Third molars& its significance in orthodontic treatment & relapse /certified fixed orthodontic courses by Indian dental academy

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THIRD MOLARS :
IT’S SIGNIFICANCE IN
ORTHODONTIC
TREATMENT AND
RELAPSE


INTRODUCTION
• Third molars are the teeth which are most

often missing, impacted and with altered
morphology.
• Advances in dental anthropology states that
there is a reduction in the number of teeth
and size of jaws on evolutionary basis for
the past 1,00,000 years.
• Third incisors ,third premolars and fourth
molars have disappeared already.

• At present human third molars often fail to
develop, which indicate that these teeth
may be on their way out.
• Although there are some who advice the
early removal of the third molars , many
strongly believe that the retention of
asymptomatic third molars may be useful
in later years as a substitute for badly
decayed teeth or may even be useful as a
transplant.

DEVELOPMENT AND ERUPTION
• There is great variation in the timing of
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development, calcification, and eruption of third
molars.
Development may begin as early as 5 years or
as late as 16 years, with the peak formation
period at 8 or 9 years.
Calcification can start at age 7 years in some
children and as late as age 16 years in others.
Enamel formation is normally complete between
12 and 18 years and root formation is normally
completed between 18 and 25 years.

• Hellman reported that the average age of

eruption was 20.5 years.
• In 1962,Fanning reported average ages of
eruption of 19.8 years for females and
20.4 years for males.
• Early formation of third molars is generally
regarded as predictive of early maturation
but not always of early eruption.
• Most surveys report that more than 17%
of lower third molars become impacted.

• Lower third molars normally have

their occlusal surfaces tilted slightly
forwards and lingually during early
calcification.
• As the mandible increases in length,
with bone resorption at the inner
angulation between the body and the
ascending ramus of the mandible, the
third molars become more upright.

• In contrast, upper third molars erupt

downwards, backwards, and often
outwards.
• There is, therefore, a possibility of
crossbite, but tongue pressure on lower
crowns and buccinator pressure on upper
crowns will often correct this. If there is a
lack of space, then normal eruptive paths
cannot be followed, and crossbites can
result.

ERUPTIVE PATHWAYS OF THIRD MOLARS
• Richardson investigated the development of lower
third molars between ages 10 and 15 years,using
models and four cephalometric radiographs (90 degree
left lateral, straight posteroanterior and 60 degree left
and right lateral views).
• She found that the angle of the occlusal surface of the
lower third molars to the mandibular plane was 41
degree On average she found this decreased by 11
degree by age 15.


• Successful eruption of the lower third

molar occurs by the tooth continuing to
decrease its angle to the mandibular plane
and moving occlusally into sufficient
space.


• J.B.Fayad et al in AJO 2004 determined the

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relationship between the maxillary molar’s sagittal
inclination and the eruption of third molars using
CT scans.
In their study the sagittal inclination of maxillary
first and second molars were greater in the
subjects with erupted maxillary third molars than
in those with impacted third molars and
particularly in the younger subjects.
They concluded that the vertical position of the
first maxillary molar in the sagittal plane is a
predictor of the eruption of the adjacent third
molar; and that the sagittal inclination of the
maxillary molars increases with age which could be
the effect of a mesial drift.

• Kahl et al evaluated orthopantomograms

of 58 orthodontically treated patients with
asymptomatic impacted third molars.
• In a 15 year follow up ,they observed that
some of the maxillary and mandibular
molars have rotated to a more upright
position while others had an increase in
the mesio or disto-angulation.
• They found that age, period of impaction,
extent of space deficiency, developmental
stage, level of eruption and bone
conditions had no predictive values.

ASSESSMENT OF SPACE FOR THIRD MOLARS

• Shortage of space between the second

molar and the ramus has long been
identified as a major factor in the etiology of
lower third molar impaction.
• Henry and Morant suggested a technique for
predicting impaction of lower third molar
using their third molar space index; obtained
by expressing the mesiodistal width of the
third molar as a percentage of the space
available measured on bimolar radiographs.

• If this index, exceeded a value of 120 for a

person at maturity, impaction could be
predicted.
• This index decreases as the growth continues
and the space available increases.
• Ledyard, studying lateral jaw radiographs,
found that less than a 2 mm increase in
space between the lower second molar and
the ramus could be expected after the age of
14 years and a negligible increase after 16
years

• Ricketts claimed that if 50% of the third

molar crown lies ahead of the external
oblique ridge at maturity, there is a 50%
chance of eruption.
• Schulhof in 1976 claimed that growth
prediction can estimate the adult dimension
from Xi point to the mandibular second molar
on a lateral cephalogram taken at the age of
9 years, with a standard error of 2.8 mm
Schulhof suggested that lower third molars
could not be classified as likely to erupt to
good occlusion if the Xi point to lower second
molar was measured less than 25mm

• Richard Olive et al in AJO 81 in a study

on dried human skulls, examined the
reproducibility of estimates of a space
width ratio (space available between lower
second molar and the ramus divided by
mesiodistal width of mandibular third
molar) on the lateral cephalogram,
rotational tomograms(OPG), intraoral
bitewings and 60 degree cephalograms.


