ball retainer

例句：

1. 1. The patient needs a ball retainer to prevent the tooth from shifting back into its original position.
   病人需要球保持器来防止牙齿重新回到原来的位置。
2. 2.The dentist recommended that the patient wear a ball retainer while the tooth was being treated.
   牙医建议患者在治疗期间佩戴球保持器。
3. 3.The ball retainer helps to stabilize the tooth and prevent it from moving during chewing.
   球保持器有助于稳定牙齿，防止在咀嚼过程中移动。