Orthognatic Surgery

Question 1

When does craniofacial embryogenesis begin and what are the key processes?

Answer 1

Begins during the third week of gestation. Key processes: Gastrulation (formation of trilaminar disk) and neurulation.

Question 2

Which structures form from the first pharyngeal arch at 4 weeks?

Answer 2

Maxillary prominence and Mandibular arch.

Question 3

What are the two types of craniofacial bone formation?

Answer 3

1. Membranous neurocranium (e.g., parietal, frontal bones)
2. Cartilaginous viscerocranium (e.g., mandible, hyoid)

Question 4

What is the chronological order of ossification?

Answer 4

1. Mandible → 2. Maxilla → 3. Palatine → 4. Cranial base → 5. Cranium
   - Membranous sites precede endochondral centers

Question 5

When do primary tooth germs appear?

Answer 5

6 weeks: Anterior and first molar germs
7 weeks: Second molar germs.

Question 6

What distinguishes a growth center from a growth site?

Answer 6

Growth center: Primarily genetic control (e.g., cranial base)
Growth site: More influenced by function (e.g., mandible).

Question 7

What is the order of postnatal craniofacial growth completion?

Answer 7

1. Cranial vault → 2. Cranial base → 3. Nasomaxilla → 4. Mandible (last).

Question 8

How do viscerocranium proportions change from neonate to adult?

Answer 8

Neonate: Viscerocranium = 1/5 skull height
Adult: Viscerocranium proportionally larger.

Question 9

Which grows faster postnatally?

Answer 9

Neurocranium develops ahead of viscerocranium.

Question 10

Why is understanding growth timing important for orthognathic surgery?

Answer 10

Mandibular procedures (e.g., BSSO) should wait until growth completion (~16-18 years).