• A template of cellulose acetate was prepared with

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a right angle T drawn in line through the tips of
the most superior, anterior and posterior cusps of
the first premolar to second molar section of
buccal segment.
The template was placed over the radiograph with
the horizontal part of the T on the occlusal plane
and the vertical part touching the most distal part
of second molar crown.


• The space available (AB),the mesiodistal

width of the lower third molar(CD) and
space width ratio (AB/CD) were computed
from the digitized data.
• A ratio of less than 120% will indicate a
high probability of impaction.
• The rotational tomogram, intraoral bitewing
and 60 degree rotated cephalogram were
superior to the lateral cephalogram on the
basis of reliability of results and
reproducibility of radiograph technique for
estimating the space width ratio.

• The results suggested the difficulties in

landmark location on lateral cephalogram.
Locating anterior border of the ramus on
lateral cephalogram is often difficult, which
militates against good reproducibility of
results.
• It was shown that the reliability for the
lateral cephalogram technique alone was
not as good as for the other techniques.
• The rotational tomograms yielded the most
accurate estimates of space width ratio.
• Intraoral bitewings yielded the next best
estimates.

IMPACTIONS
• Archer defined an impacted third molar as ‘One

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which was completely or partly erupted and
positioned against another tooth,bone or soft
tissue, so that its further eruption was unlikely.
Dachi and Howell in their study found that the
incidence of patients with atleast one impacted
tooth was 16.7%.
Teeth most often impacted in order of frequency
were the maxillary third molars,mandibular third
molars,maxillary canines and mandibular
premolars.No sex differences were noted.

• Bjork and colleagues identified 3 skeletal

factors that are separately influencing third
molar impaction
– Reduced mandibular length,measured as the
distance from the chin point to the condylar
head.
– Vertical direction of condylar growth as
indicated by the mandibular base angle.
– Backward directed eruption of mandibular
dentition determined by the degree of alveolar
prognathism of lower jaw.

• Capelli in a 1991 study evaluated 60

patients who had four first premolar
extractions.
• The findings from pretreatment and
posttreatment cephalograms suggested that
third molar impactions were more likely to
occur in patients with pretreatment vertical
mandibular growth.
• A long ascending ramus, short mandibular
length, and greater mesial crown inclinations
of third molars, seem to be indicative of third
molar impaction.

TYPES OF IMPACTION
Richardson suggested five categories of impaction
• Type A : The tooth can follow the pattern of an
ideally developing third molar, by decreasing its
angle to the mandibular plane and becoming more
upright, but the uprighting may not be enough to
allow full eruption.


• Type B : The angular

developmental position
relative to the mandibular
plane may remain unchanged

• Type C :

The tooth can
increase its angulation to
the mandibular plane ,and
become more mesially
inclined .There is at
present no reliable way
of predicting which teeth
will follow this unfavourable
pattern,which sometimes occurs unilaterally and leads
to horizontal impaction

• Type D :The tooth can

be seen to make favourable
changes in angulation ,but
fail to erupt owing to lack
of space.These are so called
vertical impactions.

• Type E :The tooth can

continue to change its
angulation beyond the ideal
occlusal position,and show
disto angular impaction

MECHANISM FOR ERUPTION AND IMPACTION

• Differential root elongation might explain
differences in eruptive behaviour among
lower third molars.

• Richardson offered a theoretical

explanation for favorable or unfavorable
rotational movement.


• Favorable change in angulation ,to a more
upright position ,seemed to occur in teeth
where the mesial root developed ahead of
the distal crown surface and root.
• The typical root configuration showed a
mesial root which was curved in a distal
direction and was slightly longer than the
distal root.


• Unfavorable mesial tipping, leading to horizontal

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impaction, seemed to occur when the distal root
became the same length, and then longer than
the mesial root.
The distal root on such teeth was seen to appear
to have a mesial
curvature.


FACTORS INFLUENCING AVAILABILITY OF SPACE

• GROWTH
Bjork et al measured the distance from the
anterior border of the ramus to the second
molar,and concluded that the bigger the
space,the better the chance of
eruption.Richardson measured an average of
11.4 mm of growth between the age of 10 and
15 years.


• BONE RESORPTION
In 1987 Richardson examined the
creation of space for third molars in 51
subjects.
She found that increased space was
obtained from both the mesial movement
of the dentition and bone remodeling
along the anterior border of the ramus.
On average 2 mm of posterior space
was created by bone remodeling

SPACE RELEASED BY ATTRITION
In so-called primitive dentitions, where considerable
attrition takes place, the third molars erupt to take up the
space released.
Begg felt that lack of this attrition,due to highly refined
diets,was a mojor cause of third molar impaction. Other
authors,such as Profitt,have questioned this hypothesis.
Early and extensive interproximal caries could also
reduce the size of erupted teeth, owing to disappearance of
proximal contacts.


