6Sanghoon Han, and Yoon Gi Hong, The Inverted Nipple: Its Grading and Surgical Correction[J]. Plast Reconstr Surg, 1999,104:389-395.
7Schwager RG, Smith JW, Gray GF, et al. Inversion of the human female nipple with a simple method of treatment[J]. Plast Reconstr Surg, 1974, 54: 564-569.