orthodontic biomechanics of different skeletal deformities are discussed .

1. Biomechanics and treatment
of dentofacial deformity
Part 3
dr Maher FOUDA
Faculty of Dentistry
Mansoura Egypt
Professor of orthodontics

2. Maxillary advancement
Maxillary advancement with distraction can be performed
with an appliance directly attached to the
maxilla and supporting cranial bones superior and
posterior to the maxilla. Usually the zygomatic structures
or temporal regions are used as anchorage to
protract the maxilla.

3. Alternatively, a rigid frame may
be skeletally fixated to the cranium, from which a
screw device may be attached to progressively move
the maxilla forward and downward.
Simple mechanism to measure and adjust distraction forces

4. The maxilla is
used to anchor an intraoral device, and the direction
of traction may be modified to conceptually deliver
forces relative to a theoretical center of resistance
of the osteotomized maxilla. The advantage of this
device is that modification of the vector of force is
easy to achieve as the patient’s individual response
is reviewed .

5. (a and b) A rigid external frame has been used to anchor an
externally activated screw device to distract the osteotomized
maxilla. (c) Pretreatment occlusion.

6. (d) A fixed appliance is cemented to the maxilla. This device has arms
extending from the mouth, which
will be attached to the screw mechanism. The screw device has the ability
to be adjusted to modify the displacement during treatment. (e
and f) Forces are delivered relative to the center of resistance of the
osteotomized maxilla to aid in planning movement, but there are still
many confounding factors.

7. Distraction osteogenesis of the maxilla is particularly
useful in cleft lip and cleft palate patients with
many purported advantages. However, there are a
number of intraoral complications with the distracters,
such as pain and infection.
Direct assessment of distraction forces in a patient. There were no
complications, such as pain, discomfort, or procedural delays in
measuring and adjusting the distraction forces

8. A recent comparison
of distraction and orthognathic surgery revealed
similar surgical and speech outcomes with both techniques.
Distraction osteogenesis therefore appears
to be indicated for the larger advancements that
would challenge the tissue compliance during an
acute advancement.

9. Management of Postoperative
Morphologic Complications
There are a number of routine consequences associated
with any intervention, and the purpose of this
section is not to explore these in detail. However,
such issues as pain, hemorrhage, swelling, infection,
antral health issues, reduced range of motion, and
neurosensory disturbances are encountered relativelyfrequently.

10. Bad splits of the osteotomy site,
root transection or damage, periodontal damage,
and oronasal fistulae secondary to segmental surgery
are less frequently encountered.
Adolescent with significant maxillary retrusion with dental malocclusion (top)
and after LeFort I and asymmetric genioplasty (bottom). Note improvement in
location of upper jaw and dental relations.

11. Complications arising from inappropriate diagnosis
and treatment planning are often difficult
to manage and may only present either prior to or
after surgery. It is possible that the surgical procedure
may not achieve the desired esthetic outcome
or occlusal relationship.

12. Moreover, patients require
appropriate psychologic counseling to ensure that
they are prepared for the issues associated with the
orthodontics and surgery.

13. The immediate postoperative
period requires a significant support network
from both the clinician and the patient’s home environment.
Patients with possible psychologic problems
such as depression, somatoform disorders, or
body dysmorphic disorders need to be carefully considered
and counseled before a decision is made to
subject them to this type of treatment.
A LeFort I osteotomy was performed with segmentation
of the maxilla in four mobile segments. Vertical interdental
osteotomies were implemented between the maxillary
lateral
incisors and the canines. Two horizontal osteotomies,
parallel with the septum were performed to expand the
maxilla
transversally. Following the osteotomy, the maxillary
segments were anteriorly repositioned and connected to
the mandible in the correct occlusal relationship. The
mandibular and maxillary arches were wired together and
acted as a unit, rotating around the condylar heads.

