompanied
with
mandibular
expansion
and
myofunctional
therapy.

10

(Kondo
2000)

He
also
reported
that
he
was
able
to
maintain
stable
results
4
years
after
treatment.

(Kondo
2005)

Extraction
Treatment
History

Proffit
detailed
the
trends
in
extraction
orthodontics
at
the
University
of
North
Carolina
(UNC)
Graduate

Orthodontic
clinic
from
the
1950s
to
1990s.

Four
first
premolar
extractions
accounted
for
10%
of

orthodontic
cases
at
UNC
in
1953,
this
jumped
to
50%
in
1963;
the
rate
remained
high
between
35%-‐45%

until
the
1980s
where
the
rate
regressed
back
to
the
lower
rate
of
the
1950s.

Proffit
stated
that
the

increase
in
first
premolar
extractions
in
this
time
was
due
to
the
belief
that
greater
post
treatment

stability
would
be
achieved
with
4
premolar
extractions.

The
decline
in
extractions
since
the
1980s
has

been
attributed
to
greater
concern
with
extraction
impact
on
facial
esthetics,
no
guarantee
that

extractions
provide
greater
stability,
concern
for
temporomandibular
dysfunction,
and
changes
in

techniques.

Extractions
for
class
II
camoflouge
(maxillary
first
premolars
alone
or
maxillary
first-‐
mandibular
second
premolars)
peaked
in
1968
at
16%,
but
then
declined
similarly
to
10%
by
the
1980s.

Other
types
of
extraction
patterns
remained
constant
throughout
the
time
period
of
the
study.

Overall

extraction
orthodontic
treatment
was
30%
in
1953,
peaked
in
1968
at
76%
and
then
declined
to
28%
in

1993.

(Proffit
1994)

First
Premolar
Extraction
Treatment

Cases
with
moderate
to
large
amounts
of
TSALD
require
a
greater
amount
of
space
than
IPR
or

expansion
can
achieve.

Baumrind
identified
TSALD
as
“the
most
important
factor
necessitating
the

decision
to
extract
premolars.”

(Baumrind
et
al.
1996)

It
has
been
recognized
several
times
throughout

the
literature
that
TSALD
is
one
of
the
most
important
factors
influencing
treatment
planning.
(Paquette

et
al.
1992,
Luppanapornlarp
et
al.
1993,
Beattie
et
al.
1994)

Why
extract
first
premolars?

First
premolars
have
both
optimal
size
for
extraction
space
closure
and

arch
location
for
utility
to
the
clinician.

Extraction
rates
among
all
clinicians
are
impossible
to
measure

11

because
of
varying
preferences
of
all
clinicians
in
treating
orthodontic
cases.

Evaluating
extraction
rates

the
University
of
North
Carolina
described
the
general
trend
as
an
increase
in
extractions
in
the
1960’s

and
then
a
steady
decline
to
the
present
day.
(Proffit
et
al.
2012)

GV
Black
stated
that
the
average
mesiodistal
length
of
a
first
premolar
is
7.2mm;
therefore
by
extracting

2
first
premolars
the
arch
length
gained
would
be
14.4mm.

(Black
1902)

The
extraction
space
is
closed

by
the
distal
movement
of
anterior
teeth
and
the
mesial
movement
of
posterior
teeth.
(Williams
et
al.

1976)

Movement
is
reciprocal;
however
there
is
a
greater
amount
of
movement
of
the
anterior
teeth.

Jepsen
stated
that
the
greater
amount
of
movement
of
the
anterior
teeth
is
seen
because
large
multi-‐
rooted
posterior
teeth
resist
movement
more
than
smaller,
single-‐rooted
anterior
teeth.
(Jepsen
1963)

Anterior
teeth
will
have
greater
movement
through
bodily
and
tipping
movements,
whereas
posterior

teeth
will
have
less
movement
and
be
mostly
bodily
movement.
(Williams
et
al.
1976)

Steyn
also
noted

that
since
the
extraction
space
is
located
more
anteriorly
it
allows
for
greater
amount
of
incisor

retraction.
(Steyn
et
al.
1997)

Creekmore
calculated
that
all
of
the
previously
discussed
factors
resulted

in
the
anterior
teeth
closing
2/3
of
the
extraction
space
and
the
posterior
closing
1/3
of
the
extraction

space.
(Creekmore
1997)

The
space
gained
from
extractions
is
used
for
leveling,
aligning,
and
correction

of
lower
anterior
inclination.
(Bishara
et
al.
1995)

Due
to
the
mechanics
involved
and
the
closing

movements
seen
first
premolar
extractions
are
indicated
in
treatment
situations
that
require
a
greater

amount
of
anterior
space.

Considerations
effecting
the
decision
to
extract:

• Evaluation
of
profile

• Amount
of
TSALD

• Location
of
TSALD

• Evaluation
of
Curve
of
Spee

• Incisor
angulation

12

• Second
molar
angulation

Indications
for
first
premolar
extractions:

• Protrusive
lower
facial
profiles

• TSALD
is
moderate
to
severe

• TSALD
is
located
in
the
anterior
dental
arch

• Excessive
lower
incisor
angulations

Second
Premolar
Extraction
Treatment

Facial
esthetics
is
an
important
factor
in
determining
treatment
plan
and
options
for
orthodontic

patients.
(Talass
et
al.
1987,
Boley
et
al.
1998,
Ismail
et
al.
2002,
Kim
et
al.
2003,
Stephens
et
al.
2005,

Germec
et
al.
2008,
Konstantonis
2012)

The
extraction
of
first
premolars
can
result
in
over-‐retraction
of

lower
anterior
teeth.
(Dewel
1955)

Over-‐retraction
results
in
a
flat
or
retrusive
lower
facial
profile.

When
less
space
is
needed,
clinicians
will
extract
second
premolars
to
prevent
over-‐retraction
of
lower

anterior
and
preserve
facial
esthetics.

(De
Castro
1974)

Second
premolar
extraction
provides
a
similar
amount
of
extraction
space
as
first
premolar
extraction,

however
the
mechanics
of
the
space
closure
are
different.

Second
premolar
extraction
creates
space

more
distal
in
the
arch
as
well
as
creating
less
anchorage
for
the
posterior
segment
and
greater

anchorage
of
the
anterior
segment.

The
resulting
movement
of
teeth
leads
to
a
more
truly
reciprocal

movement
of
the
anterior
and
posterior
segments.

(Brandt
et
al.
1975)

De
Castro
calculated
that
in

second
premolar
extraction
the
anterior
segment
moves
distally
7.5mm
and
the
posterior
segment

moves
mesially
7.5mm.
(De
Castro
1974)

Alignment
and
retraction
of
anterior
teeth
can
be
done
on

cases
with
moderate
TSALD
without
over-‐retracting
anterior
teeth.

Since
the
amount
of
space
gained

after
space
closure
is
less
than
first
premolar
extraction,
proper
case
selection
is
crucial.

Schoppe

advised
to
extract
second
premolars
in
cases
with
TSALD
of
7.5mm
or
less.

(Schoppe
1964)

De
Castro

recommended
second
premolar
extraction
in
cases
with
TSALD
5mm
or
less.
(De
Castro
1974)

Despite

13

varying
opinions
of
exact
numbers
of
TSALD
the
idea
of
second
premolar
extraction
is
done
in
cases
of

moderate
crowding
without
changing
facial
profile.

Indications
for
second
premolar
extractions:

• Acceptable
to
retrusive
lower
facial
profiles

• TSALD
is
minor
to
moderate

• TSALD
is
located
in
the
posterior
dental
arch

• Normal
and
retrusive
lower
incisor
angulations

• TSALD
without
protrusive
profile

• Open
bite
cases

Extraction
Considerations

Extracting
First
vs.
Second
Premolars

1st
Premolar
Extraction

2nd
Premolar
Extraction

Profile

Protrusive
Normal

Amount
of
TSALD

Moderate
to
Severe
Mild
to
Moderate

Location
of
TSALD

Anterior
Posterior

Incisor
Angulation

Excessive
Normal

Space
for
2nd
Molar
Eruption

Adequate
Limited

Esthetic
Impact
of
Extraction
vs
Nonextraction
Treatment

Bowman
studied
before
and
after
profiles
of
orthodontic
patients
having
had
either
extraction
or

nonextraction
treatment
in
Caucasian
patients;
58
laypersons
and
42
dentists
evaluated
the
profiles.

The
profiles
of
the
extraction
group
had
more
retraction
of
the
soft
tissue
(average
1.8mm)
and

therefore
had
“flatter”
faces
post
orthodontic
treatment.

Both
laypersons
and
dentists
preferred
the

esthetics
of
a
flatter
face
in
a
Caucasian
patient.

The
retraction
of
the
soft
tissue
or
“flattening”
of
the

face
had
the
most
esthetic
improvement
in
patients
that
had
more
protrusive
lips,
greater
than
2-‐3mm

14

behind
Rickett’s
E-‐line.

The
studied
concluded
that
patients
with
protrusive
profiles
and
crowding
could

be
improved
by
extraction.

(Bowman
2000)

Lim
et
al.
found
similar
results
in
regards
to
facial
profile

esthetic
improvement
in
extraction
patients
in
the
Korean
population.

(Lim
2008)

Xu
et
al.
found

similar
results
in
regards
to
extraction
facial
profiles
vs
nonextraction
profiles
in
the
Chinese
population.

(Xu
et
al.
2006)

Scott
also
found
that
African
American
patients
benefitted
from
an
improvement
in

facial
profile
in
the
extraction
versus
nonextraction
treatment.

However
this
study
cited
that
the
race
of

the
patient,
the
orthodontist,
and
layperson
significantly
affects
the
determination
of
the
most
esthetic

result.

In
other
words
most
caucasain
orthodontists
preferred
profiles
with
the
lips
2mm
behind
the

Rickett’s
E-‐line,
where
as
African
American
orthodontists
preferred
the
lips
4mm
anterior
to
the
E-‐line
in

African
American
patients.

(Scott
1999)

The
studies
stated
above
found
that
nonextraction
treatment
resulted
in
little
change
to
the
profile.

All

panelists
preferred
the
look
of
post-‐treatment
profiles
to
pre-‐treatment
profiles
regardless
of
extraction

or
nonextraction
treatment.
(Scott
1999)

Konstantonis
studied
resulting
facial
esthetics
in
borderline

class
I
malocclusion
extraction
cases.

He
found
that
nonextraction
treatment
resulted
in
upper
lip

retraction
and
lower
lip
protraction.

He
also
found
that
in
extraction
treatment
there
was
a
significant

change
in
the
soft
tissue
of
the
upper
and
lower
lips,
as
well
as
a
reduction
in
the
nasiolabial
angle.

(Konstantonis
2012).

Johnston
studied
the
long-‐term
effects
of
extraction
and
non-‐extraction
treatment
in
patients
on

average
15
years
post-‐orthodontic
treatment.

(Paquette
1992)

All
patients
were
class
II
prior
to

orthodontic
treatment,
the
initial
debond
records
reflected
similar
results
as
studies
above
where
there

was
more
hard
and
soft
tissue
retraction
in
extraction
cases.

However
after
15
years
both
groups
of

patients
experienced
similar
changes
in
decreased
profile
convexity
and
dental
changes/relapse
that

corresponded
with
antero-‐posterior
mandibular
displacement.

The
initial
crowding
and
protrusion

15

associated
with
the
extraction
cases
actually
produced
more
protrusive
profiles
at
the
15-‐year
follow
up.

(Paquette
1992)

Nonextraction
vs
Extraction
Orthodontic
Treatment
Outcomes

Is
there
a
difference
in
treatment
outcome
of
extraction
vs
nonextraction
orthodontic
treatment?

Anthopoulou
compared
class
I
malocclusion
patient
treatment
outcomes
of
patients
treated
by

extraction
and
nonextraction
orthodontics
by
using
the
American
Board
of
Orthodontics
objective

grading
system
(ABO-‐OGS).

Patients
selected
for
grading
were
patients
that
were
determined
to
be

“borderline”
patients
to
be
treated
with
or
without
extactions.

Using
the
ABO-‐OGS
it
was
determined

that
there
was
no
significant
difference
in
the
treatment
outcomes
of
“borderline”
class
I
patients

treated
by
nonextraction
or
extraction
orthodontics.

(Anthopoulou
2014)

Posttreatment
Stability

Proponents
of
extraction
therapy
in
orthodontics
have
long
claimed
that
there
is
increased
stability
in

extraction
treatment
over
nonextraction
treatment.

(Tweed
1944)

Kahl-‐Nieke
studied
the
long-‐term

stability
of
nonextraction,
extraction
of
1-‐2
incisors,
4
premolars
and
3
rd

molar
orthodontic
treatment.

It

was
concluded
that
the
majority
of
orthodontic
cases
were
stable
regardless
of
type
of
treatment
and

treatment
time.

The
severity
of
the
original
malocclusion,
type
of
treatment
(extraction/nonextraction),

amount
of
treatment,
and
end
of
treatment
alignment
all
played
a
role
in
the
amount
of
relapse
seen
in

all
cases.

The
study
further
concluded
that
post
treatment
stability
can
be
optimized
by
setting

treatment
goals
within
anatomical
limits.

