preorthodontic biomechanics of different forms of severe malocclusion is explained before doing orthognathic surgery

1. Biomechanics and treatment
of dentofacial deformity
Part 1
dr Maher FOUDA
Faculty of Dentistry
Mansoura Egypt
Professor of orthodontics

2. Patients in need of significant dentofacial skeletal changes
involving surgery, distraction
osteogenesis, and implants require detailed work-ups and
treatment planning. The problem
list should be specific so all problems can be addressed.
The ideal goal list must be narrowed
to the final practical goals. The biomechanics of leveling in
a patient requiring surgical
mandibular advancement can influence the final outcome.

3. The decompensation of axial
inclinations necessary to achieve desirable surgical
changes is limited by orthodontic tooth
movement considerations. The use of bone plates
solves many of these problems, and their
use and biomechanical principles involved are
discussed in this chapter.

4. The biomechanics
of combined orthodontic and orthognathic surgery for
difficult cases such as open bites,
facial asymmetries, and stable skeletal width expansion are
also explored. In addition, considerations
for selecting bone or tooth anchors are presented.

5. Surgical patients are not
always stable, and the role of muscle and soft tissue
factors must be considered in order to
achieve the best stability. If the surgery fails to
obtain the established goals, the solution
may be immediate intervention after surgery.

6. Algorithm outlining
the process of developing
a treatment plan.

7. Special considerations in treatment planning are required
for orthodontic patients in need of surgery.
These considerations are usually tailored for the
specific type of treatment. In all patients, however,
a series of diagnostic procedures is conducted to establish
a database from which a problem list can be outlined.

8. This will usually include the following:
• A primary complaint
• Medical and dental history with any associated
psychologic issues
• Facial and soft tissue problems
• Skeletal problems, which can be further subdivided
into:
– Anteroposterior (AP) discrepancies
– Vertical discrepancies
– Transverse discrepancies
• Dental problems

9. After the problem list is reviewed, an essential
component of treatment planning involves prioritizing
this list to ensure that the clinician can identify
the most important issues. It is essential that this
prioritization process is developed in close consultation
with the patient.

10. Often treatment plans are
developed that do not address each problem, and it
should be clear from the outset which issues need to
be addressed ahead of other issues to improve the
likelihood of satisfying the patient’s desires.

11. Once the prioritized problem list has been established,
the clinician should develop a series of ideal
goals associated to address each problem. Often it
is impossible to achieve each ideal goal, so several
treatment options are usually explored with modified
goals and relative advantages and disadvantages.
This is a complex process that necessitates full
engagement of the patient and wisdom from the
treating practitioner .

12. In combined surgical-orthodontic treatment, it is
necessary to have a series of guidelines to establish
optimal facial form and dental esthetics. It is possible
to reorient the skeletal and dental structures to ideal
positions, and there are many mechanisms that can
assist the practitioner and patient in decision making.

13. A sequence of processes should be considered:
1. AP projection of the midface
2. Vertical position of the maxillary incisor
3. AP position of the maxillary incisor
4. AP position of the mandible
5. AP position of the mandibular dentition
6. AP and vertical position of the chin
7. Transverse relationship of the maxilla, zygomatic
projections, gonial angles, and chin
8. Maxillary arch width

14. A number of methods have been employed to
assist the clinician in decision-making related to reorientation
of the hard and soft tissue structures.
Routine anthropometry and cephalometrics can
be utilized and compared with historical norms.
A Moorrees mesh
diagram superimposed
over a cephalometric
radiograph to act as a
guide for planning
surgical and dental
movements. The relative
proportions of the jaws
can be compared
with the norm.

15. These cephalometric analyses can be utilized in
template form, such as the Bolton standards or
Moorrees mesh diagram, and overlaid in two di-
mensions to appraise facial form and establish
morphologic goals.
A Moorrees mesh
diagram
superimposed over
a cephalometric
radiograph to act as
a guide for planning
surgical and dental
movements. The
relative proportions
of the jaws can be
compared
with the norm.

