I have braces and on the bottom of my teeth, i have almost a butter color yellowish stain. it wasn't there when i got braces but has now appeared.

Oral Hygiene: Your oral hygiene may not be as good as it can be. Sounds like you have calculus or plaque in that area. You'll need to see your dentist to have it removed.

Stain: May be from foods (coffee, tea, colas, etc.) or from compromised Oral Hygiene. Schedule a professional cleaning with your Dentist. Talk to both your General Dentist and your Orthodontic Specialist about oral hygiene practices that will help prevent staining.

Not clean enough: The appliances that are bonded to the teeth make it very difficult to clean completely between the bracket and the gum line. Make an extra lap after your regular brushing to angle your brush at the gum line. You might also want to consider investing in a sonicare tooth brush