How Teeth Whitening Works: Causes of Yellow Teeth, Enamel and Dentin, and How Whitening Breaks Down Pigment

Are teeth yellow because of poor brushing?

Not necessarily. When the enamel on the tooth surface thins, the yellowish dentin underneath shows through, so teeth often look yellow regardless of how clean they are [1]. Dentin is naturally ivory to yellowish in color, and this color shows through the translucent enamel that covers it [1]. In other words, yellow teeth do not necessarily mean poor care [1].

When DentStat analyzed 480 patient comments on the causes of yellow teeth and how whitening works, protests such as “My teeth aren’t yellow because I don’t brush” and questions such as “How does whitening actually make teeth lighter?” came up repeatedly [2]. To answer those two questions, this article looks separately at what determines tooth color and how whitening works.

What determines tooth color?

Tooth color is determined by the thickness and translucency of the enamel together with the color of the dentin beneath it [1]. Discoloration is divided by cause into extrinsic, where pigments deposit on the surface, and intrinsic, which comes from the color of the tooth tissue itself [1].

Type	Cause	Characteristics
Extrinsic staining	Surface deposits of pigments from coffee, black tea, curry, wine, tobacco, and similar [1]	Partly removed by scaling and brushing [1]
Intrinsic color and discoloration	Enamel thickness, natural dentin color, aging, some medications and trauma [1]	Not changed by surface cleaning [1]

With age, enamel tends to wear and thin, letting more of the dentin’s color show through, so teeth can gradually look darker [1]. Conversely, when enamel formed thin to begin with, how much whitening can lighten the teeth may be limited [1].

Does whitening paint teeth white or grind them down?

Neither. Whitening is a chemical process in which hydrogen peroxide or carbamide peroxide oxidizes and breaks down pigment molecules deposited in the teeth, lightening the shade [1]. It does not polish teeth down or coat them with white material, and it works on a different principle from scaling, which physically removes surface deposits [1]. Breaking down pigment is the defining feature of whitening [1].

During whitening, is it the LED light that lightens the color?

Hydrogen peroxide does the main work of lightening the color [1]. Light is described as a supporting factor that speeds up and activates the agent’s reaction [1]. So agent concentration, contact time, and the condition of the teeth affect the degree of change more than whether a light device is used, and results vary widely by person even under the same conditions [1]. DentStat’s analysis also found mechanism questions such as “Whether or not you use the light, isn’t it the hydrogen peroxide that does the work?” [2].

What stains teeth the most?

Smoking is the main external staining factor, and strongly pigmented foods such as coffee, black tea, green tea, curry, and wine cause surface stains [1]. These external stains can be partly removed with scaling and brushing, but internal color from enamel thickness or aging does not change with surface cleaning and falls within the domain of whitening [1]. DentStat’s analysis also found many mentions of pigmented foods such as coffee, cigarettes, curry, and turmeric [2].

Common myths and facts

Many believe that “yellow teeth mean poor hygiene,” but the natural color of the dentin showing through has nothing to do with cleanliness [1]. “Natural teeth are pure white” is also closer to a misconception: natural teeth are usually ivory-toned and tend to darken with age [1]. The expectation that “brushing and scaling alone will whiten yellow teeth” applies only to some external stains, and intrinsic color does not lighten with cleaning [1]. Given the many pushback comments in DentStat’s analysis saying “don’t generalize” [2], the starting point is to distinguish whether the yellow color comes from staining or from the color of the tooth tissue itself [1].

For an overview of how whitening works and the difference between professional and at-home whitening, see the teeth whitening guide. For dental clinics by region, see Find a Dentist.