lower labial frenum

例句：

1. 1. The patient's lower lip mucosal fold was visible during the examination.
   在检查过程中，病人的下唇粘膜褶皱可见。
2. 2. The doctor advised him to keep his lower lip mucosal fold clean and dry.
   医生建议他保持下唇粘膜褶皱清洁干燥。
3. 3.The patient complained of a soreness in his lower lip mucosal fold.
   病人抱怨他的下唇粘膜褶皱处疼痛。