(This phrase acts like a noun. It is the direct object of the verb stopped. This phrase is a gerund phrase.) I stopped believing in Santa Claus when my mother took me to see him in a department store, and he asked for my autograph. (This phrase acts like a noun. It is the subject of the adverbial clause when my mother took me to see him in a department store.) I stopped believing in Santa Claus when my mother took me to see him in a department store, and he asked for my autograph.  It is the object of the preposition for.)
Ive googled 'white in extraction site'(!) and had some conflicting info: 'The white material is the blood clot; your rinsing has merely washed away the red blood cells and left the clotted fibrin material, which is white. This is normal, and is of no concern'. The second: 'White color in the extraction cavity...
Once the tooth has been pulled, a blood clot usually forms in the socket. The dentist will pack a gauze pad into the socket and have you bite down on it to help stop the bleeding. Sometimes the dentist will place a few stitches -- usually self-dissolving -- to close the gum edges over the extraction site. Sometimes, the blood clot in the socket breaks loose, exposing the bone in the socket.