Crossbites

Question 1

What type of discrepancy is a crossbite?

Answer 1

Transverse discrepancy in tooth relationship

Question 2

What is a cross bite?

Answer 2

Discrepancy in the buccolingual relationship of the upper and lower teeth

Question 3

List the types of crossbites

Answer 3

Posterior crossbite

• Buccal
• -> Unilateral buccal xb with displacement
• -> Unilateral buccal xb without displacement
• -> Bilateral buccal xb
• Lingual
• -> Unilateral lingual xb
• -> Bilateral lingual xb (scissorbite)

Anterior cross bite

Question 4

Describe a buccal crossbite

Answer 4

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

Question 5

Describe lingual crossbites

Answer 5

Buccal cusps of the lower teeth occlude lingual to the lingual (palatal cusps) of the upper teeth

Question 6

Describe anterior crossbites

Answer 6

One or more upper incisors are in lingua-occlusion relative to the lower arch

Question 7

What is the general aetiology for bilateral crossbites?

Answer 7

Most likely a skeletal discrepancy

Question 8

What is the general aetiology for unilateral crossbites?

Answer 8

Most likely due to local factors e.g. crowding, displacement of teeth

Question 9

Describe the skeletal aetiology of crossbites?

Answer 9

• Discrepancy in the relative widths of dental arch
• Gross anterior posterior discrepancy
• Genuine asymmetry of the dental bases

Question 10

List the skeletal discrepancy in width of the arches and what cross bite occurs as a result

Answer 10

• Maxilla narrower than mandible = buccal XB

- Mandible narrower than maxilla = lingual XB

Question 11

What AP discrepancies are associated with crossbites?

Answer 11

• Class III base = bilateral buccal cross bite and anterior cross bite
• Class II = lingual crossbite

Question 12

What type of cross bite is associated with asymmetry of dental bases?

Answer 12

Unilateral cross bite without displacement

Question 13

Describe the soft tissue factors in cross bite formation

Answer 13

• Low tongue position results in unbalanced pressure in upper buccal segments causing narrowing of upper arch (buccal cross bite)

Question 14

Describe digit sucking as an aetiological factor in cross bite formation

Answer 14

• causes low tongue position and increased buccal pressure as the digit is sucked
• Causing narrowing of upper arch forming buccal crossbite

Question 15

What are some other less common causes of cross bites

Answer 15

• Mouth breathing (lowered tongue position)

- Surgical repair of cleft palate (contraction of scar tissue = unilateral buccal XB)

Question 16

Which dental factors are highlighted in cross bite formation?

Answer 16

• Displacement of teeth out of the arch

- Cuspal interferences - displacement of mandible

Question 17

Why is treatment of XB with displacement important?

Answer 17

They may predispose susceptible individuals to TMJ disorders

Question 18

Which cross bite may be accepted?

Answer 18

Bilateral buccal without displacement

Question 19

List treatment options for bilateral buccal crossbites

Answer 19

• FA using expanded arch wires +/- cross elastics to expand maxilla
• URA to expand upper maxilla (quad helix most common)

Question 20

What considerations are required for use of fixed appliances to treat bilateral buccal cross bite?
How can you overcome this?

Answer 20

• If LFH is already increased - this method may increase it further by palatal tipping of upper teeth
• Overcome using high pull headgear or buccal torque

Question 21

How does rapid maxillary expansion work treat crossbites?

Answer 21

Skeletal expansion rather than tooth movement

Question 22

Treatment options for a unilateral buccal cross bite

Answer 22

• URA - T spring for premolars or Z spring for canines

- If severely displaced tooth - extraction

Question 23

Treatment options for lingual crossbite

Answer 23

• May need surgery and FA if there is a severe skeletal discrepancy
• If localised - FA to move tooth palatally or extract

Question 24

Treatment options for anterior cross bite

Answer 24

• URA - using Z spring if one or two in anterior cross bite

- Extract tooth if severely displaced/crowding