SECOND MOLAR EXTRACTION
• Richardson and Richardson in AJO 93

investigated 63 patients after extraction of
lower second molars and found that all the
lower third molars erupted more or less
successfully after an average observation
period of 5.8 years.
• There was considerable variation in the
time taken for eruption, ranging from 3 to
10 years and Richardson noted that it is not
possible to predict how long eruption will
take.

• Bonham Magness in JCO 86 suggests

that upper third molars has a much more
predictable eruption pattern than lower third
molars.
• He suggested the extraction of upper
second molars in some cases to assist first
molar positioning and increase space for
upper third molars.


• Tae-Woo Kim et al in AJO 2003

confirmed the findings of Faubion and
Kaplan that impaction of mandibular
third molars occurs about twice as
often in non-extraction patients than in
extraction patients.
• The mechanism may be that premolar
extraction therapy is associated with
an increase in the amount of mesial
movement of the maxillary and
mandibular molars and an increase in
the eruption space for the third molars.

• Cephalometric growth studies suggest 2

important mechanisms for development of
the retromolar space in the mandible;
Resorption at the anterior border of the
ascending ramus and the anterior migration
of the posterior teeth during the functional
phase of tooth eruption.
• More than 60% of the patients in the study,
with a distance of 23 mm or less from the
distal of the mandibular second molar to the
Ricketts’ Xi point at the end of the active
treatment experienced eruption of
mandibular third molars.

• The retromolar space can increase about 2
mm from age 15 to adulthood.
• They also showed that as many as 60% of
the subjects with a distance from the
anterior border of the ramus to the distal
of second molar of 5 mm or less
experienced eruption.
• These suggest that the size of third molar
eruption space associated with a high risk
of impaction might be smaller than
previously suggested

UPRIGHTING IMPACTED MOLARS

• Third molar retention may be beneficial in
many situations.
• Some investigators maintain that third
molars could be used at a later date as
replacements or for prosthetic abutments
in case of loss of first and second molars.
• Third molars could also be used as
transplants


• In shallow mesio-angular impactions Richardson
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used a one stage method.
A second molar tube can normally be bonded onto
the buccal aspect of a partly erupted lower third
molar, if enough enamel is visible.

• It is then possible to include the tooth in full
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treatment ,if other teeth are already bonded and
bracketed.
If the case is not fully banded,
then lower second or first
molars alone can be used,
with a lingual arch for support

• In deep mesio-angular impactions,a two-stage
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method is used.
If it is not possible to bond onto the buccal
surface,a different technique is used which can be
delayed until 18 –19 years of age, to allow time
for the tooth to improve its position.
The first stage involves bonding a second molar
tube onto the occusal surface of the lower third
molar.


• The hook is removed from the tube, before bonding.
• Lower first or second molars are banded with a
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lingual arch, using first molar bands and brackets.
A small sectional archwire, with a compressed coil
spring, is used to provide a distalizing and uprighting
force to the crown of the impacted molars.
After some uprighting using this method, it is
normally possible to bond a tube buccally for the
second stage.


• Ike Slodov et al in AJO 89 describes an

orthodontic uprighting technique similar to
‘Sling shot’ appliance described by Moyers
and by Profitt.
• Modified impaction related surgical
procedures provide easy application of
techniques to facilitate exposure of
unerupted and partially erupted third
molars and allow orthodontic manipulation


• After surgical exposure a cleat is bonded in center
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of mesial marginal ridge.
The wire portion of the appliance is fabricated from
0.032 inch stainless steel wire and adapted closely
to the mucosa.
The mesial hook is placed 3 mm distal to the distal
portion of the third molar.
Standard soldering techniques are used to attach
the wire to the buccal (or lingual) surface of the
band. Appliance is cemented in place and is
activated with elastic modules


• By manipulation of the distal arm of the appliance

either buccally or lingually ,depending on the desired
movement,teeth can be directed or rotated
with some effectiveness.
Variation can also be accomplished
by alteration of the bond position
of the cleat.

• Following activation,rapid uprighting and distalisation
will occur in 3 to 6 months in most cases.Grinding of
occlusal surface is not necessary.
When the third molars are upright,
the appliances are removed and
the third molars are banded, leveled
and aligned with the rest of the teeth.