Heiser
evaluated
the
long-‐term
stability
of
extraction
and

nonextraction
treatment
and
changes
to
the
dentition
posttreatment
of
patients
6-‐6.5
years
out
of

retention.

Mandibular
canine
distance
decreased
from
pretreatment
to
follow-‐up,
while
maxillary
arch

had
a
net
increase
over
the
same
time.

Measuring
to
the
axis-‐orbital
plane,
the
maxillary
canine

guidance
angle
at
the
end
of
retention
was
highly
associated
with
the
changes
in
mandibular
intercanine

distance.

It
was
proposed
that
the
torque
of
maxillary
canines
be
evaluated
before
treatment
to

16

coordinate
with
the
guidance
angle
and
help
to
prevent
decrease
in
mandibular
intercanine
distance.

(Heiser
et
al.
2008)

Heiser
showed
that
relapse
is
not
isolated
to
each
arch
individually
but
rather
the

total
harmony
of
the
complete
dentition
is
important
to
posttreatment
stability.

17

Fig.
1:
Buccal
view
of
TSALD

18

Fig.
2:
Occlusal
view
of
TSALD

19

Fig.
3:
Anchorage
Considerations

Second
premolar
extractions
have
a
more
distal
extraction
space
and
a
premolar
in
the
anterior

segment.

First
premolar
extractions
have
a
more
anterior
extraction
space
and
a
premolar
in
the
posterior

segment.

20

Chapter
2:
Third
Molar
Impactions

Background
Information

The
majority
of
orthodontic
patients
are
adolescents
which
have
developing
third
molars.

Orthodontists

are
most
well
equipped
to
assess
the
status
of
third
molar
eruption
and
the
prognosis
of
eruption

because
of
initial,
progress,
and
final
panoramic
radiographs
taken
throughout
orthodontic
treatment.

In
the
United
States
impacted
third
molars
lead
to
an
annual
average
of
10
million
extractions.

(American
Journal
Public
Health
2007)

Impaction
is
not
the
only
reason
for
extraction
of
third
molars,

other
reasons
include:
prophylaxis,
pericoronitis,
orthodontics,
caries,
pulpitis,
cysts,
tumors,
root

resorption,
and
other
factors.
(Lysell
et
al.
1988)

For
many
people
jaw
growth
is
completed
when
third
molars
are
the
last
teeth
to
erupt
in
the

permanent
dentition.
(Rantanen
1967)

It
has
been
shown
that
race
plays
a
factor
in
the
timing
of
third

molar
eruption;
for
example
Nigerians
show
eruption
as
early
as
14
years
old
(Odusanya
et
al.
1991)

whereas
in
Europeans
eruptions
has
been
shown
as
late
as
26
years
old.
(Kruger
et
al.
2001)

Brown

showed
that
race
also
has
a
correlation
in
impaction
rates
with
tooth
impaction
occurring
more

commonly
in
Whites
than
African
Americans.
(Brown
et
al.
1982)

Gender
has
also
been
shown
to
play
a

role
in
third
molar
eruption
with
eruption
occurring
3
to
6
months
earlier
in
males
than
females.
(Hattab

1999)

Some
studies
have
shown
that
females
have
higher
rates
of
impactions
than
males.
(Sanhu
et
al.

1982,
Narda
et
al.
1959)

Specifically
focusing
on
mandibular
third
molar
impaction,
females
have
higher

rates
of
impaction
than
males.
(Kruger
et
al.
2001,
Hattab
et
al.
1999,
Yuasa
et
al.
2004,
Hellman
1961)

The
higher
rate
of
impaction
amongst
females
has
been
attributed
to
the
fact
that
most
females
have

completed
growth
before
the
eruption
of
third
molars,
while
most
males
continue
to
grow
through
the

eruption
period.
(Taranger
et
al.
1980,
Engstrom
et
al.
1983)

However
other
studies
have
called
into

question
this
reasoning
for
the
higher
impaction
rate
amongst
women
by
showing
that
there
was
no

21

gender
predilection
for
impaction.
(Haidar
et
al.
1986)

The
Haidar
study
did
not
specifically
refer
to

mandibular
third
molars
but
still
raises
some
questions
about
impaction
rates
between
men
and
women.

Third
molar
crown
formation
is
completed
by
age
14
and
root
formation
is
completed
by
age
18.

(Engstrom
et
al.
1983)

Third
molars
tend
to
erupt
toward
the
latter
stages
of
root
development,

between
the
ages
of
17
to
21.
(Ash
1993,
Proffit
et
al.
1993)

Removal
of
third
molars
is
generally

recommended
to
be
done
when
1/3
to
2/3s
of
the
roots
are
formed,
between
the
ages
of
17
to
20.

(Hupp
et
al.
2014)

According
to
a
study
done
by
Alling
72.7%
of
the
world
population
has
at
least
one
impacted
tooth.

(Alling
et
al.
1993)

Lysell
and
Rohlin’s
study
on
Swedish
dental
students
found
that
33%
had
at
least
1

impacted
third
molar.

They
also
reported
that
third
molar
impaction
was
more
common
in
the
lower

jaw.

(Schersten
et
al.
1989)
In
general
third
molars
are
regarded
as
the
most
commonly
impacted
tooth

(Hupp
et
al.
2014,
Dachi
et
al.
1961,
Grover
et
al.
1985),
however
the
rate
of
impaction
is
reported

varyingly
in
the
literature.

Hellman
reported
as
little
as
9.5%
(Hellman
1938),
whereas
Ricketts
reported

50%
(Ricketts
1972)
and
both
Bjork
and
Richardson
fell
in
the
middle
with
25%
and
35%
respectively.

(Bjork
et
al.
1956,
Richardson
1977)

Another
variable
is
the
percentage
of
the
population
that
actually
has
third
molars
present
in
the
mouth.

Hugoson
found
that
95%
of
all
adolescents
have
at
least
1
third
molar
and
75%
have
all
4
third
molars.

(Hugoson
et
al.
1988)

Silling
stated
that
given
the
high
proportion
of
the
population
with
third
molars

and
high
rate
of
impactions,
third
molars
pose
one
of
the
major
problems
in
the
dental
profession.

(Silling
1973)

Given
the
commonality
of
the
problem
amongst
the
population
and
dental
professionals

resolving
this
problem
several
researchers
have
investigated
third
molar
impactions.

Richardson
studied
third
molar
development
in
children
average
age
of
11
years
to
determine
the

developmental
position
and
angulation
of
third
molars.

Obviously
at
this
young
age
several
changes
will

occur
in
third
molar
angulation
and
position
from
mandibular
growth.

His
study
provided
a
starting

22

point
reference
to
where
third
molar
begin
to
form.

The
average
angulation
of
third
molars
to
the

mandibular
plane
is
38°
with
a
range
of
11°
to
83°.

She
also
stated
that
the
third
molar
is
spaced
from

the
distal
of
the
second
molar
an
average
of
1.2mm
with
a
range
of
7mm-‐0mm.
(Richardson
1970)

The

average
angulation
of
developing
third
molars
in
38°,
which
means
that
there
is
a
significant
amount
of

uprighting
that
must
occur
in
order
for
that
tooth
to
erupt
properly.

Cone
Beam
Computed
Tomography
(CBCT)

Recent
improvements
to
imaging
techniques
have
led
to
many
different
studies
involving
CBCT
and
the

evaluation
of
third
molars.

Many
of
the
studies
in
the
current
literature
are
concerned
with
the
dangers

and
complications
of
third
molar
removal,
there
are
few
studies
in
relation
to
this
current
project
in

relations
to
orthodontic
treatment
and
positional
changes
in
third
molars.

However
Halicioglu
et
al.

used
CBCT
to
compare
the
volumes
of
third
molars
in
normal
side
and
a
side
in
crossbite.

They
found

that
the
volume
of
third
molars
in
a
mandible
in
crossbite
were
less
in
the
crossbite
side.

(Hacioglu
et
al.

2014)

Thereby
confirming
as
has
been
done
before
that
the
development
of
third
molars
is
a

multifactorial
process.

Previous
Studies

In
1956,
Bjork
conducted
a
study
to
determine
the
factors
involved
with
mandibular
growth
affecting

third
molar
eruption
space.
(Bjork
et
al
1956)

Using
lateral
cephalograms
he
measured
the
distance

from
the
distal
surface
of
the
second
molar
to
the
anterior
edge
of
the
ramus
along
a
line
parallel
to
the

occlusal
plane
of
the
lower
arch.

There
was
a
decrease
in
the
amount
of
eruption
space
distal
to
the

second
molar
in
90%
of
the
impaction
cases.
(Bjork
et
al.
1956)

Bjork
identified
3
developmental
factors

that
affected
third
molar
space:
(1)
amount
of
increase
in
length
of
the
mandible,
(2)
direction
of

condylar
growth,
and
(3)
direction
of
tooth
eruption.

Mandibular
length
increases
by
growth
of
the

posterior
ramus
and
resorption
of
the
anterior
ramus.
(Silling
1973)

Broadbent
reasoned
that
third

molar
impaction
is
a
result
of
insufficient
mandibular
growth.
(Enlow
1968)

Third
molar
space
is

23

significantly
influenced
by
changes
in
condylar
shape
during
development.

Eruption
space
was
greatly

benefitted
by
horizontal
growth
of
the
condyle
and
hindered
by
vertical
growth.

Distally
erupting

second
molars
can
occupy
some
of
the
space
that
was
meant
for
the
eruption
of
third
molars.

Ricketts
studied
third
molar
eruption
and
he
found
that
50%
of
his
orthodontic
patients
had
impacted

third
molars.
(Ricketts
1972)

Interesting
to
his
research
was
the
fact
that
he
noticed
a
greater
rate
of

eruption
of
third
molars
in
his
orthodontic
extraction
cases.

Evaluation
of
the
anterior-‐posterior

positioning
of
third
molars
relative
to
the
external
ridge
of
the
ramus
led
to
the
conclusion;
third
molars

with
a
greater
portion
of
the
crown
mesial
to
the
ridge
had
a
greater
chance
of
eruption,
while
those

with
a
greater
portion
distal
had
a
poor
prognosis
of
eruption.

Mandibular
growth
studies
using
the
ramus
as
a
reference
point
is
unreliable
due
to
the
remodeling
that

occurs
in
the
ramus
during
mandibular
growth.
(Enlow
1968)

Ricketts
developed
his
X
i

point
located
in

the
center
of
the
ramus
to
overcome
the
surface
variation
and
unreliability
of
using
the
ramus
as
a

reference
point.

Several
authors
duplicated
Bjork’s
studies
measuring
the
space
from
the
second
molar

to
a
reference
point
to
determine
the
retromolar
length
and
the
probability
of
eruption.
(Schulhof
1976,

Ricketts
1979)

Ricketts
measured
the
distance
from
the
distal
of
the
lower
second
molar
to
X
i

point

along
the
mandibular
occlusal
plane.

Using
lateral
cephalograms
of
patients
from
8-‐9
years
of
age
and

growth
prediction
curves,
he
predicted
the
amount
of
eruption
space
that
would
be
available.

Using
his

predictions
he
concluded
that
a
predictive
distance
of
30mm
or
more
would
result
in
eruption
of
third

molars;
a
distance
less
than
20mm
would
likely
result
in
impaction.
(Ricketts
et
al.
1976)

Ricketts
believed
that
his
method
of
third
molar
eruption
prediction
could
provide
the
clinician
with
a

diagnosis
of
eruption
or
impaction
with
90%
certainty.
(Ricketts
et
al.
1976)

However,
Olive
and

Basforth
showed
that
Ricketts
study
results
were
not
reproducible
and
that
predictability
of
third
molar

eruption
was
unreliable.
(Olive
et
al.
1981)

Their
study
showed
that
prediction
measuring
the
distance

24

of
X
i

point
to
the
distal
of
the
second
molar
on
lateral
cephalograms
was
an
unreliable
method
of

prediction.

Forsberg
set
out
as
did
Ricketts
to
develop
a
method
for
orthodontists
to
predict
eruption
versus

impaction
of
third
molars.

Using
lateral
cephalograms
and
analyzing
the
space
available
he
was
unable

to
develop
a
reliable
method
for
predicting
third
molar
eruption.

He
cited
that
part
of
the
problem
was

that
when
space
was
predicted
to
be
inadequate
for
eruption,
half
of
those
patient’s
third
molars
still

erupted
normally.

(Forsberg
1988,
Forsberg
et
al.
1989)

Richardson’s
study
of
third
molar
eruption
followed
patients
from
10-‐11
years
of
age
until
eruption
or

diagnosis
of
impaction
of
third
molars.

Using
lateral
cephalograms
she
separated
the
patients
into

eruption
and
impaction
groups
and
compared
the
results.

She
found
that
impaction
was
related
to

reduced
mandibular
growth
and
a
higher
developmental
angulation
of
third
molars
to
the
mandibular

plane
resulted
in
impaction.

From
her
study
she
concluded
that
accurate
prediction
of
third
molar

eruption
could
not
be
made
at
10-‐11
years
of
age.

She
cited
the
variability
of
the
third
molar
eruption

path
as
the
main
obstacle
in
developing
an
accurate
prediction
method
of
third
molar
eruption.

