SKELETAL AND FUNCTIONAL-EFFECTS OF TREATMENT FOR UNILATERAL POSTERIORCROSSBITE

Unilateral posterior crossbite (UPXB) is a common malocclusion, freque ntly presenting a lower midline deviation, accompanied by Class II sub division relationships in final closure and a very high prevalence of the reverse sequencing (RS) pattern of jaw movement. These features of ten persist even after the elimination of the crossbite. The purpose o f the present study was to examine in detail the morphologic, skeletal , and functional effects of the treatment for this malocclusion catego ry. The experimental group consisted of 24 children in the mixed denti tion stage with UPXB who were treated with removable expansion plates and a control group of 10 age-matched children with normal occlusion. Longitudinal follow-up revealed a stable dental maxillary arch expansi on of at least 1.5 mm but a complete elimination of crossbite in only 50% of the cases. The frequent persistence of Class II subdivision rel ations and lower midline deviation that were not due to functional man dibular shift was striking. The pretreatment posteroanterior (P-A) cep halograms indicated reduced facial and maxillary widths. After treatme nt, the achieved maxillary width increase was greater than expected wi th normal growth. Longitudinal assessment of the mandibular movement r esponse revealed by the electrognathograph showed a high prevalence of RS, which was reduced after treatment. In conclusion, (1) a higher th an expected prevalence of skeletal transverse aberrations at the maxil lary and zygomatic levels were found in the UPXB group; (2) the remova ble expansion appliance induces transverse growth of the maxilla; and (3) an inherent pattern of jaw movement is characteristic to the UPXB and does not change significantly with orthodontic treatment.