Why Whitening Won't Work on Your Crowns and Fillings

Whitening gel lightens natural tooth structure and nothing else, so crowns, veneers, composite fillings and amalgam do not change shade at all when you whiten. The natural teeth around them get lighter, and the restorations stay exactly as they were — which is why they often look darker and more obvious afterwards than they did before.

That is not a fault in the whitening. It is how the chemistry works, and it is entirely predictable, which means it can be planned around.

Whitening is a cosmetic treatment for adults. It is not offered to anyone under 18.

If you have restorations on your front teeth and are thinking about whitening, have the sequence planned before you start.
Call (02) 9649 6468 · Book online · WhatsApp

How does whitening actually lighten a tooth?

Whitening products contain hydrogen peroxide, or carbamide peroxide which breaks down into hydrogen peroxide. In the mouth, that breaks down further into small, reactive oxidising molecules.

Those molecules are small enough to pass through enamel and into the dentine underneath. Natural tooth structure is porous at a microscopic level: enamel has spaces between its mineral rods, and dentine is threaded with fluid-filled tubules. The gel does not sit on the surface. It travels in.

Once inside, the oxidising molecules break apart the larger pigment molecules that have accumulated in the tooth over years, splitting them into smaller molecules that reflect light differently. The tooth reads as lighter because the pigment inside it has been chemically altered.

Two conditions are therefore required for whitening to do anything. The material has to be porous enough for the gel to enter, and it has to contain the kind of pigment the gel can break down.

Why does none of that apply to a restoration?

Restorative materials fail both conditions.

• Porcelain and ceramic — used for crowns and veneers. Glazed, dense and effectively non-porous. The colour is built into the material during manufacture.
• Composite resin — used for white fillings and bonding. A resin matrix with glass or ceramic filler particles. Its shade comes from pigments locked into the set resin.
• Glass ionomer — used in some fillings and under others. Again, its shade is inherent to the set material.
• Amalgam and gold — metals. Nothing about peroxide chemistry affects them.

In every case, the gel cannot penetrate in the way it penetrates enamel, and there is no age-accumulated internal pigment for it to break down. The shade of a restoration after whitening is the shade it was before. This is not a matter of degree or of using a stronger product.

Why do restorations look darker afterwards?

Because shade is judged by comparison.

A composite filling on a front tooth was originally matched to the shade of the tooth around it, so it disappeared. Lighten the tooth by several shades and the filling has not moved, but the gap between them has opened up. It now reads as a distinctly darker patch on a lighter tooth.

The same applies to a crown on an upper front tooth, a veneer, or the composite edge on a repaired chip. The effect is most noticeable on the front teeth, which is precisely where people care about it, and it can be more apparent than the original mismatch ever was.

Back teeth are far less of an issue in practice, because they are rarely visible in speech or smiling.

Is it stain on the restoration, or the restoration itself?

This distinction matters, because the two have completely different answers, and people frequently want the first while asking for the second.

Surface stain that has built up on a composite, or in the fine line at a crown margin, is deposited material sitting on the outside. It comes from coffee, tea, red wine, smoking and plaque. That can usually be polished off during a professional clean.

Polishing removes what is sitting on the surface. Bleaching alters pigment inside natural tooth structure. They are different processes with different targets, and a clean will not lighten a natural tooth in the way whitening does, just as whitening will not remove surface film from a composite.

A good number of people who ask about whitening a discoloured filling actually want it polished, and find the result acceptable without any bleaching. Whether stain is on the surface or in the material is established by looking at it, which is one reason an examination comes first. Coffee and tea staining versus erosion covers what these habits do to teeth more broadly.

If the concern is a single darker patch on a front tooth, an examination will establish whether it is stain, the material, or something underneath it.
Call (02) 9649 6468 · Book online · WhatsApp

What is the right order of treatment?

Where visible restorations are going to be replaced anyway, the sequence that avoids the mismatch is straightforward.

• Whiten first. Establish the natural teeth at the shade you want to keep.
• Wait for the shade to stabilise. Commonly around two weeks. The shade rebounds slightly after bleaching rather than holding at its immediate post-treatment point, so matching straight away matches to a shade that will not last. Bonding strength is also reduced immediately after bleaching because of residual oxygen in the tooth surface, so restorations placed too soon are more likely to debond.
• Then match and replace the visible restorations to the settled shade.

