Teeth Whitening

Last updated: November 6, 2026·Reviewed by Soo Jin Kim, DDS

Teeth whitening lightens natural teeth that have yellowed with age or picked up stains from coffee, tea, red wine or tobacco, without drilling or covering the tooth. A hydrogen peroxide or carbamide peroxide gel bleaches the colored compounds inside the enamel and dentin, either in a single in-office visit with a concentrated gel or at home over days to weeks with custom-fitted trays and a lower-strength gel. How much lighter teeth become depends on the type of stain, and crowns, veneers and fillings keep their original color. Teeth whitening at ConfiDental's Carlstadt office is part of the cosmetic care Dr. Kim provides. We offer both in-office and take-home whitening, and either can be one step in a smile makeover.

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Overview

Teeth whitening, also called tooth bleaching, uses hydrogen peroxide or carbamide peroxide to lighten the natural color of the teeth. Discoloration comes in two kinds. Extrinsic stains build up on the enamel surface from tobacco and from pigmented foods and drinks such as coffee, tea, red wine, cola and dark fruits. Intrinsic stains sit inside the tooth and come from causes such as aging, when enamel thins and the yellower dentin beneath shows through, tetracycline antibiotics taken while the teeth were forming, excess fluoride, decay, or damage to the tooth's nerve. Bleaching can lighten both kinds, which sets it apart from whitening toothpastes that only polish away stain on the surface.

How much a tooth lightens depends on the stain. Yellowish teeth generally bleach well, brown teeth may respond less, and teeth with gray tones may not lighten at all. Brown stains from fluorosis or tetracycline can lighten, although tetracycline staining may take three to four months of nightly treatment, while white spots from fluorosis or past braces respond less but can look less noticeable as the rest of the tooth lightens. Stains bound to metal compounds are much harder to bleach. The final shade a tooth can reach depends on the tooth itself.

Bleaching works only on natural tooth structure. Crowns, veneers, bonding, tooth-colored fillings and implant crowns keep the color they were made in, so whitening the teeth around them can leave those restorations looking darker by comparison. Existing restorations are identified and recorded before treatment so the result can be planned around them, and bleaching may reduce how strongly composite and ceramic materials bond to enamel. A single tooth that has darkened after root canal treatment may be lightened from the inside with internal (intracoronal) bleaching. Where a stain does not respond to bleaching, bonding or veneers can mask it instead.

Professional whitening comes in two main forms. In-office whitening applies a concentrated hydrogen peroxide gel after the gums are covered with a protective gel or rubber shield, sometimes with a light, and usually takes a single visit. Take-home whitening uses trays made to fit the teeth, which hold a lower-strength gel against the enamel while limiting contact with the gums. These gels typically range from 10% to 38% carbamide peroxide, and wear time depends mainly on strength, from about 30 minutes to 10 hours a day over several days to six weeks. Pooled trials comparing the two approaches found similar shade change on shade guides, with sensitivity less intense on average for take-home bleaching. Over-the-counter strips, gels and toothpastes contain less bleaching agent and usually take longer to reach a similar shade. Some carry the ADA Seal of Acceptance, for which professional products are not eligible.

When It's Recommended

Teeth that have yellowed or darkened with age
Surface stains from coffee, tea, red wine, cola or tobacco
Brown intrinsic stains, including some fluorosis and tetracycline staining
A single tooth darkened after root canal treatment, through internal bleaching
Maintaining an earlier whitening result with touch-up treatment

What are the risks of Teeth Whitening?

