A woman who had just returned to Guangzhou from Australia found her teeth blackened during lunch with her son and one of her friend's daughters.

The two children's tongues and teeth were also blackened during the meal.

The woman, Ms Liu, complained to the restaurant manager who was unable to explain what had happened as the dishes they ordered were quite common _ pork steak with fruit juice, steamed perch, a vegetable dish and a pot of tea.

The manager took them to a nearby hospital and, after an examination, the doctor suggested them to try brushing their teeth with toothpaste. The manager bought the toothpaste and brushes and the stains were removed with brushing.

The doctor thought the staining could have been caused by a chemical reaction in the mouth from the dishes with vinegar in the pork steak, acid in the fruit juice and tannic acid in the tea while the perch was alkaline, said the doctor.

Editor: Catherine