Orthognathics

Question 1

Cephalometric AP Maxillomandibular Relationship (Steiner)

Answer 1

SNA = 82 +/- 4 degrees
SNB = 80 +/- 3 degrees
ANB = 2 +/- 4 degrees
Negative ANB denotes class III malocclsusion

Question 2

How many mm of arch space is needed for each degree of dental compensation?

Answer 2

Approximately 0.8mm of arch space per degree

Question 3

Maxillary blood supply

Answer 3

Facial artery - ascending palatine artery (retained)
Internal maxillary artery - ascending pharyngeal (retained), descending palatine, nasopalatine, posterior superior, infraorbital arteries

Question 4

Distraction phases

Answer 4

Phase I: Osteotomy
Phase II: Latency, 3-7 days
Phase III: Activation, 0.5mm twice per day
Phase IV: Consolidation, 12 weeks (at least twice the time of the activation phase)

Question 5

Bolton Anaylsis

Answer 5

Mandibular / Maxillary
12 teeth = ~91.3% (less means maxillary excess)
6 teeth = ~77.2% (less means maxillary excess)

Question 6

Decompensation of anterior teeth

Answer 6

Class II - upper incisors usually retroclined, lower incisions typically proclined
Class III - upper incisors usually proclined, lower incisors typically retroclined

Question 7

Alignment of incisors

Answer 7

Maxillary - 102 degrees to SN

Mandibular - 90-95 degrees to the mandibular plane

Question 8

Facial Contour

Answer 8

Males = -11 +/- 4
Females = -13 +/- 4

Question 9

Frontal View

Answer 9

Facial Thirds / facial fifths
Symmetry / Asymmetry

Greater than 4mm of tooth show may indicate lip incompetence
Rule of Fifths (one eye = one fifth of the face)
Lateral canthus = gonial angle
Medial canthus = alar base
Pupil = commissure of the mouth
Intercanthal distance = 29 - 36mm
Interpupillary distance = 61 - 64mm

Question 10

Profile View

Answer 10

Malar eminence = 15 lateral, 15mm inferior to the lateral canthus
Nasolabial angle = 100 +/- 10 degrees
Chin-throat angle = 110 degrees
Labiomental fold = 130 degrees
Lip competence

Question 11

Cephalometric Mandibular Plane Angle

Answer 11

Steiner:
Mandibular plane (Go-Gn) and anterior cranial base (S-N)
Normal = 32 degrees
>39 degrees is high
<28 degrees is low

Question 12

Cephalometric Occlusal Plane Angle

Answer 12

Occlusal plane (OP) and anterior cranial base (S-N)
Normal = 14 degrees
High angle = longer anterior facial height
Low angle = shorter anterior facial height

Question 13

Cephalometric Incisor Position

Answer 13

Maxillary - 22 degrees to NA, 4mm anterior (4-6 mm ahead of true vertical A point line)d
Mandibular - 25 degrees to NB, 4mm anterior

Question 14

Holdaway Ratio

Answer 14

NB line through the inferior border of the mandible. Compare lower incisor distance to Pog distance.
Males = 1:1
Females = 0.5:1

A 2:1 ratio equals dental proclination. 2mm is acceptable, 3mm is less desirable, 4mm indicates correction

Question 15

Hierarchy of stability

Answer 15

Highly Stable:
| Maxilla Up
| Mandible Forward
| Genioplasty
Stable:
| Maxilla Forward
| Maxilla Up / Mandible Forward
| Maxilla Forward / Mandible Back
Less Stable
| Mandible Back
| Maxilla Down
| Maxilla Wider

Question 16

Maxillary Hyperplasia

Answer 16

Posterior vertical excess - anterior open bite
Anterior vertical excess - increased gingival / incisor show
AP excess - acute nasolabial angle, increased gingival / incisor show, maxillary protrusion

Question 17

Maxillary Hypoplasia

Answer 17

Posterior vertical deficiency - posterior open bite, steep mandibular plane
Anterior vertical deficiency - no tooth / gingiva visualization
AP deficiency - No piriform rim support, no tooth / gingiva visualization

Question 18

Rapid Palatal Expansion

Answer 18

Children have 50% tipping, 50% expansion (65% tipping in adolescents)
High relapse (40-60%, recommend 50% overcorrection)

Question 19

SARPE Indications

Answer 19

V-shaped maxilla / nasal stenosis
>7mm expansion
Avoids segmental surgery
Decreased relapse (30% versus 50% with LeFort)

Question 20

Cephalometric Wits Appraisal

Answer 20

A-O and B-O (lines dropped vertically to occlusal plane). BO should be 1mm anterior in males and lines should be coincident in females

Question 21

Cephalometric Middle Facial Height

Answer 21

N-ANS-FH

Normal = 54 +/- 3

Question 22

Cephalometric Lower Facial Height

Answer 22

ANS-Me-FH

Normal = 65 +/- 4

Question 23

Mandibular Hyperplasia

Answer 23

Class III skeletal appearance

Shallow labiomental fold

Question 24

Mandibular Hypoplasia

Answer 24

Class II skeletal appearance
Micrognathia
Short mandibular ramus
Short mandibular body

Question 25

Condylar Hyperplasia

Answer 25

Mandibular asymmetry, chin deviation to the contralateral side Ipsilateral posterior open bite Ipsilateral maxillary cant downward

Question 26

Condylar Hypoplasia

Answer 26

Mandibular asymmetry, chin deviation to the ipsilateral side Contralateral posterior open bite Contralateral maxillary cant downard

Question 27

IVRO Indications

Answer 27

``` Large setback procedures V-shaped mandible Less risk for paresthesia Thin anterior mandibular ramus Symptomatic TMD ```

Question 28

IVRO Contraindications

Answer 28

Large counterclockwise movements (can lengthen the pterygomasseteric sling) Can increase the gonial width Period of IMF

Question 29

Interincisal Angle

Answer 29

Steiner Mean value of 130-131 Reduced angle = class II, division 1 Increased angle = class II, division 2

Question 30

Facial contour

Answer 30

S-line = soft tissue menton through the "S" of the nose Ricketts analysis = soft tissue menton through tip of the nose, measuring distance of lower lip

Question 31

C-spine films

Answer 31

Skeletal maturity stages based on the analysis of cervical vertebrae are determined by observing the development of concavities in the lower edge of the vertebral bodies and the change of their shape from trapezoid tapering from posterior to anterior, through rectangular with a larger horizontal dimension of the rectangle, square and again rectangular with a larger vertical dimension of the rectangle

Question 32

Soft tissue changes

Answer 32

Maxillary advancement: 0.9 : 1 hard tissue to soft tissue changes 0.6 : 1 incisor display Genioplasty advancement: 0.9 : 1 hard / soft tissue tissue changes Genioplasty setback: 0.55 : 1 hard / soft tissue tissue changes

Question 33

Lateral cephalometric findings of posterior airway

Answer 33

Soft palate length = 35mm Posterior airway space = 11mm Hyoid to mandibular plan distance = 15mm