• This procedure is contraindicated when the

molar to be uprighted has no antagonist; is
severely malformed or is abnormally large
or small, and it should be done carefully
when there is a tendency for open bite.
Advantages are:
1. Ease of fabrication and manipulation
2. Rapid treatment
3. Little discomfort
4. No demands for patient cooperation

• Orton and Jones in JCO 87 described a simple
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whip spring that is unobtrusive and fairly fast
acting with a treatment time of 4 to 12 months.
It is used for disimpacting , mild to severe mesially
impacted lower terminal molars (LTM).
LTM crown must be accessible for an edgewise
tube, preferably on a band.
Partial seating of the band on the mesial surface is
acceptable at first, which can be fully seated as
correction proceeds.
If the impacted molar has not sufficiently erupted
then surgically expose distobuccal surface and
bond an attachment.

• The whip spring is fabricated with 0.018X

0.025 wire for 0.022 slot and 0.017X0.022
wire for 0.018 slot.
• A circular loop is placed mesial to the tube to
prevent posterior displacement of the wire
and to provide attachment of an elastic
module that anchors the wire in the tube.


• Wire extends mesially from the loop. A vertical bend
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is placed occlusally next to the midbuccal fissure of
the anchor molar.
The wire is curved lingually to pass through the
midbuccal groove onto the occlusal surface. It is
then contoured distally to run along the occlusal
surface.
Moving the whip to the occlusal surface of the
anchor molar activates the appliance.


• The whip spring can be reactivated in the

mouth by lifting the wire away from occlusal
surface and gently squeezing the arm of the
spring between loop and vertical bend with
Tweeds loop forming plier.
• After initial adjustment at 3 to 4 weeks,
adjustments every 6 week seen to be
adequate. Overcorrection is advised.


• The force of the whip tends to extrude the impacted
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molar and intrude the anchor molar.
If there is too much intrusion of anchor molar, a
new whip can be made that extends to another
anchor tooth.
The couple tends to disimpact the LTM by a
combination of distal crown tipping and mesial root
movement, resulting in root paralleling of the
molars.


• If the vertical development of the LTM is

impeded by an upper molar, then the
overerupted upper molar must be intruded
by a removable appliance with an intrusive
arm


REPLACEMENT OF THIRD
MOLARS FOR SECOND MOLARS
• During growth of maxilla ,space to accomodate

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the erupting first, second, and third molars must
be created by growth in the posterior region of
the tuberosity.
The maxillary growth in this area must normally
be downward and forward to create room for
the eruption of each succeeding molar.
If growth in this region is insufficient, abnormal
eruption or lack of eruption will be the result.

• According to Malcolm.R.Chipman in AJO 1961

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the third molars can be substituted for the second
molars in certain situations and solve some of the
problems of maxillary tuberosity area.
The indications for eliminating maxillary second
molar and replacing it with third molars are
1.Maxillary third molars of fair size and shape
with the possibility of good root development
2.Small,restricted maxillary tuberosities and the
possibility of interference with distal
movement in maxillary posterior region.
3.Second molars erupted buccally.

4.Second molars decayed ,badly decalcified or having
large restorations.
5.Maxillary third molars in favourable position and
angulation relative to second molars and maxillary
tuberosity.
6.Maxillary third molars in favourable relation to
mandibular second molars.
7.Desirability of relieving the anchorage units of an
overload.
• The replacement of maxillary second molar
will be considered in both Class I and Class II
malocclusions

• The contraindications for substitutions are
1.Maxillary third molars too high in the
tuberosity.
2.Maxillary third molars too low in relation to the
second molars
3.Poor angulation in relation to second molar
and the tuberosity.
4.The possibility of third molars involving
maxillary sinus.
5.Small,odd shaped third molars or an indication
of the formation of small roots.

• There is a great variation in the time of

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development of third molars, and this together
with the amount of development in the
tuberosity region, has a bearing on the decisions
to be made in the event of a needed maxillary
distal movement and a possible replacement of
the second molar by third molar.
For this reason the dental age as evidenced by
the development of dental components, must be
given as much considerations as chronological
age.


• The shape of third molar crowns is also

considered.
• Small crowns with narrow width at the
cervical margin do not lend themselves to
development of normal sized roots.
• Many third molars have odd shaped
crowns with irregular cusp formations
,and, while occlusal grinding frequently is
needed, there is a limit to its use and
these teeth cannot be recommended.


• During its eruption following a second molar

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extraction ,the third molar rotates or tip mesially
as it descends; the amount of rotation being
directly associated with the degree of
angulation.
The greater the degree of angulation the greater
is the amount of rotation, with the center of
rotation being based on root apex.
This rotation together with the downward and
forward path of eruption ,is a major factor in
determining when the second molar extraction
may be planned.
The ideal condition calls for the descending third
molar to come into contact with the maxillary
first molar and into occlusion with the
mandibular second molar at the same time.

• In a Class I malocclusion,the third molar should

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have descended to the extent that the occlusal
surface is approximately level with the vertical
midline of second molar root and the mesial surface
of unerupted third molar is fairly in line horizontally
with the distal surface of mandibular second molar.
Following extraction of second molar, the third
molar will then descend in a downward and
forward arc, rotating into contact and occlusion at
the same time.
If third molar is at a much higher point there is a
possibility of impaction or premature contact.
before occlusion is attained.
If it is at a lower level in relation to second molars,
it is likely to erupt into occlusion before contact is
established with first molar, resulting in open
contacts and poor interproximal situations.

