5. Orthognathic and Obstructive Sleep Apnea Flashcards
Normal incisor angulation
Maxillary incisors 102 degrees to SN
Mandibular incisors 90-95 degrees to mandibular plane
What is Bolton Analysis
Determines disproportion of size of permanent maxillary and mandibular teeth (tooth size discrepancy between upper and lower teeth). Two ratios can be calculated (overall ratio and anterior ratio).
Overall ratio: sum of MD width first molar to first molar of mandibular teeth divided by sum of MD width first molar to first molar of maxillary teeth (91.3%)
Anterior ratio: canine-canine 77.2%
How much orthodontic expansion can be achieved
~5mm (greater than 5mm = severe maxillary transverse discrepancy –> SARPE or segmental osteotomy).
How are vertical facial proportions analyzed (facial thirds)
Upper third: trichion (Tr) to glabella. Assess eyebrow shape, position, symmetry.
Middle third: glabella to subnasale. Includes eyes, nose, and cheeks. Scleral show, flattening of cheek bones may indicate midface deficiency.
Lower third: subnasale to menton. Ratio of middle third to lower third vertical height should be 5:6.
How are transverse facial proportions assessed? (rule of fifths)
Divide sagitally into 5 equal parts. Each segment is the width of one eye.
Outer canthi coincide with gonial angles. Medial canthi coincide with alar bases of nose. Interpupillary distance coincides with corners of mouth.
Describe the Steiner analysis.
Assess maxillary AP position: Maxillary AP positions in relation to anterior cranial base (S-N). SNA 82* is considered normal.
Assess mandibular AP position: mandibular AP position in relation to anterior cranial base (S-N). SNB 80* is considered normal
Assess AP maxillomandibular relationship. Normal relationshiop is indicated by ANB of 2*. Class III <2; Class II >2.
Maxillary incisor axillary position should be 22* to NA and most anterior point should be 4mm ahead of NA. Facial surface of maxillary incisor should be 4-6mm ahead of vertical line through A point.
Mandibular incisor angulation to NB line should be 25* and most labial point of incisor should be 4mm anterior to the line.
Describe Ricketts analysis
Ricketts analysis uses maxillary depth. Measures angle at the intersection of FH line and NA line. Angle of 90 +/- 4* is ideal. Angle less than 86* indicates retrognathia, while angle greater than 94* indicates prognathism.
Describe McNamara analysis
Assess maxillary AP position: measures distance from A point to nasion perpendicular (a line that crosses N and is perpendicular to FH), normal range 0-1mm. A negative number indicates retrognathia, while a positive number greater than 1 indicates prognathism.
Assess mandibular AP position: measures the distance from Pog to N perpendicular. Ideal number for mixed dentition is -8 to -6mm, adult female -4 to 0mm, adult male -2 to 2mm.
Describe Downs analysis
Assesses AP position of mandible with facial angle.
Indicates relative AP position of mandible to cranium.
An angle formed by intersection of the facial line, N-Pog’ line and FH line. Mean is 82-95*.
What is Wits Appraisal?
Linear relationshiop between maxilla and mandible not influenced by cranium.
Points BO and AO established by dropping perpendicular lines from A point and B point onto occlusal plane.
BO 1mm ahead of AO in males
BO and AO coincide in females.
Describe mandibular plane angle. What is normal? What is associated with an increase or decrease in plane angle?
Mandibular plane angle (Steiner) formed between mandibular plane (Go-Gn) and anterior cranial base (S-N), normal value 32*
> 39* is high; <28* is low.
Increased plane angle = dolichocephaly, class II malocclusion, vertical maxillary excess, apertognathia.
Decreased plane angle: bradycephaly, skeletal deep bite, notched gonial angles.
What assessment is used for chin position?
Holdaway ratio:
Extend NB line to inferior border of the mandible and compare the distance between L1 (incisal edge of mandibular incisor) and Pog from this line.
1:1 is ideal in males and 0.5-1 in females.
Only of value if lower incisors are in the proper position!
Describe your technique for a LeFort Osteotomy
- K wire nasofrontal suture
- Maxillary vestibular incision from one zygomaticomaxillary buttress to the other (5mm non-keratinized mucosa for closure).
- Bony exposure via FTMPF
- Dissection to nasal aperture and protect nasal mucosa by lifting it up with freer elevator. Tunnel to pterygoid plates bilaterally.
- Dissect ANS free, dissect nasal floor off palatal shelf using freer.
- Horizontal cut from posterior maxilla to piriform rim bilaterally.
- Nasal septum separated with nasal-guarded osteotome
- Pterygoid plate osteotomies with pterygoid osteotome
- Lateral nasal wall osteotomies with guarded osteotome.
