retainer|retainers

她晚上戴保持器。

She wears a ___retainer at night.

这位贵族雇佣了三个侍从来照料他的日常生活。

The nobleman hired three ___retainers to take care of his daily needs.

矫正器用来移动牙齿，保持器用来固定牙齿。

___Braces move the teeth, and a ___retainer keeps them in place.