14. Clinicians
will often regret proceeding to surgery early, which
inevitably results in extended treatment time with
associated iatrogenic issues including possible significant
psychologic issues.
Diagram showing effects of
the inclination
of the osteotomy cut when
advancing the maxilla –
osteotomy inclination to
increase incisor exposure
and potentially increase
lower face height.

15. Complications related to errors of positioning or
postsurgical movement of osteotomized fragments
are encountered less frequently, and fortunately
most are often overcome by timely diagnosis and
management. Immediately following discharge
from surgery, the fit of the maxillary and mandibular
teeth into the surgical splint must be assessed.
A Le Fort I osteotomy with rigid fixation was performed for the advancement and
A. placement of the surgical
splint, B. fixation, C. chin grafts,
D. final postsurgical occlusion.

16. It is essential for clinicians to review the immediate
postsurgical outcome radiographically. The presurgical
prediction tracing should be overlaid on the
postsurgical radiograph to assess the outcome and
accuracy of the surgery. First, the condylar seating
in the glenoid fossa must be confirmed. The clinician
should then compare the angulation of the
ramus and consider if it has been retropositioned
or inclined forward.

17. This may affect the postoperative
response as the patient is released from wire
or elastic fixation. The orientation of the fragments
can then be appraised and compared with the prediction
tracing. In maxillomandibular surgery, the
position of the maxilla in all three planes must be
reviewed, and particular attention should be directed
to assessment of the vertical position of the maxillary
incisor and molar.
A Le Fort I osteotomy was performed to
improve the
anterior-posterior and transverse
deficiency, which
was fixed with titanium mini-plates.
Because the FMA
was high, it was possible to
perform surgical superior
repositioning of the maxilla
with counterclockwise
mandibular autorotation.

18. Maxillary repositioning
Errors in maxillary positioning are probably most
significant in the vertical dimension, with the impact
on final tooth display anteriorly, and in the posterior
dimension, which will influence the cant of the
occlusal plane. Significant steepening of the occlusal
plane posteriorly may have a deleterious effect
on the relative chin projection.
Diagram showing effects of
the inclination
of the osteotomy cut when
advancing the maxilla –
osteotomy inclination to
reduce incisor exposure and
potentially reduce lower face
height.

19. This may influence
patient satisfaction if chin projection was an important
consideration in the patient’s treatment goals.
Surgically, Le Fort I osteotomy was performed using piezoelectric device for 10 mm impaction of the maxilla
and 5 mm advancement in the region of teeth #11 and #21; 6.5 mm impaction in teeth #16 and #26, and
mentoplasty was executed with reciprocating saw for 8 mm advancement. For osteosynthesis of the
maxilla, we used two 1.5 mm pre-molded L-shaped plates with four holes, positioned on the zygomatic
pillars, and two Le Fort plates with 11 holes; for mentoplasty, we used the advancement plate with five
holes

20. If the occlusion is related well in the surgical splint
but significant errors are evident in positioning of
the maxilla, then it is unlikely that any significant
changes in position can be achieved by postsurgical
orthodontics, and the clinician and patient must
decide whether they are prepared to accept this discrepancy.
If not, it may be necessary to return to the
operating room.
A surgical splint for orthognathic surgery: (a) wearing surgical splint and (b) the surgical splint is placed in its
position to allow the accurate position of the jaws and good surgical fixation

21. If the teeth do not fit into the
splint immediately
following surgery, it is important
to identify where
the discrepancy lies and
consider whether a period
of elastic traction with or
without some type of extraoral
traction is required .

22. (a to c) This woman presented for what was considered a routine
maxillary advancement to address her midface deficiency and
Class III relationship

23. (d) The teeth were aligned, and a relatively simple plan was established by the surgical team. Unfortunately, the patient
had a significant bleed in the operating room from a rare bleeding disorder that was not detected by routine blood
screening. The surgical
team fought to keep her alive and were more concerned with controlling the bleeding than correcting the jaw position.
(e to h) As a result,
on splint removal the occlusion (g and h) looked similar to the presurgical position (e and f).

