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