here are multiple factors that cause teeth to become dull and lose their bright, white sparkle.
Certain foods can stain your enamel, which is the outermost layer of your teeth. Additionally, plaque build-up on your teeth can cause them to look yellow.
This type of discoloration can usually be treated with regular cleaning and whitening remedies.
However, sometimes teeth look yellow because the hard enamel has eroded away, revealing the dentin underneath. Dentin is a naturally yellow, bony tissue that lies underneath the enamel.