16. More sophisticated
three-dimensional (3D) facial masks of average faces
can also be overlaid on a photograph of the patient’s
face or skeleton to identify any deviations.
As with any type of analysis, these masks
can be customized for age, sex, and facial width and
height and can be modified according to numerous
possible parameters.
Comparison of a
patient’s face in
three dimensions (a)
with a constructed
normalized face (b).

17. Once specific treatment goals have been identified
and outlined for a treatment plan, it is essential
for the clinician to progress through a systematic
plan of dental and skeletal movements.

18. The ultimate goal of treatment for any dentofacial
deformity is ideally to place the skeletal structures
(maxilla, mandible, and chin) in the optimal
positions to reflect an ideal soft tissue form. For this
to be achieved, it is often necessary to place the
maxillary and mandibular teeth in the ideal position
within their respective jaws in all three dimensions.

19. Teeth have been demonstrated to compensate in all
three dimensions in patients with aberrant skeletal
jaw base relationships. In Class II skeletal patterns,
the mandibular teeth often compensate forward
and procline while the maxillary teeth may compensate
backward and retrocline .
Frequently encountered decompensations
include the need to retract the
mandibular incisors (a) or procline the
maxillary
incisors (b) in patients with Class II
skeletal problems, retract the maxillary and
procline the mandibular incisors in patients
with Class III skeletal problems (c), and intrude
the incisors in open bite patients (d).

20. Conversely,
in Class III skeletal patterns, compensations are
characterized by maxillary incisor proclination and
mandibular incisor retroclination. In the transversely
narrow maxilla, the mandibular posterior teeth
tend to compensate by tipping lingually, while the
maxillary teeth may compensate by tipping buccally
Transverse compensations for a narrow maxilla with buccally
tipped maxillary posterior teeth and lingually tipped mandibular
posterior teeth.
Class III skeletal patterns

21. It has been shown that the objective
of removing all compensation in three dimensions
is generally difficult to achieve in most combined
surgical-orthodontic patients due to structural and
biomechanical limitations. This invariably results in
a less than ideal relationship of the skeletal structures,
which may lead to slight deviations from
ideal facial form.

22. If the teeth are inadequately decompensated,
adjunctive surgical procedures such
as genioplasty or maxillary autogenous or synthetic
onlays may be required.
Dental relationship before orthodontic
treatment
Dental relationship after surgery Unilateral cross-bite
Dental relationship after orthodontic
decompensation. (Exaggerated
reverse overjet visible)

23. Therefore, the following objectives should be considered
in the treatment-planning stage:
1. Identify a treatment occlusal plane around which
the teeth will be moved in all three planes.
2. Determine the extent of vertical movements of
the anterior and posterior teeth relative to the
occlusal plane.
3. Determine the relative AP tooth movements of
the maxillary and mandibular anterior teeth on
their respective skeletal bases.
.

24. 4. Establish the optimal vertical and AP positions of
the maxillary and mandibular skeletal bases, including
reorientation of the occlusal plane.
5. Determine the extent of dental and skeletal
transverse changes to achieve a balanced occlusal
relationship and smile width.
6. Evaluate the final chin position and possible need
for chin modification in the AP and vertical dimensions

25. General Considerations in
Orthodontic Mechanotherapy
Combined surgical-orthodontic treatment usually
progresses through the following sequence:
1. Presurgical orthodontic treatment
2. Presurgical reassessment and progress
records
3. Prediction processes and model
surgery/surgical
simulation with preparation of surgical splints
4. Definitive surgery
5. Postsurgical orthodontics
6. Retention

26. Presurgical Orthodontic
Treatment
In most circumstances, clinicians use contemporary
preadjusted appliances with the dimensions of either
0.018 × 0.025 inch or 0.022 × 0.028 inch. These preadjusted
appliances facilitate the objectives of achieving
ideal inclinations of teeth in all three dimensions
within the respective jaws.

27. The second-order and
third-order adjustments will assist in moving the
teeth toward their ideal inclinations, unlike many
routine orthodontic treatments in which the clinician
considers compensatory tooth movements to
camouflage a skeletal problem.