(Richardson
1977)

Third
molar
crown
angulation
and
path
of
eruption
plays
a
role
in
impaction
of
mandibular
third
molars.

Maxillary
third
molars
are
distally
angulated,
whereas
mandibular
third
molars
are
mesially
angulated
at

the
time
of
calcification
and
root
development.
(Sicher
1965,
Richardson
1992)

Maxillary
third
molars

have
a
distal
path
of
eruption,
while
mandibular
third
molars
have
a
mesial
path
of
eruption.

Mesioangular
impaction
of
mandibular
third
molars
is
the
most
common,
43-‐46%.
(Peterson
1992,
Kan

et
al.
2002)

Distoangular
impactions
only
made
up
6-‐3%
of
all
impactions.
(Kan
et
al.
2002,
Hupp
et
al.

2014)

Third
molar
impaction
is
a
multifactorial
process,
however
most
researchers
agree
that
eruption
space
is

a
key
element
to
eruption.

Third
molars
are
the
last
teeth
to
erupt
and
are
thus
affected
by
the

25

eruption
or
space
requirements
of
the
rest
of
the
dentition.

If
the
dentition
limits
the
amount
of

eruption
space
available
then
impaction
will
likely
occur.
(Bjork
1963,
Bishara
et
al.
1983)

Third
molars

are
the
most
common
impactions
followed
by
maxillary
canines
and
mandibular
premolars.
(Hupp
et
al.

2014)

Maxillary
canines
and
mandibular
premolars
are
the
last
teeth
to
erupt
in
the
anterior
of
the

dental
arches
therefore
they
are
affected
similarly
as
third
molars
by
the
amount
of
space
available
at

the
time
of
eruption.

Another
contributing
factor
to
impaction
of
third
molars
is
the
crown
length,
which
on
average
is

10.5mm.
(Ash
1993)

Richardson
found
that
larger
third
molars
were
more
often
impacted
and
smaller

third
molars
were
more
often
fully
erupted.

Skull
studies
have
also
indicated
that
third
molar
impaction
is
caused
by
inadequate
spacing.

Studies

have
shown
that
third
molar
impactions
were
relatively
infrequent
in
primitive
populations.
(Murphy

1964,
Alling
et
al.
1993)

Begg
believed
that
attrition
in
the
anterior
teeth
created
space
for
the
dentition

to
move
forward,
and
this
movement
created
space
for
the
erupting
thirds.
(Begg
1954)

As
man
has

evolved,
better
diets
and
oral
hygiene
have
led
to
a
decrease
in
attrition.
(Lombardi
1982)
According
to

Begg's
theory,
this
lack
of
anterior
space
limits
the
amount
of
forward
movement
by
the
dentition,
and

decreases
the
amount
of
eruption
space
available.
(Mehta
et
al.
1966)

Faubion
studied
the
mesial
drift
of
the
dentition
using
extraction
spaces.

He
found
that
the
rate
of
third

molar
impaction
was
reduced
by
premolar
extractions.
(Faubion
1968)

Richardson
conducted
a
study
of

the
effects
of
lower
second
molar
extraction
on
developing
third
molars.

She
evaluated
63
patients
that

had
lower
second
molars
extracted.

Third
molars
erupted
3-‐10
years
after
extractions;
99%
of
third

molars
uprighted
mesiodistally,
not
as
upright
as
second
molars
they
were
replacing.
(Richardson
1993)

Richardson’s
findings
were
supported
by
Cavanaugh
and
Artun;
they
stated
that
third
molar
impaction

was
rarely
observed
when
second
molars
were
extracted.
(Gooris
et
al.
1990,
Cavanaugh
1985)

26

Artun
evaluated
the
cephalograms
of
157
patients
from
a
post-‐retention
sample
at
the
University
of

Washington
reviewing
the
mesial
molar
movement
and
eruption
space
in
nonextraction
and
extraction

cases.

He
calculated
third
molar
angulation
by
measuring
the
angle
between
the
occlusal
plane
and
a

line
bisecting
the
occlusal
surface
of
the
third
molar.
Linear
mesial
molar
movement
was
measured
by

calculating
the
distance
between
the
distal
surface
of
the
lower
second
molar
and
a
point
on
the
ramus.

This
study
found
that
premolar
extraction
therapy
reduced
the
frequency
of
third
molar
impaction.
He

confirmed
that
impaction
of
mandibular
third
molars
occurred
twice
as
often
in
nonextraction
patients

compared
to
extraction
patients.
(Kim
et
al.
2003)
He
attributed
this
to
the
increased
eruption
space
due

to
mesial
molar
movement
during
space
closure.
Panoramic
and
cephalometric
radiographs
were

valuable
in
determining
impactions
radiographically
rather
than
clinically.
This
allowed
the
clinician
to

determine
impactions
based
on
apex
formation
and
cessation
of
eruption.

Artun’s
studies
had
several
limitations,
the
use
of
lateral
cephalograms
introduced
possible
inaccuracies

through
superimpositions.

It
is
difficult
to
accurately
trace
developing
third
molars
and
the
distal
aspect

of
second
molars
with
superimpositions.

The
occlusal
plane
as
a
reference
plane
posed
another

limitation
to
his
study
because
orthodontic
treatment
inherently
changes
the
occlusal
plane.

Also
in
his

study
first
and
second
premolar
extractions
were
not
separated
out
into
groups,
thereby
negating
any

affects
that
may
be
seen
differently
from
second
versus
first
premolar
extractions.

Premolar
extractions
result
in
varying
amounts
of
posterior
movement
as
discussed
previously.

Nonextraction
treatment
offers
minimal
space
creation,
and
has
little
expected
molar
movement.

Premolar
extraction
treatment
offers
greater
space
creation,
with
differing
molar
movement
based
on

extraction
location
and
anchorage
considerations.
Cumulatively,
these
factors
lead
to
greater
mesial

molar
movement
in
second
premolar
extractions.
Since
the
molar
is
moving
forward
a
greater
distance,

it
is
also
increasing
the
space
behind
it,
and
therefore
increases
the
eruption
space
available
for
the

third
molar.
Artun's
study
evaluates
the
angulation
affects
that
are
changed
because
of
this
distance.

27

The
mandibular
retromolar
space
can
increase
about
2
mm
from
age
15
to
adulthood,
due
to
growth

alone.
(Ledyard
1953)
Richardson
found
that
there
was
an
average
change
of
11.2
degrees
in
the

mandibular
third
molar
between
the
ages
of
10
and
15
years
of
age.
(Richardson
1970)
Based
on
this

information,
one
could
reason
that
the
best
prognosis
for
third
molar
eruption
is
to
maximize
the

amount
of
eruptive
space
and
allow
for
greater
uprighting
of
the
third
molar.
Nance
et
al
suggested
that

if
unerupted
third
molars
were
more
vertical,
eruption
to
the
occlusal
plane
was
more
likely
than
if
the

third
molars
were
inclined
more
mesially.
(Nance
et
al.
2006)
Extraction
of
second
premolars
would

cause
more
mesial
molar
movement
and
could
offer
a
better
prognosis
for
third
molar
eruption.

Turkoz
and
Ulusoy
conducted
a
retrospective
study
on
the
mandibular
third
molars
of
44
patients
at

Gazi
University.
They
evaluated
the
linear
and
angular
changes
of
the
third
molar
in
extraction
and

nonextraction
treatment.
The
lower
occlusal
plane
was
used
to
measure
the
amount
of
space
available

from
the
distal
of
the
lower
second
molar
to
the
anterior
ramus.
It
also
used
the
long
axis
of
the
second

molar
to
evaluate
the
angulation
of
the
erupting
third
molar.

They
found
that
in
the
nonextraction

group,
81.8%
of
third
molars
were
impacted,
while
only
63.6%
of
third
molars
were
impacted
in
the

extraction
group.
(Turkozet
al
2013)
They
also
found
that
retromolar
distance
increased
significantly
in

the
extraction
group
with
a
mean
distance
of
1.30
±
1.25mm.

Studies
have
shown
a
decreased
rate
of
impaction
in
orthodontic
extraction
cases,
(Dierkes
1975)
while

other
studies
have
shown
an
increased
rate
of
impaction
in
nonextraction
cases.
(Kaplan
1975,

Richardson
1975)

However
studies
done
by
Haavikko
and
Graber
have
shown
only
very
small

differences
in
the
rate
of
impaction
between
extraction
and
nonextraction
treatment.
(Haavikko
et
al.

1978,
Graber
et
al.
1981)

It
is
unclear
if
extraction
therapy
positively
effects
the
angular
position
of
third

molars.
Developing
third
molars
continually
change
their
angular
positions
and
pre-‐eruptive
rotational

movements.
(Silling
1973,
Richardson
1978,
Huggins
1962)

Using
longitudinal
studies
Richardson

showed
that
mandibular
third
molars
upright
during
early
adolescence
without
orthodontic
treatment.

28

(Richardson
et
al.
1984,
Richardson
1973)

Some
researchers
have
found
that
premolar
extractions

improve
the
angulation
of
the
developing
third
molar,
(Al
Kuwari
et
al.
2013,
Feng
et
al.
2013,
Saysel
et

al.
2005)
and
rationalize
that
the
increase
in
space
is
responsible
for
the
uprighting.
Staggers
led
a

similar
study
and
found
that
there
were
no
significant
differences
in
the
change
in
third

molar
angulation
in
either
group.
(Staggers
et
al.
1992)
In
addition,
Capelli's
study
found
that
it
is
unclear

whether
angulation
can
be
used
as
a
predictive
factor
for
impaction.
(Capelli
1991)

Race
or
Sex
Indicators
of
Impaction

Carter
and
Worthington
performed
systematic
review
and
meta-‐analysis
on
predictors
of
third
molar

impaction.

Jaw
size
has
been
proven
to
be
a
reliable
predictor
of
third
molar
impaction.

However,

women
with
typically
smaller
mandibles
show
conflicting
results
of
whether
the
impaction
rate
is

increased
over
men.

Of
the
studies
sampled
it
was
found
that
men
and
women
have
the
same

incidence
of
impaction.

They
also
compared
different
ethnic
groups
for
variations
in
impaction
rates.

Significant
differences
were
found
amongst
different
populations,
however
the
only
pair-‐wise

comparison
with
significant
results
was
from
a
Middle
Eastern
vs.
African
populations.

The
difficulty
in

comparison
amongst
ethnic
groups
could
be
due
to
the
variation
in
similar
ethnic
groups
from
different

geographical
areas.

Patients
from
urban
environments
are
more
likely
to
incur
impacted
third
molars

than
patients
from
rural
areas.

(Carter
and
Worthington
2015)

Recent
Studies

Nance
et
al.
studied
the
angulation
of
mandibular
third
molars
and
their
eruption
probability
based
on

panoramic
radiographs.

Initial
panoramic
radiographs
were
taken
from
patients
with
a
median
age
of

26
years
and
a
follow
up
pan
2
or
more
years
later.

They
found
that
of
patients
with
mesial/horizontal

impacations
greater
than
or
equal
to
25°
at
the
initial
records
only
11%
of
those
third
molars
erupted
at

the
follow
up
interval.

They
also
found
that
of
the
patients
with
mesial/horizontal
impactions
greater

than
or
equal
to
35°
at
the
initial
records
only
converted
to
3%
of
those
patients
with
fully
erupted
third

29

molars
at
the
follow
up
interval.

In
contrast
of
third
molars
that
were
vertical/distal
impacted
greater

than
or
equal
to
25°
one
third
of
these
third
molars
were
erupted
at
the
follow
up
interval.

(Nance
et
al.

2006)

Patients
with
third
molars
in
more
vertical
positions
will
have
a
greater
chance
of
eruption.

In
2009,
Jain
and
Valiathan
used
panoramic
radiographs
to
evaluate
third
molar
angulation
changes

referenced
to
the
palatal
plane.

The
two
sample
groups
were
patients
that
underwent
either
first

premolar
extractions
or
nonextraction
treatment.

Their
study
used
a
modified
version
of
the
midline

reference
plane
(MRP)
that
was
developed
by
Elsey
and
Rock.
(Elsey
et
al.
2000)
The
MRP
was

determined
by
bisecting
the
nasal
septum
and
the
anterior
nasal
spine.
A
line
was
then
drawn

perpendicular
and
defined
as
the
horizontal
reference
plane
(HRP).
A
line
parallel
to
the
third
molar

occlusal
plane
was
then
traced
and
initial
and
final
angulations
between
third
molars
and
HRP
were

calculated.

They
found
a
significant
difference
in
angulation
between
the
extraction
and
nonextraction

groups.
Extraction
treatment
resulted
in
a
significant
improvement
in
third
molar
angulation
on
both

right
and
left
sides.
(Jain
et
al.
2009)

Proffit
performed
a
study
evaluating
the
angulation
of
third
molars
on
panoramic
radiographs,
in
his

study
he
separated
the
patients
into
a
nonextraction,
first
premolar,
and
second
premolar
extraction

groups.

The
long
axes
of
the
second
and
third
molars
were
then
traced
on
initial
and
final
panoramic

radiographs.

