Orthognathic surgery

Question 1

Indications for Orthognathic Surgery

Answer 1

1. Severe dentoalveolar discrepancy which cannot be corrected with orthodontics alone
   * Consider the envelopes of discrepancy for tooth movement and growth modification
2. Severe skeletal discrepancy which cannot be corrected with orthodontics alone
   * Growth modification limits:
   o Severe Class II  It is difficult to restrain growth of the maxilla or stimulate growth of the mandible
   o Severe Class III  It is difficult to restrain mandibular growth
3. Unacceptable aesthetics with orthodontic camouflage

Question 2

Class II Orthognathic Surgical Procedures

Answer 2

A. Mandibular advancement (bilateral sagittal split osteotomy)
B. Maxillary impaction and mandibular auto-rotation
C. Maxillary impaction, mandibular auto-rotation, and mandibular advancement (may include a genioplasty)

Question 3

Class III Orthognathic Surgical Procedures

Answer 3

A. Mandibular setback (may include asymmetric rotation)
B. Maxillary advancement
C. Maxillary advancement and mandibular setback
D. Maxillary downgraft and mandibular autorotation (may include genioplasty)

Question 4

Transverse Orthognathic Surgical Procedures

Answer 4

A. Surgically assisted maxillary expansion (SAME)
B. Segmental maxillary surgery
C. Mandibular asymmetric rotation (also affects AP dimension)

Question 5

Cleft lip?

Answer 5

o Opening in the upper lip which may extend to the nose
o Failure of the maxillary process(es) to fuse with the medial nasal process(es)
o May be unilateral or bilateral

Question 6

Cleft palate?

Answer 6

o Opening in the roof of the mouth (communication between oral and nasal cavities)
o Failure of the embryonic fusion of the two palatal shelves of the maxillary process

Question 7

Surgical repair of cleft lip

Answer 7

• Performed within the first 12 weeks of life by the plastic surgeon
• To facilitate this surgery, some preparation may be recommended to improve lip and nasal aesthetics:
  A. Pre-surgical orthopaedics - an orthopaedic appliance used to mould and approximate the cleft segments  improved lip position
  B. Lip adhesion – a surgery which repairs the superficial skin tissue of the lip
• Sometimes CL repair is combined with a bone graft placed in the alveolus
  A. However, early grafting in infancy is now rarely used because studies have shown the practice to be detrimental to midfacial growth
  B. Mixed dentition bone grafts are now the standard practice

Question 8

Surgical repair of cleft palate

Answer 8

• Performed between 1-2 yrs of age
• Exact timing is controversial because the speech pathologist would prefer the repair to occur early so that an intact palate is present for speech development, while the surgeon and orthodontist would prefer to wait until there is sufficient development to decrease the chance of impaired growth of the maxilla
• At present, the palate is usually repaired around 1 year of age
• The surgery involves lifting soft tissue flaps from the cleft halves of the palate and suturing the flaps in the midline to close the bony defect (no bone is placed in the midpalatal defect)

Question 9

What is a Sagittal Split Osteotomy (Mandible)

Answer 9

• The most frequently used orthognathic procedure is the SSO to advance the mandible
  o An incision is made in the mandibular vestibule
  o A cut is then made through the medial cortical bone of the ramus (above the lingula), and extended diagonally across the front of the ramus to the molar area and down to the lower border
  o With the cut complete, an osteotome is used to split the ramus in such a way that the inferior alveolar neurovascular bundle is with the tooth-bearing segment, this allows it to be moved forward and rotated as desired
  o If a backward (and not forward) movement is planned, then bone is carefully measured and removed
  o Teeth are wired together temporarily so that screws can be placed in the ramus for fixation
  o Finally, the interdental wires are removed, and the patient can function while bone healing occurs

Question 10

What is a leofort osteotomy

Answer 10

• Involves sectioning the sinus walls above the roof of the mouth and roots of teeth
• The maxilla is then separated from the pterygoid plates
• Allows movement of the maxilla in all three planes of space

Question 11

What is surgically assisted maxillary expansion

Answer 11

• Usually indicated in patients needing maxillary expansion that are > 16 years for females and > 17 years for males
• Involves a mid-palatal osteotomy to break the inter-maxillary suture; followed by rapid maxillary expansion with an intra-oral device over a period of a few weeks