28. In general, bands are better selections for at least
the first and/or second molars; bonded molar attach
ments may be more likely to become debonded
during surgery when the surgeon is fixing the arch
into the surgical splint.

29. In addition to the routine
attachments, palatal sheaths should be considered
routinely on the maxillary bands, and occasionally
mandibular lingual attachments may be considered
to facilitate active expansion or contraction as indicated.

30. The hinge cap attachment is recommended
because it facilitates placement of lingual arches
even when mouth opening may be limited in the immediate
postoperative period.
Temporary anchors such as bone plates may be placed at the time of jaw surgery
in cases in which extrusive movement may be of concern during postsurgical finishing. The
bone plates are placed lateral to the molars, and extrusive forces may be placed from the
molars to the bone plates.

31. Maxillary
horseshoe palatal arches are simple to place
after surgical segmental maxillary expansion, even
with limited opening, to stabilize surgical healing.
The Goshgarian-type lingual attachment can also be
used, but placement of lingual arches, particularly in
the immediate postoperative period, may be more
challenging .
Goshgarian-type
transpalatal arch
and sheaths.

32. The immediate requirements during presurgical
orthodontics usually include:
1. Alignment
2. Leveling
3. Decompensation (removal of any compensations)
in the dentition for the skeletal discrepancy in all
three planes of space

33. Alignment
Alignment of arches is often efficiently achieved using
round, superelastic nickel-titanium (Ni-Ti) archwires,
although small multistranded or looped steel
wires may be used based on the clinician’s individual
preference. The clinician may then progress to
rectangular Ni-Ti through to titanium-molybdenum
alloy (TMA) or large steel archwires to initiate arch
form coordination.

34. Although most orthodontists
do not progress beyond a 0.019 × 0.025–inch archwire,
in open bite patients it is important to progress
through to full-dimensional archwires such as
0.021 × 0.025–inch TMA wires to ensure that ideal
axial inclinations or third-order corrections are
achieved before surgery.

35. This is an important issue
because correction of axial inclinations will often
result in vertical biomechanical side effects such
as extrusion and intrusion. These side effects may be
quite undesirable in the immediate postsurgical period
if the orthodontist needs to correct significant
axial inclination deviations.

36. Most orthodontic tooth
movements will inevitably result in some extrusive
side effects, but minimizing these adverse effects
during finishing in patients with previous open bite
malocclusion may be quite challenging. In other
words, patients with open bites should be prepared
to fit as closely as possible to ideal occlusion at the
time of surgery.

37. In deep bite patients, on the other
hand, it is possible that these side effects may work
in their favor to improve the occlusal relationships.
As a consequence, it is sometimes possible with
these patients to proceed to surgery at an earlier
stage in the orthodontic treatment

38. In patients with problematic occlusal relationships,
temporary anchors may be placed as an adjunct to
control the vertical dimension during finishing
procedures.
Temporary anchors such as bone plates may be placed at the time of jaw surgery
in cases in which extrusive movement may be of concern during postsurgical finishing. The
bone plates are placed lateral to the molars, and extrusive forces may be placed from the
molars to the bone plates.

39. Leveling
The fundamental issue in developing a biomechanical
plan in orthodontics is to establish treatment
goals based on the diagnostic findings and problem
list. In surgical orthodontics, as in routine nonsurgical
treatment, establishment of a treatment occlusal
plane is the first stage in planning .
This patient presented with a Class II skeletal pattern but did not wish to consider a surgical plan. Once the treatment occlusal
plane had been established, tooth movements could be planned related to the occlusal plane. The mandibular incisors would be intruded
(a) prior to maxillary incisor retraction (b) if the vertical dimension was to remain constant. If the patient had selected a surgical plan, again
a treatment occlusal plane would be considered and the mandibular incisor intruded (a) before surgical mandibular advancement (c) if
vertical facial dimensions were to be maintained.

