Orthognathics Flashcards
Miloro 2015
What are the landmarks of facial thirds?
How is the lower third split?
Which third do orthognathic procedures usually affect?
Vertical thirds:
trichion ( Hairline in midline) -> Glabella - > Subnasale -> menton
Subnasale -> Oral commisure = 1/3
Oral commisure -> menton = 2/3
Most orthognathic procedures affect lower 1/3rd.
Waht are the proportions of facial fifths?
Horizontal fifths:
Based on length of eyes
ICD ~ Alar width
OCD~ Medial limbus distance
Judging Asymmetry
Use bite stick on each arch separately and compare cant of each arch to interpupillary lines
What is the best clinical examination to determine maxillary position?
Incisor display at rest (treat to this!)
- normal 2.5 +/- 1.5mm
- in animation smiles include 80-100% of crown +2-4 mm of gingiva
Other factors include
- length of clinical crown, length of upper lip, amount of vermillion,
- Age lowers smile line by 2-3 MM so it is better to overcompensate (show more incisor)
CR what is it?
CO what is it?
Centric Relation - most anterior superior position of condyle (independent of tooth contact)
- hard to reproduce - in surgery usually push condyles most posterior and superior
- anesthesia cause laxity of the joint due to lack of muscle tone and stripping of soft tissues.
Centric occlusion = habitual occlusion
What is the normal Orthognathic profile angle?
Wher is frankfort horizontal
Convex - 13 degrees from glabella to subnasale to menton.
Porion ( EAC) to orbitale.
Angles of profile? What are normals of NLA, FNA, LMA, NCT angles?
FNA = frontonasal = 125-135 NLA = nasal labial= 90-95 LMA= Labiomental = 110-120 NCT= neck chin throat =120
Chin position from profile is based on
Zero meridian line ( line perpendicular to FH that passed through nasion) - Pogonion should be +/- 4 mm from this line
Absolute vs relative transverse discrepancy?
Relative discrepancies can be corrected by moving jaws forward and/or back.
What is correct diagnosis in patient who is class three with anterior open bite and transverse discrepancy (lateral ceph showing maxillary deficiency)?
Maxillary AP deficiency
Rocky Mountain transverse analysis
used to analysis maxillary transverse discrepancies form J point to J point on PA Ceph
Patient presents with class I on the left and class II occlusion on the right without a midline discrepancy. What will be needed?
a. Segmental osteotomy
b. body ostectomy
c. extraction of teeth
d. rotationall SSO and VRO setback
Extraction of teeth
- neededfor 1. crowsding, 2 compensatio needed, 3. correcting curve of spee.
correcting curve of spee (curve from posteriro to anterior)
In order to fix a large curve of spee ( deep) you need 1.25 mm of space for every 1 mm of correction.
How can you increase arch space (4 ways)
- Premolar extractions
PM1 removed if you want ti retract anterior teeth
PM2 removed if you want to protract the posterior teeth - Widen arch with RPE or O(orthopedic) Expansion
- Inter-proximal reduction
- Incisor proclination
Which is contraindicated in the presurgical orthodontic tx of malocclusion II elastics?
a. Class II elastics
b. Class III elastics
c. Decompensate retroclined upper incisors
d. decomponesate proclined lower incisors
Class II elastics (class II elastics correct class II bites by pulling from anterior of upper to posterior of lower; class III elastics correct class III bites by pulling opposite) would not be used so orthodontist can maintain the overjet that is there currently for decompensation.
What reference is used to decide if you want to extract lower premolar one vs lower premolar two?
Occlusal plane must be maintained
- take out PM1’s with class III elastics to retract lower anterior
- take out PM2’s with class II elastics to protract posterior teeth
A 16 yo with class II malocclusion is beginning orthodontics with LeFort advancement and mandibular setback. There is significant crowding in both arches with dental compensations. What pattern of premolars should be extracted?
a. Max PM1 and Mand PM2
b. Max PM2 and Mand PM1
c. Max and Mand PM2
d. Max and Mand PM2
A. Maxillary PM1 and Mandibular PM2
Lefort advance + setback = Class III
Class III = compensated teeth (retroclined mandibular incisors and proclined maxillary incisors) - ext PM1 max to retract maxillary incisors and ext PM2 mandible to bring lower posteriors forward.
Class III patient will finish in a class II molar occlusion
Class II = deficient mandible with compensated teeth (proclined mandibular incisors and retroclined maxillary incisors) - EXT PM 2 Maxillary and EXT PM1 mandible to retract anteriro teeth
Class II patient will finished in a class II molar occlusion.
Hard and Fast:
EXT PM2 if you want to maintain incisor postion in that arch ( if they are retroclined or relative normally)
EXT PM1 if you want to retract incisors in that arch (they are proclined)
Orthodontic goals and what are 3 exceptions
Level, align, decompensate
Exception to this rule
- Class II deep bite with short face
- prefer tripod occlusion to maintain curve of spee and lengthens facial height - close posterior open bites with elastics - planned segmental surgery
- Iowa/Casko spaces (between k9 and laterals) used to maximize mandibular movement and can close after with ortho.
