Importence of lower incisor position in treatment plan

IMPORTANCE OF LOWER
INSICOR POSITION IN
TREATMENT PLANING
www.indiandentalacademy.com

INTRODUCTION
 For nearly two decades Dr Charles.H.
Tweed through his experience found out
that the axial inclination & position of the
mandibular incisor has been regarded as
a factor of primary importance in the
attainment of facial esthetics
 But now over the years there has been a
progression towards more precise
definition of stability in incisor positioning
based on 3 important factors - facial
esthetics,lip protrusion & perioral
function. www.indiandentalacademy.com

INCISOR POSTION AND
FACIAL ESTHETICS
 Aligning dentoalveolar segment alone does
not plays an important role in achieving
facial esthetics.
 Dentoalveolar segment and soft tissue
covering are the important factors in
achieving facial esthetics.
 Considering Ricketts concept in lower incisor
position 3 clinical situations can taken into
account

SOFT TISSUE PROFILE
 Thick upper & lower
lips extreme lip
protrusion with a
thin soft tissue
covering the chin
accentuates the lip
protrusion.

SOFT TISSUE PROFILE
 Average lip
protrusion and
average soft tissue
facial convexity.

SOFT TISSUE PROFILE
 Retrusive lip that are
also thin in relation
to the thickness of
the soft tissue in the
chin area.

SOFT TISSUE PROFILE
 Normal profile shows a facial convexity
(glabella-subnasale-soft tissue pogion) of
13 degree. Upper & lower lip protrusion is
measured in relation in relation to the
subnasale-pogion line, which offers the
advantage of not being directly associated
with the nose. The upper lip protrudes
3.5mm and the lower lip protrudes
3.0mm. This measurement of lip
protrusion remains relatively stable ,
reduces only slightly with the age.

Tweed’s facial esthetics(1954)
 Charles.H.Tweed with
his clinical experience
found out a
cephalometric norms in
relation to lower incisor
angulation in relation to
-FMA-25 degree.
-FMIA-65 degree.
-IMPA-90 degree.

Rickett’s lower incisor position
(1957)
 A-pog line used as
references line.
 In an average lower incisal
was located approximately
0.5mm anterior to the
reference line.
 Angular measurement-a line
through the long axis of the
lower to the A-pog plane-
incisor inclined at an
average of 20.5 degree.
 E-plane-upper lip 1.0mm
posterior , lower lip 0.3mm
ahead.

Bell, White & Profit norms
 Lower incisor to A-pog
- Angular measurement- 24+5
-Linear ,, -3mm(males)
1mm(females).
-L 1 to Mandibular plane angle-95+7
degree.

Burstone
 Lower incisor to mandibular plane
angle-95.9+5.2 degree.

Down’s analysis
 Lower incisor to
mandibular plane-
91.7+4 degree.

MCNAMARA ANALYSIS
 Mandibular lower
incisor to A-Pog
line-1-3mm.

Steiner analysis
 Lower incisor to NB-
4mm & 25 degree.

Rotation of Mandible and Incisor
Compensation
 Growth of jaws creates a space into
which the teeth erupts . The rotational
pattern of jaw growth obviously
influences the magnitude of tooth
eruption. It can also influences the
direction of eruption and the ultimate
anterior-posterior of the incisor teeth.

Rotation of Mandible and Incisor
Compensation
 Internal rotation of mandible.
 Upward & forward of mandible.
 Results in eruption of incisor posteriorly.
 Molar migrates mesially.
 Decreases in arch length.

Incisor Compensation in Short
Face individuals
 Excessive rotation .
 Incisor tend to be
carried into
overlapping position.
 Results in deep bite.
 Displacing them
lingually results in
crowding.

Incisor Compensation in Long
Face individuals
 Clockwise rotation of
mandible.
 Result in open bite
due to lack of over
eruption in incisor
region.
 Proclination of
incisors.

Skeletal Discrepancy & Incisor
Compensation.
 Cephalo-caudal growth determines the rate of
growth of maxilla & mandible which normally
leads to Cl-I skeletal relationship where maxilla
stops its growth earlier than mandible and
controls the mandibular growth by safety value
mechanism and accordingly the dentition
undergoes a stable adaptation. In a situation
where maxilla & mandible is altered and not in
concurrent with each other which can lead to
clinical situation like Cl-III,Cl-II for this condition
the anterior segment arch undergoes
compensation.

Cl-III Situation
 Prognathic mandible
and retrognathic
maxilla, the upper
incisor lean labially
more than average and
lingual inclination of the
lower incisor for
compensation of
prognathic denture
base relationship.

Cl-III Situation
 Normal maxilla with
prognathic mandible,
the upper incisor
position and axial
inclination are normal
but the lower incisor
usually lean lingually for
compensation of
prognathic denture
base relationship( tight
lower lip will tend to
retruded the lower in
lingual).

Cl-II Situation
 Prognathic maxilla
and retrognathic
mandible.
 Lower incisor are
flared and the upper
incisor are
retruded ,this dental
compensation result
in proclination of
normal over jet.