When to Avoid

Untreated tooth decay or active gum disease, until treated
Known allergy to hydrogen peroxide, carbamide peroxide or other ingredients in the whitening gel
Pregnancy
Children with primary teeth or a mix of primary and permanent teeth (full-arch cosmetic bleaching)

Possible risks

Tooth sensitivity, usually mild to moderate and temporary, reported by up to two-thirds of users early in treatment
Gum irritation or burning where peroxide gel touches the gums, most often from poorly fitting trays or a gap in the protective barrier
Uneven color where crowns, veneers, fillings or bonding do not lighten along with natural teeth
Reduced bond strength between enamel and composite or ceramic restorations
Restaining over time, particularly with coffee, tea, red wine or tobacco
Enamel softening, surface roughness or greater susceptibility to demineralization with aggressive, high-concentration bleaching, reported in laboratory studies
Surface softening or color change in composite, glass ionomer, sealant or ceramic materials exposed to bleaching gel
Dehydration and demineralization of the tooth with very aggressive regimens, which can make teeth look whiter only temporarily
Damage to enamel or gums from overuse of whitening products
External cervical resorption, a rare complication of internal bleaching of root-canal-treated teeth

Who needs extra care

A history of tooth sensitivity, where lower peroxide concentrations and shorter contact times are associated with less sensitivity
Existing or planned crowns, veneers, bonding or tooth-colored fillings on visible teeth, which do not change color and may bond less strongly to bleached enamel; they are recorded before treatment so the final shade can be planned around them
Tetracycline staining or other deep intrinsic discoloration, which may need three to four months of nightly tray treatment
A single darkened tooth after injury or root canal treatment, which is evaluated before whitening and may be treated with internal bleaching
Adolescents using at-home bleaching products, which the American Academy of Pediatric Dentistry encourages to be supervised by an adult

What to Expect During Treatment

An examination of your teeth and gums looks for the likely cause of the discoloration and records existing fillings, crowns and veneers, and x-rays may be taken
Your health and dental history is reviewed, including any allergies and past tooth sensitivity
Any decay or gum disease is treated before whitening begins
A professional cleaning may remove surface stain and tartar, and your starting shade may be recorded with a shade guide
For in-office whitening, your gums are covered with a protective gel or rubber shield and a concentrated hydrogen peroxide gel is applied to the front surfaces of your teeth, sometimes with a light
The gel is left on for a set time, up to about 30 minutes per application, and you may be asked to report any burning on your gums, which can mean gel is seeping past the shield
For take-home whitening, impressions or a digital scan of your teeth are used to make custom trays, and you are shown how much gel to place in them and how long to wear them
You wear the trays for the set time each day, over several days to a few weeks depending on the gel strength
A follow-up visit may compare your new shade with the starting shade and check for sensitivity or gum irritation

How does Teeth Whitening work?

Hydrogen peroxide is the active bleaching agent. Carbamide peroxide, common in take-home gels, breaks down in water and releases about one-third of its content as hydrogen peroxide. Carbamide peroxide gels work more slowly than hydrogen peroxide gels and carry a lower risk of tooth sensitivity.

Hydrogen peroxide passes through tiny spaces between the enamel rods into the dentin and can reach the pulp within about 15 minutes. Along the way, reactive oxygen oxidizes the colored organic compounds (chromophores) in the enamel and dentin and breaks them into smaller, less concentrated pieces, so the tooth looks lighter.
Stains bound to metal compounds, such as iron, copper or old amalgam fillings, resist this reaction and are much harder to bleach.
The reaction takes place in natural enamel and dentin, so porcelain, composite and other restorative materials keep their original color.
Higher concentrations shorten the treatment time needed, but higher concentrations and longer contact times also raise the chance of sensitivity, which is thought to come from temporary inflammation of the pulp as peroxide reaches it.
Whitening toothpastes work differently. Most rely on mild abrasives and polishing agents that remove surface stain without changing the tooth's underlying color.