24. (i) The surgeons had no desire to put her back
in the operating room, so with the osteotomized maxilla, a reverse
headgear was prescribed in an attempt to protract the maxilla. (j) The
maxilla moved quite rapidly, and the small right lateral incisor was
restored to normal size and form.

25. (k to n) The final outcome was excellent,
although this was not envisaged in the
immediate postoperative period.

26. This will depend
on the goals of the postsurgical orthodontics.
If significant effort has been made to reduce tooth
display by superior repositioning of the maxilla, and
the patient were to return with an anterior open
bite, it is probably unwise to simply run vertical elastics
to the anterior teeth and indiscriminately extrude
the maxillary and mandibular teeth.

27. A J-pull
headgear may be considered with light seating
elastics to control the mandibular incisor position
differentially. However, incisor display may need to
be increased, in which case elastics and a headgear
with long outer bow should be considered to rotate
the occlusal plane downward anteriorly.

28. In summary,
the selection of facebow headgear for the maxillary
arch or J-pull headgear for either arch with appropriately
directed elastic forces relative to the
center of resistance and associated elastic traction
should be routinely considered to facilitate goal oriented
postsurgical tooth movements.

29. Mandibular repositioning
It is essential for the surgeon to accurately place the
condyles in the glenoid fossa prior to applying skeletal
fixation. Methods have been proposed to assist
in locating the condyle in its preoperative position,
but they have been unpopular because they add operating
time to the procedure.

30. With the development
of rigid fixation, this issue is more important
because minor variations in absolute or angular location
in the joint will reflect in postsurgical movements
at tooth level as the condyle aims to assume
its original orientation. This may reflect as nonocclusion
or AP discrepancies in occlusion.

31. Condylar sag
Condylar sag was a term used to describe a problem
encountered with fixation with wire osteosynthesis.
The condyle would be located out of the glenoid
fossa because of traction applied during fixation or
edema encountered during the operation or postoperatively.
This has been described as “central”
condylar sag when the condyle is completely displaced
from the fossa or “peripheral” condylar sag
when the condyle is displaced onto the medial, lateral,
anterior, or posterior walls and interferes with
full seating of the condyle ..
Central condylar sag. The condyle is
positioned inferiorly in the glenoid
fossa with no contact with bone, while
the teeth are in occlusion and
rigid fixation is placed (A). After
removal of IMF the condyle moves
superiorly leading to immediate
relapse (B).

32. Errors in positioning the condyle
in the glenoid
fossa at the time of placing
fixation wires or screws will
result
in significant discrepancies
between retruded contact
position and intercuspal
position. In severe cases, if the
condyles are displaced
significantly, when the mandible
returns
to its position in the fossa, the
vertical displacement
results in premature contacts on
the posterior teeth, which
will result in an anterior open
bite.

33. (a) This patient returned from having maxillary and mandibular
surgery with a genioplasty. (b) Review of the cephalometric
radiograph reveals significant differences in the position of the
posterior ramus between the right and left sides.

34. (c to e) The intraoral photographs
reveal a relatively symmetric occlusal relationship.

35. (f and g) Further evaluation of the condylar position demonstrated that the right
joint (f) was displaced 5 mm from the glenoid fossa. With 1 to 3 mm of
displacement, it is possible to compensate the teeth by removing
the fixation and running seating elastics; however, the magnitude of this problem
probably requires further surgery and repositioning of
the ramus back into the fossa.

36. Condylar sag
can be defined as an immediate or late change in position
of the condyle in the glenoid fossa after surgical establishment
of a preplanned occlusion and rigid fixation of
the bone fragments, leading to a change in the occlusion.
Central condylar sag. The condyle is positioned inferiorly in the glenoid fossa with no
contact with bone, while the teeth are in occlusion and
rigid fixation is placed (A). After removal of IMF the condyle moves superiorly
leading to immediate relapse (B).