Cl-II Situation
 Normal maxilla and
retrognathic
mandible.
 The angulations and
position of the upper
incisor are normal
but the lower incisor
are proclined labially
to establish normal
over jet.

Order of frequency of congenitally
missing teeth
 Maxillary & Mandibular 3rd
molar.
 Maxillary lateral incisor.
 Mandibular 2rd premolar.
 Mandibular incisor.
 Maxillary second premolar.

Lower extraction
 Extraction of teeth to resolve
crowding has been an accepted
treatment strategy for decades.
Non-extraction therapy in crowded
cases is usually thought to lead to
post retention relapse.

Indication for incisor extraction
(Albert Owen)
 Cl-I molar relationship.
 Moderately crowded lower incisor.
 In cases of bone loss, periodontitis & fracture.
 Mild or no crowding in upper arch.
 Acceptable soft tissue profile.
 Minimal to moderate over bite & over jet.
 Minimal growth potential.
 Missing lateral incisor or peg laterals.
 Mandibular tooth material excess.

Contd
 Witzel found that premolar extraction had less
tendency to become crowded then patient
treated non extraction. He found no signifant
corelation between pretreatment and post
retention incisor alignment and no significant
corelation between stability and changes in
mandibular incisor changes in mandibular
position or angulation.
 Kokich and Shapiro believe that in case
selection for intentional extraction of
mandibular incisor can simplify orthodontic
mechanics and enhances both theocclusal
and cosmetic results of treatment.

Contd
 Riedel has suggested that in patient with
severely crowed mandibular arches the
removal of 1 or more mandibular incisor is
only the logical alternative which may allow
for increased stability of the mandibular
stability of the mandibular anteriors without
retention and in mainting arch form without
expansion of inter canine width when
compared with non extraction and premolar
extraction.

Disadvantages of incisor extraction
 Disturbances in occlusion.
 Reopening of extraction spaces.
 Increased overjet.
 Increased overbite.

Methods for eliminating over jet in
lower incisor extraction cases
 Extraction of upper 4s &lower incisor
result in good occlusion.
 In case of unilateral extraction of incisor
the molar on the affected side will be in
Cl-I or Cl-III relationship.
 In case of unilateral missing incisor it is
advisable to avoid extraction in that
quadrant and use canine as an incisor.

Lower central incisor tip & torque
values of various PAE systems
 Andrews- 2/-1
 Roth- 2/-1
 Alexander- 0/-5
 Burstone- 0/-1
 Hilgers- 0/-1
 Ricketts- 0/0
 Bench- 2/-1
 Level anchorage- 2/0
 Hasund - 0/0
 Cetlin- 0/0
 Orthos - 2/-5
 MBT- 0/-6

Lower lateral incisor tip & torque
values of various PAE systems
 Andrews- 2/-1
 Roth- 2/-1
 Alexander- 0/-5
 Burstone- 0/-1
 Hilgers- 0/-1
 Ricketts- 0/0
 Bench- 2/-1
 Level anchorage- 2/0
 Hasund - 0/0
 Cetlin- 0/0
 Orthos - 4/-5
 MBT- 0/-6

Prevention of lower incisor
flaring during treatment
 Functional appliances
-Incisal capping
-Avoid acrylic contact on lingual surface of
lower incisor.
 With fixed appliance.
-Torque incorporated arch wires.
-5 degree torque.
-filling the slot by full size arch wire.

Prevention of lower incisor
flaring during treatment
 Fixed appliances
-Avoid looped arch wires.
-Avoid long term use of Niti,Cu niti.
-Reverse torqueing auxillaries.
-Lace back.
-Cinch back of arch wires.
-Rectangular arch wire.
-Segmental mechanics.
-Filling the slot by full size arch wire.

Lower incisor position
and stability
Raleigh williams(1986-JCO)
Six keys in eliminating lower retention

FIRST KEY
 The incisal edge of the lower incisor should be placed
on the A-P line or 1 mm in front of it. This is the
optimum position for lower incisor stability .It also
creates optimum balance of soft tissues in the lower
third of the face for all the variations in apical base
differences within the normal range.
 The angulation of lower incisors has not proven to be
relevant to their stability. A lower incisor angulation of
90° to the mandibular plane, or 65° to the Frankfort
plane, may be esthetically appropriate and stable for
those who have optimal Northern European skeletal
configurations, but not for members of other ethnic
groups.

Contd
 Appliance control is required to achieve optimal
position of the lower incisor consistently at the end of
treatment. Point A on the upper end of the A-P line can
be retracted. Point P, at the lower end, will move
forward or not depending on mandibular growth. With
experience, the clinician will know how each end of this
line changes, which procedures will place the lower
incisor 1 mm in front of the line, whether extractions
are necessary, and which teeth should be extracted.
 If the lower incisor is advanced too far beyond the A-P
line, relapse and crowding will occur. Lower incisors
that are overly proclined in treatment— beyond one
standard deviation— can only be maintained in such
an untenable position with a fixed retainer. When the
retainer is removed, the incisors will move lingually and
become crowded. www.indiandentalacademy.com

Second key
 The lower incisor apices should be spread
distally to the crowns more than is generally
considered appropriate and the apices of the
lower lateral incisors must be spread more
than those of the central incisors. The Begg
technique is geared to achieve the necessary
progressive spreading, but none of the
current straightwire systems provides
adequate lower incisor slot angulations to
bring about sufficient progressive spreading
of lower incisor apices. When the lower
incisor roots are left convergent, or even
parallel, the crowns tend to bunch up and a
fixed lower retainer is usually needed to
prevent post-treatment relapse.

