spring.14.4.2 Posterior cross-bite with displacement
Bilateral posterior cross-bites are often accepted as they usually reflect a transverse
skeletal discrepancy and cause no functional problem. Where the upper arch is
slightly narrow, the buccal teeth may initially occlude cusp to cusp and only achieve
full intercuspation when the mandible displaces laterally (923HFig. 14.12 (a) and (b)),
causing a unilateral posterior cross-bite. This can be difficult to detect if the patient
cannot relax the jaw muscles fully during examination, but it is important to
determine whether or not there is a lateral displacement. A unilateral posterior cross-
bite with a displacement is easily corrected during the mixed dentition, but one
without an associated displacement is probably skeletal in origin and correction
should not be attempted.
A unilateral posterior cross-bite with a displacement is treated by expansion of the
upper arch to remove the initial cusp-to-cusp contact, using an appliance such as that
shown in 924HFig. 14.12 (c). It has a mid-line expansion screw which is turned by the
parent once or twice a week, and double Adams clasps on 6e|e6. The d|d are usually
unsuitable for clasping as they have little or no undercut. The appliance should
contact c|c as these usually need to be expanded, but need not contact the incisors
unless a bite plane is required.