Teeth bleaching:

When will it work? / When won't it? - This page explains the types of color issues that a tray-based whitening system typically can or can't resolve. | Common treatment time frames.

It's impossible to know beforehand how much effect your whitening treatments will have. But, as outlined on this page, dentists do have some general guidelines they keep in mind when explaining to their patients what level of success is likely and how long it might take.

What whitening method?

In regard to the information on this page, we're referring to the use of a dentist-dispensed tray-based teeth whitening process utilizing a 10% carbamide peroxide whitener with 2-hour daily treatment sessions.

This could be considered to be a standard entry-level system. The use of whitening strips is sometimes comparable to this type of system.

You play a role in your treatment's success.

Beyond the type of discoloration being treated and the product being used, the specific result a person is able to get and the amount of time it takes to achieve it will hinge on how closely they comply with their system's instructions.

Types of tooth staining and their treatment solutions.

Type of discoloration -

  • Exposure to dark consumables (beverages, foods, tobacco).
  • Age-related.
Before and after pictures of a routine tooth-whitening case.

The results of routine cases can be as dramatic as this, yet still look natural.

It's common for a person's teeth to darken (become dingy-looking or yellowed) over time. This is usually due to two factors:

What level of results can be expected?

This type of tooth discoloration will usually respond favorably to whitening treatments, often surprisingly so. This is especially true for people whose teeth once had a light coloration, as opposed to those whose original baseline shade was always comparatively dark.

Rules of thumb.

  • Teeth that have a yellow to brown tint typically respond more quickly and favorably than those displaying shades of grey.
  • A realistic treatment time frame can be two to six weeks of daily bleaching, with each session lasting on the order of two hours.

    It's certainly possible, however, that a person will start to see improvement in as little as just a few whitening sessions.

  • Relatively darker staining, such as that caused by a person's heavy smoking habit (nicotine staining), might take upward of three months of treatment to successfully resolve.


Type of discoloration -

  • Naturally dark teeth.

There's a normal range of shades of white that human teeth usually display. And it's just a fact of life that the color of some people's teeth (their baseline color) is naturally darker or lighter than others due to genetic factors.

What type of results can be expected?

The level of success that's possible for people who have naturally dark teeth often isn't as dramatic as with other types of tooth discoloration. A tray-based system can be expected to make at least some noticeable improvement. But just how much is difficult to predict.

Rules of thumb.

  • An extended treatment time frame may be needed, possibly extending over several months.
  • Even then, the amount of improvement may fall short of what had initially been hoped for.

More details.

This digital smile makeover case can give you an idea of some of the issues involved with treating teeth whose baseline color is naturally dark.

Type of discoloration -

  • Tetracycline.
  • Brown fluorosis.

Teeth that have tetracycline (or related antibiotic) staining or brown fluorosis typically have a reputation for being stubborn to treat.

There are published case studies (see box below) documenting the use of tray-whitening technique to successfully resolve this type of discoloration. But one would have to assume that both the patient and the dentist supervising their efforts were highly motivated to be able to achieve this success.

Rules of thumb.

  • The specific whitening process used might be at-home or professional (in-office) treatments, or some combination of both.
  • The bleaching process should be monitored by a dentist and it may need to involve an extended number of treatments. Durations for difficult cases like these can easily range between 2 and 6 months, possibly even a year.
  • Even with the option of extended treatment, an acceptable outcome may not be possible. For example, after some initial success, a point may be reached beyond which little additional lightening effect takes place.

    If so, the dentist and patient may be forced to come to the realization that while the teeth have responded somewhat (or even significantly), achieving any additional improvement is unlikely and the treatments should be terminated.

  • (If the bleaching treatments were able to make a substantial yet not complete improvement with the appearance of the patient's teeth, then those isolated regions on each tooth that didn't respond (like the areas originally the darkest) could be masked by placing dental bonding.

    If the whitening treatments really didn't even come close to resolving the staining in a manner that the patient found satisfactory, then placing porcelain veneers could be considered.)

