A Tooth That Darkens After an Impact: Why It Happens and What Can Be Done
An impact in childhood can cause a single tooth to darken years later. The cause of the discolouration, why external whitening falls short, and the internal bleaching approach.
Why Does a Single Tooth Darken?
When one tooth gradually darkens among neighbours of the same shade, it is usually because that tooth sustained an impact in the past. The colour change may appear not immediately after the impact but months or even years later, so the person may not connect the two. This picture is commonly seen in front teeth damaged by a fall in childhood.
The process behind the discolouration
At the moment of impact, bleeding can occur in the pulp tissue inside the tooth. Blood components spread into the dentinal tubules and, over time, their breakdown products colour the tooth tissue from within. The shade can range from grey to dark yellow, and sometimes a purplish tone. In root-treated teeth, loss of tissue vitality and residues of certain materials can produce a similar result.
Why don't whitening toothpastes and strips work?
Whitening toothpastes and strips address externally sourced stains on the enamel surface and are useful for surface discolouration from tea, coffee and smoking. The discolouration here is located in the inner layer of the tooth. No surface application can reach that layer.
What about in-office whitening?
This is a common misconception. Conventional whitening is applied to all the teeth and lightens them all to some degree. As the darkness of the single tooth persists, the difference does not close; it may even become more noticeable as the neighbouring teeth lighten.
What kind of approach is internal bleaching?
Because the colour change is inside the tooth, the bleaching agent must also be placed inside it. A precondition for this approach is that the tooth's root canal treatment is adequate, so radiological evaluation is carried out beforehand. An access is opened from the back surface of the tooth, the upper part of the root filling is removed to a certain level and a sealing barrier is placed at the canal entrance. The agent is placed in the pulp chamber, temporarily sealed and renewed at intervals.
For details of the procedure, suitability conditions and session structure, see our internal bleaching page.
How permanent is the result?
The degree of lightening achieved and its permanence vary between individuals. Partial colour relapse may be seen over time and the procedure may need to be repeated. Expectations are therefore discussed together beforehand.
If another problem accompanies the discolouration
If the tooth also has a fracture, marked loss of structure or deformity, whitening alone may not be sufficient; options such as composite restoration or a laminate veneer may come into question. Which route is suitable depends on the current condition of the tooth.
This article is for general information purposes and does not replace a clinical examination. The condition of your tooth and the possible approach are determined after clinical examination and radiological assessment.
Frequently Asked Questions
Why does a tooth darken after trauma?
The nerve and blood supply inside the tooth can be damaged during an impact. Blood breakdown products released by bleeding seep into the dentinal tubules, and the tooth gradually takes on a grey to brown shade. The discolouration may appear not immediately after the injury but weeks or even months later. For this reason a tooth that has suffered an impact should be reviewed at intervals even in the absence of symptoms.
Can a single darkened tooth be whitened?
If the discolouration originates from within the tooth, whitening applied externally will not be sufficient. In such cases internal (intracoronal) bleaching applied to a tooth whose root canal treatment is complete may be considered: the bleaching agent is placed inside the tooth and the shade is lightened from within. Applicability depends on the state of the root canal treatment and the remaining tooth tissue, and is determined by examination and radiological evaluation.
Can a darkened tooth be corrected without a crown?
Where loss of structure is limited and the discolouration originates internally, options aiming to lighten the shade without a crown are considered first. The advantage of this approach is that sound tooth tissue is preserved. Where there is a fracture, extensive loss of structure or previous large restorations, however, a crown may come into question. The decision is made according to the current condition of the tooth.
What if a baby tooth darkens after an injury?
Discolouration after trauma is common in baby teeth and does not always require treatment. What matters is whether there is swelling of the gum, a sinus opening, mobility of the tooth or pain; if these are present, assessment should not be delayed. Whether the underlying permanent tooth germ has been affected is also monitored radiologically. In the absence of symptoms, review is usually sufficient.