Orange "stains" on teeth, is it plaque?

[RubyBlueberry]

My lovely little DS - 16 months, has 4 teeth on top and 4 on bottom. They started off being little white smooth pearls, absolutely beautiful, now they look like he has eaten 3 bags of wotsits.
I brush his teeth twice a day,with baby toothpaste, for a good minute in the morning with a baby vibrating toothbrush and at night with a soft brush and these stains won't come off, he's never gone to bed with a bottle or anything, what would you suggest?
Does he have to go to a dentist? cos I can't imagine him putting up with that!!

any suggestions would be great!

It could be a problem with the gums. See a dentist ASAP.

Thank you, good idea, will do that.

He let me have a bit scrape on them with a fingernail (bit unhygienic I know) and most of it's come off, so I'm wondering WTF it was!

Mu niece had something like that, and turned out to be a very small absess on her gum that was secreting orange stuff. Keep an eye out in case it reappears.