(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...
After an extraction, a blood clot forms in the tooth socket. This is an important part of the normal healing process. You should therefore avoid activities that might disturb the surgical area. Do not rinse your mouth vigorously or probe the area with any objects or your fingers.