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ABOMS > Orthognathics > Flashcards

Orthognathics Flashcards

1
Q

Cephalometric AP Maxillomandibular Relationship (Steiner)

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

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

A

Approximately 0.8mm of arch space per degree

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3
Q

Maxillary blood supply

A

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

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4
Q

Distraction phases

A

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)

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5
Q

Bolton Anaylsis

A

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

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6
Q

Decompensation of anterior teeth

A

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

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7
Q

Alignment of incisors

A

Maxillary - 102 degrees to SN

Mandibular - 90-95 degrees to the mandibular plane

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8
Q

Facial Contour

A 
Males = -11 +/- 4
Females = -13 +/- 4
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9
Q

Frontal View

A

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

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10
Q

Profile View

A 
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
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11
Q

Cephalometric Mandibular Plane Angle

A 
Steiner:
Mandibular plane (Go-Gn) and anterior cranial base (S-N)
Normal = 32 degrees
>39 degrees is high
<28 degrees is low
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12
Q

Cephalometric Occlusal Plane Angle

A 
Occlusal plane (OP) and anterior cranial base (S-N)
Normal = 14 degrees
High angle = longer anterior facial height
Low angle = shorter anterior facial height
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13
Q

Cephalometric Incisor Position

A

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

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14
Q

Holdaway Ratio

A

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

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15
Q

Hierarchy of stability

A 
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
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16
Q

Maxillary Hyperplasia

A

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

17
Q

Maxillary Hypoplasia

A

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

18
Q

Rapid Palatal Expansion

A 
Children have 50% tipping, 50% expansion (65% tipping in adolescents)
High relapse (40-60%, recommend 50% overcorrection)
19
Q

SARPE Indications

A

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

20
Q

Cephalometric Wits Appraisal

A

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

21
Q

Cephalometric Middle Facial Height

A

N-ANS-FH

Normal = 54 +/- 3

22
Q

Cephalometric Lower Facial Height

A

ANS-Me-FH

Normal = 65 +/- 4

23
Q

Mandibular Hyperplasia

A

Class III skeletal appearance

Shallow labiomental fold

24
Q

Mandibular Hypoplasia

A

Class II skeletal appearance
Micrognathia
Short mandibular ramus
Short mandibular body

25
Q

Condylar Hyperplasia

A

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

26
Q

Condylar Hypoplasia

A

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

27
Q

IVRO Indications

A 
Large setback procedures
V-shaped mandible
Less risk for paresthesia
Thin anterior mandibular ramus
Symptomatic TMD
28
Q

IVRO Contraindications

A

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

29
Q

Interincisal Angle

A

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

30
Q

Facial contour

A

S-line = soft tissue menton through the ā€œSā€ of the nose

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

31
Q

C-spine films

A

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

32
Q

Soft tissue changes

A

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

33
Q

Lateral cephalometric findings of posterior airway

A

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

ABOMS (13 decks)

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