Active ingredients: For optimal teeth whitening results at home, "look for the active lightening ingredients hydrogen or carbamide peroxide," advises Sharon Huang, D.D.S., MICOI, a cosmetic dentist and founder of Les Belles NYC in New York City. Note that although hydrogen peroxide produces excellent whitening effects, it can sometimes result in temporary tooth sensitivity, Dr. Gonchar says. Whitening pens or gels: These formulas contain the active teeth lightening ingredient hydrogen peroxide in a pen or gel form that you glide over your teeth to whiten them. Some are left on teeth (even created to be left on overnight), while others are meant to be rinsed off. Because the ingredients can be diluted or washed away in your mouth over time, the whitening results are generally more moderate. Find out which dental treatments are available on the NHS How do I find out about getting my teeth whitened? Home kits also carry risks. Talk to your dentist first, before using a home kit. What are the risks of home kits and salon teeth whitening? The whitening effect won't last as long if you smoke or drink red wine, tea or coffee, which can all stain your teeth. Will teeth whitening work on false teeth?

Laser whitening, also known as power whitening, is another type of teeth whitening system that a dentist can provide. A bleaching product is painted onto your teeth and then a light or laser is shone on them to activate the whitening. Laser whitening takes about an hour. Can any dentist whiten teeth?At-home teeth whitening kits are a more accessible alternative to professional whitening treatments, which can deliver instant and more dramatic results but at a higher price. DIY teeth whiteners can include whitening strips, trays, gels, pens, toothpastes, mouthwashes and LED lights as accelerators, which can provide noticeable effects both immediately and with use over time. "They use various chemical or abrasive agents to lighten or remove stains on your teeth to make them appear whiter," explains Marina Gonchar, DMD, orthodontist and owner of Skin to Smile in Morristown, New Jersey. Only go to a registered dental professional for teeth whitening because whitening by people who aren't qualified, for example in beauty salons, is illegal.

Try to talk to other people who've had the same treatment or visit another dentist for a second opinion until you feel confident. Always ask for a written treatment plan and price estimate before going ahead. Is teeth whitening permanent?

Come back when you're older

What you eat and drink and whether you smoke also contribute to the longevity of teeth whitening effects. "If you’re meticulous at avoiding anything that will stain teeth and upkeep with whitening touch-up products, results will last longer," she explains. "Some of the most teeth-staining foods and drinks are tea (which actually stains more than coffee!), tobacco and red wine, then dark foods and juices like turmeric, beets, curry and blueberries." Don't be afraid to ask simple questions about the types of whitening treatment available, what results you can expect and how long they are likely to last. It depends on whether you go pro and your lifestyle habits. "Professional whitening will provide results that last longer — people usually get touch-ups every six months to a year," Dr. Huang says, but "with at-home products like teeth whitening strips, you may need a touch-up every month to take the superficial stains off and keep teeth white over time." Some home kits don't contain enough whitening product to be effective. Also, if a dental professional isn't doing the whitening, the mouthguard provided may not fit properly so some of the bleaching gel may leak out onto your gums and into your mouth, causing blistering and sensitivity. Potency level: The maximum percentage of active teeth lightening ingredients is 10% for over-the-counter products, Dr. Huang says. "Higher concentrations will result in faster and better results, yet may cause tooth sensitivity," Dr. Gonchar explains. "Lower-concentration products will take longer to achieve the desired results, but may be more appropriate for those with sensitive teeth or other dental needs."

If you are not happy with the results, speak to the dental professional who carried out your treatment to ask for advice. More and more people are paying for brighter, whiter teeth. But does teeth whitening work and is it safe? Here are the answers to common questions about the treatment. What is teeth whitening? Teeth whitening involves bleaching your teeth to make them lighter. It can't make your teeth brilliant white, but it can lighten the existing colour by several shades. Who can do teeth whitening? Teeth whitening is a form of dentistry and should only be carried out by a dentist or another regulated dental professional, such as a dental hygienist or dental therapist, on the prescription of a dentist.Teeth whitening doesn't work on dentures, crowns, fillings or veneers. What are the risks of teeth whitening?