Q: “Nothing hurts. Could it still be a cavity?”
Ans: Yes. Whether you experience pain or not will be dependent on a few factors, such as:
1) how deep the cavity is … in the picture, the red portion is the nerve of the tooth. Generally, the closer to the nerve, the more likely to sense pain
2) if the cavity is acute or chronic… slow developing cavities tend to hurt less compared to a quick developing cavity
3) age can play a factor
4) if the cavity is really deep and chronic, the nerve may be necrotic already
Each situation is different. There may be other, more rare situations that may be a reason why you don’t always have to feel pain to know you have a cavity.