• In Class II malocclusions,the crown of maxillary
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third molar is horizontally advanced in relation to
the mandibular second molar.
In Class II cases in which second molar is to be
extracted,the most ideal location of third molar is
approximately at the junction of crown and root
of second molar.
The angulation of maxillary third molars to the
plane of occlusion and their relation to the
tuberosity must be carefully considered.
The usable angulation will range from 0 to +30
degree.(distal tip) to occlusal plane.

• Orton-Gibbs et al in AJO 2001 described the

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eruptive path of maxillary and mandibular third
molars after extraction of second molars with the
use of radiograph and assessed the final position
from study models.
They showed that the angulation of the
mandibular third molar crown long axis showed
progressive uprighting from a mean of 55 to the
occlusal plane at the start of active treatment
(SAT).
Uprighting of mandibular third molars from SAT to
end of active treatment (EAT) was limited (mean
6 ). However the third molars continued to
upright thereafter on average a further 13 .

• Clinically it is important to note that EAT
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radiographs will not give a true picture of the
likely final mandibular third molar angulation.
Approximately 50% of the space closure occurs
by EAT. Interestingly space closure is not a result
of mesial tipping but is due to significant
horizontal translation.
The relationship of the first and the
third molar crown should be the
most important indicator of
successful outcome, not angulation
of the whole tooth.
The results confirm findings by
Dacre, and Richardson and Richardson
that the original angulation of the third
molar is not a reliable predictor of
outcome for third molar position.

• In contrast to the mandibular third molars,
the maxillary third molars upright rapidly
by 14 degree on average from SAT to
EAT.
• Angular changes is minimal as the
maxillary molars settle into occlusion.
• The rate of vertical change is
rapid, with almost 7 mm of
eruption occurring by the
completion of active treatment
and a further 6 mm after
active treatment

• The third molars in the study were invariably in a
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position that maintains a good functional occlusion.
The periodontal health of the sample was excellent.
There was no correlation between third molar
position and the presence of gingivitis or
periodontitis.
The results showed that relief of crowding by
removal of second molar is a realistic option in
appropriate cases with mild to moderate crowding,
particularly in patients in whom third molar
impaction is predicted and in reducing the
likelihood of increasing crowding through the
teenage years

AUTOTRANSPLANTATION OF THIRD MOLARS
• Autotransplantation of teeth has become an accepted
and reliable treatment modality in patients with early
loss of teeth or aplasia.
• According to William Northway in AJO 80
autogenic tooth transplantation can give the concept
of space management a much broader horizon.
• Third molars have been frequently used for
transplantation. These teeth, which are often
extracted have served well as replacements, for
cariously destroyed first molars.
• Their root development which continues into the late
teens and twenties makes these teeth suitable for use
into adulthood.
• The last tooth in the arch may offer better access for
removal, and it is essential that the root not be
damaged in any way during its relocation

• The prognosis for successful transplantation is
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diminished as the root apex nears closure.
Revascularisation must take place. While post
operative resorption is rarely reported, the
effective reduction in root length is minimized by
allowing adequate development prior to
transplantation.
Hale believed that the most favourable time for
transplanting was at 3 to 5 mm of root formation.
Apfel stressed the need for delaying
transplantation until after furcation formation.
Andreasen,Baum,Peskin and Guralnick have
contented that the results will be maximized if
the operations are performed sometime between
one third and three fourth of completion of root
formation.

• Proper alveolar architecture is essential for
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housing the transplant.
The recipient site should be covered with
adequate attached, keratinised tissue to allow
proper coverage or approximation to the
transplant and it should be free of chronic
inflammation.
Mesiodistal space deficiencies be eliminated prior
to the surgical procedure,either by orthodontic
means or by slicing of adjacent teeth.
Also there should be adequate labiolingual width
on the ridge to accommodate alveolar plates on
both surfaces

SURGICAL PROCEDURE
• A full thickness mucoperiosteal flap should be
employed,allowing adequate exposure for
atraumatic preparation of the recipient site.
• A very gentle handling of the soft tissue is
ensured. The socket is prepared with bone burs
and rongeurs.
• Once the socket is judged to be of adequate
depth and circumference, a trial insertion of
presterilised dummy tooth can be made.
• Ideally, the preparation of the recipient site will
allow insertion deep enough that the cusp tips
will be at or apical to the alveolar crest height.
This allows eruption and hence root formation
postoperatively.

