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OMFS > Orthognathic surgery > Flashcards

Orthognathic surgery Flashcards

1
Q

What are causes of severe class 2 malocclusion with condylar destruction and bird-face deformity

A 
Inflammatory: Juvenile RA
Degenerative:
Idiopathic: ICR
Congenital: mandibular hypopasia, maxillary hyperplasia, syndromes
Autoimmune: 
Trauma: condylar fracture
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2
Q

what are information required in traditional surgical planning of a case?

A
  1. Complaints and concerns
  2. Medical and drug history
  3. Examination
  4. Photographic documentation
  5. Dental casts, bite registration, facebow transfer
  6. Radiographs - Lat ceph, PA ceph, OPG, CBCT
  7. Growth status
  8. Psychological status
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3
Q

what are information required in virtual surgical planning of a case?

A
  1. Complaints and concerns
  2. Medical and drug history
  3. Examination
  4. Photographic documentation
  5. Dental casts, bite registration, facebow transfer
  6. Radiographs - Lat ceph, PA ceph, OPG, CBCT
  7. Growth status
  8. Psychological status
  9. Digital dental models
  10. CT scan correctly oriented to anatomical frame of reference
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4
Q

What are the components assessed in lateral cephalogram?

A
  1. maxilla to cranium
  2. mandible to cranium
  3. maxilla to mandible
  4. facial height
  5. profile
  6. dentoalveolar
  7. soft tissue
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5
Q

Indications and contraindications in surgery first approach

A

Indications:
Well-aligned to mild crowding
Flat to mild curve of Spee
Normal to mild proclination/retroclination of incisors
Minimal transverse discrepancy
Achievable surgical movement after overcorrection to allow decompensation

ContraIndx:

  1. Severe malocclusion with severe crowding needing extractions
  2. Arch discrepancy with excessive or reverse curve of Spee
  3. Transverse discrepancy needing SARPE
  4. Severe facial asymmetry
  5. Class II div 2 with deep bite - severe vme cases
  6. Inexperienced orthodontist
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6
Q

Advantages of surgery first and the disadvantages

A
  1. Shorter duration of tx
  2. Improved motivation for tx since ptn gets to benefit the result early
  3. Faster orthodontic movement
  4. Surgical relapse can be compensated during orthodontic treatment

Disadvantages:
Difficult to predict the final occlusion after complete tx
Planning is time consuming
Requires experienced orthodontist

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7
Q

How does surgery first approach accelerate orthodontic tooth movement

A

It was already reported that corticotomy or alveolar osteotomy improves the orthodontic tooth movement.

In OgS
Increase in blood flow during postsurgical healing above the presurgical levels facilitates the healing process and stimulates bone turnover that potentially speed up orthodontic tooth movement

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8
Q

What are pre-surgical orthodontics goals?

A

Align the teeth in arches - relieves crowding
Level the arch and normalize the curve of spee
Coordinate the upper and lower arches in transverse
Decompensate the teeth to be in the basal bone
Diverge the roots if segmental osteotomies is indicated

(Normalization of the arches and coordinated arches)

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9
Q

What is normalization of arch?

A
  1. Aligned
  2. Levelled vertically
  3. Flat/minimal curve of spee
  4. Interdental spaces closed unless needed for osteotomy
  5. Dental compesation removed
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10
Q

What is coordinated dental arch?

A
  1. Maxilla and mandibular arch have same shape

2. Same corresponding size

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11
Q

What do we have to make sure prior to surgery?

A 
Archwires are passive
Rectangular wires should be engaged fully in slots
Surgical hooks (soldered or crimpd) should be in place to facilitate mmf
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12
Q

Indications of Le Fort 1 osteotomy

A

To advance, setback, downgraft, impact, decat, derotate the maxilla
Le Fort 1 in 2 pieces - To correct transverse discrepancy
Le Fort 1 in 3-4 pieces
- to allow differential movement of the anterior and posterior segment
- to close AOB
- to allow more setting back of the anterior segment using extracted socket space

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13
Q

How to perform Le Fort 1 osteotomy

A

Incision - 5mm above mucogingival junction from 6-6
Soft tissue dissection
- to expose pyriform aperture, infraorbital foramen, zygomatic buttress, pterygomaxillary fissure (or tuberosity)
- nasal floor, caudal septum (using nasal osteotome), lateral nasal wall
Osteotomy
- horizontal osteotomy from pyriform rim to tuberosity
- lateral nasal wall (25-35mm safe margin for distance to DPA)
- septal separation
- tuberosity cut or pterygomaxillary dysjunction
Downfracture
- finger pressure
Mobilization
- maxillary freely mobile downwards, side to side, and anteriorly, posteriorly
Vessel management - preserve DPA
Segmentation
Fixation
Closure

