Management of Posterior Crossbite

Question 1

Crossbite

Answer 1

Buccal cusps of the lower teeth occlude lateral to the buccal cusps of the upper teeth

Question 2

Buccal CB

Answer 2

Buccal cusps of mandibular teeth occlude buccal to the buccal cusps of the maxillary teeth

Question 3

Lingual CB

Answer 3

Scissors bite
Buccal cusps of the mandibular teeth occlude lingual to the lingual cusps of the maxillary teeth

Question 4

Displacement

Answer 4

Any deflection occurring on closing from RCP to ICP demonstrated by a deviation in the mandible in the transverse or A-P to achieve maximum interdigitation

Question 5

Prevalence

Answer 5

8-22% of population
10% of orthodontic pts
2% are bilateral
3x more common in pre-normal occlusions

Question 6

Classification

Answer 6

1. Unilateral buccal crossbite
   - with displacement
   - without displacement
2. Bilateral buccal crossbite
3. Unilateral lingual crossbite
4. Bilateral lingual crossbite

Question 7

Bilateral CB

Answer 7

Skeletal
Often combined with skeletal III

Question 8

Unilateral CB without displacement

Answer 8

Asymmetry of the skeletal bases, usually pathological in origin
Underling CLP
Condylar hyperplasia

Question 9

Aetiology of CB

Answer 9

Hereditary factors – skeletal
Environmental factors – digit sucking/mouthbreathing

Question 10

Dentoalveolar or skeletal

Answer 10

Transverse anomalies can be dentoalveolar or skeletal
combination of both

Question 11

why tx

Answer 11

some evidence that displacing contacts may predispose a susceptible individual to tmd
although the evidence is weak, cb with a displacement is therefore a functional indication of ortho tx
preparation for bone grafting in patients with CLP

Question 12

which CB should we tx

Answer 12

Eliminate displacing contacts
Facilitate spontaneous correction

Question 13

Appliances

Answer 13

Dentoalveolar crossbite
- upper removable appliance
- quad helix
- fixed appliance

Skeletal crossbite
- rapid maxillary expansion
- surgery

Question 14

Quadhelix MOA

Answer 14

Fixed expansion screw
Orthodontic and orthopaedic movement <11 yrs
1mm Hard ss
slow continuous force
activated by 1/2 tooth width on either side

Question 15

Rapid maxillary expansion

Answer 15

Pt turns the non-spring loaded jackscrew once per day (0.2-0.5mm per day) for 1-3 weeks
warn pt that median diastema may develop
2-5kg force
PL hyalinisation
Bends alveolar process
Opens mid-palatal suture
40% of expansion may be due to skeletal change

Question 16

RME indications

Answer 16

MX molars and PMS Buccally inclined
Discrepancy >4mm B/N MX & MD molars
Upper limit 10-12 mm > surgery
age 13-15 years
Mid palatal suture usually fuses around 15 years. Surgically assisted rapid palatal expansion may be considered after this time.