37. This appears to be due to inadvertent twisting of
the condyle during fixation. The condyle slowly
adapts by displacement and resorption in the weeks
following surgery. In these patients, it is essential to
examine them within the first 2 to 3 weeks following
surgery and possibly consider removing their fixation.
Elastics can then be used to guide their teeth
into occlusion while the bony fragments are manipulated.
Frontolateral view of the glenoid fossa,
condyle, and proximal and distal bone
segments. The condyle is in correct
relation to the glenoid
fossa. Note, however, the gap (G) between
the bone segments (a). Rigid fixation
forces the segments of bone together
applying tension on the
condyle and ramus causing a bowing (B)
effect (b). Once the IMF is removed, the
tension on the ramus is released causing
the condyle to move
medially and slide inferiorly on the
medial wall of the fossa causing a
posterior openbite. The vertical change in
condylar position (V) is equal to the
posterior openbite (V) (c).

38. Ramus angular errors
Accurate angular positioning of the condyle is
essential
to minimize postoperative positional changes in
the occlusion. If the ramus is displaced
backward,
the mandible will slowly move forward following
removal of fixation. This will result in an edge-
toedge
occlusal relationship extending to a negative
horizontal overlap.

39. Control of the proximal fragment is one of the most crucial aspects of positioning the mandible accurately
following jaw surgery.
In some circumstances, surgeons are determined to push the condyle back into the glenoid fossa, which may
rotate the proximal segment
backward. Although this may be of little significance in the immediate postoperative period, once fixation is
released, the muscles have a
tendency to move the ramus back to its original position, which rotates the anterior mandible forward, often
leading to a negative horizontal
overlap.

40. This problem must
be differentially diagnosed from failure of fixation,
which may require different management. Conversely,
if the ramus is displaced forward at the time
of fixation, the opposite problem may occur with
progression toward Class II relationships at the dental level .
Condyle changes 6 weeks and 1 year after surgery in a patient following two-jaw surgery involving LeFort I with
mandibular setback using SRRO procedure. A: Posterior view of the condyle showing its rotation and a
noticeable rotation of the ramus in both the first 6 weeks (left panel) and 1 year (right panel) following surgery.
B: Lateral view showing the postero-superior condyle changes at 6 weeks after surgery (left panel) and its
adaptation toward the original position 1 year after surgery (right panel).

41. Angular ramal positioning errors may occur
unilaterally or bilaterally. This problem can generally
be managed with traction to the mandibular arch
with elastics in most circumstances, but in severe
cases, the patient may have to be returned to the
operating room. In the retropositioned ramus, it is
possible to even consider a J-pull headgear to facilitate
movement of the mandibular arch .
Changes in the ramus and chin 6 weeks and 1 year after surgery in a patient following two-jaw surgery
involving LeFort I with mandibular setback using SRRO procedure. A: Surgical changes 6 weeks after
surgery showing posterior displacement of the gonial angle. B: Post-surgical adaptation of ramus and chin
moving forward between 6 weeks and 1 year following surgery. C: Pre-surgery to 1 year post-surgery
changes showing the net amounts of surgical changes that were maintained for both the maxilla and
mandible.

42. (a) Presurgical cephalometric radiograph of a Class II patient who requires mandibular surgery. (b
and c) Postsurgical cephalometric
radiograph with tracing showing that the proximal fragment has been rotated backward, which
resulted in the mandibular teeth moving
into a negative horizontal overlap.

43. (d and e) A J-pull headgear and elastic traction were
instituted to address the positional issue with the
mandible, and the problem was resolved rapidly. (f) Final
occlusion.

