Depends on your local consumer protections. Over here you're entitled to a product that is fit for purpose. A defective product is clearly not that, with or without dent. Of course getting the store to honor that is going to be a lot of effort pretty much anywhere in the world, but I don't feel like a small dent contributes to that.
To take a random example: I bought ear defenders in a hardware store. I used them fairly frequently for a couple of months, after which I put them on my head and the headband promptly snapped right down in half. I had to argue with the store that that's not a normal way for ear defenders to "wear down", but I got a new pair in the end which have been holding up for years now.
That's an interesting story, but to relate it to my previous comment, we have to ask: did you purposely damage the ear defenders for emotional reasons? If so, did you tell them that?
No, but as long as the damage is unrelated to the defect it's not relevant as far as the law is concerned. I have a right to a product that's fit for purpose. That right doesn't specify anything about the state of the product otherwise.
To take a random example: I bought ear defenders in a hardware store. I used them fairly frequently for a couple of months, after which I put them on my head and the headband promptly snapped right down in half. I had to argue with the store that that's not a normal way for ear defenders to "wear down", but I got a new pair in the end which have been holding up for years now.