space maintaier

I left earlier the office today and took my daughter to the dentist. Her dentist wanted to check her mouth, so she had two teeth out 3 weeks ago. One of them, an adult tooth has already come out, but the other side, it has not yet. They told us that my daughter needs "space maintainer"(in Japanese "HO GE KI SO U CHI"). It is to keep the space not to become narrower for adult tooth. To make this thing, they took her impression. I thought they could finish her treatment today, but we have to get back there in 2 weeks.