Third
molar
angulations
were
then
calculated
using
the
long
axis
of
the
second
molar
as
a

reference
plane.

This
study
found
that
the
average
angulation
change
during
treatment
was
not

significantly
affected
by
group,
but
a
higher
proportion
of
third
molars
were
more
vertical
by
at
least
5°

in
the
second
premolar
extraction
group.

Proffit
also
stated
that
a
decrease
of
5°
or
more
in
the

angulation
of
third
molars
was
considered
clinically
favorable,
however
an
increase
of
5°
or
more

clinically
worsened
the
prognosis.
(Russell
et
al.
2013)

The
Proffit
study
was
one
of
few
studies
that
separated
and
evaluated
the
different
effects
of
extraction

treatment
on
first
and
second
premolars.

However
the
study
was
limited
by
using
the
long
axes
of
the

30

second
and
third
molars
as
reference
planes.
Second
molars
are
commonly
involved
in
orthodontic

treatment.
Using
the
long
axis
of
the
developing
third
molar
is
limiting
due
to
the
changing
morphology.

The
third
molar
develops
additional
root
structure,
possibly
changing
the
long
axis
of
this
tooth
between

initial
and
final
radiographs.

Tarazona
studied
the
angular
and
positional
changes
of
third
molars
in
extraction
and
nonextraction

orthodontic
treatment.

Tarazona
also
studied
the
variation
in
gonial
angle
and
the
degree
of
inclusion
in

initial
and
final
orthodontic
records.

They
studied
the
long
axis
of
third
molars
similarly
to
other
studies

using
the
mandibular
occlusal
plane
using
panoramic
radiographs.

The
difference
in
this
study

compared
to
others
was
the
degree
of
inclusion
using
panoramic
radiographs.

They
measured
the

proportion
of
manibular
third
molar
emergence
from
a
vertical
line
drawn
adjacent
to
the
ramus.

The

study
included
88
patients
divided
into
nonextraction,
first
premolar,
and
second
premolar
groups.

Third
molar
angulation
improved
regardless
of
treatment
method.

They
found
greater
disinclusion
of

third
molars
in
cases
with
extractions,
citing
the
mesialization
of
the
dentition
as
the
cause.

Tarazona

concluded
that
other
factors
than
what
they
studied
are
involved
in
third
molar
eruption
and
could
not

confidently
create
an
accurate
method
of
third
molar
prediction.
(Tarazona
et
al.
2010)

Sameshima
and
Denny
studied
the
long
axis
angulation
change
in
third
molars
over
the
course
of

orthodontic
treatment
in
non-‐extraction,
first
premolar
extraction,
and
second
premolar
extraction

groups.

They
found
that
the
average
change
in
third
molar
inclination
did
not
differ
significantly
among

the
three
study
groups.

Although
not
significantly
different,
they
stated
that
the
extraction
groups
had

more
instances
of
third
molar
uprighting
than
the
nonextraction
group.
Out
of
a
total
of
60
third
molars

in
each
group,
positive
uprighting
was
seen
in
23
in
the
second
premolar
group,
25
in
the
first
premolar

group,
and
22
in
the
nonextraction
group.
The
first
and
second
premolar
extraction
groups
also

experienced
a
higher
proportion
of
third
molars
that
underwent
a
5°
more
vertical
change
than
the

31

nonextraction
group.

Extraction
treatment
was
not
a
statistically
significant
explanatory
factor
for
a

clinically
favorable
change
in
angulation.
(Sameshima
and
Denny
2014)

Indications
for
Third
Molar
Removal

Current
Care
Guideline
suggests
that
prophylactic
removal
of
third
molars
at
a
young
age
is
indicated

when
mandibular
teeth
are
partially
impacted
in
the
horizontal
position,
partially
erupted
in
vertical

position
and
incomplete
roots
growing
close
to
mandibular
canal.
(Venta
2012)

Coulthard
et
al.
listed
common
indications
for
third
molar
removal
as,
infection
from
partially
erupted

tooth
impacted
against
hard
or
soft
tissue.

Other
indications
included
pulpal
and
periapical
pathology,

fracture
of
tooth,
cyst,
and
unrestorable
caries.

(Coulthard
et
al.
2014)

Steed
also
addressed
the

ongoing
concern
of
when
to
remove
third
molars.

Currently
most
dentists
remove
third
molars
when

the
presence
of
symptoms
or
pathology
associated
with
third
molars
is
discovered.

The
study
showed

that
some
third
molars
which
previously
had
no
indication
for
removal,
then
showed
symptoms
or

pathology
after
a
few
years.

He
advocated
the
regular
follow-‐up
and
assessment
of
retained
third

molars
and
also
showed
that
prophylactic
removal
of
third
molars
is
still
a
valid
treatment
today.
(Steed

2014)

Third
Molar
Anatomical
Anomalies

Third
molars
vary
in
size
and
root
shape
and
number.

Using
CBCT
images
Park
et
al
showed
that
in
a

Korean
population
57%
of
patients
had
two
rooted
third
molars
and
38%
had
single
rooted
third
molars.

They
also
showed
that
root
anatomy
was
similar
on
both
sides
of
the
mandible
in
81%
of
the
patients.

(Park
et
al.
2013)

Morbidity
of
Third
Molar
Extractions

Kaminishi
found
that
between
1997
and
2002,
there
was
an
increase
in
patients
over
the
age
of
40

requiring
third
molar
removal.
Out
of
all
age
groups
requiring
third
molar
extractions,
the
percentage
of

over
40
year
olds
requiring
extraction
went
from
10.5%
in
1997
to
17.3%
in
2002.
(Kaminishi
et
al.
2006)

32

This
increase
in
extractions
of
older
patients
poses
a
problem
for
the
dental
community
due
to
the
fact

that
with
the
increase
in
age
also
comes
an
increase
in
complications
from
extractions.
(Punwutikorn
et

al.
1999)

Bruce
evaluated
operative
and
postoperative
morbidity
associated
with
the
removal
of

impacted
mandibular
third
molars
in
patients
of
various
ages.
He
found
a
significant
increase
in
surgical

morbidity
as
patients
became
older.
He
found
all
risks
associated
with
third
molar
removal
to
increase
in

patients
over
the
age
of
35.
(Bruce
et
al.
1980)
Similar
studies
have
shown
a
generalized
increase
in
risk

correlated
with
increasing
age.
(Mercier
et
al.
1992,
Bui
et
al.
2003,
Valmaseda-‐Castellon
et
al.
2001)

Periodontal
defect
risk
following
third
molar
extraction
is
also
increased
with
age,
occurring
twice
as

often
in
patients
over
26
years
old
when
compared
to
patients
less
than
25
years
of
age.
(Kugelberg

1990)

Risks
for
second
molars
were
also
increased
in
older
groups.
Comparing
groups
of
patients
that

were
older
and
younger
than
25,
periodontal
defects
were
2-‐3
times
more
common
after
third
molar

extraction
in
the
older
group,
and
the
persistence
of
the
defects
were
age
related.
(Kugelberg
et
al.
1991,

Kugelberg
et
al.
1985)

A
study
by
Krimmel
showed
the
major
risk
factor
for
fracture
to
be
advanced
age

and
a
full
dentition,
rather
than
degree
of
tooth
impaction.
(Krimmel
et
al.
2000)

Possible
nerve
damage
is
an
additional
treatment
complexity
that
needs
to
be
considered.
Studies
have

shown
an
existence
of
persistent
nerve
involvement
after
third
molar
extraction.
(Valmaseda-‐Castellon

et
al.
2001,
Schultze-‐Mosgau
et
al.
1993,
Gulicher
et
al.
2001,
Queral-‐Godoy
et
al.
2005)
Although
some

of
these
cases
spontaneously
recover,
some
cases
need
additional
surgeries
for
repair,
and
other
cases

completely
fail
to
recover.

Identifying
a
future
impaction
would
allow
the
clinician
to
take
a
prophylactic
approach
to
the
removal

of
third
molars.

A
germectomy
procedure
removes
the
developing
tooth
before
the
tooth
has
formed.

Studies
of
germectomy
procedures
in
younger
patients
have
shown
no
cases
of
periodontal
defects,

nerve
damage,
or
second
molar
damage.
(Ash
et
al.
1962,
Chiapasco
et
al.
1995,
Chossegros
et
al.
2002)

33

From
these
studies
it
appears
that
a
germectomy
procedure
may
be
beneficial
in
lowering
the
incidence

of
third
molar
morbidity.

Financial
Impact
of
Third
Molar
and
Premolar
Extractions

There
is
a
wide
range
of
costs
that
can
be
incurred
by
our
patients
when
going
for
any
kind
of
extraction.

The
cost
is
dependent
on
(1)
the
type
of
extraction
(surgical
vs
nonsurgical),
(2)
type
of
anesthesia,
and

(3)
who
performs
the
extraction
(specialist
vs
general
dentist).

For
the
sake
of
this
paper
we
will
use
the

2015
fee
schedule
of
Delta
Dental
to
provide
insight
into
these
costs.

Premolar
extractions
are
usually

done
on
teeth
that
are
fully
erupted
and
would
be
coded
as
D7140
extraction
of
erupted
tooth,
the
cost

would
be
$73.

The
low
cost
is
due
to
the
ease
of
the
extraction
and
general
dentists
commonly
do
it.

Third
molar
removal
costs
vary
greatly
and
are
significantly
more
money.

The
surgical
removal
of
an

erupted
tooth
(D7210)
is
$149;
impacted
tooth
soft
tissue
only
(D7220)
is
$221,
impacted
tooth
partial

bony
(D7230)
is
$261,
and
impacted
tooth
full
bony
(D7240)
is
$323
(if
there
are
unusual
complications

then
its
$337).

The
cost
of
these
extractions
with
local
anesthesia
is
only
$17
more,
however
many

patients
elect
to
have
some
other
form
of
sedation
which
can
cost
another
$175
for
the
first
30
minutes

and
then
another
$70
for
every
15
minutes
after.

34

Chapter
3:
Our
Current
Study

General
Overview

The
purpose
of
the
current
study
was
to
calculate
the
angulation
change
of
3
rd

molars
in
extraction
of
1
st

premolars,
2
nd

premolars,
and
non-‐extraction
orthodontic
treatment.

Several
studies
have
measured

the
vertical
axis
of
third
molars,
our
study
measure
the
horizontal
axis
of
third
molars
in
relation
to
a

horizontal
plane.

Measuring
the
horizontal
axis
of
third
molars
addresses
the
limitations
of
determining

the
vertical
axis
of
developing
third
molars.

Also
using
a
set
horizontal
plane
eliminates
any
variation

that
may
occur
from
orthodontic
treatment.

The
second
objective
of
this
study
was
to
calculate
the
proportional
change
in
retromolar
length
in

extraction
of
1
st

premolars,
2
nd

premolars,
and
non-‐extraction
orthodontic
treatment.

Using
the

proportion
of
the
measurement
of
third
molar
width
and
retromolar
length
allowed
this
study
to

compare
changes
in
initial
and
final
panoramic
radiographs.

Increased
retromolar
length
improves
the

likelihood
that
third
molars
will
erupt.

By
using
the
proportional
change
allowed
this
study
to
use

panoramic
raidographs,
which
most
clinicians
will
have
at
the
start
and
end
of
orthodontic
treatment.

This
is
especially
useful
because
some
clinicians
do
not
take
final
cephalograms,
but
they
do
take
final

panoramic
radiographs.

Treatment
Mechanics

Our
study
incorporates
segmental
mechanics
for
second
premolar
extractions.

While
segmental

mechanics
does
not
offer
an
increase
in
anchorage
compared
to
traditional
mechanics,
it
does
offer

other
advantages.
Segmental
mechanics
allows
for
immediate
space
closure
in
a
fresh
extraction
site.

The
clinician
can
immediately
close
space,
rather
than
waiting
for
aligning
and
leveling.
These
steps
take

additional
time
and
allow
bone
apposition,
which
causes
increased
resistance
during
space
closure.
In

addition,
aligning
and
leveling
a
crowded
anterior
dentition
results
in
distalization
of
these
teeth
into
the

35

extraction
space
to
relieve
crowding.
This
partially
closes
the
extraction
space
before
any
molar
traction

is
applied
to
close
the
space.
A
decreased
extraction
space
means
that
there
is
less
distance
for
the

molar
to
mesialize.
By
starting
space
closure
before
leveling
and
aligning,
a
greater
space
exists
and

possibly
greater
mesial
molar
movement.

Closing
space
immediately
also
allows
for
the
maximum
amount
of
time
for
eruption
space
to
influence

third
molar
angulation.
The
earlier
this
space
is
created,
the
lower
the
developing
third
molar
tooth
bud

is
located,
and
the
longer
amount
of
time
that
this
space
will
influence
the
eruption
of
the
third
molar.

Segmental
mechanics
offers
several
advantages
for
the
developing
third
molar
over
traditional

mechanics.
36

Chapter
4:
Hypotheses

Research
question

Will
the
angulation
and
retromolar
length
be
significantly
changed
from
extraction
orthodontic

treatment?

Testable
null
hypotheses

There
is
no
significant
difference
in
the
angulation
and
retromolar
length
in
non-‐extraction,
1
st

premolars
or
2
nd

premolar
extraction
treatment.

