Dentist Assisted. While there are many over the counter whitening products the safest will be doctor assisted. Based on their training and experience, your dentist can pick the best product/technique.
Lots. With so many whitening systems around...They all work well and with very little side effects. You can get fda approved products at the mall even. But...If you wish to be picky and have peace of mind then use the products that you need to get thru a dental professional.
Teeth whitening. You can use over the counter tooth paste or crest 3D whitening strips or pens. However, they are not so effective and/or stable. OTC bleach and whitening tooth paste could be used as a supplement only. A professional teeth whitening without laser, followed by home whitening system with custom trays for the long term effect. You will be very happy with the results.
By dentist. Only those prescribed by and recommended by a dentist.
2 BEST. Whitening products with either carbamide or hydrogen peroxide. The whiteners that work the fastest and the best are ones monitored by a dentist. There are various strengths used to get the best results. Watch out for otc brands, because if they cause tooth sensitivity, you may have to see a dentist anyway for desentization treatment. Don't play games with your teeth. See a dentist.