A smile is one sign we all look for when we meet a new face, say psychologists. It is something we can spot 30 metres away, according to Paul Ekman, professor of psychology at the University of California Medical School in San Francisco. 'A smile lets us know that we are likely to get a positive reception, and it is hard not to reciprocate,' he said in an article in Psychology Today. Surveys carried out by the British Dental Health Foundation during Smile Week last year found that 70 per cent of people think a healthy smile makes you more successful, while almost as many said they would be more likely to speak to someone they did not know if that person had smiled at them. A similar survey by the Academy of General Dentistry in Britain found that 96 per cent of people saw a smile as very important to a person's appearance. But a smile is only as good as your teeth. Even people with the most beautiful faces cannot compensate if their teeth are in poor health, discoloured or showing signs of decay. Taking care of your teeth requires much more than a quick brush and floss twice a day. Like the rest of your body, teeth require a good diet and healthy habits if they are to last a lifetime and retain their dazzling form. Feed your smile Maintain a healthy, balanced diet that includes at least five portions of fruit and vegetables a day. A poor diet can cause a wide range of oral health problems, including decay, erosion and gum disease. A diet rich in vitamins, minerals and fresh produce can help prevent gum disease, a condition that affects 19 out of 20 of us at some point in our lives and is one of the major reasons behind people having to wear dentures. Cut the sugar Avoid or at least limit sugary foods and drinks known to cause decay. Sugar reacts with the bacteria found in plaque to produce harmful acids that attack the teeth and destroy the protective enamel, which can lead to cavities that will eventually need filling. If you cannot resist sugar, save it for mealtimes and choose only healthy sugar-free foods, vegetables, fruit or cheese at snack times. Read the labels All sugars cause decay, so read ingredient labels when buying food. Glucose, sucrose and fructose are sugars, despite their names, and can still cause damage to teeth. Processed foods often contain sugar - which is another reason to head for the fresh counter when shopping for food. And do not forget that drinks or condiments such as ketchup also carry a high sugar content. Avoid the acid attack Fizzy drinks, vinegar, pickles and even curry can destroy your smile because they contain a high proportion of acid that attacks and dissolves tooth enamel if consumed often and in big quantities. The resulting erosion takes the shine off your teeth, exposing the darker dentine underneath. Don't smoke Smoking - along with too much alcohol - is one of the biggest causes of oral cancer, a disease that kills hundreds of people every year. Smoking also causes bad breath, gum disease and, like red wine, can result in discoloured teeth which will take the dazzle right out of your smile.