I mean, good to know that this is the radical that the Kanken considers as the correct radical, but the data sources used here on Jisho.org differ. There's no single authority in the world that decides what the correct radical for a given kanji should be (after all, the concept of radicals comes from paper dictionaries, and the authors are free to find their own favorite way of organizing the entries).
If you mouse over the radical information here on Jisho.org, it will also tell you that in the classic Nelson, the radical is listed as 齒 (the long version of 歯). But in the new Nelson, it is listed as 止. Is the new Nelson wrong here? Well, you could take it up with John Haig if you ever vacation in Hawaii.
As noted above, different resources will categorize different things differently. Kanken isn't authoritative. But if you want to know what they accept as an answer for something, you should always check their resources.
Their official kanji dictionary website is kanjipedia.jp
Thank you both for your replies. I've learned some new things.
Wrong radical
Hello, I just realised that the radical written in 歯 is apparently wrong. According to the official Kanken books, the radical for 歯 is 歯（は）, but in here, the written radical is 止 (Stop).