37

Chapter
5:
Methods

This
was
a
retrospective
study
analyzing
the
before
and
after
orthodontic
treatment
panoramic

radiographs
of
non-‐extraction,
first
premolar
extraction,
and
second
premolar
extraction
patients.

Using
the
patient
archive
from
the
University
of
Southern
California
orthodontics
department
30

patients
were
selected
that
met
all
inclusion
criteria
for
each
of
the
three
treatment
groups.

Patients

selected
were
between
the
ages
of
9
to
16
years
old
at
the
time
of
initial
records;
there
was
no

restriction
on
ethnicity
or
gender.

Each
patient
included
had
complete
initial
and
final
orthodontic

records,
and
2
lower
third
molars
at
the
start
and
end
of
treatment.

Exclusion
criteria
included:

craniofacial
anomalies,
surgical
cases,
missing
teeth,
and
extraction
of
third
molars
prior
to
final
records.

Patients
did
not
differ
significantly
at
the
start
of
treatment.
The
subjects
were
an
average
of
12.4
years

at
the
start
of
treatment,
and
similarly
divided
by
gender.

Study
approve
by
USC
IRB
UP-‐14-‐00596.

Using
Dolphin
Imaging
software
(Dolphin
Imaging
and
Management
Solutions,
Chatsworth,
Calif),
a

custom
analysis
was
created
to
evaluate
the
horizontal
axes
of
2
nd

and
3
rd

molars
as
well
as
the

proportional
distance
of
the
retromolar
length.

A
horizontal
reference
plane
was
drawn
by
connecting

points
through
the
condylar
notches.

A
vertical
reference
plane
was
drawn
perpendicular
to
this
line

and
touching
the
mesial
border
of
the
left
ramus.

The
horizontal
axes
of
2
nd

and
3
rd

molars
were
drawn

using
the
occlusal
table
as
a
reference
plane;
their
angulation
was
measured
against
the
horizontal

reference
plane.

The
proportional
distance
of
the
retromolar
length
was
calculated
by
measuring
the

distance
from
the
distal
of
the
2
nd

molar
to
the
vertical
reference
plane
and
the
distance
from
the
width

of
the
3
rd

molar.

The
distance
from
the
2
nd

molar
to
the
vertical
reference
line
was
divided
by
the
width

of
the
3
rd

molar
to
calculate
the
proportional
distance
of
the
retromolar
length.

All
measurements
were

done
on
initial
and
final
panoramic
radiographs.

Method
error
was
tested
two
weeks
after
initial

38

measurements
were
made
with
intraclass
correlation
coefficients;
there
was
no
significant
difference.

All
initial
variables
were
tested
using
one-‐way
ANOVA
test
(see
table
1).

Significance
was
set
at
α
=
0.05.

Horizontal
angulation
changes
that
decreased
in
number
or
came
closer
to
0
degrees
(parallel
to
the

horizontal
axis)
showed
improvement
over
the
treatment
period.

A
proportion
that
decreased
showed

an
increase
in
retromolar
length.

Proportions
that
were
less
than
equal
to
1
would
theoretical
have

enough
retromolar
length
to
allow
the
eruption
of
the
3
rd

molars.

Retromolar
width
and
third
molar

proportional
changes
among
the
three
study
groups
were
tested
using
chi-‐square
test.

Third
molar

angulation
changes
among
the
three
study
groups
were
tested
using
chi-‐square
test.

Third
molar

angulation
changes
greater
than
5°
or
less
than
-‐5°
among
the
three
study
groups
were
tested
using
chi-‐
square
test.

Fig.
4:
Horizontal
reference
plane
and
horizontal
axes
of
2
nd

and
3
rd

molar
traced
and
their
angulation
as

compared
to
horizontal
axis.

39

Fig.
5:
Horizontal
and
vertical
reference
planes
and
the
measurement
of
the
width
of
the
3
rd

molar.

Fig.
6:
Horizontal
and
vertical
reference
planes
and
the
measurement
of
retromolar
length
from
distal
of

2
nd

molar
to
vertical
reference
plane.

40

41

Chapter
6:
Results

The
average
change
in
third
molar
angulation
did
not
differ
significantly
among
the
three
study
groups.

The
average
third
molar
angulation
change
was
6.3±13.1°
for
the
2
nd

premolar
extraction
group
and
the

first
premolar
extraction
group
had
an
average
change
of
10.0±16.7°
(see
table
3).

Both
of
these
results

are
above
the
5°
change
that
Profitt
stated
would
be
a
clinically
significant
angulation
change
(see
table

2).

The
non-‐extraction
group
had
an
average
angulation
change
of
3.1±11.6°,
which
has
no
clinical

significance
(see
table
3).

The
extraction
groups
showed
a
greater
number
of
third
molars
that
had
an

improvement
or
uprighting
over
the
course
of
treatment,
however
this
result
is
not
clinically
nor

statistically
significant
(see
table
4).

The
ideal
ratio
of
third
molar
width
to
retromolar
length
would
be
less
than
equal
to
1.

Using
these

criteria
we
separated
out
the
patients
who
had
a
ratio
of
less
than
equal
to
1
from
those
with
a
ratio
of

greater
than
1.

We
did
this
for
each
of
the
treatment
groups
(see
table
6).

We
found
that
there
was
a

highly
statistically
significant
difference
between
non-‐extraction
and
both
of
the
extraction
groups
was

seen
in
the
ratio
of
retromolar
length
to
third
molar
width
(see
table
5).

The
p-‐value
was
0.01,
highly

significant
difference,
using
individual
chi
square
tests
showed
non-‐extraction
treatment
was

significantly
less.

The
2
nd

premolar
extraction
group
(n=28)
had
12
patients
and
the
1
st

premolar

extraction
group
(n=28)
had
13
patients
with
a
third
molar
width
and
retromolar
length
ratio
less
than

or
equal
to
1.

Whereas
the
non-‐extraction
group
(n=27)
only
had
1
patient
with
a
third
molar
to

retromolar
length
ratio
less
than
or
equal
to
1.

42

Figure
7:
3
rd

Molar
Angulation
Change
non-‐extraction,
see
table
2.

Figure
8:
3
rd

molar
angulation
change
1
st

premolar
extraction,
see
table
2.

39%

18%

43%

3rd
Molar
Angula-on
Change

(Non-‐Ext)

Yes
No

Same

59%

17%

24%

3rd
Molar
Angula-on
Change

(1st
Premolar
Ext)

Yes
No

Same

43

Figure
9:
3
rd

molar
angulation
change
2
nd

premolar
extraction,
see
table
2.

52%

14%

34%

3rd
Molar
Angula-on
Change

(2nd
Premolar
Ext)

Yes
No

Same

44

45

46

47

48

49

50

51

52

53

54

55

56

57

Chapter
7:
Discussion

Orthodontists
are
keenly
placed
to
make
decisions
on
third
molar
extractions
due
to
the
timing
of

treatment
in
adolescents
and
the
use
of
panoramic
radiographs.

For
several
decades
orthodontists
have

tried
varying
methods
to
predict
third
molar
eruption
prior
to
orthodontic
treatment.

(Ricketts
et
al.

1976,
Forsberg
et
al.
1989)
The
ability
to
predict
third
molar
eruption
would
enable
orthodontists
to

include
third
molars
in
their
diagnosis
and
treatment
planning.

Previous
methods
of
prediction
have

proven
to
be
inaccurate
and
time
consuming
for
clinical
orthodontists.

(Olive
et
al.
1981)

Sameshima

and
Denny
followed
the
evidence
of
Nance,
which
showed
that
third
molars
that
are
more
upright
have

an
increased
likelihood
of
eruption.

(Nance
et
al.
2006)

Their
study
of
the
vertical
angulation
change
of

third
molars
over
the
course
of
orthodontic
treatment
showed
that
it
was
difficult
to
predict
whether

third
molars
would
upright
in
extraction
orthodontic
treatment.

(Sameshima
and
Denny
2014)

In
our

study
we
used
panoramic
radiographs
for
the
ease
of
use
for
clinical
orthodontists;
we
measured
third

molar
angulations
and
the
proportion
of
third
molar
width
to
retromolar
length
before
and
after
in
non-‐
extraction
and
1
st

premolar
and
2
nd

premolar
extraction
groups.

Previous
studies
examined
the
long
axis
of
3
rd

molars
in
comparison
to
the
long
axis
of
2
nd

molars;
in
our

study
we
examined
the
horizontal
axis
of
third
molars
in
comparison
to
a
horizontal
reference
plane.

(Russell
et
al.
2013,
Sameshima
and
Denny
2014)

We
hypothesized
that
there
would
be
greater

angulation
change
in
the
extraction
groups
when
compared
to
the
non-‐extraction
group.

Any
change

greater
than
5°
was
considered
a
clinical
improvement,
whereas
any
negative
change
greater
than
5°

was
considered
to
be
a
clinical
worsening
of
position.
(Russell
et
al.
2013)
The
average
angulation

change
over
treatment
did
not
differ
significantly
among
the
three
groups;
these
results
confirmed
the

results
from
Sameshima
and
Denny’s
study
using
the
vertical
axis
of
third
molars.
(Sameshima
and

Denny
2014,
Russell
et
al.
2013)

Improvement
in
third
molar
eruption
angulation
or
uprighting
cannot

be
predicted
from
the
type
of
orthodontic
treatment.

(Sameshima
and
Denny
2014,
Tarazona
et
al.

58

2010)

For
the
examples
where
third
molar
eruption
improved
in
extraction
treatment
the
same
number

of
improvements
in
3
rd

molar
angulation
was
seen
in
the
non-‐extraction
group.

The
anterior
movement

of
2
nd

molars
is
not
correlated
to
angulation
improvement
in
3
rd

molar
angulation.

Arch
length
for
the
eruption
of
mandibular
third
molars
is
gained
by
the
resorption
of
the
anterior

portion
of
the
ramus.
(Silling
1973)
Third
molars
are
often
impacted
due
to
a
lack
of
space
in
the

mandible;
we
hypothesized
that
extraction
orthodontic
treatment
would
create
more
space
distal
to
the

2
nd

molar
for
third
molar
eruption.
(Bjork
et
al.
1956)

Using
the
proportion
of
third
molar
width
to

retromolar
length
we
found
that
there
was
a
highly
significant
difference
between
the
extraction
and

non-‐extraction
treatment
groups.

Adequate
arch
length
for
third
molar
eruption
was
much
more
likely

to
be
seen
in
extraction
treatment.

Tarazona
et
al.
measured
the
degree
of
inclusion
of
mandibular

third
molars
using
panoramic
radiographs.

They
found
that
there
was
a
tendency
for
greater
emergence

in
the
extraction
orthodontic
cases;
however
their
results
were
not
statistically
significant.
(Tarazona
et

al.
2010)
Cases
of
3
rd

molar
impaction
are
observed
even
when
the
space
necessary
for
third
molar

eruption
is
present.

Third
molar
eruption
is
a
multifactorial
process,
which
makes
it
impossible
to

predict
eruption
from
one
single
factor.

(Tarazona
et
al.
2010)

One
of
the
purposes
of
this
study
was
to
use
a
method
of
analysis
that
would
be
easy
for
clinicians
to

use,
so
we
used
panoramic
radiographs
for
our
analysis.

There
are
obvious
distortion
problems
and

magnification
problems
found
using
these
radiographs.

Our
analysis
tried
to
overcome
these
errors
by

creating
a
mathematical
ratio
of
third
molar
width
to
retromolar
length,
however
this
could
be
measure

more
accurately
using
lateral
cephalograms
or
CBCT.

The
anterior
portion
of
the
ramus
is
variable
in

adolescent
patients;
we
could
have
used
a
more
reliable
reference
plane
if
we
wanted
to
calculate
the

exact
amount
of
space
gained
from
extraction
treatment.

However,
in
our
study
we
were
only

interested
in
the
actual
retromolar
space
to
third
molar
width
ratio
to
determine
if
there
would
be

enough
space
for
eruption.

Future
studies
using
lateral
cephalograms
or
CBCT
could
differentiate
the

59

amount
of
space
gained
from
extraction
orthodontic
treatment
and
mandibular
growth.

The
use
of

panoramic
radiographs
or
lateral
cephalograms
is
only
a
2D
study
of
a
3D
process
in
the
angulation
and

eruption
pathway
of
3
rd

molars.

Using
CBCT
3
rd

molar
angulations
and
eruptive
pathways
could
be
more

fully
analyzed
in
the
hopes
of
developing
a
reliable
method
for
3
rd

molar
eruption
prediction.

60

Chapter
8:
Conclusion

From
this
study
we
can
conclude
that
it
is
difficult
to
predict
third
molar
eruption
because
of
the

multifactorial
nature
of
eruption.

Angulation
changes
in
third
molars
following
1
st

and
2
nd

premolar
and

non-‐extraction
orthodontic
treatment
do
not
differ
significantly.

However
the
space
necessary
for
third

molar
eruption
is
more
likely
to
be
gained
through
extraction
of
1
st

or
2
nd

premolars.

Further
studies

using
CBCT
may
help
to
solve
the
shortcomings
of
the
current
study.