40. The decision to level the curve of Spee will depend
on the specific treatment goals. In patients
with deep bite, the geometry of the curve of Spee
is essential to determine the specific nature of tooth
movements . As with all deep bite corrections,
the tooth-to-lip relationships, incisor inclinations,
and locations of steps in the occlusal plane
must be evaluated carefully.
Leveling options
• Maxillary incisor intrusion
• Mandibular incisor intrusion
• Maxillary incisor proclination
• Mandibular incisor proclination
• Posterior extrusion

41. As with all deep bite corrections,
the tooth-to-lip relationships, incisor inclinations,
and locations of steps in the occlusal plane
must be evaluated carefully.

42. On the other hand, open bite patients may present
with multiple-level occlusal planes, and careful
consideration of the locations of the steps and incisor
inclinations are necessary before developing a
biomechanical strategy to level the occlusal plane.
Leveling of the occlusal planes may be
considered prior to surgery, at the time of surgery,
and after surgery.
Open bites may present in many geometries. Steps may be found between the
incisors and canines (a) or between the canines
and premolars (b), or the occlusal planes may diverge completely anteriorly (c).

43. Leveling of the occlusal plane prior to
surgery
In many circumstances, leveling of the occlusal plane
is performed prior to surgery. The orthodontist will
consider the desired tooth movements. An essential
goal of treatment is to prepare the anterior and posterior
alveoli to the ideal vertical dimension prior to
surgical procedures to idealize the jaw relationships.
Levelling and alignment was
started using Niti wires. The arch-
wire size in the maxilla and
mandible was gradually sequenced
until 0.019 × 0.025” stainless
steel wires were placed. This
resulted in a decrease in the
maxillary
anterior teeth proclination and
deepening of the bite.

44. component of the problem may be the mandibular
retrognathism with minimal vertical problems.
For example, a patient may present with the need to
intrude and flare the maxillary incisors as part of a
Class II, division 2 malocclusion, and the significant

45. The maxillary incisor positions alone may be the major
contributor to the vertical occlusal problems, and after
these teeth are repositioned to their ideal positions
in the maxilla, all that is needed is a mandibular
advancement without significant vertical
change.
(a to d) A woman with a skeletal Class II malocclusion characterized by a retrognathic mandible and
normal facial height. The
maxillary incisors are retroclined and relatively extruded with resultant gingival display on smiling.

46. (e) Leveling is achieved
by a simple force
at the brackets (A), which
will rotate the anterior
teeth counterclockwise,
decreasing the vertical
projection (B). (f) The
required force system
at the bracket (A) with
equivalent force system
at the center of
resistance (B). This may
be achieved by placing a
straight wire with or
without
an overlay piggyback
wire that can be tied
down to the brackets (C).

47. (g and h) The presurgical
cephalometric radiograph
and intraoral
photograph demonstrate
good leveling of the
maxillary curve of Spee. (i
and j) The postsurgical
cephalometric radiograph
and intraoral
photograph reveal an
occlusion that will be easy
to detail and finish.

48. (i and j) The postsurgical cephalometric radiograph and intraoral
photograph reveal an occlusion that will be easy to detail and finish. (k to
n) Clinical photographs of the final outcome reveal an excellent
occlusion and improvement in both the profile and smile line.

49. The required force system is a simple
anterior force. In other circumstances,
vertical and AP changes may be required in both
anterior segments as the treatment goals dictate.
(f) The required force system
at the bracket (A) with equivalent force system at the center of resistance (B).

50. Open bite patients remain one of the significant
challenges in surgical orthodontics. A systematic review
demonstrated that nearly half of all patients
who undergo combined surgery and orthodontics
will not retain incisor contact in the long term.16 This
leaves the clinician with the dilemma of carefully assessing
what will influence the success of treatment.

51. If it is essentially the maintenance of open bite correction,
there must be careful consideration of the
risks of treatment with the associated gains.
Hyperdivergence caused by global
mandibular hypoplasia. Both condyles
are reduced in size.

52. If, on
the other hand, significant facial changes are envisaged,
such as changes in facial height and gingival
display or changes in profile convexity, then there
may be a number of issues that together will define
a successful outcome.

