The desire for and pursuit of whiter teeth is not new. Even though it's completely normal to have a dingy or stained smile as you get older, less yellow has been the aesthetic mantra for decades. And, for the past century, the core principle of how to efficiently bleach one's teeth — often a mix of a peroxide compound and light — has changed little except for an improvement in scientific sophistication and ease of use. Despite their widespread use, professional tooth-whitening treatments conducted in dentists' offices continue to be shrouded in mystery and misinformation. Here's what you should know:

1. Not everyone is a good candidate for professional teeth whitening
Unfortunately, while many people prefer whiter teeth, the ingredients and processes employed in professional tooth-whitening treatments prevent some people from becoming suitable patients.

Veneers, root canals, caps, or infected teeth will prevent proper whitening. Furthermore, individuals with exposed roots might feel significant discomfort during whitening.

Though you should always check with your dentist before beginning a whitening treatment, an exam may not be necessary to determine whether you are a good candidate for this cosmetic dentistry procedure.

2. You may feel some pain, even if you have healthy natural teeth
Discomfort, even pain, is not uncommon among patients undergoing or who have recently completed an in-office tooth-whitening treatment. This is usually related to the technique of desiccating the teeth.

Bleaching can induce interior dryness, which normally lasts between 24 and 48 hours. The strength of the material and the quantity of contact time are the primary players in that game. Some whitening systems include built-in desensitizers to assist prevent or alleviate discomfort.

Some people have 'zingers' after teeth whitening operations, which is a sharp increase in sensitivity. To alleviate this sensitivity, take an anti-inflammatory such as Advil.

3. Not all in-office tooth-whitening treatments are the same
In-office whitening lights are classified into three varieties based on the manufacturer: UV, LED, and halogen. The LED light causes the least degree of sensitivity and is the most often utilized light in both in-office and at-home tooth-whitening systems (though many at-home systems do not include lights).

Some dental practices also provide laser tooth whitening.

However, the procedures rely on the bleaching chemicals that the lights and lasers assist activate (though they can whiten teeth without illumination). The cost can vary depending on the type of treatment and your location, but an appointment for tooth whitening will cost between $400 and $1,000.

4. You won't get truly white teeth — and that's a good thing
During your session, your dentist may show you a shade chart that will help you understand the difference between the shade your teeth are now and the brighter shades you may wish to aim for. If you want to get as white as possible but are concerned about looking like Ross did when he had his teeth bleached on that one episode of Friends, don't worry - your teeth will not shock people with their phosphorescence.  

5. Your whitening won't last forever
In reality, it is unlikely to last more than a year. Teeth whitening is not something that happens only once in a lifetime. Drinking and eating certain beverages and foods, such as wine, coffee, red sauce, curry, and others, can stain your teeth.

Even if you avoid most staining foods and beverages after your appointment — raw, crunchy fruits and vegetables such as carrots, celery, and apples are always a good choice because they not only do not stain but also help mechanically remove surface stains from teeth — you can expect to see results in about six months.

6. But you shouldn't whiten too often
To achieve and keep your whitening results, you should only need treatment twice a year. Professional whitening more than twice a year is unnecessary and may dry out enamel. This will make your teeth sensitive and chalky-looking.

7. You can achieve similar results at home — but not quite the same
Finally, in-office whitening is the best option for achieving the brightest, fastest, and most durable results. However, attaining comparable results using at-home solutions is not out of the question. However, depending on numerous conditions, it may take longer, produce less consistent results, or lose brightness sooner.