Plural form of dentin, the hard yellowish tissue that makes up the bulk of a tooth beneath the outer enamel.
From Latin 'dentis' (tooth) + '-in' (material or substance suffix). Dentin is the tissue discovered to lie beneath tooth enamel, named for its tooth location.
Dentin is porous and yellowish, so when your white enamel wears away from brushing too hard, the dentin shows through and your teeth look yellower—it's not that your teeth are staining, it's that you're exposing the naturally darker layer underneath.
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