Recovery & Aftercare

Tooth sensitivity usually appears during treatment and lasts several days; with tray or strip whitening it typically resolves by the fourth day after treatment ends
Gum irritation tends to start within a day of treatment and also settles over several days
You can pause whitening and resume later if sensitivity becomes uncomfortable, and a desensitizing toothpaste may ease it
Contact the dental office if sensitivity persists after whitening has stopped
With regular coffee, tea, red wine or tobacco, some restaining can appear within a month, while teeth kept away from those stains may hold their shade for up to about a year
Periodic touch-up whitening at home, daily brushing and flossing, and regular cleanings help maintain the result

Alternative Treatments

Professional cleaning or a stain-removal toothpaste for surface stains only
Over-the-counter whitening strips or gels, ideally products carrying the ADA Seal of Acceptance
Enamel microabrasion for stains or spots confined to the enamel surface
Composite bonding to mask a deep or isolated stain that does not improve with bleaching
Veneers for widespread discoloration that whitening cannot lift
Crowns for discolored teeth that are also weakened, decayed or heavily restored

What the Research Says

Whitening products use hydrogen peroxide or carbamide peroxide, which break stain compounds into smaller pieces so the color is less concentrated and teeth look brighter[2]
Carbamide peroxide releases about one-third of its content as hydrogen peroxide, the oxidizing agent that does the bleaching[1]
A 2018 Cochrane review of 71 trials found that home bleaching agents whitened teeth compared with placebo over periods of 2 weeks to 6 months[4]
Only natural teeth are lightened by bleaching; crowns, implant crowns and other tooth-colored restorations do not change color[1]
Whitening toothpastes and over-the-counter gels typically lighten teeth by about one or two shades, and professionally applied products can lighten them further[6]

Who provides this at ConfiDental Family and Cosmetic Dentistry

Soo Jin Kim

DDS

NYU-trained family and cosmetic dentist with a hospital residency at Mount Sinai

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Frequently Asked Questions

What is teeth whitening?

Teeth whitening, or tooth bleaching, lightens natural teeth that have yellowed with age or picked up stains from coffee, tea, red wine or tobacco. A hydrogen peroxide or carbamide peroxide gel bleaches the colored compounds inside the enamel and dentin. It can be done in the office in a single visit or at home with custom-fitted trays over days to weeks. Crowns, veneers and fillings do not change color.

Does teeth whitening hurt?

Whitening is usually not painful. Numbing is usually not used during in-office whitening, so any burning on the gums from gel seeping past the shield can be noticed and reported straight away. The most common side effect is temporary tooth sensitivity, often mild to moderate, which typically fades within a few days after treatment ends. Lower-strength gels and shorter wear times are associated with less sensitivity.

Is teeth whitening safe?

Peroxide-based whitening is considered safe and effective when the product's directions are followed, and its most common side effects are generally mild and temporary. An examination beforehand identifies decay, gum disease and restorations that affect whether and how whitening is done, and lower-strength gels are available for teeth prone to sensitivity.

How many teeth whitening sessions are needed?

In-office whitening is usually completed in a single visit of about an hour. Take-home whitening with custom trays typically runs from a few days to a few weeks, depending on the gel strength and daily wear time. Deep stains take longer, and tetracycline staining can need three to four months of nightly treatment. Touch-up treatments can be repeated later to maintain the shade.

How long do teeth whitening results last?

How long whitening lasts depends mostly on diet and habits. With regular coffee, tea, red wine or tobacco, some restaining can appear within a month, while teeth kept away from those stains may hold their shade for up to about a year. Periodic touch-up whitening at home, daily brushing and flossing, and regular cleanings can help maintain the result.

How is professional teeth whitening different from over-the-counter whitening?

Over-the-counter strips, gels and toothpastes contain less bleaching agent than professional products, usually take longer, and typically lighten teeth by about one or two shades. In one study, an over-the-counter product took 16 days to reach the shade a take-home tray system reached in seven days and an in-office treatment in one. Professional whitening also starts with an examination, and take-home trays are made to fit, which limits gel contact with the gums.

Who should not get teeth whitening?

Whitening is generally postponed until tooth decay or gum disease has been treated, and it is not appropriate for people with a known allergy to peroxide or other ingredients in the gel. The American Academy of Pediatric Dentistry discourages bleaching during pregnancy and full-arch cosmetic bleaching in children who still have primary (baby) teeth. A dental examination can determine whether whitening suits a particular set of teeth.

Sources & References

This article draws from 10 peer-reviewed sources.

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