The Science Behind Teeth Whitening

The Science of Teeth Whitening | Concentration, Exposure Time & Enamel Biology

The two key factors that influence whitening are concentration and exposure time. Increasing either one increases the effect of the whitening gel, to a point. Understanding the science of teeth whitening — what actually makes teeth dark, and what chemistry reverses it — is what separates a predictable result from a patchy, sensitive one. Below, Dr. John Slate walks through the biology and the chemistry, then explains which treatment approach fits which type of discoloration.

Whitening options include professional in-office whitening, custom take-home trays, and over-the-counter products. They are not equivalent, and the reason why comes down to the science.

What is The Biology Behind Natural Tooth Color?

Your tooth has several layers that contribute to its color. Enamel is the characteristically white outer layer of your tooth that’s visible to the eye. Dentin is the layer below the enamel which is naturally yellow in appearance.

The inner chamber of the tooth is the pulp chamber that contains blood vessels, nutrients, and nerve fibers. The combination of these layers is what gives your tooth its natural color.

What Causes Discoloration of Teeth?

A tooth’s color is a result of the convergence of anatomy and genetics of a tooth, environmental factors, and oral hygiene.

External stains are a result of stain molecules attaching to a bacterial biofilm on the tooth. This biofilm is the initial phase of plaque build-up and calculus build-up on your teeth. It’s also relatively easy to remove with good personal home care.

Some areas of the tooth may be inaccessible at home. Your dental hygienist will scrape away the plaque and calculus build-up which is the basis for these external stains. The teeth can discolor by the external stain penetrating the outer layer of the enamel. These discolorations are relatively easy to treat.

Internal stains aren’t a result of your diet and home hygiene. Genetics, aging, systemic conditions, environment, medications, and even trauma can cause them. These stains develop from the pulp layer and outward toward the dentin.

As you age, the pulp chamber shrinks and the dentin layer thickens. This causes a more yellow appearance to the teeth because of increased color from dentin. Medications can alter the color of teeth during development.

Tetracycline is a drug used to treat bacterial infections. But when taken during tooth development, it can cause a gray or yellow stain deep within the tooth.

Trauma can cause damage within the pulp of the tooth, which can cause shrinkage of the pulp or even death of the nerve and vessels. The shrinkage of the pulp has the same effect of aging, where the colored dentin layer thickens. Death of the vessels and nerve chamber can cause the dentin to stain because of discolored remnants in the vessels and nerves.

What Causes Sensitivity When Whitening?

Patients experience sensitivity after whitening for several reasons, such as:

• Contact of the surrounding gums and tissues with the whitening solutions
• Aggressive and improper use of heat causing reversible inflammation of the pulp
• Glycerine, ammonia, and acidic byproducts from the breakdown of carbamide peroxide (a common whitening solution)

Whitening Treatment Options

Both in-office and take-home whitening are supervised by your dentist. It begins with an initial consultation to determine initial shades of your teeth. Then you will either get in-office whitening, or take-home whitening with instructions.

In-office Whitening

During in-office whitening procedures, we treat the teeth with a high concentration hydrogen peroxide material (24-30%). Then we apply consistent heat in a controlled environment. The controlled environment isolates the whitening material to the teeth only. This prevents leakage to the surrounding gums and tissues, thereby preventing sensitivity.

Temperature accelerates the reaction process leading shorter whitening treatment time (~30 minutes). With shorter treatment times, there’s less contact of the whitening material leading to less sensitivity. In-office whitening can achieve results in a very short period of time because of the highly concentrated materials and heat.

Take-home Whitening

Take-home whitening uses custom fit trays which hold the whitening material against the tooth for extended periods of time (2 hours or more). The whitening material is a low concentration hydrogen peroxide (9%) or carbamide peroxide (10% – ⅓ of the strength of hydrogen peroxide). Take-home whitening takes advantage of exposure time, bathing the teeth in whitening gel for hours at a time.

However, increased exposure time increases the likelihood of sensitivity and for leakage to surrounding tissues. Take-home whitening is still effective with the disadvantages of sensitivity and increased treatment times.

Over the counter (OTC) Whitening Treatments

OTC treatments are available almost anywhere including the pharmacy, malls, and spas with no dental professional oversight. Extrinsic stains are not removed beforehand, concentrations are low, and there’s no customized whitening regimen. You also risk not applying the whitening compound equally across all teeth.

Despite the various treatment options, the safest and most effective treatment is the “dual whitening” system. The dentist-prescribed treatment uses a combination of in-office whitening and take-home whitening.

When Whitening Alone Is Not the Answer

Peroxide chemistry lifts stain from within the enamel matrix. It cannot correct a defect in the enamel itself. Patients with white spot lesions, mild fluorosis, or post-orthodontic decalcification often find that whitening makes those spots more visible rather than less, because the surrounding tooth lightens while the lesion does not.

For those cases we typically sequence enamel microabrasion before whitening, and reserve selective composite bonding for anything that remains. Understanding which problem you actually have is what keeps you from paying for a treatment that cannot solve it.

Professional Whitening in Northwest Washington, DC

Dr. John Slate provides shade evaluation and professional whitening from Slate Dental in Foxhall Square on New Mexico Avenue NW, serving patients across Wesley Heights, Spring Valley, Cathedral Heights, the Palisades, American University Park, Georgetown, Forest Hills, Chevy Chase, and Bethesda.

Every whitening case begins with identifying whether your discoloration is extrinsic, intrinsic, or structural — because the answer determines whether whitening will work at all, and which protocol will get you there with the least sensitivity.