53. The timing of occlusal plane leveling is a controversial
issue. Some clinicians recommend that
stepped occlusal planes be leveled prior to surgery
via extrusive movements of the incisors in order to
simplify the surgical procedures, thereby eliminating
more complex and risky segmental surgery

54. Other clinicians have suggested that extrusive
movements of the incisors performed prior
to surgery increase the likelihood of postsurgical
orthodontic relapse, with recurrence of the open bite .
Options for leveling a
stepped
occlusal plane
include extrusion of
the
maxillary incisors
with orthodontic
tooth
movement or
surgical
repositioning of the
posterior teeth
superiorly (A), the
anterior
teeth inferiorly (B), or
both.

55. Leveling of the occlusal plane at the time of
surgery
Significant steps in the occlusal plane may be present
in both open bite and deep bite patients. Historically,
segmental subapical osteotomies were performed
to intrude and possibly retract the maxillary
and mandibular anterior segments in patients with
severe anterior open bite or increased horizontal
overlap (also known as overjet).

56. This represented
a time when orthodontic appliances were not routinely
utilized as part of the surgical correction and
when effectiveness of orthodontic mechanotherapy
was more limited. The use of leveling appliances
with or without the use of temporary anchors has
expanded the range of possible tooth movements.
Post decompensation intra-oral photographs
“Converting a bi-jaw surgery to a single-jaw
surgery:” Posterior maxillary dentoalveolar
intrusion with microimplants to avoid the need of
a maxillary surgery in the surgical management of
skeletal Class III vertical malocclusion
2016 APOS Trends in Orthodontics

57. This has reduced the likelihood of these segmental
procedures being universally applied, thereby
reducing their associated morbidities such as root
damage with possible periodontal and pulpal
compromise.
Posttreatment intra-oral photographs with thermoplastic
retainers
Posttreatment intra-oral photographs

58. open bite malocclusions
can present with a variety of occlusal planes, from
flat maxillary and mandibular occlusal planes that
diverge anteriorly to complex steps between anterior
and posterior teeth that may commonly present
between lateral incisors and canines or between
canines and premolars.

59. Many clinicians believe that
stepped occlusal planes should be retained during
presurgical orthodontics and segmental surgical
procedures utilized to level the occlusal plane.
Moreover, it has been suggested that the open bite
should be worsened prior to surgery to encourage
orthodontic relapse almost as a mechanism for compensating
for any postsurgical skeletal changes.

60. However, it has been recommended that clinicians
be somewhat conservative in exaggerating steps,
because the extrusive side effects on the posterior
teeth have been observed to relapse in retention
with posterior teeth moving out of occlusion.

61. Leveling of the occlusal plane after surgery
Leveling of the curve of Spee is often considered
as part of the postsurgical orthodontics.
The lower arch was not
levelled pre-surgically, by
maintaining the curve of
Spee, an increase in lower
anterior face height can be
achieved with the
mandibular advancement
surgery. The post-surgical
mechanics involved closure
of the resulting lateral open
bites with the use of
bilateral box elastics. In
order to facilitate this post-
surgical settling, the lower
archwire was changed to a
19 × 25-inch braided
stainless steel.

62. In patients
with a skeletal Class II malocclusion with deep bite
and decreased facial dimension, mandibular surgery
will often advance the mandible with a clockwise
rotation of the distal segment of the mandible .
Why Has the Overbite Not Been Completely Reduced Pre-Surgically?
Maintaining an increased overbite will facilitate some increase in the lower anterior face height as the mandible is
advanced, which was thought desirable in this case

63. (a to c) A woman with significantly increased vertical overlap (also
known as overbite) and mandibular retrognathism with reduced
facial height.

64. (d and e) The presurgical cephalometric radiograph and intraoral
photograph reveal the mandibular retrognathism and
decreased facial height with vertical overlap; note that the
mandibular curve of Spee remains as in the pretreatment
relationship.

65. (f and g)
After mandibular surgery to advance and rotate the mandible
clockwise, the posterior teeth are kept out of occlusion.