More details.

a) This digital smile makeover case can give you an idea of some of the issues involved with treating tetracycline cases. And this one, dark brown fluorosis stains.

b) The article linked to in the box below gives an example of how dentists use at-home bleaching methods to resolve tetracycline staining for their patients.

Study details.
Study name: Daily use of whitening strips on tetracycline-stained teeth: comparative results after 2 months.

We'd like to mention a few things about this article, just so you keep them in mind when reading it.

  • We chose this particular paper in part because of its old (2002) publication date. There is nothing new about this type of treatment. This is routine (although extended) bleaching that any dentist should be able to help you with.
  • This paper compares the use of both a whitening strips product (6.5% hydrogen peroxide) and tray-based bleaching (using 10% carbamide peroxide). These are the low peroxide concentration versions of these methods. They make the right choice because they are both effective and help to minimize side effects.
  • This particular study found both strips and tray technique to be effective (the study was sponsored by the makers of WhiteStrips®). (From reading other case studies, it would be our impression that dentists generally lean toward the use of tray technique for relatively more difficult cases.)

Here's a link to the study on ResearchGate.net - Daily use of whitening strips on tetracycline-stained teeth: comparative results after 2 months. (A new browser window will open.)

Look for the "Full-Text" link to view the actual article.


Results of whitening treatments used to treat fluorosis.

Treating fluorosis with whitening treatments.

Type of discoloration -
  • White fluorosis.
The most common form of fluorosis (staining caused by a child's ingestion of fluoride during tooth formation) is one where the tooth's enamel is marred with opaque white patches or streaks.
(This page explains fluorosis A to Z: Causes, pictures, prevention, treatment options.)
It may be possible to improve the overall appearance of affected teeth via the use of whitening treatments. The specific process used might be at-home or professional (in-office) treatments, or else some combination of both.

The idea is that the process is used to lighten the tooth enamel that surrounds the staining, thus making it less obvious.

Rules of thumb.

  • The outcome of this approach hinges on how white the fluorosis is and if the tooth's enamel can be lightened that much. Success will be easiest for teeth that already have a relatively light baseline color.
  • The treatment results can be one where at a distance the color of the teeth looks uniform enough but on close inspection the individual patches of fluorosis can still be seen.


More details.

This digital smile makeover case can give you an idea of some of the issues involved with treating fluorosis cases.

Takeaways from this section.

Even if the final results aren't perfect, from a standpoint of cost, effort and the fact that the structural integrity of the tooth doesn't have to be altered, they might be considered to be quite a success.


Type of discoloration -

  • White-spot lesions.
White spot lesions that have formed during orthodontic treatment.

Using whitening treatments to mask white-spot lesions.

If patients who wear dental braces don't brush well, white-spot lesions can form on the tooth enamel that surrounds their brackets. (These lesions are the earliest visible sign of cavity formation.)
If this has occurred, once the brackets are removed the affected teeth will look like they have a "bulls-eye" on them.

It may be possible to use whitening treatments to mask this type of damage. The treatments are used to lighten the tooth's unaffected enamel, thus making the color mismatch with the white-spot lesion less visible.

Whitening treatments may mask the smaller lesions seen here.

White spot lesions resulting from dental braces.

It may take placing dental fillings to fully mask the larger ones.

What type of outcome can be expected?
  • The success of this approach hinges on how light the white spots are and if the tooth's surrounding enamel will lighten that much.
  • Teeth that already have a light baseline color will typically be the easiest to successfully treat.
  • The results can be one where at a distance the color of the teeth looks uniform. But on close inspection the individual white spots can still be picked out.



  • Before this technique can be initiated, the dentist must first determine that the lesions are inactive and benign.
  • It's important to understand that this approach should never be attempted on your own. Only a dentist has the knowledge and expertise to be able to make the above determination.


Takeaways from this section.

Once again, even if the final results aren't perfect, from a standpoint of cost, effort and the fact that the structural integrity of the tooth doesn't have to be altered, they might be considered to be quite a success.