• Now the transplant can be removed. Again,

adequate flaps allow exposure and a minimum
of trauma.
• With gentle manipulation of surgical
instruments the dental follicle is removed from
around the crown.
• The tooth is removed and transferred
immediately to the previously prepared crypt.
• It is preferable that the tooth be manipulated
only by its crown. In the event that
buccolingual width does not allow proper
placement, it can be inserted in a rotated
position.

• This will allow preservation of

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alveolar crest and the tooth
can later be repositioned
orthodontically as desired.
Mucoperiosteal flap is
repositioned and sutures are
placed over the crown to
hold the tissues together and
tooth in its crypt.
After a week or 10 days
sutures are removed and
direct bonded stabilization
can be employed for upto 6
weeks


• Oskar Bauss et al in AJO 2004 in their
study determined the influence of
orthodontic tooth movements on pulpal
and periodontal conditions in transplanted
immature third molars.
• The indication for transplantation was
aplasia of premolars or early loss of
molars.


• In patients with horizontal atrophy of alveolar

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process, with narrow alveolar ridges and
unfavourable root morphology, transplants were
placed in 45 to 90 degrees distally rotated
positions.
Derotation to a correct position in the dental arch
was performed with a couple of forces.
The initial rotational force varied between 200 to
300 grams/mm.
Mean rotation time was 12 weeks. After complete
derotation, all transplants were integrated into a
fixed appliance for leveling and approximal space
closure.
Average Orthodontic treatment time was 15.2
months.

• In vertically atrophied jaw sections,transplants

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were fixed in distinct infraocclusion (average 5.1
mm) Transplants were leveled to the occlusal
plane before closing the approximal spaces.
Mean orthodontic treatment time was for 14.4
months.
For determining pulpal and periodontal
conditions,clinical and radiologic examinations
were carried out.
Autotransplanted third molars without subsequent
orthodontic treatment had the best pulpal and
periodontal results.
All transplants were at the developmental stage
with their open apices providing a high chance of
pulp revascularization.

• The results suggest that orthodontic extrusion

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and minor lateral tooth movement have no
harmful effects on the pulpal and periodontal
condition of autotransplanted immature third
molars.
Atrophy of the alveolar process did not affect
pulpal and periodontal healing of the transplants
in the extrusion group.
A certain amount of spontaneous eruption had
occurred in most patients by the time orthodontic
treatment began.
The formation of new alveolar processes was
observed during subsequent orthodontic
treatment.

• Revascularisation started on the fourth

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postoperative day with an ingrowth of new
vessels and was usually completed after 30 days,
with the entire pulp containing new vessels.In
contrast to pulpal revascularization ,first signs of
pulpal reinnervation cannot be demonstrated until
at least a month after transplantation and are
limited to the apical part of the pulp.
Even after 2 years, the restored pulpal nerves are
described as sparse, and the new axons are small
in diameter.
By postponing the onset of orthodontic treatment
to the third to sixth month after transplantation
and slower derotation of multirooted transplants
might increase the success rate.

THIRD MOLARS AND CROWDING

• Lower arch crowding after establishment of the
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permanent dentition during teenage period (post
adolescent crowding) is a common orthodontic
problem.
This late lower arch crowding is caused by pressure
from the back of the arch. Whether this pressure
results from a developing third molar, physiologic
mesial drift or the anterior component of force derived
from the forces of occlusion on mesially inclined teeth
is not clear.
There is also a school of thought holding the view that
in the absence of third molar, the dentition has room
to settle distally under anterior pressures caused by
late growth or soft tissue changes.
Thus the third molar plays, at the very least, a passive
role in the development of late lower arch crowding

• Bishara et al evaluated the changes in the
lower incisors between 12 and 25 years of
age and then re-evaluated the same
subjects at 45 years of age.
• Their findings indicated that there was an
increase in the tooth size-arch length
discrepancy with age.
• The average changes amounted to 2.7 mm
in males and 3.5 mm in females.
• These changes were attributed to a
consistent decrease in arch length that
occurred with age.

• Margaret Richardson in AJO 92

examined changes in the lower arch
crowding in young adults and showed that
between the ages of 18 and 21 years, the
lower arch is stable in terms of tooth
alignment and mesial drift, regardless of
third molar status or continuing
mandibular growth.


STUDIES RELATING THIRD MOLAR TO CROWDING

• Bergstrom and Jensen in 1961 examined

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•

sixty dental students, of whom thirty had
unilateral agenesis of the upper third molars,
twenty-seven had agenesis of the lower third
molar and three had one third molar absent or
lost.
They found that there was more crowding in
the quadrant with a third molar present than in
the quadrant with a third molar missing.
There was a mesial displacement of the lateral
dental segments on the side with the third
molar in the mandibular arch, but not in the
maxilla.

• They found no evidence of a correlation

between age and the degree of crowding
or mesial tooth displacement.
• Bergstrom and Jenson concluded that the
presence of a third molar appeared to
exert some influence on the development
of the dental arch but not to the extent
that would justify either the removal of
tooth germ or the extraction of third
molar.

