Why does a black coating form on the socket after tooth extraction?

The black discoloration isn't quite what the question makes it sound like. It's not "buildup" in the sense of an infection, but more like pigmentation that appears through a completely natural process. When the socket heals, a blood clot forms in it, which darkens and turns brownish over time - that's a normal part of healing. The surrounding tissue can also darken because of dying blood cells and hemoglobin pigments. A week ago is actually right about when all this becomes especially noticeable.

An infection looks completely different. If there were pus, you'd feel pain, swelling, maybe a puffy cheek, an unpleasant smell or taste from the socket. Red flags are when your temperature spikes or pus oozes from the wound. You don't have any of that, the socket is healing, there's no pain - so everything's fine.

Just keep up the normal care: rinse your mouth with warm salt water after meals, don't poke the wound with your tongue or a toothpick, avoid hot food and alcohol. In a week or two that discoloration will lighten on its own. If after two weeks nothing changes or you get pain and swelling - then see a doctor, but there's nothing to worry about right now.

After a tooth extraction, blood accumulates in the socket and darkens over time - this is a completely normal healing process, nothing to worry about. If there's no pain, swelling, or bad odor, there's nothing to be concerned about; the darkening is just blood oxidation and the formation of a protective clot. In a couple of weeks everything will return to normal, and the dark coating will disappear on its own.

How many days have passed since the extraction? A week is a normal timeframe when the socket is still actively healing, and all kinds of dark spots there are completely ordinary.

At the extraction site, a blood clot forms that protects the bone and tissues underneath. This clot darkens over time - it's not plaque and not dirt, but just a chemical process, like when blood on a bandage dries out and turns brown. Your body gradually reabsorbs it, replacing it with new tissue. At the same time, food particles can get in there, and they also create the visual effect of dark plaque.

The main thing to watch for: if there's no pus (it's usually yellow or greenish), if your cheek isn't swelling, there's no sharp unpleasant smell from the socket, and your temperature is normal - then everything is going as it should. Black or dark brown color is just the color of a healing socket. Sometimes it looks scary, but there's no need to worry. If the concern persists, you can go see a dentist for a checkup, but based on your description this is a completely normal process.