Other applications for whitening treatments.

This dental crown no longer matches well.

A dental crown that no longer matches the color of its neighboring teeth.

It likely did at the time of its placement, but the color of the natural teeth has since faded.

1) Color mismatches involving dental crowns.

Due to the normal aging process and/or continued exposure to chromogenic agents (coffee, colas, etc...), it's common that a previously placed dental crown will no longer match its now stained neighboring teeth.

As a solution, it may be possible to use whitening treatments to return the natural teeth back to their original color. The one they were when the crown was first placed.

How this works.


With some cases, this same phenomenon can also be a detriment. People who initiate whitening treatments on their own (without consulting with their dentist first) may unexpectedly find that their treatments have created a color mismatch between their natural teeth and their existing dental restorations. The only solution is to replace the dental work, which can be both time consuming and expensive.

Teeth with veneers can often be successfully whitened.

The whitener penetrates from the backside of the veneered tooth.

2) Lightening porcelain veneers.

One exception to the rule that whitening treatments won't lighten the color of existing dental work is porcelain veneers.

How this works.

  • Veneers are translucent shells of porcelain bonded onto the front side of teeth.
  • When a tray-based system is used, the whitener can't penetrate the tooth's veneered surface but it can its backside.
  • Since the tooth does get some dosing of the whitener, there's potential that it will lighten.
  • If the veneer is translucent enough, as its tooth becomes lighter, it will look whiter too.


There can be cases where it is inappropriate to expose porcelain restorations to whitening agents. You'll need to consult with your dentist on this issue.

When won't tray whitening work?

An individually darkened tooth.

An individually darkened tooth.

(It needs or has had root canal treatment.)

1) Individually darkened teeth.

Tray-based technique can be used to bring a single dark tooth back into harmony with its neighbors. But because this method tends to treat teeth as a group rather than individually, an adjustment needs to be made.

Portions of the tray are trimmed away so it just covers over the tooth requiring treatment and not the teeth to each side.

  • People using a stock tray may find it difficult to trim their tray to this configuration.
  • As alternative approaches, in-office or paint-on techniques provide a way where treatment can be limited to just a single tooth.
  • Dark teeth that have had root canal treatment are usually lightened using a method where the bleaching agents are placed directly inside the tooth.


2) Unnatural levels of whiteness.

Teeth only have so much potential to lighten. And even in those situations where a person's motivation and compliance with instructions are high, a point will finally be reached where no further lightening will occur. This endpoint may or may not be the one originally hoped for.


In an attempt to reach an impossible goal, some people will exceed their product's recommendations. This can place them at risk because they are using the whitener in a realm beyond where its safety has been evaluated. It also places them at increased risk for side effects.

3) Existing dental work.

As mentioned above, with just a few exceptions (see the link below) the peroxide-based whiteners used with tray-based whitening technique won't lighten existing dental restorations.

That means:
  • The only solution for dental work that no longer matches its tooth is to replace it.
  • When new or replacement dental work is planned, if the person wants to whiten their teeth too, it must be done first. Otherwise, their new restorations won't match the new color their teeth end up being.
  • Beyond the time frame needed to complete the whitening process, a dentist will usually want to wait an additional 2 weeks before placing any new dental work so to allow for color stabilization.

For more information: What are the effects of peroxide whiteners on existing dental work?

4) Teeth that have gum recession.

After gum recession has occurred, that part of the root that now shows typically has a darker color (yellow, tan) than the rest of the tooth. That's because tooth roots are composed of a tooth tissue called dentin.

Peroxide whiteners do a good job of lightening enamel but not dentin. And that means, after treatments, the color discrepancy between the root and the rest of the tooth may become even more obvious.

Despite this ineffectiveness, our Dietschi (2006) reference found that tray-based whitening as a method was more effective at lightening dentin than whitening strips or in-office bleaching.

Takeaways from this section.

As a solution, the root's darker color can be masked by placing a white filling. In other cases, periodontal surgery may be able to restore the original positioning of the gums.



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