I find that when someone is interested in whiter teeth, I often get asked the same handful of questions. My hope for this post is to provide information that may answer questions about tooth whitening that you may have, including how it works, its safety, and what to expect as you whiten your teeth.
Types of Stains
Before we can discuss how whitening works, let’s differentiate between the types of stain that darken the appearance of our teeth
- EXTRINSIC: Extrinsic stains are superficial stains within the biofilm on the tooth. These are the stains that can be addressed with home care and professional cleanings.
- INTRINSIC: Intrinsic stains are deep stains within the tooth that cannot be removed with oral hygiene. Stain molecules from foods and beverages penetrate through the enamel into the dentin. Intrinsic stains also result from aging, trauma, and medications. These pigments in the tooth contain double carbon bonds, which absorb light and therefore make the tooth appear yellow or darker.
How Does Whitening Work?
Whitening products contain either hydrogen peroxide (H2O2) or carbamide peroxide. Carbamide peroxide is essentially a slower acting but more stable “form” of hydrogen peroxide (see below).
- Hydrogen peroxide: As hydrogen peroxide is exposed to air (the instant you open your whitening product), it breaks down into water and peroxide radicals (oxygen ions). When present on the tooth, the peroxide radicals diffuse into the tooth. Because the peroxide radicals have unstable electrons, they react with those aforementioned double carbon bonds. This reaction results in single carbon bonds, which reflect light and thus make the tooth appear whiter and brighter!
- Carbamide peroxide: When carbamide peroxide is exposed to air, it breaks down into hydrogen peroxide and urea. Urea slows down the breakdown of hydrogen peroxide (hence: slower acting but more stable than hydrogen peroxide).
How Can I Whiten My Teeth Quickly?
Whitening time is influenced primarily by the following factors:
- Contact time/Frequency
These are self-explanatory and make perfect sense. The longer/more frequent the teeth are exposed to the whitening gel, and the higher the concentration of whitening gel, the faster the teeth will whiten. However, there is no long-term difference in effectiveness between concentration strengths. What would the downsides be of an over rigorous whitening routine? Read on below.
Are There Side Effects with Whitening?
- Tooth Sensitivity: Hydrogen peroxide and biproducts diffuse into the pulp within 5-15 minutes. This causes pulpitis (inflammation of the pulp). The pulpitis does subside once the circulation has enough time to "wash away" the peroxide/biproducts away, which is typically after 12-24 hours, but you may experience tooth sensitivity in the mean time. If tooth sensitivity becomes an issue for you during your whitening process, consider implementing the following:
- Decrease wear time or reduce wear interval (i.e. every other day instead of daily)
- Decrease bleach concentration
- Toothpastes marketed for tooth sensitivity (see here)
- Gingival Irritation: In the concentrations used for whitening, hydrogen peroxide and carbamide peroxide can cause gingival irritation or burning. If you have custom whitening trays, it is easy to wipe the excess whitening gel off of the gingiva once the trays are seated on the teeth to avoid gingival irritation.
Is Whitening Safe?
There are just a few specific exceptions/contraindications for whitening due to safety:
- If saturation point is reached and the teeth no longer contain any stain molecules, bleaching then results in breakdown of enamel. (Note: Research shows that loss of calcium from teeth and decrease in microhardness do occur with exposure to peroxides in the absence of saliva. However, this demineralization is not seen in the presence of saliva, ie normal oral environment)
- Chronic exposure of peroxides should be avoided in tobacco users due to concerns that peroxides may potentiate the effect of other known carcinogens
- Although bleaching gels are primarily applied to front teeth where there usually are no silver amalgam restorations, having many amalgam restorations may be considered a contraindication for whitening because mercury may be released in presence of H2O2 or carbamide peroxide.
Do whitening toothpastes and mouthwashes work?
Whitening toothpaste and mouthrinses act, for the most part, by removing superficial stains. Some whitening toothpastes now contain hydrogen peroxide, but likely the concentration and contact time will be ineffective to obtain the whitening that most hope to obtain when they think of whitening.
How Long Does the Whitening Last?
I have heard various answers to this question. One lecturer reported 5-15 years, another lecturer quoted a study that said at 1.5 years, 74% of patients were satisfied with shade lightening. At 3 years, 76% were satisfied. Variation, obviously, will be greatly dependent on patient factors that lead to staining.
Anything Else to be Aware of?
Whitening can compromise the bond strength between a tooth and composite restorations. I recommend waiting a minimum of 2 weeks following whitening before any new bonded restorations are placed.