• Vego in another study examined forty patients with
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•

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lower third molar present and 25 patients with third
molar congenitally absent.
Each individual arch was measured first after the
eruption of second molar at an average age of 13
years and second at an average age of 19 years.
Crowding was defined as loss of arch perimeter,
manifested as closure of space or by slipping of
contacts resulting in rotation or adverse movement
of teeth.
Vego found that all cases showed a decrease in arch
perimeter. The decrease was less noticeable in
persons without lower third molars.
Vego also indicated that there are multiple factors
involved in the crowding of the arch.

• According to Richardson in AJO 89 the Belfast
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•

third molar study produced further evidence in
support of the ‘pressure from behind’ theory.
A group of 51 subjects with intact lower arches and
bilateral third molars present were examined at
ages 13 to 18 years.
On average these cases had an increase in lower
arch crowding of slightly more than 1mm on each
side during the five-year observation period. In
some quadrants the crowding increased by as
much as 4mm.


• Molar space measured along the maxillary

•

•

horizontal as the distance between the distal
contact point of the first molar and the junction of
the ramus with the body of the mandible was also
examined.
The changes in molar space condition were
calculated by subtracting the size of second and
third molars from the measurement of molar space.
A significant correlation between increase in
anterior crowding and initial degree of molar
crowding was found suggesting that a person who
lacks adequate space in the molar region in early
permanent dentition is likely to show an increase in
crowding anterior to first molar in subsequent
years.

• They also showed that conditions in the

molar region were only partly responsible
for increased crowding.
• Mesial inclination of lower canine usually is
considered to be a sign that the buccal
segment has moved forward.
• Richardson also investigated the effect of
second molar extraction on the
development of late lower arch crowding
ands found that there was a slight
decrease in crowding (-1.5mm) and a slight
distal movement of first molar (-1.3mm).

STUDIES INDICATING LACK OF CORRELATION
BETWEEN THIRD MOLAR AND CROWDING
• Kaplan in 1974 compared pre-treatment, posttreatment and 10year post-treatment study models
and lateral cephalograms of 75 orthodontically
treated patients.
• Three groups with third molars erupted, impacted
and congenitally missing were compared. Kaplan
showed that some degree of lower anterior
crowding relapse occurred in majority of cases.
• He concluded that the presence of third molars
does not produce a great degree of lower anterior
crowding or rotational relapse after cessation of
retention.
• According to Kaplan the theory that third molars
exert pressure on the teeth mesial to them could
not be substantiated.

• Ades et al in AJO 1990 studied pretreatment,

posttreatment and postretention study models and
lateral cephalometric radiographs of 97 patients. The
subjects were divided into those with lower third
molar erupted, impacted, agenesis and extracted at
least 10 years before. The study showed that:
a. With time, mandibular incisor irregularity usually
increases whereas arch length and intercanine width
typically decreases
b. The persons with third molars erupted into
satisfactory function was not having a different
mandibular growth pattern than those with third
molars impacted or congenitally missing
• In majority of cases some degree of mandibular
incisor crowding took place after retention, suggesting
that the recommendation for mandibular third molar
removal with the objective of alleviating or preventing
long term mandibular incisor irregularity may not be
justified.

• Lifshitz in 1982 evaluated the effect of lower

•

premolar extraction versus non extraction as well
as the presence or absence of lower third molars
on mandibular incisor crowding.
He concluded that in all groups evaluated, there
was a significant increase in crowding, but there
were no significant difference between the groups
that did or did not have premolar extractions or
whether third molars were present or missing.


• In 1981 Little et al observed that 90% of

the extraction cases that were well treated
orthodontically ended up with an
unacceptable amount of lower incisor
crowding.
• These studies indicate that incidence of
mandibular incisor crowding increased
during adolescence and adulthood in
untreated as well as orthodontically treated
patients after retention is discontinued.


EXTRACTION OF THIRD MOLARS
The third molars need to be considered as
part of overall treatment planning, and this
may include a recommendation for
extraction.

The timing of extractions requires an
understanding of the various techniques
available.


EXTRACTION BEFORE TREATMENT
• It is not common practice for third molar
teeth to be enucleated before orthodontic
treatment of adolescents.
• Orthodontists are normally reluctant to
make surgical extractions a prerequisite of
providing treatment.
• They may feel that ramus growth and lower
third molar eruptive pattern cannot be
predicted, and take the view that the third
molars may erupt eventually.

• Those in favour of enucleation believe that many

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•

young adults between the age of 18 and 22 years
experience problems with their third molars and
that at later ages, pathologic changes often
occur.
Ricketts et al indicated that removal of the third
molar bud at the age of 7 to 10 years is
surprisingly simple and relatively atraumatic.
Schulhof recommended that enucleation should
be considered for any lower third molars which,
after careful diagnosis, had a greater than 50%
chance of impaction.
Enucleation is not, however, a generally accepted
procedure. Later caries experience, space
conditiond, and the effect of orthodontic
treatment are unknown at this early age.