66. (h and i) Following
surgery, the posterior teeth are extruded using an extrusion arch. The green line
indicates the postsurgical position, and the yellow molar
represents the anticipated molar extrusion.

67. (j and k) The postsurgical facial outcome demonstrates a favorable
increase in facial height and
softening of the chin projection due to the clockwise rotation of the
mandible. The posterior teeth have been extruded into occlusion.

68. This achieves two objectives. First,
a vertical space is opened between the maxillary
and mandibular posterior teeth that can be readily
used to extrude the mandibular posterior teeth
and establish a new vertical dimension of the face.

69. Second, the clockwise rotation
of the distal segment projects what usually is a
relatively prominent chin to assume a more vertical
position. Moreover, this may have the added benefit
of unfolding a deep mentolabial sulcus. Overall, the
effect is frequently observed as a softening of the
chin-to-lip curves and a steepening of the mandibular
border .

70. The presurgical orthodontic goals in short-faced patients
with Class II skeletal problems include leveling
and aligning the maxillary arch to idealize maxillary
dental positions within the face.

71. A large-dimension
rectangular arch such as a 0.019 × 0.025–inch staina
less steel wire is used in the maxillary arch. The maxillary
incisors will become the focal point for repositioning
the mandibular incisor during mandibular
surgery.

72. During this surgery, the existing curve of
Spee or steps will remain in the mandibular arch
without attempts made to level them. The wire may
be left in segments or as one uniform wire, if desired.
Although it is usually unnecessary to progress
to a large rectangular wire, arch forms are better
coordinated if larger wires are used.

73. The sequence of leveling the
mandibular curve of Spee after surgery.
(a) The arches are prepared, and the mandibular
curve of Spee is maintained with a
0.019 × 0.025–inch stainless steel wire.
(b) The mandible is advanced, and the
patient is left to function in the splint.

74. (C)After 4 weeks, the mandibular archwire
is sectioned, and a 0.017 × 0.025–inch
stainless steel extrusion archwire is placed
in the auxiliary tube and tied to the anterior
teeth.

75. (d) With the assistance of elastics
to facilitate the extrusive side effects
on the molars, the molars extrude within
a month.

76. (e) A continuous, low-load Ni-Ti
wire is used to realign the arches prior to
the placement of finishing wires to detail
the occlusion.

77. (f to i) Diagrammatic representation
of the mechanics. (f) The mandibular
arch remains in two levels prior to
surgery.

78. (g) After surgery, the mandible is
rotated clockwise, and the posterior teeth
are brought into occlusion via an extrusion
spring after the mandibular archwire
is segmented. The arrow represents the
force on the wire to engage it in the anterior
segment.

79. (h) The posterior teeth extrude
with a counterclockwise moment with the
help of a seating elastic.

80. (i) The extrusive
effect on the mandibular molars may tip
them lingually, and a lingual arch may be
required to assist in controlling the transverse
dimension.

81. If the mandibular posterior teeth present in an upright
relationship, it may be necessary to leave a
small space behind the canines to provide the necessary
space for leveling. However, if the posterior
teeth are tipped, space may be gained during uprighting
of these teeth after surgery.

82. Following mandibular repositioning and splint
removal, usually a progress radiograph is taken to
assess the surgical outcome and ensure that the desired
position has been realized. The postsurgical
orthodontics may then commence with the use of
an extrusion arch constructed from 0.018 × 0.025–
inch stainless steel. Elastic bands will be used as an
adjunct to assist with extrusion of the mandibular
. posterior teeth into occlusion

83. This process is usually
very rapid, with the segments aligning within a 6- to
8-week period. Once the posterior segments have
been extruded, a wire with a low load deflection
may be used to facilitate alignment, followed by a
rectangular TMA wire as desired to detail and finish
the treatment .

84. In patients who require significant extrusion,
transverse side effects may be encountered from the
joint vertical extrusive forces of the extrusive arch
and elastics. The mandibular posterior teeth may tip
lingually, necessitating insertion of a lingual arch
into the hinge cap attachments to control the transverse
dimension.

85. Reference: