If you practice smiling in front of a mirror, it will become easier, and you'll look less strained when you do it. Practice what you feel to be your most attractive smile, and it will eventually look and feel more natural.  Look at photos of yourself smiling in different ways. Decide what type of smile you like best and replicate it in front of the mirror. Once you’re comfortable with the smile, practice without a mirror. Practice smiling at random strangers. Simply make brief eye contact with a person and smile. As you do so, think happy thoughts. Not everyone will smile back, but note how you feel when they do. A genuine smile will naturally include your eyes. It is called a Duchenne smile, and it's not something that is easily faked. When you practice smiling, work to include your eyes in the expression so you wind up with a warm, genuine smile.  To get a feel for how to make your eyes smile, stand in front of a mirror and practice smiling, but concentrate only on your eyes. You may find it helpful to cover the lower part of your face with a piece of paper. When your eyes do smile, remember how it feels, including which muscles are working and how. With practice, you may be able to smile with your eyes at will by relying on your feelings and muscle memory. You may be reluctant to smile if you are self-conscious about your teeth or breath. Eliminate these worries by taking active steps to ensure that your teeth and gums are as healthy as possible.  Brush your teeth and tongue regularly, carry floss wherever you go so that you can clean up after eating, and have breath freshener on you at all times. See your dentist regularly for teeth check-ups and cleaning, as well as discussing options for teeth straightening or other treatments if this is a concern for you. If your teeth are stained, consider any lifestyle habits that contribute to the discoloration, such as smoking and drinking too much red wine, coffee, or soft drinks, and try to cut down them. Look into whitening treatments if that will help boost...

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Write a summary of the previous text in Vietnamese:
Tập mỉm cười thường xuyên. Mỉm cười bằng đôi mắt. Duy trì vệ sinh răng miệng tốt.