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Introduction: With many advances in orthodontic and
surgical techniques, more focus has shifted toward the incisors position planning
as a starting point. Today, instead of using the molars as a starting point,
the incisor position based treatment planning is possible. Then the treatment
mechanics can be planned to position the incisors ideally, around which all the
other teeth will fit subsequently. Controlled upper incisor tooth movement is
needed to achieve the treatment goal. It is helpful to consider the upper arch
in isolation when planning treatment mechanics to position the upper incisors
at planned position. The purpose of this article therefore is to emphasize the
key aspects of diagnosis and treatment planning of incisor positioning in all
the three plane of spaces.
Conclusion: The majority of the orthodontic cases
require changes in incisor position. It is helpful first to plan the upper
incisor corrections and second to plan the lower incisor corrections. Having
decided on an incisor position for a case will allow more clear and systemized
organization of treatment mechanics.
Keywords: 3D planning, Incisor position, PIP
INTRODUCTION
In late 1920s Angle introduced his
classification which was primarily focused on molar relationship. In that
period the treatment of choice was generally non-extraction and expansion. In
1940s, Tweed [1] emphasised more on extraction treatment plan and his concern
was more on lower incisors position. At that time surgical correction or
functional appliance was not available therefore there was more emphasis on the
lower incisors, with minimized emphasis on the upper incisors [1]. Today,
treatment planning can be done on the position of the upper incisors, instead
of using the molars or the lower incisors as a starting point. At the start of
treatment planning, it is possible to envision an ‘ideal’ position for upper
incisors [1].
ANTERO-POSTERIOR
PLANE
Steiner’s sticks
The basal discrepancies are compensated by
position of the teeth and if there is not adequate compensation of these
discrepancies the position of incisors influences the position of lips.
Steiner’s expressed the sagittal relation of
the jaws by using ANB angle.
According to him the position of upper and
lower incisors changes as ANB angle changes (Figure 1).
For 1 degree change in ANB angle 1 mm and 1
degree change in upper incisors-NA and 0.25 mm and 1 degree for lower
incisor-NB is seen.
Steiner acceptable compromises indicate how
it is possible to adjust the position of the upper and lower incisors to the
size of the ANB angle and at the same time maintain a normal over jet and
overbite. Find the position of the incisor that best compensates a basal
sagittal discrepancy which is only indicated with positive ANB angle [1,2].
Planned incisor
position
Definition of PIP: The intended end of treatment
position for upper incisors (Figure 2).
How the PIP is
determined for a case?
For determination of PIP three questions
should be asked:
·
What is the ideal position for the upper
incisors in the face in terms of A/P position, torque and vertical positioning?
·
Can ideal upper incisor position be
achieved?
·
If not, can an acceptable incisor position
be achieved by orthodontics alone or is it necessary to consider maxillary
surgery?
In such a way, for a case PIP is determined.
Realistic treatment goal changes from case to
case. In some cases, perceived ideal upper incisor position can become PIP
whereas in other cases the perceived ideal position of incisors has to be
compromised. These cases include less cooperative patients or patients with
less growth potential. Then a PIP has to be accepted which is not ideal, but
which is acceptable for the case [1].
Anchorage need: By comparing the starting
position of upper and lower incisors with PIP at the end of treatment the
anchorage control needs of a case can be determined. It can be determined early
in the treatment. During tooth leveling and aligning, the anchorage control
should be managed to ensure that the upper and lower incisors either show no
change or they should move favorably relative to PIP. Ideally, throughout
leveling and aligning incisor movement should be favorable, relative to PIP; so
that the amount of tooth movement needed later in the treatment will be
reduced.
A/P changes are most commonly concerned, but
torque control and vertical issues need to be considered as well and properly
managed, where appropriate.
Dental VTO can be used to predict the
anchorage needs for the molars and canines. These teeth should show no change,
or preferably favorable change, relative to the VTO requirements. Every
orthodontic case will be different, and the anchorage control needs will be
determined by the position of the incisors relative to PIP and not by the
Angle's classification of the molars [3,4].
PIP components in
class II cases
The four-stage treatment planning process.
During treatment planning, these four stages
should be considered:
Stage 1 - Setting a PIP for the upper
incisors
Stage 2 - The lower incisors
Stage 3 - The remaining lower teeth
Stage 4 - The remaining upper teeth
Treatment for each case, in the upper
incisors for having correct A/P and vertical positioning with appropriate torque
it is necessary to set a PIP as a treatment goal.
It consists of 3 components:
·
A/P component
·
Torque Component
·
Vertical Component
A/P component: The upper incisor A/P position in
relation to the A-Po line has a conventional cephalometric value of +6 mm. In
Arnett analysis the upper incisor position to a True Vertical Line (TVL) is
measured, in which the linear measurement from the lip of the upper incisor to
the true vertical line is calculated. The male upper central incisor tip is ideally
-12 mm to the line and the female is at -9 mm [5-7].
Torque component: Traditionally in orthodontics
upper incisor torque has been related to the maxillary plane, with a
cephalometric value of 110° to 115° being a typical goal. The Arnett analysis
relates upper incisor torque to the maxillary occlusal plane and lower incisor
torque to the mandibular occlusal plane [5-7].
The male upper central incisor torque being
ideally 58° and the female 57°.
PIP components in
class III cases
The four-stage treatment planning process.
During treatment planning of class III cases,
these four stages should be considered:
Stage 1 - Setting a PIP for the upper
incisors
Stage 2 - The lower incisors
Stage 3 - The remaining upper teeth
Stage 4 - The remaining lower teeth
This involves deciding what would be the
ideal position for the upper incisors. Is this achievable? If not, can
orthodontic tooth movements be used to reach a position which is less than
ideal, but acceptable? Or will maxillary surgery be needed to reach an acceptable
upper incisor position? In this way, a PIP (planned incisor position) for the
upper incisors can be established.
The first stage in Class III treatment
planning concerns upper incisor position. It is necessary to determine an ideal
position and then decide whether it can be achieved. If not, a modified
position may be appropriate, which is less than ideal, but acceptable. In this
way a ‘planned incisor position’ or PIP, is determined.
The second stage of treatment planning
involves positioning of the lower incisors. This is frequently a key concern in
Class III cases with mandibular excess. The answer may be ‘possibly, but there
is concern about future growth, and it is preferable to wait for this to
express itself’.
The third stage in Class III treatment
planning involves deciding on treatment mechanics to position the rest of the
upper teeth correctly to fit the PIP for the upper incisors. The dental VTO
will confirm the required movement of molars and canines.
The final stage of Class III treatment
planning includes assessment of lower arch crowding or spacing and decide how
to position the rest of the lower teeth to fit the planned lower incisor
position.
In some Class III marginal extractions case,
second molars may be considered (Table
1).
Facial tetragon
Fastlight in
June 2000, presented a discussion on the facial ‘tetragon’ consisting of four
angles (Figure 3) [4].
·
Upper incisor
to palatal plane
·
Lower incisor
to mandibular plane
·
Inter-incisal
angle
By dividing the
tetragon in half, two triangles are formed.
The upper
triangle has angles as follows (Figure 4):
1.
Palatal plane
to occlusal plane
2.
Upper incisors
to palatal plane
3.
Upper incisors
to occlusal plane
The lower
triangle has angles as follows (Figure 5):
1. Mandibular
plane to occlusal plane
2. Lower
incisors to occlusal plane
3. Lower
incisors to mandibular plane
Envelope of discrepancy
The maximum
amount of movements possible by three different means of treatment is given by
Epker envelope discrepancies. The perimeter of each envelope gives the maximum
range of movements possible by different methods of treatment. The three
envelopes given by Epker are described in Table
2.
The potential for retraction is more than proclination of teeth. The growth modification envelope for the two jaws is the same as the growth of maxilla cannot be modified independently of mandible. The Surgery to move the lower jaw back has more potential than surgery to advance it (Figures 6 and 7) [8-11].
Planned incisor position:
PIP components in Class II cases.
Treatment for
each case, in the upper incisors for having correct A/P and vertical
positioning with appropriate torque it is necessary to set a PIP as a treatment
goal.
It consists of
3 components:
·
A/P component
·
Torque
component
·
Vertical
component
The Arnett
analysis calculates the vertical positioning of upper incisors. In this
analysis an overbite of 3 mm is required, upper incisor exposure should be 4 mm
below the relaxed upper lip in males and 5 mm in females. In class 11/2
malocclusion cases the high lip line is a contributory factor. In such cases
there is a need to procline and intrude upper incisors to assist in stability.
Envelope of discrepancy
The ideal
position of the upper and lower incisors has shown by the origin of the x and y
axes. There is more potential for extrusion (correction of open bite) than
intrusion (correction of deep bite). The growth modification envelope for the
two jaws is the same as the growth of maxilla cannot be modified independently
of mandible. The potential of surgery to extrude is more than surgery to
intrude (Table 3) [9-11].
Transverse plane
Midline discrepancies: One
of the most important diagnostic features in orthodontic treatment planning is
maxillary midline position. Maxillary midline position is done relative to
facial midline, any deviation of this midline is considered abnormal. Often the
patients which are undergoing orthodontic treatment presents with the midline
deviation so in orthodontic diagnosis the extent of deviation is measured from
the soft tissue midline, presumably because an objective will be for the two
midlines and the mandibular midline to be coincident after the treatment [12,13].
The facial
landmarks such as the nose, philtrum and chin are often used as references for
maxillary midline positioning, may not themselves be centered on the face or
with each other. Because the location of these midline landmarks are not
generally altered as a result of orthodontic treatment, it would be useful to
know their relative importance for determining optimum esthetic goals for
positioning of the dental midline. According to Arnett and Beggman the philtrum
is usually a reliable midline structure and can be used as the basis for
midline assessment [14,15].
Diagnosis of midline discrepancies
In each patient
an appropriate database for detection of midline asymmetries should be
assembled to aid in making an appropriate diagnosis of the nature; extent; and
location of the midline asymmetry. A detailed facial and intra-oral examination
should be done; intra- and extra-oral photographs or video; dental models
trimmed to centric relation occlusion; an occlusogram; a lateral cephalogram; a
posteroanterior cephalogram; panoramic radiograph; and a submentovertex
radiograph should be used for a thorough diagnosis. This thorough examination
will aid in the visualization of the facial and the dental midlines; as well as
their inter-relationship [7].
There are six
important midlines that must be determined [16-18]:
·
Facial midline
·
Skeletal
midline
·
Maxillary
apical base midlines
·
Mandibular
apical base midlines
·
Maxillary
dental midlines
·
Mandibular
dental midlines
DETERMINATION OF TREATMENT PLANNING
The first thing
to be done in planning the treatment and mechanics is selection of a treatment
midline. The final goal is represented by this midline. The treatment midline
may coincide with either the upper or lower dental midlines or in sudden
instances both upper and lower midlines may have to be moved to make them
coincident with the facial midline [17].
In cases where
both upper and lower dental midlines are coincident but the upper and lower
soft tissue/skeletal midlines are not then the treatment midline should be
assessed along with surgical alternatives [17].
Often apical
base discrepancies are associated with asymmetric left and right molar
occlusion so the apical base midline asymmetries require careful attention
during the treatment planning process. If the apical base discrepancy is up to
2.0 mm; it is advisable to select either the upper or lower midline; whichever
is closest to the facial midline as a treatment midline for larger apical base
discrepancies; both upper and lower midlines may need correction [18].
Apical base
midline discrepancy may be present with or without tipping of the incisors if
both apical base midline discrepancy and tipped incisors are involved; the
treatment mechanics should make adjustments for the treatment of two separate
problems [18,19].
CONCLUSION
§ Possibility
of each type of treatment is not symmetric with respect to plane of space. For
example tooth movement by orthodontic means alone is more possible
antero-posteriorly than vertical direction.
§ Growth
modification is more effective in mandibular deficiency (10 mm) than mandibular
excess (5 mm).
1. Mchlaughlin B (1961) Systemized
orthodontic treatment mechanics. Trevisi: MOSBY CO.
2. Steiner CC (1960) The use of
cephalometrics as an aid to planning and assessing orthodontic treatment. Am J
Orthod 46: 721-35.
3. Servos JM (1971) Derivation of
acceptable arrangements in the Steiner’s analysis. Am J Orthod 41: 146-149.
4. Fastlight J (2000)Tetragon: A
visual cephalometric analysis. J Clin Orthod 34: 353-360.
5. Arnett GW, Jalic JS, Kim J (1999)
Soft tissue cephalometric analysis: Diagnosis and treatment planning of
dentofacial deformity. Am J Orthod Dentofacial Orthopedics 116: 239-253.
6. Arnett GW, Bergman RT (1993)
Facial keys to orthodontic diagnosis and treatment planning - Part I. Am J
Orthod Dentofacial Orthopedics 103: 299-312.
7. Arnett GW, Bergman RT (1993)
Facial keys to orthodontic diagnosis and treatment planning - Part II. Am J
Orthod Dentofacial Orthopedics 103: 395-411.
8. Bennett J, McLaughlin RP (1997)
Orthodontic management of the dentition with the pre-adjusted appliance. Isis
Medical Media: Oxford, pp: 233-250.
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Diagnosis and treatment planning. In: Graber TM and Swain BF, Eds. Current
Orthodontic Concepts and Techniques, Chapter 1: Mosby, St. Louis, pp: 3-100.
10. Bailey LJ, Proffit WR, White R Jr.
(1999) Assessment of patients for orthognathic surgery. Semin Orthod 5:
209-222.
11. Proffit WR (2007) Contemporary
orthodontics. 4th Edn. Mosby, St. Louis, pp: 107-129; 689-691.
12. Beyer JW, Lindauer SJ (1998)
Evaluation of dental midline position. Semin Orthod 4: 146-152.
13. Kronmiller JE (1998) Development
of asymmetries. Semin Orthod 4: 134-137.
14. Brunetto AR (2015) Orthodontic
retreatment of a class III patient with significant midline asymmetry and
bilateral posterior cross-bite. Dent Press J Orthod 20: 118-126.
15. Lee JK, Jung PK, Moon CH (2014)
Three-dimensional cone beam computed tomographic image reorientation using soft
tissues as reference for facial asymmetry diagnosis. Angle Orthod 84: 38-47.
16. Sanders DA, Chandhoke TK, Uribe
FA, Rigali PH, Nanda R (2014) Quantification of skeletal asymmetries in normal
adolescents: Cone-beam computed tomography analysis. Prog Orthod 15: 26.
17. Burstone CJ (1998) Diagnosis and
treatment planning of patients with asymmetries. Semin Orthod 4: 153-164.
18. Van Steenbergen E, Nanda R (1995)
Biomechanics of orthodontic correction of dental asymmetries. Am J Orthod 107:
618-624.
19. Pair J (2011) Movement of a
maxillary central incisor across the midline. Angle Orthod 81: 341-349.
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Table 1 -
Table 2
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Table 3
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