44. Condylar resorption is an undesirable consequence
of mandibular surgery that has been reported
to occur in 3% to 10% of patients and may occur
throughout the postoperative period. The length
of the mandible has been shown to decrease in
10% of patients who underwent mandibular ramus
surgery (by less than 2 mm in one sample group).
However, in half of these patients, no discernable
change in occlusion was observed because the dentition
compensated for these changes. In the short
term, compensatory strategies may be considered,
but many of these changes may occur after removal
of appliances with few long-term functional consequences.
Condylar degenerative changes

45. CBCT of the right
temporomandibular joint (TMJ) depicting a posterior slope of the condylar
process, osteoarthrotic changes, and a well-preserved joint space; CBCT of
the
left TMJ depicting a posterior slope of the condylar process, osteoarthrotic
changes, and a severely diminished joint space (white arrow).

46. Significant condylar breakdown can be observed
when the occlusion undergoes significant change,
excluding as a result of systemic conditions such as
rheumatoid arthritis and other autoimmune conditions.
Splint therapy should be considered to reduce
the loads on the joint. This condition usually
stabilizes, and then the clinician must consider the
risk-to-benefit ratio of reoperating, with further uncertainty
in the joints following surgery .
Preoperative Occlusion. Demonstration of Relapse Due To
Condylar Resorption One Year After Bilateral Sagittal
Split Osteotomy To Correct Apertognathia and
Mandibular Deficiency.

47. Preoperative
Frontal Repose.
Preoperative
Frontal Smile.
Preoperative
Cephalometric
Radiograph.
Preoperative Occlusion 6-month Postoperative.
6-month
Postoperative.
6-month
Postoperative
12-month Postoperative 12-month Postoperative

48. Panoramic radiograph, lateral cephalogram, cone-beam computed
tomography (CBCT), and clinical frontal photograph of patient 2. (A)
Panoramic
radiograph, CBCT, and cephalometric radiograph at age 16.5 years before the
first orthognathic procedure to correct severe retrognathia and open bite. The
radiographs depict several risk factors that could lead to postoperative
condylar
resorption: small condyles, posterior sloping of the condylar process, and an
antegonal notch at the mandibular angle. (B) Status after relapse of the open
bite due to bilateral condylar resorption after the first orthognathic surgery.
Osteosynthesis plates in the lower jaw have been removed. Clinical picture
(right image) shows poor oral hygiene and an anterior open bite extending into
the premolar area. No class II development due to compensatory orthodontic
inclination of the lower incisors. (C) Patient status 1 year after a corrective 3-
piece Le Fort I osteotomy. The malocclusion has been corrected and has
remained stable (right image) in spite of ‘‘total loss’’ of condylar volume, as
can
be seen in the panoramic radiograph. (D) Patient CBCT at 1-year postoperative
after the 3-piece Le Fort I osteotomy, illustrating the complete disappearance
of
condylar volume. Enlargement of the coronoid process. Narrowing of the joint
space. In spite of these radiographic changes, this patient at no time
developed
temporomandibular joint symptoms, and the occlusion remained stable after
the second orthognathic surgery (3-piece Le Fort I osteotomy).

49. (a) A woman who initially presented with a Class II malocclusion was managed by maxillomandibular
surgery to advance and
impact her maxilla and advance her mandible to an acceptable outcome. (b and c) Two years later, there
were significant changes in her
jaws, which continued due to condylar resorption. (d) The patient opted for further surgery after
significant consideration of the relative
risks and gains. The positions of the jaws remained stable.

50. Alternatively, the maxilla can be set back if it had
been advanced as part of the initial surgery, or an
advancement genioplasty can be considered if esthetic
concerns are expressed by the patient.
Inferior resection of the pterygoid process allows
maxillary setback.