Also
further
studies
comparing
the

amount
of
space
gained
in
patients
who
have
high
mandibular
plane
angles
versus
patients
with
normal

mandibular
plane
angles.

61

Bibliography

1.
Angle
E.
Malocclusion
of
the
Teeth.
Seventh
Edition.
1907;
3:66.

2.
Pollock
H.
The
Extraction
Debate
of
1911
by
Case,
Dewey,
and
Cryer.

American
Journal
of

Orthodontics.
1964;
50:
656-‐658.

3.
Tweed
C.
Indication
for
Extraction
of
Teeth
in
Orthodontic
Procedure.
American
Journal
of

Orthodontics
and
Oral
Surgery.
1944;
30:405-‐28.

4.
Lusterman
E.
Treatment
of
a
Class
II,
Division
2
malocclusion
involving
mesiodistal
reduction
of

mandibular
anterior
teeth.
Am.
J.
Orthod.
1954;
40:44–50.

5.
Sheridan
J.
Air-‐rotor
stripping,
J.
Clin.
Orthod.
1985;
19:43-‐59.

6.
Baumrind
S,
Korn
E,
Boyd
R,
Maxwell
R.
The
decision
to
extract:
part
II.

Analysis
of
clinicians’
stated

reasons
for
extraction.
American
Journal
of

Orthodontics
and
Dentofacial
Orthopedics.
1996;
109:393-‐
402.

7.
Paquette
D,
Beattie
J,
Johnston
L.
A
long-‐term
comparison
of
nonextraction
and
premolar
extraction

edgewise
therapy
in
“borderline”
Class
II
patients.
Am
J
Orthod
Dentofacial
Orthop.
1992;
102:1-‐14.

8.
Luppanapornlarp
S,
Johnston
L.
The
effects
of
premolar-‐extraction:
a
long-‐term
comparison
of

outcomes
in
“clear-‐cut”
extraction
and
nonextraction
Class
II
patients.
Angle
Orthod.
1993;
63:257-‐72.

9.
Beattie
J,
Paquette
D,
Johnston
L.
The
functional
impact
of
extraction
and
nonextraction
treatments:
a

long-‐term
comparison
in
patients
with
“borderline”,
equally
susceptible
Class
II
malocclusions.
Am
J

Orthod
Dentofacial
Orthop.
1994;
105:444-‐9.

10.
Proffit
W,
Fields
H.
Orthodontic
Treatment
Planning:
Limitations,
Controversies,
and
Special

Problems.
In:
Proffit
WR,
Fields
HW,
editors.
Contemporary
Orthodontics.
Fifth
ed.
St.
Louis:
Mosby
Year

Book;
2012.
p.
279.

11.
Black
G.
Descriptive
Anatomy
of
the
Human
Teeth,
2nd
ed.
Philadelphia:
Wilmington
Dental

Manufacturing
Company,
1902.

12.
Williams
R,
Hosila
F.
The
effect
of
different
extraction
sites
upon
incisor
retraction.
Am
J
Orthod.

1976;
69:388-‐410.

13.
Jepsen
A.
Root
surface
measurement
and
a
method
for
x-‐ray
determination
of
root
surface
area.

Acta
Odontol
Scand.
1963;
21:35-‐46.

14.
Steyn
C,
Du
Preez
R,
Harris
A.
Differential
premolar
extractions.
Am
J
Orthod
Dentofacial
Orthop.

1997;
112:480-‐6.

15.
Creekmore
T.
Where
teeth
should
be
positioned
in
the
face
and
jaws
and
how
to
get
them
there.
J

Clin
Orthod.
1997;
31:586-‐608.

62

16.
Bishara
S,
Cummins
D,
Jakobsen
J,
Zaher
A.
Dentofacial
and
soft
tissue
changes
in
Class
II,
division
1

cases
treated
with
and
without
extractions.
Am
J
Orthod
Dentofacial
Orthop.
1995;
107:28-‐37.

17.
Talass
M,
Talass
L,
Baker
R.
Soft-‐tissue
profile
changes
resulting
from
retraction
of
maxillary

incisors.
Am
J
Orthod
Dentofacial
Orthop.
1987;
91:385-‐94.

18.
Boley
J,
Pontier
J,
Smith
S,
Fulbright
M.
Facial
changes
in
extraction
and
nonextraction

patients.
Angle
Orthod.
1998;
68:539-‐46.

19.
Ismail
S,
Moss
J,
Hennessy
R.
Three-‐dimensional
assessment
of
the
effects
of
extraction
and

nonextraction
orthodontic
treatment
on
the
face.
Am
J
Orthod
Dentofacial
Orthop.
2002;
121:244-‐56.

20.
Kim
E,
Gianelly
A.
Extraction
vs
nonextraction:
arch
widths
and
smile
esthetics.
Angle
Orthod.
2003;

73:354-‐8.

21.Stephens
C,
Boley
J,
Behrents
R,
Alexander
R,
Buschang
P.
Long-‐term
profile
changes
in
extraction

and
nonextraction
patients.
Am
J
Orthod
Dentofacial
Orthop.2005;
128:450-‐7.

22.
Germec
D,
Taner
T.
Effects
of
extraction
and
nonextraction
therapy
with
air-‐rotor
stripping
on
facial

esthetics
in
postadolescent
borderline
patients.
Am
J
Orthod
Dentofacial
Orthop.
2008;
133:539-‐49.

23.
Konstantonis
D.
The
impact
of
extraction
vs
nonextraction
treatment
on
soft
tissue
changes
in
Class
I

borderline
malocclusions.
Angle
Orthod.
2012;
82:209-‐17.

24.
Dewel
B.
Second
premolar
extraction
in
orthodontics:
Principles,
procedures,
and
case
analysis,
Am
J.

Orthod.
1955;
41:107-‐120.

25.
De
Castro
N.
Second
premolar
extraction
in
clinical
practice.
Am
J
Orthod.
1974;
65:115-‐37.

26.
Brandt
S,
Safirstein
G.
Different
extractions
for
different
malocclusions.
Am
J
Orthod.
1975;
68:15-‐41.

27.
Schoppe
R.
An
analysis
of
second
premolar
extraction
procedures.
Angle
Orthodontist.
1964;
34:292-‐
302.

28.
American
Journal
of
Public
Health,
V.97(9),
Sept.
2007.

29.
Lysell
L,
Rohlin
M.
A
study
of
indications
used
for
removal
of
the
mandibular
third
molar.

International
Journal
of
Oral
and
Maxillofacial
Surgery.
1988;
17(3):161-‐164.

30.
Rantanen
A.
The
age
of
eruption
of
the
third
molar
teeth.
A
clinical
study
based
on
Finnish
university

students.
Acta
Odontol
Scand.
1967;
25:1–86.

31.
Odusanya
S,
Abayomi
I.
Third
molar
eruption
among
rural
Nigerians.
Oral
Surg
Oral
Med
Oral
Pathol.

1991;
71(2):151-‐4.

32.
Kruger
E,
Thomson
W,
Konthasinghe
P.
Third
molar
outcomes
from
age
18
to
26:
findings
from
a

population-‐based
New
Zealand
longitudinal
study.
Oral
Surg
Oral
Med
Oral
Pathol
Oral
Radiol

Endod.
2001;
92(2):150-‐5.

63

33.
Brown
L,
Berkman
S,
Cohen
D,
Kaplan
A,
Rosenberg
M.
A
radiological
study
of
the
frequency
and

distribution
of
impacted
teeth.
J
Dent
Assoc
S
Afr.
1982;
37(9):627-‐30.

34.
Hattab
F,
Alhaija
E.
Radiographic
evaluation
of
mandibular
third
molar
eruption
space.
Oral
Surg
Oral

Med
Oral
Pathol
Oral
Radiol
Endod.
1999;
88(3):285-‐91.

35.
Sandhu
S,
Kapila
B.
Incidence
of
impacted
third
molars.
J.
Indian
Dent.
Assoc.
1982;
541:441-‐444.

36.
Narda
R,
Chawla
T.
Status
of
third
molar
teeth.
J.
All
India
Dental
Assoc.
1959;
31:19-‐29.

37.
Yuasa
H,
Sugiura
M.
Clinical
postoperative
findings
after
removal
of
impacted
mandibular
third

molars:
prediction
of
postoperative
facial
swelling
and
pain
based
on
preoperative
variables.
Br
J
Oral

Maxillofac
Surg.
2004;
42(3):209-‐14.

38.
Hellman,
M.
Our
third
molar
teeth;
their
eruption
presence
and
absence.
Dental
Cosmos.
1961;

78:750-‐762.

39.
Taranger
J,
Hagg
U.
The
timing
and
duration
of
adolescent
growth.
Acta
Odontol
Stand.
1980;
38:57-‐
67.

40.
Engström
C,
Engström
H,
Sagne
S.
Lower
third
molar
development
in
relation
to
skeletal
maturity

and
chronological
age.
Angle
Orthod.
1983;
53(2):97-‐106.

41.
Forsberg
C.
Growth
changes
in
the
adult
face.
A
longitudinal
roentgen
cephalometric
investigation

on
men
and
women
in
early
adulthood.
Karolinska
Institutet.
1976.

42.
Haidar
Z,
Shalhoub
S.
The
incidence
of
impacted
wisdom
teeth
in
a
Saudi
community.
Int
J
Oral

Maxillofac
Surg.
1986;
15:569-‐571.

43.
Ash
M.
Wheeler's
Dental
Anatomy,
Physiology,
and
Occlusion.
7th
ed.
Philadelphia:
W.B.
Saunders

Co.
1993:24-‐45.

44.
Proffit
W,
Fields
H.
Early
stages
of
development.
In:
Proffit
W,
Fields
H,
editors.
Contemporary

orthodontics.
2nd
ed.
St.
Louis:
Mosby
Year
Book.
1993:56-‐86.

45.
Hupp
J,
Ellis
E,
Tucker
M.
Prevention
and
Management
of
Surgical
Complications.
In:
Contemporary

Oral
and
Maxillofacial
Surgery,
6th
Ed.
St
Louis:
Mosby
Year
Book.
2014:174.

46.
Alling
C,
Helfrick
J,
Alling
R.
Impacted
Teeth.
Philadelphia.
W.B.
Saunders.
1993:99.

47.
Scherstén
E,
Lysell
L,
Rohlin
M.
Prevalence
of
impacted
third
molars
in
dental
students.
Swed
Dent

J.
1989;
13(1-‐2):7-‐13.

48.
Dachi
S,
Howell
F.
A
survey
of
3874
routine
full-‐mouth
radiographs
II.
A
study
of
impacted
teeth.
Oral

Surg
Oral
Med
Oral
Pathol.
1961;
14:1165–1169.

64

49.
Grover
P,
Lorton
L.
The
incidence
of
unerupted
permanent
teeth
and
related
clinical
cases.
Oral
Surg

Oral
Med
Oral
Pathol.
1985;
59:420–425.

50.
Hellman
M.
Some
aspects
of
Wisdom
Teeth
and
their
impactions.
Arch.
Clin.
Oral
Path.
1938;
2:125.

51.
Björk
A,
Jensen
E,
Palling
M.
Mandibular
growth
and
third
molar
impaction.
Acta.
Odont.
Scand.
1956;

14:231-‐272.

52.
Ricketts
R.
The
principle
of
arcial
growth
of
the
mandible.
Angle
Orthodont.
1972;
42:368-‐386.

53.
Richardson
M.
The
etiology
and
prediction
of
mandibular
third
molar
impaction.
Angle
Ortho.
1977;

47(3):165-‐72.

54.
Hugoson
A,
Kugelberg
C.
The
prevalence
of
third
molars
in
a
Swedish
population.
An
epidemiological

study.
Community
Dent
Health.
1988;
5(2):121-‐38.

55.
Peterson
L.
Rationale
for
removing
impacted
teeth:
when
to
extract
or
not
to
extract.
J
Am
Dent

Assoc.
1992;
123:198–204.

56.
Silling
G.
Development
and
eruption
of
the
mandibular
third
molar
and
its
response
to
orthodontic

therapy.
Angle
Orthod.
1973;
43:271-‐8.

57.
Broadbent
B.
The
influence
of
third
molars
on
the
alignment
of
the
teeth.
American
Journal
of

Orthodontics.
1943;
29:312.

58.
Enlow
D.
The
Human
Face.
Hoeber
Med.
Division,
Harper
&
Row,
Inc.
1968.

59.
Schulhof
R.
Third
molars
and
orthodontic
diagnosis.
J
Clin
Orthod.
1976;
10:272-‐81.

60.
Ricketts
R.
Studies
leading
to
the
practice
of
abortion
of
lower
third
molars.
Dent
Clin
North
Am.

1979;
23:393-‐411.

61.
Ricketts
R,
Turley
P,
Chaconas
S,
Schulhof
R.
Third
molar
enucleation:
Diagnosis
and
technique.
J
Calif

Dent
Assoc.
1976;
4:52-‐7.

62.
Olive
R,
Basford
K.
Reliability
and
validity
of
lower
third
molar
space-‐assessment
techniques.
Am
J

Ortho.
1981;
79:45-‐53.

63.
Forsberg
C.
Tooth
size,
spacing
and
crowding
in
relation
to
eruption
or
impaction
of
third
molars.
Am

J
Orthod
Dentofacial
Orthop.
1988;
94(1):57-‐62

64.
Forsberg
C,
Vingren
B,
Wesslen
U.
Mandibular
third
molar
eruption
in
relation
to
available
space
as

assessed
on
lateral
cephalograms.
Swed
Dent
J.
1989;
13:23–31.

65.
Sicher
H.
Oral
Anatomy.
St
Louis.
C
V
Mosby:
1965;
129–131

66.
Richardson
M.
Changes
in
lower
third
molar
position
in
the
young
adult.
Am
J
Orthod
Dentofacial

Orthop.
1992;
102:320-‐7.

65

67.
Kan
K,
Liu
J,
Lo
E,
Corbet
E,
Leung
W.
Residual
periodontal
defects
distal
to
the
mandibular
second

molar
6–36
months
after
impacted
third
molar
extraction.
J
Clin
Periodontol.
2002;
29(11):1004-‐11.

68.
Hupp
J,
Ellis
E,
Tucker
M.
Principles
of
Management
of
Impacted
Teeth.
In:
Contemporary
Oral
and

Maxillofacial
Surgery,
6th
Ed.
St
Louis:
Mosby
Year
Book;
2014.
p.
143.

69.
Bjork
A.
Variations
in
the
growth
pattern
of
the
human
mandible:
longitudinal
radiographic
study
by

the
implant
method.
J
Dent
Res.
1963;
42:400-‐11.

70.
Bishara
S,
Andreasen
G.
Third
molars:
a
review.
Am
J
Orthod.
1983;
83:131-‐7.

71.
Ash
M
Jr.
Mandibular
second
molar.
In:
Ash
MM
Jr,
editor.
Wheeler’s
dental
anatomy,
physiology

and
occlusion.
7th
ed.
Philadelphia:
W.
B.
Saunders;
1993.
p.
291-‐9.

72.
Murphy
T.
Reduction
of
the
dental
arch
by
approximal
attrition.
Br
Dent
J.
1964;
116:483-‐8.

73.
Alling
C
III,
Alling
R.
Indications
for
management
of
impacted
teeth.
In:
Alling
C
III,
Helfrick
J,
Alling
R,

editors.
Impacted
teeth.
Philadelphia:
W.
B.
Saunders;
1993.
p.
46-‐9.

74.
Begg
P.
Stone
Age
man’s
dentition.
Am
J
Orthod.
1954;
40:298-‐312,
373-‐83,
517-‐31.

75.
Lombardi
A.
The
adaptive
value
of
dental
crowding:
a
consideration
of
the
biologic
basis
of

malocclusion.
Am
J
Orthod.
1982;
81(1):38-‐42.

76.
Mehta
J,
Evans
C.
A
study
of
attrition
of
Teeth
In
the
Arkansas
Indian
Skulls.
The
Angle
Orthodontist.

1966;
36:3.

77.
Faubian
B.
Effect
of
extraction
of
premolars
on
eruption
of
mandibular
third
molars.
Journal
of
the

American
Dental
Association.
1968;
76:316.

78.
Richardson
M,
Richardson
A.
Lower
third
molar
development
subsequent
to
second
molar
extraction.

Am
J
Orthod
Dentofacial
Orthop.
1993;
104(6):566-‐74.

79.
Gooris
C,
Artun
J,
Joondeph
D.
Eruption
of
mandibular
third
molars
after
second
molar
extractions:
a

radiographic
study.
Am
J
Orthod
Dentofacial
Orthop.
1990;
98:161-‐7.

80.
Cavanaugh
J.
Third
molar
changes
following
second
molar
extractions.
Angle
Orthod.
1985;
55:70-‐6.

81.
Kim
T,
Artun
J,
Behbehani
F,
Artese
F.
Prevalence
of
third
molar
impaction
in
orthodontic
patients

treated
nonextraction
and
with
extraction
of
4
premolars.
Am
J
Orthod
Dentofacial
Orthop.
2003;

123(2):138-‐45.

82.
Ledyard
B.
A
study
of
the
mandibular
third
molar
area.
Am
J
Orthod.
1953;
39:366-‐73.

83.
Richardson
M.
The
early
developmental
position
of
the
lower
third
molar
relative
to
certain
jaw

dimensions.
Angle
Orthodontist.
1970;
40:
226.

66

84.
Nance
P,
White
R
Jr,
Offenbacher
S,
Phillips
C,
Blakey
G,
Haug
R.
Change
in
third
molar
angulation

and
position
in
young
adults
and
follow-‐up
periodontal
pathology.
J
Oral
Maxillofac
Surg.
2006;
64:424–
428.

85.
Türköz
C,
Ulusoy
C.
Effect
of
premolar
extraction
on
mandibular
third
molar
impaction
in
young

adults.
Angle
Orthod.
2013;
83(4):572-‐7.

86.
Dierkes
D.
An
investigation
of
the
mandibular
third
molars
in
orthodontic
cases.
Angle
Orthod.
1975;

45:207-‐12.

87.
Kaplan
R.
Some
factors
related
to
mandibular
third
molar
impaction.
Angle
Orthod.
1975;
45:153-‐8.

88.
Richardson
M.
The
development
of
third
molar
impaction.
Br
J
Orthod.
1975;
2:231-‐4.

89.
Haavikko
K,
Altonen
M,
Mattila
K.
Predicting
angulational
development
and
eruption
of
the
lower

third
molar.
Angle
Orthod.
1978;
48:39-‐48.

90.
Graber
T,
Kaineg
T.
The
mandibular
third
molar:
its
predictive
status
and
role
in
lower
incisor

crowding.
Proc
Finn
Dent
Soc.
1981;
77:37–44.

91.
Richardson
M.
Pre-‐eruptive
movements
of
the
mandibular
third
molar.
Angle
Orthod.
1978;
48:187–
193.

92.
Huggins
DG.
Eruption
of
lower
third
molars
following
orthodontic
treatment.
Trans
Br
Soc
Study

Orthod.
1962:67.

93.
Richardson
E,
Malhotra
S,
Semenya
K.
Longitudinal
study
of
three
views
of
mandibular
third
molar

eruption
in
males.
Am
J
Orthod.
1984;
86:119-‐29.

94.
Richardson
M.
Development
of
the
lower
third
molar
from
10
to
15
years.
Angle
Orthod.
1973;

43:191-‐3.

95.
Al
Kuwari
H,
Talakey
A,
Al-‐Sahli
R,
Albadr
A.
Influence
of
orthodontic
treatment
with
first
premolar

extraction
on
the
angulation
of
the
mandibular
third
molar.
Saudi
Med
J.
2013;
34(6):639-‐43.

96.
Feng
G,
Zou
B,
Gao
X,
Zeng
X,
Wang
X,
Yan
Y.
Influence
of
the
mandibular
second
premolar

extraction
on
the
angulation
of
the
mandibular
third
molar.
Beijing
Da
Xue
Xue
Bao.
2013;
45(1):77-‐80.

97.
Saysel
M,
Meral
G,
Kocadereli
I,
Taşar
F.
The
effects
of
first
premolar
extractions
on
third

molar
angulations.
Angle
Orthod.
2005;
75(5):719-‐22.

98.
Staggers
J,
Germane
N,
Fortson
W.
A
comparison
of
the
effects
of
first
premolar
extractions
on
third

molar
angulation.
Angle
Orthod.
1992;
62(2):135-‐8.

99.
Capelli
J
Jr.
Mandibular
growth
and
third
molar
impaction
in
extraction
cases.
Angle
Orthod.
1991;

61:223-‐9.

67

100.
Elsey
M,
Rock
W.
Influence
of
orthodontic
treatment
on
development
of
third
molars.
Br
J
Oral

Maxillofac
Surg.
2000;
38:350–353.

101.
Jain
S,
Valiathan
A.
Influence
of
first
premolar
extraction
on
mandibular
third
molar
angulation.

Angle
Orthod.
2009;
79(6):1143-‐8.

102.
Russell
B,
Proffit
W,
Philips
C.
The
association
between
orthodontic
treatment
with
removal
of

premolars
and
the
angulation
of
developing
mandibular
third
molars
over
time.
The
Angle

Orthodontist.
2013;
83:376-‐380.

103.
Kaminishi
R,
Lam
P,
Kaminishi
K.
A
10-‐year
comparative
study
of
the
incidence
of
third
molar

removal
in
the
aging
population.
J
Oral
Maxillofac
Surg.
2006;
64:173.

104.
Punwutikorn
J,
Waikakul
A,
Ochareon
P.
Symptoms
of
unerupted
mandibular
third
molars.
Oral

Surg
Oral
Med
Oral
Pathol
Oral
Radiol
Endod.
1999;
87:30.

105.
Bruce
R,
Frederickson
G,
Small
G.
Age
of
patients
and
morbidity
associated
with
mandibular
third

molar
surgery.
J
Am
Dent
Assoc.
1980;
101:240.

106.
Mercier
P,
Precious
D.
Risks
and
benefits
of
removal
of
impacted
third
molars.
A
critical
review
of

the
literature.
Int
J
Oral
Maxillofac
Surg.
1992;
21:17.

107.
Bui
C,
Seldin
E,
Dodson
T.
Types,
frequencies,
and
risk
factors
for
complications
after
third
molar

extraction.
J
Oral
Maxillofac
Surg.
2003;
61:1379.

108.
Valmaseda-‐Castellon
E,
Berini-‐Aytes
L,
Gay-‐Escoda
C.
Inferior
alveolar
nerve
damage
after
lower

third
molar
surgical
extraction:
a
prospective
study
of
1117
surgical
extractions.
Oral
Surgery,
Oral

Medicine,
Oral
Pathology,
Oral
Radiology,
and
Endodontology.
2001;
92:377.

109.
Kugelberg
C.
Periodontal
healing
two
and
four
years
after
lower
third
molar
surgery.
A
comparative

retrospective
study.
Int
J
Oral
Maxillofac
Surg.
1990;
19:341.

110.
Kugelberg
C,
Ahlstrom
U,
Ericson
S
et
al.
Periodontal
healing
after
impacted
lower
third
molar

surgery
in
adolescents
and
adults.
A
prospective
study.
Int
J
Oral
Maxillofac
Surg.
1991;
20:18.

111.
Kugelberg
C,
Ahlstrom
U,
Ericson
S,
Hugoson
A.
Periodontal
healing
after
impacted
lower
third

molar
surgery.
A
retrospective
study.
Int
J
Oral
Surg.
1985;
14:29.

112.
Krimmel
M,
Reinert
S.
Mandibular
fracture
after
third
molar
removal.
J
Oral
Maxillofac
Surg.
2000;

58:1110.

113.
Schultze-‐Mosgau
S,
Reich
R.
Assessment
of
inferior
alveolar
and
lingual
nerve
disturbances
after

dentoalveolar
surgery,
and
of
recovery
of
sensitivity.
International
Journal
of
Oral
and
Maxillofacial

Surgery.
1993;
22:214.

114.
Gulicher
D,
Gerlach
K.
Sensory
impairment
of
the
lingual
and
inferior
alveolar
nerves
following

removal
ofimpacted
mandibular
third
molars.
Inte

rnational
Journal
of
Oral
and
Maxillofacial
Surgery.

2001;
30:306.

68

115.
Queral-‐Godoy
E,
Valmaseda-‐Castellon
E,
Berini-‐Aytes
L,
Gay-‐Escoda
C.
Incidence
and
evolution
of

inferior
alveolar
nerve
lesions
following
lower
third
molar
extraction.
Oral
Surgery,
Oral
Medicine,
Oral

Pathology,
Oral
Radiology,
and
Endodontology.
2005;
99:259.

116.
Ash
M,
Costich
E,
Hayward
R.
A
study
of
periodontal
hazards
of
third
molars.
J
Periodontol.
1962;

33:209.

117.
Chiapasco
M,
Crescentini
M,
Romanoni
G.
Germectomy
or
delayed
removal
of
mandibular

impacted
third
molars:
the
relationship
between
age
and
incidence
of
complications.
J
Oral
Maxillofac

Surg.
1995;
53:418.

118.
Chossegros
C,
Guyot
L,
Cheynet
F.
Is
lingual
nerve
protection
necessary
for
lower
third
molar

germectomy?
A
prospective
study
of
300
procedures.
Int
J
Oral
Maxillofac
Surg.
2002;
31:620.

119.
USC
clinic

120.
Tarazona,
B.,
V.
Paredes,
Jm.
Llamas,
R.
Cibrian,
and
Jl.
Gandia.
"Influence
of
First
and
Second

Premolar
Extraction
or
Non-‐extraction
Treatments
on
Mandibular
Third
Molar
Angulation
and
Position.

A
Comparative
Study."
Medicina
Oral
Patología
Oral
Y
Cirugia
Bucal
(2009):
E760-‐766.

121.
S.
Jay
Bowman
and
Lysle
E.
Johnston
Jr
(2000)
The
Esthetic
Impact
of
Extraction
and
Nonextraction

Treatments
on
Caucasian
Patients.
The
Angle
Orthodontist:
February
2000,
Vol.
70,
No.
1,
pp.
3-‐10.