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14
Q

Complications of Le Fort 1 osteotomy

A

Intraoperative

  • bleeding (DPA, Pterygoid plexus, PSA art, sphenopalatine, internal maxillary artery)
  • damage to teeth
  • nerve injury
  • bad splits
  • anosmia
  • blindness

Postoperative

  • hemorrhage and vascular compromise
  • avascular necrosis
  • malocclusion or malpositioning (eg: inadequate impaction)
  • infection
  • nasal deformity
  • pulpal necrosis
  • relapse/instability
  • hardware failure
  • malunion/nonunion
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15
Q

How do u manage when u encounter bleeding intraop during

Le Fort 1

A
  1. Reverse Trendelenburg
  2. Local vasoconstrictors
  3. Hypotensive anaesthesia
  4. Ligate/cauterise source of bleeding
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16
Q

What are hierarchy of stability

A 
Based on Profitt et al
Least stable to most stable
1. Maxillary widening
2. Maxillary inferior repositioning
3. Mandibular setback
4. Maxillary advancement + mandibular setback (class 3)
5. Maxillary impact + mandibular advancement (class 2)
6. Maxillary advancement
7. Mandibular advancement
8. Maxillary impaction
17
Q

What are risk factors for avascular necrosis

A 
Injury to DPA (but blood supply comes from buccal mucoperiosteum, therefore rare)
Smokers
Vascular disease
Cleft palate
Second surgery
Maxillary segmentation
Laceration of palatal tissue
Impingement of mucosal by splints
18
Q

Presentation of avascular necrosis

A
  1. Pulp necrosis
  2. Periodontal defect, gingival recession
  3. Bone resorption
  4. Segmental or complete loss of maxilla

Tx: hyperbaric oxygen, debridement, reconstruction

19
Q

How to achieve hypotensive anaesthesia

A

Beta blockers

Deep anaesthesia thru anaesthetic gas

20
Q

Difference between positional screws vs lag screws

A

Lag screws has gliding hole to allow compression of bone segments

Positional screws does not have gliding hole to sit the head of screw therefore no compression of bony segments allowing bone to be fixed at its wanted position

21
Q

How to assess stabilisation of facial growth?

A

Dental casts comparisons
Serial radiographic tracings every 6 months (gold standard)
Handwrists - fusion of …
Vertebrae - c2, c3 matures with concavity at the inferior border
Bone scan - activity of condyle growth center

22
Q

Mandibular soft tissue prediction

A

90% of the skeletal changes

Eg. If mandible is setback by 10mm, soft tissue will have 9mm setback

23
Q

Mandibular osteotomies for ogs

A

SSO
VRO
Inverted L

24
Q

What do you describe when a surgical procedure being asked

A

Incision
Soft tissue dissection (exposure)
Osteotomy
Fixation

25
Q

Complications of SSO

A

Intraoperative

  • bleeding
  • nerve injury
  • bad splits
  • changes in the intercondylar width

Postoperative

  • infection
  • Immediate malocclusion (dt condylar malposition)
  • late malocclusion (dt relapse, occlusal interference from ortho movement)
  • nonunion
  • relapse
27
Q

What is the rate of paraesthesia immediate postop bsso

A

85%

28
Q

Rate of permanent paraesthsia for bsso?

A 
10% (longer than 12 months) Caused by
Intraop nerve transection
Injured by screw placement
Impinged by proximal and distal bony segments (setback/rotation)
Stretched too much during advancement
29
Q

Causes of relapse of bsso

A

Poorly understood. Possible causes

  • condylar resorption
  • postop changes in the mandibular architecture
  • muscle pull (failure of muscles and soft tissues to adapt to new position)
  • larger movement >7mm
30
Q

Risk factors for relapse

A

Large movements
Infection
Hardware failure

31
Q

What is the indication of single maxillary osteotomy? (Le fort 1 only)

A
  1. When the mandibular dental midline and chin midline coincides with facial midline
  2. When theres no mandibular occlusal cant
  3. When theres no facial asymmetry
  4. When upon movement of maxilla either advancement setback or impaction, does not affect the mandibular position after autorotation
32
Q

For AOB cases, what are most stable surgical movement

A

Posterior impaction and advancement of maxilla

33
Q

Least stable surgical movement for AOB

A

Counter clockwise rotation of mandible

OMFS (54 decks)

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