Table 2.

PICOS model for search strategy.

PICOS Model	Description
P: patients/population	Children with primary or mixed dentition who have unilateral posterior crossbite
I: intervention	Palatal expansion with different techniques
C: comparison	No treatment
O: outcome	Resolution of the crossbite
S: study design	Randomized controlled trials (RCTs), prospective and retrospective studies with concurrent untreated as well as normal controls, and clinical trials comparing at least two treatment strategies without any untreated or normal group involved