122.
Lim,
Hoi-‐Jeong,
Kwang-‐Taek
Ko,
and
Hyeon-‐Shik
Hwang.
"Esthetic
Impact
of
Premolar
Extraction

and
Nonextraction
Treatments
on
Korean
Borderline
Patients."
American
Journal
of
Orthodontics
and

Dentofacial
Orthopedics
133.4
(2008):
524-‐31.

123.
Scott,
Steven
H.,
and
Lysle
E.
Johnston.
"The
Perceived
Impact
of
Extraction
and
Nonextraction

Treatments
on
Matched
Samples
of
African
American
Patients."
American
Journal
of
Orthodontics
and

Dentofacial
Orthopedics
116.3
(1999):
352-‐58.

124.
Konstantonis,
Dimitrios.
"The
Impact
of
Extraction
vs
Nonextraction
Treatment
on
Soft
Tissue

Changes
in
Class
I
Borderline
Malocclusions."
The
Angle
Orthodontist
82.2
(2012):
209-‐17.

125.
Paquette,
David
E.,
John
R.
Beattie,
and
Lysle
E.
Johnston.
"A
Long-‐term
Comparison
of

Nonextraction
and
Premolar
Extraction
Edgewise
Therapy
in
“borderline”
Class
II
Patients."
American

Journal
of
Orthodontics
and
Dentofacial
Orthopedics
102.1
(1992):
1-‐14.

126.

Xu,
Tian-‐Min,
Yan
Liu,
Min-‐Zhi
Yang,
and
Wei
Huang.
"Comparison
of
Extraction
versus

Nonextraction
Orthodontic
Treatment
Outcomes
for
Borderline
Chinese
Patients."
American
Journal
of

Orthodontics
and
Dentofacial
Orthopedics
129.5
(2006):
672-‐77.

127.

Kahl-‐Nieke,
B.
"The
Role
of
Extraction
in
Stability
of
Orthodontic
Treatment."
Journal
of
Orofacial

Orthopedics
Oct
57.5
(1996):
272-‐87.

128.
Rinchuse,
D.
J.,
and
S.
Kandasamy.
"Implications
of
the
Inclination
of
the
Mandibular
First
Molars
in

the
Extractionist
versus
Expansionist
Debate."
World
Journal
of
Orthodontics
2008
Winter
9(4):
383-‐90.

69

129.

Williams,
M.
O.,
and
L.
W.
White.
"A
Rationale
for
Expansion."
World
Journal
of
Orthodontics
6.4

(2005):
406-‐10.

130.

Castro,
Luma
O.,
Iury
O.
Castro,
Ana
Helena
G.
De
Alencar,
José
Valladares-‐Neto,
and
Carlos
Estrela.

"Cone
Beam
Computed
Tomography
Evaluation
of
Distance
from
Cementoenamel
Junction
to
Alveolar

Crest
before
and
after
Nonextraction
Orthodontic
Treatment."
The
Angle
Orthodontist
(2015):
n.
pag.

131.

"Explore
Dental
Insurance
Plans."
Delta
Dental.
N.p.,
n.d.
Web.
30
Oct.
2015.

132.

Jing,
Yan,
Xianglong
Han,
Yongwen
Guo,
Jingyu
Li,
and
Ding
Bai.
"Nonsurgical
Correction
of
a
Class

III
Malocclusion
in
an
Adult
by
Miniscrew-‐assisted
Mandibular
Dentition
Distalization."
American
Journal

of
Orthodontics
and
Dentofacial
Orthopedics
143.6
(2013):
877-‐87.

133.

Chung,
Kyu-‐Rhim,
Seong-‐Hun
Kim,
Hyeran
Choo,
Yoon-‐Ah
Kook,
and
Jason
B.
Cope.
"Distalization

of
the
Mandibular
Dentition
with
Mini-‐implants
to
Correct
a
Class
III
Malocclusion
with
a
Midline

Deviation."
American
Journal
of
Orthodontics
and
Dentofacial
Orthopedics
137.1
(2010):
135-‐46.

134.

Kondo,
Etsuko,
and
T.j.
Aoba.
"Nonsurgical
and
Nonextraction
Treatment
of
Skeletal
Class
III
Open

Bite:
Its
Long-‐term
Stability."
American
Journal
of
Orthodontics
and
Dentofacial
Orthopedics
117.3

(2000):
267-‐87.

135.

Kondo,
Etsuko,
and
S.
Arai.
"Nonsurgical
and
Nonextraction
Treatment
of
a
Skeletal
Class
III
Adult

Patient
with
Severe
Prognathic
Mandible."
World
Journal
of
Orthodontics
6.3
(2005):
233-‐47.

136.

William
R.
Proffit
(1994)
Forty-‐year
review
of
extraction
frequencies
at
a
university
orthodontic

clinic.
The
Angle
Orthodontist:
December
1994,
Vol.
64,
No.
6,
pp.
407-‐414.

137.
Steed,
Martin
B.
"The
Indications
for
Third-‐molar
Extractions."
The
Journal
of
the
American
Dental

Association
145.6
(2014):
570-‐73.

138.

Coulthard
P,
Bailey
E,
Esposito
M,
Furness
S,
Renton
TF,
Worthington
HV.
Surgical
techniques
for

the
removal
of
mandibular
wisdom
teeth.
Cochrane
Database
of
Systematic
Reviews
2014,
Issue
7.
Art.

No.:
CD004345.
DOI:
10.1002/14651858.CD004345.pub2.

139.

Ventä,
Irja.
"How
Often
Do
Asymptomatic,
Disease-‐Free
Third
Molars
Need
to
Be
Removed?"

Journal
of
Oral
and
Maxillofacial
Surgery
70.9
(2012):
n.
pag

140.

Park,
Jun-‐Beom
et
al.
“Evaluation
of
Number
of
Roots
and
Root
Anatomy
of
Permanent
Mandibular

Third
Molars
in
a
Korean
Population,
Using
Cone-‐Beam
Computed
Tomography.”
European
Journal
of

Dentistry
7.3
(2013):
296–301.
PMC.
Web.
5
Nov.
2015.

141.

Anthopoulou,
Chrysi,
Dimitrios
Konstantonis,
and
Margarita
Makou.
"Treatment
Outcomes
after

Extraction
and
Nonextraction
Treatment
Evaluated
with
the
American
Board
of
Orthodontics
Objective

Grading
System."
American
Journal
of
Orthodontics
and
Dentofacial
Orthopedics
146.6
(2014):
717-‐23.

70

142.

Sabri,
Roy.
"Treatment
of
a
Severe
Arch-‐length
Deficiency
with
Anteroposterior
and
Transverse

Expansion:
Long-‐term
Stability."
American
Journal
of
Orthodontics
and
Dentofacial
Orthopedics
137.3

(2010):
401-‐11.

143.

Heiser,
Wolfgang,
Martin
Richter,
Andreas
Niederwanger,
Nikolaus
Neunteufel,
and
Siegfried

Kulmer.
"Association
of
the
Canine
Guidance
Angle
with
Maxillary
and
Mandibular
Intercanine
Widths

and
Anterior
Alignment
Relapse:
Extraction
vs
Nonextraction
Treatment."
American
Journal
of

Orthodontics
and
Dentofacial
Orthopedics
133.5
(2008):
669-‐80.

144.

MARGARET
E.
RICHARDSON
(1970)
The
Early
Developmental
Position
of
the
Lower
Third
Molar

Relative
to
Certain
Jaw
Dimensions.
The
Angle
Orthodontist:
July
1970,
Vol.
40,
No.
3,
pp.
226-‐230.

145.

Un-‐Bong
Baik,
Yoon-‐Ah
Kook,
Mohamed
Bayome,
Je-‐Uk
Park,
and
Jae
Hyun
Park
(2015)
Vertical

eruption
patterns
of
impacted
mandibular
third
molars
after
the
mesialization
of
second
molars
using

miniscrews.
The
Angle
Orthodontist
In-‐Press.

146.
Nance,
Paige
E.,
Raymond
P.
White,
Steven
Offenbacher,
Ceib
Phillips,
George
H.
Blakey,
and

Richard
H.
Haug.
"Change
in
Third
Molar
Angulation
and
Position
in
Young
Adults
and
Follow-‐Up

Periodontal
Pathology."
Journal
of
Oral
and
Maxillofacial
Surgery
64.3
(2006):
424-‐28.

147.

Carter,
K.,
and
S.
Worthington.
"Predictors
of
Third
Molar
Impaction:
A
Systematic
Review
and

Meta-‐analysis."
Journal
of
Dental
Research
(2015):
n.
pag

148.

Halicioglu,
Koray,
Mevlut
Celikoglu,
Suleymankutalmis
Buyuk,
Ahmetercan
Sekerci,
Farukizzet
Ucar,

Ibrahim
Yavuz.
"Three-‐dimensional
Evaluation
of
the
Mandibular
Third
Molars′
Development
in

Unilateral
Crossbite
Patients:
A
Cone
Beam
Computed
Tomography
Study."
European
Journal
of

Dentistry
Eur
J
Dent
8.3
(2014):
389.

149.

Sameshima,
Glenn,
and
Cabot
Denny.
Premolar
Extraction
Influence
on
Third
Molar
Angulation.

Thesis.
University
of
Southern
California,
2014.

Abstract (if available)

Abstract Introduction: Previous studies evaluating premolar extraction influence on third molar angulation have always evaluated the changes of the 3rd molar by examining the long axis of the tooth. However many orthodontic patients begin treatment when root formation has not begun on 3rd molars. This study will examine the angulation changes in 3rd molars using a horizontal axis in the occlusal plane. Retromolar length has been found as a contributing factor to impaction versus eruption. This study will examine the change in retromolar length before and after orthodontic treatment in extraction and non-extraction cases. Methods: In this retrospective study, 90 patients were divided into 3 groups of 30 patients each. Groups were compared using one-way ANOVA by extraction pattern (nonextraction, first premolar extraction, second premolar extraction). The horizontal axes of the second and third molars were traced on initial and final panoramic radiographs. The angulation change between the molars was determined between initial and final angulations. The retromolar length was determined by comparing the width of the 3rd molar to the space available from the distal of the 2nd molar to the ramus. The initial and final proportions were compared using chi-square analysis to calculate the proportional change over the treatment period. Results: The mean third molar angulation change in the non-extraction group was 3.1±11.6°, first premolar extraction group was 10.0±16.7°, and second premolar extraction group was 6.3±13.1°. The final retromolar length to third molar width proportion among the three groups was: non-extraction 1.88±1.38, first premolar extraction group 1.26±0.53, and second premolar extraction group 1.19±0.37. Discussion: There was not a significant difference in 3rd molar angulation changes among the three groups. Extraction orthodontic treatment did not help improve eruption angles of third molars. There was a highly significant difference (p value< 0.01) between the extraction groups and non-extraction group in the proportion of third molar width to retromolar length. Extraction orthodontic treatment results in mesial movement of the mandibular dentition and more space distal to second molars for eruption of third molars. Conclusion: Further studies could be performed using CBCT images pre- and post-treatment to calculate accurately the positional changes in mandibular third molars and retromolar length.

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

Premolar extraction influence on third molar angulation

PDF

The mesiodistal angulation and faciolingual inclination of each whole tooth in three dimensional space post non-extraction orthodontic treatment

PDF

Mandibular plane angle changes with or without premolar extraction treatment in adult orthodontics measured using 3-D cone beam technology

PDF

Comparison between tooth mesiodistal angulation measurements from constructed panoramic images and three-dimensional volumetric images

PDF

Comparison of premolar extraction rates between one-phase and two-phase class II malocclusion

PDF

Whole tooth tip and torque comparison of orthodontically treated extraction cases versus a non-treated near normal group using CBCT analysis.

PDF

Maxillary sinus floor and alveolar crest alterations following extraction of maxillary molars: a retrospective CBCT analysis

PDF

Three dimensional analysis of maxillary retromolar alveolar bone before and after en‐masse distalization

PDF

3D assessment of virtual bracket removal for modern orthodontic retainers: a prospective clinical study

PDF

Cone beam computed tomographic measurements of buccal alveolar bone widths overlying the maxillary premolars

PDF

Maxillary sinus floor and alveolar crest alterations following extraction of maxillary molars and ridge preservation: a retrospective CBCT analysis

PDF

Orthodontic rotational relapse: prevalence and prevention

PDF

An overview of the dental and skeletal relationships in individuals of Vietnamese ancestry

PDF

Overbite correction with fully customized lingual appliances

PDF

The long-term cephalometric and respiratory outcomes of mandibular distraction osteogenesis in infants with Pierre Robin sequence

PDF

Monitering of typodont root movement via crown superimposition of single CBCT and consecutive iTero scans

PDF

A comparative study of caucasian and African American mandibular clinical arch forms

PDF

Comparison of premolar extraction rates between one-phase and two-phase class II malocclusion

PDF

Relationship between dental and alveolar bony arch form and whole tooth mesiodistal angulation and faciolingual inclination in three-dimensional space

PDF

3D ssessment of bracket position accuracy for lingual appliances using CAD/CAM technology: a pilot study