Doing it the other way round means placing new work to match teeth that are about to change, which produces the same mismatch with a new restoration.

The cost consequence people should be told up front

This sequence has a financial implication that belongs in the quote, not in a conversation afterwards.

Replacing a crown to match a new shade is a new crown, at the full fee. The same applies to veneers. Composite is less costly to replace, but it is still a fresh restoration on each tooth involved.

So the real cost of whitening front teeth is not always the whitening fee alone. Where several visible restorations exist, it is the whitening plus the replacements, and that total should be set out in writing before anything begins. There is more on the cosmetic dentistry page.

What if you already have a lot of restorative work?

There are three honest options, and it is reasonable to choose any of them.

• Accept the mismatch. If the restorations are on back teeth or are barely visible, whitening the natural teeth may still be worth it and the difference may not show.
• Whiten and replace. The complete result, at the higher total cost and over several appointments.
• Do not whiten. Have a professional clean to remove surface stain, and keep the shade you already have matched across the whole smile. This is a legitimate outcome, not a failure.

Which of the three suits you depends on how many restorations are visible, where they are, and what you are prepared to spend. That is a conversation to have before starting, not partway through.

What about a single dark tooth after root canal treatment?

A tooth that has had root canal treatment sometimes darkens over time. The discolouration in that case is internal, within the dentine, and it does not respond to external whitening in the same way as the teeth around it.

Different approaches exist for internal discolouration, and which is appropriate depends on the tooth, the condition of the root filling and how much tooth structure remains. It is assessed individually rather than treated as a whitening question.

Is whitening safe, and can anyone have it?

Professionally supervised whitening starts with an examination, and that is not a formality.

Whitening over untreated decay, a leaking filling or active gum disease is not appropriate. Peroxide reaching a cavity or the pulp through a defective restoration causes problems rather than solving them, and inflamed gums react badly to gel contact. The examination establishes whether the mouth is in a suitable condition first. More on fillings and whitening options ranked.

Two side effects are common and usually temporary:

• Sensitivity — sharp, cold-triggered sensitivity during and shortly after treatment, generally settling within a few days. It can be managed with desensitising products and by adjusting how the treatment is delivered.
• Gum irritation — whitish or sore patches where gel has contacted the gum, most often from poorly fitting trays. Custom-made trays reduce this considerably compared with generic ones.

No particular shade result can be promised. How much a tooth lightens depends on the cause of the discolouration, the starting shade and the individual. General information on dental care is available from healthdirect.

What does it cost?

• In-chair whitening — $900
• Take-home whitening kit — $400
• Composite filling — $250 to $450 per tooth
• Crown — $1,500 to $1,800
• Check-up, X-rays and clean — $250

These figures assume no health-fund contribution. A fund may contribute, and funds often treat cosmetic items differently from restorative ones, so what your policy does is a question to put to your fund directly. A written quotation is given before treatment begins, and where a sequence of whitening followed by replacement restorations is planned, that quotation covers the whole sequence. Current fees are listed on the fees page.

Quick answers

Will whitening lighten my white filling even slightly?

No. Composite resin does not lighten with peroxide. Surface stain on it can be polished off at a clean, which sometimes improves the appearance, but the material's own shade does not change.

How long should I wait after whitening before having a filling matched?

Commonly around two weeks. The shade rebounds slightly in that period, and bonding to freshly bleached enamel is compromised, so waiting improves both the match and the bond.

Which whitening method should I choose?

That is a separate question from this one, and it is covered in in-chair versus strips versus trays. Whichever method is used, none of them will change the shade of a restoration.

Can I whiten if I have crowns on my front teeth?

You can, but the crowns will stay as they are and may end up looking darker than the teeth beside them. If the crowns are recent and you are not intending to replace them, that is worth thinking through before starting.

Where to start

An examination first, then a plan that covers the order of treatment and the total cost, then the whitening. Further reading: in-chair versus strips versus trays compares the methods, what lasts and what needs maintaining covers the longer view, and the cosmetic dentistry page sets out what is offered here.

If you would like to know what whitening would realistically achieve for your teeth, an assessment will tell you before you spend anything on the treatment itself.
Call (02) 9649 6468 · Book online · WhatsApp

Written and reviewed by Humzah Aly, Oral Health Therapist. This article is general information only and is not a substitute for personalised dental advice. Please see a dental practitioner to discuss what is right for you.