51. Failure of fixation
Failure of fixation is a significant problem that can
result in the osteotomized maxilla or mandible moving
following surgery. Fixation screws may not have
been placed securely in the bone, or significant muscular
or soft tissue tension may have mobilized the
screws. It is important for the clinician to differentially
diagnose this condition and comprehend the
possible implications on both short-term and longterm
stability .
MMF screw below the level of the
osteotomy, with room for
eventual plates
MMF screws in the region of the
cuspids (may be anterior or
posterior depending on the density of
the bone and proximity of the roots)
Wires tied to the splint without engaging
the bonded brackets
(may be over or under the orthodontic
wire)

52. Failure of fixation is a significant
problem that requires early diagnosis
and
timely management. It is the result of
failure, either partial or total, of the
hardware
securing the osteotomized mandible.
The upward pull on the distal fragment
by the
medial pterygoid and the downward
pull on the chin may effect a clockwise
rotation of
the distal fragment. Concomitantly, the
temporalis muscle may pull upward on
the coronoid
process. This has to be differentially
diagnosed from posterior ramus
positioning.

53. In some circumstances, failure
is complete, and significant movement occurs;
in such cases, the patient will have to be returned
to the operating room. However, in a number of
patients, this movement is more subtle, which may
be observed as minor to moderate changes in the
occlusion. Early identification and an appropriately
directed strategy can avoid the need for additional
surgery. It is important for both the orthodontist
and the surgeon to examine the patient together or
at similar times to facilitate the appropriate
management
protocol.
Two loose (displaced) brackets, one in the maxillary
vestibule and
one in the oral pharynx; radiologist arrows point to the one
in the pharynx
and the hyoid bone

54. The most frequently encountered problem with
failure of fixation is encountered after mandibular
osteotomies following a sagittal split osteotomy. The
muscular pull of the medial pterygoid muscle will
pull the distal fragment upward, rotating the mandibular
incisors forward and downward .
Immediate postoperative
radiograph showing lateral and
inferior
displacement of the condylar
segment following vertical
subsigmoid
osteotomy.
Radiographic appearance
of the same patient
following trimming
of the inferior tip and
suturing of the condylar
segment to the
ramus of the mandible.

55. This patient had distraction of the
mandible followed by refinement orthognathics.
Fixation screws were not held in the bone
as securely as with normal bone, so the muscular
pull rotated the distal fragment clockwise.
Because the maxilla had been impacted to reduce
the gummy smile, elastic bands should
be used with caution because the maxillary
incisors could be pulled down again. The
negative horizontal overlap could also reflect
mandibular ramus positioning errors. Accurate
interpretation of the cephalometric radiograph
displays the etiology of the problem (ie, failure
of fixation).

56. The strategy for managing this problem ranges from
replacement of maxillomandibular fixation with wires
or strong elastics in isolated mandibular surgery to a
combination of extraoral traction and elastics to the
mandibular arch
Placement of maxilla-
mandibular fixation screws
between in the maxilla and
mandible between roots of
teeth
Maxillo-mandibular
fixation achieved through
the use of 25 guage
stainless steel wires in
combination with the
screws.
3-dimensional reconstructed CT image
showing that two mini-sized,
bioabsorbable plates are fractured 7
weeks after implatation

57. run significant elastic traction from the maxillary to
the mandibular anterior teeth, as this may bring the
maxillary anterior teeth downward. It may be wiser
to consider a mandibular J-pull headgear attached
to the rigid surgical wire in the mandible to rotate
the mandibular distal fragment superiorly .
Elastics can be simultaneously considered, but the
force levels must be more moderate.
If the patient has had significant
vertical maxillary impaction, it is probably unwise to

58. (d) Complete failure of
fixation was observed on discharge from
the hospital, with significant
counterclockwise
rotation of the proximal fragment
from the temporalis muscle and clockwise
rotation of the distal fragment from the
medial pterygoid and suprahyoid muscles.
This required reoperation, but the patient
and surgeon did not want to redo the
surgery.
(a and b) This patient presented
with an asymmetric Class III
malocclusion
with negative horizontal overlap that
required fairly straightforward
maxillomandibular
surgery, as outlined in the prediction
tracing (c).

59. Reference: