Why are cat's teeth brown streaked???

I just adopted my cat. He's supposed to be about 4 years old. All the other cats I've owned over the years had white teeth. This guy has brown looking teeth. His long ones have vertical brown stripes on them. It looks like the coloring is actually in the tooth, not on the outside. It does not scrape off....I tried....my kitty is very tolerant! He does have some tarter buildup on the back ones, so after he settles more into his new home, I plan to get him to the vet for a dental cleaning. But his back ones, despite some tarter, are white.

Why do his front long teeth have brown lines in them? Is this normal? Does this mean he is older than 4 years old (I really dont think he is much older though...his coat and eyes are very young looking). Could he have had a nutritional deficiancy as a kitten maybe?

I have no idea, but my cat has this on one of her teeth also. We don't know her age but she's probably almost 2. She was just at the vet yesterday and the vet didn't seem concerned about it so I don't think it's abnormal.

Interesting. At least other cats have it too. At first I thought his teeth might be rotting out! But they seem fine other than the coloring.

I wonder if cats teeth can get discolored by too much fluoride in drinking water like human's can? My mom has dark brown streaks in her teeth from too much fluoride in her drinking water as a child and young adult. Perhaps the same thing can happen to a cat's teeth?

I'll be sure to ask my vet when I take him.