唇齿相依 | chún chǐ xiāng yī
Xi Jinping used this chengyu during his Spring Festival Address on January 18th, 2020.
Meaning
Closely related, interdependent, lit. as close as lips and teeth (造句)
Original
“这一重要政治共识，深刻诠释了中缅两国唇齿相依、休戚与共的特殊关系，生动体现了两国人民患难与共、守望相助的兄弟情谊，全面擘画了双边关系未来发展的崭新蓝图。”
Source
http://www.xinhuanet.com/politics/leaders/2020-01/18/c_1125476462.htm