They're not impervious to the user regardless of how they are made. The pitting on that stem and scrapes around the button look pretty rough.
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On a smaller note, the marks on the bottom of the bit is actually some unprofessional work I done on the bit ONLY with wet sandpaper, and I guess some scratches ended on the stem itself, so it wasn't from rough handling a 15 grams pipe. The button was too sharp and circular and was irritating my gums when resting the pipe, so I had to do some work on it to make the button more low profile. I don't have the best hands, but that pipe was for me and I didn't care for some blemishes.
Here is an image which shows a clearer view, you can see the mark is only on that side, and it isn't deep or rough. The bite through was in the opposite too. For sure it wasn't my teeth that caused it. And a side by side with a mike bay poker which I used for 2 months now, nearly daily and in some days, a couple of times, it handled my sharp tooth scratches pretty well, similar to my other pipes that I had for years and the many pipes had that I sold now.