LATERAL TREPANATION

• At about age 12 years ,the need for third

molar extraction may be more obvious.
• Conventional surgical removal of the
calcified crowns, at this age is difficult.
• The tooth rolls in its crypt with considerable
trauma to the adjacent tissues.
• There is also a risk of gingival damage,with
a pocket formation to the distal of the lower
second molars due to the U shaped
incision involved.

• Henry recommended a deep lateral

approach ,calling it ‘Lateral trepanation’ for
third molars in an early stage of partial
development.
• Burgess et al and Henry recommended
lateral trepanation as an easier technique,
with less complications and more rapid
healing.


EXTRACTION DURING TREATMENT

• If orthodontic treatment includes

orthognathic surgery to one or both jaws,
and third molars also require extractions,
surgeons prefer to do it at the same
operation.
• However, some prefer to remove lower third
molars 6 months before orthognathic
surgery,so that bone healing can occur in
the surgical site.

EXTRACTION AFTER ORTHODONTIC TREATMENT
• Extraction of third molar after orthodontic treatment
with a view to prevention of relapse should seldom
be necessary.
• Lindquist and Thilander in 1982 attempted to
determine the effect of the prophylactic removal of
mandibular third molars on the lower incisors.
• They extracted a third molar on one side at an
average age of 15.5 years and left the third molar on
the other side as a control.
• They measured study casts and cephalograms on
these patients 3 years postoperatively.
• They evaluated numerous parameters but were
unable to predict which patient would benefit from
such a procedure as both sides essentially had similar
changes.

• Southard et al in 1991 measured

proximal contact tightness between the
mandibular teeth in cases with bilateral
unerupted third molars.
• The measurements were taken before and
after the unilateral removal of one third
molar.
• They found that surgical removal of third
molar did not have a significant effect on
contact tightness.

• Pirttiniemi et al in 1994 evaluated the

effect of removal of impacted third molars on
24 individuals in their third decade of life.
• Dental casts were evaluated before and after
one year after extractions.
• They found that the extractions allowed for
slight distal drift of the second molar but had
no significant change in the lower anterior
area.
• From the available data it can be concluded
that third molars do not play a significant,
quantifiable role in mandibular anterior
crowding.

• Two consensus conferences were dedicated to the

1.

management of third molars ,one sponsored by the
National institute of Dental Research in 1979 and the
other by the American Association of Oral and
Maxillofacial Surgery in 1993. Points of the concensus
which were important to Orthodontics were:
Crowding of the lower incisors is a multifactorial
phenomenon that involves a decrease in arch length,
tooth size, shape and relationship, narrowing of the
intercanine dimension, retrusion of the incisors, and
growth changes occurring in adolescence.
Therefore, it was agreed that there is little rationale
based on the available evidence for the extraction of
third molars solely to minimize present or future
crowding of the lower anterior teeth.
If adequate room is available for third molar
eruption, every effort should be made to bring these
teeth into functional occlusion.

2. Orthodontic therapy, in both maxillary and
mandibular arches, may require posterior
movement of both first and second molars by
either tipping or translation, which can result in
the impaction of third molars.
To avoid impacting third molars and to facilitate
retraction, it may be deemed advisable in some
cases to remove third molars before starting
retraction procedures.
3. There is no evidence to suggest that a third molar
is needed for the development of the basal
skeletal components of the maxilla and mandible.

4.There was agreement that postoperative pain,
swelling, infection, and other possible
consequences of surgery are minimized when
surgery is performed in patients who are dentally
young, as judged by the third molar roots being
about two thirds developed.
• As a result, it is important to instruct the clinician in
recognizing the benefit of early removal of third
molars in those cases in which extraction is
definitely indicated.
5. Although there are orthodontic reasons for the
early removal of third molars, the consensus was
that enucleation of third molar buds based on
measurements obtained at age 7 to 9 years is not
acceptable.
This is because the present predictive techniques
for third molar eruption or impaction are not highly
reliable and should be used with caution.

6.Patients should be informed of potential
surgical risks including any permanent
condition that has an incidence greater
than 0.5% or any transitory condition that
occurs with an incidence of 5% or more.
On this basis, patients should be
informed about hemorrhage, pain, swelling,
alveolar osteitis, trismus, and nerve injury.


• Bonding techniques allow placement of fixed lower

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retainer which allows stabilization of lower
incisors, while awaiting further development of
third molars.
Bonding techniques also allow uprighting of some
third molars.
Thus the case for ‘wait and see’ with third molars
is stronger than it was, and the case for
extractions has become weaker.
Kahl et al who carried out a long term
radiographic follow up of asymptomatic impacted
third molars recommend every 2 year radiographic
review of former orthodontic patients.

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