* Absence of something vital: A lost index page makes a book difficult to navigate and understand. Similarly, the lack of teeth in the smile signifies a loss of something essential - youthfulness, vibrancy, and possibly even strength.
* Disconnection from the past: An index page is a guide to the contents of a book. Its absence signifies a disconnect from the past, perhaps hinting at a loss of memory or a sense of detachment from previous experiences.
* A sense of incompleteness: A lost index page leaves the book feeling incomplete. The toothless smile is also incomplete, suggesting a sense of longing, sorrow, or perhaps even vulnerability.
* A focus on the essence: While the index is missing, the book's contents still exist. Similarly, the simile implies that the smile, while missing teeth, still holds a sense of warmth, affection, or even humor. The absence of teeth doesn't diminish the essence of the smile.
Overall, the simile paints a picture of a person who has experienced some kind of loss or aging but who still holds onto their essence and ability to connect. It's a poignant image that suggests the beauty and strength that can be found even in the face of loss.