What is bolton analysis used for?
tooth crowding and need for extractions
- Anterior vs overall analyses
- compares tooth width to arch length
After 2-jaw surgery, the maxillomandibular complex is noted to be off axis what caused this?
a. condyle note seated properly
b. rigid fixation failure
c. dental interferences
d. inaccurate model surgery
d. inaccurate model surgery
Maxillary surgery is usually completed first in most double jaw surgeries. When you the mandible be completed first (5 reasons)?
- Steep occlusal plane with plan for maxillary downgraft. (huge open bite)
- Inaccurate interocclusal records.
- Difficulty with intraoperative MMF in intermediate position (intermediate splint is too bulky or OJ to large for wires).
- basically too large a class two or too large a class III. - TMJ surgery concomitantly
- Uncertain in condylar position ( usually due to condylar resorption)
Segmental Surgery requires (for stability) 2 options?
- Transpalatal arch wire
2. Fine splint with partial palatal coverage
What causes variations in ceph analyses?
What is the center of rotation of the condyles?
a. Condylion (Co)
b. Articulare (Ar)
c. Center of condyle (c)
d. Instantaneous center of rotation (ICR)
cranial base variations
D. ICR - center changes all the time
- Dolphin uses condylion (most posterior superior aspect of condylar head)
What is Steiner analysis used for?
Evaluating incisor position
- SNA, SNB, ANB
Rarely uses final splint why?
To avoid anterior open bite - tough to close
When does skeletal maturity occur in the female patient?
a. 11-13
b 14-16
c 16-18
d. >18
B.14-16
Girls 15-17
Boys 16-18
Other than serial lateral cephs what is the best method for estimating facial skeletal maturity?
C-spine evaluation (Cervical Vertebrae 2) (most accurate)
- increased convexity in lower border of C2
- height becomes taller than wider (c2)
- Shape goes from wedge -> square -> rectangle (mature)
Serial cephs q6m
Hand wrist not as accurate but uses Fishman maturation index
Can you do surgery during growth?
yes - for low angle class II hypoplasia
What is envelope of discrepancy?
It is a chart showing three circles that correlate to the amount of movement possible with that method.
Smallest = ortho Medium = ortho with growth modification (herbst/head gear) Largest = ortho and surgery
TMJ and orthognathics?
Anteriro disc displacement associated with class II malocclusion
Must treat preexisting TMJ disease prior.
Tough to get CR of TMJ due to general anesthesia, supine position, muscle stripping.
Epidemiology of Malocclusion
Class II is more common but less often requires surgery.
Class III is much less common but usally requires treatment
BSSO History
Dalpont modification?
Hunsuck?
Trauner and Obwegeser in 1957
Dalpont - 1961 modification to bring vertical ostectomy forward to first molar - allows for more bony contact = increased success
Hunsuck - 1968 modification to bring horizontal medial ostectomy to retrolingular depression
During SSO, injury to the IAN can be minimized by placing the vertical osteotomy lateral to which area?
a. 1st molar
b 2nd molar
c. 3rd molar
d. retromolar pad
a. 1st molar
- CT studies show this is when IAN is most lingual (4.1mm), cortex is 2-3 mm
Is L configuaration or straight configuration more stable?
L is more stable, but bicortical screws can widen intercondylar distance.
Single monocortical plate along champy’s line of tension is effective. along external oblique ridge, and allows for some play.
Prescence of third molars in SSRO results in ?
a. Less IAN injury
b. more bad splits
c. more stable fixation
d. less operative morbidity
b. more bad splits
- also increased risk of poor fixation and IAN/LN injury
- remove 9-12 months prior
Precious 2012 wrote a study refuting this
seating condyle in class II vs class III patients?
Class II = “firmly”
Class III = looser
Following SSO advancement and elimination of bony interferences, a bony gap remains between anterior extent of the proximal and distal segments. If a lag screw is used for fixation what happens?
a. distal segment advances anteriorly
b. anterior open bite develops
c. medial condylar displacement
d. lateral condylar displacement
d, lateral condylar displacement
- lag screws will bring segments together in this case it will bring the anterior portion of the proximal segment closer to the distal segment (more medial) kicking out the posterior of condylar portion laterally.
What causes a IAN paresthesia with VRO? a. Setback > 10 mm b. Medial displacement of proximal fragment c. Excessive medial dissection D. Use of rigid fixation
VRO used only for setbacks and useful for asymmetries.
c. Excessive medial dissection
What is the best osteotomy design for avoiding the IAN during VRO?
a. Depth of sigmoid notch to antegonial notch
b. 5mm posterior to antilingula
c. mid ramus
d. from depth of sigmoid to any point in the posterior border above the gonion.
b. 5mm posterior to antilingula
Better v shaped mandible - u shapped are tough to access and visualize
- the mandibular foramen is located 7mm from the posterior boder of the ramus in 3% of patients.
- use oscilalting saw (7mm depth) with LeVassaeur-Merril retractors for adequate depth
