Coffee and caffeine consumption and risk of periodontitis: National Health and Nutrition Examination Survey 2009–2014 oleh Wan‐Zhe Liao, Zhi‐Yi Zhou, Xian‐Nan Wu, Xiao‐Feng Zhu, Song‐An Li, Jun‐Huang Zheng, Jia‐Nuo Tan, Hao‐Kai Chen, Ting‐Yu Gu, Zhe Xu, Ya‐Han Li, Xu‐Guang Guo