Gummy smile always consitutes an unesthetic smile characterized by excessive exhibition of the gums during a full smile. There are several etiologies for gummy smile, and the most commonly overlooked etiology is altered passive eruption（APE）. APE is a clinical situation produced by excessive gum overlapping over the enamel limits, resulting in a short clinical crown appearance, which is due to failure in concluding the passive eruption phase. APE can be corrected by periodontal surgery. However, it is essential to establish a differential diagnosis for achieving an esthetic, biological and stable result that satisfies both clinician and patient. This article will review the concept of APE, its classification and epidemiology, clinical diagnosis, treatment modalities and esthetic considerations and also the process of tissue healing.