Third key
 The apex of the lower cuspid should be
positioned distal to the crown.
 This angulation of the lower cuspid is important in
creating post-treatment incisor stability because it
reduces the tendency of the cuspid crown to tip
forward into the incisor area. If this happens, the
lower incisors crowd up, even if their roots are
spread and the incisal edges are on the A-P line
or 1mm in front of it. Distal inclination of the lower
cuspid should be a standard treatment objective
and is easily accomplished with the Begg or any
straightwire technique.

Fourth key
 All four lower incisor apices must be in the same labiolingual
plane . Spreading the apices of the lower incisor roots distally
causes a strong reciprocal tendency for the crowns to move
mesially. Moreover, as the roots are spread, the contact areas
between the incisor crowns move upward toward the anatomical
contact points, which are small, rounded, and near the incisal
edge. Because of the strong mesial pressure on the crowns
during the root spreading process, there is a tendency for these
contact points to displace each other labiolingually. This results
in a reverse movement of the apices linguolabially.
 The displacement forces are considerably augmented by the
increasing width of the lower incisor crown toward the incisal
edge and contact point. This means that provision for the
additional space must be made during the spreading process.
Otherwise, labiolingual apical displacement of the lower incisors
will tend to occur, and the degree to which it occurs will affect
lower incisor posttreatment stability.

Contd
 Experience has shown that the labiolingual apical
displacement of the lower incisors can occur easily if
round wires are used during the spreading process.
To maintain labiolingual apical control during the
spreading process— using uprighting springs in the
third stage of Begg treatment— an edgewise
sectional auxiliary in the incisor region along with the
main round archwire is effective. With the edgewise
technique, spreading begins at the start of treatment,
so any labiolingual apical displacements occurring
from the initial use of round wires can be corrected
later when rectangular arches are used.

Fifth key
 The lower cuspid root apex must be positioned
slightly buccal to the crown apex. This is extremely
important because of its influence on post-treatment
stability. All sorts of occlusal forces await their
chance to exert lingual pressure on the lower cuspid
crown. If the apex of the lower cuspid is lingual to the
crown at the end of treatment, the forces of occlusion
can more easily move the crown lingually toward the
space reserved for the lower incisors because of
these functional pressures plus a natural tendency for
the crown to upright over its root apex. Even if a
lower cuspid with abnormal lingual position of the
apex were supported for many years with a fixed
retainer, the crown would eventually move lingually
when the restraint was removed.

Sixth key
 The lower incisors should be slenderized as needed after
treatment. Lower incisors that have sustained no proximal wear
have round, small contact points, which are accentuated if the
apices have been spread for stability . Consequently, the
slightest amount of continuous mesial pressure can cause
various degrees of collapse in the lower incisor segment.
 There are two sources for post-treatment pressure on the lower
incisors that may bring about a shifting or collapse even though
all other key treatment requirements have been accomplished.
One source is the molars. Current evidence indicates that
natural mesial pressure is limited to the upper and lower molars.
Molar pressure can cause displacement of lower incisor contact
points. Removal of third molars does not eliminate the mesial
pressure derived from the first and second molars, and "there is
little rationale, based on present evidence, for the extraction of
third molars solely to minimize present or future crowding of
lower anterior teeth".

Contd
 The second source of hidden pressure
is an adverse tooth-jaw relationship.
 Flattening lower incisor contact points
by slenderizing or stripping creates flat
contact surfaces that help resist
labiolingual crown displacement. This
treatment also helps eliminate the need
for lower incisor retention .

Occlusal forces in stability of incisor
 Depending on the axial inclination and
position of the incisor different effects
are produced.
-incisal force through the centre of
resistance
-lingual force anteriorly to the incisor.
-lingually directed biting forces passes
superior to the centre of resistance.

Mandibular incisor school of thought
 Grieve &Tweed suggested that the
mandibular incisor must be kept upright
over basal bone.

BASIC THEOREM-6
 If the lower incisor are placed upright
over basal bone, they are more like to
remain in good alignment.
 Attention should be directed to the
proper angulation and placement of the
mandibular segment.

BASIC THEOREM-9
 Arch form ,particularly in the mandibular
arch, cannot be permantly altered by
appliance therapy. Therefore treatment
should be directed towards maintaing
the arch form presented by the
malocclusion as much as possible.

Conclusion
 Modification of the facial profile by
orthodontic means depends on other
factors besides inclination of anterior
teeth, diagnostic criteria based solely
on this factor are likely to be unreliable.

Importence of lower incisor position in treatment plan

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