The procedure of teeth whitening
Tooth whitening is normally achieved by bringing a dental bleach such as hydrogen peroxide or carbamide peroxide into contact with the teeth. This may be done using high concentrations in one visit to your dentist, or by using lower concentrations over a period of weeks at home.
Studies of at-home whitening effects
One of the longest studies of the effects of teeth whitening assessed participants 9 to 12 years after they had undergone six weeks of overnight home whitening using 10% carbamide peroxide. Of these patients 33% reported no obvious change, 27% reported a slight change and 6% reported moderate to severe change. Remaining participants stated they had already redone the bleach process.
Studies of in-chair whitening effects
Many follow-up studies of whitening treatments performed in the dental chair have also shown that teeth are still lighter two years after treatment but are not as white as immediately after treatment. The general consensus is that use of an activation light can reduce treatment time overall but it does not extend the duration of the whitening.
Studies comparing home- and in-chair whitening
The studies that compare at-home and in-chair whitening show a similar rate of colour rebound after the two processes, regardless of the length of initial treatment. This holds true for 45 minute in-chair whitening, 10 day home whitening and 4 week home whitening.
Factors affecting longevity of results
The duration of your results can be affected by your original shade, dental health, previous experience with whitening, diet and smoking. The main factors that you can control are dental health, diet and smoking. Dental health issues can be identified and prevented with regular check-ups and cleans.