I've dealt with nothing so extreme but I have white teeth speckled with brown divots which I was told was from well
water with too much flouride in it as a kid. (I hated it as a young adult so when I got money from a car accident, I got porcelain veneers). I have healed cavities in my family over the years. Are his teeth sensitive? Only curious.
My best tips are:
limit sugar (refined and natural) and refined carbs- WAPF style
comfrey is amazing for teeth mineralization and safe (I'd probably make a tea with xyltiol and do a 10 minute swish 2x daily)
raw milk and other
dairy products (yogurt, cheese, cream)
xylitol- there's a podcast episode of Dr. Peter McCullough's "The McCullough Report" from sometime in 2023 where he interviews a female dentist that explains xylitol's benefits that is pretty compelling (xylitol can come from corn or birch
trees in case source is important to you)
One of my kids' teeth yellows a lot more and an orthodontist asked years ago if he was a swimmer. He was. He said he'd noticed a correlation. FWIW. He's a young adult now and hardly swims in a pool and his teeth aren't nearly as yellowed.