Orthognathics Flashcards
Cephalometric AP Maxillomandibular Relationship (Steiner)
SNA = 82 +/- 4 degrees SNB = 80 +/- 3 degrees ANB = 2 +/- 4 degrees Negative ANB denotes class III malocclsusion
How many mm of arch space is needed for each degree of dental compensation?
Approximately 0.8mm of arch space per degree
Maxillary blood supply
Facial artery - ascending palatine artery (retained)
Internal maxillary artery - ascending pharyngeal (retained), descending palatine, nasopalatine, posterior superior, infraorbital arteries
Distraction phases
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)
Bolton Anaylsis
Mandibular / Maxillary
12 teeth = ~91.3% (less means maxillary excess)
6 teeth = ~77.2% (less means maxillary excess)
Decompensation of anterior teeth
Class II - upper incisors usually retroclined, lower incisions typically proclined
Class III - upper incisors usually proclined, lower incisors typically retroclined
Alignment of incisors
Maxillary - 102 degrees to SN
Mandibular - 90-95 degrees to the mandibular plane
Facial Contour
Males = -11 +/- 4 Females = -13 +/- 4
Frontal View
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
Profile View
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
Cephalometric Mandibular Plane Angle
Steiner: Mandibular plane (Go-Gn) and anterior cranial base (S-N) Normal = 32 degrees >39 degrees is high <28 degrees is low
Cephalometric Occlusal Plane Angle
Occlusal plane (OP) and anterior cranial base (S-N) Normal = 14 degrees High angle = longer anterior facial height Low angle = shorter anterior facial height
Cephalometric Incisor Position
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
Holdaway Ratio
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
Hierarchy of stability
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
Maxillary Hyperplasia
Posterior vertical excess - anterior open bite
Anterior vertical excess - increased gingival / incisor show
AP excess - acute nasolabial angle, increased gingival / incisor show, maxillary protrusion
Maxillary Hypoplasia
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
Rapid Palatal Expansion
Children have 50% tipping, 50% expansion (65% tipping in adolescents) High relapse (40-60%, recommend 50% overcorrection)
SARPE Indications
V-shaped maxilla / nasal stenosis
>7mm expansion
Avoids segmental surgery
Decreased relapse (30% versus 50% with LeFort)
Cephalometric Wits Appraisal
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
Cephalometric Middle Facial Height
N-ANS-FH
Normal = 54 +/- 3
Cephalometric Lower Facial Height
ANS-Me-FH
Normal = 65 +/- 4
Mandibular Hyperplasia
Class III skeletal appearance
Shallow labiomental fold
Mandibular Hypoplasia
Class II skeletal appearance
Micrognathia
Short mandibular ramus
Short mandibular body
Condylar Hyperplasia
Mandibular asymmetry, chin deviation to the contralateral side
Ipsilateral posterior open bite
Ipsilateral maxillary cant downward
Condylar Hypoplasia
Mandibular asymmetry, chin deviation to the ipsilateral side
Contralateral posterior open bite
Contralateral maxillary cant downard
IVRO Indications
Large setback procedures V-shaped mandible Less risk for paresthesia Thin anterior mandibular ramus Symptomatic TMD
IVRO Contraindications
Large counterclockwise movements (can lengthen the pterygomasseteric sling)
Can increase the gonial width
Period of IMF
Interincisal Angle
Steiner
Mean value of 130-131
Reduced angle = class II, division 1
Increased angle = class II, division 2
Facial contour
S-line = soft tissue menton through the āSā of the nose
Ricketts analysis = soft tissue menton through tip of the nose, measuring distance of lower lip
C-spine films
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
Soft tissue changes
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
Lateral cephalometric findings of posterior airway
Soft palate length = 35mm
Posterior airway space = 11mm
Hyoid to mandibular plan distance = 15mm
