Whether or not arch expansion is recommended for children at age 7 depends on the individual case. If the maxillary dentition is significantly crowded, the upper arch is narrow or a posterior anticuspension has developed, a spiral expander can be used to expand the arch, prompting the maxillary mesial crevice to crack open and continually form bone deposits, realizing that the teeth will move toward the cheeks as the arch width grows, thus aligning the teeth. If a 7-year-old child’s first permanent molar has not erupted yet and the root of the molar has begun to resorb, it is difficult to obtain enough support to fix the spiral expander, so it is not suitable for expanding the arch.