Whitening gel applied to the outside of the teeth lightens all of them, which can leave a single dark tooth looking even more obvious than before. That is because the discolouration in a tooth that has been knocked or root filled usually sits deep inside it, in the dentine, where surface gel has little effect. Internal bleaching works from the other direction: the bleaching agent is placed inside the tooth, through the small opening already made for the root canal treatment.
It is a conservative option, since it removes no extra tooth, but it only suits teeth with a sound root filling and the colour can drift back over time.
The stain sits inside the tooth
When the nerve and blood supply inside a tooth die, whether from a knock, deep decay or a crack, the tissue inside breaks down. Pigments from that breakdown, including iron-containing compounds from blood, work their way into the dentinal tubules, the microscopic channels that run through the dentine. The result shows through the enamel as a grey, brown or yellow tone, sometimes months or years after the injury.
Root canal treatment removes the source, but not the stain that has already soaked into the dentine. Some older filling materials left in the crown of the tooth can add to the colour as well.
Make sure of the cause first
A dark tooth is not always a dead one. Shadowing from an old filling, surface stain, white or brown marks from fluorosis, and grey bands from certain childhood medicines all look different on close inspection, and each has its own treatment. An X-ray and tests of how the tooth responds tell the dentist which is present. Our guide to grey teeth and whether they can be whitened covers the other causes.
If a tooth has darkened and has never had a root canal, it needs assessing before anything else, because a dying nerve can lead to infection. Our article on the signs of a dead or dying tooth explains what to look for.
A sound root filling comes first
Internal bleaching is only suitable for a non-vital tooth that already has a good, well-sealed root canal filling. If the root filling is incomplete or leaking, or there are signs of infection at the root tip, that is dealt with first, sometimes with a new root canal treatment.
Bleaching changes colour, not strength. A dark tooth that is also cracked, heavily filled or missing a lot of structure may be better served by a bonded restoration or crown.
What happens at each visit
The usual approach is called the walking bleach technique, because the agent keeps working inside the tooth between appointments.
- An X-ray confirms the root filling is sound and the tooth is free of infection.
- The small access opening at the back of the tooth is reopened and some of the root filling near the gum line is removed.
- A protective seal, often glass ionomer cement, is placed over the root filling so the bleaching agent stays in the crown of the tooth and away from the root surface.
- A bleaching agent, such as sodium perborate, is placed inside the tooth and sealed in with a temporary filling.
- At review visits the dressing is replaced and the colour compared with the neighbouring teeth. A review by Plotino and colleagues (Journal of Endodontics, 2008) describes changing the agent every 3 to 7 days.
- When the colour is right, the opening is sealed with a permanent tooth-coloured filling, usually after a short wait so leftover oxygen from the bleach does not weaken the bond.
Because the tooth has no living nerve, the procedure is usually comfortable and local anaesthetic is often not needed.
What a study of 255 teeth found
Abbott and Heah followed 255 internally bleached teeth in 203 patients, reported in the Australian Dental Journal in 2009. Most were upper front teeth, and trauma was the most common cause of the darkening. The colour change was judged good in 87 per cent of teeth and acceptable in the remaining 13 per cent. Dark yellow and black teeth needed more applications than grey or light yellow ones, and no teeth developed external resorption.
That is encouraging, but it is a single study, and each tooth responds differently. No particular shade can be promised in advance.
Protecting the root surface
The complication to know about is external cervical resorption, where the root surface near the gum line starts to break down. In an analysis of 257 teeth with this kind of resorption, Heithersay (Quintessence International, 1999) found internal bleaching was the only likely predisposing factor in about 4 per cent of teeth, and part of a combination with trauma or orthodontics in about 10 per cent.
Older techniques carried more risk. A review of published cases by MacIsaac and Hoen (Journal of the Canadian Dental Association, 1994) found that every affected tooth had been bleached without a protective base over the root filling, and most had been treated with heat. Today's approach of a sealing base, a milder agent and no heat is designed to keep this risk low. Because resorption causes no symptoms early on, an X-ray at later check-ups is a sensible precaution.
The colour can drift back
Some teeth darken again over the years. In the Abbott and Heah study, teeth sealed with glass ionomer and composite kept their colour well, while results were less predictable with other restorations. If the shade slips, a short repeat course is often possible. It helps to think of internal bleaching as something that may need a top-up later.
Existing white fillings on the tooth do not lighten, so they are often replaced once the new colour has settled.
Other ways to change the colour
If bleaching does not lighten the tooth enough, or the tooth also needs strengthening, covering options remain available afterwards. The figures below are typical Australian market ranges, not Lumi fees.
| Option | Tooth removed | Suits | Typical market range per tooth |
|---|---|---|---|
| Internal bleaching | None beyond the existing opening | A dark, root-filled tooth that is otherwise sound | Varies with the number of visits; ask for a written treatment plan with fees |
| Composite bonding | Little or none | Masking colour with a small change in shape | $250 to $800 |
| Porcelain veneer | Some, from the front surface | Colour and shape with a durable finish | $1,500 to $2,500 |
| Crown | The most, all walls reduced | A dark tooth that is also weak or heavily filled | $1,500 to $2,500 |
Our comparison of bonding, veneers and crowns goes into the covering options. If your other teeth are also darker than you would like, professional teeth whitening beforehand lets the single tooth be matched to the lighter shade.
What patients ask about a dark front tooth
Can a tooth be bleached internally without a root canal?
No. The technique needs access to the space inside the tooth, so it must already be root filled. A dark tooth that has not been treated needs assessing first.
How many visits does it take?
It varies. Each dressing stays in for several days, and darker teeth tend to need more applications than lighter ones, followed by a final visit to seal the tooth.
Will it hurt?
Usually not. The tooth has no living nerve, and the work is done through the small opening at the back of the tooth.
Having a dark tooth checked
The team at Lumi Dental in Melrose Park can examine a dark tooth, take the X-rays needed and explain which options suit it. Read about our cosmetic dentistry, or see our current offers to book a free cosmetic consult.
