crossbites

Question 1

what is the definition of a cross bite?

Answer 1

A Crossbite is apparent when the buccal cusps of the lower teeth occlude lateral to the buccal cusps of the upper teeth.

Question 2

what is the difference between a buccal cross bite and a lingual cross bite?

Answer 2

> Buccal crossbite: buccal cusps of mandibular teeth occlude buccal to the buccal cusps of the maxillary teeth

> Lingual crossbite (scissors bite): buccal cusps of mandibular teeth occlude lingual to the lingual cusps of the maxillary teeth

Question 3

what is the definition of displacement?

Answer 3

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

Question 4

what is the prevalence of crossbites?

Answer 4

> Affects 8-22% of the population

> 10% of orthodontic patients

> only 2% are bilateral

> 3 times more common in pre-normal occlusions (Class III)

Question 5

what are the classifications of crossbites?

Answer 5

1. Unilateral buccal crossbite
   
   • with displacement
   • without displacement
2. Bilateral buccal crossbite
3. Unilateral lingual crossbite
4. Bilateral lingual crossbite (scissors bite)

Question 6

what are bilateral crossbites often associated with?

Answer 6

> always skeletal in origin

> often combined with a skeletal III

> treatment should be approached with caution, may cause cusp to cusp

Question 7

what causes a unilateral crossbite without displacement?

Answer 7

> due to a true asymmetry of the skeletal bases, usually pathological in origin

> this could be due to cleft palate or condylar hyperplasia (condyle grows excessively on one side)

Question 8

what is the aetiology of a cross bite?

Answer 8

1. Hereditary factors … skeletal
2. Environmental factors =

       i. Digit sucking
       ii. Mouth breathing

Question 9

are transverse anomalies bento alveolar or skeletal?

Answer 9

> Transverse anomalies like A-P anomalies can be dentoalveolar or skeletal or a combination of both

> accurate diagnosis is important for effective and stable treatment

Question 10

why do we treat cross bites?

Answer 10

> Some evidence that displacing contacts may predispose a susceptible individual to TMD.

> Although this evidence is weak, a crossbite with a displacement is therefore a functional indication for orthodontic treatment.

> Preparation for bone grafting in patients with CLP.

Question 11

which crossbites should we treat?

Answer 11

> NOT unilateral or bilateral crossbites without displacement.

> The malocclusion is of minor importance.

> There is a considerable tendency towards relapse – up to 40% with all for, sof active expansion

Question 12

what was an old recommendation of treatment for child with a cross bite?

Answer 12

> Some recommend Grinding away cusps =

1. To eliminate the displacing contacts.
2. To facilitate spontaneous correction

N.B. But NOT recommended! as subjecting young child to invasive treatment that might not work and may suffer from hypodontia, this can also impact cooperation

Question 13

what are the conflicting views in treatment of crossbites in the mixed dentition?

Answer 13

> NO – Leighton (1986) – spontaneous
correction frequently occurs.

> YES – Schroder (1981) & Petren (2003) – high
frequency of transmittance to
permanent dentition.

Question 14

what is the general consensus in treatment of cross bite in a mixed dentition?

Answer 14

> Do not burn up patient co-operation as they will often require further tx

> Best with quadhelix.

> Consider leaving until later definitive Rx.

Question 15

what is used for treatment of a dentoalveolar crossbite?

Answer 15

> Upper Removable Appliance

> Quadhelix

> Fixed appliances

Question 16

what is used for treatment in a skeletal cross bite?

Answer 16

> Rapid maxillary expansion

> Surgery

Question 17

how does a quad helix work?

Answer 17

Fixed expansion spring.

Orthodontic & orthopaedic (<11 yrs)
movement.

1 mm hard SS.

Slow continuous force 0.5-1 kg.

Activated by half a tooth width on either side

Works by a combination of buccal tipping and skeletal expansion (6:1 ratio)

Question 18

why is a quad helix preferred over URAs?

Answer 18

> Remains firmly in place.

> Does not rely on patient co-op.

> Can de-rotate 1st molars.

> Cost / benefit (URA 40% more expensive).

Question 19

what fixed appliances are used for crossbites?

Answer 19

> expanded archwires

> (through- the bite elastics)

Question 20

when would you use rapid maxillary expansion?

Answer 20

> only for skeletal crossbites

> should not be used indiscriminately

Question 21

what are the mechanics behind a rapid maxillary expansions?

Answer 21

> Pt turns the non – spring loaded jackscrew once per day (0.2-0.5mm/day) for 1-3 weeks. Bell, 1982

> Warn patients that a median diastema may develop quickly during treatment.

> 2-5 kg force

> P.L. Hyalinisation

> Bends alveolar process

> Opens mid-palatal suture

> 40% of expansion may be due to skeletal change

Question 22

what are the indications for a rapid maxillary expansion

Answer 22

> Mx molars & PMs buccally inclined.

> Discrepancy >4mm b/n Mx & Md molars.

> Upper limit 10 -12 mm > surgery.

> Age 13 – 15 years.

> The mid-palatal suture usually fuses around 15 years, surgically assisted rapid palatal expansion (Sarpe) may be considered after this time

Question 23

what are the 3 main tx methods for fixing a posterior cross bite?

Answer 23

1. Rme followed by a Transpalatal arch to hold the expansion during fixed appliance treatment
2. A quadhelix
3. Fixed appliances with through the bite elastics