- Vertical interdental osteotomies at this time if multiple-piece.
- Induced hypotension MAP 50-65 mm Hg
- Downfracture
- Trim bony interferences of septum and lateral walls
- Ensure mobility of maxilla
- If multi-piece, cut palatal paramedian osteotomy just lateral to nasal septum.
- Place splint, MMF
- Rotate maxillomandibular complex up. Grind as needed to achieve correct vertical position. Place maxilla into new position with plates at piriform and zygomaticomaxillary buttresses.
Bleeding sources LF1 osteotomy
Pterygoid plexus
Posterior superior alveolar artery
Greater palatine artery
Terminal branches of maxillary artery.
Note that internal maxillary artery is 25mm superior to the base of the junction of the pterygoid plates in a normal maxilla. Pterygoid osteotome is 15mm in height, leaving 10mm margin for safety.
How do you treat bleeding from the maxillary artery after LF1
Attempt pressure packing with gauze or hemostatic agent. If no resolution, try to identify vessel for cautery. If continues, consider IR intraoperative consult for embolization.
Prevention: in extremely small maxillas i.e. cleft or syndromic patient, pre-op CT angiogram may be useful to ID these vessels.
Anterior open bite after MMF release in LF1
Condyles were not seated in fossa or area of premature bone contact. Remove fixation, check for bony interferences, ensure passive condylar positioning, replace fixation.
Epiphora following LF1
More common in high LeFort osteotomies due to damage of nasolacrimal system, nasoseptal deviation, or swelling. If no resolution after 6 weeks, CT scan to r/o source. May require dacryocystorhinostomy or nasoseptoplasty depending on etiology.
How much transverse maxillary expansion can you achieve by dental tipping?
5mm with healthy periodontium and upright teeth.
Tipping vs. expansion children vs. adolescents
Orthodontic rapid palatal expansion takes advantage of growth potential in growing children and adolescents.
Transpalatal dental-borne and/or micro implant borne (MARPE) orthopedic expander opens midpalatal suture, tips teeth, and bends and remodels the alveolus.
Older patients have more sutural resistance that results in less expansion and more dental tipping, lateral tooth displacement, and periodontal defects.
Children 50% tipping and 50% expansion
Adolescents 65% tipping and 35% expansion
High relapse (40-60% depending on age) with up to 50% overcorrection recommended.
More widening at canines than molars (3:2)
Indications of SARPE
> 7mm expansion
Desire to avoid segmental maxillary surgery
Thin, delicate soft tissue with gingival recession in bicuspid-canine region
Significant nasal stenosis
Level occlusal plane
Constricted V-shaped arch form
Benefits of SARPE
Greater arch expansion
May avoid extractions
Better orthodontic alignment before definitive orthognathic surgery
Improved periodontal health, esthetics, and buccal corridor
Segmental LF vs. SARPE + single piece LF
For expansion >7mm, SARPE stability (30% relapse at canine and molars) far exceeds segmental LF and RPE (50% relapse).
More expansion at canines than molars due to lateral nasal wall and palatine bone resistance
Describe the SARPE surgical procedure
Maxillary vestibular incision from one zygomaticomaxillary buttress to the other. FTMPF.
Bilateral maxillary osteotomies from piriform rim to pterygomaxillary junction
Release of nasal septum
Dissect mucosal tunnel between #8-9 from alveolar crest to the nasal floor.
Use thin spatula osteotome between 8 and 9 and extend osteotomy to PNS.
Osteotomy of anterior portion of lateral nasal walls for 1.5cm.
Bilateral pterygoid plate osteotomies
Activate distractor to allow passive expansion of 3-4mm. Then decrease expansion to a bony gap of 0.5-1.5 mm at the end of the procedure.
Close any perforations of palatal tissue
Close with alar base cinch and V-Y closure
5-7 days latency
Rate and rhythm 0.25mm twice/day (0.5mm/day)
Palatal expansion within 4 weeks of surgery. Allow 4 months retention before removing expander.
Timing of SARPE. Latency, rate/rhythm, retention.
5-7 days latency
Rate and rhythm 0.25mm twice/day (0.5mm/day)
Palatal expansion must occur within 4 weeks of surgery. Allow 4 months of retention before removing expander.
Expansion is asymmeteric following SARPE. Explain.
Most common expansion complication. Results from incomplete release of the pterygomaxillary junction on one side. Half the time, the asymmetry self-corrects. Others may require segmental osteotomy to correct asymmetry at least 4 weeks after SARPE.
Expansion stops prematurely after SARPE
Can result in pain, dental tipping, periodontal breakdown, palatal tissue impingement by expansion device, relapse. Treat with adequate mobilization and removal of bony interferences.
