Manochiopinig, S. ., A. . Chuangsuwanich, and S. . Taweepraditpol. “The Nasoendoscopy Study of Velopharyngeal Closure Patterns in Normal Thai Volunteers”. Siriraj Medical Journal, vol. 57, no. 5, May 2005, pp. 118-21, https://he02.tci-thaijo.org/index.php/sirirajmedj/article/view/245585.